Wikipedia:Reference desk/Archives/Science/2007 January 28 & 29

January 28

Another rice question

I've been trying to find this out for a while, and now seems like the perfect time to ask. Certain types of rice come with the instruction to 'rinse carefully until the water runs clear'. I always do it, and as I'm standing there washing the stupid stuff over and over and over, I wonder exactly what am I rinsing away that's sooo important to get rid of? Is it pesticide? Dirt? Powdered mouse poop? Did the farmer spit in the rice paddy a lot? Or is it just excess starch that would make the rice sticky? Anchoress 03:59, 28 January 2007 (UTC)

Rinsing rice several times can help remove stickiness, and also helps the rice to cook better. Rya Min 05:48, 28 January 2007 (UTC)

I remember eating someone's unwashed rice once and it didn't taste very good, but maybe that was their cooker. --Wirbelwindヴィルヴェルヴィント (talk) 05:57, 28 January 2007 (UTC)

Our rice article says that “The white rice may then be buffed with glucose or talc powder (often called polished rice, though this term may also refer to white rice in general).” I guess I’ll keep washing the rice. S.dedalus 07:55, 28 January 2007 (UTC)

But what about other types of rice? Anchoress 07:56, 28 January 2007 (UTC)

Here are two links mentioning all of the above, plus having different opinions regarding the loss of added vitamins and minerals caused by washing: Faunton's Fine Cooking (talc, maybe starch, no significant loss of added vitamins through washing), food network (mainly starch, mentions loss of added minerals and vitamins, separation of grains in case of basmati rice). Sage V Foods mentions bran and other contaminants that get removed through the process of rinsing but also claims there is a significant loss of vitamins, they say it's a trade-off between nutrition and gourmet quality. I admit I never questioned this and thought I was removing remainders of the hull (and maybe starch) when mindlessly washing not only rice, but other grains too. ---Sluzzelin 11:26, 28 January 2007 (UTC)

The labelling should really say 'rinse until practically clear'; it's a terribly laborious task otherwise, with rapidly diminishing returns after the second or third rinsing. Vranak

Yeah I know. I shiver at the amount of water I use; it takes me about 8 rinses with fresh water to get it that clean. Tastes really good tho. Anchoress 05:50, 29 January 2007 (UTC)

Thanks to all for the answers. Anchoress 05:50, 29 January 2007 (UTC)

Oxygen concentration

~moved from the Entertainment desk~

if using two oxygen concentrators with one on 5liters per min and the other on 5 liters per min what oxygen concentration would you get?

Sounds like a homework question to me. --Zach 04:00, 28 January 2007 (UTC)

It doesn't make very much sense either. A litre is a measurement of volume, not of concentration, and without knowing the size of the container or the pressure of the oxygen or anything, what are we supposed to do? -- Consumed Crustacean (talk) 05:59, 28 January 2007 (UTC)

Who makes Wankel Engines?

I am interested in, from an investor's perspective, wankel engines and other rotary engines. However, for the life of me, I cannot find a publicly traded company that builds them. Only mazda comes up in searches, are they big on this? Thank you. ChowderInopa 04:40, 28 January 2007 (UTC)

Mazda have done a lot of work with Wankel engines since the '60s, most prominently the Renesis engine in the RX-8 and before that the RX-7. Another company which was once heavily involved with Wankel cycles was the German firm NSU Motorenwerke AG in the 1960s-1970s, but they were bought out by Volkswagen, largely because the early engines were unreliable and they got thoroughly shafted by warranty costs. See the relevant articles for more info. I believe (and the article says) that Mazda is the only company currently building Wankel engines. --YFB ¿ 05:09, 28 January 2007 (UTC)

Don't forget the hobbyist market, pioneered by (and still made today by) the Japanese company OS in the 70s. The large (automotive scale) rotary engine is also used by a variety of prominent companies in racing applications, Google is your friend!--66.195.232.121 15:11, 29 January 2007 (UTC)

Seizure / sleep paralysis / lucid dreaming / extreme long-windedness

This is not a request for medical advice, and I would appreciate if no one posted advice. I'm not going to do anything about this; it's been more than 5 years. I probably do not need to go into all this detail, but I'm bored, so what the hell.

When I was younger I hit a short period where I was mildly interested in odd occult and paranormal things. This was fairly brief, but an interest in lucid dreaming lingered. I was 13 around this time. Having read the lucid dreaming websites (many of which are "out there"), I got a lot of weird information about "out of body experiences", which I dismissed but still read. Bored over the summer, I decided to begin doing the whole dream journaling thing, recording every dream I could recall upon waking up.

One fine sunny day I awoke, decided it wasn't worth getting up, and went back to sleep. Almost immediately (perceptually) I found myself in a dream. I realized I was dreaming after a short time, and decided to check my watch as a "dream test" - the websites indicated that it should appear garbled while in a dream. Before I could manage to do so I found myself in another dream, in which I was in my own room, though with slight differences that I only realized after the fact. Being a lazy young adolescent, I decided to fall asleep again, despite already being in a dream.

This is where it actually gets weird. After closing my eyes in this dream, everything went pitch black. The letters "HBO" suddenly appeared in the blackness, in an intense white, and I felt quite startled. This reminded me of "OOBE" for no reason; OOBE being an acronym for "out of body experience" that I had read on the mentioned lucid dreaming websites. Thinking that in turn caused me to wake up, though for real this time.

I didn't simply wake up though. I began to shake uncontrollably, as well as hearing a slight "humming" noise as one hears when their head shakes or their jaw is overly tensed (err). This was not fun. It ended after maybe a minute, but scared the hell out of me.

This thing is strange though. I have never before, nor since suffered from seizures, nor any neurological disorder. The shaking is also something which I may have come to expect due to it being described quite vividly on those crazy websites as a precursor to out of body experiences.

So, after all of that crap, I finally come to the question(s): Is it likely that it was merely a coincidence that I had this happen to me after having read about something exactly like it, and having developed my interest in lucid dreaming, or did I actually manage to self-induce a seizure? Is there any scientific work on self-induced seizures? Was it even a seizure? Are there any reported connections between, perhaps, sleep paralysis and convulsions? What happened? Am I making a crazy fool of myself? Have I posted this before? Is this far too verbose? -- Consumed Crustacean (talk) 05:41, 28 January 2007 (UTC)

Interestingly enough, I read a book that talked about astral catalepsy (no article about it, though), and it sounds like something similar to that phenomenon. Google it for some interesting info. Titoxd^(?!?) 08:51, 28 January 2007 (UTC)

That just sounds like a paranormal explanation for sleep paralysis, though semi-voluntarily induced. This is exactly the type of thing I read about while trying to read up on lucid dreaming, which is why I think my expectations to have such an experience may have helped shape it (as in the placebo effect). Again, because of my own experience and the numerous reports, I'm just wondering if there has been any scientific research into this. Considering the connotations, I've got a feeling that's a negative. -- Consumed Crustacean (talk) 18:23, 29 January 2007 (UTC)

I noticed something similar a little while ago:) Everything seemed to be somehow connected to something I was interested in, things in books would remeind me of it, I had dreams about it &c:( Maybe you want this to happen so much you are persuading yourself you are seeing it:) The stuff that happens in our dreams doesn't actually happen at all, unlike in books and films where someone has already decided what you will see:)Hidden secret 7 12:25, 28 January 2007 (UTC)

I have had an experience very similar to yours, though not after a lucid dream (I have only had once when I was quite young). I saw the word GOD in intense yellow letters spelled before a dark background (though in my dream the dark background looked a lot like my bedroom window). I woke up paralyzed (see sleep paralysis) and remained so for about a minute. As far as I know, sleep paralysis is not normally accompanied by convulsions, the strange thing with my sleep paralysis (which happens often) is that I always experience convuslions in one single muscle (eyelid, foot, ...) while being otherwise completely paralyzed. The convulsions are both voluntary and involuntary at once: I seem to be straining to get any muscle into action and somehow that muscle seems to respond, although I do not intend it to convluse. As for the word I saw, I think that what I really saw wasn't the word GOD, but I interpreted it that way (I thought I was dying then). It's very likely I saw/interpreted this word because of my then-obssession with theological issues (possibly similar to your obssession with OOBE?). I only woke up because I felt the enormity of what I saw was too much and it felt like my heart had somehow exploded (again, I thought I was dying), not merely "thinking about it". I hope this wasn't too confusing. —LestatdeLioncourt 14:16, 28 January 2007 (UTC)

That sounds eerily similar. -- Consumed Crustacean (talk) 18:23, 29 January 2007 (UTC)

---

Is it likely that it was merely a coincidence that I had this happen to me after having read about something exactly like it?

In my experience, we tend to become interested in things that are relevant to our current stage of intellectual development. Once we 'pass through' a stage, our interest wanes.

As for the unpleasant episode itself, all I can say is that our minds and bodies can and will do all sorts of unsettling things in order to 'sort itself out'. The best analogy I can think of is defragmenting a hard-drive. All sorts of disparate data passes through a computer's CPU as it cleans up a hard drive. If a CPU had consciousness, it might get all bugged-out from the garbled data passing through its core. But it is purely an artifact of how data is stored; there's no higher meaning.

Also, from the aforementioned article: "[Defragmentation] is a memory intensive operation [...]", i.e. it's best to do it when your computer isn't doing anything else. So if the analogy holds true, this is why we can only afford to have these wierd experiences when we're at rest. Vranak

That's like one of the theories of dreaming. Considering that I expected it to happen though, that explanation doesn't do it for me. I'm leaning towards it being something like the subject-expectancy effect or placebo effect. -- Consumed Crustacean (talk) 18:23, 29 January 2007 (UTC)

Stuff on my toungue

What is the white stuff on the back of my tongue that I have to brush off when I brush my teeth? Imaninjapirate^{talk to me} 06:15, 28 January 2007 (UTC)

Plaque. See tongue scraper, albeit a small article. --Wirbelwindヴィルヴェルヴィント (talk) 06:31, 28 January 2007 (UTC)

Antimatter

What would have to be the diameter of a particle accelerator that could produce a gram of antimatter in a year? Using todays technologies.67.125.157.144 06:43, 28 January 2007 (UTC)

Our article on antimatter says: The biggest limiting factor in the production of antimatter is the availability of antiprotons. Recent data released by CERN states that when fully operational their facilities are capable of producing 107 antiprotons per second. Assuming an optimal conversion of antiprotons to antihydrogen, it would take two billion years to produce 1 gram of antihydrogen. This data comes from this FAQ on antimatter from CERN . I think a larger particle accelerator would not necessarily make more antiprotons, it would just make faster antiprotons, which is exactly what you don't want - you want to produce slow antiprotons which are easier to contain with electromagnetic fields. But the biggest problem in antimatter production is how to contain the antimatter and stop it interatcing with ordinary matter and destroying itself. Charged particles like antiprotons and positrons can be contained with electromagnetic fields (see Penning trap, for example), but you can't keep large numbers of the same particle together because they strongly repel one another. If you let them combine into, say, antihydrogen then you have a neutral atom which is even more difficult to contain. Gandalf61 12:50, 28 January 2007 (UTC)

Antihydrogen is easy to contain. You just need an anti-matter tank! anonymous6494 12:51, 29 January 2007 (UTC)

History of Pause Button

can anyone please help in finding the history of invention of Pause button/key?

The earliest use of the pause button that I can recall is on reel-to-reel audio tape players/recorders in the 1960s, like this one. It was used to temporarily halt the tape when recording - using the stop button would have created a noticeable break in the reording. Certainly the pause button/key was a standard feature on cassette decks such as this one, where it is the smaller key to the right of the stop key. Gandalf61 09:58, 28 January 2007 (UTC)

I think one could argue that turntables, especially the professional turntables used for radio broadcasting contain an even earlier implementation of the same feature. You could "cue up" a record to the exact starting point of a song and then there were two methods of rapidly starting it at the exactly correct moment. One was mechanical, much like a "pause" key. The other was to hold the record from spinning while the turntable continued to turn underneath it. When you released the record, it almost instantly accelerated to full speed. But the mechanical method wasn't much slower, and it left your hands free to do other things while the record remained "paused".

Atlant 01:06, 29 January 2007 (UTC)

The recording device and the reproducer could be lifted off the recording via a lever in the Edison cylinder phonograph in the 19th century. That is a Pause control. Did you mean when was it first labelled as a pause control? That must have come later. Some tape recorders had a pause control ion the 1950's. Before that as on wire recorders, one just pressed stop, the play or record. Some devices did not distinguish that from pause. Pause allowed a tape or cassette recorder to begin recording almosfaster than pressing record from the off position. Edison 05:34, 29 January 2007 (UTC)

Firing a gun in space

If you were to fire a gun in space (ignoring whether or not it's actually possible to fire a gun in space) would you be propelled backwards at the same speed as the bullet? Battle Ape 10:18, 28 January 2007 (UTC)

Not at the same speed. While the force applied to both objects is the same, the mass is not. If you're twice as heavy as the bullet, you'll only go half as fast as the bullet. -- Ec5618 10:29, 28 January 2007 (UTC)

To elabortate, your speed would equal the speed of the bullet multiplied by the ratio of the bullet's mass to your mass. (See linear momentum) —LestatdeLioncourt 11:22, 28 January 2007 (UTC)

(after edit conflict) Twice?

According to 5.56 × 45 mm NATO the standard NATO round weighs 4-5 g, an adult male about 75000 g. So you'd have to fire 15000-18750 bullets before you would have the same speed as the bullet. - Dammit 11:29, 28 January 2007 (UTC)

You could fire most modern guns, just obviously not old flintlock guns! Mathmo ^Talk 23:54, 28 January 2007 (UTC)

This talk started me thinking off about firing underwater, and I've just by chance came across this interesting weapon. [1] Is a bit off at a tanget, but still somewhat related and interesting.... Mathmo ^Talk 15:22, 29 January 2007 (UTC)

Yes, most bullets will fire in space or even under water, because the cartridge contains the propellant and oxidant necessary for the reaction. The reason why a lot of guns fail underwater is because of mechanical reasons not chemical ones, eg, the water can't get out of the way fast enough. I actually think it would take fewer bullets then your total mass, think about the explosion it self, it would also impart some energy, i.e. if you fired a blank, it would act like a tiny little rocket for a split second, the expanding gas would also act on you because the gun barrel is acting like a nozzle, the effect is probably small but I doubt negligible when you are talking about firing 15000 times. Vespine 02:42, 29 January 2007 (UTC)

But I thought mass and weight didn't matter in zero gravity, since both yourself and the bullet technically weigh nothing while you're up there? Battle Ape 12:44, 29 January 2007 (UTC)

mass is not the same as weight (the intro to weight explains this adequately). — Lomn 16:04, 29 January 2007 (UTC)

Blackpowder contains an oxygen-supplying compound so even flintlocks should work in space. A gun has been fired in space before. The Russian Salyut 3 space station used its aircraft cannon to target a satellite. They were uncertain how bad the resulting vibrations would be on the space station and fired the gun by remote after the cosmonauts left. Rmhermen 01:17, 31 January 2007 (UTC)

Handheld GPS and Map Datum

Hello,

I recently bought an entry level handheld GPS receiver (The Magellan eXplorist 100). I live in Canberra, Australia (this will become important later). I am planning a hike using 1:25000 topographic maps provided by the NSW Department of Lands, based on the GDA94 datum. However, my GPS only supports AUS66, AUS84 and WGS84, as well as many other useless datums (IRAN, ADIND, etc.). It does support a USER setting, but I must enter in the following information:

• Delta A (meters)
• Delta F (X 10,000)
• Delta X (meters)
• Delta Y (meters)
• Delta Z (meters)

I have no idea what numbers to put in, does anybody know? I have found these details of the GDA94:

• Equatorial Radius (semi-major axis): 6378137.0000 m
• Flattening: 1/298.257223563
• Polar Radius (semi-minor axis): 6356752.3142 m
• Eccentricity: 0.00669437999013

Also, would it be okay just to use WGS84?

Thankyou in advance,

--Alexs letterbox 11:43, 28 January 2007 (UTC)

WGS84 and GDA94 are practically the same. The algorythm is almost identical with a small change in the flattening term. You will not notice a difference on your map at that scale. All GPS receivers get coordinates in WGS84 and transform them to the chosen datum. The difference is about 200m as far as I can tell but this will vary depending on location.

See this.

and for a transform from X to DGA94 see this. --Tbeatty 04:52, 29 January 2007 (UTC)

Gallium

From gallium

Gallium also attacks most other metals by diffusing into their metal lattice — another reason why it is important to keep gallium away from metal containers such as steel or aluminum

Exactly how corrosive is gallium and at what temperature - I've added a to this part of the gallium article. See Talk:Gallium#diffusion

Can anyone give figures for the rate of this diffusion at different temperatures.

Surely no one is suggesting that this occurs at around room temperature?87.102.33.144 12:24, 28 January 2007 (UTC)

I put in a citation! This looks most likely that the diffusion takes palce at room temperature.--Stone 22:58, 28 January 2007 (UTC)

electrolytes

i am drinking a bottled water product called smartwater is there any danger in using this on a daily basis? can one ingest too many electrolytes? --Kmessick 12:24, 28 January 2007 (UTC)k

How can we possibly answer this? You've given us virtually no info, and even if you did you are basically asking medical advice.What does it say on the bottle? Do whatever it says there, however people have managed to live on tap water up until now perfectly healthily. Why waste money on a bottled product? Theresa Knott | Taste the Korn 13:36, 28 January 2007 (UTC)

A facile answer is that if it tastes good, and you gulp it down, it's probably good for you, and if it tastes wierd, and you only take little sips, you're probably wasting your money. The relationship between taste and nutritional value is not random, haphazard, or arbitrary. No citations on this however.

Another facile answer is that if you have to ask, the answer to both your questions is probably yes.

^{As this response makes no attempt to establish evidence, it may be summarily removed.} Vranak

Vranak, Coca-cola tastes pretty good, so that means the sugar is good for my weight, the phosphoric acid for my bones, and the caffeine for my nerves and blood pressure? See how circumstance-dependent and worthless that guideline is? alteripse 17:27, 28 January 2007 (UTC)

Well, when do you usually drink Coca-cola? All that high-glucose corn syrup can't be good in the long term, but it may help kickstart digestion after a particularly heavy meal. What you drink will depend on what you eat, as in wine matching. Vranak

Note that what is marketed as electrolytes is often just disolved salt (for example, sports drinks). Assuming the electrolytes in smartwater is just salt, is drinking extra salt on a daily basis bad? It'd depend on your diet. As a side note, I remember watching a program on Gatorade where their "scientists" were doing all these research and using all these fancy words, when it basically came out to... We wanted to find how salty to make our water. --Wirbelwindヴィルヴェルヴィント (talk) 18:17, 28 January 2007 (UTC)

(Addendum) I found the site Glaceau, which claims to contain no impurities, while adding electrolytes in the form of magnesium, potassium, and calcium, without the use of salt. Sounds excessive to me, but now the limit is digesting more magnesium, potassium, and calcium instead of sodium. Personally, I think it's just way too expensive. --Wirbelwindヴィルヴェルヴィント (talk) 18:25, 28 January 2007 (UTC)

copper iron

Are there any uses for copper iron alloys? could any of these alloys be describe as stainless eg resistant to rust.

Does anyone know the appearance of, or have pictures of these alloys.

Thanks.87.102.33.144 12:48, 28 January 2007 (UTC)

Search Wikipedia, there's plenty of info. Here's an example for you. http://wiki.riteme.site/wiki/Special:Search?search=copper+iron+alloy&go=Go . Cheers, Dr_Dima

Properties_and_uses_of_metals --Parker007 22:07, 28 January 2007 (UTC)

Seriously both of those answers are useless.87.102.2.226 10:05, 29 January 2007 (UTC)

Cunife is the closest I can find to a copper-iron alloy. Any help? Oh, and you might like to reword your reaction up there. While it's frustrating when people don't provide answers that meet your needs, a polite response can ensure they keep trying and answer next time :-) Perhaps something along the lines of "That's not really what I'm looking for." "Those links don't contain the information I'm looking for." or similar. Oh, and if you do change your reaction to something along these line, you can remove this bit from my reply :-D Skittle 19:02, 29 January 2007 (UTC)

Thanks for your response - though the very short article wasn't useful.

As for my response - I think it sums up the answers perfectly - a little impolite perhaps - but so are non-answers - obviously I have the ability to search for 'copper iron' and did. I was looking for some intelligence - not useless directions on how to begin a search. Maybe you could explain how "Properties_and_uses_of_metals "" is anywhere even slightly close to an answer - it isn't - it would be better if people unable to give a reply didn't try. Sorry to be so grumpy but this happens a lot.87.102.13.207 15:08, 30 January 2007 (UTC)

For an answer to your first question, see copper.org which came from a simple and obvious Google search of copper+iron+alloy (see, we can be testy too and I "liked" your obscene remark on the Misc Desk):

Copper-infiltrated iron parts are particularly suitable for applications requiring good resistance to shock loading and good fatigue strength accompanied by resistance to wear.

That alloy was created using powder metallurgy. BTW, I do agree with you that there is no reason to post a non-answer. I just wonder if you are making a WP:POINT as you say it has happened to you a lot. --Justanother 15:44, 30 January 2007 (UTC)

Thanks87.102.13.207 16:32, 30 January 2007 (UTC)

You are welcome. --Justanother 16:35, 30 January 2007 (UTC)

kinematics

Please help me solve this problem:

Water drips from the nozzle of a shower onto the floor 200cms below.The drops fall at regular (equal)intervals of time,the first drop striking the floor at the instant the fourth drop begins to fall.Find the locations of second and third drops when the first strikes the floor. —The preceding unsigned comment was added by 59.93.70.85 (talk) 14:43, 28 January 2007 (UTC).

Do your own homework. Where are you getting stuck? –EdC 15:16, 28 January 2007 (UTC)

Consider the water droplet starts at v, d and t = 0 and a constant acceleration of 9.8m/s per second is applied to it then work out what the t is at d = 0.2m. Then simply solve the exuation for 1/4 t, 1/2 t and 3/4 t. Vespine 21:41, 28 January 2007 (UTC)

I think those times should be 1/3 t and 2/3 t - see fencepost error. Gandalf61 15:00, 29 January 2007 (UTC)

Indeed. Anyone trying to do this sort of problem (eg, the questioner) could avoid such an error by drawing a diagram. Specifically, they could draw a diagram of the situation described (with 4 drops: one at the top, one at the bottom and two in between), then follow Vespine's advice with the necessary corrections. Skittle 18:57, 29 January 2007 (UTC)

genetic parentage

i had read in an article that molecular markers are used in genetic parentage.can u help me understand it? —The preceding unsigned comment was added by 59.95.203.167 (talk) 16:15, 28 January 2007 (UTC).

Boltzmann distribution

I'm confused by the pages relating to the boltzmann distribution. Can someone clarify what the assumptions are in the model that is used as a basis for the distribution. (I thought it was that each energy state is equally likely and each distinct energy state is counted once?)87.102.44.44 12:41, 21 January 2007 (UTC)

The Boltzmann distribution applies to a classical system that consists of a number of particles that are in a canonical ensemble. That means that temperature T is fixed and well defined, the volume V is fixed, and the number of particles N is fixed. There are additional necessary conditions: 1. each state must have occupation probability much smaller than unity; 2. The interaction between particles must be relatively weak and/or short-ranged. The second condition is the most problematic, as it formulates differently for different systems. What system do you have in mind? Dr_Dima

1. Say there are 3 particles, is the total energy of those particles fixed at a given temperature?87.102.32.146 18:54, 28 January 2007 (UTC)

2. And if so is each distribution of energy amongst the particles considered equally likely (excluding degeneracy) or is the situation more complex?87.102.32.146 19:06, 28 January 2007 (UTC)

(assuming question 1 and 2 are answer yes) If I have understood this correctly then for total energy 5, with 3 particles with equally spaced energy levels (singly degenerate) there are 21 possible states, with state (5,0,0) occuring 3 times, (4,1,0) occuring 6 times, (3,2,0) occuring 6 times, (3,1,1) occuring 3 times and (2,1,2) occuring 3 times. Where (3,2,0) means one particle has energy 3, another energy 2, and another has energy 0.

Is this the type of counting situation used in the boltzmann distribution (albeit simplified?)87.102.32.146 19:24, 28 January 2007 (UTC)

A few remarks (without bothering to answer the question fully): The OP assumes that all "energy states" are populated with the same probability. This may hide a misunderstanding. The so-called ergodic principle, which is the underlying assumption, states that any microstate has the same probability. A microstate is, in the classical case, a point in phase space, i.e. one complete specification for position and momentum for each particle. Now, many microstates have the same energy, but not every possible energy value is associated with the same number of microstates. Hence, some energy values are more probable than others, and so, the Boltzmann formula $p(E)dE=\exp(-E/kT)dE$ gives the probability density that the system has energy E, which is proportional to the volume in phase space (number of microstates) with this energy. Note also a possible confusion of terminology: The Maxwell-Boltzmann distribution deals with classical systems in thermal equilibrium at a temperatur T. The Boltzmann factor $\exp(-E/kT)$, however, appears as well in the derivation of the quantum-mechanical analoga, the Bose-Einstein statistics and the Fermi-Dirac statistics. Simon A. 20:16, 28 January 2007 (UTC)

What fucking use is that - you've just stated that 'the boltzmann distribution' is the answer without any explanation.87.102.2.226 10:03, 29 January 2007 (UTC)

Power draw on US Home electical supply

Someone asked me why Americans always use stove-top kettles, and not the far more convenient electrical kettles. My answer was that it is likley that US power couldn't draw the amperage required for them. A 2000W kettle (as we use here) would draw 18A at 120V which is more that our standard outlets are rated for.

Is this the sensible reason? Or is it just tradition with the kettles. How do they use other high wattage devices in the US then, like vacuum cleaners (the one we have is rated at 2500W)? Things like electrical ovens have there own circuit (and perhaps use 3 phase 240V in the US?), but I'm talking about the stuff you plug into the wall. 86.133.205.209 17:11, 28 January 2007 (UTC)

It's true that in the U.S., there's a limit to what you can plug into the wall. Outlet circuits are normally fused at 20 amps, but there's an expectation that no one appliance will draw more than 15 amps, or 1800 watts. In practice, most high-wattage appliances (e.g. hair dryers) top at out 1200 or 1500 watts.

(An appliance that actually needs 20 amps at 120V, such as a medium-sized air conditioner, uses a slightly different style of plug, that only fits into a dedicated 20A outlet.)

You're correct that appliances that need more power than that, such as electric stoves and ovens, electric water heaters, electric clothes dryers, and whole-house air conditioners, normally run on 240V (and often using dedicated circuits of 30, 40, or even 50 amps). But in normal residential usage this is still single-phase. Three-phase power is typically available only in commercial and industrial zones.

With all of that said, it's also the case that "far more convenient" is to some extent in the eye of the beholder. Me, I don't boil much water, but I'd rather use a pot on the stove than a fussy special-purpose appliance. YMMV. (In other words, yes, a lot of this is just tradition.)

And there are electric hotpots in the U.S., but they're not 2000 watts like yours are. (And is your vacuum cleaner really 2500W? My goodness! How do you keep from sucking up the carpets and floorboards? :-) ) —Steve Summit (talk) 17:33, 28 January 2007 (UTC)

I suppose in the real world, not _that_ many house hold appliances do need more than 1500W. Yes, our vacuum cleaner rates at 2500W, but I'm a 'bigger number better shopper', and the majority rate around 1200W I think.

Of course we constantly boil water for our 50 cups of tea a day :) When I say more convenient, it's usually faster (our big wok burner on the stove is 3kW, but I think most hobs are only 1.5kW), and more so you can use it where you don't have a cooker, like in the office. (How does that work then?) I suppose if the latter is needed a lower wattage kettle is fine, just slower.

These super high wattage sockets. Are they common, i.e. one in each room?

Well, no. A 40 or 50 amp stove outlet is common in the kitchen if the house is to have an electric rather than a gas stove. A 30 or 40 amp dryer outlet is common in the laundry area if the house is to have an electric dryer. Most other high-current appliances (whole-house air conditioners, heat pumps, electric water heaters, some electric stoves) are permanently wired, with no plug at all.

20 amp (as opposed to 15 amp) outlets are becoming more common in commercial construction, but they're still rare in residential. You can see what they look like in the diagram at http://www.quail.com/nema.cfm. A standard 15 amp outlet ("receptacle") is a NEMA 5-15R. The standard plug for an appliance that draws no more than 15 amps is a 5-15P. The special 20 amp outlet I spoke of is a 5-20R. Notice that one of the slots is T-shaped. The plug on an appliance that draws 20 amps (such as a medium-sized air conditioner) will be a 5-20P. Notice that one prong is horizontal. Notice also that a 15-amp plug (the conventional one with both prongs vertical) will plug into either kind of outlet. See also NEMA connector. —Steve Summit (talk) 21:50, 28 January 2007 (UTC)

We have separate circuits for cookers that are 30/50A, but normal sockets are fused at 13A (or at least the plugs on the appliance are never higher than this, most sockets on the wall I don't /think/ have fuses). But things like free standing air conditioners (or more likely 3 bar heaters :) ), can be plugged anywhere.

I'm trying to work out if I should pity the US and their substandard electrical system full of inconveniences ;). 86.133.205.209 18:29, 28 January 2007 (UTC)

Electric kettles are used in England because they drink tea much more freuqently than the U.S. and it is simply faster. They are certainly available in the U.S. and I have two myself. European electric power is more expensive than U.S. power and my experience is that the U.S. power to homes (especially to new construction) has more capacity than European counterparts.

Typical U.S. homes have a 200 Amp meter service (200A at 240V). 120V is available at standard wall sockets. 240V, 30A is used for the Electric water heater tank (Europe is going tankless, probably more efficient). 240, 30A is for the electric clothes dryer. 240V, 50A for the oven/stovetop. 240/50 for the Air Conditioner. Kitchens have 120v/20A circuits for small appliances. Living areas have 120V/15A circuits for general lighting and small appliances such as TVs and radios. --Tbeatty 19:57, 28 January 2007 (UTC)

Maybe the main reason is for tea, but I don't drink that much tea and I'd find it very inconvenient not to have an electric kettle, at work and in the kitchen. Apart from normal tea and herbal tea, you use it for hot chocolate, instant coffee and cafetiere coffee. You can use it for noodles (whether Pot Noodles or plain noodles). You can use it whenever hot water is needed, like to get water to boiling point before cooking rice, pasta or vegetables in it (much faster that way), or if you need to melt chocolate, or clean something, or get a spoon hot before trying to spoon golden syrup or treacle. Do Americans not do any of these things? Skittle 21:12, 28 January 2007 (UTC)

Just looking at kettles, the current ones all seem to be 3000+W these days(/me puts new kettle on shopping list). But here is a question: Why can you not just have standard 120V@30A. Would it require thicker wiring, thicker than 240V@15A (i.e. what would be in the non cooker circuits in UK houses)? 86.133.205.209 00:20, 29 January 2007 (UTC)

Yes, the loss from electrical wirings grows exponentially with current, P=I²R, and thus if you double the current your wires need to dissipate 4 times more heat from the losses, or be a lot thikcer. --antilived^{T | C | G} 04:59, 29 January 2007 (UTC)

s/exponentially/quadratically/ :) -- mattb @ 2007-01-29T05:15Z

As to that last question, the current that determines the thickness you need for the actual wire while the voltage determines the thickness you need for the insulation. In practice all modern wiring in North America is rated for at least 250 V, but yes, a 30 A circuit would need thicker wiring than a regular 15 A one. There is no strong reason why 30 A couldn't be provided at 120 V on one circuit -- there's even a standard plug design for that specification -- it just isn't one that's ordinarily used. Note that North American homes typically have 240 V power in the form of two opposite phases of 120 V, so it's easy to provide 240 V for high-power appliances, as described above.

Above, Steve Summit says that in the US, "outlet circuits are normally fused at 20 amps, but there's an expectation that no one appliance will draw more than 15 amps." Canada follows US electrical standards in most respects, but none of the places I've lived in Canada has had more than 15 A fusing for ordinary outlets. My guess is that 15 A is an older standard in the US (for ordinary 120 V circuits) and that there are still a lot of 15 A circuits in some places.

Oh, and I have an electric kettle. They're common here. It's so old that the sticker that probably had rating on it has come off, but I expect it draws about 1000-1200 W. Let's see, say 600 ml for the teapot, heated from 5° to 100°C, that's 57 cal or about 240 J. If all the heat went into the water, 1200 W would do it in 200 seconds, or 3.3+ minutes; that sounds about right. No doubt if many people had experience with high-wattage British kettles they'd find it unreasonable, but we don't.

--Anonymous, January 29, 2007, edited 05:12 (UTC).

Mr. Anonymous means 57 capital Calories (kcal) and 240 kJ, but the 3.3 minute figure is correct.

Also, with respect to insulation thickness (in North Americal, at least) conventional building wire is rated at 600V. Above 600V, you not only need to use special wire, but completely different sections of the NEC apply.

The situation with current, voltage, and power is quite interesting. Everything else being equal, the higher the current the thicker (and heavier and more expensive) the wires need to be. Everything else being equal, the higher the voltage, the more power you can carry without increasing the current and without having to use heavier wires. That's why cross-country transmission lines use such high voltages (hundreds of thousands of volts). But, alas, as with so many other aspects of nature, everything else is not equal, after all. We can't further reduce the I²R losses of transmission lines by making the voltages even higher, because at extremely high voltages (above 750,000 volts or so) you lose even more energy due to corona discharge; basically the electricity starts leaking out into the air, sort of like low-grade lightning. —Steve Summit (talk) 02:53, 31 January 2007 (UTC)

yeah really, i couldnt live without a kettle, if fact i dont know anyone (in the UK) who does. i suppose americans have coffee machines typically and drink less tea than we do, so for the other stuff maybe they just put up with waiting.. (maybe its a case of them not knowing any better, i mean, only 10% have passports..) but seriously, all that manly chat about electric voltages kind of washed over me, in a yes or no answer, is the lack of kettles in America becuase of the energy supply? 87.194.21.177 18:30, 29 January 2007 (UTC)

I think the conclusion is that yes, they can't have the super-fast kettles that we have in the UK. Theoretically stove-top kettles are therefore faster, but the main reason they use them is simply tradition. Back 10 years, I don't think electric kettles were quite so good, they were slower and not fancy flat bottomed (but we still used them), back 30 years I think stove-type whistle kettles were actually quite common in the UK.

Another point, good hobs are not that common. How about all those bed-sits with exceptionally crappy two-coil electric hobs? Stove-top kettles are only good if you have a massive 3kW burner on the hob.

Perhaps the reason we use electric kettles now is because we are used to having kettles _everywhere_. In the office, in a porta-cabin on a building site, I have one in my bedroom. Americans probably have coffee machines in these environments. (And to be honest I drink more tea than coffee and would love a coffee machine in the office so I don't have to drink nasty instant) 86.145.143.21 00:16, 31 January 2007 (UTC)

Yes, the reason we don't have electric kettles is that we don't drink tea. Remember we chucked it all in the harbor. (Actually per capita yearly tea consumption in Britian is 2.5 kg compared to 0.3 kg in the U.S. and remember we drink a lot of our iced.[2]) Besides stovetop kettles work plenty well - when you are done frying your chicken you slide the pan onto a cool burner so the grease doesn't get baked on so badly. Then you slide the kettle onto the hot burner so the children don't burn their fingers - and it humidifies the room as well. I hear you can boil water for hot chocolate in one as well - if it is winter. (While some hotels provide coffee makers in rooms, I wonder how many people have them in their own bedrooms?) Rmhermen 01:04, 31 January 2007 (UTC)

morning breath

hey, what is it that makes your mouth feel horrible after you've slept? (even, it seems if you nod off for 5 minutes). i'm sure there's an article on it but sadly i dont know the big grown-up name.. thanks. —The preceding unsigned comment was added by 87.194.21.177 (talk) 17:16, 28 January 2007 (UTC). oops, forgot to sign,87.194.21.177 17:17, 28 January 2007 (UTC)

Halitosis? --Wirbelwindヴィルヴェルヴィント (talk) 18:10, 28 January 2007 (UTC)

Yup, that is the "big grown-up name" you are looking for. Morning breath is even a redirect to Halitosis. Mathmo ^Talk 00:01, 29 January 2007 (UTC)

The article list possible causes as dryness, stress, hunger (ketosis), eating certain foods such as garlic and onions, smoking, or poor oral hygiene. I'd add one more: cheese, though it's a delayed effect. Vranak

Somebody has asked this before, last year. The verdict was actually just dryness. [Mαc Δαvιs] X (How's my driving?) ❖ 18:50, 28 January 2007 (UTC)

No one has accused bacteria! I accuse bacteria! − Twas Now ( talk • contribs • e-mail ) 05:12, 29 January 2007 (UTC)

But why is it dry:?

My theory is that if you sleep with your mouth open, it dries up. When you exhale, you lose moisture. Also, air tends to be less humid (more dry) than a mouth, so when you inhale through your mouth, the mouth dries up. − Twas Now ( talk • contribs • e-mail ) 10:25, 31 January 2007 (UTC)

Spaghetti Bridge

Anyone have any ideas on building a spaghetti bridge without compromising weight? —The preceding unsigned comment was added by 66.82.9.49 (talk) 18:13, 28 January 2007 (UTC).

This question was asked last week. The most interesting answer is to create a suspended bridge by using thick spaghetti tubes for the vertical poles and boiled (soft) spaghetti for the cables. --Kainaw ^(talk) 18:46, 28 January 2007 (UTC)

Avoid soft spaghetti. It will be heavier because of the water content, and it has virtually no tensile strength. I've never done this myself, but I would have thought a truss bridge design would be the way to go.--Shantavira 19:52, 28 January 2007 (UTC)

The intention was to let the spaghetti dry out again once formed into the proper parabolic shape of the evenly-loaded support cables.

Atlant 01:18, 29 January 2007 (UTC)

I'm not sure what's meant by "compromising weight", but: the most interesting way to answer the question is to think about the material properties of spaghetti versus the material properties of building materials in general, and versus the necessary material properties for various types of bridges.

• Some materials are great in compression: stone, wood, concrete, steel.
• Some materials are great in tension: rope, wood, steel.
• Some materials are lousy in compression: rope, steel cables, cooked spaghetti.
• Some materials are lousy in tension: stone, concrete.
• Some materials are lousy in both modes: sand.

(From the above you can see that a few materials are good in both modes: wood and steel.)

Sometimes a structural element must act, in effect, in both tension and compression at the same time. The most obvious example is a beam, which while carrying a load ends up in compression along its top edge and in tension along the bottom. Wood and steel can obviously be used to make beams, but other materials must be used in combination (the canonical examples being reinforced and prestressed concrete). I might call this third mode of stress flexion, but I'm not sure if that's the official term.

Now, to bridges. One of the oldest types of constructed bridge, I suspect, is the stone bridge, where everything acts in compression. Most other bridge types involve some elements which are in compression and some elements which are in tension. Our bridge article talks about the various types, and in the Bridge structural and evolutionary taxonomy section, talks specifically about the various materials and stresses I've mentioned.

Finally, think about spaghetti. It's okay in tension. It might be okay in straight compression, if you could keep it straight, but a single strand is very likely to bow out if you pushed it from both ends. Many individual strands bundled together somehow (if the contest rules allow it) would make a decent post, i.e. would act pretty well in compression. A single strand is obviously terrible in flexion. Several strands glued together along their entire length (again, if the rules allow it) might be okay in flexion.

So, thinking about all these things, take a look at various bridge designs and try to figure out what their requirements are, in terms of building materials that work well in compression, and in tension, and in flexion. Think about which design could be most readily realized using (and capitalizing on the strengths of) spaghetti. Or perhaps you can think of a brand new design uniquely suited to the particular strengths of spaghetti!

But of course, this is not just a theoretical exercise. It will also be necessary to do plenty of experimentation. Don't just ask on the net how to do it, or listen to me blathering from my armchair about how you might do it -- go out and get a bunch of spaghetti, and some glue and thread and whatever else the contest rules allow, and try building some bridges, and put some weights on them, and see if they break. When (not if!) they break, examine how they broke: which parts broke, and what stresses those parts were subjected to that they couldn't handle. Redesign your next bridge differently, either with more material in the spot that broke, or using a different design that doesn't subject your building material to that particular stress. (And, most importantly, do stress your early designs to failure! Don't spend so much time building them that you come to think of them as works of art, that you can't bear to break. To learn where their weak points are, you're going to have to break them. You won't learn anything if you don't.)

—Steve Summit (talk) 20:55, 28 January 2007 (UTC)

Oh, and here's another angle. If those words "compromising weight" have to do with a requirement to minimize the mass of the bridge while maximizing the load it can carry, then you have an additional, optimization task. Not only must you strengthen the parts of the bridge that break under load, you must also seriously consider weakening those portions that don't break under load -- because they're stronger than they need to be, and hence contributing dead weight to the body of the bridge without increasing its carrying capacity.

Rumor has it that Henry Ford was especially partial to this technique, hounding his engineers to scrimp on the materials in all the parts of his cars that weren't breaking, since they were "wasting" materials and hence increasing the manufacturing cost (and hence decreasing profits).

I also heard a story about the builders of military aircraft in Britain during WWII. Whenever a plane limped home after barely surviving damage done by an opposing fighter or by antiaircraft fire, the builders would reflexively strengthen the parts that had broken. But this was faulty logic -- though those parts had broken, the plane had managed to limp home safely. What the builders should have been doing (so the argument goes) was strengthening all the parts of the plane that weren't broken in planes that limped home, since those were presumably the parts that, if they broke, caused a plane to crash and never come home... —Steve Summit (talk) 01:48, 31 January 2007 (UTC)

Cf. The Deacon's Masterpiece.

Ooohh, definitely! I like this version, with pictures. —scs

Incidentally, by "stone bridge" above, Steve means a stone arch bridge. A clapper bridge, of course, would have the upper surface in tension. --Anonymous, January 31, 2007, 02:34 (UTC).

CuSO4.5h20

In a lab, we were asked to grind some crystals of CuS0₄.5H₂O into a powder, heat it over a Bunsen Burner in Cone B, and then add water after a minute or so. The crystals changed color from blue to white and then to teal. When water was added, it bubbled up and rose up in the test tube. Is heating CuS0₄.5H₂O a physical or a chemical change? How can you support it? And also, what exactly happens in that reaction? Thanks so much, Katie. —The preceding unsigned comment was added by 75.4.65.143 (talk) 18:19, 28 January 2007 (UTC).

I haven't done this lab in school...I'm in high school, grade 12, but the colour change you observed changing to white most likely was removing the water of hydration, i.e. making anhydrous cupric sulfate from the pentahydrate. Maybe the second part was rehydrating it? 74.102.89.241 00:38, 29 January 2007 (UTC)

This is the very first chemistry experiment I did at school so I remember it quite well. I believe the above post is an accurate represemtation of whats going on-- although I dont remenber the CuSO4 going teal. OTOH, you could always ask your chemistry teacher if this is not homework.--Light current 08:57, 30 January 2007 (UTC)

well perhaps it was not the first expt I did. But anyway I still have my schoolbook detailing the expt. THe expt was to find the percentage of water of crystallisation in hydrated copper suplfate .

The substace was weighed before heating. Then heat was gently applied (must have been a bunsen burner) until the poweder became white. It was reweighed. The substance was heated some more until the final two weights were equal. THis showed that all the water had been driven off. My experiment showed that the percentage of water in CuSo4. 5H2O was 36.3%. I believe the correct theoretical value is 36%. But dont take my word for it IANAC 8-)--Light current 12:12, 30 January 2007 (UTC)

volcano age

how old is the kilauea volcano in hawaii —The preceding unsigned comment was added by 141.152.246.102 (talk • contribs).

Check the infobox of Kilauea. --Wirbelwindヴィルヴェルヴィント (talk) 19:48, 28 January 2007 (UTC)

Mitochondria Reproduction

If mitochondria reproduce independently of the cell, what controls their reproduction? Why do they not reproduce wildly and clog up the cell?

I understand that a lot of their former DNA has been transferred to the nucleus; does this do the job? If so, how does the nucleus establish a reproduction rate, and how does it differentiate between the mitochondria to be reproduced (e.g. between those whose DNA has mutated in a bad way and those which still function adequately)?

Philip Day —The preceding unsigned comment was added by Madphilday (talk • contribs) 19:35, 28 January 2007 (UTC).

According to the article, mitochondria within a cell reproduce when the cell needs more energy, but then are destroyed or quit working when the cell doesn't need so much. It doesn't mention the specific mechanism though. Vitriol 21:53, 28 January 2007 (UTC)

Quantum mechanics

Your article is all on physics, it omits biological psychology and the quantum mechanics of the brain, I also looked under biological psychology and I did not find it. Im taking a biological psychology class and I was looking for extra information and I am disappointed I could not find it at your site. —The preceding unsigned comment was added by MarkJam (talk • contribs) 21:33, 28 January 2007 (UTC).

You didn't read it well enough. See the quantum mind link on the "See also" section. — Kieff | Talk 21:57, 28 January 2007 (UTC)

It probably should be pointed out that quantum mechanics is, in fact, a physical theory. The biological application is a lot more speculative and less widely accepted. QM has given us an understanding of things like semiconductor devices and lasing and a way to describe three of the fundamental forces of nature in terms of particle interactions. In other words QM is well supported by experimental results. As yet, the quantum mind theories are little more than conjecture (in fact, I don't think they even make any concrete predictions that could be measured, so their status as "theory" is also questionable). -- mattb @ 2007-01-28T22:28Z

If your looking for "Free Will" in quantum mechanics, your looking in the wrong place. --Tbeatty 08:46, 29 January 2007 (UTC)

No. of chromosomes in Neanderthals?

I know that it is not a well researched topic. But it'd be great if anyone could give me an idea about the number of chromosomes in the genome of Neanderthals? Thanks.nids(♂) 22:19, 28 January 2007 (UTC)

Neanderthals are now widely believed to have bred with homo sapiens, therefore they must have had a corresponding number of chromosomes, 46. Vespine 00:42, 29 January 2007 (UTC)

Widely believed? I thought this was merely a theory. Do you have some references? Clarityfiend 03:03, 29 January 2007 (UTC)

Isn't it truer to say that, if Neanderthals bred with homo sapiens then they must have had 46 chromosomes and therefore must have been human beings and therefore the distinction between Neanderthals and homo sapiens breaks down; or, if they didn't have 46 chromosomes then they were not humans and could never have bred with homo sapiens? JackofOz 03:09, 29 January 2007 (UTC)

Recent genetic work (e.g. the work of Krings [3], Bryan Sykes, and others) strongly argues that the humans and Neanderthals did not interbreed. Samples of mitochondrial DNA from well preserved Neanderthal fossils are too distinct from modern humans for the gene pools to have been mixing. Given that the two populations almost certainly had opportunities to interact, a lack of interbreeding would likely indicate that they were genetically incompatible, and one plausible (but by no means certain) explanation for that would be that Neanderthals had a different number of chromosomes from modern homo sapiens. Notably, homo sapiens have 46 chromosomes, while living great apes have 48, and that transition could have occurred after the Neanderthal population split from the pre-homo sapien line. Dragons flight 05:42, 29 January 2007 (UTC)

No it isn't, number of chromosomes isn't a unique species identifier, a domestic cat and a domestic pig has 38, doesn't mean they are the same species, nor that they can interbreed. But animals that DO interbreed do need to have the same number of chromosomes. Neanderthals had 46 chromosomes but that doesn't mean they were the same as humans, but they were probably close, it doesn't 'prove' that they bred. And I think recently it went beyond being just a theory, there was evidence found that Neanderthals could have actually just been bred into the population, not died out due to homo sapiens as previously thought. I'll try to find the sources. Vespine 05:15, 29 January 2007 (UTC)

We can have both the scenarios. i.e. Neanderthals had 48 chromosomes and they interbred with humans to produce Hybrids (they would be mostly sterile though). Also, Neanderthals may be having 46 chromosomes but still unable to interbreed with Humans. So, even if they interbred with humans, this does not prove that they had 46 chromosomes. But have you read somewhere that Neanderthals had 46 chromosomes. I am not asking for a source, just confirming if you had read that in a reliable source.nids(♂) 10:30, 29 January 2007 (UTC)

Skull suggests human-Neanderthal link. Anchoress 05:55, 29 January 2007 (UTC)

This skull, by itself, suggests nothing. For all we know, he could have been just a sterile hybrid.nids(♂) 10:11, 29 January 2007 (UTC)

Just another note. It is not required that species that breed have the same number of chromosomes (see Donkey, Horse, Mule). If the homo sapien population exploded and interacted with Neanderthals, cross breeding (and the subsequent sterile offpsring) would have wiped Neanderthals off the planet quickly and with no genetic trace. Imagine 10,000 horses and 100 donkeys. Females are almost constantly pregnant and the large majority of female donkeys would be carrying sterile offspring. Homo Sapien/Neanderthal offspring wouldn't be sterile for the same reason as mules but they may be for other reasons. (This is my own pet theory, no pun intended :) ). --Tbeatty 06:25, 29 January 2007 (UTC)

The Cell paper from Svante Pääbo's group that was linked to, studied mitochondrial DNA. Humans are but a medium in which mitochondria propagate themselves. The fact that Neanderthal mtDNA is not found in contemporary populations, only shows that there is no unbroken maternal line between contemporary humans and neanderthals. If the carriers of particular mitochondrion variants had even the slightest disadvantage compared to others, they would be less likely to have children, and those mitochondria would die out. This does not mean that the people that carried these mitochondria have no ancestors today, only that there is no unbroken chain of maternal ancestors. Consider also, that the fitness of mitochondria reasonably might depend on climate, since they are the cells' "power plants". And the neanderthals lived in a climate that was very different from today's. Therefore, to me it proves absolutely nothing that neanderthal mitochondria are extinct. I also disagree with the statement made in the Cell paper, that the observation that the time of divergence between neanderthal mitochondria and modern human mitochondria, being much longer ago than than the estimated divergence time of modern human mitochondria, argues against interbreeding. The fact that all contemporary human mitochondria stem from the mitochondria that lived in a woman some 200,000 years ago only proves that mitochondria are subjected to evolutionary pressure. Studies of the Major histocompatibility complex of primates, show that humans, chimps, orangutans and gorillas share many polymorphisms, particularly in the class II region. This argues strongly against very narrow bottlenecks in the size of the human (and ape) populations, and also shows that speciation is not an event that happens in a single individual, but in large groups which, while diverging, gradually lose the ability to interbreed. Jan Klein wrote a very interesting review on this way back in 1987 (Origin of major histocompatibility complex polymorphism: the trans-species hypothesis. Hum Immunol. 1987 Jul;19(3):155-62.). Note, incidentally, that this also shows that a difference in the number of chromosomes cannot be an absolute obstacle to interbreeding. --NorwegianBlue ^talk 20:22, 29 January 2007 (UTC)

NITRIC OXIDE AND THE IMMUNE SYSTEM

Could someone please give me a detaile d explanation of the role of nitric oxide in the human and mammalian immune system? —The preceding unsigned comment was added by Wizzybone (talk • contribs) 22:47, 28 January 2007 (UTC).

January 29

Human "Radio Wave" Transmitter

For at 20 years (maybe even more) I have been able to effect street lights or the gas in them somehow to make them go out when I walk under them. This particular type gas (whatever it is in these bulbs) apparently is sensitive to radio waves. I can not effect ALL street lights, but perhaps 10% of them. The ones that go out I can then go back later (after it eventually comes back on in 5 minutes to 5 hours) and I can make this same bulb go out again. At my apartment complex where I live they have outside lights (of apparently the same type inner gas) that I also effect about 10% of them. It is so predictable that I have been able to video record the event many times (proving it is not happenstance). Also it proves that it is not mechanical in any way (i.e. loose or intermittent connection). Also street lights do not have "On / Off" switches, so there is not a person turning it off when I walk under it (many times no person within 1000 feet). I have many eye witnesses (i.e. apartment complex maintenance people, apartment complex managers, friends, relatives, and complete strangers). Many times when the bulb is out I walk under them and the bulb pops back on when apparently my "human radio waves" are with range (about 20 feet +/- 10 feet). Is these such phenomena as "human radio waves" or a "human radio transmitter" or something like this known in science? --Doug ^talk 00:37, 29 January 2007 (UTC)

Sure, it's called black body radiation, though the EM radiation you should be emitting ought to be at a slightly shorter wavelength... -- mattb @ 2007-01-29T00:45Z

You do understand that high-intensity discharge lamps "cycle" at the end of their lives, going on and off on a, say, five minute cycle. You might also want to check Magical objects in Harry Potter for the "put-outer".

Atlant 01:26, 29 January 2007 (UTC)

As it happens, we do have an article about that! It's at Street light interference. (Yes, sometimes it seems Wikipedia has an article about everything.) --cesarb 02:16, 29 January 2007 (UTC)

Wow! Thanks for that! I always figured that this was just another hint that Jesus hates me. There's a light that does this outside the security gate to my workplace. I didn't realize people actually did some research into it. Dismas|^(talk) 05:51, 29 January 2007 (UTC)

I've had a similar experience, and always figured that there was some sort of sensor on the lights that turned them off if it saw any reflected light, and that my car or clothing or whatever reflected just enough light, in those circumstances where my presence seemed to turn them off, to trip the sensor. I suppose I do walk past an awful lot of street lamps on a daily basis, some are bound to turn off, and of course I wouldn't notice those that didn't. ^tucker/_rekcut 12:48, 29 January 2007 (UTC)

The sensors, at least the ones I've taken apart, wouldn't be affected by your passing by for at least two reasons: One, they include substantial time delays for both turn-on and turn-off; they don't change their minds quickly. Two: If properly installed, they tend to be arranged to look towards the northern sky rather than down at you walking by.

Atlant 13:42, 29 January 2007 (UTC)

i agree with Atlant (again?) that the sensors I had experience of for cotrolling street lighting were mounted on top of the lamp housing looking at the sky. Its difficult to see these sensors from the ground.

I did not however know about this discharge lamps cycling. Is that a design feature or are you taking us for a (bike) ride 8-)--Light current 12:34, 30 January 2007 (UTC)

:-). But "cycling" is a well-known phenomenon in the life cycle of HID lamps. It's a natural result of the Work function of the cathodes rising as the emissive material is blasted off of them over the life of the lamps, combined with the way the voltage across the arc tube rises as temperature (and so, pressure) rise in the arc tube as the lamp heats up.

Atlant 12:59, 30 January 2007 (UTC)

Hmmm IDKT. You learn something new every day. THanks for illuminating the process! 8-)--Light current 13:02, 30 January 2007 (UTC)

I cant see anything in the article about end of life cycling. Maybe someone could add it?--Light current 14:31, 30 January 2007 (UTC)

I wrote text for Street light interference yesterday; I'll go swipe it into the HID articles.

Atlant 16:56, 30 January 2007 (UTC)

(Done, although the various cut-n-pastes may have some redundant Wikilinks.

Atlant 17:38, 30 January 2007 (UTC))

You all have given me excellent answers. Appreciate it very much. I figured that probably I was not unique on this phenomena so was looking for others where this happens. The Wikipedia article Street light interference has touched on the subject pretty close. Now I can call myself either a "SLIer" or a "Puter-Outer". For the "skeptics" I will respond:

• Not the "Pauli effect" or "Synchronicity", closer to that of a "Put-Outer". Somehow I am sending out a type of "radio signal" that has a frequency that interfers with the gases igniting within the bulb itself. Also I am not effecting the electrical ballast or associated electronics. It is definitely the igniting of the gases that produces the light.
• Recorded it several times on video. To prove that I am the one "sending out a signal" I have had several other people go under the same Street Light and nothing happens; however when I go under it, then "Out" goes the bulb. Or if the bulb is already out, then I turn the bulb back "On" igniting the gases withing the bulb to ignite with a type of a microwave signal.
• I have watched the Street Light from a distance with several other witnesses and nothing happens to the bulb for hours. However the minute I go under it, "Out" it goes (video recorded). If it was something mechanical (i.e. light at the end of its life cycle) then it would happen with no person coming close to it - however nothing happens to it on its own.
• Many times, once I put "Out" the Street Light, it never comes back on until the electrical power is turned off the following morning at daybreak. Then the Street Light works normally again the next day for hours on end, until I walk under it. If it was of a mechnical or electronic nature then the bulb would re-ignite on its own, however it does not (most times). When other people I send out to go under this same Street Light, nothing happens. Tested this several times to prove it is beyond just a "happenstance" event. It is definitely a type of "radio signal" or "micro-wave signal" or of this nature. It is some sort of electrical signal sent out from the brain interfering with the gases igniting as they were designed to do to produce the light. Also I have figured it is not something I can control; nor is it good or bad. It is just a phenomena that happens, apparently to only a few people worldwide.
  

Apparently it looks like it is less than 1-in-a-million this happens to. I didn't even know what this was called or that it had an official name ("SLI"), however I knew for a fact it does exist. Is there others out there this happens to also? I would like to hear from others; maybe we can pinpoint its exact source, which is probably a type of a microwave "radio signal".
For the "skeptics": never read Harry Potter, never went to any of the movies. I am an old retiree interested in articles on Francesco Petrarch. --Doug ^talk 14:57, 30 January 2007 (UTC)

It seems out of the realm of science to answer your question... As alluded to earlier, the chance that you're emitting any significant microwave EM radiation is pretty infintesimal.. -- mattb @ 2007-01-30T15:05Z

It is definitely a science question. Just because the "skeptics" didn't have it happen to them or video record the event themselves, doesn't mean it doesn't exist. Video recording the event takes away "happenstance". This phenomena definitely exist, as others already responded to and know. So, bottomline: Is there others out there this happens to also? I would like to hear from others; maybe we can pinpoint its exact source. Thanks "SLIers" for responding. We will figure out what it really is (scientifically).--Doug ^talk 15:28, 30 January 2007 (UTC)
Since I started this article, I would like to add some additional information to this article of Street Light Interference after doing additional research recently on the internet. I believe this would relate to primary source and proving this phenomena exists instead of it being a mere coincidence. I have video recorded this on many occassions and it was definitely repeatable. I have several eye witnesses at the time of the video recording the event taking place. One was an apartment maintenance manager to a very large apartment complex. I could get him to sign a statement that he was an eye witness to the event. He held the camera when he took this video when I went under the bulb and make it go out (several times). He had several people adjacent next to him at the time. They are all eye witnesses. Would this then be considered a primary source that this information could be entered into the article Street light interference? Would this be sufficient proof (at least for a start)? What additional proof would be needed to show this phenomena is real?--Doug ^talk 19:53, 30 January 2007 (UTC)

See Wikipedia:Reliable sources, in particular the part about primary sources. --cesarb 23:52, 30 January 2007 (UTC)

If the effect is caused by EM waves, then the effect should cease whenever the transmitter (you!) is enclosed within a metal shield. A simple metal waste can placed over your head and upper torso might make a difference. But if you can totally enclose your body in a metal shield, yet the streetlight reliably goes out when you approach, then it's not caused by EM waves. Another experiment: apply DC high voltage to a small neon pilot light, with a current-limiting resistor in series. Measure the voltage at the terminals of the neon lamp. Parts: NE-2 lamp, twelve 9v batteries in series, 100K resistor. Now let someone observe the voltage reading while you retreat to great distance and then again approach. Does the neon lamp voltage change significantly? (This experiment tests whether your body can somehow raise the arc voltage of an HID lamp, which might cause it to "cycle" one time.) --Wjbeaty 21:18, 31 January 2007 (UTC)

Suicide question

I've been thinking about suicide a lot lately, and I was wondering if you shoot yourself in the head with a gun (whether it be to the side of the head or in the mouth), do you die in pain because of the incredibly loud gunshot blast? I would assume a gunshot at that close range (literally a few inches from your ear) would be well above 200 decibels and the threshold of pain is 120. I think about 300 is instantly deafening. So would you hear the gunshot a second before you die, thus causing you immense pain in your last second of life? Thanks. NIRVANA2764 01:26, 29 January 2007 (UTC)

I thought bullets travel faster than the speed of sound anyway. And besides, it would take awhile for the pain to register since 1) Your body would be in shock 2) You'd be dead --froth^T 01:35, 29 January 2007 (UTC)

Typically bullets travel around the speed of sound. That's beside the point, if you've been 'thinking about suicide' even if you haven't been thinking of actually doing it, please be careful because thinking about it is actually a warning sign, it's on those lists of 'things to look out for'. I've been there too and it sometimes seems too hard to overcome on your own, no matter where you live if you have access to the internet you no doubt have access to suicide support services, it's not something to take lightly, you only get one chance. Vespine 02:32, 29 January 2007 (UTC)

It takes a long time for signals to travel from the ear to the brain. By the time that happens, you'd always be dead. What I don't understand, though, is why you don't want to endure only a very short-lived pain if you truly want to suicide. If even that small pain matters, then your life is probably not horrible enough for something like suicide to be warranted. --Bowlhover 04:35, 29 January 2007 (UTC)

People who commit suicide also don't think about the impact that it has on the people around them. Families and friends see a life that has been wasted, and have immense trouble coming to grips with the fact that someone they care about decided to kill themselves. Suicide is not a solution. Problems are only temporary, and suicide is permanent. It cannot be undone. BenC7 01:43, 30 January 2007 (UTC)

Not to defend the OP (i obviously don't know anything about him; he certainly might be crazy as a loon), but that is a bull-shit arguement. No-one is obligated to keep families and friends feeling warm and fuzzy, especially not if it involves suffering for them. This is the same arguement relatives sometimes use when they disapprove of a person's life-style -- e.g., Don't marry that man, can't you see it's killing your mother? How can you be so selfish? or How can you be gay? This will crush your father. Can't you think of anybody but yourself?

Certainly suicide is a pretty serious issue that often (but not always) has its roots in some mental illness, and this is a factor to consider, but the last thing a person in such a position should have to worry about is somebody guilt-tripping them about wanting to end their suffering. ~ lav-chan @ 23:11, 30 January 2007 (UTC)

Pain travels at around 1.7 metres per second I believe, so you would be well out of pain before you died if it was a clear shot. However, I don't condone suicide & think it a selfish act. Try seeing a counsellor if you are having difficulties... Spawn Man 05:23, 31 January 2007 (UTC)

Wrist Pain

I don't think it's carpal tunnel (wrong side). I'm getting it by typing in a very weird position, with my laptop on about a 45 degree angle up against my knees. On the upper side of my right wrist-to-forearm which is (currently) typing not only at this incline but at another 45 or so degree angle into the keyboard (so my arm is laying from the corner of the keyboard plane to the center), I'm getting what may or may not just be muscle tiredness from typing in this weird position. The muscle that's tired is the one on the upper-front forearm that stiffens (ie flexes) when you cock your hand back to be nearly perpendicular to your forearm. It's tired close to the wrist. I know you aren't supposed to give medical advice, but does anybody think this is something to worry about? If I keep typing like this, will the muscle get used to it so I can continue, or will I get an injury? Thanks, Sashafklein 03:47, 29 January 2007 (UTC)

If it was me, I'd stop. A 45 degree angle is a lot for the wrist to keep bending at while typing and operating. Try sitting cross-legged so the laptop will be flatter, so sit at a coffee table. But this is not medical advice, just advice. --Wirbelwindヴィルヴェルヴィント (talk) 03:55, 29 January 2007 (UTC)

^{The following could be considered medical advice and may be removed summarily.}

If you want to cripple yourself, keep typing as you have been. If the muscles 'get used to it', they will basically be seizing up, and you may lose flexibility, range of motion, and sensitivity. If you absolutely must keep typing, change your typing arrangement whenever you begin to feel discomfort. Vranak

So nobody thinks there's any chance that it's just a rarely used muscle group in need of some exercise? It doesn't feel acutely painful or anything, just sort of like doing a weird weightlift you've never tried before and tireing out immediately. Sashafklein 04:46, 29 January 2007 (UTC)

Nobody is going to be able to say that, because this is a medical question, and suggesting to you that a pain you have developed is nothing to worry about would be extremely irresponsible. All we can say is "see a doctor", and I really mean that. If you keep working on, for example, a repetitive strain injury, you could make it much worse and give yourself problems for life. Go and see someone who's qualified to tell you what's wrong and what to do. Skittle 22:34, 29 January 2007 (UTC)

Symptoms of Insomnia -- Burning Eyes

Hi,

I was wondering why your eyes burn after not getting enough sleep? I also am curious if there is a way to counteract this effect?

Thanks,

Best Username Ever 06:25, 29 January 2007 (UTC)

Counteract? Sleep. Problem solved. -- mattb @ 2007-01-29T06:27Z

Thank you so much! I've tried eye drops but those are a hassle and don't work very well. Anyone know why it happens?--Best Username Ever 06:33, 29 January 2007 (UTC)

There's an eye massage that I use that works fairly well for me. With two fingers on each hand, massage in circular motions (approx 10 circles counterclockwise and 10 circles clockwise) 4 areas: Roughly the center of the eye-lids when you close your eyes, where you can feel the bottom part of your eye socket under your eye, the area between your eyes at the top of your nose (bridge? forgot what it's called), and about an inch forward of your temples. Do it fairly gently. I learned it from my sister who learned it from her teacher, many years ago, and I still use it when my eyes are sore because it seems to work. Also note that this is not medical advice, and it's what I personally do. --Wirbelwindヴィルヴェルヴィント (talk) 06:46, 29 January 2007 (UTC)

Thanks!--Best Username Ever 11:43, 29 January 2007 (UTC)

Your eyes are dry. You blink less frequently when you get sleepy in an attempt to make your eyes dry, to make your eyes close to alleviate the problem. (that's what I read on the desk last year) I take care of this by... squirting out more water. I don't know how to explain that one! [Mαc Δαvιs] X (How's my driving?) ❖ 18:55, 29 January 2007 (UTC)

I think burning eyes is a symptom of your eyes being on fire..... Sorry, couldn't help it! Vespine 21:40, 29 January 2007 (UTC)

I myself have had this problem too. After a couple of eye-doctor visits I solved my own problem myself. I began drinking close to a half a gallon to one gallon of water a day. My problem (personally) was not being completely hydrated enough. It did take some time though [and alternatively my kidneys go through the rinse cycle too]

Power Grid Failure Solution

We know that throught the nearly full loaded grid, if one line were to overload , it would trip thereby causing the entire grid to trip causing a blackout. Instead Why NOT place additional circuit breakers at every distribution point, so in case that node is causing the overload, only that node distribution point would trip saving that particular grid and then avioding the blackout?Somewhat similar analogy to the domestic Fuses in our house.

Your supposition is false. Power grids are WAY more complicated than just cascaded loads and cascade failure is designed out meaning it takes multiple failures of the system to induce a cascade failure. Tbeatty 08:43, 29 January 2007 (UTC)

But even if it were true, reflected energy from an instantaneous open is a problem just as big (or bigger) than cascade failure. Imagine a power plant that generates 3,000 MegaWatts and delivers it 1000 miles. It takes time to go 1000 miles. If suddenly the load is no longer there, that energy is reflected back to the generator. This is animpedance mismatch and can destroy the generator. Tbeatty 08:43, 29 January 2007 (UTC)

The whole picture is indeed a bit complex. Quick summary (will vary depending on where you live): the power network has three or four voltage levels: distribution voltage (e.g. 400 kV), high voltage (e.g. 100 kV), medium voltage (e.g. 20 kV) and low voltage (e.g. 0.4 kV which gives 230 V in a two phase wall socket). The line that comes out of a generating plant is HV (the generator is really more like MV, but there's a transformer.) HV gets converted down to MV in a distribution substation. The substation has a big transformer or two with e.g. 10-20 feeders (outgoing MV lines). The feeders are guarded by microprosessor-driven relays. The relays automatically trip if there is an MV short circuit or similar fault specific to that feeder. The relays can also be remote controlled. If the frequency in the whole network starts to drop (i.e. there is a general overload), a centralized computer will start reducing load by tripping MV feeder relays. Each MV feeder trip will black out a couple of city blocks or a handful of residential streets. This happens automatically and takes a few seconds, until an acceptable frequency is restored. It can also be done to a pre-engineered plan, resulting in rolling blackouts. As the article on power outage mentions, complications may arise in this process. Weregerbil 12:56, 29 January 2007 (UTC)

Another problem is defining exactly what we mean by an "overload". Because of the diversity factor, you won't find that (to radically simplify things) the generator has a 100 amp circuit breaker and there are five loads with 20 amp circuit breakers. Instead, because power system designers know that the likelihood of every customer having everything switched on all at once is essentialy nil, there may be 20 loads with 20 amp circuit breakers. The downside is that on a hot summer day or a cold winter day, the generator can be overloaded even while every individual 20 amp branch is running well under its limit.

This is why the entire grid can go down even though no individual distribution circuit has faulted. That's why adding more breakers won't solve the problem.

Atlant 13:37, 29 January 2007 (UTC)

What may be slightly surprising at first is that overload (of the non-short-circuit kind) is not detected by looking at amperage or voltage, but frequency. When there is too much load, the generators at the power station won't have enough input energy (water, steam, etc) to turn them fast enough. Generator turns slower = frequency drops. This is bad because then different generators are trying to feed electricity into the same wires at different frequencies and different phases. So in high quality networks (discounting developing countries etc) the frequency tolerance is pretty strict. If frequency drops, first power stations will try to increase input energy; e.g. open another dam hatch to let in more water. If that fails to fix the frequency, load reduction and other measures can start. Weregerbil 15:00, 29 January 2007 (UTC)

The frequency drops when the load is greater than the connected generators can supply. Witin limits the governors on the generators open or close steam valves or the equivalent on diesels to regulate the frequency within a narrow range, until they have adjusted as far as they can go. Frequency drop beyond a certain limit causes relays to automatically drop preselected loads (ones with no critical load such as the water pumping plant or a hospital) untili the load matches the generating capability. Then, once a generator is brought back on line or a tie line is reclosed to another utility, the load can be restored. If the whole system goes down, it can take many hours to restart the system, since most generators have to trip off line when the connected grid goes dead, and cannot restart without large amounts of auxiliary power from the grid to operate pumps etc. As for line relays, the relays are usually set to trip for fault current, which is usually much more than it takes to overload the line and cause it to fail from overheating. Such overloads should sound an alarm at the control center, and the operator should take action, such as closing a bus tie or correcting an abnormal switching configuration due to an oops error (OOPS, WE PUT THE TOWN ON A 1 LINE FEED WHEN IT TAKES 3 LINES TO SUPPLY IT.) Some utilities have "transformer overload relays" which do trip a transformer when it is so overloaded as to exceed its short term emeregency rating, because transformers can take months to replace, much longer than burned down conductors. Unlike in, say, radio transmission lines, the impedance of the generator is usually way less than the system impedance, which means the voltage is easier to keep constant as the load varies. There are lightning arrestors or similar overvoltage surge protection which would probably reduce the high voltage spikes from switching transients. Therefore, I would not expect a switching transient from an opened line to destroy a generator. The transient would also be intercepted by the impedance of the generating unit transformer. But stability considerations might well require the generator to trip offline if a large portion of the load were suddenly dropped by a system disconnection. Large utility generators trip offline a lot, since they would rather have a false trip than buy a replacement generator. The original questioner's observation that a trip of one line can cause a cascading blackout has held true numerous times since the U.S. Northeast Blackout of 1965. A lot of thought has gone into system relaying, improved operator training and improved system monitoring and displays. A good system does contingency analysis 245 hours a day, to see if the loss of, say, any generator and any line, or any transformer and any line, would start a cascading blackout. They can arrange for more purchased power, or tell interruptible rate customers to shut down or go on generators to reduce the hazard. If the cascade starts, they must initiate rolling blackouts and voltage reduction to keep the system alive until the overload is corrected. A bad utility system has poorly trained operators and does not give them the big picture of where the overloads are and what has tripped, so each individual utility has only a limited view of the expanding problem, This can allow a failure of 1 or 2 lines to snowball into outages in 2 countries. Automatic relays are best, because then no operator is too afraid of losing his job to do his duty without calling some executive at home to get permission, as happened in the 1965 New York blackout. It is an exhilarating experience to see a system control room in action on a new peak load day, with operators sweating to see if they will make it through the peak load, without knowing how high the peak will be, and ready to initiate the dreaded relief measures if necessary. It has been described as being like a guy with a hotrod car going 100 miles an hour and wondering if it can go 110. Edison 21:43, 29 January 2007 (UTC)

renewable energy sources and non-renewable energy sources

what are the differences between renewable energy sources and non-renewable energy sources? —The preceding unsigned comment was added by 61.246.87.56 (talk) 06:57, 29 January 2007 (UTC).

You should check out the links I've added to your question...all shall be answered! -- Scientizzle 07:12, 29 January 2007 (UTC)

Name of multi-step action

When you set up objects to affect each other in consecutive motions to result in one ultimate action, what is the name of the action? (i.e. To get toothpaste on my toothbrush, I might set up a 16 step operation that starts with dropping a ball on a lever.) Is there a name for this? —The preceding unsigned comment was added by 64.19.108.85 (talk) 07:12, 29 January 2007 (UTC).

Domino effect? --Wirbelwindヴィルヴェルヴィント (talk) 07:25, 29 January 2007 (UTC)

Algorithm, perhaps, is what you are looking for... --Proficient 07:51, 29 January 2007 (UTC)

Err, this sounds like you want a Rube Goldberg machine. —The preceding unsigned comment was added by 149.135.104.21 (talk) 09:08, 29 January 2007 (UTC).

Or Heath Robinson contraption. Skittle 17:38, 29 January 2007 (UTC)

Also see Decomposition (computer science) (although the concept is far more generic to all engineering disciplines than just computer science).

Atlant 13:39, 29 January 2007 (UTC)

Thank you for your help. Rube Goldberg machine is what I was trying to remember.

Mistake in The Blind Watchmaker?

There is a part The Blind Watchmaker where Dawkins analyzes the doppler effect wrt echolocation/sonar in bats:

It is relative motion that matters, and as far as the Doppler Effect is concerned it doesn't matter whether we consider the sound source to be moving past the ear, or the ear moving past the sound source. If two trains pass in opposite directions, each travelling at 125 m.p.h., a passenger in one train will hear the whistle of the other train swoop down through a particularly dramatic. Doppler Shift, since the relative velocity is 250 m.p.h.

Isn't the statement that only relative motion matters in sonar a mistake? I seem to recall that the calculations for the doppler shift with sound waves include the speed of the observer and the speed of the source as distinct entities (rather than just subtracting them for the relative speed). From my reading of Wikipedia's article on doppler effect, it seems that this is because the two speeds are judged with respect to a stationary medium, air. On the other hand relative motion is in fact the only thing that matters if you consider radar, which has no medium.

Is this passage in fact mistaken, or is it my reasoning that's flawed? --JianLi 08:58, 29 January 2007 (UTC)

The relative motion includes both speeds of the observer and sound emiiter -so both are right - 87.102.2.226 09:59, 29 January 2007 (UTC)

Our article is confusing. I think it is written to include the case of a strong wind! Other sources make it very clear: The Doppler effect is the apparent change in the frequency of a wave motion when there is relative motion between the source of the waves and the observer. So, Dawkins is right, and our article has been written for philosophers! --Zeizmic 14:03, 29 January 2007 (UTC)

For waves that travel in a medium (e.g., sound; not light, as you said) there are in fact two shifts (although they need not be non-zero): the waves in the medium away from the source have a different frequency than the source's frequency if the source is moving with respect to the medium, and the observed waves differ from that in the medium if the observer is moving with respect to it. These two effects are distinct, and have different equations, even; you will in fact get a Doppler shift even between two objects moving at the same velocity through the medium, so long as they are far enough apart that they do not force the intervening medium to adopt their velocity. As a special, singular case, consider two jets moving at the speed of sound along the same course: though they have no relative motion, the front one can never hear the back one because the waves can never catch up (corresponding, with some abuse of the mathematics, to 0 frequency). The point there about motion at the speed of sound negating all sound from the rear (as in directly behind) applies regardless of the speed of the source, of course, so Dawkin's analysis is fundamentally incorrect. That said, for velocities that are small relative to the wave velocity, they will approximately add as he suggests; note, however, that $250{\text{mph}}\not \ll c_{\text{sound}}$ at normal conditions. --Tardis 17:57, 29 January 2007 (UTC)

Thanks, that makes sense. --JianLi 01:36, 30 January 2007 (UTC)

Water and Ice

How much does water expand by when it freezes? —The preceding unsigned comment was added by 193.120.72.83 (talk) 12:53, 29 January 2007 (UTC).

Ice#characteristics "Ice has a density of 0.917 g/cm³ at 0 °C, whereas water has a density of 0.9998 g/cm³ at the same temperature"

Volume =mass/density therefore volume change = mass x(1/0.917 - 1/0.9998) = mass x 0.0903 (4decimal places)

I cubic centimeter of water at 0 C weighs 1/0.9998 g

So the volume change for 1 cubic centimeter = 1/0.9998 x(1/0.917 - 1/0.9998) = 0.0903

Thats an increase of 9%.87.102.4.142 13:35, 29 January 2007 (UTC)

Fourier transform on random signals

Consider a chord of three notes. The resulting signal in time will be the sum of these wave functions, and therefor a periodical function. If I have understood well, performing a fourier transform on this function results in a new function that is zero everywhere except at the three frequenties of the notes, right? Now consider a random signal (eg a phone call). Is it useful here to fourier transform that signal, for it is not periodical? If so, how? Thanks for any help--Gnorkel 14:11, 29 January 2007 (UTC)

Sure it's useful.. "Real" signals are seldom composed of a couple of simple pure frequencies that lend themselves to the easy continuous Fourier transform. See DFT and FFT. -- mattb @ 2007-01-29T15:16Z

The reason the transform can still be very useful is that a signal can often be much-more-compactly represented in the frequency domain rather than in the time domain. This is easy to see: I'll hum a note for you. In the time domain, you need a long sequence of samples with the samples continuing for as long as I hum. But take the Fourier transform of my humming and you've basically got it captured and that one sample represents my humming for as long as you care to go on.

It's not quite that simple, of course, but the Fourier transform is the basis for many of the audio compression algorithms out there today. I believe you'll find that that's the case for DAT, MP3, and AAC encoding among others.

Essentially, we take "time slices" (say, 100 ms) out of the waveform and perform the transform on those slices.

Atlant 17:24, 29 January 2007 (UTC)

What you mean by "random" here is really "posessing dominant frequencies which change over time", yes? That's what characterizes, say, music. Then what you want is the Short-time Fourier transform or some variant thereof. Does that help? --Tardis 17:27, 29 January 2007 (UTC)

If you want to be pedantic, sure, but a lot of the DSP texts I've seen refer to "random signals" in the treatment of the DFT... It's a pretty physically accurate description. -- mattb @ 2007-01-29T20:17Z

Thanks for helping me out. The concepts of time slices an stft were what I was searching for. --Gnorkel 17:50, 29 January 2007 (UTC)

Time slices slowly and silently its bread for breakfast. -- DLL ^{.. T} 19:18, 29 January 2007 (UTC)

postgraduate studies

what are the functions of the postgraduate medical institute? —The preceding unsigned comment was added by 204.16.125.203 (talk) 15:38, 29 January 2007 (UTC).

Well if it isn't obvious, to offer postgraduate education in the field of medicine. There is a little more to it then that but it varies, if you google postgraduate medical istitute you can read the different things they do. Vespine 21:16, 29 January 2007 (UTC)

Ringing in the ears

My ears ring all the time. Usually, most other sounds drown it out, but if I concentrate, I can hear it. Or at night or in a very quiet place, I can hear it really well. What causes it, is there a fix, and what is the long-term effects? Thanks Civil Engineer III 17:26, 29 January 2007 (UTC)

While I would say it sounds a lot like tinnitus, it's very possible it could be something else. I would recommend you ask a real-life doctor about it, as he would be far more able to answer this question safely. Also, he's more likely to be able to do something about it! Skittle 17:31, 29 January 2007 (UTC)

It is tinnitus; that's just a general term that refers to hearing noise when no external sound source exists. It can be caused by a multitude of different things though. We most definitely can not figure out the cause for you, nor the long-term implications, nor possible treatments. -- Consumed Crustacean (talk) 18:32, 29 January 2007 (UTC)

We can only refer you to your doctor. Tinnitus contains some general information on the subject, and says it can have a variety of causes and a variety of possible treatments or remediation methods. A white noise generator such as the "Sleep Sound" [4] consisting of a fan in a plastic box, can mask sounds such as tinnitus, traffic noise, or someone's snoring while you're sleeping. But definitely see a doctor if it is a medical question. Edison 22:01, 29 January 2007 (UTC)

Get some real dope hear! [5]--Light current 14:38, 30 January 2007 (UTC)

(not medical advice) I have the same issue but it's always been there since I've been a kid. I've been told that as long as it doesn't become greater in volume or intensity it's usually not harmful

Out of band emission regulations in the United States

I am looking for out of band emission limits for intentional radiators in various frequency bands for in the US. I work for a company that is doing research into UWB transmission techniques and we have become aware of a company which seems to be doing UWB in areas (centered in the 900MHz unlicensed band but covering other bands)other than those set aside for UWB (3.1-10GHz). This company is a larg(ish) start-up and is traded on the london "AIM" market thus they are probably not just "flying under the radar". Also they claim to have received FCC "approval". Anyway I am wondering how this works and what the power limitations are for other bands thna the 900MHz band (i.e 2.4GHz and licensed band such as those used for cellular communications).

Note: I called the FCC and was directed to an area of there web. This was helpful but since there were thousands of pages of information it was a little to much to wade through...I am looking for someplace where it is neatly summarized.

THANKS!Duncan St. Ives 19:41, 29 January 2007 (UTC)

You've seen our articles at Unintentional radiator, Intentional radiator, Incidental radiator, and Product certification, right?

Atlant 19:36, 29 January 2007 (UTC)

Yeah but I need specific numbers... In power or some reletive measure (such as percentage or DB down from the carrier). Also I forgot to sign my earlier post :)Duncan St. Ives 19:41, 29 January 2007 (UTC)

NITRIC OXIDE AND IMMUNITY

What is the role of nitric oxide in the immune system?Wizzybone 18:30, 29 January 2007 (UTC)

See Nitric_oxide#Biological_functions! [Mαc Δαvιs] X (How's my driving?) ❖ 18:44, 29 January 2007 (UTC)

Sex

How long does an average man take to orgasm? what about average woman? what about for masturbation, are these times different? —Preceding unsigned comment added by 209.53.180.18 (talk • contribs)

Premature ejaculation is an interesting read, and it may raise questions to whether or not premature ejaculation is something normal, due to the definitions posed. "How long" greatly depends on the circumstances; I'm sure somebody else can give a better answer. [Mαc Δαvιs] X (How's my driving?) ❖ 23:20, 29 January 2007 (UTC)

The general belief is that men can reach a climax faster than woman. As MD said, this depends on the circumstances. Sometimes, a woman may not reach an orgasm at all, even with prolonged stimulation. Research shows that as much as 70% of woman don't orgasm all the time every time. Tantric sex also changes things. Masturbation usually allows a person to reach climax faster as the person can pleasure themselves at their own speed & do what they like. All in all, orgasms are tricky things to pin point down & it's different for everyone. Spawn Man 05:17, 31 January 2007 (UTC)

Condoms

Is there any harm in wearing it tight enough to supress semen excretion? would that comprimise pleasure? would it even still be possible for the man to orgasm? —Preceding unsigned comment added by 209.53.180.18 (talk • contribs)

IF you'd actually achieve the feat of putting a condom on tight enough to supress semen excretion in this manner, yes, that would be quite harmful I'd suppose. --Ouro 21:17, 29 January 2007 (UTC)

I believe that most condoms have a pocket for semen in front, as in Image:Condom_unrolled.jpg. Thus it doesn't seem anatomically possible to wear it tight enough to do what you describe. -- SCZenz 21:21, 29 January 2007 (UTC)

The old joke is, a man asks an advice columnist 3 questions: 1)How can I keep from getting the girl pregnant and also prevent STDs? 2) How can I ensure that I don't orgasm too quickly? 3)How can I make my member seem larger? And the answers were 1) Wear a condom. 2) Wear 2 condoms. 3) Wear 3 condoms. Of course this is only presented as lame humor, and you should get all condom advice from a doctor or condom expert. Edison 22:07, 29 January 2007 (UTC)

A chemestry major once told me that wearing two increases the chance of malfunction cause it rips. Well, didn't tell -me-, specifically. --Wirbelwindヴィルヴェルヴィント (talk) 23:01, 29 January 2007 (UTC)

Last time I was at the condom page it had instructions on proper technique for putting one on. As I remember, it recommended pinching the end so there is a small bit of space at the tip (if it doesn't come with one). Also, retrograde ejaculation in males can be harmful and painful. It would still be possible for the man to orgasm, that doesn't even take ejaculation. [Mαc Δαvιs] X (How's my driving?) ❖ 23:25, 29 January 2007 (UTC)

I also doubt the validity of the assumption that you can wear a condom tight enough to supress semen at all. If the condom is pulled back so tight that there is no "air pocket", the semen excretes down the side of the penis, which is why you're supposed to make sure that there's some air in the first place. I find it hard to believe that you could maneuver on a condom tight enough to supress exretion on the sides, while fitting snug enough to remove the air pocket. You'd probably risk serious damage to your penis.  freshofftheufoΓΛĿЌ  01:39, 30 January 2007 (UTC)

Animal mating

Do animals rape one another? —Preceding unsigned comment added by 209.53.180.18 (talk • contribs)

Male orcas have been observed appearing to 'gang up' on lone females and copulate with them. I read that item a while ago, don't know if the observations have been repeated, refuted or analysed since I first encountered the info. But in a broader sense, the concept of 'rape' is dependent upon the wishes of the 'victim', and there are arguably few species of animals that have sufficient social, intellectual and emotional complexity (combined with the ability to resist hormonal urges) to be able to object to sexual activity. Anchoress 21:39, 29 January 2007 (UTC)

I watched a documentary on koalas (on the Discovery Channel, I think) where a male jumped onto a female in a tree, began copulating with her. There were screeches, but it wasn't clear which of the two was making the sounds, and eventually—perhaps after he had finished—she got him off and aggressively chased him away. − Twas Now ( talk • contribs • e-mail ) 22:41, 29 January 2007 (UTC)

In Richard Wrangham and Dale Peterson's book Demonic Males, they recount a few instances of rape in primates, specifically orangutans. Mature male orangutans develop very striking features, including large size and prominent cheek pouches. Females invariably choose to mate with these mature, dominant males. But some adolescent, undeveloped males have been observed forcing sex on unwilling females. The book even recounts an instance in which an orangutan in a wildlife preserve raped a (human) female employee. TheSPY 00:54, 30 January 2007 (UTC)

I once saw a male duck attempt to rape a female duck, then another male stopped him. I thought he just wanted a go but the saviour duck didn't have sex with the female he'd saved. Maybe it was a relative? Anyway it was obviously attempted rape.

Shaving

why does shaving make hair grow thicker and stronger? also, how does hair "know" when to stop growing? for example, i shaved my eyebrows off once, and as expected, they grew back steadily until 6 or 7mm then stopped growing. why? why doesnt head hair and beard "know" when to stop?

To the first question, I'm not sure that it does. Shaving a) makes the regrowth blunt at the tip, which can make it seem stiffer; b) sometimes makes the regrowth lie differently, at a more obtuse angle to the skin; and c) makes the hair feel stiffer while it's shorter. Anchoress 21:35, 29 January 2007 (UTC)

Hair typically grows for a while and then falls out. If the average time until falling out is enough time to produce 6 or 7 millimeters of hair, that's how much you get; the hair never actually stops growing. --Tardis 21:52, 29 January 2007 (UTC)

The notion that shaving can cause hair to grow in faster seems like a meltdown of logic to me, whether or not it's true. I mean, what is the objectionable thing here, the rate of growth, or the hair itself? Vranak

I was under the impression that hair growing faster was an urban legend. Splintercellguy 05:39, 30 January 2007 (UTC)

Yup. http://www.snopes.com/oldwives/hairgrow.asp --Shantavira 09:20, 30 January 2007 (UTC)

Lk to hairy site. [6]

There's been a long history of study in this field. The general consensus is that shaving doesn't make hair grow back thicker or tougher, however it may seem that way. (The cut tip of the hair is blunter than an uncut tip; short, bristly hairs seem more rigid than longer strands.)

There's significantly more dispute over the effect on growth rate. Published studies on this question go back more than a century; if your university library has an online subscription to the American Journal of Physiology, you can start with Raymond J. Seymour, "THE EFFECT OF CUTTING UPON THE RATE OF HAIR GROWTH", Am J Physiol (1926) 78:281-6. Seymour found that beard hair growth was fastest in the 12 hours immediately after cutting, and later slowed.

On the other hand, Lynfield and Macwilliams report that shaving has no effect on leg hair growth rate in "SHAVING AND HAIR GROWTH" (1970) Journal of Investigative Dermatology 55:170-172.

Those of you trying to conceal your age will be disappointed by W. Nagl's report "Different growth rates of pigmented and white hair in the beard: differentiation vs. proliferation?" Brit J Dermat (1995) 132(1):94-97, which found that white beard hairs grow nearly three times as fast as pigmented hairs.

I saw a fairly recent result that suggested the stimulatory effect of shaving was short-lived, and was followed by a period of quiescence in which growth rate slowed; this meant that over a day or two following a shave, the average rate of hair growth was comparable to that observed in an unshaven control. Unfortunately, I can't find the reference, so if anyone can help out it would be appreciated. TenOfAllTrades(talk) 15:21, 30 January 2007 (UTC)

(1) As mentioned, it doesn't make it grow thicker or stronger. It only appears thicker. (2) Hair grows in three stages. The length and frequency of these stages depend on the area of the body the hair is growing in. In the case of eye brows, i've heard that these hairs go through their cycle relatively quickly (i don't remember the exact number, i think it's like one or two weeks). At the end of this cycle, the hair stops growing, and eventually it is displaced by a new hair, which goes through the same cycle all over again. This keeps the hair at a relatively constant length. ~ lav-chan @ 22:58, 30 January 2007 (UTC)

Dependance on humans

Wikipedia articles state that cats and dogs are carnivores. What about small dogs like poodles, and some domestic cats.. they look too small and helpless to hunt. if abondoned in the wild, would they be able to feed themselves? are all or at least any of the common breeds of domestic dogs and cats evolved into dependence on humans? —The preceding unsigned comment was added by 209.53.180.18 (talk) 21:15, 29 January 2007 (UTC).

I'm no expert, but I'd be inclined to believe that thanks to domestication and selective breeding, certain breeds of dogs and cats are indeed now quite useless at survival and would be quite unlikely, in the wild, to survive more than a couple of generations before being wiped out. We've been creating breeds that would surely be ill-equipped for life outside of human care. Maelin (Talk | Contribs) 23:37, 29 January 2007 (UTC)

Cats certainly can go feral if released into the wild, they can feed on birds and rodents, they obviously have more of a wild streak then dogs like poodles, I would guess dogs like pugs would indeed probably not survive very long in the wild, but then again, so would probably most humans that grew up in a city if released into the wiild. Dogs were, by the way, the very first animal to be domesticated, the domestication article is very interesting. Vespine 00:55, 30 January 2007 (UTC)

The article's reference to "carnivore" was to their diet, rather than their behavior. It's talking about the types of things their teeth and digestive systems are designed to eat. "Carnivore" doesn't necessarily mean "hunter." And I haven't checked the article recently, but it should probably state that domestic dogs are omnivores, not strict carnivores. Most domestic animals (and many plants) end up dependent on humans. If we "freed" domestic chickens, even a poodle would be able to dispatch them pretty easily. If we "freed" corn, it would die in a generation or so, because it's not really capable of breeding in its domestic form. TheSPY 01:00, 30 January 2007 (UTC)

Tree shrews are the smallest mammals, but the most ferocious. They will attack and kill a mouse weighing twice as much as they. So a little predator needs only find a smaller prey. "So naturalists observe, the flea hath little fleas upon his back to bite'em. And little fleas hath lesser fleas, and so proceeds, ad infinitem." Edison 05:56, 30 January 2007 (UTC)

Is it against Wikipedia policy to express felicity regarding the concept of "freeing" corn? --Seans Potato Business 23:42, 31 January 2007 (UTC)

There have been lots of reports of domestic pigs going wild within days of being relased into the wild. they litterly grow darker hair and small tusk withen the month. (saw this on the discovery channel or animal planet) Maverick423 22:38, 31 January 2007 (UTC)

Pet breeds

are all breeds of pet dogs subspecies of the same species? what about for domestic cats?

The answer to both questions is yes. --NorwegianBlue ^talk 22:26, 29 January 2007 (UTC)

Actually, all dogs are the same subspecies. Some recent discussion of this has occurred here and here − Twas Now ( talk • contribs • e-mail ) 22:30, 29 January 2007 (UTC)

Yeast

What is the one thing that yeast can do that no other living organism can. Deniselemons 21:39, 29 January 2007 (UTC)

Is this a riddle? Is the answer 'turn water into wine'? Anchoress 21:41, 29 January 2007 (UTC)

Make more yeast? --Tardis 21:49, 29 January 2007 (UTC)

Be yeast. − Twas Now ( talk • contribs • e-mail ) 22:33, 29 January 2007 (UTC)

Well, according to the Bible, Jesus turned water into wine, and I don't think he was yeast. --Wirbelwindヴィルヴェルヴィント (talk) 22:58, 29 January 2007 (UTC)

And the Yeast shall be the Foist. --Justanother 15:33, 30 January 2007 (UTC)

Perhaps Jesus was yeast. Who are we to say? − Twas Now ( talk • contribs • e-mail ) 23:47, 29 January 2007 (UTC)

Yeast does float on water... DMacks 23:55, 29 January 2007 (UTC)

So do some people ;) Aecis^Brievenbus 00:05, 30 January 2007 (UTC)

I feel I should point out that yeast cannot turn water into wine. Theresa Knott | Taste the Korn 00:37, 30 January 2007 (UTC)

A valid point! − Twas Now ( talk • contribs • e-mail ) 04:28, 30 January 2007 (UTC)

Tom Pryce/Jansen Van Vuuren collision

hey folks, i have a doubt about the tom pryce fatal crash: i dont know how much a f1 racing car weighed at 1977 but i think that jansen, who was crossing the track at 2km p/h weighed 68 kgs, and he was hit by the car at 350 km p/h, please i wanna know how much the impact weighed, thanks.--201.9.73.29 21:50, 29 January 2007 (UTC)

I'm sorry, but your question about Tom Pryce doesn't make sense as written. Could you perhaps explain what your doubt is about the crash, rather than asking for a specific quantity (collisions don't have mass), and maybe somebody could help. --Robert Merkel 23:07, 29 January 2007 (UTC)

He was asking about Tom Pryce. I don't know what the weight is without knowing the acceleration. However, here are some calculations for momentum (in SI units), assuming Pryce was moving at 5.0 km/h (2km/h is very slow):

Momentum_{Pryce walking} = 68kg × 5.0 km/h × 1000 m/km × 1h/3600s = 94.44444444 kg m/s

Momentum_Car = 605kg × 350 km/h × 1000 m/km × 1h/3600s = 58,819.44444 kg m/s

|Momentum_Sum| = √ (Momentum_{Pryce walking}² + Momentum_Car²) = 58,819.52027 kg m/s

Angle = tan(94.44444444 ÷ 58,819.44444) = 0.091998025°

I hope these are correct (and helpful), it's been a while since I've done trig. − Twas Now ( talk • contribs • e-mail ) 23:33, 29 January 2007 (UTC)

Actually was Jansen Van Vuuren(who was a safety marshal) who was walking the track, and Pyrce was the guy piloting the f1 car, being hit by 58 tons is really scary, but this helped, thanks.--201.9.11.148 00:30, 30 January 2007 (UTC)

If by "what the impact weighed", you mean the force imparted, then the impulse imparted to Vuuren, assuming that he was crossing the track perpendicular to the direction of the car (hence his velocity in that direction was 0), would have been ~58,819 kg m/s (or Ns). The collision would have taken place in a fraction of a second, so he would have experienced a force of well over 59,819 Newtons, equivalent to almost 6 tonnes of force. Laïka 14:54, 30 January 2007 (UTC)

Craters on Mars

According to the planetary nomenclature, small craters on Mars are named after towns on Earth with a population of less than 100,000. But how come there's also a crater called Amsterdam? Aecis^Brievenbus 22:22, 29 January 2007 (UTC)

See Amsterdam. :-) --NorwegianBlue ^talk 22:28, 29 January 2007 (UTC)

Thanks for the quick answer. I could have guessed... I've corrected the list of craters on Mars. Aecis^Brievenbus 22:51, 29 January 2007 (UTC)

Sorry, it was a joke, and I realise now that it was not a very good one. --NorwegianBlue ^talk 23:51, 29 January 2007 (UTC)

I am much more inclined to believe it is Amsterdam (city), New York (not to be confused with Amsterdam (town), New York). The town in Saskatchewan has less than 25 people! − Twas Now ( talk • contribs • e-mail ) 22:59, 29 January 2007 (UTC)

And I've made the appropriate change at List of craters on Mars. There must be a database out there with which we can verify this. − Twas Now ( talk • contribs • e-mail ) 23:02, 29 January 2007 (UTC)

According the USGS, it was named after the Dutch port city (i.e. the capital) in 1979 [7]. Aecis^Brievenbus 23:19, 29 January 2007 (UTC)

Same according to NASA's list of craters. Most of NASA's staff are men, they are from Mars and should know. (I made one appropriate change at List of craters on Mars, but maybe the less-than-100,000 bit needs to be removed or the exception(s) need to be named. ---Sluzzelin 23:26, 29 January 2007 (UTC)

Perhaps (I'm just speculating here) those craters were named after the cities before the criterion of less-than-100,000 was established. That, or we've missed/omitted a criterion. Because there are quite a few exceptions to this rule: Amsterdam, Bordeaux, Bremerhaven, Bristol, Cadiz, Cairns, Canberra, Charleston, Innsbruck, Johannesburg, Kaliningrad, ... Aecis^Brievenbus 23:55, 29 January 2007 (UTC)

Drugs that increase semen volume

We've heard of all the ones that decrease sperm production, what about increase semen volume? [Mαc Δαvιs] X (How's my driving?) ❖ 23:18, 29 January 2007 (UTC)

Check out Spermatogenesis#Influencing_factors − Twas Now ( talk • contribs • e-mail ) 23:35, 29 January 2007 (UTC)