Science desk
< March 7	<< Feb \| March \| Apr >>	March 9 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

March 8

sodium azide

wat are the exact steps in making this? do u mix the chemicals in water,ect. —Preceding unsigned comment added by Steweydewey (talk • contribs) 00:04, 8 March 2008 (UTC)[reply]

please read sodium azide first. Furmanj (talk) 01:09, 8 March 2008 (UTC)[reply]

Just a word to the wise. If you plan on actually making sodium azide, please be careful with it. Wisdom89 _{(_T / ^C)} 03:10, 8 March 2008 (UTC)[reply]

ok,ok but can i get measurments?? —Preceding unsigned comment added by 76.14.124.175 (talk) 05:56, 8 March 2008 (UTC)[reply]

Despite its common use in airbags, sodium azide appears to be a fairly toxic substance that requires careful handling. If your only resource for relevant information is Wikipedia, then you probably shouldn't be trying to make it. Gandalf61 (talk) 10:10, 8 March 2008 (UTC)[reply]

It's not just fairly toxic. It's highly toxic, and death can (and has) occurred with the ingestion of as little as a milligram. Seriously, don't mess with this stuff. – Clockwork Soul 19:27, 8 March 2008 (UTC)[reply]

The Massive Multiverse Question

I'm not a nuclear physicist in any way but there is something that I can't shake from my mind. The multiverse. Is the Multiverse purely a hypothetical concept or is it something that exists (or could exist) in reality? I understand that everytime I make a decision, whether to turn left or right for example, a new universe is born. This seems bonkers to me, billions of people spawning trillions of universes. Is this really possible? I guess my question is... Is the multiverse theory something that just fits the equations and balances out the maths or is it a true, physical possibility for the reality that we live in? Do the multiverses ever overlap? Could I ever meet myself? I have a feeling that this question is a bit of an argumentative mine field. Any help and explanation (in simple terms!) would be greatly appreciated. Kirk UK —Preceding unsigned comment added by 87.242.131.156 (talk) 00:22, 8 March 2008 (UTC)[reply]

what makes you think that this existence is so unique? Or even real? This might make it even worse, but i'll point you to uniqueness and well defined. I know thats somewhat obscure but keep in mind your frame of reference to reality Furmanj (talk) 01:16, 8 March 2008 (UTC)[reply]

The many-worlds interpretation is just one possible interpretation of quantum mechanics, most do not create other universes. Basically, at this point, it's purely hypothetical, but is favored among those who think the laws of physics are deterministic (i.e. you can't have a simultaneously "half-alive/half-dead cat", it's either 100% dead or 100% alive, depending on your universe). As for "overlap" or traveling to other universes, I believe that the answer currently is almost definitely not (they're referred to as "non-communicating" parallel universes), but until we know whether it's true or not I don't think it can be ruled out entirely. That brings us to whether it's real or not, and at this point we don't know, and it may be that we never know, but I don't think that will keep us from looking. Hope that helps! -- Hi Ev 01:57, 8 March 2008 (UTC)[reply]

An example I saw a while back at some talk (where I freely admit I was not paying much attention) was ripples in a pool of water. There is the "big bang" as a rock hits the smooth surface of the water. Each ripple emanating from the center is a "world" that exists on its own. The further form the center, the further along the timeline it progresses. Pick a point in time (a specific distance from the center) and watch it. The ripples go past one after the other. Each one is a separate "world" and each one can have completely conflicting choices. So, at a specific point in time you may choose left, you may choose right, you may not exist at all. It depends on which ripple you are talking about. That's about all I picked up from the talk. Perhaps someone else knows what the guy was talking about and can explain it better. -- kainaw ™ 02:07, 8 March 2008 (UTC)[reply]

I guess you've seen our article on the Multiverse hypothesis? Julia Rossi (talk) 06:12, 8 March 2008 (UTC)[reply]

The idea that we are "creating" universes with every choice we make is really quite silly. I think this idea comes from people misunderstanding one way of viewing multiverses in that one could see the differences as differences in choices made. Of course, the infinite number of universes with no life and therefore no possibility of "choices" would still be ifferent from each other and so the real differences between universes has to do with the playout of random events (both microscopic and macroscopic), which then affect choice. — Æµ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 09:28, 8 March 2008 (UTC)[reply]

Is the Multiverse purely a hypothetical concept or is it something that exists (or could exist) in reality?

In short, this question, and many like it, are unanswerable. If believing in a multiverse helps you cope with your day-to-day existence, then go ahead and believe in it. If not, then it's just superstitious clutter that you can happily forget about. Vranak (talk) 15:36, 11 March 2008 (UTC)[reply]

solar or wood what is best for hot water

Why fire wood water heater is better than solar in winter and rainy season —Preceding unsigned comment added by Joseph-d-alappat (talk • contribs) 03:05, 8 March 2008 (UTC)[reply]

Well, since you're discussing specifics, consider how the conditions (rainy or windy) can effect wood heat and solar power. Wood just burns, and solar power is most effective in direct high-angle sunlight. — Lomn 06:15, 8 March 2008 (UTC)[reply]

Siamese communication

I have a Siamese cat. Like every other Siamese I know, he has three states: sleeping, eating, and meowing. He has the typically large Siamese vocabulary and expresses himself almost constantly when people are in the room. Obviously, he's doing it to communicate something to us (he doesn't meow at the chair when I'm not there, for example). What I was wondering was - do Siamese cats owned by deaf people meow less? Do they learn that talking doesn't work and try communicating in other means? Besides idle curiosity, it might also shed light on feline intelligence. Matt Deres (talk) 03:28, 8 March 2008 (UTC)[reply]

I would test that theory some how. good question. But never underestimate animal intelegence —Preceding unsigned comment added by 76.14.124.175 (talk) 05:58, 8 March 2008 (UTC)[reply]

It's not just siamese cats that miaow a lot. One of mine, who is just some form of moggie (probably british shorthair tuxedo cat) likes to miaow a lot, and you can have conversations with him. I have no idea what I'm saying, but he seems to enjoy them. -mattbuck (Talk) 17:24, 8 March 2008 (UTC)[reply]

My parents have a cat (generic short hair black cat) that has a toy that is just feathers on the end of a stick. She now picks it up in her mouth, drags it to one of us, drops it, and meows until one of us plays with her. -- MacAddct  1984 ^{(talk  contribs)} 19:52, 8 March 2008 (UTC)[reply]

My cats meow when they want food (or are otherwise unhappy), but otherwise seem to talk to each other and not to me. However, there doesn't seem to be much variety in their conversation: it's mostly "where are you?" as best I can tell. --Tardis (talk) 00:02, 11 March 2008 (UTC)[reply]

Schrödinger Equation

Can someone please give me an example of the Schrödinger equation with each step, please? Thanks, Zrs 12 (talk) 04:39, 8 March 2008 (UTC)[reply]

I'm no scientist, but → Schrödinger equation. --~~MusicalConnoisseur~~ Got Classical? 06:57, 8 March 2008 (UTC)[reply]

If you wanted an example of a solution to Schrödingers equation for a specific system, then perhaps the easiest to understand is Particle in a box. You can find a list of Wikipedia articles with analytical solutions for other geometries here. SpinningSpark 14:15, 8 March 2008 (UTC)[reply]

How Halbach array works ?

is it necessary for all the magnets of a halbach array to be of same strength ? iwe know every magnet have two poles but in cace of halbach array, the law is violated ; what's the explanation of strange behaviour of halbach array ? —Preceding unsigned comment added by Shamiul (talk • contribs) 05:43, 8 March 2008 (UTC)[reply]

See our Halbach array article. It does not mention different strengths, so I would assume that, yes, the magnets in the array are all the same strength. We also have an article on the Halbach cylinder. Gandalf61 (talk) 09:50, 8 March 2008 (UTC)[reply]

The Magnet article explains that magnets can have any number of poles, except one, so the Halbach array does not violate anything. Refrigerator magnets are common examples of multipole magnets. --Heron (talk) 13:42, 8 March 2008 (UTC)[reply]

what mathematician (von neumann? erdos?) strongl argued for preemptive annihilation of Russia?

What famous mathematician campaigned during the cold war for a preemptive annihilation of russia via nuclear weapons, based on Game theory? Citation? —Preceding unsigned comment added by 79.122.0.69 (talk) 13:55, 8 March 2008 (UTC)[reply]

According to the von Nuemann article he was in favour of a pre-emptive strike to prevent the USSR developing nuclear weapons. However, Game Theory is not mentioned in the article. SpinningSpark 14:30, 8 March 2008 (UTC)[reply]

Yeah I'd go with Von Neumann. He was very hawkish, and remember that he died while the US still had a massive nuclear lead over Russia. --98.217.18.109 (talk) 14:57, 8 March 2008 (UTC)[reply]

As for a citation, Steven Heims says Von Neumann as an advocate of preemptive war at least around 1950 (when, as I note, it was still feasible, as the USSR only had a bomb or two ready to go), in his book John Von Neumann and Norbert Wiener: From Mathematics to the Technologies of Life and Death. --98.217.18.109 (talk) 15:58, 8 March 2008 (UTC)[reply]

It was definitely von Neumann, who had a special hatred of Communists due to his background. He's widely quoted as saying "If you say why not bomb them tomorrow, I say why not today? If you say today at 5 o'clock, I say why not one o'clock?" (refs). Note also that at the time there was a careful distinction made between preemptive war and preventive war, with the latter more extreme position being von Neumann's. Curtis LeMay had similar feelings, along with many other deeply fearful and pessimistic people of that scary new era. --Sean —Preceding unsigned comment added by 69.134.115.242 (talk) 17:21, 8 March 2008 (UTC)[reply]

Note that Von Neumann later changed his position. I can't remember the details, but I believe the talk I heard this in to be similar to this (which I can't get to work). Algebraist 17:48, 8 March 2008 (UTC)[reply]

Von Neumann's position changed to support of the MAD strategy as the USSR capabilities increased and first strike started to look more dangerous. SpinningSpark 19:21, 8 March 2008 (UTC)[reply]

radiation protection

i wnat to design a radiography department in a health care centre wat kind of radiation protection measures should i use and why should i use themRowin.r (talk) 14:34, 8 March 2008 (UTC)rowin.r[reply]

I've got to assume here that this is not a practical question (because no one would be given such a job who didn't know about how to do it), but is probably some sort of homework or assignment question. Look at your course materials; any answers we give will probably not be the ones your teacher is looking for. --98.217.18.109 (talk) 14:55, 8 March 2008 (UTC)[reply]

We have an article on radiation protection you might want to look at. Bear in mind that only some of the ideas in the article would be applicable to a radiology department. SpinningSpark 17:22, 8 March 2008 (UTC)[reply]

Red-eared sliders?

Hi. A friend had wanted me to ask, is it safe to put together two red-eared sliders of different age (eg. one a few months old and one three years old)? What about gender? How much space do they need, if you put two together? Thanks. ~A H 1^(TCU) 17:32, 8 March 2008 (UTC)[reply]

Quoth this site (used as a reference in our red-eared slider article) [1]:"A hatchling should never be added with adult turtles because of accidental or intentional injuries. Only turtles of a generally similar size with similar habitat requirements should be together in a confined enclosure. "

The site also has other information on keeping red-eared sliders, including this on space: "A guideline to determine this size used by many keepers, as a minimum, is 10 gallons of tank per each inch of shell length (refer to SCL for correct shell measurement). Therefore, a single adult RES will require anywhere between a 90 to a 120 gallon tank."

AlmostReadytoFly (talk) 19:26, 8 March 2008 (UTC)[reply]

Blueshifted stars?

Hi. What are all the known blueshifted stars (ones with a negative radial velocity)? This is not homework. Should we have an article such as "list of blueshifted stars" or "list of stars with a negative radial velocity" or "list of stars with decreasing distance"? Thanks. ~A H 1^(TCU) 17:37, 8 March 2008 (UTC)[reply]

That would be one humungous list, mostly filled with redlinks (does that mean the articles are receding from Wikipedia?). Clarityfiend (talk) 18:02, 8 March 2008 (UTC)[reply]

Exploration of the Universe (Abel, Morrison, Wolf) lists 16 amongst the nearby stars. As there are several blue-shifted galaxies out there, the total number of blue-shifted stars is going to be uncatalogable. However, if you would like the data from the tables in this book for an article, drop a note on my talk page and I will provide it. SpinningSpark 18:12, 8 March 2008 (UTC)[reply]

There are several blueshifted galaxies? Which are they and are they in the local group? Thanks. ~A H 1^(TCU) 18:34, 8 March 2008 (UTC)[reply]

According to AMW, the galaxies in the local group with negative radial velocity are; NGC6822, NGC185, NGC205, M32 (NGC221), IC1613, Andromeda galaxy (M31) and M33 (NGC598). As I said, if you want all the figures (velocities, positions etc) for an article, let me know. SpinningSpark 18:48, 8 March 2008 (UTC)[reply]

hi guys, I'm just someone else but can you tell me why it's not the case that half of all stars are blue-shifted? it's a toss-up between red and blue shifted, right? There aren't any that aren't shifted are there, by however little.... —Preceding unsigned comment added by 79.122.0.69 (talk) 18:36, 8 March 2008 (UTC)[reply]

Not so. The majority of the red shift is caused by the expanding universe and increases with distance dramatically, see Hubbles law. It is only a bit of nearby (local galaxies) local stuff that can be blue shifted and not completely swamped by the universal expansion. SpinningSpark 18:42, 8 March 2008 (UTC)[reply]

(edit conflict, my cordless mouse is so f***ed up and slow)Hi. Well, the universe is expanding, so especially the far-away stars and galaxies are moving towards us. Parts of the milky way movement are uneven. It's also likely that if two stars are moving in 3D space in the same direction that most of them will move away from us. Also, I was right that Andromeda and Triangulum are blueshifted! So in an expanding universe, blueshifted galaxies, even close-by ones, mean that they might merge with us, as in the case with Andromeda and Triangulum. Blueshifted stars will soon be redshifted anyway, because they will soon reach minimum distance from us and move away. Redshifted stars will likely continue to be redshifted as they continue to move away. Thanks. ~A H 1^(TCU) 18:47, 8 March 2008 (UTC)[reply]

Image search related question

Is there any algorithm that search image using image has been develop? For example I would like to search apple image so I'm using an image of apple to find the image that I want. If it has could you provide with some useful links? Thanks. roscoe_x (talk) 18:32, 8 March 2008 (UTC)[reply]

yes. what language are you using? —Preceding unsigned comment added by 79.122.0.69 (talk) 18:39, 8 March 2008 (UTC)[reply]

Wait, are you saying you want to search for other similar images based on a source image? If so, then I'd say no, or at least I'm not aware of any such search algorithm existing currently. The problem is that computers are really terrible at image recognition at this point, so a computer's idea of "similar" isn't much like a human's idea of "similar". I doubt any search using current technology would do exactly what you're looking for. There is Google Image Search which allows you to search for images using words, but that's not quite the same thing. -- Hi Ev 19:41, 8 March 2008 (UTC)[reply]

Note that to a computer a picture of an an apple is just something round-ish and red. It won't know it's a fruit and it won't know it's edible and it won't know that there are green ones too, or sliced ones, or anything else. It doesn't have the complex range of associations that a human would have. You'd probably as likely find a beach ball in response to your query as another apple. --98.217.18.109 (talk) 20:35, 8 March 2008 (UTC)[reply]

I use C, C++, and Java. But I don't intend to develop such a program. I just want to know the algorithm. Every object has pattern, the apple only a sample. The application might be used in finding finger-print, facial recognition, or maybe other useful things. roscoe_x (talk) 01:20, 9 March 2008 (UTC)[reply]

You should start with our article on computer vision. If you're looking for a single algorithm to recognize an apple, you're going to be disappointed; computers are dum. That said, here's something neat: take a Google Image Search like say, http://images.google.com/images?q=wikipedia, and add '&imgtype=face to your query: http://images.google.com/images?q=wikipedia&imgtype=face. Neat! Maybe if someone gives you a better answer than me, Google will hire you to implement imgtype=apple. :) --Sean —Preceding unsigned comment added by 69.134.115.242 (talk) 03:00, 9 March 2008 (UTC)[reply]

O well that's very cool too. I've check 10 pages and they all giving me correct results. And what amaze me is no mistake and the search result could gives different facial expressions. Do you know the basic? Are they using edge detection? I understand if its classified. Thanks. roscoe_x (talk) 13:37, 9 March 2008 (UTC)[reply]

One thing I would think computers could do at this point is find the same image, perhaps at a different scale or color depth. This alone might be useful, if you have a small, greyscale pic and want a large color version of the same thing. Perhaps different cropping, aspect ratios, mirror images, image formats, etc., could also be accommodated. Some of the same technology used to compare fingerprints could be used here. This technology could then be put to use to solve one of the greatest frustrations facing mankind, how to use a nude pic of a celebrity with their naughty bits blacked out to find the original. :-) StuRat (talk) 18:19, 9 March 2008 (UTC)[reply]

See OPTIMOL. This is a project out of Princeton that builds a set of images based on a couple of "seed" images of the object class of interest. Sancho 18:54, 9 March 2008 (UTC)[reply]

Characteristics of skin Types

I am trying to find the characteristics of the skin type of chinese skin and also black skin. I am learning about skin and the differences of there skin types, other than the colour I cant find anything else. Please help me do my college research. I have done european and asain. but the other two I cant find anywhere on the internet. Beechview (talk) 18:41, 8 March 2008 (UTC)[reply]

Hair follicles are part of the skin, so any differences in hair type would also technically be differences in skin type. Beyond that, I don't know. If you look hard enough for differences and can't find them, you could conclude that scientists may not be aware of any. --Allen (talk) 19:03, 8 March 2008 (UTC)[reply]

But even if there are no differences beyond skin color and hair texture, there's still a lot to be said on the subject of human skin color. You may also be asking too much of categories like "Chinese skin" and "black skin"... it's really all a big continuum, as the map at human skin color suggests, with a lot of variation at all scales. --Allen (talk) 19:12, 8 March 2008 (UTC)[reply]

FYI - If you've done Asian skin then you've already done "Chinese skin", since China is a part of Asia. -- Hi Ev 19:44, 8 March 2008 (UTC)[reply]

Asia is a large group of different people. The OP most likely meant a specific group, such as Japanese. Because he is referring to the skin, I am reminded of one of Bruce Lee's movies where the Japanese refer to the Chinese as "sick yellow men of China" - referring their skin tone. Of course, China itself has a wide variety of people in height, weight, and skin color due a long history of being invaded and, for the most part, absorbing the invaders into the collective whole of the country. -- kainaw ™ 02:54, 9 March 2008 (UTC)[reply]

Hi. Here's a link if you want to know about the invasion of China and related matters during world war II (warning: potentially disturbing content). Thanks. ~A H 1^(TCU) 23:52, 9 March 2008 (UTC)[reply]

Adding salt to boiling what-have-you

If adding salt lowers the boiling temperature, why not just cook the stuff at that lower temperature (say 90 or 95 degrees or whatever it may be). What's so special about making the water boil around the potatoes? I think they'll soften just fine at 90 or so sans bubbles. ----Seans Potato Business 18:51, 8 March 2008 (UTC)[reply]

Adding salt doesn't lower the boiling point of water; indeed, it doesn't significantly affect the boiling point at all. (The boiling point will be elevated very slightly – less than one degree [2] – with the quantities of salt typically used in the kitchen.)

The addition of salt may, however, affect the flavour or texture of the cooked food. TenOfAllTrades(talk) 19:09, 8 March 2008 (UTC)[reply]

Adding salt elevates the boiling point (colligative), which means that the water boils at a higher temperature which means your spaghetti cooks faster.--Mmoneypenny (talk) 00:40, 9 March 2008 (UTC)[reply]

No, as Ten points out, the amount of salt added to, say, a pot of water to cook spaghetti in, is not enough to cause any appreciable degree of boiling point elevation. The idea that salt is used in cooking to manipulate the boiling point is simply a wide-spread misconception. The salt is added for taste. If you added enough salt to make a significant difference in boiling point, the food would be so salty it would be inedible. Any (marginal) increase in boiling point from the pinch of salt that's actually used in cooking is incidental and unimportant. - Nunh-huh 05:10, 9 March 2008 (UTC)[reply]

It is certainly true that adding salt to a pan of hot, but not quite boiling, water can suddenly produce a rolling boil. Of course, this may possibly be less to do with the salt in solution lowering the boiling point and more to do with the salt crystals providing nucleation sites for the steam to form. SpinningSpark 01:18, 9 March 2008 (UTC)[reply]

Adding salt is a lot to do with food colour too. Try purple sprouting brocoli in two pans one with one without salt: the difference is very striking. --BozMo talk 08:25, 9 March 2008 (UTC)[reply]

If the addition of salt produces a rolling boil, then the pot of water was actually already above the boiling point of water—at least at the bottom of the pot. Water in the bottom of the pot can become slightly superheated; this process is aided by two factors. First, if the pot is particularly smooth, there will be few nucleation sites around which bubbles can form. Second, if the water is fairly deep and/or is unstirred, hot water can be trapped at the bottom of the container; the weight of the water on top slightly elevates the pressure at the bottom of the pan and thereby also slightly elevates the boiling point.

Agitating the liquid in the pot (to bring hot water to the surface) or providing nucleation sites for bubble formation will both encourage sudden, rapid boiling. Adding salt can drive both processes. (Incidentally, this is one reason to use extreme care in heating mugs or cups of liquid in the microwave. An apparently not-quite-boiling cup of liquid can suddenly boil violently when disturbed: [3], YouTube video.) TenOfAllTrades(talk) 16:39, 9 March 2008 (UTC)[reply]