Wikipedia:Reference desk/Archives/Science/2012 June 19

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June 19

Is there a medical term for the physical feature of a very "triangular" head?

For instance (not to label a living person with something, just to give an example of what I'm talking about), there's this video footage of Arsenio Hall. When he's face-on, you can see the very pronounced pointedness of his head. We humans like to name things, so what about that? 69.243.220.115 (talk) 00:52, 19 June 2012 (UTC)

Hi. While there almost certainly isn't a specific term for the triangular head shape, it is possible that Hall could have been born with a condition known as Craniosynostosis, which causes the bones in the skull to fuse earlier than they should, it's caused by either a failure of the bones to grow correctly, or in some cases, by a failure of the brain to grow.  BarkingFish  01:04, 19 June 2012 (UTC)

Let's invent one: mantis head. :-) StuRat (talk) 01:07, 19 June 2012 (UTC)

Maybe people like that are just from France. --Jayron32 03:18, 20 June 2012 (UTC)

I don't think I understand Modulation (music) , but I did have a question about it.

Or may be I don't understand Key (music) either. These are articles that are probably just fine for people with at least some musical background but are incomprehensible for people like me. Lines like "The methods by which the key is established for a particular piece are not easy to explain" or "The key signature is not a reliable guide to the key of a written piece", don't help much either. Could someone add Key (music) (for nerds) that says: "To recognize the key , the software would have find the first note probably played by calculating the average of all notes played and look up the frequency in a table" or something like that? There is nothing in either article that is a recipe to find out if Frère Jacques even has a key or what it could be. The question I wanted to ask is, is http://www.youtube.com/watch?v=OSRCemf2JHc Popcorn modulated at 1:07 but I've come to realise that that would be like a 6 year old asking why the exact value of Pi cannot be written on a piece of paper without understanding multiplication. Joepnl (talk) 01:31, 19 June 2012 (UTC)

I agree that the article is too technical. Here are the basic things it helps to understand. (1) An octave is divided into 12 intervals that are equally spaced in pitch -- the interval between consecutive notes is called a semitone. In other words, there are twelve semitones in each octave. (2) A key consists of a subset of semitones. The two most common types of key are called major and minor. (3) In a major key, the notes are at intervals of 2-2-1-2-2-2-1 semitones. The starting note of the sequence is called the keynote. (4) In a minor key, the notes are at intervals of 2-1-2-2-1-2-2 semitones, starting from the keynote. There are also other kinds of keys with different numbers of notes and different spacing. (5) The easiest way to tell the keynote of a tune is to know that the tune usually ends with that note, or with a chord based on that note. Looie496 (talk) 02:19, 19 June 2012 (UTC)

You can change one major key into another one by changing only one note in it by a semitone. C major is the white notes on a piano keyboard:

     ... C D EF G A BC D EF G A BC D EF G A B ...
     ... * * ** * * ** * ** * * ** * ** * * * ...
     ... \__________/\__________/\__________/ ...

If you shift the star under each F up by a semitone, making it F#, then you get

     ... C D EF G A BC D EF G A BC D EF G A B ...
     ... * * * ** * ** * * ** * ** * * ** * * ...
     ... ______/\__________/\__________/\____ ...

which, as I've marked, is the same repeating pattern of stars, but starting from G instead of C. That's G major. Instead of sharping F, you can flat B, which gets you F major. Those are the only two "directions" you can go from C—other single-semitone changes don't get you the same repeating pattern. If you go in the flat direction from G it takes you back to C. If you keep sharping things from G you go to D, A, and so on. Eventually, after sharping everything, you get to C# major (seven sharps). You can keep going, double sharping the notes until you get to C-double-sharp major (fourteen sharps), then triple-sharping them, etc., but composers don't stray that far from their original key. You'll see the occasional double sharp and that's it. The principle of modulation between keys is that keys like F, C, and G major are close to each other in the sense of having a lot of notes in common, so in principle you can shift imperceptibly between them by altering notes that you happen to not be playing at the moment. Thus the exact moment at which the key changes is not well defined.

Equal temperament is a thing that exists, but it's not especially relevant here. If you want to play a lot of different keys on an instrument that can only play a fixed set of pitches, like a piano, you may want equal temperament. If you're playing an instrument that can produce a continuous range of pitches, like a violin or the human voice, then temperament is meaningless, but you still have this system of related major keys. In equal temperament C and B-sharp and A-triple-sharp and so on are the same sound frequency, but in general they're not the same, because the half steps and whole steps above are not generally all the same size—they are adjusted slightly so that certain intervals between them sound pleasing to the ear. By the time you get from C major (zero sharps) to B-sharp major (twelve sharps) the frequency has shifted a bit—specifically, by a factor of (3/2)¹² / 2⁷ ≈ 1.014. -- BenRG (talk) 07:25, 19 June 2012 (UTC)

Find and listen to Howard Goodall's five-part documentary Big Bangs on the history of music. A large part of his focus is on tone, key and temperament. See http://www.youtube.com/watch?v=AJX76zHAaFA but look for better links. It is quite excellent and will educate you on all you need to know. μηδείς (talk) 05:41, 19 June 2012 (UTC)

(Also, listen to http://www.youtube.com/watch?v=IZ4LCejQg8o μηδείς (talk) 05:41, 19 June 2012 (UTC))

I watched about three minutes of the first one and gave up. I don't see what this question has to do with equal temperament, except in a very indirect way. The second one seems even less relevant, though it is pretty, I guess. -- BenRG (talk) 07:25, 19 June 2012 (UTC)

My point was the documentary would give you concrete perceptual examples, rather than just abstract theory on paper. (Although if you just want abstract theory reading will be quicker than a five hour documentary.) Kind of like the difference between a guided tour through a painting gallery or being blind and listing to a lecture on wavelengths in respect to colour. The second video was just a pleasant digression, sorry. μηδείς (talk) 16:51, 20 June 2012 (UTC)

On propositional logic

In Propositional logic, under the heading of "Basic Concepts", they list the possible cases that may occur when one considers two propositions and an operation "connecting" (in lack of a better term) them, namely:

1 - P is true and Q is true

2 - P is true and Q is false

3 - P is false and Q is true

4 - P is false and Q is false

then, when the operation "material conditional" (P -> Q, read as "if P, then Q") is discussed, the following is written: "(...)It expresses that Q is true whenever P is true. Thus it is true in every case above except case 2, because this is the only case when P is true but Q is not. Using the example, if P then Q expresses that if it is raining outside then there is a cold-front over Kansas.(...)"

My question is: Should case 3 not represent a failure for the operation as well?200.119.78.115 (talk) 01:43, 19 June 2012 (UTC)

No, because there is no statement making the state of P conditional on Q, only vica-versa. 203.27.72.5 (talk) 02:01, 19 June 2012 (UTC)

If you said "Q if and only if P" then 3 would fail.165.212.189.187 (talk) 14:03, 19 June 2012 (UTC)

(EC) No. "If P, then Q" says nothing about whether Q will be true or not in the case of P being false, so case 3 doesn't contradict "if P, then Q". Looking at it another way, if Q is true, then "if P, then Q" doesn't imply anything about whether or not P is true. You can look at the mistake you are making as being the logical fallacy called affirming the consequent. Red Act (talk) 02:10, 19 June 2012 (UTC)

I don't really like the way they wrote that, though, as we don't have enough info to know if 3 or 4 are correct. It should be stated, that "If P is true, then we know that Q is true. However, if P is false, then we know nothing about whether Q is true or false." For a specific example "If it has been raining for an hour, then the ground is wet". However, if it hasn't been raining, that doesn't guarantee that the ground is dry. Snow could have melted, a water main could have broken, etc. StuRat (talk) 02:13, 19 June 2012 (UTC)

And that, StuRat, is why we have the Simple English Wikipedia article on propositional logic. 203.27.72.5 (talk) 02:21, 19 June 2012 (UTC)

It seems that our article is both unnecessarily complex and misleading, I can't see how that's an improvement in any case. And the Simple English version is just a stub and doesn't address this issue. StuRat (talk) 02:25, 19 June 2012 (UTC)

How is it misleading? And I don't think it's unnecessarily complex. It's just rigourous, as demanded by the subject matter. 203.27.72.5 (talk) 02:28, 19 June 2012 (UTC)

I just added to the Simple English version, to cover this case. The portion of logic discussed in this question is quite simple, and yet many probably couldn't understand it reading through our overly complex article. This is true of many of our math and science articles. (There are topics that can't be accurately described in simple terms, like quantum mechanics, but this isn't one of them.) StuRat (talk) 02:42, 19 June 2012 (UTC)

My thoughts on the quality and usability of Wikipedea articles: As time goes on, more and more articles seem to be written longer and longer, and more and more difficult for lay people to asimilate. A large fraction of Ref Desk questions ask things that the OP's could have answered for themselves by consulting relevant WP articles. So why do they ask? Because a) lazyness, b) they didn't think to search, c) they didn't know the terminology to search with, or d) they did consult a relavent article, but it di not answer their question because (1) it didn't cover it or (2) they didn't understand it. Item (d) is significant and we should adress that. I think that if a WP article is longer than about 100 - 150 lines, and/or uses lots of specialised terms (whether linked to term articles or not), there should be a sort of executive summary - a short few paragraphs that 1) give an overview of the deeper coverage to follow, 2) avoid as much as possible the use of specialised terms, 3) allow the reader to decide quickly whether the following content is likley to be of interest/help or not.

In some articles, I also think there should be a standard section "Common misconceptions" - this can significantly improve understanding, and reduce cyclic editing. Common misconceptions in science can range from silly urban myths thru to non-obvious errors in early textbooks that just keep on being copied from one reference to another.

Wickwack121.215.61.16 (talk) 03:32, 19 June 2012 (UTC)

I agree, except that long and complex aren't the same thing. A short article can be utterly incomprehensible, while a long one can make perfect sense. (At some point a long article should be broken into smaller articles, though, just because it's easier to load pages and navigate that way.) For an example of an article where I provided the easy to understand intro, see Weighted mean#Examples. StuRat (talk) 20:49, 19 June 2012 (UTC)

Thanks to RedAct and StuRat for addressing the question, but wouldn't that just imply nothing about the material conditional itself? What I mean to say is that, even though it may be the case that statement 3 doesn't contradict "if P, then Q," statement 3 does not imply anything at all about its truth. The OP.200.119.78.115 (talk) 04:45, 19 June 2012 (UTC)

The fact that it doesn't tell you anything is why it needs to be true. Saying "all ravens are black" is equivalent to saying "for every thing in the world, if that thing is a raven, then that thing is black". The only way to ensure that these statements are equivalent is to make the "if P then Q" part true whenever P is false (in this case, make it true for all non-ravens). If it was false for any non-raven then the whole sentence would be false independently of whether we had found a non-black raven, which wouldn't make sense. Only a non-black raven can falsify the sentence, not any of the other three cases. -- BenRG (talk) 05:51, 19 June 2012 (UTC)

There's something implicit here that needs to be said: "if", the English word, has lots of layers of meaning, and interacts with concepts like relevance and causality. "if", in propositional logic, is a lot simpler (and less informative). Various exotic logics bring some of these features back, but they can be a big pain to work with; it turns out that what is going on in people's heads when they speak and understand sentences is very complicated. (also, for most purposes, simple logics are powerful enough to reconstruct those features on an as-needed basis) Paul (Stansifer) 23:45, 19 June 2012 (UTC)

The semantics of the material implication is as it is. If this captures the "intuitive meaning" of a conditional statement, and if not, if there is anything better, has been discussed a lot among philosophers and logicians. At least for propositional logic, the answer sems to be "not quite, but no" ;-). --Stephan Schulz (talk) 10:01, 19 June 2012 (UTC)

Right — it's the closest you can get by looking only at the truth values of the component parts. The natural-language conditional looks at more than that; it also looks at the meaning of the component parts. This is much harder to get at formalistically, but attempts have been made. The OP may want to look at relevance logic for more information. --Trovatore (talk) 21:01, 19 June 2012 (UTC)

Inventory of asteroid contents?

Where can one find an inventory of the contents of asteroids within the asteroid belt, or closer? (iron, titanium, uranium. gold, H3 etc) Electron9 (talk) 03:54, 19 June 2012 (UTC)

Do you want to know what the average elemental composition of the entire population of asteroids is, or do you want a list of asteriods with their individual elemental compositions? And also, what is H3? 203.27.72.5 (talk) 04:16, 19 June 2012 (UTC)

"list of asteriods with their individual elemental compositions?" is the favorite. Ie which asteroid does one select to mine X ..? Electron9 (talk) 13:15, 19 June 2012 (UTC)

H3 is the most common substance in the universe. Evanh2008 ^{(talk|contribs)} 04:18, 19 June 2012 (UTC)

Correction: Most common molecular ion in the universe. Someguy1221 (talk) 04:29, 19 June 2012 (UTC)

Correction: Ions have charges. "H3" (no charge indicated and the 3 is not subscript) doesn't mean anything as far as I can see other than a 2001 film. 203.27.72.5 (talk) 04:39, 19 June 2012 (UTC)

Truer than what I said originally. How about: "H3 is the most common molecular ion of the most common element in the universe"? Evanh2008 ^{(talk|contribs)} 04:31, 19 June 2012 (UTC)

(EC)So H₃ then? I doubt much hydrogen is going to be present on asteroids except as water or ammonia. According to hydrogen it is most commonly found in the plasma and atomic state, not as H₃ or any ion thereof. 203.27.72.5 (talk) 04:36, 19 June 2012 (UTC)

Look up trihydrogen cation. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 11:38, 19 June 2012 (UTC)

The original poster may have meant Helium 3 rather than the very unlikely triatomic hydrogen or H3+ ion. Graeme Bartlett (talk) 13:03, 19 June 2012 (UTC)

Correct :-) Electron9 (talk) 13:15, 19 June 2012 (UTC)

So ³He then? Not very likely on asteriods other than as a product in a decay chain, so very trace amounts. Anyway, I still don't know what the OP is asking for, a catalogue of asteriods with their individual compositions, or the abundance of chemical elements in the solar system's asteriods in general. 203.27.72.5 (talk) 20:45, 19 June 2012 (UTC)

There's presumably He-3 on asteroids for the same reason it's on the moon - they've been bombarded by solar wind for billions of years and it builds up. --Tango (talk) 21:55, 19 June 2012 (UTC)

Which, from the article on He-3, is present only at ppb levels, and it's the product from tritium beta decay. 203.27.72.5 (talk) 22:47, 19 June 2012 (UTC)

He-3 is useful in fairly small quantities, so ppb is enough for people to be considering going to the moon to extract it. If you're mining asteroids anyway, you might as well keep hold of the He-3 while you're at it (most plans for asteroid mining involve extracting pretty much everything of value from an asteroid, rather than mining them for a specific thing). --Tango (talk) 13:51, 20 June 2012 (UTC)

milk and aging?

have there been any studies on whether consumption of milk affects aging? 99.43.78.36 (talk) 04:14, 19 June 2012 (UTC)

I can't speak to studies, but it's high in lactose so bad for diabetes and annoying to the lactose intolerant, but high in calcium and vitamin D so good for osteoporosis. Jeanne Calment swore by chocolate, cigarettes and, especially, olive oil. μηδείς (talk) 05:19, 19 June 2012 (UTC)

illegal immigrants in the us

see the humanities desk
The following discussion has been closed. Please do not modify it.
see http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Humanities#illegal_immigrants_in_the_us

Paramagnetism

Why are $BN^{-}$ and $BN^{3-}$ paramagnetic but not $BN^{2-}$? --150.203.114.37 (talk) 09:59, 19 June 2012 (UTC)

Paired and unpaired electrons. Plasmic Physics (talk) 10:08, 19 June 2012 (UTC)

We have a paramagnetism article that talks about its causes and the relevance of electron-spin. DMacks (talk) 10:09, 19 June 2012 (UTC)

Are you sure that you have the correct formulae? Plasmic Physics (talk) 10:10, 19 June 2012 (UTC)

Yes. --150.203.114.37 (talk) 11:25, 19 June 2012 (UTC)

SO for clarity, is it true that $NO$ is paramagnetic? Yes? --150.203.114.37 (talk) 22:23, 19 June 2012 (UTC)

Yes. Plasmic Physics (talk) 22:50, 19 June 2012 (UTC)

NO and BN2-

How do you derive molecular orbital diagrams for molecules, and in particular, nitric oxide (NO) and $BN^{2-}$? --150.203.114.37 (talk) 11:28, 19 June 2012 (UTC)

You have to run modelling software, or run spectroscopy experiments to find the energy levels. Plasmic Physics (talk) 11:34, 19 June 2012 (UTC)

You can make an educated guess, but there is a good chance to be wrong. Plasmic Physics (talk) 11:36, 19 June 2012 (UTC)

Radium

Is there a commercial source for a gramm of radium bromide? I know that this is highly regulated and neither possessing nor transporting it would be possible if it is not a university or research institute. Extracting was done during the uranium production, but I doubt all companies producing uranium would also isolate radium our days. The alternative method to produce it directly by irradiating a lighter atom with neutrons seems less favorable in the radium case.--Stone (talk) 12:24, 19 June 2012 (UTC)

If you can get your hands on an old borehole logging neutron generator, then you could extract the radium-beryllium neutron source and make some radium bromide (provided the radium hasn't substantially decayed into radon. It will need to be an old source, as the new ones use americium-beryllium. You'd also be breaking the law unless you're properly licensed to do all of this work with radioactive materials and have access to a hot cell. It's not available commercially as far as I can see. There are better radioactive sources available so the uses would be very specialised and most likely research only. 203.27.72.5 (talk) 21:08, 19 June 2012 (UTC)

Whatever you do, don't say something like "I am an Al Qaeda terrorist agent interested in making a dirty bomb" or you may come to the unwanted attention of various intelligence agencies. μηδείς (talk) 22:56, 19 June 2012 (UTC)

T.h.e.i.r/s.y.s.t.e.m.s/h.a.s/a.l.r.e.a.d.y/s.p.o.t.t.e.d/t.h.i.s/d.i.s.c.u.s.s.i.o.n\ Plasmic Physics (talk) 23:50, 19 June 2012 (UTC)

They have software that scans the internet for keywords. Something's going to be flagged, if it mentions this and air bus on the page. Plasmic Physics (talk) 23:54, 19 June 2012 (UTC)

Actually, it turns out they do still use radium sources for density measurments over long distances (up to 300m) in the construction industry. They also still use it as a neutron generator because some states in the US apparently regulate Ra less strictly than Am. Get your hands on one of those, crack it open, and Bob's your uncle. The material inside may already be radium bromide since it appears to be one of the more stable chemical species. It's probably bound up in some kind of ceramic matrix though. 203.27.72.5 (talk) 03:00, 20 June 2012 (UTC)

No no I want to know who is producing that stuff. Buying is less of a problem for small quantities, but where do the people producing the small radium radiation sources get their material for manufacturing? There are only a few possibilities, one is that they have a few gramm stockpile somewhere from the good old times in the first quarter of the 20th century when the stuff was produced mainly in US from Utah and Canadian uranium ore or in Belgium from Kongo uranium ore or in Austria from Joachimsthal uranium ore. The other possibility is that some body somewhere is still operating an extraction plant.--Stone (talk) 09:00, 20 June 2012 (UTC)

AIR BUS A380

DOES AIRBUS A380 NEED FOUR WHEEL NOSE LANDING GEAR. — Preceding unsigned comment added by 78.93.35.44 (talk) 13:17, 19 June 2012 (UTC)

No. 2 wheels. More at Airbus_A380#Integration_with_infrastructure_and_regulations. --Tagishsimon (talk) 13:49, 19 June 2012 (UTC)

Don't you mean "No. 2 wheel"? There is only one No. 2 wheel. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:02, 20 June 2012 (UTC)

No, he means exactly what he said. (You have read the first word as an abbreviation for "number"; it is actually a full sentence: "No.") -RunningOnBrains^(talk) 17:50, 20 June 2012 (UTC)

Well, actually, it's not a full sentence, as it lacks a verb. But I guess that's really one for the language desk... 203.27.72.5 (talk) 21:40, 20 June 2012 (UTC)

Ah, thanks. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:53, 20 June 2012 (UTC)

Shower Cream

what exactly is Shower Cream and how does it work? Its a alternative to soap. How does cream rinse off? does it leave a oily film behind?--Wrk678 (talk) 13:42, 19 June 2012 (UTC)

We have an article Shower gel. What it doesn’t appear to say is that the thickening agent is often Sodium polyacrylate. Being water soluble, it all washes off. --Aspro (talk) 16:40, 19 June 2012 (UTC)

Logically, it should be easier to rinse off, being closer to a liquid in it's natural state than bar soap. You probably have already used liquid detergents, such as hand dish washing liquid, so you know it can rinse off. StuRat (talk) 17:06, 19 June 2012 (UTC)

That makes no sense. Diesel is closer to liquid than NaCl at STP but that doesn't make it easier to rinse off. 203.27.72.5 (talk) 21:25, 19 June 2012 (UTC)

The underlying assumption is that both are water soluble, as Aspro already stated. Given that assumption, my statement is correct. StuRat (talk) 03:20, 20 June 2012 (UTC)

The bar soap is already dissolved when it's in the lather on your skin. The difference in solubility and viscosity between a lather of bar soap on the body and a lather of shower gel is going to determine the ease with which it can be rinsed off not whether the bar soap was a solid before you formed the lather or not. 203.27.72.5 (talk) 03:35, 20 June 2012 (UTC)

When using an old shriveled bar of soap, it can break up, leaving me with solid chunks in my armpit hair. This is not particularly water soluble (apparently the more soluble parts already dissolved in water, leaving behind the less soluble bits) and much harder to get out than liquid soap/detergent. StuRat (talk) 03:41, 20 June 2012 (UTC)

I believe that is just because the pieces are large. If they really dissolved in your armpit as quickly as you wanted too then you'd have to spend alot more money soap. Unless you use some special soap that has pieces of oatmeal or pumice or rocks in it or something like that. Sagittarian Milky Way (talk) 16:58, 20 June 2012 (UTC)

Yes, I've used bar soaps containing oatmeal and pumice. However, just being completely dried out seems to make regular soap less water soluble, too. I'm sure it would dissolve eventually, once the water soaks back in, but that's longer than I have in the shower, so I'm left trying to pick the chunks out of my pit hair as the water turns icy cold. Thus, I've switched to liquid soap/detergent. StuRat (talk) 18:18, 20 June 2012 (UTC)

It would seem that some of you folks do not have to clean your own shower cubicle. Those of us that do know that having to clean soap scum off the walls is a problem that does not exist with shower gel. This is the reason why hotels these days leave shower gel in the rooms/suites, and not soap cakes - it saves them cleaning labour. They get less incidence of blocked drains too. Wickwack121.221.33.192 (talk) 06:50, 20 June 2012 (UTC)

You're right, I don't clean my own shower cubicle, but I also use shower gel, so apparently I'm saving someone some effort. 203.27.72.5 (talk) 07:57, 20 June 2012 (UTC)

I still say Sorbolene is best. -- ♬ Jack of Oz ♬ ^{[your turn]} 00:04, 23 June 2012 (UTC)

I think you guys missed the boat here what I was referring to the shower cream it's not the same thing as shower gel I've seen videos of doctors recommending something called shower cream for people with eczema because it does not contain detergents that's why I was asking how washes off, If it is cream--Wrk678 (talk) 17:44, 21 June 2012 (UTC)

The difference between cream and gel is the proportions of the ingredients use. So from the point of view of your question - the terms interchangeable. If they weren’t we would have said so.--Aspro (talk) 22:53, 22 June 2012 (UTC)

Oh yeah, I used something like that once. It was made from dairy milk and was called moo-goo or something like that. It was awful and definitely made me feel dirtier after I showered than before. 203.27.72.5 (talk) 21:21, 21 June 2012 (UTC)

If it really does contain milk cream and no soaps or detergents, then it won't wash off, but neither does leave-in conditioner. And, yes, I'd expect it to feel slimy, much like moisturizer does when first applied. StuRat (talk) 21:20, 23 June 2012 (UTC)

Thermodynamics

If I have a freshly-boiled cup of tea and pour milk in, will it be cooler in 10 minutes than if I wait until 10 minutes are up before pouring the milk in?--Gilderien Chat|List of good deeds 19:20, 19 June 2012 (UTC)

Why dont you try it and tell us your findings?165.212.189.187 (talk) 19:25, 19 June 2012 (UTC)

I can't start drinking caffeinated drinks at this time in the evening....I'm playing keys for the olympic torch tomorrow.--Gilderien Chat|List of good deeds 20:13, 19 June 2012 (UTC)

I don't think that all the 270 results you get if you put "coffee cooling" into the "Search the Reference desk archives" at the top of the page are people who have previously asked just this question, but certainly many of them are. --ColinFine (talk) 20:14, 19 June 2012 (UTC)

Argh.....this is turning out to be much more complicated than I imagined....I initially thought that as heat lost through radiation is something like $t^{4}$ the milk added first would be cooler, but now I see it could depend on the shape of the cup, the specific heat of the cup, the thickness of the cup...--Gilderien Chat|List of good deeds 20:22, 19 June 2012 (UTC)

And, as we have pointed out in the past, the only really relevant thermal loss processes are conduction and convection; these are empirically well-modeled using Newton's law of cooling, for an appropriately-chosen time-constant. If you want to correctly model the effects of radiative cooling, you'll need incredibly precise thermometers - the sort of equipment that few people have at hand for kitchen chemistry. Nimur (talk) 20:24, 19 June 2012 (UTC)

Adding the milk right before you drink it will cool it the most, if we assume the milk is in the fridge during that 10 minutes. However, if both the milk and the tea were out, then it would depend on the relative initial temps of each versus room temp, the types of containers, etc. StuRat (talk) 20:27, 19 June 2012 (UTC)

I was assuming the milk remained at a constant temperature until pouring....though am I to believe that the same overall answer, if not precisely the same temperature change, is obtained whether radiative cooling is included or not?--Gilderien Chat|List of good deeds 20:32, 19 June 2012 (UTC)

If you pour your tea out into a cup that is in a Environmental chamber maintained at the same temperature as the tea it will obviously be at the same temperature when you come to put the cow juice in. However, if the ambient temperature is lower, the tea will loss heat at a rate depending on that ambient temperature. The lower the ambient temperature the less local heat energy will be available to radiate back into the cup of Rosie Lee -hence it will cool faster due to its higher energetic state. Pour the in milk first (the proper way) and the infusion of tea after. Then it will be warmer ten minutes later than if you had done it vicky-verky. In a power station it is the done thing to add more heat to steam after the first turbine because it is easier to add heat to something already hot, than when its cold -so it goes the other way too.--Aspro (talk) 20:46, 19 June 2012 (UTC)

An easy way to visualize it is to consider a cup half full of water at 100°C. It will cool at a rate that decreases over time e.g. takes 1 minute to reach 90°C, 3 minutes to 80°C, 6 minutes to 70°C, 10 minutes to 60°C and so on and so forth. The reason its rate of cooling decreases is because the temperature difference decreases i.e. very hot things transfer heat to very cold things faster than moderate temperature things do.
If when it reaches 60°C (or after 10 minutes) we add to it exactly the same amount of water again but this time at 0°C, the final temperature of the now full cup will be 30°C.
If instead of that, we add the 0°C water right at the start, the full cup will be at 50°C and over the next 10 minutes will cool at a much slower rate (following the above trend it would take 21 minutes to reach 40°C).
If you think of the first half-cup as your tea, and the second one as your milk, it's easy to see that in the first case the tea ends up much colder than in the second one. The exact rate of cooling will depend on your cups dimensions, material, etc. but the cooling will always be fastest at the start and slow down as the temperature difference between the ambient and the tea decreases. 203.27.72.5 (talk) 22:41, 19 June 2012 (UTC)

If you leave the milk out to warm as well, both liquids will cool (come to room temperature) more quickly, since smaller masses having greater surface areas. If the milk is kept refrigerated and added later it will depend on the relative volumes, temperatures, and surface areas. You'd have to do the calculus, which is what I believe StuRat said above. μηδείς (talk) 22:53, 19 June 2012 (UTC)

Not quite. I said that the refrigerated milk should always be added last, if the object is to cool the tea the most. It's only when the milk is warming as the tea is cooling that it gets rather iffy. StuRat (talk) 03:12, 20 June 2012 (UTC)

If you leave the milk out it will warm, not cool. One mass will cool and the other will get warm. The net effect will be that the temperature of the tea with milk in it will be slightly higher (by an amount proportional to the fraction of the drink made up by the milk, the temperature change in the milk between when it was taken out of the fridge and when it was poured, and the heat capacity of milk). 203.27.72.5 (talk) 23:02, 19 June 2012 (UTC)

Actually, it has been observed that, under certain conditions, water at or near the boiling point will actually drop in temperature due to radiative heat loss faster than colder water. Sometimes extremely hot water will freeze before water that was actually closer to the freezing point to begin with. See Mpemba effect. If that effect always holds true (and it doesn't), I would say that the tea would actually be cooler if the milk were added immediately. Evanh2008 ^{(talk|contribs)} 23:09, 19 June 2012 (UTC)

No controlled experiment has confirmed that supposed effect. I hope the relevant artilce doesn't say otherwise. μηδείς (talk) 02:34, 20 June 2012 (UTC)

Inventory of asteroid contents per body?

Is there an inventory per asteroid body on what contents they have, within the asteroid belt or closer? (iron, titanium, uranium. gold etc) Electron9 (talk) 22:27, 19 June 2012 (UTC)

No one has been there yet to check. Assumptions of contents would be made on surface features which would indicate whether they were carbonaceous asteroids or stony asteroids or so forth. See asteroid spectral types. μηδείς (talk) 22:48, 19 June 2012 (UTC)

For small bodies we generally assume there is no differentiation i.e. if the surface is iron then we assume it's a lump of iron, if the surface is ice we assume it's a lump of ice. For the larger ones there is most likely different materials in the different strata. The spectral data is also only any good for materials that are present in some decent concentration. If there's a few ppm of gold (or ppb of He-3), you won't see that from spectral data. 203.27.72.5 (talk) 23:08, 19 June 2012 (UTC)

I had some thought of some space organization like NASA etc would have either used the reflected wavelengths from the sun or a high energy laser to figure out the contents through absorption/emission spectrum ? maybe there are other methods that works better. Electron9 (talk) 00:31, 20 June 2012 (UTC)

That's exactly what they do. But you can't see trace elements that way because the signal from them is so weak, and you can only see surface materials, not the interal structure. The other ways are to send probes to sample them directly, which would take a long time per asteriod, or sample directly from meteorites. Watching gravitational interactions with other objects may also help to deduce their mass, and if their volume is known the density and likely composition can be established. 203.27.72.5 (talk) 01:11, 20 June 2012 (UTC)

Has any such laser/sun or mass to gravity interaction measurements been done, or is planned? Electron9 (talk) 01:27, 20 June 2012 (UTC)

I'm not aware of any volume of data available from gravity interaction analyses, but if you have a look at asteroid spectral types as μηδείς suggested, it explains how asteriods are classified according to surface composition. 203.27.72.5 (talk) 02:18, 20 June 2012 (UTC)

Why would Body surface area be the perfect measure for medication dosages?

From the article: "For many clinical purposes BSA is a better indicator of metabolic mass than body weight because it is less affected by abnormal adipose mass." The article also has a few lines of criticism.

I've heard, from a pharmacist, the rumour that while finding correct formulas to calculate the body surface area from length, weight, etc has been studied at length, the very ratio behind using BSA instead of, for instance, weight, has not been studied for ages. Is that true? My (layman) guess would be that you'd have a range of formulas for the right dosage depending on the kind of medicin. One might include age and weight, another might be sugarlevels combined with gender, etc. Instead, the amount of skin seems to be holy. Is the rumour true and is this some kind of "soft" Lysenkoism? Joepnl (talk) 22:37, 19 June 2012 (UTC)

The BNF uses the formula: ((surface area of kid in m ²) / 1.8) x Adult Dose. The figure of 1.8 refers to the average surface area of an adult.--Aspro (talk) 22:54, 19 June 2012 (UTC)

1.8 is an adult? My surface area was a full 2.7 m ² when I was so young I was 5'6" or several inches shorter. On the pediatrician's medical record. Now I had some potbelly but everything else is slim like a snake. If your limbs are thinner and shorter than adults and your torso not wider, significantly rounder (fatter), or taller and your head/neck is small and thin then where is the extra 50% surface area going to come from? Sagittarian Milky Way (talk) 16:46, 20 June 2012 (UTC)

Isn't giving a figure for body surface area akin to giving a figure for the length of the coastline of Britain. It depends on the fineness of the measurement. SkyMachine ⁽⁺⁺⁾ 00:56, 20 June 2012 (UTC)

Not really, the skin is rather smooth, unless you go down to the level of including the surface area of pores, and nobody would do that. StuRat (talk) 03:06, 20 June 2012 (UTC)

The clinical purpose of calculating body surface area is for determining the dosage of certain types of drugs and expecially for determining chemotherapy dosage. Many of these drugs or their metabolites are mainly excreted via the kidneys. It appears that the rate at which the kidneys can do this is roughly proportional to an eqivalent or notional internal surface area, and this is in turn proportional to body surface area. A similar situation arises for drugs that are exceted via the intestines - there is a rough alignment of intestine internal surface area and body surface area. There may be no rigorous science in this, but basing dosage on BSA has been found to work fairly well. The weight of intestines and other organs tends to the cube of height whereas the processing area tends to the square of height, but weight is of little importance when the rate at which a given quantity of drug excreted is proportional to the internal surface area. So many factors affect the half life of drugs in the body that any sort of precision in dosage is pointless. Wickwack121.221.33.192 (talk) 04:58, 20 June 2012 (UTC)

Would women get extra drugs compared to a man the same height & build just because their beautiful curves and breasts add surface area? Sagittarian Milky Way (talk) 16:46, 20 June 2012 (UTC)

BSA is a notional value calculated by a simple formula (engineers and scientists will note that it make no dimensional sense) based on only height and weight. Within the precision required (which is no real precision at all), there is no difference between males and females. In real life, men have slightly greater surface area due to wider shoulders while lacking visually apparent curves at breasts and thighs but, as explained, this is of no importance in regard to required dosing precision. Wickwack121.215.54.198 (talk) 02:34, 21 June 2012 (UTC)

Fine then, a man of the same mass and height would be denser due to less body fat and have less surface area. Sagittarian Milky Way (talk) 23:57, 21 June 2012 (UTC)

Your Body surface area is 2.7 m ² at 5 foot something and skinny as a bean pole? Please post a photo on Wikipedia Commons and I'm sure we can find an article to add it to.--Aspro (talk) 22:10, 20 June 2012 (UTC)

Maybe it was a typo then. At the time I pictured a square meter with my cross section and it didn't seem like there's enough but it's from the doctor so.. I supposed maybe it would work out if you really did the math. Sagittarian Milky Way (talk) 23:57, 21 June 2012 (UTC)

Hum...Typo. That's a shame! Don't get me wrong; I wasn’t thinking about you as a freak or anything like that but we need images on our articles such as 'Homunculus'. For example this [1]. To think I might have discovered a hitherto unknown and new example, out in the wild, got me rather exited there -for a moment. It was purely out of academic interest that I was curious as to what you might look like.--Aspro (talk) 16:33, 22 June 2012 (UTC)

Diamagnetism

What causes diamagnetism in a molecule of two atoms? --150.203.114.37 (talk) 22:38, 19 June 2012 (UTC)

The largest contributor is the spin multiplicity. Only singlet state molecules tend to be diamagnatic. Plasmic Physics (talk) 22:44, 19 June 2012 (UTC)

Is it true that anything which is not paramagnetic is diamagnetic? --150.203.114.37 (talk) 22:41, 19 June 2012 (UTC)

Yes. Plasmic Physics (talk) 22:44, 19 June 2012 (UTC)

(edit conflict)

1. Molecular orbital theory will show whether there are any unpaired electrons in the molecule. If there are none the molecule is diamagnetic for reasons I can't understand yet.
2. Not quite. Some substances are ferromagnetic (a stronger form of paramagnetism), but yes if it isn't that either the substance is diamagnetic.--Jasper Deng (talk) 22:45, 19 June 2012 (UTC)

(edit conflict) In your question earlier today about paramagnetism, you were advised to read the article paramagnetism. I bet if you use the search box at the top of this helpdesk you can find an article that might have information about diamagnetism among our 6,916,270 articles. You might even be able to guess what its name might be. It has information about what causes this effect at an atomic/molecular/electronic level and what types of materials exhibit it vs other types of magnetism (in particular, giving a clear "no, but may be overwhelmed and un-noticeable" to question #2). DMacks (talk) 22:45, 19 June 2012 (UTC)