Wikipedia:Reference desk/Archives/Science/2012 February 9

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February 9

Ionic gases

When an ionic compound is vaporised, does it form individual molecules or does it separate into its component ions? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:24, 9 February 2012 (UTC)

Stays as molecules, like water vapor. StuRat (talk) 01:26, 9 February 2012 (UTC)

Water is covalently bonded. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:30, 9 February 2012 (UTC)

Just to correct Stu, in the solid phase, there is no such thing as an ionic molecule. Sodium chloride doesn't form molecules in the solid phase. In something like Ionic liquids, the situation is complex, but roughly speaking the individual ions are free moving, though they can group up in molecule-like structures. Ionic gases form ion pairs or complexes which behave kinda like molecules, near as I can find from a quick literature review. Such clusters are called "molecules", except that they are held together purely by the electrostatic interaction of the positive and negative ions. See this paper from 1951 which gives an overview. If heated enough, such an ionic gas may form a plasma as the individual ions are seperated. --Jayron32 04:44, 9 February 2012 (UTC)

Did I say anything about the solid phase ? I just said that ionic particles stay bonded, just like water vapor (which is covalently bonded) does. And, of course, I was assuming conditions short of those needed to form a plasma. StuRat (talk) 04:53, 9 February 2012 (UTC)

In sodium chloride gas, there are weakly bonded polar molecules. This gas consists of a mixture Na, NaCl, Na
₂, Na
₂Cl, Cl, NaCl
₂ and a variety of other shortlived species. Upon collision, individual molecules always exchange partners. Plasmic Physics (talk) 01:01, 10 February 2012 (UTC)

The percentage of DNA sharing in Monozygotic twins

what is the "exact" percentage? (if known), and, could be variants? thanks. — Preceding unsigned comment added by 81.218.145.251 (talk) 03:43, 9 February 2012 (UTC)

Almost 100%. At least a handful of mutations will inevitably occur prior to the splitting of the embryo. Even if the split occurred at the two cell stage, one would expect genetic variance of 1 part per billion (99.9999999% identicalness, if that's a word). In practice, copy number variation has been observed between "identical" twins, as well as variation in DNA methylation patterns. Someguy1221 (talk) 03:52, 9 February 2012 (UTC)

Could someone please draw up a schematic of an obvicopter?

Or link one if it already exists?

Some Californian Hispanic dude named "Juan Carlos" drops the term "obvicopters" occasionally - "Can't hear, obvicopters too loud," "...it is ##obvicopters," etc. Another user around him stated that their engine sound would sound slightly different from the helicopters'.

How would an obvicopter be built differently? Is it, perhaps, the mystery jet-run tilt-rotor craft seen in the film, I, Robot?

Apparently it's a concept helicopter that isn't in full production yet, but Google seems to prefer to keep it under wraps. _{Perhaps under government order to keep it classified...}

Or it's not forthcoming for other reasons. Anyway, what could you dig up about this? --70.179.174.101 (talk) 11:47, 9 February 2012 (UTC)

It seems fairly obvious you're referring to Meta:Foundation wiki feedback/Archive/2011#Talk:Staff, Meta:IRC office hours/Office hours 2011-02-11, [1] (connection between names apparently self disclosed on publicly logged IRC channels Meta:IRC office hours/Office hours 2012-01-20) so why don't you just ask user:killiondude rather then coming up with another random wacky conspiracy theory? Seems fairly likely it's a joke, although it wouldn't surprise me if the joke continues if you indicate you think it's otherwise as done so here. Nil Einne (talk) 14:48, 9 February 2012 (UTC)

Guessing, based on Nil Einne's provided information: "Obvi-" looks to be "obvious". "-copter" is a throwaway. The statement is a jesting reply to a correction: "I can pretend I didn't hear that, so I can pretend I wasn't wrong / didn't make that mistake / have eleventy billion dollars." Should killiondude appear and clarify, the obvicopters will no doubt be flying low over my area. — Lomn 15:21, 9 February 2012 (UTC)

It's probably derived somewhat from roflcopter, an undoubtedly hilarious internet meme of times gone by. - Cucumber Mike (talk) 16:09, 9 February 2012 (UTC)

Is his accent that thick or do you mean Ornithopter? (Juan's email address is also Ornithopterman@ ------.com). Sound-wise, if a helicopter goes thwhaat-thwaat-thwaat then a ornithopter goes more like whaap-whaap-whaap-whaap. The air flowing over the rotor blades of a heli is accelerated to much higher speeds, hence the sharper attack and decay of the beats. The engines should not (as far as I can make out) sound any different. Maybe he is just talking simply. --Aspro (talk) 21:11, 9 February 2012 (UTC)

I see the Reference Desk continues its celebrated tradition of indulging in trolls. It's just a meme that I did not initiate but did perpetuate. Killiondude (talk) 22:57, 9 February 2012 (UTC)

Do permanent magnets generate heat at all?

I had someone argue with me that if you use a permanent magnet to "launch" a projectile (in space), it would not generate any heat. I'm not entirely sure what the hell he was talking about, but I wanted to confirm if his claim was true or not. ScienceApe (talk) 13:31, 9 February 2012 (UTC)

Magnets are not magical physics-violating devices, and byproduct heat results from all useful work, per the second law of thermodynamics. — Lomn 14:30, 9 February 2012 (UTC)

Launching a projectile into space with a permanent magnet would be quite a feat, unless you live on an asteroid. But there should be some heat from eddy currents in any changing magnetic field. Wnt (talk) 14:58, 9 February 2012 (UTC)

That's what I thought, thanks. ScienceApe (talk) 21:27, 9 February 2012 (UTC)

question about plutonium

I've seen pictures on the Internet of workers holding objects such as the plutonium buttons and working directly in front of weapons grade plutonium. How is this possible because during Chernobyl people would die from radiation exposure just from looking briefly at the plutonium rods. --208.83.61.116 (talk) 17:43, 9 February 2012 (UTC)

Plutonium-238 decays by alpha decay. Alpha particles are blocked by very little material (see alpha decay#Toxicity), so it's pretty safe to handle (when it's in a big block; you wouldn't want to be breathing or drinking this stuff). Other radionuclides decay by gamma emission, which is very penetrative. Used nuclear fuel elements, such as one would find in an burning reactor, contain a variety of daughter products, of which plutonium is one of the lesser hazards. -- Finlay McWalterჷTalk 18:14, 9 February 2012 (UTC)

You may find Chernobyl#Radioactive release useful. It says, among other things: "While the general population often perceives plutonium as a particularly dangerous nuclear fuel, its effects are almost eclipsed by those of its fission products." --Tango (talk) 18:47, 9 February 2012 (UTC)

The fuel rods used uranium, not plutonium, although there was plutonium present as a consequence of the nuclear reactions. As others point out, irradiated fuel rods are dangerous to directly observe (through air - water of sufficient depth is a good shield) due to radiation created by decay products, not because of inherent danger posed by uranium or plutonium, which can be handled with due precaution. I believe Richard Rhodes described a piece of plutonium in The Making of the Atomic Bomb that when handled (with gloves) was warm, rather like a live rabbit. Short exposure, and avoidance of ingestion, is not particularly perilous. Acroterion (talk) 18:55, 9 February 2012 (UTC)

I suspect that in almost all cases of the photos of people handling plutonium, the people are working with glove boxes. (E.g. This guy.) That means they're behind glass. I've never seen any where there wasn't a glovebox, anyway. or some kind of containment (e.g. even just a plastic bag, much less more complicated shielding devices).

But in any event, the main exposure-based health hazard from plutonium is through inhalation. Most plutonium in the real world, if not in a glove box, is either coated in something or is not handled except with gloves and by people trained to handle it. It's not particularly radioactive in and of itself, compared with the sorts of things that are inside of a working nuclear reactor (where the problem are the fission products, which are highly radioactive). But still, people are on the whole pretty careful in how they handle plutonium, though if you aren't aware that these photos are generally taken in glove boxes, I could see you thinking people were being rather cavalier about it. --Mr.98 (talk) 01:42, 10 February 2012 (UTC)

About Chernobyl, people did not fall over dead from looking at rods. 31 people died in the three months after the event - mainly from radiation from breathing the smoke. See also Acute radiation syndrome. 75.41.110.200 (talk) 05:06, 10 February 2012 (UTC)

Though physical proximity to unshielded control rods does expose one to a lot of radiation, even without the added issue of inhaling radioactive particles. But yes, "looking at" states that poorly. --Mr.98 (talk) 13:58, 10 February 2012 (UTC)

Human hair

Does an adult's body need some DHL for living healthily? If I would cut a hair off completely(even under the skin without the root), how much time it will take for it to grow up beyoned the scalp? — Preceding unsigned comment added by 87.68.222.18 (talk) 21:29, 9 February 2012 (UTC)

I'm guessing you don't mean the parcel company, but that's all Google, Wikipedia and Wiktionary can find with that acronym... --Tango (talk) 22:32, 9 February 2012 (UTC)

Nothing that acronymfinder.com brings up seems appropriate, though I am intrigued by "Dynamic Head Loading". Anybody know what that is? Clarityfiend (talk) 22:43, 9 February 2012 (UTC)

A pubmed search for "DHL nutrition" gives one, irrelevant hit (with DHL being part of the name of a cell line). Human hair grows by about 1.25 cm per month, see Human hair growth. --NorwegianBlue ^talk 23:16, 9 February 2012 (UTC)

Is it possible the OP means Docosahexaenoic acid (DHA) and is remembering wrong? DHA seems to be a common supplement and is evidentally sometimes marketed to reduce hair loss, although it's not clear to me that OP was suggesting 'DHL' was needed for anything related to hair anyway. Nil Einne (talk) 23:37, 9 February 2012 (UTC)

Or maybe they mean DHT (dihydrotestosterone) ? StuRat (talk) 05:48, 10 February 2012 (UTC)

I thought of that but it's definitely not something many people should be taking even if they have it naturally present. Nil Einne (talk) 09:40, 10 February 2012 (UTC)

But they didn't ask if they should take it, only if the human body needs it. StuRat (talk) 19:18, 10 February 2012 (UTC)

Yes but if it's not something you consume in some way, the meaning of 'need some ... for living healthily' is questionable. Nil Einne (talk) 14:00, 11 February 2012 (UTC)

Based on his follow-up post below Wikipedia:Reference_desk/Science#Dihydrotestosterone, it looks like I guessed right. Let's close this Q and answer below. StuRat (talk) 05:16, 12 February 2012 (UTC)

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