Wikipedia:Reference desk/Archives/Science/2007 November 15

= November 15 =

Criticality weapon
Has anyone or any country (more likely) developed a criticality weapon, i.e. ray (radiation) gun versus a bomb (neutron bomb)? Adaptron 06:23, 15 November 2007 (UTC)


 * I doubt it, there's no easy way of controlling the trajectory of neutrons, so everyone (including yourself) will be radiated, which is not very useful as a gun. --antilivedT 10:28, 15 November 2007 (UTC)
 * Not true at all. Put the entire thing into a sphere of neutron-reflecting material. Open up one small hole in one end. Bang, a simple, aim-able neutron gun. They use stuff like that in physics all the time—even a reactor's neutrons can be directed in a single direction for use with experiments via this method. Not useful as a weapon, but it isn't about not being able to aim them. --24.147.86.187 04:37, 16 November 2007 (UTC)
 * Can you carry that around though? It's not very portable... --antilivedT 10:08, 17 November 2007 (UTC)


 * It could be. There are lots of small neutron sources. The problem is that they are usually one-shot sorts of things. The problem isn't the casing, though—you could basically have a sphere of beryllium surrounded by something else (since beryllium is itself toxic) and that would work (beryllium is an excellent neutron reflector). Again, it'd be a lousy weapon for reasons already stated, but aiming isn't the issue. --24.147.86.187 (talk) 17:08, 17 November 2007 (UTC)


 * See Particle beam weapon, Directed-energy weapon. The utility of such a gun would be limited; the kind of radiation required to do immediate damage to a person is vast; the largest recorded dose of ionising radiation (180,000 REM) still resulted in the victim surviving 36 hours. If you really want to kill someone with radiation, spiking their sushi with nuclear material or lobbing a dirty bomb at them would be far more effective. Remember that the most destructive elements of the atom/hydrogen/neutron bomb are not the initial radiation burst, but the explosive force and nuclear fallout which results. Laser guns do exist to some extent, but most, like the Active Denial System, are so big that they need to be mounted on the back of a Humvee and all they do is warm up the skin, although Israel shoots down enemy missiles with the giant Tactical High Energy Laser. Laïka  13:49, 15 November 2007 (UTC)


 * You could do it, though it would probably be heavy (imagine a pulsing TRIGA on wheels) and not be at all useful in the short-term since radiation takes a long time to kill by itself. (Imagine how un-useful it would be to have your enemies know that you had just killed them, but that they'd be alive another day or so. Think we have problems with suicide attackers as it is?) So nobody has tried or bothered to. --24.147.86.187 04:41, 16 November 2007 (UTC)

Emergen-C etc
Welcome to Wikipedia. About your question: please see Vitamin C and Multivitamin and the cited references on those pages. A useful source of information. --JWSchmidt 16:38, 15 November 2007 (UTC)

We're not really qualified to offer this sort of advice about your health here at the Reference Desk. If you're looking for guidance on the appropriateness of combining vitamin supplements (particularly in larger doses) you should speak to your pharmacist or physician. TenOfAllTrades(talk) 13:08, 15 November 2007 (UTC)
 * Discussion moved to talk page. --Milkbreath 14:26, 15 November 2007 (UTC)
 * There was no request for medical advice. --JWSchmidt 16:38, 15 November 2007 (UTC)

in vitro-fertilisation
what is the latest research or essay about the in vitro-fertilisation in mare? --84.56.215.32 14:02, 15 November 2007 (UTC)
 * here is one starting point for information on in vitro fertilisation. --JWSchmidt 16:17, 15 November 2007 (UTC)

Human Eating Habits
Which is the correct posture for human beings while they are eating? Sitting or standing and why?

Food or water taken in. How hot or cold must your food/liquids be for the body to efficiently digest it?

196.26.82.146 14:21, 15 November 2007 (UTC)


 * As temperature goes, everything will equalize to body temperature pretty quickly. As long as you're not causing injury while swallowing, you're fine.  Similarly, posture is irrelevant so long as you're swallowing and not choking. &mdash; Lomn 14:53, 15 November 2007 (UTC)
 * You may want to check out peristalsis, which is the process by which food is transported from the mouth to the stomach (i.e. swallowed). Because the food travels down the esophagus via muscle contractions, it makes no difference what position you are in when you swallow. &mdash; dcole 17:44, 15 November 2007 (UTC)
 * I dispute this. One of the reasons waterboarding is so effective is that it is administered in the prone position where gravity can not pull food or liquid from the throat down into the esophagus. As a result it can accumulate and block the trachea or windpipe. 71.100.6.233 01:19, 16 November 2007 (UTC)

Principles of plasmid dna isolation
While isolating the plasmid dna from e coli, wy do we always take new lysis solution every time? —Preceding unsigned comment added by 59.180.126.4 (talk) 15:44, 15 November 2007 (UTC)
 * Do you have any enzymes in your lysis solution? Some people include lysozyme in the solution they use. --JWSchmidt 16:01, 15 November 2007 (UTC)


 * I'm not quite sure what you mean by "new" lysis solution. In the standard alkaline lysis procedure for plasmid purification, a strong solution of sodium hydroxide lyses the cells due to its basicity (this is the simple version of the explainations). The lysate is then neutralized by an acidic solution of sodium acetate. If you mean "new" as in "not used", this solution no longer has the pH to lyse cells (not to mention the contamination with the plasmid/other cell components). If you mean "new" as in "not old" (that is "freshly prepared"), the lysis solution needs to have a high pH in order to lyse the cells. If not tightly sealed, carbon dioxide in the atmosphere can dissolve in the solution, forming carbonic acid and dropping the pH. That said, I've successfully used plasmid-prep lysis buffer that was over a year old - you just need to keep it tightly sealed. -- 18:02, 15 November 2007 (UTC) —Preceding unsigned comment added by 128.104.112.105 (talk)

principles of plasmid dna isolation
Whatr is the difference in using isopropanol and ethanol as precipitating agent in plasmid isolation? —Preceding unsigned comment added by 59.180.126.4 (talk) 16:23, 15 November 2007 (UTC)
 * I may be wrong but, is the answer "do your own homework"? SGGH speak! 16:45, 15 November 2007 (UTC)


 * From the article "Ethanol precipitation": "Isopropanol can be used instead of ethanol; the precipitation efficiency of the isopropanol is higher. However, isopropanol is less volatile than ethanol and needs more time to air-dry in the final step (see below)." - I'll also note that, due to it's lower polarity (higher hydrophobicity), it takes a smaller volume of isopropanol than ethanol to precipitate the (hydrophilic) DNA. -- 18:08, 15 November 2007 (UTC) —Preceding unsigned comment added by 128.104.112.105 (talk)


 * My protocols guide includes steps for isopropanol precipitation and ethanol precipitation in the DNA/RNA exctraction methods it details. I haven't figured out why yet, but I've always been sure they had a reason for using both.  Someguy1221 19:19, 15 November 2007 (UTC)


 * Because ethanol is more volatile than isopropanol, most isopropanol precipitation steps include a 70% ethanol wash immediately afterwards. This removes residual traces of isopropanol. The residual ethanol than can be easily removed by evaporation (say by leaving the tubes open on the bench). If it's at two different steps in the protocol (i.e. not immediately afterwards), it's probably a volume issue. You only need ~0.7 volumes of Isopropanol, whereas you need ~2.5 volumes of Ethanol. If you have 25 mL of sample in a 50 mL tube, it's simple to do an isopropanol precipitation, whereas to do an ethanol precipitation, you would need to split the sample into multiple tubes first. -- 20:41, 15 November 2007 (UTC) —Preceding unsigned comment added by 128.104.112.105 (talk)

Most probable method of attaining pure fusion?
There are many types of attaining pure fusion, laser fusion, bubble fusion, etc... Which is the most probable to occur? 64.236.121.129 18:35, 15 November 2007 (UTC)
 * Do you mean in terms of generating electricity? The ITER project looks to be the first one likely to result in a net power generation, even if only experimentally.  It uses magnetic confinement fusion as contrasted with inertial confinement fusion, of which laser and (allegedly) bubble fusion are subtypes. &mdash; Lomn 18:53, 15 November 2007 (UTC)
 * I guess for both electricity and as a pure fusion weapon. What would be the most probable for each. 64.236.121.129 18:55, 15 November 2007 (UTC)
 * I think most people would consider the Teller-Ulam design to be a "pure" fusion weapon. Energy to start the fusion chain reaction has to come from somewhere, and a fission bomb is the most compact and easily-engineered representation of that seed energy.  Note in the "Soviet developments" section that the first (non-T-U) Soviet H-bomb's fusion component was 1/4 that of the fission component; their largest test (Tsar Bomba) had a fusion component 30 times the size of the fission seed. &mdash; Lomn 19:01, 15 November 2007 (UTC)
 * But that's not a pure fusion weapon. A pure fusion weapon is usually described as a weapon that doesn't use a fission reaction at all to avoid the nasty radiation fallout. The Tsar bomba was certainly a clean bomb, but not 100% clean. 64.236.121.129 19:04, 15 November 2007 (UTC)
 * In that case, I doubt anybody is working on a pure fusion weapon. There's simply no currently-plausible means of packing the energy of a fission bomb into a fusion bomb apart from the fission bomb itself.  Were I to stray into the realm of science fiction, I'd say that an antimatter-matter reaction might serve the same purpose -- but as soon as it's feasible, I'd just make antimatter bombs instead of fusion bombs.  Our article on pure fusion weapons notes that the US is not developing one and has found no credible design after approximately 40 years of research. &mdash; Lomn 19:18, 15 November 2007 (UTC)


 * At the moment the prospects for generating fusion power are pretty dim; it turns out to be just very, very hard. Personally I'd put my bet on laser fusion, because it doesn't suffer from the problem of trying to confine plasma (which is very, very hard) and instead just tries to implode fusion fuel (which—thanks to weapons design—they have a very good idea of how to do already and a lot of experience with, it's "just" a matter of adapting it to the different driver and "just" getting rid of the asymmetries, etc.). Personally I'd be surprised if ITER worked as well as they hope it will, but hopefully I will be wrong! In any case, even if the technical bits are in some way overcome, the economics of it don't work out very well, though if the price of enegy severely rises they could be competitive. But note that I am not at all a plasma physicist or someone with deep scientific knowledge on the subject: these opinions are ones that I have glommed from other scientists and from reading around the non-technical literature. There is a lot of pessism there (except, of course, for the boosters, whose incomes require them to be optimists) and with good reason: they've been chasing after this dream since the 1940s and every advance has been coupled with a greater understanding of the difficulties ahead.
 * As for a pure fusion weapon—seems doubtful to me. You need to be able to generate many gigabars of pressure on the fusion fuel to get adequate compression before heating it. That's hard to do—there aren't a lot of things that can do that to anything of any size. Fission bombs as drivers make it look easy, but they're already extraordinarily powerful at that. Though the comparison is not exactly perfect, compare how much fusion material is compressed in a hydrogen bomb with a fairly mid-sized (in terms of mass) fission weapon, versus how tiny of a bit of fusion material they can compress using something as massive as the National Ignition Facility (a laser the size of a football stadium). The question is: where are you gonna get the energy from to compress the fusion material? Unless there's some other compact energy source out there, it's not gonna happen. Which is essentially what the US government concluded—if the boys at Los Alamos and Livermore couldn't come up with a pure fusion weapon after working on it for five decades, it's unlikely that it can be done at all with existing technology.
 * Note that I don't know anything much about bubble fusion, though I don't exactly see any possibilities for weaponization even if it turns out to be valid. --24.147.86.187 (talk) 00:19, 17 November 2007 (UTC)

How do whales drink water?
The amount of salt in the ocean is too much for a human to drink... But can whales drink it? I'm assuming they do... But if that's true, what allows for them to tolerate that much salt, but not humans? 64.236.121.129 18:57, 15 November 2007 (UTC)
 * Here's a good writeup: . The short answer is they get most of their water from their prey, don't sweat, and have giant kidneys for excreting salt.  --Sean 20:16, 15 November 2007 (UTC)
 * Interesting, thanks. But I guess this kinda turns into a catch-22. How does their prey (fish for example) get fresh water? 64.236.121.129 20:28, 15 November 2007 (UTC)
 * Fish, whales, and other marine vertebrates have a relatively simple problem: their kidneys just have to produce urine that is slightly more concentrated than sea water. This ability allows them to extract as much water as they need, since they have an unlimited supply of sea water. The real masters at the urine-concentrating business are desert dwellers like kangaroo rats, some of which don't drink at all. Their urine can be five times as concentrated as human urine, and 14–17 times as concentrated as the rats' body fluids.   --mglg(talk) 20:44, 15 November 2007 (UTC)


 * (By the way, to help with Google searches, the general term for this topic is Osmoregulation.) Fish have complex salt regulation systems to keep water balance. From the "Gill" article: "Gills' large surface area tends to create a problem for fish seeking to regulate the [[osmolarity] of their internal fluids. Saltwater is less dilute than these internal fluids; as a consequence, saltwater fish lose large quantities of water osmotically through their gills. To regain the water, they drink large amounts of seawater and excrete the salt. Freshwater is more dilute than the internal fluids of fish, however, so freshwater fish gain water osmotically through their gills." (Basically, saltwater fish actively pump salt out of their body, and freshwater fish pee a lot.) External link: -- 21:03, 15 November 2007 (UTC)  —Preceding [[Wikipedia:Signatures|unsigned]] comment added by 128.104.112.105 (talk)

Zinc restoration
I have some steel items that were zinc plated to keep them from rusting. In some places the zinc has been penetrated and needs repair. Can I simply use a piece of zinc as the anode and the damaged piece as the cathode and replate the steel with a few volts of electricity in an electrolyte acid bath of some kind or do I have to throw the work piece away? 71.100.6.233 21:01, 15 November 2007 (UTC)
 * it may be plated, or hot dipped galvanized in molten zinc. Unless you know what you are doing, or the items are very cheap you can use a commercial plater to do the job for you.  Even with a few holes the zinc should still stop rust. Graeme Bartlett 01:46, 16 November 2007 (UTC)


 * The cost of a commercial plater is more than triple the cost of the item. Extensive surface area was also damaged from being under rotting oak tree leaves that released tannic acid which leached the zinc. Oh well, I was hoping to proceed with enough information to do things right but in absence of any information I will be forced to experiment with use trial and error. 71.100.6.233 03:23, 16 November 2007 (UTC)


 * There's some misinformation here. You can plate something with zinc through a redox reaction or electrolysis, as you seem to already know. Basically, you don't want an acid bath, because then all products of the reaction go into making hydrogen gas. Instead, use a solution with zinc ions in it (you can get it from a science supply store. I'm not sure about OTC zinc solutions). Put your material in the solution and have a separate salt solution with an electrode (you can use an electrode with a higher oxidation potential than zinc, in which case you won't need to hook up a battery. Otherwise, use one with a lower oxidation potential), connect the two solutions with a cotton wad dipped in ammonia for a salt bridge, and then connect the two electrodes to a battery to plate your zinc. I may have some of the details wrong, but basically this is your setup. Just make sure you have a zinc solution to put the material to be plated in. SamuelRiv 04:52, 16 November 2007 (UTC)

the salt bridge is use to connect the 2 solution.EX is is used in the calomal electrode
 * You can get hold of zinc sulphate from a fertilizer shop, and zinc chloride can be available as a solder flux. The science supply store zinc compounds will probably be many times the cost of the others, you don't need huge purity, it does not matter if you have some cadmium in your plate. -- Graeme Bartlett (talk) 22:07, 16 November 2007 (UTC)