Wikipedia:Reference desk/Archives/Science/2010 February 3

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February 3

Stopping nuclear reactions with a jamming field

In the anime Gundam Seed, they have this device called a neutron jammer which stops fission reactions from taking place by jamming the flow of neutrons and preventing them from striking the nucleus of a fissionable atom. Is there anything like this in real life, and/or is it possible to make one? 192.12.88.10 (talk) 05:02, 3 February 2010 (UTC)

1. Almost certainly NO, and
   
2. Almost certainly NO--220.101.28.25 (talk) 05:35, 3 February 2010 (UTC)

You'd be better off trying to slow down the speed of neutrons (though sometimes this backfires as slow neutrons are vulnerable to neutron capture). John Riemann Soong (talk) 05:51, 3 February 2010 (UTC)

See Wikipedia Articles Slow neutron, Fission reactions and Physics.
ps. The answer is most likely a resounding NO to both questions, but I am not a Nuclear Physicist. Don't despair, a Physicist (or a close facsimile of one) will most likely be along to answer this question in some detail. It may be a bit late in the US, but our English volunteers will likely be up and about in a few hours. --220.101.28.25 (talk) 06:44, 3 February 2010 (UTC)

Anybody here recall a science fiction short story about psychics who were able to prevent nuclear weapons from detonating, and who were used when the USSR attempted to blackmail the US by threatening to detonate a couple of dozen bombs they had smuggled into various cities? (The psychics were able to sense the presence of the bombs and control them without initially knowing their precise location.) I seem to recall it as being by Heinlein, but it doesn't sound quite like his style. 124.157.247.221 (talk) 10:37, 3 February 2010 (UTC)

Indeed by Heinlein: "Project Nightmare" (1953). Deor (talk) 13:56, 3 February 2010 (UTC)

The conceit was also used by Larry Niven, in Protector (truly excellent story, by the way). Phthsspok's alliance discovers a way to suppress the fission trigger in fusion bombs and is able to make a good life for its breeders for a while. Then the rival alliance finds a way to set off a fusion bomb without fission, and kills all Phthsspok's descendants. That makes him a childless protector, which is where our story really starts. --Trovatore (talk) 21:24, 3 February 2010 (UTC)

I recall a story called (maybe) "Christmas Present" about psychic children who deactivate the "sparkly stuff" in ICBMs because it "makes grownups unhappy" and are discovered when they innocently teleport into an army base. Does someone remember more? Cuddlyable3 (talk) 14:06, 3 February 2010 (UTC)

The closest you get is that in the 1940s, one of the ways that was investigated as a means for preventing attacks by atomic bombs was to FIRE lots of neutrons at an incoming plane. The idea was that you could get the bomb to predetonate (fizzle), which isn't great but is better than a full explosion. The idea was abandoned pretty early on, though, because it's not that easy to shoot out a beam of neutrons like that, and it would be pretty trivial to shield the bomb from outside neutrons (and, in fact, the cores usually are pretty shielded anyway), and even then, the defense isn't much better than just trying to shoot down the plane normally. (And once you have rockets, that rules this out pretty completely.)

Did they try Tesla's "Teleforce Death Ray? Worked for Flash Gordon. Edison (talk) 14:59, 3 February 2010 (UTC)

But other than that... no. There's no way to stop a nuclear detonation from going off other than dispersing the core (e.g. blowing up the bomb before it really fires). Certainly no way to jam the neutrons before they hit the uranium/plutonium atoms. Inside the core of a bomb you have LOTS of plutonium/uranium atoms that suddenly are confronted by a HUGE burst of neutrons from the initiator. Even if there were some way to somehow manipulate the neutrons from a distance, the idea that you could somehow block enough of those to not start a chain reaction seems pretty impossible. --Mr.98 (talk) 13:39, 3 February 2010 (UTC)

Superman throws an atomic bomb into the Sun where it goes "Mummph" (Video). Cuddlyable3 (talk) 14:23, 3 February 2010 (UTC)

Well I'll guess you could inhibit an ongoing fission reaction by beaming in a super-dense flash of protons. But that would unavoidably destroy anything else remotely in this direction. 95.112.189.37 (talk) 21:14, 3 February 2010 (UTC)

I was just assuming that Duck and cover would be good enough. SteveBaker (talk) 17:12, 3 February 2010 (UTC)

Or 'kiss your ass goodbye'. Where are our resident Physicists? As said above I know its unlikely, but I'm very intererested in the why. --220.101.28.25 (talk) 20:25, 3 February 2010 (UTC)

I'm not sure you have a mechanism for inhibiting/slowing neutrons at a distance anyway (they are fairly non-reactive—anything you do that is going to interfere with neutrons is also going to do a lot more than just that), and, as noted, slow neutrons are worse in some ways that fast ones—they increase the U-235/Pu-239 cross-section (which seems counter-intuitive until you consider how the DeBroglie relation works with neutrons), which should be even worse for the first generation of fissions. I also think one easily underestimates how many neutrons we're talking about in a chain reaction... it's a lot, on the order of 2⁸⁰. Naturally you don't have to inhibit/block all of those with your magic neutron-blocker gun, but it isn't like you have your work cut out for you. I'm not a physicist, though. --Mr.98 (talk) 20:56, 3 February 2010 (UTC)

superacids that aren't corrosove?

"The carborane superacid H(CHB11Cl11), which is one million times stronger than sulfuric acid,[1][2] is entirely non-corrosive" (from superacid). This makes me curious -- why should this be? Is it because carborate is a non-coordinating anion and not very soluble in water whereas chloride is weakly coordinating (e.g. it can form halohydrins) and water-soluble? John Riemann Soong (talk) 05:10, 3 February 2010 (UTC)

HCl is also noncoroding. However, H₂SO₄ contains a highly oxidized form of sulfur (S⁺⁶), and so will tend to be a good oxidizing agent, and thus oxidize (corode) metals. Being a strong acid, or even a super acid, has nothing to do with corrosiveness, the H+ ion will itself not protonate metals (what are you going to do, create metal anions? Possible, but not very likely with most metals). Any acid can catalyze a corrosion reaction in the presence of other oxidizers, but by itself acid has zero effect on metals. --Jayron32 15:54, 3 February 2010 (UTC)

That's totally bogus. Acids can corrode certain more reactive metals because the hydrogen is reduced from the H⁺ ion to H₂ gas. See for example the question about Magnesium and Hydrochloric acid a couple of days ago. I agree that that isn't enough for certain metals (like gold), in which case it doesn't matter how strong the acid is. However, I'm not sure where Mr. Soong is finding that the carborane superacid is non-corroding. I looked in both the carborane and Superacid article, and I didn't see that it ever said it's not corrosive. Buddy431 (talk) 16:24, 3 February 2010 (UTC)

Well, I'm not sure you'd call Mg + HCl a "corroding" reaction. Yeah, its chemically identical in that it involves the oxidation of a metal to its ionic form. But calling that reaction "corrosion" would be akin to calling the formation of rust: Fe + O₂ --> Fe₂O₃ a "combustion" reaction. Yeah, technically it is a combustion because it involves a reaction with oxygen. But if you made someone watch iron rust, and asked them if it were "combusting", they'd say "no way". The strength of the acid will affect the rate of corrosion reaction, but any metal that will not oxidize in the presence of H⁺ will not do so regardless of the source of the H⁺. Take copper, for example. It is unreactive with acids, except for nitric acid, which it will readily dissolve in, but not because of the H⁺ (or rather, not because of the H⁺ alone). In this case, its the nitrate anion which acts as the oxidizing agent. In superacids like carborane, there's nothing present that will oxidize any metals that themselves would not already be oxidized by any acid. With the most of the so-called "strong acids", like sulfuric acid, nitric acid, and perchloric acid, the anion itself is a fairly strong oxidizing agent. So, if you want a strong acid which will not cause any oxidation because of its anion, you are limited to hydrochloric acid and or superacids like carborane. The issue is not that no acid ever oxidizes anything, its in finding acids where the non-acid-bit will not oxidize stuff. --Jayron32 18:53, 3 February 2010 (UTC)

If this is some technical chemical meaning of non-corrosive, that should probably be explained in the article. To me "totally non-corrosive" means "you can stick your hand in it, and it won't destroy your skin (though of course it could still poison you systemically)". --Trovatore (talk) 22:15, 3 February 2010 (UTC)

Wouldn't it be nice is we had a free source of information, like an encyclopedia, where terms were explained. Oh yeah, you're soaking in it. From the article corrosion, and I quote: "Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen.". You are bathed in oxygen right now, it makes up 20% of the atmosphere, and your skin is fine. And yet that oxygen is busy corroding all sorts of the world around you. The definition is right there as the first sentance of the Wikipedia, just in case you didn't know what corrosive meant. It has nothing to do with what it does to your skin. Lots of stuff is corrosive and harmless to living tissue, likewise lots of stuff is harmful to living tissue and noncorrosive. And then theirs some stuff thats both. And some stuff that is neither. --Jayron32 02:53, 4 February 2010 (UTC)

Fine, that's the chemist's meaning of the word corrosive. Ordinary usage is different, and the reader is not warned about it. Now granted, most people who don't understand chemistry are unlikely to have access to carborane superacid, but supposing they did (literally) get their hands on it, the outcome could be unhappy, no? As I say, this should probably be explained in the article. --Trovatore (talk) 07:24, 4 February 2010 (UTC)

No - it's NOT just the chemist's meaning. Is warm salty water corrosive? Well, our bodies are mostly made of the stuff - and swimming in it doesn't seem to harm us noticably. But immerse your car in warm salty water and you'll soon discover that it's corrosive as all hell to bodywork. Warm salty water is (by any reasonable definition) "corrosive". That's a pretty close fit to the definition given in our article and quoted by Jayron...and it's definitely the "day-to-day" meaning of the word. You just need to be aware of the context in which you are using it. Arguably, our article on this acid should be specific on how dangerous the stuff is to human skin just to be sure - but context matters. SteveBaker (talk) 12:04, 4 February 2010 (UTC)

Sure; ordinary usage includes the chemist's meaning — I can't think of anything that would fit what Jayron is calling corrosion, that wouldn't also be corrosion in ordinary usage. But I think ordinary usage is more inclusive; it includes any chemical process that tends to degrade a surface. That's roughly how I'd formulate it, anyway — I haven't thought about all the corner cases; there might be some that don't exactly fit. --Trovatore (talk) 21:19, 4 February 2010 (UTC)

Sorry, it's actually in the strong acid article. John Riemann Soong (talk) 18:30, 3 February 2010 (UTC)

Wal-Mart Orange Early Rise Drink Mix

Good Morning, I buy Wal-Mart's... ahem... Crystal Light knock-off "Orange Early Rise". I like it because it doesn't have any carbonation or caffeine, and only or has 5 calories per serving. I usually mix it in a jug (shaken, not stirred), put it in the freezer and then a few hours later, shake it into a slush. (Yum.) Sometimes I forget to put it in the fridge before I leave work, and by the next morning, a white cloudy substance settles to the bottom. I'm just curious what it might be. I'm confident that it's not harmful, but I'm not sure I care to drink it, whatever it is. I e-mailed Wal-Mart Customer Service a few months ago, but never heard back. (However, I'm pretty sure they don't actually *make* the stuff. I think they just package it and sell it.) Ingredients and nutrition information are found within the link above. Also, I think they've slightly modified the recipe in months past, because the "white stuff" used to be more granular and less soluble, and I used to mix it with hot water in a clear plastic mug, let the white stuff settle, and pour the concentrate off the top until I could simply rinse the "sediment" down the drain. Now it must be more ground up, though, because I don't even notice it unless it sits at room temperature for a few hours. It's rather "unsettling." Ha. Thanks much! Kingsfold (talk) 13:49, 3 February 2010 (UTC)

The ingredients list is at [1], and also probably on the side of the container. Among the ingedients are the following generally insoluble stuff: calcium carbonate, calcium phosphate, magnesium oxide, cellulose. The white stuff is probably a slurry of the above. Those substances are probably a very small percentage of the overall ingredients, but its probably enough to create a noticable precipitate at the bottom of the drink. Its all pretty harmless; I would be much more worried about substances like aspartame, which is used to sweeten the drink and is known to have some adverse effects in some people (see Phenylketonuria). --Jayron32 15:49, 3 February 2010 (UTC)

Err, though if you have PKU you probably already know that. It is tested for at birth these days. --Mr.98 (talk) 00:50, 4 February 2010 (UTC)

How long have they tested on newborns? If this is something they started in 1990, that advice would not apply to those of the age of 20 for example. Googlemeister (talk) 13:58, 4 February 2010 (UTC)

Different species named "E. coli"

When I first began biology several years ago, I thought that "E. coli" was an amoeba species. What similarity is there between this species and Escherichia coli, that they have the same species name? I understand that they're not somehow related; I just don't understand why both were given the name "coli". Nyttend (talk) 13:51, 3 February 2010 (UTC)

I would assume it's because both are found in the colon (genitive coli means "of the colon" in Latin). Deor (talk) 14:25, 3 February 2010 (UTC)

I'll add that lots of particular words are used as specific names for a variety of organisms. Consider sativa/sativus ("cultivated") in Medicago sativa, Lactuca sativa, Cannabis sativa, Pastinaca sativa, Crocus sativus, and many more. Deor (talk) 15:12, 3 February 2010 (UTC)

I should add that 99 times out of 100, the abbreviation E. Coli is used to refer to the bacterial Escherichia coli, and not the ameobic species. E. Coli is one of the more studied strains of bacteria in history. It's used as a "protein factory" in all sorts of recombinant DNA technology, the K12 variety is the "model bacterium" for just about any bacterial study in the past 50 years. Entamoeba coli is an endemic amoebic parasite, but far less interesting, since its main purpose, according to our article, is to be confused with more harmful Entamoeba strains. --Jayron32 15:29, 3 February 2010 (UTC)

My understanding of Binomial nomenclature is that every species is uniquely identified by its genus name and its specific name. Species of different genera may share a specific name, so confusion that may result from abbreviation of the genus name must be resolved by context. 124.157.247.221 (talk) 07:11, 4 February 2010 (UTC)

At what percentage alcohol does beer dehydrate rather than rehydrate?

Resolved

I've read the articles about small beer and alcohol and seen related questions in the reference desk archive but didn't find what I was looking for.
At low levels of alcohol, the overall effect of beer is rehydrating (e.g. small beer) . At higher levels of alcohol the overall effect is dehydrating (I have researched this extensively but don't think it's OR and my results are unreliable).
Is it possible to say at what percentage-alcohol this boundary occurs?--Frumpo (talk) 15:24, 3 February 2010 (UTC)

I'm not sure its the percentage of alcohol in the drink as much as it is the Blood alcohol content. Broadly speaking, alcohol is a Diuretic in that it increases the rate at which the kidneys eliminate water from your body. That's why drinking tends to "dehydrate" you; the higher your BAC, the more your kidneys work to eliminate the excess alcohol, and in the process, also remove lots of water from your blood stream, which is what dehydrates you. If you consumer higher-alcohol containing beers at a slower pace, maintaining a low BAC all the time, the net effect would probably be hydrating. If you were to slam a whole bunch of lower-alcohol containing beers really fast, raising your BAC to a high level, you may end up with a net dehydrating effect.

Historically, in lots of cultures, alcoholic beverages (beer and/or wine) are often the predominant means to actually get hydrated, as the only other common options were milk (and many adults are Lactose intolerant) and water (which in the past, often contained nasty stuff like Cholera and Dysentery). So people drank either beer or wine or some other alcoholic beverage since the alcohol preserved both the caloric content (the grain and/or fruit) AND the water. And they weren't drunk all the time, they drank an appropriate amount. For many cultures, drinking till you got drunk is like eating until you puke; yeah its possible, but why? --Jayron32 15:40, 3 February 2010 (UTC)

I never really understood the sanitation aspect. Even hard liquor has a problem killing germs, so I can't really believe that beer and wine help clean the water at all. —Preceding unsigned comment added by 67.243.7.245 (talk) 16:11, 3 February 2010 (UTC)

Beer is boiled as part of the brewing process, I don't know about the rest. Nanonic (talk) 16:21, 3 February 2010 (UTC)

(ec) It's not just the alcohol content that's important. Remember that in brewing beer, the wort is boiled for an extended period of time — the beer can't go bad if it doesn't have any living pathogens in the bottle or cask. Similarly, distilled spirits are obviously raised to high temperature during their manufacture, and they have a high enough alcohol content to kill (or at least inhibit the growth of) nearly all human pathogens. Wine, meanwhile, has a higher alcohol content that beer and so is at least somewhat inhibitory to the growth of pathogens; the fermentation process also consumes many of the sugars which pathogens could use as a food source. The tannins (particularly in red wines, but present in all barrel-aged wine) are naturally antimicrobial as well. Nevertheless, spoilage remains a potential problem in winemaking, and in recent decades preservatives such as sulfur dioxide and potassium sorbate are often employed. TenOfAllTrades(talk) 16:33, 3 February 2010 (UTC)

I don't think there is a clear answer to this question. According to this article, "roughly every extra 10 grams of alcohol results in an extra 100 cc urine excretion". With ethanol's density of 0.789 g/ml, this would be equivalent to 7.89% alcohol. However ethanol undergoes zero order kinetics. The duration of action of the ethanol is highly dependent on the quantity consumed, more so than the concentration. More original research is required. Axl ¤ [Talk] 10:12, 4 February 2010 (UTC)

Where do I sign up? 87.81.230.195 (talk) 11:30, 4 February 2010 (UTC)

Although wikipedia is against original research, I also hope to find a budget somewhere. Volunteers of all countries, unite!!!! 95.112.161.160 (talk) —Preceding undated comment added 22:23, 4 February 2010 (UTC).

Thanks everyone. That's very interesting. --Frumpo (talk) 18:14, 4 February 2010 (UTC)

Putting a very small satellite into orbit in space

1) If you wanted to put a small ball-bearing that weighed 1g into LEO, how big would the rocket have to be? 2) If you wanted to fire a bullet into LEO, how big or long would the gun have to be? 3) Is it correct that that some modern artillery shells have electronics in them? 4) Why cannot satellites be minaturised down to the size of a matchbox? 84.13.53.3 (talk) 16:37, 3 February 2010 (UTC)

I don't know about (1) or (2) but Saddam Hussein tried to build a Space gun capable of putting a payload into orbit. Our article covers some of the details. Some artillery shells can steer themselves in mid-flight to correct for the wind, etc - others have fancy fuzes - both require some electronics. Satellites can be made fairly small - if they don't have to do anything. But if you want to use the satellite for communications or photography or something useful like that then you're going to need solar panels, batteries, antennae and other bits and pieces - and the size soon adds up. But you could launch a really small object if you had a reason to. You should read Miniaturized satellite for more information about some really tiny satellites that have actually been launched. Occasionally, schools and universities have managed to get this kind of microsatellite launched for free alongside a commercial launch of some kind. Those launchers sometimes carry ballast to even out the weight of an unevenly balanced payload - and sometimes, they'd be just as happy to launch your science project as they'd be to send up a lump of lead. SteveBaker (talk) 17:10, 3 February 2010 (UTC)

(edit conflict) 1) and 2) see Gerald Bull and related articles 3) yes: M712 Copperhead among others 4) you might find cubesat interesting -- Finlay McWalter • Talk 17:20, 3 February 2010 (UTC)

I was typing this while others were replying so may cover same areas.
Re question #2, Project HARP may provide some answers.
#3 Yes, some 'modern' artillery shells definitely have electronics in them, in fact since WW2, so early 1940's or over 65 years. See Proximity fuse as an example. In fact these early electronics used Vacuum tubes!
#4. Perhaps the largest part of most satellites is the solar panels used to power them, about which there are size limitations. They have to be a certain minimum size to power the electronics. Some other parts, such as RF waveguides and dishes, have a certain minimum size by virtue of the laws of physics they operate with. Getting rid of heatThermal management can be a factor so heat sinks and radiators also place limits on minimum size. Any optical instruments ie telescopes have some similar constraints, thought they have certainly got better & smaller with technological improvements. Possibly the most important reason is many satellites require attitude control systems (ie rocket motors) for orientation and 'station keeping' ie, geostationary orbit. That is to keep it pointing where it needs to (for ground comms/control etc), and to keep it in orbit. Satellite life is AFAIK largely determined by the life of its 'thrusters', which relies on the amount of fuel carried. For a single use satellite, it could be made very small, but a literal matchbox size would seem to be too small to be of any use. Question 1 I can't answer--220.101.28.25 (talk) 18:29, 3 February 2010 (UTC)

Just yesterday MIT published this release which details a tiny propulsion system for cubesats based on electrospraying, which they say makes particularly efficient use of the reaction mass and has a particularly light and small "engine". As to antennas, it seems cubesats already use self-unrolling antennas (I think they're mostly metal tape measures); it doesn't seem unreasonable that very thin antennas of this type could be made and packed small enough to fit into the OP's proposed matchboxsat. -- Finlay McWalter • Talk 13:41, 4 February 2010 (UTC)

There is a company called "Interorbital Systems" who will sell you a basic kit for a 0.75kg "TubeSat" (about the size of a coffee can) and will launch it for you into a LEO that will decay after several months (necessary in order to avoid becoming space-junk). The price of this (including kit AND launch costs) is $8,000. See: http://www.interorbital.com/TubeSat_1.htm

SteveBaker (talk) 02:59, 4 February 2010 (UTC)

It is easy to put a tiny satellite into orbit, since the same launch system could be used as for a much large satellite, or a 10 cm cube satellite built by students could be launched along with like minisatellites or larger serious satellites. (great way to increase the population of space junk that we have to dodge in the future). But I did not see a clear answer as to how small of a rocket could get a small satellite into orbit. There is likely diminishing returns as the satellite is scaled down, with some bare minimum size and mass of rocket needed to get a final stage to orbital velocity. Maybe a multistage rocket several meters long and less than a meter across could get a final stage into orbit, but if you keep scaling down the payload and the rocket, there is likely a minimum, at least with 21st century technology. Firing it from advanced artillery appears to be a shortcut to get it off the ground, or all the way into orbit for that matter, but let's stick to rockets. For instance, if I wanted to put a 1 gram satellite into orbit, I probably could not do so with a rocket a meter tall. If I wanted to put one bacterium into orbit, I could not do so with a rocket the size of a fountain pen. Edison (talk) 15:57, 5 February 2010 (UTC)

A gun cannot fire a passive object into stable orbit. The object will strike the planet within its first orbit or escape. See Space gun. Cuddlyable3 (talk) 02:04, 6 February 2010 (UTC)

If the rocket and its controls could withstand the acceleration (vacuum tubes in WW2 proximity fuzes could) the firing from a gun (or launching from a rail gun) would be an efficient start to the trip to space, with some adjustment of the orbit by rocket stages. Launching from a high altitude balloon or from an airplane at high altitude and high speed would also be a nice start to the trip to orbit. Still not answers as to the smallest rocket which could place something in orbit? Edison (talk) 02:47, 6 February 2010 (UTC)

Vanguard rocket, maybe? I know this is ancient history, but that thing clunker was pretty small, as rockets go. 24.23.197.43 (talk) 02:15, 7 February 2010 (UTC)

Disease and disorder

I was intrigued to see Autism and ADHD listed in List of childhood diseases. While it doesn't help that the disease article is unclear about the definition of a disease, both the Autism and ADHD articles identify them as developmental disorders rather than diseases caused by an infectious agent. Should they still be listed there? Astronaut (talk) 17:45, 3 February 2010 (UTC)

The linguistic subtleties between terms like "disease" and "disorder" and "syndrome" and "disability", now with autism, the odd term "spectrum", is somewhat arbitrary and imprecise. There are not hard borders between what gets termed a "disease" and a "disorder" in certain contexts, sometimes it can just be political or social in nature. For example, sometimes certain terms do, with time, carry "perjorative" connotations; words like "disease" come to carry some social weight that people with certain conditions may not want to associate with themselves; being "diseased" sounds contagious (but then again, cancer is a "disease" and not contagious), and a "disorder" makes it sound like you are broken or substandard in some way(and so people, understandably, don't want to admit that they are substandard people). The desire to have an unambiguous language to describe medical conditions runs headlong into the desire of individuals to feel respected and valued when they are talked about. --Jayron32 18:29, 3 February 2010 (UTC)

It may be that since some people would look for these disorders in the "List of childhood diseases" article, a fix would be to rename the article "List of childhood diseases and disorders" instead of pruning the list of things that are not, in some technical sense, diseases. Comet Tuttle (talk) 18:43, 3 February 2010 (UTC)

 Done. Article moved as suggested; good idea. --Jayron32 18:58, 3 February 2010 (UTC)

A good move, but I do wish you could have avoided the soapboxing above, particularly since you characterise the issue as if it were one between absolute scientific accuracy and people's feelings, when classification of things is much more complicated than that. Once you include 'spectrum' in your list of terms that you imply are chosen out of respect for feelings rather than facts, you just sound uninformed. This is a shame, given you are a good editor who usually makes it clear when you are speaking from knowledge as opposed to opinion. 86.179.145.61 (talk) 22:05, 3 February 2010 (UTC)

There was no soapboxing and no offense was intended. I am quite sorry it was taken by you, and if I gave you the impression that I was trying to be offensive, I wholly apologize. The fact remains that the terms we use to describe things evolve over time, and that evolution is often based in social reasons as much as anything. There was a time when a term like "mentally retarded" carried no perjorative weight, but over time the term came to mean more than its original intent, so it has been supplanted by other terms. It is not that such evolution is undesired, or bad, or whatever. If a term has come to mean something unpleasant or nasty, even if it didn't used to, it is perhaps better that it be changed. However, the fact remains that there are still not hard lines between what is a "disease" and what is a "disorder" or a "syndrome". These things are a bit fuzzy around the borders. --Jayron32 00:56, 4 February 2010 (UTC)

"Spectrum" makes sense in the case of Autism because it's not a simple yes/no thing. You can't be a little bit infected with a cold - you either are or you aren't. But Autism ranges all the way from super-mild Asperger syndrome cases to the worst afflicted who are completely cut off from the world. There are no 'steps' - it's a complete continuum. It's a shame that the various terms are not applied more rigorously - it would be useful to be able to tell whether something was caused genetically, through injury, bacterial, fungal or viral infection, etc. SteveBaker (talk) 01:43, 4 February 2010 (UTC)

Astronaut, the more you learn about medicine, diseases, and disorders, the more you will underatand that the definitions are extremely imprecise, and usually the result of social negotiation. If you did not get that message from our disease article, it is not clear enough, but not for lack of trying. No doctors, and no informed people, waste time arguing about whether to call a condition a "disease" or "disorder". Only the ignorant. alteripse (talk) 02:30, 4 February 2010 (UTC)

anyone here good at both ecology and materials science?

So uhhh, I'm trying to get the interesting equilibria math of my ecology class, and I notice a lot of the discussion about stable versus unstable equilibria seem awfully familiar to coursework I've taken about phase transitions, just in a different form. In fact, my professor said that several particular models of species competition (one species coexisting with another ... or being driven to extinction) could be thought of as ecological versions of phase diagrams, e.g analogous to one phase stably coexisting with another phase or regions where one starts out at one position on the diagram and steadily (because of some thermodynamic process) progresses towards another, "snuffing" out the other phase. This intrigues me indeed! Are there any good reviews out there connecting the two concepts? John Riemann Soong (talk) 18:25, 3 February 2010 (UTC)

At its core, the mathematics of equilibrium will be the same whether you are talking about chemical equilibrium or ecological equilibrium or physical equilibrium (like, say, if you are building a bridge). Aspects of calculus cover this, though my math background is terrible, my understanding is that once you get down to the core differential equations, the math ends up very similar for all of these. --Jayron32 18:32, 3 February 2010 (UTC)

You wouldn't get phase transitions unless there is spatial structure to the interactions. Pretty much all of the mathematical ecology I've seen has assumed strong mixing in the spatial domain, but a quick Google search shows that there have been at least some sketchy attempts at combining statistical mechanics with ecology, for example this proposal. A Google Web search for "ecological phase transitions" finds a substantial amount of stuff, including PMID 12211328. Looie496 (talk) 18:54, 3 February 2010 (UTC)

Footnote: phase transitions are examples of multistability -- the ability of a system to have multiple stable states separated by unstable intermediate states. Multistability comes up very often in mathematical ecology, but only rarely in the guise of phase transitions. Looie496 (talk) 19:06, 3 February 2010 (UTC)

I think John is using "phase" in a different sense. My impression is that the original post is considering different taxa in the same (or similar) niche as different "phases". For example, deer and caribou might be different "phases" of grazing quadrupeds. Under certain conditions they can coexist (like water and ice coexist at the melting point) but if you push the external parameters too much in one direction or another and you end up with just one type of grazer just as you would have only one type of water. Anyway, that's what I think he is trying to communicate, and it doesn't require spatial structure (or stat mech). Dragons flight (talk) 19:47, 3 February 2010 (UTC)

This reminds me of what Richard Dawkins called an "evolutionarily stable strategy" (ESS), and applies to intraspecies competitions as well. 67.243.7.245 (talk) 23:46, 3 February 2010 (UTC)

Website that gives comprehensive info on chemicals

Wikipedia lacks many chemicals whose properties like molecular weight, structure, etc. that I want to know. I need to find the molecular weight and formula of disodium EDTA and can't find it despite googling it. I knew a site that gave you info on any chemicals you search for, but I forgot what site it is. Please suggest any such sites. Thanks. —Preceding unsigned comment added by 142.58.129.94 (talk) 20:08, 3 February 2010 (UTC)

Our EDTA article tells you lots of structural information about the parent compound. Googling "disodium EDTA" gave me that article as the first hit. The second hit had the chemical formula of the actual disodium variant you wanted. The fifth hit had lots of chemical/safety properties and includes molecular weight. A few of the major chemical companies' websites include lots of basic chemical information about their products (www.sial.com and www.fishersci.com are popular). You can also include the keyword "MSDS" in your google searches...an MSDS exists for almost all commercially available chemicals, and includes things like formula and mol-wt. DMacks (talk) 20:34, 3 February 2010 (UTC)

Sodium EDTA is prolly a more strongly chelating agent than neutral EDTA. Sodium EDTA is to EDTA like sodium acetate is to acetic acid. John Riemann Soong (talk) 00:03, 4 February 2010 (UTC)

I suppose the easiest thing to do would be just add up the RMM of EDTA and then add twice the RMM of sodium, but that may not be immediately obvious, depending on the extent of your chemical knowledge. And John: I wonder if disodium EDTA would become even more chelating if you threw in some 15-crown-5 to mop up the sodium ions. One ligand to boost another, so to speak. Brammers (talk) 08:11, 4 February 2010 (UTC)

Not quite sure what "RMM" is, but in conventional names for this series of chemicals, "disodium EDTA" is not "EDTA + 2Na". Each Na atom replaces something else (a hydrogen atom) in the original EDTA structure structure rather than simply being added. See the sodium acetate/acetic acid comparison. DMacks (talk) 14:15, 4 February 2010 (UTC)

Ah, my bad. I just assumed EDTA on its own would be treated as if it were its anionic form (i.e. already deprotonated) but now I come to think of it that was premature of me. And RMM is an abbreviation of relative molecular mass. Somewhat outdated, but I think there are quite a few terms for the same thing bandied about so I used it because it would be simpler to type. Brammers (talk) 23:10, 4 February 2010 (UTC)

Snow Depth

In your snow article, density is described and there are flakes that are less dense and therefore sit further apart from each other and more dense settling closer to one another. Does this affect the depth of the snow? If so, by how much? What factors affect how dense the snow will be? Temperature? Humidity? For example, if it is 30 degrees and very humid, will the snow be less deep than if it were 10 degrees and very dry?199.34.4.20 (talk) 21:27, 3 February 2010 (UTC)

Degrees Centigrade or Fahrenheit? Cuddlyable3 (talk) 22:49, 3 February 2010 (UTC)

I think we can assume Fahrenheit — snow at 30 C is relatively uncommon. --Trovatore (talk) 23:31, 3 February 2010 (UTC)

But why make that assumption: see here? -Falconus^{p t c}

Because we are intelligent, thinking humans and not mindless robots who have to nit-pick at every teeny-tiny thing even when what the questioner asks is completely freaking obvious from the context. I think it's just possible that if the OP wanted to know about the possible density of tellurium snow on Venus at 30 degrees centigrade/absolute/Rankine/Delisle/Newton/Réaumur or Rømer then he/she/it would probably have mentioned it in passing. Also we are here to help people and not humiliate them (except you and Cuddlyable3 whom I'm going to humiliate anyway because you're behaving stoopidly). For what it's worth, our OP also didn't specify whether this was happening in our universe or some other 26 dimensional one...but I think it's safe to make some assumptions about that too. Now, how about we put away our "Look how clever I am" attitudes and actually provide the OP with a useful answer. SteveBaker (talk) 11:51, 4 February 2010 (UTC)

The small text meant implies I wasn't being serious at all in this case. I just thought that the extraterrestrial snow was interesting, that's all. Sorry if I did something wrong. Falconus^{p t c}

Are these air temperatures above the snow or temperatures measured inside the snow ? Personal matters in stricken small text should be addressed on the Talk page. Cuddlyable3 (talk) 16:02, 4 February 2010 (UTC)

Certainly it must affect the density. When snow is compressed, the fragile snowflakes break and take up less space. With enough compression, you wind up with a solid block of ice. So the range of density is from the lightest it can be (our Snow article says that soft snow is 92% air and 8% water) down to ice - which is as dense as water...so the range of density (and therefore of depth) is something like 13:1...ie, an inch of "rainfall" could come down as anything from 13 inches of snow down to maybe close to 1" of dense ice/hail. The 'fluffiness' of an individual snowflake depends crucially on how it formed in the cloud before it fell - so the density of the snow will depend on that also. For a given amount of water being turned into snow, the depth of the snow would clearly vary a lot depending on the precise weather conditions in the cloud beforehand. Atmospheric pressure and temperature would clearly play a part maybe the altitude of the cloud, the strength of the wind - I'm not so sure about humidity though because the humidity inside a cloud has gotta be 100%...or it wouldn't be a cloud! SteveBaker (talk) 11:51, 4 February 2010 (UTC)199.34.4.20 (talk) 13:11, 4 February 2010 (UTC)

Actually, ice is only about 0.9 times as dense as water... 24.23.197.43 (talk) 02:25, 7 February 2010 (UTC)

We got started on this discussion because there is a forcast of anywhere between 7 and 24 inches of snow. My co-worker suggested that it is such a range because "drier" snow will be deeper than "wet" snow. I would expect that there would be a difference. I don't think it would account for a 17 inch difference. Thanks for your colorful insights.

I'm assuming that this forecast is for somewhere within 200 miles of Pendelton, Oregon, where your IP geolocates to. This area being a mountainous region, what might be the cause of the imprecise snow forecast is the forecast zone having a large elevation spread...for example this zone, which appears to include both mountains (thus the 2 feet of snow) and lower elevations that would receive less snow. Another possibility is that forecasters had low confidence in their forecast, which can be caused by the forecast models having run-to-run inconsistencies. Hope this helps, Ks0stm ^(T•C•G) 13:28, 4 February 2010 (UTC)

It may be that they can predict the amount of water in the cloud and therefore know the amount of snow that would fall in terms of weight with reasonable precision. But because small differences in temperature gradients, pressure, etc might dramatically influence how fluffy the snow is, predicting the depth it might reach on the ground is perhaps not such an exact science. At any rate - if (as I suggested before) snow can vary by a factor of 13:1 between the fluffiest kind and the densest then a 3:1 uncertainty in the forcasted depth (between 24 and 7 inches) is not at all unreasonable.

Snow depth is also succeptable to urban heat island effects. For example, it's rare for me to be unable to get to work due to snow depth, but a co-worker who lives ten miles upwind of me (and thus, outside the heat island) will spend a week or more every winter working from home due to snow. --Carnildo (talk) 01:01, 5 February 2010 (UTC)

Really small space probes

What prevents space probes to be really, really small. The size of a mobile phone or even smaller? Think of the computing capacity of a mobile without the need for a "big" display but instead an high area, low mass solar cell to provide energy. 95.112.189.37 (talk) 21:29, 3 February 2010 (UTC)

This question was asked about 5-6 hours ago on this reference desk HERE. Or look back 5 questions "Putting a very small satellite into orbit in space". Please see part 4) "Why cannot satellites be minaturised down to the size of a matchbox?" The reasons given for satellites also apply to 'space probes'. --220.101.28.25 (talk) 22:08, 3 February 2010 (UTC)

Global history of Europa

Was Europa moon once beleive to be cover with oceans without ice? This is possible or have Europa once have a larger size than now? Europa was definitely warmer billion of years ago. Is this known theory or is just same original sources from certain sites.--209.129.85.4 (talk) 22:24, 3 February 2010 (UTC)

Progressive disease

173 articles on Wikipedia use the term progressive disease but we don't have a page for it, nor is there a single mention of "progressive" or "progress" on the disease page. If this term is actually a "thing" we should probably have a page for it. If it's not, then the articles should use a different term. Does anyone know more about the subject? Best regards, -Craig Pemberton 22:38, 3 February 2010 (UTC)

That's the term, or perhaps progressive neurological disease/condition, in that it gets progressively worse over time. I'll look at it. -- Flyguy649 ^talk 23:40, 3 February 2010 (UTC)

This is an interesting observation. A quick look at degenerative disease seems to be the article you are looking for. I do wonder if there is some sort of scientific distinction between progressive disease and degenerative disease. Cheers, CoolMike (talk) 00:59, 4 February 2010 (UTC)

Disease being what it is, there are probably none of them that become progressively less bad, assuming that's not identical to healing. Perhaps progressive could be worked into degenerative and redirected to it (it'd be easier than changing all references to progressive). DRosenbach ^{(Talk | Contribs)} 01:34, 4 February 2010 (UTC)

Progressive disease just means spreading, getting worse, or becoming more severe and life-threatening. I'm not sure it really needs its own page. While it is true that some degenerative conditions, like amyotrophic lateral sclerosis are progressive, a whole variety of conditions, such as cancer, congestive heart failure, infectious diseases, cystic fibrosis, rheumatoid arthritis, etc. can become progressively worse, more widespread, or more severe over time. Here are a few links from a google search of "progressive disease": [2], [3], [4] --- Medical geneticist (talk) 02:04, 4 February 2010 (UTC)

Or simply look up our article about progressive disease. alteripse (talk) 02:24, 4 February 2010 (UTC)

That was quick. APL (talk) 02:49, 4 February 2010 (UTC)

Beautiful. Thanks Alteripse. -Craig Pemberton 07:16, 4 February 2010 (UTC)

Sorry to rain on this parade, but creating the progressive disease article was a bad idea. What was wrong with the degenerative disease article? The article even lists a disease known as Progressive supranuclear palsy. I think the Progressive disease article should be merged into the degenerative disease article. Having two articles seems redundant, unless someone can produce a verifiable reference claiming there is a significant difference between a degenerative disease and a progressive disease. —Preceding unsigned comment added by CoolMike (talk • contribs) 18:31, 4 February 2010 (UTC)

Thanks for your input. The relationship between progressive and degenerative diseases is explained in the article. A separate article was requested. Feel free to add the relevant info to degenerative disease, but there is no harm in 2 articles. alteripse (talk) 19:42, 4 February 2010 (UTC)

At this point, that's not a reference desk issue anymore - you should discuss it on the talk pages of the two articles. SteveBaker (talk) 22:53, 4 February 2010 (UTC)

Surely all diseases are progressive in as much as they progress through various stages, infectious diseases have distinct stages infection, incubation, reaction, recovery, for example. A cancer will progress to increase in size until it impinges on other tissues or organs. A 'slipped disc' will progress by improvement and healing. Many progressive diseases will be self limiting and will remit spontaneously. These are random examples. A degenerative disease is characterised by the degeneration of the function of certain tissues or organs, often for unknown reasons, that lead to a chronic irremediable condition. Degenerative diseases were in my young days one of the classified groups of illnesses.

• Genetic
• Traumatic
• Infectious
• New growths
• Degenerative
• Metabolic

Still a handy list to have in the back of one's mind when ticking boxes to identify a medical problem. I would contend that the term progressive when applied to certain illnesses is an erroneous epithet, rather like 'mad cow disease', the cows (and others)had a neurological disease not a mental disease. Richard Avery (talk) 20:03, 5 February 2010 (UTC)