Wikipedia:Reference desk/Archives/Science/2010 May 26

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May 26

What's wrong in this picture?

That it was ever posted in the first place. 71.100.8.229 (talk) 00:12, 31 May 2010 (UTC)

According to the description of this image, the photographer had a cellulitis infection on his knee. How would he know that the knee is infected, since the only discolouration is at or below the middle of the photo, and the knee is above the top of the photo? Nyttend (talk) 02:28, 26 May 2010 (UTC)

Best guess: he meant to say "shin". --Jayron32 02:37, 26 May 2010 (UTC)

Better idea: Ask him. He doesn't appear to be active at Wikipedia any more, but you could always try the "email this user" function. --Jayron32 02:43, 26 May 2010 (UTC)

Nyttend (talk · contribs) seems pretty active to me. hydnjo (talk) 03:07, 26 May 2010 (UTC)

Nyttend didn't upload the image. He asked the question... Duh... --Jayron32 04:54, 26 May 2010 (UTC)

The actual contributor of the photograph was User:RafaelLopez - and he hasn't edited Wikipedia since 2007. However, there is an email link on his user page (although it may no longer work after so much time has passed). So I suppose you could try emailing him to ask. SteveBaker (talk) 13:41, 26 May 2010 (UTC)

I'm not that interested; it was simply curiosity, since all I could see was the discolouration in the lower part of the picture. I'm somewhat colourblind, so I was wondering if perhaps there was something above the dark splotch that my eyes couldn't see. Nyttend (talk) 01:29, 27 May 2010 (UTC)

No, I think you're seeing it correctly, and he probably meant "shin" or "under the knee". I recently had it in the same place due to scraping my shin open from stepping in a hole. It got infected, diagnosed as cellulitis, but it looked a lot worse than the picture. I was tempted to upload a shot to Wikipedia but decided against it. ~Amatulić (talk) 19:32, 28 May 2010 (UTC)

types of life

With the recent news about "synthetic life" I've read a couple of articles talking about the "definition of life" and how it is probably not worth arguing, but I felt that it might be useful to at least define certain limits to the description of life and non-life by attaching names to features of natural systems. I've just quickly put together a few names, if they seem off, awkward, contrary, unjustified, or irrelevant in any way let me know! I've used the suffix -ate rather arbitrarily. The point here is that each category should be necessary for the following category, so for example 2 shouldn't be possible without 1, and 3 shouldn't be possible without 2. If there are exceptions, then I'll have to scratch these and think some more lol.

• 1) syntropate (or negentropate) from "syntropathy", basically any natural system that mantains or lowers entropy. I don't know if anything exists exclusively in this category, but I think it's possible. maybe crystals could be considered syntropate?

• 2) holoplicate (holo "whole" plico "copy"), or a holoplicatic syntropate, would be a sytropate that has the ability to replicate, though no mutation is possible, either because replication is perfect (which as far as I know isn't possible), or because any flaw results in complete failure of the system (which may be the case for man-made artificial life, i.e. replicating robots, though I'm a bit unsure about this)

• 3) ateloplicate (atelio "imperfect"), or a ateloplicatic syntropate, would be a syntropate that replicates introducing flaws in its copy. all commonly recognizable life would be included in this group.

I was thinking of another group that would include systems capable of accessing it's own code and modifying it on the fly, but I'm not sure if that warrants a category because it could include some microbes as well as humans, and it might be exclusive of (3).

Any thoughts? Or anything to add? 210.165.30.169 (talk) 02:52, 26 May 2010 (UTC)

You're free to do whatever you want in your own head. Getting another person to use your system would require you to get published in a peer-reviewed journal or something like that... --Jayron32 03:04, 26 May 2010 (UTC)

Well of course, I'm just curious if a categorization such as this has any relevance towards describing the types of life/non-life that might exist in the universe! 210.165.30.169 (talk) 03:09, 26 May 2010 (UTC)

I'm fairly certain that maintenence of entropy is a common theme in attempts to define life eg eg I've seen the idea many(?) times. As far as I know the old fashioned definitions are still used. (I assume you've seen the disclaimer on Wikipedia:Reference desk/Science at the top "does not ..opinions ..debate" etc ..77.86.125.207 (talk) 03:49, 26 May 2010 (UTC)

Hmm... you're right. I'm pretty sure that rule wasn't there when I last revised the header some 6 years ago, but it's not really my place to argue. Sorry, I'll retract my question? comments? then. 210.165.30.169 (talk) 04:03, 26 May 2010 (UTC)

As far as I know nothing apart from life is capable of maintaining it's own entropy (definately not crystals) .. are further definitions really needed. Just use No.1 that's my suggestion - perhaps there is an exception.77.86.125.207 (talk) 03:55, 26 May 2010 (UTC)

I think a photocell coupled to a battery and put outside in the sunlight would be an exception Androstachys (talk) 12:52, 27 May 2010 (UTC)

What animals can use the widest range of useful light strengths?

Some animals are mostly nocturnal. Some have vision that is mostly useful in the day time. Some animals, such as cats, have vision useful both in the day, and in low nighttime light levels. Which animals have the greatest useful visual range? —Preceding unsigned comment added by 24.130.145.253 (talk) 04:13, 26 May 2010 (UTC)

Any animal which has cone vision and goes out in bright daylight can use daytime illumination,(adapting by contraction of the iris in addition to retinal adaptation) so the medal must go to one of the animals which also had nocturnal vision via rods, a large pupil, and a reflective Tapetum lucidum to maximize night vision (though there is a decrease in acuity in bright light). It would be an animal specialized for nocturnal life which can function in full daylight (one not "blinded by the light" as the Mole (animal) and Bat are sometimes claimed to be). Zoos have some scary looking animals specialized for nightlife, with really big eyes. Owls would be in the running. Huge eyed mammals like the Bushbaby, the Aye-aye and other Lemurs seems like another candidate if it can function in daylight. They lose points for having no fovea, thus poor visual acuity in daylight. Primates seem to do better in daylight with a good fovea "The topography of primate retina: a study of the human, bushbaby, and new- and old-world monkeys.". Cats, dogs and raccoons have good night vision, with the reflective tapetum, and also see pretty well in daylight. Edison (talk) 04:50, 26 May 2010 (UTC)

Humans with Sunglasses and Night vision device. Cuddlyable3 (talk) 21:10, 26 May 2010 (UTC)

Cuddlyable3 with Welding goggles and a night vision device or a large optical telescope would definitely exceed the useful light range of any lemur or owl not so equipped, so it looks like humans win. Edison (talk) 22:06, 26 May 2010 (UTC)

Strangely we had no article on Welding goggles, so I wrote one. Edison (talk) 23:16, 26 May 2010 (UTC)

We do however have Welding helmet. Perhaps a merge/redirect is in order (or maybe the items are sufficiently different to warrant separate articles). Buddy431 (talk) 03:28, 27 May 2010 (UTC)

Uses of Stars

What are uses of stars?ugygdyowerg —Preceding unsigned comment added by 76.174.168.105 (talk) 05:04, 26 May 2010 (UTC)

There's one star we use a LOT, see Sun. Otherwise, people have used the stars to make constellations, i.e. draw pictures in the sky and tell stories about them. Stars have been used as navigation aids (see Celestial navigation). Hope that gets you started on some ideas. --Jayron32 05:28, 26 May 2010 (UTC)

I believe that stars still are used as navigation aids by many indigenous people. Many people attempt to use them to predict the future, compatibility between people and all sorts of things. -- Q Chris (talk) 09:00, 26 May 2010 (UTC)

Stars are not used to predict the future. You are probably thinking of astrology, which uses the planets.--Shantavira|^{feed me} 15:39, 26 May 2010 (UTC)

Stars are also used to derive the calendar and to know how long a year is, and to determine where the earth is in space. Stars are also used for navigation by space ships. They have also led to some discoveries such as helium and nuclear fusion. Graeme Bartlett (talk) 10:35, 26 May 2010 (UTC)

I'm not really sure what an "indigenous person" is, but I suppose I might count - I certainly use the stars for navigation. --Tango (talk) 11:27, 26 May 2010 (UTC)

Would Harold Gatty or Fred Noonan also be considered "indigenous persons" based on this criterion? LOL 67.170.215.166 (talk) 02:31, 27 May 2010 (UTC)

Stars provide some light at night - especially the milky way. Ariel. (talk) 11:31, 26 May 2010 (UTC)

Stars consume light elements like hydrogen and helium and use a fusion reaction to make heavier elements like oxygen, carbon, iron, uranium, etc. When a star 'dies', the result is often the explosive release of these heavy elements out into the surrounding regions of space. At the start of the universe (at the big bang) there were only light elements, it's safe to say that without stars, there would be no nice rocky planets, no atmosphere, no water, no animals, plants or people. Without stars, the universe would be nothing more than a big fuzzy ball of hydrogen gas. SteveBaker (talk) 13:35, 26 May 2010 (UTC)

Stars are a very useful way of motivating children at school, red ones are the best. They are given (awarded sounds better) for good work or behaviour. They are also used in WP to help people feel recognised - and why not I say. Caesar's Daddy (talk) 13:48, 26 May 2010 (UTC)

Wikipedians are encouraged by gifts of stars. Cuddlyable3 (talk) 21:05, 26 May 2010 (UTC)

The best stars are self-contained fusion reactors that produce amazing amounts of energy, even enough to provide light and heat 100 million miles away. 65.121.141.34 (talk) 16:15, 26 May 2010 (UTC)

Some stars entertain us and provide material for gossip columnists. Edison (talk) 22:01, 26 May 2010 (UTC)

Obviously this is a joke question. The ugygdyowerg at the end gives it away. But in any case, see dyson sphere. ScienceApe (talk) 17:54, 30 May 2010 (UTC)

Residual stresses in the coatings given on insetrs

What are the methods avialable to find the residual streses present in the coatings given on carbide inserts? —Preceding unsigned comment added by 122.248.132.54 (talk) 07:44, 26 May 2010 (UTC)

Xray diffraction is one method ie search "x ray diffraction surface stress" or similar.77.86.125.207 (talk) 16:55, 26 May 2010 (UTC)

Is blood group a factor in organ transplantation ?

I was just waching an episode of CSI:NY in wich they speculate that crime was comited to harvest victims liver ecause she had AB+ lood type which is very rare. To my knowledge the idea of AB blood type being rare is quite popular misconception (as people with that type of blood can receive blood of all other types). So I am wondering if lood type can acctualy play any role in organ transplantation ? (I figure there wouldn`t be much blood left in the organ...)--~~Xil (talk) 08:55, 26 May 2010 (UTC)

Here's a compatibility chart. Seems like CSI got it quite wrong. AB is not a type in high demand as a donor - AB can only give to AB, but AB can get from anyone. BTW to avoid Graft vs host disease the compatibility chart is reversed - but that's for bone marrow, not livers. Ariel. (talk) 11:12, 26 May 2010 (UTC)

To clarify; yes, blood type matters. You can read more here. Nowadays, blood type incompatible transplants are possible by a process known as immunoadsorption which removes the antibodies from the blood of the recipient. This patient, for example, was treated with a device from a Swedish company, Glycorex. [http://ndt.oxfordjournals.org/cgi/content/full/24/1/298 Here's a paper that describes the process in depth. Sjö (talk) 20:35, 28 May 2010 (UTC)

buying lemon juice

this site says "lemon juice an inexpensive, readily available acid for use in educational science experiments." but my store sells only tiny bottles 6 oz of it. its expensive too. im looking to buy it by the liter or gallon. iv looked online and cant find it either. it needs to be food grade. and not have any other chemicals or preservatives in it. —Preceding unsigned comment added by Tom12350 (talk • contribs) 09:00, 26 May 2010 (UTC)

Just buy food grade citric acid, it will likely have the same function for you. If you just want cheap, buy sulfuric acid or hydrochloric acid and dilute it, but they will not be food grade. 10:32, 26 May 2010 (UTC)Graeme Bartlett (talk)

It isn't that inexpensive, lemons are expensive too. Go with acetic acid (vinegar) or hydrochloric (muriatic) acid or even possibly food-grade phosphoric acid.

--Chemicalinterest (talk) 11:04, 26 May 2010 (UTC)

I usually buy frozen Minute Maid lemon juice. Ariel. (talk) 11:07, 26 May 2010 (UTC)

it needs to be liquid so citric acid powder is out. iv tried vinegar ect i Need lemon juice for my application. iv bought the frozen Minute Maid lemon juice but it only comes in tiny bottles. i need it by the liter or gallon.

You might want to be a bit more specific about what type of experiment or demonstration you're conducting. (Incidentally, citric acid dissolves very readily in water; it's the acid that gives lemon juice its bite.) TenOfAllTrades(talk) 11:45, 26 May 2010 (UTC)

I agree - you shouldn't dismiss citric acid. Dissolve the stuff in water first - now you have a liquid containing citric acid - which is what you really wanted the lemon juice to be. It has three major advantages over lemon juice: (1) It doesn't contain all the other junk (sugar, pulp, etc) that lemon juice has that could mess up your results (2) It's much cheaper (3) You have good control over the concentration. Since "food grade" citric acid is the "active ingredient" in lemon juice, it's just as safe for the kids. IMHO, it's better to tell them it's "citric acid" and that they are under no circumstances to eat it/taste it/whatever than to give them the impression that it's safe to do that with random chemicals in a science experiment! In other words - you can be 100% safe if they do screw up and start drinking the experiment - but still give the impression that this is a "proper" science experiment and start to instill the kinds of discipline they'll need when they move on to experiments with more dangerous chemicals. When the experiment is done, you can explain that citric acid is a major ingredient of lemon juice and that they could subsitute lemon juice if they wanted to repeat the experiment at home. SteveBaker (talk) 13:20, 26 May 2010 (UTC)

i dont want to have to dissolve it i just want to buy it in liquid form. i need it for degreasing items and for cleaning food surfaces as well as to drink (i like to drink lots of lemon aid as well) —Preceding unsigned comment added by Tom12350 (talk • contribs) 13:32, 26 May 2010 (UTC)

Try washing up liquid - it is specially designed for cleaning grease and will do a better job than lemon juice. --Tango (talk) 14:15, 26 May 2010 (UTC)

iv already tried it. lemon juice works well for what im doing. thats what i want to use. —Preceding unsigned comment added by Tom12350 (talk • contribs) 15:12, 26 May 2010 (UTC)

My grocery store has lemon juice in 24oz bottles in the juice aisle, so it is available in some places anyway. 65.121.141.34 (talk) 16:12, 26 May 2010 (UTC)

It seems like vinegar would be much more convenient to use in bulk for educational science experiments, and the pH for concentrated vinegar is hardly different from the pH of lemon juice. Looie496 (talk) 21:58, 26 May 2010 (UTC)

Why buy it in liquid form?!? That's just silliness. When you have lemon juice, you are buying (essentially) a mixture of citric acid and water. If you buy pure citric acid, you can just add your water and make ersatz lemon juice. The cost difference per gram between lemon juice and the powdered citric acid is simply the cost of water. Why pay extra cash for something you get almost for free out of your faucet?!? --Jayron32 00:46, 27 May 2010 (UTC)

Plus, even concentrated lemon juice contains significant amounts of sugar, which makes it a lousy cleaning agent. If you really want an acid to clean stuff, just buy white distilled vinegar. Its one of the cheapest, best cleaning agents out there. --Jayron32 00:50, 27 May 2010 (UTC)

I wonder if one of the OP's issues is he's thinking he's going to have to dissolve it every time. There's of course no reason to do this. Just dissolve an amount suitable for days, weeks or whatever and store it in a suitable container (e.g. an old bottle). It shouldn't be too hard to dissolve either. I'm not sure if you'll even need hot water. Nil Einne (talk) 13:04, 28 May 2010 (UTC)

how stationary is geostationary?

If someone were hanging just above the ground from a cable depending from a geostationary satellite, how much would they be moving around? Would they be swinging? bobbing up and down? racing to and fro? or would they be more or less still?

thanks Adambrowne666 (talk) 09:09, 26 May 2010 (UTC)

The satellites in these orbits move around in a figure 8 shape. The satellite operator will try to contain this inside a specified cube, while minimising fuel use. Allow for a tenth of a light millisecond (30 km) up and down each day, and with east west and north south added in. The angle should stay withing about 0.1 degree unless it is abandoned and goes into an inclined orbit. Graeme Bartlett (talk) 10:29, 26 May 2010 (UTC)

It's a bit more complicated than that. The weight of the person will change the orbit of the satellite. In order to compensate you will need to raise the orbit, but then it won't be geosynchronous. More accurately the center of mass of the satellite/person combo will (could) be in geosynchronous orbit - BUT - if the cable was rigid everything would be fine, but with a flexible cable the orbits of the person and the satellite won't match. Ariel. (talk) 11:00, 26 May 2010 (UTC)

Indeed - see space elevator. Gandalf61 (talk) 13:45, 26 May 2010 (UTC)

Anothing thing -- a person "hanging just above the ground" would be subject to the wind. The person and cable would swing freely like a pendulum on a string, its period depending on the mass of the cable (some of which is high enough that gravity is appreciably weaker) compared to the mass of the person, but a rather long period in any case. Each change of wind would change the motion, and this effect would combine with the orbital effects already described. Also to be considered is that the cable would certainly have some elasticity, so anything generating a vertical motion would tend to initiate a slow bouncing action. --Anonymous, 20:45 UTC, May 26, 2010.

Sorry - just remembered I forgot to thank you all for your interesting, prompt and detailed answers. Adambrowne666 (talk) 06:34, 30 May 2010 (UTC)

Sagrada Familia (Barcelona)

Two triangles marked 19-1-07 and a crack in Sagrada Familia inner wall. Help needed: What is the purpose of the two triangles? Thanks! Etan J. Tal 10:19, 26 May 2010 (UTC) —Preceding unsigned comment added by Etan J. Tal (talk • contribs)

It's some sort of telltale designed to enable someone to evaluate the extent to which the crack is developing, and or the relative directions of travel of the two plates as they move relative to eachother. --Tagishsimon (talk) 10:40, 26 May 2010 (UTC)

Similar to this I think: Ariel. (talk) 11:04, 26 May 2010 (UTC)

Given that the line between the two triangles isn't straight, it might be a tie to hold the crack together, that has snapped under the strain. Otherwise, I'd go with Tagiahsimon. CS Miller (talk) 12:59, 26 May 2010 (UTC)

I agree - it's obviously a tell-tale to let someone monitor how bad the crack is - whether it's growing or slipping, etc. Hence the reason for putting a date on it. Personally - when my house was new and started to develop a crack, I just drew a line across the initial hair-line crack with a pencil and dated it (fortunately mine was just a 'stuff drying out and settling after construction' kind of a crack and all was well). That's enough to let you know how much it grew in how much time - and (critically) whether there is any lateral slippage that might indicate a dangerous situation. SteveBaker (talk) 13:24, 26 May 2010 (UTC)

I thought it has to do with some earthquake, but couldn't find any on that day. It seems you are right - thanks to all of you! Etan J. Tal 20:36, 26 May 2010 (UTC) —Preceding unsigned comment added by Etan J. Tal (talk • contribs)

It is common in old historic buildings to monitor cracks by cementing a piece of glass or ceramic across the crack. If the crack is widening or narrowing, or the two pieces are moving relative to one another, the little brittle piece will tell the story. It would have little chance of preventing the crack from widening. Edison (talk) 21:57, 26 May 2010 (UTC)

four classes of consumables

(NOTE: This question is NOT about "calories.") Years ago I read the basic formula, Fat: 1 gram = 9 calories. Protein: 1 gram = 4 calories. Carbohydrates: 1 gram = 4 calories. Alcohol: 1 gram = 7 calories. (Again: This question is not about calories or about the preceding formula.) What's always seemed strange to me (ignorantly) is the aspect of "one of these things is not like the other": i.e., that "alcohol" seems somehow not to fit in this apparently comprehensive list. SO, Q: Is this list comprehensive, and if so, in what category? Are there other things with "calories" but which aren't digestible and so are not included? Also, three of the four are necessary, in the long run, for nutrition; is alcohol in any way necessary? Does everything we consume fit into one of the four categories (excluding bizarre things, like eating chalk or clay or whatever). And so on, on the basic theme of this list of four and only four classes of consumables. 63.17.33.231 (talk) 11:11, 26 May 2010 (UTC)

The list is most definitely not complete. For example there are sugar alcohols with a wide range of calories (see the article). Carbohydrates don't all have the same calories per gram (some have less). And there are also organic acids. See Food energy for a chart. And BTW carbohydrates are not necessary, protein and fat is enough. Ariel. (talk) 11:22, 26 May 2010 (UTC)

Thanks, Ariel. So there's fat, carbs, protein, alcohol (I presume sugar alcohol is alcohol), and organic acids. Anything else? And what "category" does this list compose? 63.17.33.231 (talk) 11:58, 26 May 2010 (UTC)

Sugar alcohol is not alcohol (ethanol). And like I said, see Food energy for the list. There are probably other things too, but none that are commonly eaten. I don't think the list could ever be considered complete. The food energy article calls these things Cellular respiration, so I guess that's your category - it's a list of things that can be oxidized by the body. It also mentions how bacteria can use metals - I wonder if humans can use them in tiny amounts. The reason this list can never be complete is that lots of things can be oxidized. For example humans can oxidize acetone (and ketones in general, are used by the brain, but I don't think are eaten directly, and are not on the list). Ariel. (talk) 12:02, 26 May 2010 (UTC)

The term macronutrient is usually applied to the collection of fats, proteins, and carbohydrates. But not alcohol. 198.161.238.18 (talk) 15:37, 26 May 2010 (UTC)

That is just a condensed list for ease of calculation of the number of calories in a food when they find out how many carbohydrate grams, fat grams, etc. are in the food. --Chemicalinterest (talk) 19:32, 26 May 2010 (UTC)

At first I thought "you might not want acetone on a list of foods" until I read about it's apparently low toxicity. Learn something new every day, huh? Kind of like how glycol will kill you, and glycerol will (safely) sweeten your food. --Jmeden2000 (talk) 20:52, 26 May 2010 (UTC)

science

Is a neutral body chargeless? —Preceding unsigned comment added by Rtbnsngpt (talk • contribs) 12:12, 26 May 2010 (UTC)

A neutral body is one that has no net charge. Whether that qualifies as being "chargeless" may depend on the textbook you use for definitions. — Lomn 13:00, 26 May 2010 (UTC)

To clarify, it's possible for a molecule to possess segments which are charged but that overall, produce no net charge. An example could be an amino acid, which possesses both an amine group and a carboxylic acid. While they may technically not exist as charged terminal portions at the same time, theoretically, you can understand, and perhaps someone else with more chem knowledge could provide a real-lie example. DRosenbach ^{(Talk | Contribs)} 15:31, 26 May 2010 (UTC)

Examples in zwitterion.77.86.125.207 (talk) 16:42, 26 May 2010 (UTC)

Or even like a hand-full of of table salt...50/50 mixture of Na⁺ and Cl^– so every atom is charged and but is overall (net charge, sum of all the pieces) neutral. DMacks (talk) 17:58, 26 May 2010 (UTC)

Or the atoms themselves, the nucleus is positively charged; the electron cloud is negative. CS Miller (talk) 18:07, 26 May 2010 (UTC)

And while we're there, those neutrons are composed of (balanced/net-neutral) charged quarks. DMacks (talk) 18:21, 26 May 2010 (UTC)

What is the definition you are using for "neutral body?" That would help in formulating an answer. Edison (talk) 02:37, 27 May 2010 (UTC)

Astronomical query

Το μικρότερο γνωστό αντικείμενο της Ζώνης του Κάιπερ.

Which is the name of the smallest Kuiper belt object, which was discovered in January, 2010, from Hubble Space Telescope? —Preceding unsigned comment added by ArgGeo (talk • contribs) 12:45, 26 May 2010 (UTC)

It's quite possible that it hasn't been named - it's a pretty boring lump of rock amongst billions of other boring lumps of rock - so it doesn't really need a name. It's also possible that some boring astronomical naming panel has to meet to agree on a name. If you are desperate to know - then at the bottom of this article are the email addresses of two of the scientists involved in the search. You could ask them. Incidentally - the article I linked to is really fascinating. Aside from it's size, the most interesting thing about the object in question is how it was discovered. It's 100 times dimmer than the dimmest thing the Hubble's best imaging system can see! They actually used some rather interesting techniques using the telescopes guide-scope to discover the rock as it occluded light from a distant star that the Hubble happened to be using to stabilize itself! (Incidentally - the picture our OP linked to is an artist's impression - which for a rock whose only known properties are roughly where it is and approximately how big it is - is something of a stretch!) SteveBaker (talk) 13:05, 26 May 2010 (UTC)

It is strange that neither that article or the description of the picture on the NASA site give the designation of the object. It may well not have been named, but it should automatically get an alphanumeric designation (see Provisional designation in astronomy). --Tango (talk) 14:02, 26 May 2010 (UTC)

Yeah, I'm pretty unhappy about that artist's depiction — for me, being fanciful about what it may look like is fine, but I dislike physical impossibilities: What is lighting that thing up?? Comet Tuttle (talk) 17:29, 26 May 2010 (UTC)

Another spaceship off to the right somewhere, with a huge spotlight, isn't it obvious? The Sun is just visible at the top-left of the object. CS Miller (talk) 18:05, 26 May 2010 (UTC)

sticker

what type of glue is on stickers such as childrens stickers or stickers found on food products. —Preceding unsigned comment added by Tom12350 (talk • contribs) 15:18, 26 May 2010 (UTC)

Our article on labels says dextrin, starch or Polyvinyl acetate (PVA). Regards, --—Cyclonenim | Chat  17:53, 26 May 2010 (UTC)

it dosent appear to say that anywhere in the article —Preceding unsigned comment added by Tom12350 (talk • contribs) 18:54, 26 May 2010 (UTC)

Have a look at the Attachment section. --Kateshortforbob _talk 19:26, 26 May 2010 (UTC)

The specific glue used also has to be classified as food safe.77.86.125.207 (talk) 19:34, 26 May 2010 (UTC)

That would include rice glue. ~AH1^(TCU) 01:49, 27 May 2010 (UTC)

Organ donor death statistics

Any data on how often something happens during a living organ transplant (kidney, liver) and the donor dies during or shortly after the operation? —Preceding unsigned comment added by 20.137.18.50 (talk) 17:14, 26 May 2010 (UTC)

[This] says that for kidney donation it was less than 1 death in 3000 operations. That figure used data that ended in 1992 and they expected the modern rate was even less frequent. 75.41.110.200 (talk) 20:14, 28 May 2010 (UTC)

Soccer matches often played under heavy rain

Wouldn't this increase the chances of pneumonia etc.? I thinkn a U.S. president died after making a speech in rain. 67.243.7.245 (talk) 18:39, 26 May 2010 (UTC)

That would be William Henry Harrison. He died one month after giving his inaugural address; two hours in the pouring rain on a cold March day. CS Miller (talk) 18:47, 26 May 2010 (UTC)

(ec) Not really. The connection between cold weather and illness is mainly due to people spending lots of time indoors in close proximity to other people. A US president may well have died after making a speech in the rain, but I doubt he died because he made a speech in the rain. (If you actually get hypothermia, then that is bad, but you certainly won't get that running around on a football field (they wear hats and gloves in cold weather) and it would be hard to get it giving a speech.) --Tango (talk) 18:49, 26 May 2010 (UTC)

He probably died because of the cold, but the cold weather just augmented the virus. If you aren't sick, you shouldn't have any trouble being out in the cold. --Chemicalinterest (talk) 19:30, 26 May 2010 (UTC)

He didn't develop his illness until several weeks after his inauguration, so it's likely that it had very little to do with his death. Buddy431 (talk) 21:32, 26 May 2010 (UTC)

There's also zero evidence that cold weather, in and of itself, either causes OR exacerbates upper respiratory infections (cold, flu) one gets during the winter seasons. When controlled studies have been done, there has been no connection found between being cold and wet and getting sick. --Jayron32 00:41, 27 May 2010 (UTC)

Cold temperatures may weaken the immune system as blood flow may be restricted to the head area. If an infection or viruses are already present, then the infection may be affected in the time that the blood flow and white blood cells are reduced. ~AH1^(TCU) 01:44, 27 May 2010 (UTC)

Yes, that would be a plausible mechanism to explain a connection, were any such connection observed. Jayron's point is that, under controlled conditions, no such connection is observed. --Trovatore (talk) 01:51, 27 May 2010 (UTC)

The only time I've played football (or soccer as some call it) was when I was a schoolboy. Then, whenever it rained we would all stop and seek shelter. Why would anyone want to play football in the rain? 92.15.6.183 (talk) 21:38, 26 May 2010 (UTC)

Because the cost of cancelling a professional football match is enormous. --Tango (talk) 22:55, 26 May 2010 (UTC)

(after ec)In Britian football/soccer gets played in any weather, provided that it's not so rainy that the ball is brought to a halt by waterlogged ground if you pass it low, or the pitch is frozen solid, or there's so much snow on there that it can't be cleared/flattened enough to approximate a level surface by 3pm. Just the way it is - and has always been ever since the game started. In the amateur leagues, they don't even seem to care much about that. There are some stadiums that are notorious (thinking Blackpool and Oldham in particular) for gusts of wind so strong at times that if hoofing the ball into the wind, it can actually end up behind the kicker - and they still play. It's an oft-repeated comment about South American/Southern European/African footballers (who have a reputation for being mad-skilful but 'sensitive' and 'fussy', whether it's true or not) that 'Well, he might look good now - but let's see how he does on a December weeknight in the League Cup at (insert name of lower league team with dilapidated ground and scruffy pitch) when it's -2 out and it's pissing down in sheets!'. --Kurt Shaped Box (talk) 23:06, 26 May 2010 (UTC)

There seem to be sport-by-sport conventions on this. Football (American football, you know, the real kind :-), like soccer, is not cancelled for weather unless it is truly extreme. Look up Ice Bowl, for example. But baseball games are delayed for any significant rain, and eventually cancelled if the rain doesn't stop. I'd be curious to know if that's also true for cricket.

This could be a safety thing, I guess — I really don't want a pitcher throwing a wet ball at me at 95 mph, especially when I might have trouble picking it up against the sky. --Trovatore (talk) 23:10, 26 May 2010 (UTC)

Cricket is usually called off if it starts raining significantly. The players go in and wait, the covers come on, then they maybe give it two or three hours and if it's still raining, the game/that particular day of the test is abandoned. --Kurt Shaped Box (talk) 23:20, 26 May 2010 (UTC)

Sounds about the same then (as baseball). I wonder whether this is convergent evolution (football and soccer have similar practical requirements, and so do baseball and cricket) or whether these are traditions that date back to the common ancestors of the two pairs of sports. --Trovatore (talk) 23:29, 26 May 2010 (UTC)

Having difficulty seeing the ball is usually due to poor light rather than rain (of course, rain can cause poor light, but it comes under a different clause in the laws of the game). If the bowler slips on the wet grass he can easily mis-bowl and end up bowling a beamer, which can break the batsman's arm. The ball bounces funny on wet ground too, but I guess they could learn to deal with that - I think it is the safety issues that causes them to pause the game. (It may also be because cricket is a sophisticated gentleman's game (they stop for tea and eat cucumber sandwiches made by the host team's wives) and they don't like getting muddy!) --Tango (talk) 01:01, 27 May 2010 (UTC)

Oh, right, tea and cucumber sandwiches. Just like baseball. --Trovatore (talk) 01:34, 27 May 2010 (UTC)

With cricket, I always assumed the main reason was so the pitch would not get wet. Getting a good wicket pitch seems almost like some sort of esoteric mystical art form, it has to be just the right hardness and dryness, with some cracks and not perfectly even thrown in too. I thought that getting the pitch soaked would make it just about impossible to bowl on. Vespine (talk) 02:27, 27 May 2010 (UTC)

The main reason for stopping play in cricket and baseball is that the two sides are doing very diffrent things during play. Its not fair if one team gets to bat on a dry pitch and the other side bats with a slippery unpredictable ball. Comparison of runs to determine victory in such a situation would be meaningless as it wouldn't tell you which team was actually better. In soccer its not an issue as both sides have to deal with the same problem.203.145.145.13 (talk) 07:54, 27 May 2010 (UTC)

Gamma Globulin/Is it available to the general public by prescription?

Is Gamma Globulin availble at this time to the general pubolic by prescriptiom?4annieiam (talk) 21:16, 26 May 2010 (UTC)

Depends on which one. Some are - but they are very very pricey. Ariel. (talk) 21:50, 26 May 2010 (UTC)

Gamma Globulin - used to treat Crohn's Disease

I was diagnosed with Crohn's Disease in 1972. After 6 months of treatment with Prednisone with less than adequate results, a doctor told me to try Gamma Globulin instead. He said 10% of Crohn's Disease patients responded to it. I tried it and it worked. I had no flare-ups until after 1991 when it was taken off the market.

The same doctor (in 1973)said that in earlier times there was medical literature about this use of Gamma Globulin. I looked at the Gamma Globulin information that was available at that time, but could find only one reference to it's use for Crohn's Disease, saying: 'Some people used to think Gamma Globulin could be used for the treatment of Crohn's Disease.'

My request is that if anyone can find medical information on the subject of Gamma Globulin used to treat Crohn's Disease, probably written in the 1930's - 1960's, could they please post it to Wikipedia?

Thank you very much.

4annieiam (talk) 21:36, 26 May 2010 (UTC)

Google Scholar is wonderful for this sort of thing. You can do an advanced search for "Crohn's disease gamma globulin" and set the year range to 1930-1970. Lots of the hits even give you downloadable pdf files. Looie496 (talk) 21:47, 26 May 2010 (UTC)

Lots of books mention both search terms at Google Book search: [1]. Some of these are just noting gamma globulin levels in patients with the disease, rather than using it as a treatment. Many are "snippet views" and you would need to go to a university library or large public library to access the paper or books. Edison (talk) 21:52, 26 May 2010 (UTC)

BTW, Gamma Globulin is not a specific thing. It's a type of imunoglobin, but do you know which one you were given? Each one works against against a specific (different) target. Or were you given a random collection of them from a donor? Ariel. (talk) 21:53, 26 May 2010 (UTC)

Gamma globulin is more or less synonymous with immunoglobulin, IgG in particlular. Human immunoglobulin for therapeutic use is certainly not taken off the market. It is used for the treatment of immunodeficiency, and is also used for immunomodulation of various autoimmune diseases, such as immune thrombocytopenic purpura and Guillain Barré Syndrome. It is often administered intramuscularly for the treatment of immunodeficiency, and usually intravenously when the purpose is immunomodulation. In the latter case, it is often abbreviated IVIG (see the article IVIG). There is even a case report of immunoglobulin administered orally for the treatment of Crohn's disease [2]. However, we have probably already crossed the line regarding the reference desk's rules regarding medical advice that you can read on the top of the page, and I expect this thread will soon be deleted. I am writing this only to attempt to clear up what appears to be a misunderstanding. Apart from that, these are questions you should be discussing with your physician, not with random strangers on the internet. --NorwegianBlue ^talk 17:28, 27 May 2010 (UTC)

Touching car batteries

Is it possible to touch the two poles of a 12v car battery without considerable current passing through one's body? I remember someone messing the voltage with a large voltmeter and there were sparks but this doesn't make sense for such a low voltage. —Preceding unsigned comment added by 89.243.134.212 (talk) 22:17, 26 May 2010 (UTC)

The sparks are caused by the heating effect of the power flowing - car batteries can produce a large current - which is high enough to melt (and/or vaporise) thin wires or cause sparks. A high voltage isn't necessary for sparks produced on contact. A high voltage is only required for sparks (or 'arcing') with jumps across a long distance.77.86.125.207 (talk) 23:19, 26 May 2010 (UTC)

related is Welding power supply - arc welding uses "typically between 17 to 45 volts and 55 to 590 amps" - here the voltage is not much higher than a car battery and less than mains voltage - but look at the current.

This is different to that found in Electrostatic discharge such as found in lightning and which usually requires very high voltages. Both processes are similar.77.86.125.207 (talk) 00:12, 27 May 2010 (UTC)

The question dealt with whether much current would pass through your body if you touched both 12 volt battery terminals with fingers or whatever at the same time. Key issues are the contact resistance (dry or wet or broken skin, contact area), the part of the body the current is flowing through, and the bulk resistance of the tissues, Probably much lower than the contact resistance of dry skin. In movies, people are always getting tortured or electrocuted with 12 volt batteries. Let's just let potential murderers and torturers keep thinking that painful and dangerous current would always flow, whether it is true or not.45 volts (the arc welder comparison) is not 12 volts. Some cars have battery voltages much higher than 12 volts. In general, some current would flow, and even a small current could be dangerous to some people through some current paths. If a piece of jewelry like a ring or bracelet touched a positive wire and a grounded (negative) part of the car, serious thermal burns could result from the metal heating up, since high current would flow through that low resistance path. Edison (talk) 02:30, 27 May 2010 (UTC)

It's certainly possible for 12 V to create a current through the body. In most cases, I think that you wouldn't expect it to (dry skin makes a decent insulator). Here's a guy talking about electrocution [3]. If you search the article for "12V" (no space) you'll find where he talks about 12 V batteries. If you search "12 V electrocution" or similar in your favorite search engine, you'll find plenty of results. Consensus appears that it takes special circumstances for a 12 V battery to give you a good shock, but that it can happen. Burns from jewelry and such, as Edison pointed out, are also very much a hazard. Buddy431 (talk) 03:20, 27 May 2010 (UTC)

Touch the terminals of a 9 volt battery with your tongue and report back to us. 71.100.8.229 (talk) 08:49, 27 May 2010 (UTC)

I tried the tongue thing with the 9 volt battery. It works because your tongue is wet, making it a much better conductor. Here's something you can do. Take an ohm meter and clamp your dry hands to it. The resistance could measure about 100,000 ohms. Make your fingers moist: It may drop 500%. --Chemicalinterest (talk) 10:43, 27 May 2010 (UTC)

It's all very well to talk about how safe or otherwise this stuff is - but you really can do yourself some serious harm with even small amounts of voltage and current applied in just the wrong way. This 1999 Darwin Award went to a guy who died from a shock from a regular 9 volt battery. SteveBaker (talk) 18:03, 27 May 2010 (UTC)

Electrocution by Simpson ohmmeter sounds like b.s. And it is not that easy to "in one's excitement" push Simpson meter probes through one's skin to create the supposed low resistance path. The are not hypodermic needles. If a metal bracelet, or watchband were on sweaty skin, a fairly low contact resistance would be found compared to touching dry meter probes. But there is probably circuitry in a Simpson meter besides a battery which adds resistance and decreases the available current. Again, some person might be sensitive enough to be harmed by some low current, so do not experiment. Edison (talk) 05:05, 28 May 2010 (UTC)

It says that he pushed the probes through his skin on purpose. 67.170.215.166 (talk) 06:54, 28 May 2010 (UTC)

It is a true story, contrary the Edison's belief, although his advice is well founded and should be followed. For instance gas bubbles generated in the blood stream by electrolysis can accumulate in the heart and prevent the heart from pumping. 71.100.8.229 (talk) 02:55, 29 May 2010 (UTC)

Question about closed orbits

If two bodies are interacting in a gravitational field, and r is the position vector joining them, my textbook was able, by reducing the problem to a one body problem, to show that r would trace out an ellipse (if the orbit was closed). But do each of the bodies themselves move in an ellipse? And how can you show that the barycenter of the system is at a focus of any of these ellipses (that traced out by r, or the orbits of either body)? My textbook did say that if r started at the origin, then the origin would be a focus of r's ellipse, but I don't know if that has any connection with the problem(s). Thanks! 173.179.59.66 (talk) 22:22, 26 May 2010 (UTC)

Okay I think I was able to answer the first question: r₁ or r₂ will just be constant multiples of r, making them ellipses too. 173.179.59.66 (talk) 22:54, 26 May 2010 (UTC)

See Kepler's_laws_of_planetary_motion#Derivation_from_Newton.27s_laws. I haven't read through it, so I'm not sure how clear a derivation it is, but that's what you are doing. --Tango (talk) 23:07, 26 May 2010 (UTC)

That derivation assumes that the Sun is much larger than the planet. 173.179.59.66 (talk) 23:38, 26 May 2010 (UTC)

So it does, sorry. Google will probably find you lots of derivations of Kepler's laws. --Tango (talk) 01:06, 27 May 2010 (UTC)

I've googled it but, sadly, they all do the same thing as Wikipedia, or as my textbook...173.179.59.66 (talk) 01:10, 27 May 2010 (UTC)

If you've already shown that r₁ or r₂ are constant multiples of r and the origin is a focus of r's ellipse then I think you're done. r₁ and r₂ measure the position of each object relative to the barycenter (or else they wouldn't be constant multiples of r, so that must have been an assumption in the derivation). So over time they trace out with respect to the barycenter two scaled versions of r with respect to the origin. Rckrone (talk) 02:44, 27 May 2010 (UTC)

Yeah, obviously, I don't know why I didn't see that. Thanks. 173.179.59.66 (talk) 11:54, 27 May 2010 (UTC)

Gravity express

I read online that if two points on the earth were connected via an underground tunnel, then (ignoring friction and rotation) the time it would take for a train to 'roll' between the two points would be independent of were the two points were located. I think the time came out to something like 41 minutes. Anyways, I tried to work out this is true but I wasn't successful...perhaps someone here will be? 173.179.59.66 (talk) 22:24, 26 May 2010 (UTC)

Assuming you are going to your antipode, This question has been asked here several times before, the last was here. It has links to previous discussions that might have the calculation. As gravity decays linearly as you move to the centre of the Earth (the part of the Earth that's above you reduces the gravity you feel), you need to use calculus rather than Newton's laws directly. CS Miller (talk) 22:35, 26 May 2010 (UTC)

No, apparently this is true of any two points, regardless of their distance apart. 173.179.59.66 (talk) 22:55, 26 May 2010 (UTC)

It is true. I think the best way to prove it is to use conservation of energy. Given that the train is at rest at the surface, its speed at any given point is a simple function of its distance below the surface (its kinetic energy is equal to the reduction in gravitational potential energy). Once you have the speed as a function of depth you can do some calculus to get the time taken and you'll find that it is constant. --Tango (talk) 23:11, 26 May 2010 (UTC)

(ec) Yeah I tried that, but the potential energy is a function of the distance to the center of the earth, while we need it to be written as a function of the distance travelled. I tried to relate the two, but I ended up with an integral that looked way to difficult to evaluate. 173.179.59.66 (talk) 23:35, 26 May 2010 (UTC)

Would this link help? Or was that what you used to get the ugly integral? --Tango (talk) 23:50, 26 May 2010 (UTC)

Q. Using the potential energy sounds like a good idea. But the (42 minute) solution seems to rely on the earth being solid, (ie not a point mass) - I can't find an equation for potential at distance r inside a uniform solid sphere - I'd be interested to know if it's easy to get one .. anyone know?77.86.125.207 (talk) 00:04, 27 May 2010 (UTC)

ok two points at the same distance from the centre of the earth. Assume the angle between them (and the centre of the earth) is theta , then , the angle the straight tunnel between them makes with the horizontal is theta/2. It's length is 2Rsin(theta/2). It's gravity that causes the train to roll. Like the link given above by Csmiller the motion is oscillatory. ie the start and end velocity is zero. You'll probably need to calculate the angle the tunnel makes with the gravitational force at each point along the tunnel so you can work out the component of that that causes the train to accelerate (or de-accelerate). I assume you'll also need the gravity inside the earth at radius r ; assuming a solid earth of constant density this is given by using the shell theorem - in fact this works out to be force due to gravity is proportional to r.

Did you try something like that and get stuck at solving the equations (you should get a differential equation for the motion eventually), or get stuck earlier or later? Probably the method described above by Tango is easier .. did you try something like that .. if so tell us where you got stuck.77.86.125.207 (talk) 23:31, 26 May 2010 (UTC)

Oh I completely forgot about the shell theorem...but anyways, if I understood what 77.86 said above, I tried that too but got stuck with the math. 173.179.59.66 (talk) 23:40, 26 May 2010 (UTC)

The wikipedia article on the subject is Gravity train. Ariel. (talk) 23:52, 26 May 2010 (UTC)

Yes the links from that article have derivations - similar to what I've attempted to describe below and probably easier to read. (they also don't mix up sin and cos like I did below . which helps. corrected now...) 77.86.125.207 (talk) 00:01, 27 May 2010 (UTC)

(edit conflict)

ok hint . at distance d from the surface along the tunnel the accelerating force due to gravity is proportional to r the distance from the centre of the earth and to the angle the line from the point to the centre makes with the path (call this angle alpha) - now can you see that the component of the force that causes acceleration is proportional to rcos(alpha) (r from shell theorem, cos(alpha) from the component of that force) .. now draw the construction for that value - you'll see that rcos(alpha) is equal to Rsin(theta/2)-d

( Rsin(theta/2) is half the length of the chord connecting the two points on the earth surface, and d is the distance travelled)

This makes the accelerating force linearly related to the distance the train has travelled (ie simple harmonic motion - just like a spring - and makes it a lot simpler to solve)

I think if you can get to the simple harmonic motion part you should find the rest easy. If you get stuck on the construction I've described above I'll have another go at explaining it, or upload an image)

I can see how it's easy to get stuck early on if you don't spot the simplification.77.86.125.207 (talk) 23:58, 26 May 2010 (UTC)

The statement that the time is independent of the initial and final positions is only true if curved tunels are not allowed. If curved tunels are allowed then the brachistochrone is the fastes path and will lead to shorter travel times for shorter distances between initial and final positions. this[4] shows a few examples. Dauto (talk) 04:13, 27 May 2010 (UTC)

Alright I got it, thanks a lot everyone. 173.179.59.66 (talk) 16:35, 27 May 2010 (UTC)