Wikipedia:Reference desk/Archives/Science/2013 May 3

= May 3 =

Dietary Reference Intake/Percent Daily Value
What's the relationship between Dietary Reference Intake and Percent Daily Values? Did the US government simply rename PDVs, perhaps when they made the food pyramid three-dimensional? PCV currently redirects to DRI, which doesn't mention PDV at all except in a single citation to a webpage that's now producing a 404 error, and a Google search didn't help. Nyttend (talk) 01:04, 3 May 2013 (UTC)
 * I think RDI is just the recommended amount of any particular "stuff" you should eat in a day, and so PDV is simply how much of that RDI any labelled food product contains. Just as a point of clarification, it's not technically the government which decides these things, these reccomendations are made by the Institute of Medicine which has a Congressional charter, but it's not in any way actually part of the government. Vespine (talk) 04:00, 3 May 2013 (UTC)
 * interesting that sometimes the RDI is the max amount of something you should eat, and sometimes it's the minimum amount. Tripped up a few students in health class. Gzuckier (talk) 21:10, 3 May 2013 (UTC)

recognizing a beetle
was photographed in East Talpiot, Jerusalem, Israel. anyone recognize? --SuperJew (talk) 05:11, 3 May 2013 (UTC)
 * Can't help with identity, although it looks like a weevil, but this site, What's that bug? is a very helpful resource. Richard Avery (talk) 07:15, 3 May 2013 (UTC)
 * It's not a weevil, they have snouts. μηδείς (talk) 08:16, 3 May 2013 (UTC)
 * This is a species of darkling beetle, possibly Adesmia abbreviata. --Dr Dima (talk) 08:27, 3 May 2013 (UTC)
 * here  are two pages about it. --Dr Dima (talk) 08:36, 3 May 2013 (UTC)


 * I contacted this site: http://www.nature-of-oz.com/ I quote Oz Rittner: "This is Adesmia (genus), not possible to identify the species from this photo. It belongs to the Tenebrionidae family." 196.214.78.114 (talk) 08:52, 3 May 2013 (UTC)


 * The Lord sure do love Him some His beetles, don't He? Gzuckier (talk) 21:13, 3 May 2013 (UTC)
 * "inordinate fondness for stars and beetles", indeed . --Dr Dima (talk) 22:20, 3 May 2013 (UTC)
 * Your use of some and his as specifiers at the same time is ungrammatical in the dialect you are attempting. It's like saying "This my book is interesting." μηδείς (talk) 01:57, 4 May 2013 (UTC)


 * Thanks a lot. Description updated. --SuperJew (talk) 17:57, 4 May 2013 (UTC)

Accelerator required for high intensity x-ray?
The voltage differential between cathode and anode in an x-ray tube translates into the "keV" rating of the resulting x-rays. Is it a requirement to use linear accelerators to get photons with higher energy. Or can one build a 50 MeV x-ray tube ..? An example being the Australian Synchrotron which generates 90 keV electrons using an electron gun and then accelerate these to 100 MeV. Electron9 (talk) 20:38, 3 May 2013 (UTC)


 * This might be an over simplification but once an x-ray or any other electromagnetic radiation setts off (emitted) – that's it.  You can't give it extra electron volts in the real world. If you need harder x-rays then you need a greater differential. In the old days, one could tape a metal paper clip to a bromide paper and place it near to the TV tube – and hey presto – on developing you had an x-ray photo. A Synchrotron accelerates just the 'electrons' (read: increase of potential) so the  electromagnetic radiation they 'stimulate ' (is that right in this context?) peak at  higher energies. --Aspro (talk) 21:10, 3 May 2013 (UTC)


 * The reason linear accelerators (which accelerate electrons magnetically) are used for high energy X-rays in the medical filed and for industrial X-rays is because they are much more compact and cheaper that a conventional X-ray tube (which accelerates electrostatically) would be to get the same energy. Machinery to raise 20 MV at a useful current (several mA or more) needs large insulators and would need to be the size of a house, where as linear accelerator coil assembly is only the size of a couple of shoe boxes.  That makes it a lot cheaper.  A linear accelerator can be switched on and off virtually instantly, where as a many-megavolt power supply would take a second or maybe a few seconds to build up and die down - not very desirable.
 * The business of using a TV set to take X-Ray pictures is very nearly an urban myth. Except for the very early colour sets sold in the USA (1950's), the voltage used (about 17 to 20 kV depending on size) is not sufficient to get X-rays of sufficient energy to penetrate the picture tube front glass.  The earliest coluor sets used up to 25 kV or so and a shunt triode regulator to regulate the voltage.  These regulator tubes did emit very weak X-rays, but set manufactuers limited the X-Ray emission form the set by enclosing the regulator in a metal cage, and by arranging it so the the remaining X-Rays were directed downward thru the bottom case of the set, so that two thick layers of plywood, a metal sheet, and the floor of the dwelling would have to be penetrated.
 * Ratbone 58.167.231.148 (talk) 00:16, 4 May 2013 (UTC)


 * There's something wrong with the answer above.
 * Magnetic fields don't accelerate electrons, so it makes no sense to say something is accelerated magnetically
 * Magnetic fields bend the path of an electron bean, so it makes no sense to call an accelerator that uses magnetic fields a "linear accelerator"
 * Dauto (talk) 12:32, 4 May 2013 (UTC).


 * The magnetic keeps the beam on track and the electric field accelerate the particles/photons ..? Electron9 (talk) 13:36, 4 May 2013 (UTC)


 * A STATIC (constant) magnetic field will not accelerate electrons. However, a MOVING magnetic field produces electric tension, just as a moving electric field produces magnetic tension.  By feeding the acelerating coils or cavities in a linac with an appropriate frequency, the electrons are accelerated without having to generate a high voltage.  Linacs do generally use magnetic focusing, but that is done with addition structures, not the accelerating structures.  Ratbone 120.145.203.168 (talk) 15:46, 4 May 2013 (UTC)


 * By electric tension you must mean electric field, which does indeed accelerate the electrons in a linear accelerator. I wouldn't call that "electrons magnetically accelerated". What you have is an electron riding a wave so that it is continuously accelerated by the varying electric field. Dauto (talk) 16:23, 4 May 2013 (UTC)
 * Put it this way: electrons get accelerated in linacs to a speed that would require millions of volts in a traditional Xray tube.  But there are no large voltages anywhere in a linac.  Just several structures in "line astern" carrying significant currents at appropriate frequencies.  Ratbone 120.145.65.37 (talk) 03:00, 5 May 2013 (UTC)

What are the natural controls on Eh and pH?
What are the natural controls on Eh and pH (in areas of water) besides the amount of electronegative elements (eh) and the amount of acids (ph)?--149.152.23.34 (talk) 21:43, 3 May 2013 (UTC)


 * Think that's a very good question. Soil, is a mixture of many mineral and organic  components. The answer of this question is not going to be straight forward. --Aspro (talk) 21:59, 3 May 2013 (UTC)


 * In general, see Soil pH and buffer (chemistry). More specifically, presence of limestone or sodium carbonate in the soil tends to prevent pH from going too low, or drives it up; whereas presence of humic acid / fulvic acid tends to prevent pH from going too high, or drives it down. Forest or swamp soils that are relatively poor in mineral content can be fairly acidic, while volcanic or some desert soils that are relatively poor in organic matter can be fairly alkaline. --Dr Dima (talk) 01:04, 4 May 2013 (UTC)

Was there ever a real species of dinosaur that resembled Barney?
In so much that it had the body shape and posture of a carnivorous dinosaur, but also had the blunt, wide herbivorous teeth? It's been a long time since I watched Barney The Dinosaur, but I think it's stated that he's a herbivore (or mostly so).

Discussion of the colour is optional. Though I don't suppose that a purple dinosaur would be out of the question, when you look at some of the colours we see in nature these days. Would it be any less wrong then showing them as being bright green?

Thanks. --146.90.56.134 (talk) 23:19, 3 May 2013 (UTC)
 * In my opinion Barney looks more like hadrosaurus than tyrannosaurus, but of course this is all just random. Looie496 (talk) 23:31, 3 May 2013 (UTC)


 * Barney was a guy. Don't you mean Dino?--Shantavira|feed me 06:53, 4 May 2013 (UTC)


 * See Barney & Friends. HiLo48 (talk) 07:07, 4 May 2013 (UTC)


 * The members of Hevisaurus were of specific species.--Shirt58 (talk) 07:22, 4 May 2013 (UTC)
 * I'm not certain that the fossil record supports this particular behaviour, but it's not out of the question either. Alansplodge (talk) 20:17, 4 May 2013 (UTC)


 * Very few species of dinosaurs are known to have either spoken or sung in English. ←Baseball Bugs What's up, Doc? carrots→ 09:31, 5 May 2013 (UTC)