Wikipedia:Reference desk/Archives/Science/2008 March 18

= March 18 =

More quantum physics...
I need to know, in depth, all aspects of the behavior of electrons in crystaline structures (more specifically, quantum dots). If there is an article on this, please let me know. Thanks! Zrs 12 (talk) 03:01, 18 March 2008 (UTC)


 * Quantum dot seems like a good place to start. DMacks (talk) 04:07, 18 March 2008 (UTC)


 * Read it. I need to know in depth.  I'm having to do a project over these things and apparently electrons act differently in them than in single atoms. (That probably sounds like I'm being short or rude, but I don't mean it like that). Zrs 12 (talk) 04:41, 18 March 2008 (UTC)
 * No problemo...wasn't clear from your question what if anything you already knew/had read:) By spacially constraining the electrons, the energy levels are changed, so the spectra of a quantum dot that are based on electronic transitions are different than for free atoms/molecules. Quantum well has some detail. What level and sort of project are we talking about here? "In depth" and "all aspects" sound either contradictory or unlimited in scope without knowing what kind of project and what academic level. The refs cited in quantum dot, quantum well, and potential well are good ones. DMacks (talk) 05:12, 18 March 2008 (UTC)
 * Thanks for your help. Well, I am in 9th grade.  However, I have been reading alot about the subject and am beginning to grasp some of the more in depth concepts such as the mathematical concepts in some areas of quantum physics.  This is also a project to be in the state science fair, so it probably must be done at a higher that 9th grade level to have any chance.  By the way, the specific information I seek about the electrons in quantum dots is; Why are the electrons confined to bands rather than descrete energy levels where they can have partial quanta of energy (right?).  And, how do the electrons behave.  They bounce back and forth, but between what?  Where?  Are they confined to a specific area?  How and why are the energy levels changed by spatial restriction?  To how big an area does the Pauli exculsion principle apply?  To a single atom?  A molecule?  What do the matrices of objects such as $$|\psi\rangle$$ represent?  Bra-ket notation  Is it correct to say that, for the photoelectric effect to take place $$E_g\leq{hf}$$ in which Eg is the energy of the bandgap, h is Planck's constant, and f is the frequency of the light?
 * Once again, thanks very much for your help. Zrs 12 (talk) 05:45, 18 March 2008 (UTC)
 * As the Pauli Exclusion Principle article states, it says that no two fermions may occupy the same quantum state simultaneously, fermions are a type of elementary particle, described by The Standard Model. I recommend purchasing the book Hacking Matter at the local bookstore, about quantum dot, wells, and artificial atoms. I suggest taking up your discussion at Physicsforums's physics section— they will be very helpful to you. Mac Davis (talk) 10:49, 19 March 2008 (UTC)

Infrared raman spectroscopy
Infrared rays having best penetration in skin and flesh, why can't be utilized for in-vivo non-invasive probing? Can't these rays yield good signature of bones? Neel shah556 (talk) 04:00, 18 March 2008 (UTC)


 * Infrared is strongly absorbed by many of the components in skin and flesh. Water, lipids, proteins etc. Infrared therefore does not have good penetration of skin and flesh. X-rays on the other hand are not absorbed (much) by flesh and therefore penetrate the skin and flesh to the bones, thus x-rays are used to look at bones in-vivo, not infrared.--Shniken1 (talk) 12:40, 18 March 2008 (UTC)

global warming
Will rise in sea level be even across the world? Or will the rise be more in regions near to arctic and antarctic and less in regions near equator? —Preceding unsigned comment added by 59.92.113.83 (talk) 06:46, 18 March 2008 (UTC)


 * Sea level changes are not uniform, but it's not as simple as greater rises at higher latitudes; contributing factors are tides, density due to salinity, expansion and contraction due to heat, flows around landmasses, etcetera. Most models show that the greatest rise will be seen in the arctic (due to increased runoffs causing a drop in salinity) and the lowest rise will be seen in the antarctic. FiggyBee (talk) 07:34, 18 March 2008 (UTC)


 * Dumb question then - why wouldn't the higher sea level water flow down to the lower level until the levels are equal? Franamax (talk) 08:12, 18 March 2008 (UTC)


 * It does, but not fast enough to overcome all the other factors (which are all ongoing processes, rather than one-off starting conditions). FiggyBee (talk) 08:19, 18 March 2008 (UTC)


 * Thanks! I knew it was a dumb question. :) Flow varies with square-root of water head, right? It's just hard to imagine that the Arctic Ocean could fill up with water faster than it could empty out. I forgot the factor of time. Franamax (talk) 08:39, 18 March 2008 (UTC)


 * I agree with you Franamax. While some difference seems inevitable I have a hard time imagining a significant difference.  Are we talking about fractions of an inch here ? StuRat (talk) 14:24, 18 March 2008 (UTC)


 * From Sea level : "Mean sea level does not remain constant over the surface of the entire earth. For instance, mean sea level at the Pacific end of the Panama Canal stands 20 cm higher than at the Atlantic end."  72.10.110.107 (talk) 15:22, 18 March 2008 (UTC)


 * The earth's spin alone accounts for the height of the Pacific being slightly elevated relative to the Atlantic, as I understand it, and that difference is more pronounced towards the Pacific's West end. Any of us who have spent time on bodies as small as the Great Lakes know that water level can seem to rise or fall significantly due to changes in wind direction.  And, for that matter, the Great Lakes do have a flow -- a molecule of water at the West end of Lake Superior takes 15,000 years to reach the Atlantic.  So water, as it were, doesn't settle and "even out" quite so quickly as we might suppose.Vance.mcpherson (talk) 15:41, 18 March 2008 (UTC)


 * But, of course, the Great Lakes are far more restricted in their flow to the ocean than the oceans are to each other. If the oceans were only connected via narrow channels, it would be easier to understand a difference in elevations.  The tides will also cause some areas to have far higher elevations than others at any given time.  However, none of this explains why the relative elevations would significantly change when more water is added to the system via global warming. StuRat (talk) 22:15, 18 March 2008 (UTC)


 * The Arctic Ocean may be the exception though, it only has two outlets, and some pretty big rivers flowing in, Mackenzie, Ob-Irtysh, Yenisey (I think). Plus thermal expansion as the ocean warms up, so it's plausible. I would be interested to see the models though. Rising sea levels are certainly already a problem in the Arctic. Most interesting... Franamax (talk) 01:28, 19 March 2008 (UTC)


 * A rise in sea level is not necessarily even around the world. As discussed above, mean sea level (MSL) involves complex measurement and it is attempted to accurately determine an MSL using the geoid as a level reference surface. A rise in sea level, however, would expand the geoid and mean sea level. Isostatic changes will also do this. Mac Davis (talk) 10:42, 19 March 2008 (UTC)


 * Hi. Well, I read in a book that a recent satellite measurement of the world's oceans that the mean sea level excluding waves and other anomalies in a given area was actually greatly affected by the sea bottom elevation: the surface water was generally lower near a trench and higher near an undersea mountain range. Also, a shift in sea currents could affect the amount of heat in a given area and thus the sea level. Erosion will also cause the now-undersea landforms to erode, allowing sea levels farther inland. Given the right (or should I say wrong) type of rock, the sea can either flow into the groundwater and flood a nearby low basin or create waves that enter the basin. For now, many regions in the arctic are still experiencing the shoreline recede, as the rising of the land since the last ice age is currently faster than the sea level rise, at least until the Greenland and Antarctic ice sheets start collapsing. Also, if you try to use the flood maps at flood.firetree.net, they are largely innacurate (see their disclaimer). Constant flooding in an area may also allow sea levels to creep up. If there is a river, the sea can easily flood farther inland bacause of the eroded lowlands formed by the river. Hope this helps. Thanks. ~ A H  1 (TCU) 21:11, 19 March 2008 (UTC)

I belive that the sea level will not be even around the world but I do not know the answer to your second question. But i promise I will try to find out. SilverLeaf209.226.138.43 (talk) 18:22, 23 March 2008 (UTC)

MSM expiry
TenOfAllTrades(talk) 12:55, 18 March 2008 (UTC)
 * You should ask a pharmacist and your doctor about this. They know much more than we do. Franamax (talk) 08:00, 18 March 2008 (UTC)

Doctors and pharmacists are Wikipedia editors as well.

This is not about pharmacy or medicine. The question is: Is MSM oxidized or reduced in household storage (or does it decompose)? [household chemistry]

MSM is not pharmacy; It is a mineral (sulfur) nutrient, much like calcium or magnesium. But the question is not so much about nutrition as it is about msm decomposition in household storage. Please leave this for discussion. —Preceding unsigned comment added by Zaqry (talk • contribs) 19:42, 18 March 2008 (UTC)

Is MSM oxidized or reduced in household storage (or does it decompose)? —Preceding unsigned comment added by Zaqry (talk • contribs) 22:39, 18 March 2008 (UTC)

Does MSM decompose in household storage and how (oxidation or reduction reaction for example)? —Preceding unsigned comment added by Zaqry (talk • contribs) 18:00, 19 March 2008 (UTC)

Radio transmitter power
A 50,000-watt radio station is transmitting at full power.
 * a) Is there at least 50KVA (50KVA plus the heat coming out of the building) running through the power lines into the station at all times?
 * b) Does it matter whether anyone is talking over the radio?
 * c) Is the answer different whether it's AM or FM, or VHF or UHF television?

Thanks for the help! Franamax (talk) 08:08, 18 March 2008 (UTC)

My understanding is
 * a) Yes for FM. See c
 * b) No for FM, but for AM it will increase and decrease as someone talks. There is a variation of AM known as Single-sideband modulation (SSB) that only uses power when there is some sound.
 * c) For FM and AM yes. For TV, I am not sure but I think that US digital TV uses ATSC Standards a type of SSB. I would imagine that in video there are no "silent" pauses like in audio, so the power load will be more constant. European digital TV uses Orthogonal frequency-division multiplexing, which I am unsure about. Analogue TV uses FM, and will therefore have constant power. -- Q Chris (talk) 10:02, 18 March 2008 (UTC)


 * For frequency modulation, phase modulation, and ordinary analog amplitude modulation (of 100% or less modulation depth), the average power of the carrier wave remains constant so the power inflow to the building will always be at least 50 KW. For single-sideband modulation, there's no transmitted power when no one is talking so the average power of the carrier wave varies with the average volume of the modulating signal. Analog TV uses vestigial sideband modulation (a hybrid of AM and SSB) for the video and frequency modulation for the audio.


 * Atlant (talk) 12:04, 19 March 2008 (UTC)

Atomic Radio clocks in Bulgaria
I live in Bulgaria. How do I find out whether an atomic radio clock will work in Bulgaria? Do I have to obtain one from a specific provider? —Preceding unsigned comment added by ENiklaus (talk • contribs) 12:06, 18 March 2008 (UTC)


 * Bulgaria seems to be at the edge of the region where the German DCF77 signal can be received. According to the PTB, the range is 2000 km (unfortunately that's probably not very helpful, but maybe interesting). Icek (talk) 12:54, 18 March 2008 (UTC)


 * (edit conflict)
 * There are long-wave time transmissions from Switzerland and Germany which might reach Bulgaria (depending on mountains etc.) They broadcast on slightly different frequencies, so, yes, you do need to purchase the correct receiver, and there is no guarantee that it will work where you live. I have found that the UK transmission can be picked up in some parts of buildings, but not in other parts.  Mountains and steel frames cause reception problems.  See Radio clock for more details, but the price of radio clocks is now quite low, so if they are not available for sale in your area, then it is probably because there is not a good radio signal.  A world-wide time transmission can be picked up by a GPS clock (built into most GPS units) but you need to be either outdoors or near to a large window to pick up the satellite signals.  ''  d b f i r s   13:08, 18 March 2008 (UTC)

Genetic probabilities
In a problem I'm trying to solve, there are 2 alleles, A and a. a is a defective allele, so the genotype aa induces disease. Both parents are carriers: Aa. 1) What is the probability that all three children are of normal phenotype? The way I see it, the chance of the normal phenotype in one child is 3/4, the result of a simple Aa x Aa Punnett square, so (3/4)3 = 27/64. 2) What is the probability that one or more of the children have the disease? Shouldn't it be 1/4 + 1/4 + 1/4 = 3/4? But 27/64 + 3/4 ≠ 1 ... help! Thanks, anon. —Preceding unsigned comment added by 70.23.85.120 (talk) 16:48, 18 March 2008 (UTC)


 * You can only add probabilities when they are probabilities of mutually exclusive (i.e. incompatible) events. Child A has the disease with probability 1/4, same for B, but the probability that A or B or both have the disease is not 1/4 + 1/4 because you are double-counting the case where both A and B have it, which has probability 1/16. So the probability for two children would be 7/16, which equals 1 - 9/16 that you could compute from the probability that both were normal.  With three children it is easier to start with the probability that all three are normal, and you have that already.  --Anonymous, 16:58 UTC, March 18, 2008.


 * As an exercise to help understand the probabilities you might want to list every possible combo. Each child has 4 possible combos (AA, Aa, aA, or aa).  While Aa and aA both mean they are carriers of this recessive disorder, it's probably easier to list them separately as equal probability than combine them together.  So, that gives you 4^3 or 64 possible combos.  List them out and record how many children have the disease or are carriers for each combo. StuRat (talk) 22:05, 18 March 2008 (UTC)


 * Thanks so much :-), anon. —Preceding unsigned comment added by 141.155.38.85 (talk) 17:17, 19 March 2008 (UTC)

300,000 Elephants in Chad?
In the article excepted below [and in many secondary & tertiary sources] the assertion is made that “--the Chad population was over 300,000 animals as recently as 1970 and has been reduced to approximately 10,000 as of 2006.” I have looked carefully at the publications of the African Elephant Specialist Group of the IUCN for confirmation of these figures [latest report 2007]. The IUCN folks report no data on Chad elephants before 1985. They report “no evidence” for 1981 and no figures before that time. Where did this 300,000 figure originate and who started it?


 * 2006 Zakouma elephant slaughter refers to a series of poaching massacres of African elephants in the vicinity of Zakouma National Park in southeastern Chad. These killings have been documented in aerial surveys conducted from May through August 2006 and total at least 100 animals.[1] This region has a four decade history of illegal killing of this species; in fact, the Chad population was over 300,000 animals as recently as 1970 and has been reduced to approximately 10,000 as of 2006. The African elephant nominally has Chadian governmental protection, but the implementation practices of the government (backed with certain EU help) have been insufficient to stem the slaughter by poachers.[1] The species African Bush Elephant (Loxodonta africana) occurs in several countries of Eastern Africa. —Preceding unsigned comment added by Lynmil (talk • contribs) 19:45, 18 March 2008 (UTC)


 * The first reference for 2006 Zakouma elephant slaughter is where that figure comes from, but trying to track that number further back was not very successful. It is amazing how many sites quote that "300,000 in 1970" figure and how frustrating it was to try tracking the source.  I was unable to find anything approaching an original source, but I think I may have a good idea on how that figure was calculated.  I think it may have been a backward calculation based on the Manovo-Gounda St. Floris National Park (Central African Republic) (N 475) report or some report like it.  In that report, which is not specific to Chad but could reasonably be extended in principle to all surrounding areas, they report that the region had lost 95% of its elephants.  It wasn't really clear to me what time frame they were referencing.  Ninety-five percent loss since when?  They were probably calculating the loss since poaching became a serious problem (starting around 1970 ???).  Using that figure, you simply multiply the elephant population, at the time of the report, by twenty to find the starting population.  Of course, to know that an area had suffered a 95% loss means UNESCO already had to know the starting population by some other means.  Althought I don't doubt the figure at all, I would like to see the original source for that 300,000 quote.  SWAdair | Talk 10:26, 22 March 2008 (UTC)

The IUCN report titled African Elephants and Rhinos: Status Survey and Conservation Report (1990) gave a 1987 estimate of between 200-400,000 elephants for Central Africa including Cameroon, Central Afr. Rep, Chad, Congo, Equat. Guinea, Gabon and Zaire [Now Dem Rep. of Congo]. Nearly half (195,000) of these animals were estimated for Zaire.

The IUCN 2007 African Elephant Status Report: An update from the African Elephant Database gives the Probable number of elephants in Central Africa as 48,936, with the Probable number from Dem Rep of Congo as only 7,955 animals. Thus Zaire (Dem Rep Congo) HAS lost 95% of the estimated elephant population from 1987 to 2007. The upper estimate for Central Africa in 1990 was 375,800. The upper estimate for 2007 is 48,936; thus an estimated loss of about 76%.

I agree with “SWAdair” that someone probably extrapolated from Central Africa data to Chad, but the loss of almost 300,000 savanna elephants from Chad could not have gone unnoticed. The figure is fictitious. Lynmil (talk) 19:38, 24 March 2008 (UTC)

Paramagnetic metal that do not become magnetized.
The question is what are metals called that are paramagnetic,but do not become magnetized (they are attracted by magnets, but when removed from magnetic infuences, are not magnetic)?

What metals are these? How do I reference the subject on WikiPedia?

Thank You, My Email address (removed for your protection) —Preceding unsigned comment added by 151.202.62.236 (talk) 19:55, 18 March 2008 (UTC)
 * "soft magnets", see magnet also remanence and follow the links in the 'see also' section.
 * The remanence of a material is the extent to which the material retains the magnetic field - you are obviously asking for 'low remanence'. Please ask for furhter info.87.102.47.176 (talk) 20:15, 18 March 2008 (UTC)


 * You may want to have a look at [] for a little fun. I saw a nifty powerpoint by a fellow from University of Victoria on paramagnetism some six years ago, and I'll be damned if I know how to find him.  If memory serves, and the link I provide confirms, paramagnetism isn't so much about what metal is paramagnetic as what you did to the metal, i.e. what else is it bonded to.  Gets into the realm of organic chemistry.Vance.mcpherson (talk) 20:15, 19 March 2008 (UTC)

What is cyclooctatetraene?
What is cyclooctatetraene? 66.81.43.129 (talk) 21:59, 18 March 2008 (UTC)
 * Take a look at our article, Cyclooctatetraene. It appears to have a lot of info. -- Flyguy649 talk 22:02, 18 March 2008 (UTC)