Wikipedia:Reference desk/Archives/Science/2010 December 18

= December 18 =

Maize recycling...
How to present the recycling method of maize — Preceding unsigned comment added by Raunakstha (talk • contribs) 03:20, 18 December 2010 (UTC)


 * I'm not sure I follow. One doesn't usually recycle food.  One usually eats it.  Unless you mean composting food waste?!?  I am thoroughly confused.  Could you elaborate.  -- Jayron  32  04:26, 18 December 2010 (UTC)


 * Never seen a corn field Jayron? The OP is almost certainly referring to the ~80% of the plant that's not edible - the stalk, leaves, etc. In rural China people collect it by hand and use it for heating fuel. That's not really what I'd call recycling, though. The Masked Booby (talk) 04:57, 18 December 2010 (UTC)


 * Then there's the silk, cobs, and leaves from the corn left after you eat it. StuRat (talk) 05:00, 18 December 2010 (UTC)


 * Roughly one-quarter of the world's food is wasted or uneaten. Perhaps the OP is referring to "recycling" and redistributing this food? ~ A H  1 (TCU) 15:48, 18 December 2010 (UTC)
 * It is not an uncommon practice for farmers to put cattle in the harvested field to eat the remaining vegetable material. Googlemeister (talk) 14:29, 20 December 2010 (UTC)

MCAT en Français
Hello. Are there any plans of a French equivalent of the MCAT to be recognized by Canadian medical schools underway? Thanks in advance. --Mayfare (talk) 03:25, 18 December 2010 (UTC)
 * There are three francophone medical schools in Quebec, at the Université de Montréal, the Université Laval and the Université de Sherbrooke. Sherbrooke appears to run its own equivalent of the MCAT, the TAAMUS (Test d’Aptitude à l’Apprentissage de la Médecine à l’Université de Sherbrooke), while Montréal and Laval  don't mention anything about a specific aptitude test in their publicity. Physchim62 (talk) 12:52, 18 December 2010 (UTC)

Why does warm air hold more moisture than cold air
I've heard two explanations: that the warm air transfers more energy to the water, preventing it from forming water droplets; and that there is more space between air molecules in warm air, and droplets tend to form in the spaces between air molecules. Which is right, and could anyone knowledgeable elaborate on the explanations? Thanks a lot!74.15.138.27 (talk) 08:02, 18 December 2010 (UTC)
 * It has nothing to do with "holding". You are thinking about it wrong.  There's always PLENTY of space in air (or any gas) to hold more molecules of anything.  Indeed, gases at earth atmospheric conditions are on the order of 1/1000 as dense as solids or liquids, meaning that there is generally about 1000 molecular volumes of empty space around each molecule of a gas.  So there's plenty of "room" in the air.  The reason that warm air has a higher absolute humidity has to do with the competing forces which determine the phase of a substance:
 * Intermolecular forces are the forces of attraction between the molecules of a substance. These forces are why solids and liquids exist at all.
 * Heat is the energy of molecular motion. The faster molecules move, the greater the forces needed to slow them down.
 * Now, in a gas, there will always be a range of speeds of molecules. The higher the temperature, the greater number of molecules will be moving at faster speeds.  Molecules which don't move fast "enough" to overcome the intermolecular forces will condense out of the gas phase.  So the deal with warmer air is, warmer air has a higher percentage of water molecules which will be moving fast enough to avoid sticking to each other than colder air, which is why warmer air has a higher "carrying capacity" for water vapor.  So, the first explanation you have is "closer" to the truth.  The second one, about having more space between air molecules, is pretty much bullshit.  If that were true, then there would be LESS impetus to form water droplets, because the molecules of water would be farther apart on average, and so the intermolecular forces trying to make them condense would be less effective.  -- Jayron  32  13:18, 18 December 2010 (UTC)
 * Thanks. 74.15.138.27 (talk) 02:38, 20 December 2010 (UTC)

ACMA blacklist
whats it — Preceding unsigned comment added by Kj650 (talk • contribs) 14:19, 18 December 2010 (UTC)


 * Information_published_by_WikiLeaks explains it. SmartSE (talk) 14:50, 18 December 2010 (UTC)
 * The lists leaked by Wikileaks can be still be found at their website (or one of its mirrors): AMCA blacklist. Buddy431 (talk) 23:46, 18 December 2010 (UTC)

A lead on leads
Were leads ever made from lead? Reason for asking: I have some ancient resistors and they are corroded similar to lead. --Chemicalinterest (talk) 14:32, 18 December 2010 (UTC)
 * Electronic "leads" (pronounced LEEDS) are so named because they are the point of contact between a device and other devices, and thus "lead" (LEED) the connection between the two devices. This has nothing to do with the element "lead" (LED) per se.  -- Jayron  32  14:36, 18 December 2010 (UTC)
 * From my reading of the question, the OP never suggested such a connection. Dismas |(talk) 18:13, 18 December 2010 (UTC)
 * According to its article, it's soft and has poor conductivity, so it would have been an odd choice. Clarityfiend (talk) 21:31, 18 December 2010 (UTC)


 * The resistors are most likely carbon, not lead. -- k a i n a w &trade; 21:52, 18 December 2010 (UTC)


 * Although I appreciate learning extra facts and tidbits of scientific information, I don't think my question was answered. Did leads originally contain lead? --Chemicalinterest (talk) 22:30, 18 December 2010 (UTC)
 * I have seen them made from iron, copper and silver. I am sure that somebody tried lead, but the low melting point of lead makes the use very problematic if you solder. resistance is no problem when you only have 5mm length with 0.5mm diameter.--Stone (talk) 22:53, 18 December 2010 (UTC)
 * The answer is No. "Leads" on electrical components are named from O.E. lædan "cause to go with one, lead". The name of the metal "lead" has a different root W.Gmc. loudhom. Electrical leads (LEEDS) have nothing to do with the metal (LED), though one can quip that the terminals on a Lead–acid battery are stubby leads of lead. Cuddlyable3 (talk) 23:00, 18 December 2010 (UTC)

The solder used to join leads to components is likely to contain lead. DuncanHill (talk) 00:10, 19 December 2010 (UTC)


 * Well, yes. The leads (ledes) on electronic components are likely to be tinned with solder, which contains lead (led, or perhaps Pb).  But the led is there to melt and make soldering easy, and the lede (most often copper, or Cu) is there to provide conductance and physical strength.  Led would be useless as a lede because it melts easily and doesn't conduct well at all. PhGustaf (talk) 00:36, 19 December 2010 (UTC)


 * The coating or "tinning" of tin-lead solder on the copper wires coming out of the resistor make it much easier to solder them into a device. Bare copper would oxidize and have to be scraped clean immediately before it was soldered. The Pb metal would make a lousy conductor to use in attaching a component, because it is more prone to break than copper, has higher resistivity, and would be prone to melt and separate during soldering. Old time fuse wire, dating back to 1880 or earlier, contained lead, I believe, like solder. A short link of it would melt and interrupt the current when there was a short or a sever overload, before the copper conductors could overheat and start a fire. Edison (talk) 04:18, 19 December 2010 (UTC)

The Degradation of the Human Race by Doctors
Susceptibility to certain bacterial or viral diseases is inheritable in some persons. (A doctor will sometimes ask a patient what his father died of.) If these susceptible people get the disease to which they are prone, medical science will often be able to keep them alive longer than would have been the case in the pre-medical era. The disease-prone people will therefore live longer and will be able to have children or more children. As a result, the proportion of disease-prone people in the population will continually increase. As medical science advances, the problem will accelerate. The burden of supporting and treating the unwell will eventually become intolerable on those who are healthy. Can anything be done about this? How about mandatory sterilization of these persons? This would be one more of the Draconian measures that will be needed if human life is to continue on this planet.-- Diatom. 173.189.136.110 (talk) 15:07, 18 December 2010 (UTC)
 * This article speaks to your concern, but is focused on domestic dogs . On the other hand, the fact that our medical practices may be decreasing negative selective pressure on deleterious human alleles could also result in broadening the evolutionary search space, allowing our descendants the possibility to develop beneficial mutations that would not be available without negative intermediate forms. Also, since you speak of human sterilization programs, you may enjoy reading up on ethics. SemanticMantis (talk) 15:36, 18 December 2010 (UTC)


 * I do not like the idea of enforced sterilization. But it may become a necessity as the lesser of two evils. And after all, there is always the possibility of adopting a child. As for waiting for mutations to counteract disease susceptability, the burden of supporting and treating a great many unwell persons may become intolerable. I am talking about a very long term effect - Long term versus shortt term is a known problem in ethics. Diatom. 173.189.136.110 (talk) 17:00, 18 December 2010 (UTC)


 * The fears about dysgenics have generally been considered over-exaggerated in modern medical contexts, and societies generally will not tolerate compulsory sterilizations anymore done in the name of eugenics. Consider whether you yourself would be happily compulsory sterilized if tomorrow DNA testing told you that there are a statistically higher chance that your offspring would be susceptible to some common virus or bacteria. The social medicine seems worse than the disease in most such cases. --Mr.98 (talk) 15:50, 18 December 2010 (UTC)


 * Mr.98, you refer to the Wikipedia article on compulsory sterilization. However that article does not deal with the increasing influence of medical science on prolonging life of disease-susceptible persons. That can be expected to continue, with more and more of these persons living longer and longer, and producing more children.


 * Compulsory sterilization has three aspects:
 * 1. The sterilization of persons of a certain race. The Nazis did some of that.
 * 2. The sterilization of persons who have an inheritable disease, without considering the affect medical science may have in continually increasing the proportion of such persons in the population.
 * 3. The same as item 2, but taking into consideration how medical science allows such persons to continually increase in proportion to the population.


 * As for society usually being opposed to compulsory sterilization, society takes only a short term view of it. Diatom173.189.136.110 (talk) 17:47, 18 December 2010 (UTC)
 * Diatom, are you soapboxing? It is a very complicated issue with many factors and implications and a tragic history.  I think the answers you have been given so far (above and below this post) have been quite good treatments of this difficult subject, and you should consider them more carefully before trying push further your point that "society" is taking a "limited" view of it.  Wiki Dao  &#9775;  (talk)  18:57, 18 December 2010 (UTC)


 * This process has, of course, gone on for a long time. Just blame the people who started using fires, enabling individuals with weaker teeth and stomachs to survive and beget children. Or those pesky weavers, who allowed people with insufficient body hair to survive the cold! Humans have always adapted their environment to their benefit, and then evolved to better utilise this environment. Doctors are part of our new environment. Immunity to a disease does not come for free - it comes at a biological cost. If this ability is not needed, it will vanish, and free resources that may allow us to evolve new features useful in our modern environment. Of course, sometimes changes in human lifestyle are slower than evolution. As a result, we still get fat on Big Macs, although for most of us there is little likelihood of ever experiencing life-threatening starvation. --Stephan Schulz (talk) 16:00, 18 December 2010 (UTC)


 * As for fire and weaving, a similar, partly successful, solution has been developed for disease susceptability. It is medical treatment. But that is often expensive, time consuming, and sometimes requires repeated treatment. There are somtimes serious side effects or infection. It would be muich better to eliminate the susceptability.


 * Regarding mutations, they are rare. I don't think there has been one in all of human history. Diatom.173.189.136.110 (talk) 20:11, 18 December 2010 (UTC)
 * Chances that you are not a mutant are negligible. According to this paper, there are 175 mutations per generation. Most of them are neutral, of course. Very few indeed give you superpowers ;-). --Stephan Schulz (talk) 20:24, 18 December 2010 (UTC)


 * (e/c) Right, but we can afford the expense of health-care (in an overall sense), the modern medical infrastructure has become a part of our environment to which we are adapting short-term (epigenetically, culturally, etc.) and long-term (genetically). Technology will improve those processes, at least eventually in ways that are acceptable to us and don't have unexpected bad consequences.  I don't know what you mean by there having been no human mutations, though, you should go read an article or something. ;)  Wiki Dao  &#9775;  (talk)  20:27, 18 December 2010 (UTC)


 * They are not rare. There are about 175 mutations per human genome per generation. .  Since ~98% of the human genome is not directly associated with protein coding, most of the mutations fall into innocuous regions that have no effect.  Some fall on critical genes and the resulting embryo in not viable, leading to spontaneous abortion.  But on average, you can expect every baby has around 1 gene (out of 23000) that has been mutated to be different from both their parents.  In some cases the effects are profound and deleterious, but in many cases the effects are subtle and not obvious.  Dragons flight (talk) 20:29, 18 December 2010 (UTC)


 * Well, it depends what you mean by "mutation". Every human being is different. They have a different face, for instance. Even identical twins are different - they have different fingerprints, for instance. So it could be said that every person is a mutant. But still, I think there will be a long, long wait for disease susceptability to disapear or turn into something beneficial from that cause. And it will only happen to one person at a time. Diatom.173.189.136.110 (talk) 20:42, 18 December 2010 (UTC)
 * Mutation has a very well-defined meaning, so we don't really get to choose. Some fairly well-known mutations are the development of Lactose tolerance and the Sickle cell trait. --Stephan Schulz (talk) 20:54, 18 December 2010 (UTC)

The most important thing to bear in mind when thinking about issues like this is that unless selection is extremely rigorous, its effects take dozens of generations (at minimum) to become significant. So in principle it may be correct that if current practices are continued for thousands of years, human vulnerability to disease might increase. But given the vast number of more pressing problems we face, it's hard for me to feel terribly stressed about this. Looie496 (talk) 18:52, 18 December 2010 (UTC)


 * And it is certainly not the case that people in places with better medical care and longer lifespans produce more children! In fact it is usually exactly the opposite: the more exposure to education, medicine, and wealth a population has, the more their reproduction rate declines. --Mr.98 (talk) 19:50, 18 December 2010 (UTC)


 * I don't like to ask - but are the Germans healthier than people in other countries, or is there no difference? Did their killing/murdering of disabled people have the effect on the German gene pool that they expected? 92.15.1.13 (talk) 20:01, 18 December 2010 (UTC)


 * Well, those unfortunate victims of the Nazis certainly did not pass along susceptibility to disease unless sthey had children earlier. Diatom.173.189.136.110 (talk) 20:26, 18 December 2010 (UTC)


 * This would not be measurable against the noise background, much less separable from other differences due to health system and living circumstances. Also note that eugenics was not limited to Germany, even if the Nazis were particularly ugly at it. --Stephan Schulz (talk) 20:17, 18 December 2010 (UTC)

We are just now entering the era when genetic modification is possible. I wouldn't be surprised to see medical treatments during the next century that routinely eliminate disease causing alleles. That seems a far more likely outcome than any form of forced sterilization. Dragons flight (talk) 20:09, 18 December 2010 (UTC)


 * The real genetic answer to why eugenics doesn't work is pretty simple. The kind of "weeding" you are talking about only works if there are no recessive traits. If there are recessive traits, then you have to "weed" out people who don't express the given condition as well, which is a vastly greater number than the "sick" population. The Hardy–Weinberg principle essentially makes it clear that if you only sterilize those who express a trait, it will never appreciably affect the total amount of expression in the total gene pool.
 * Now, what you can do is prevent expression in the form of aborting fetuses with expressed conditions. That is what is done on Cyprus in the instance of thalassemia — the number of carriers in the population remains constant, but the number of those born with the full disease zeroed out in a single generation, because of the use of amniocentesis and selective abortion. It's a controversial case, one that only seems to have gone over on Cyprus because the effects of expressing thalassemia are so violent were becoming such a drain on families and the health care system that people were basically not having kids. I doubt you could do that with the much more minor things you are describing above. The ethics are problematic, in any case, and you aren't actually affecting the "healthiness" of the gene pool — just the "healthiness" of those who get to be born.
 * Genetics is in any case far more complicated in most instances. There are relatively few conditions that are caused by strict Mendelian heredity. If you start adding in more complicated risk factors (e.g. genetic factors which put one at high risk for breast cancer), you start getting a much wider net of whom would have to be sterilized in order to achieve your "healthier" society. The sweep of eugenics would have to be much more radical than even the Nazis were able to accomplish under a fascist state. It's not feasible. It's not ethical. It's not really very sound science, either. --Mr.98 (talk) 21:43, 18 December 2010 (UTC)


 * Doesn't that mean that genetic diseases ought to be increasing over time, in all populations of animals? 213.122.10.39 (talk) 01:29, 20 December 2010 (UTC)


 * I agree with most of the responses above, and would like to add that eugenics (or breeding, in the case of animals) also fails because what we choose as "healthy" genes may not be what is best for society. For example, eliminating the gene for sickle-cell anemia may cause malaria to spread.  And some mental "diseases", like manic-depressive disorder, seem to lead to astonishing periods of creativity.  And there may be many other hidden benefits to some of those mutations you dislike, that we haven't yet figured out. StuRat (talk) 00:08, 19 December 2010 (UTC)


 * I agree that the degeneration of the human genome in response to poor selection should take a very long time, though it is not infinite. The success of feral pigs in many regions should attest to the potential of humanity to shake off the legacy of domestication.  In the very long term however we might need to consider the effects of increased background radiation from uranium which has been cracked into shorter-lived isotopes, which will almost inevitably tend to spread throughout the world over time.  But it is fair to say that genetic modification should be able to reverse such effects.


 * I would also contend that genetic medicine can be differentiated from eugenics. The reason is that with the broad population data that is being gathered, it becomes possible to tell how long ago a mutant allele arose in the population.  Sometimes it can be determined that it started fresh in the patient, parent, or grandparent; other times a longer estimate will be needed.  By drawing a line between recently arisen mutations and longstanding alleles, it is possible to undo the damage from "disease alleles" whose fate, most likely, was to be expunged from the gene pool in any case, while recognizing the intrinsic value of alleles that have survived many thousands and often millions of years through having some special use.  However, I'm not aware of this being a published or accepted sentiment. Wnt (talk) 05:12, 19 December 2010 (UTC)

Night vision of seagulls and other birds
I've often seen seagulls flying around after dark this winter. They may be confused by the very bright street lighting. 1) Do seagulls and other birds have good or any night vision? 2) I once heard it would probably kill a bird to disturb them from their roost after dark, as they would be unable to find another in the dark. Is this true? Thanks 92.15.1.13 (talk) 20:07, 18 December 2010 (UTC)


 * As a rule, most diurnal birds have middling-poor night vision. they are not night-blind, but probably don't have the visual acuity needed to fly through woodlands or underbrush safely.  This may not be of too much concern for gulls, since they tend to frequent 'open sky' regions without too many obstacles to run into.  And no, it won't kill a bird to disturb it from its roost at night, but it might harm itself if it smacks into a branch in the dark.  -- Ludwigs 2  20:57, 18 December 2010 (UTC)


 * Some other birds to indeed have excellent night vision (see Bird_vision). Some gull species are highly adaptable. Nocturnal Scavenging by Gulls in the Southern North Sea is one study that mentions nocturnal activity (following trawlers and their discard) among Larus argentatus, Larus marinus, and Larus fuscus. The abstract concludes with "they should be regarded as neither nocturnal or diurnal by preference in this area". Perhaps it applies to other civilized areas with yet more tasty scraps too. ---Sluzzelin talk  21:16, 18 December 2010 (UTC)


 * Hi. I was summoned... :) According to this 1914 article by R. M. Strong (page 24) "It has been my experience that the Herring Gull has nearly as good darkness vision as man at least". Just so happens that I was reading that the other day, heh. Personally, I have seen Herring Gulls happily feeding in the streets in the middle of the night and heard their contact calls as they fly overhead before sunrise. They seem to see just fine. I also read an article recently where it was mentioned that GBB Gulls will raid tern nests at night.
 * As for other birds, I can tell you that Budgerigars have *very* poor dark vision. If they fall off their perches in the night, they struggle to find them again and will flap around their cages in a panic until the light is turned on. I've heard accounts of it being a similar situation with Cockatiels. --Kurt Shaped Box (talk) 23:59, 18 December 2010 (UTC)
 * "Hi. I was summoned..." From the vasty deep? 87.81.230.195 (talk) 12:39, 19 December 2010 (UTC)