Wikipedia:Reference desk/Archives/Science/2013 June 7

= June 7 =

Cell reproduction
At what age is a human at his or her strongest and when does cell reproduction start slowing down? 119.72.194.33 (talk) 00:46, 7 June 2013 (UTC)
 * I think the 1st question can be answered by a slightly different question. If you consider "strongest" to mean physically fit and if you consider professional atheletes to be the most physically fit people (generally as a "group"), which I think aren't very unreasonable assumptions. From doing a quick search it appears most professional atheletes (in physically demanding sports at any rate) are between 18 and 28. you can probably narrow it down further if you want, but I think it would vary enough from person to person to make a very narrow range, like one or two years, almost meaningless. The 2nd question, i think there are so many cells and so many factors, i'm not sure there is one answer. I think 28 is possibly a good guess, but I have nothing but the above and my own experience (being 35 and definitely noticing a difference to being 25) to back that up. Vespine (talk) 04:25, 7 June 2013 (UTC)

sexual enjoyment
Does sexual enjoyment decrease in humans after a certain age? At what age does a human enjoy it the most from a scientific point of view. 119.72.194.33 (talk) 00:49, 7 June 2013 (UTC)
 * The lede of libido says that "Males reach the peak of their sex drive in their teens, while females reach it in their thirties". Pass a Method   talk  08:54, 7 June 2013 (UTC)
 * This answer assumes that "enjoyment" is correlated to "drive", which I think is a fair assumption (why would you really really want to do something that you don't enjoy?) but some people may disagree. --Lgriot (talk) 09:35, 7 June 2013 (UTC)
 * Can you be more specific? I'm guessing you mean 18-19? 117.55.68.44 (talk) 10:04, 7 June 2013 (UTC)
 * I think that the question is a little tricky to answer specifically. I expect that libido has been studied in more detail than enjoyment, mainly because the latter is more subjective and thus more difficult to quantify. The correlation between libido and enjoyment is unlikely to be good enough to use the one as a proxy for the other.  Factors that might lead to a mismatch include things like familiarity, types of relationship a person is likely to be in at each age etc.  For example, even though someone young might have an intense sex drive, they may be inhibited, or not comfortable with their own sexuality, which will change with age.  These and many other changing factors will have a strong influence on enjoyment of sex, and I'd suggest they may bias "peak enjoyment" to a significantly higher age.  Another significant factor is also what you mean by "sexual enjoyment" – you could mean the whole interaction, or you could even mean the intensity of the experience of orgasm: very different things.  — Quondum 11:51, 7 June 2013 (UTC)


 * This is a topic that is widely studied in the scholarly literature! Here's some refs to start you out. The abstracts are freely available, if you want to read the full article you may have to go to a library, or ask through Wikipedia's resource exchange here . The key was to search for "satisfaction", that's the word that academics will use in this context. Probably the best (and most general) is "Correlates of sexual satisfaction", which talks about age as well as other factors. "Sexual satisfaction among married and cohabiting individuals" is more specific, but has some stuff on age. Finally, there's "Sexual satisfaction among married women age 50 and older" , which is limited in scope, but part of a broader project that you can look into further. I have only skimmed these papers, but the general feel I get is that, though age can play a role, it is not a very strong correlate in sexual satisfaction. Relationship, age of relationship, and many other factors are stronger. Good news for the old folks (and those who wish to get old)! SemanticMantis (talk) 14:28, 7 June 2013 (UTC)

Light and Colour
1. We know that photon is energy carrier of light. But how does this photon is created or come from? For instance when a torch is switched on, it gives light and travel but from where do the photons come in it. Are they present all around already or they are created along with light at the speed of 300,000 km/h?

2. I have seen bull fighting in which bulls provoke towards red colour. But I have read somewhere that bulls are colorblind so they cannot see red color. If second sentence is true then how they are provoked? If first sentence is true then why only red why not blue, black, orange, white, etc? Britannica User (talk) 09:53, 7 June 2013 (UTC)


 * 1: A photon is created when an energetic particle, usually an electron, loses energy. Photon is destroyed when it is absorbed by a particle. A photon is not the energy carrier of light, it is light.
 * 2: A bull is not provoked by any one colour, it is provoked by the motion of the cloth. Plasmic Physics (talk) 10:08, 7 June 2013 (UTC)


 * ... but using a red cloth makes the spectacle more exciting for the onlookers!   D b f i r s   11:34, 7 June 2013 (UTC)


 * The simplest model of light comes from the Bohr model of the atom. Of course, it is highly simplified, and quantitatively the math only works with one-electron systems (H, He+, Li2+, etc.), but qualitatively it is fairly easy to understand, and explains both where light comes from (produced by excited electrons shedding energy to return to a less excited state) and where it goes (absorbed by electrons and exciting them).  -- Jayron  32  12:01, 7 June 2013 (UTC)


 * The Bohr model is not a model of light. It is a model of a atom with a single electron. Dauto (talk) 15:59, 7 June 2013 (UTC)


 * The Bohr models works well to explain how light is produced and absorbed by matter. As I already explained when I said "quantitatively the math only works with one-electron systems", what I meant by that was that the math only works with one-electron systems.  I'm not sure that you restating the same thing I did provided more information, but thanks for confirming my exact statement.  However, the Bohr model is also useful for understanding the interaction of light with matter, both in understanding where photons come from, and where they go.  -- Jayron  32  18:22, 7 June 2013 (UTC)


 * I didn't restate your statement. You said the Bohr model is a model of light and/or it's interaction with atoms. It isn't. Dauto (talk) 19:24, 7 June 2013 (UTC)


 * The Bohr model does not involve light interacting with atoms? Are you sure you are reading the same article I am reading?  Because I'm pretty sure light and its interaction with atoms shows up in there rather prominently... -- Jayron  32  19:30, 7 June 2013 (UTC)


 * Light shows up prominently in the article because the model is tested by comparing the predicted energy levels with the observed frequencies of the bands of light emitted and absorbed by those atoms. But it is not a model of light or it's interaction with matter. It did not introduce any new concepts about the nature of light. It uses the relationship between light frequency and the photon energy, true. But that relationship is not a new feature of the model, it had already been stablished about a decade earlier by Planck and Einstein. Dauto (talk) 20:31, 7 June 2013 (UTC)
 * But integral to the model is the way in which photons of light are absorbed or emitted by electrons. That's the entire model.  All of it.  -- Jayron  32  00:14, 8 June 2013 (UTC)


 * No, the model doesn't really say anything about how photons are emitted. If it did, you should be able to calculate the likelihood of a photon being emitted, and therefore the half-life of an excited state. The model has nothing to say about that. The Bohr model really is just a model about the energy levels of the electrons in a hydrogen-like atom. Dauto (talk) 14:25, 8 June 2013 (UTC)


 * But the OP didn't ask for likelihood of a photon being emitted. Sure, the Bohr model doesn't say that, but the OP didn't ask that question.  The OP asked for where the photons from a torch (flashlight) came from.  They come from excited electrons relaxing from higher energy levels to lower ones.  You know, exactly what the Bohr model says they come from.  -- Jayron  32  18:05, 8 June 2013 (UTC)


 * I'm not answering the OP's question. I'm commenting on your statement that the Bohr model is a model of light. Dauto (talk) 22:24, 9 June 2013 (UTC)


 * The way we understand production of a single photon is through a quantum mechanical equation. We use quantum mechanics because we are dealing with individual, countable numbers of particles; and so we can't rely on things "averaging out" - everything has to perfectly satisfy certain mechanical rules.  For example, energy must be conserved.  Momentum, in all its forms, must be conserved.  Other more abstract quantum conservation laws also apply, and our mathematical tools embodies such rules as operators.  These rules also apply to macroscopic systems, but we don't always need to worry about them - photon momentum is rarely a consideration in the design of ordinary household flashlights!  But these microscopic quantum abstractions must correspond to our real observations of real objects.
 * When you turn on a handheld flashlight, you complete a circuit; closing the switch is changing the potential energy at many places along the circuit. At the battery, this changed energy potential now allows a chemical reaction to occur; in the connecting wire, you are changing the potential energy of the wire (by applying a voltage); and finally, you get to the light emitter.  Two types of "bulbs" are now common: old-fashioned incandescent bulbs, and new light emitting diode lights.  In fact, these produce light in somewhat different ways.
 * The incandescent bulb uses a filament to carry current, losing electrical energy (kinetic energy from the electrons and electric potential from the immaterial part of the electricity that is coupled to the moving electrons). This energy becomes heat - incoherent kinetic energy of the atoms of the filament wire.  That heat is radiated through the process known as blackbody radiation.  On the average, we see heat radiating, and we know that heat is carried by lots of individual photons.  Few physics books study where these photons come from, but this detail was an important clue that led to our historical understanding of quantum mechanics.   An individual photon can be produced - because this is how energy works: when two entities are at different temperatures, they try to reach equilibrium.  If they are not in contact, the equilibrium can only be reached by exchanging electromagnetic energy - radiant heat.  The rate that the energy is released is governed by statistics - from the Stefan-Boltzmann law, you can see that the rate is related to the temperature difference; and if we zoom in to a single photon being emitted, this makes perfect sense.  A hotter atom is more probably going to "shake off" some energy in the form of electromagnetic radiation.  If a bulb were not hotter than its surroundings, it would emit and absorb photons at a constant and equal rate; and the statistics of these photons would be different: they would mostly be invisible to your eye.
 * If your light is an LED, the process is a little bit different - but at its core, it's fundamentally the same: an atom is forced into non-equilibrium by adding electric potential energy. It tries to lose the energy by "shaking off" a photon.  The difference is mostly that these atoms are excited by electric energy directly, and not by thermal (kinetic) energy.  We build special semiconductor materials with carefully-crafted energy band gaps, so that we force the energy excitation to arrive in specific sizes.  This way, we produce light of a specific color (because color of a photon is directly related to its wavelength, and therefor its energy).
 * So: photons are the embodiment of the energy and momentum that atoms shake off when they are excited. If we zoom in to look at the production of a single photon, all we can say is that the solution to a quantum-mechanical operator, subject to conservation rules, predicts the creation of a photon - i.e., the equations will be satisfied by the spontaneous generation of electric and magnetic fields that vary in time-and-space, with a specific and propagating wavelength.  In the average, across many billions of atoms, we see that the energy is "changing forms."  Nimur (talk) 16:22, 7 June 2013 (UTC)


 * There was a great Mythbuster's episode which demonstrated that bulls don't care about color. They tested red, white and blue cloths - identical results - no color preference whatever.  It ended with a scene where one of the presenters stands in the middle of a bull-ring, dressed in a bright red jumpsuit - standing very still.  A couple of professional cowboys (dressed in other colors) moved around.  The bull completely ignored the guy dressed in red.  They care about motion - and are otherwise color blind. SteveBaker (talk) 19:28, 7 June 2013 (UTC)


 * Agreed, but being a solid color might still be important. That is, it's easier for them to fixate on something which stands out from the environment.  If it was plaid, they might not stay focused on it as much.  And if it was paisley, they might avoid looking at it on principle. :-) StuRat (talk) 04:12, 8 June 2013 (UTC)


 * I suspect what Plasmic Physics said; he or she said above A photon is not the energy carrier of light, it is light. I think photon is not light, instead it is the force carrier (or mediator) of electromagnetic radiation or interaction (just like gluon is the force carrier of strong interaction, vector bosons are of weak interaction, and graviton,which is still to discovered, is of gravity), and also electromagnetic radiation includes not only light but also cosmic ray, gamma radiation, radio waves, etc. So, in my opinion Plasmic Physics is wrong. However, I am not sure whether he or she is right or wrong because I am not an expert in Physics instead I am a grade 10 student from India. 106.209.202.129 (talk) 06:27, 10 June 2013 (UTC)
 * Yes, except, of course, not all cosmic rays but only those that are gamma rays (which is usually not the case). The best way to think about this is to consider photons as excited states of the electromagnetic field. Just like the hydrogen atoms has energy levels, so does the electromagnetic field. The lowest energy state is the vacuum and the excited states are states with photons present. Just like you can describe the state of a hydrogen atom by specifying quantum numbers, the same is true for the electromagnetic field, where you have an infinite number of quantum numbers, each one can be identified with the number of photons with some momentum. Other partcles, including electrons quarks etc. have to be considered in the same way, they are just the quanta of certain fields. Count Iblis (talk) 12:32, 10 June 2013 (UTC)

Brown Pelican
What are some of the possible evolutionary pressures which resulted in the Brown Pelican's habit of diving for fish, while most other species of Pelicans engage in co-operative fishing from the surface? Llamabr (talk) 15:41, 7 June 2013 (UTC)
 * Any particular reason why this is worded like a homework question? Whoop whoop pull up Bitching Betty 16:57, 7 June 2013 (UTC)
 * Because I speak English like an educated adult? If you don't know, that's OK -- I don't know either.  I'm guessing that it's because in other parts of the world, larger pelicans spend their days in shallow water, which lends itself to successful fishing by the gulp, while brown pelicans live near the ocean, in deeper water, with waves, wind, and current.  It's just a guess, so I'm hoping for someone's more professional opinion. Llamabr (talk) 18:10, 7 June 2013 (UTC)
 * The wording of the question itself suggests that the Brown Pelican's behavior is aberrant or different from the norm. The Brown Pelican has evolved to use strategies that work in its environment to provide it with food, exactly like other species of Pelicans have (and exactly like all other life forms).  It isn't that the Brown Pelican's behavior is out of the norm if you accept that there was an ecological niche that was available and the Brown Pelican evolved a strategy to fill it.  -- Jayron  32  18:18, 7 June 2013 (UTC)
 * Thanks, Jayron. I didn't mean to make a value judgement.  I'm asking in particular, since your article on the brown pelican make this claim, "This bird is readily distinguished from the American White Pelican by ... its habit of diving for fish from the air, as opposed to co-operative fishing from the surface".  As you say, the brown pelican's behavior is well adapted to her environment, and she satisfies a particular niche.  I just wonder what that particular environmental niche is.  Deep water was my guess, but hopefully, you know better than I. Llamabr (talk) 18:35, 7 June 2013 (UTC)
 * Our article on Pelican does say that white pelicans hunt alone in deep water, which tends to support your guess. It's hard to answer this one with "epistemological" validity, because technically, in evolution there is no why; we only attribute it to explain how a design was favored by probability.  There is also the more mundane problem that most species, like the white pelican, have a wide range of behavior, though some is more common in one than another.  Actually, we can't fully rule out the possibility that the difference could be cultural (though I think it's highly unlikely), since there are cooperative feeding behaviors that have been seen to change this way, in which case there would be no physical explanation.  Still, all this aside, I'd guess you're right - it's just that I'm not sure that anyone can do more than guess at these things, when considered rigorously. Wnt (talk) 19:01, 7 June 2013 (UTC)
 * Can you follow the methods in my link below (I only get the gist...)? I think that's a bit better than guessing, but it is more focused on the nature of the process, rather than the nature of the pressure. SemanticMantis (talk) 22:23, 7 June 2013 (UTC)


 * Niches can be quantified/estimated, but of course we must fist agree on what exactly we mean by "niche" -- not an easy task! Ping my talk page if you want refs for that general question. SemanticMantis (talk) 22:27, 7 June 2013 (UTC)


 * One thing you could look into is the systematics of the clade, and see if you can figure out how/when the two bird species diverged. My guess is that it was probably sympatric speciation, with the selective pressure acting on behavior, through competition_(biology). There could also be additional reinforcement through sexual selection. Ok, now I'll dig up a ref... and see that "Lineage divergence events for which the mode of speciation could be deduced did not fit the predictions of either allopatric or sympatric models, but apparently involved either peripatric or parapatric processes.", according to "Phylogeny and Evolution of the Sulidae (Aves: Pelecaniformes): A Test of Alternative Modes of Speciation", here . I realize that this doesn't exactly answer your question of what provided the selective pressure, but it does give a name to the resultant process. Broadly, the pressure is almost always something to do with competition, predation, or environmental changes. In this case, I'd bet on competition/ needing new foraging niches. SemanticMantis (talk) 21:05, 7 June 2013 (UTC)
 * There's no demonstration of sympatric speciation in vertebrates of which I am aware, and our article shows it is rare to the point of contention. Why certain members of an interbreeding bird population would suddenly diverge into two different groups with assortative mating is a wide open question. μηδείς (talk) 22:35, 7 June 2013 (UTC)
 * I don't really see how two different styles of hunting would cause reproductive isolation. As I mentioned above, white pelicans can hunt in a solitary way in deep water (at least according to the article - I haven't researched the details, and many sources I see coming up saying that they "don't" plunge dive) so why don't they split into two species?  I don't see an obvious reason why either species of bird couldn't fly out from the nest on any given day and hunt either way, with the choice of which style to use being based on environment and physical characteristics, without being separated into two populations.  But it would be interesting to see some research on this.  In particular, white x brown pelican hybrids can exist  and so obviously it would be nice to see how they intermingle the hunting strategies.  I didn't see any obvious data about backcrosses, though, which is what you really want to get at the genes involved.  If you can find the genetic correlations you can start to speak of which traits are related, which is as close to "why" as you'll come. Wnt (talk) 23:45, 7 June 2013 (UTC)
 * Yes, in case it wasn't clear, my guess of sympatric speciation was probably wrong. The article concludes that parapatric or peripatric patterns are more likely. SemanticMantis (talk) 05:44, 8 June 2013 (UTC)

Rain
I know (bc Iread the article) that rain drops' size is limited to 6mm. But what about the density of raindrops per ft2 or even ft3? Is there a limit to how dense a rain event can be? excluding hail.165.212.189.187 (talk) 18:51, 7 June 2013 (UTC)


 * You can kinda work it out. A rainstorm that produces an inch of rain every hour is pretty decent - we get those in Texas fairly often - and they are quite impressive.


 * Math: 1" of rain over 1 square foot is 144 cu.in or 2.4 million cubic millimeters per hour - which is roughly 24,000 of your six millimeter raindrops per hour on every square foot (a 6mm raindrop is probably around 100 cubic millimeters). http://hypertextbook.com/facts/2007/EvanKaplan.shtml says that raindrops reach terminal velocities of around 10m/sec - 32 feet/sec.  If 24,000 drops have to hit the ground per hour to make an inch of rain - then around 6 raindrops hit the ground per second - but they fall over 32 feet in that second - so there so there is (very roughly) 6/32 = 0.2 raindrops per cubic foot.


 * However, this size of raindrops that you specify is "limited" to 6mm - that's the largest they can be. Rain says that the smallest raindrops are more like 0.1mm - which is 200,000 times smaller in volume than a 6mm drop - so you'd need 200,000 times more of them per cubic foot to get the same water deposition.  So if you were to get a 1"/hour rainstorm made up of the smallest droplets, you'd find 40,000 raindrops per cubic foot.  But that's more like a mist - I doubt it could fall as quickly - which would push the number per cubic foot up even further.


 * Bottom line: It's tremendously variable depending on the size of the raindrops.


 * According to our Rain article, the fastest rate of rainfall ever recorded was 1.2 inches per minute - so at that time there were 12 of the most gigantic raindrops per cubic foot.


 * Less than I'd have guessed. Great question! SteveBaker (talk) 19:23, 7 June 2013 (UTC)


 * Correct me if my logic is incorrect, but as far as density is concerned, you're looking at .00508% water per volume (if rain falls at 10m/s at a rate of 1.2 inch per minute, for an airborne volume of any given area by a height of 10m, you will have a height of .508mm of water over that same area, and .508mm*area over 10m*area is 0.000508m/10m = 0.0000508 = 0.0058%) 64.201.173.145

(talk) 20:40, 7 June 2013 (UTC)


 * That's true if you're being asked the density of water in the air - but we're being asked "the density of raindrops per...ft3" - which I take to mean "number of raindrops per cubic foot"...hence my answer. SteveBaker (talk) 20:55, 7 June 2013 (UTC)


 * Good answer!, But yes, that does seem low. But how would I know? We don't really perceive rain in drops/ft^3, we perceive it (roughly) as a flux, drops/ft^2/s. So, for the bonus round, can you convert your answer to the latter units? If we can assume they are all at terminal velocity, it shouldn't be too tough... SemanticMantis (talk) 22:21, 7 June 2013 (UTC)


 * Well, it's easiest to take it from the beginning again - 1" per hour is 24,000 6mm drops per sq.foot/hour - or about 6 drops per sq.ft per second...which seems to be about what you see if you watch ripples in a puddle in a torrential downpour. In that most extreme ever downpour of 1.2" per MINUTE, you'd see around 432 raindrops per sq.foot per second(!!).


 * But I have to caution you again: The real problem with this math is that the volume of a raindrop is proportional to the cube of the diameter and our Rain article says that raindrop diameters between 0.1mm and 9mm have been observed. That's a 730,000 to 1 ratio between the volume of the smallest and largest raindrops - and a 730,000 to 1 variation in the number of them per cubic foot or the number per square foot per second.  That enormous variation makes this result a bit like saying that the population of the US is approximately 10 people.  SteveBaker (talk) 03:20, 8 June 2013 (UTC)


 * Note that it's quite possible that you could fit more raindrops in a cubic foot than normally occur. That is, clouds just don't produce rain at the maximum rate possible.


 * Also, if rain fell at a greater rate, it would just form more complex patterns than drops. I imagine waterfalls are a good place to study the structure of large volumes of high density falling water. StuRat (talk) 03:57, 8 June 2013 (UTC)

Just to clarify: I was asking about the largest possible raindrops in the densest possible area. I was also thinking about waterfalls and additionally about the largest raindrops recombining at some point. 165.212.189.187 (talk) 14:17, 10 June 2013 (UTC)

Has anyone tried using webcams, or Skype or whatever, to allow pet parrots to communicate?
Just something I was wondering when browsing parrot videos on YouTube. Parrots do seem to love watching videos of other parrots. — Preceding unsigned comment added by 31.185.175.78 (talk) 22:08, 7 June 2013 (UTC)
 * I don't know, but that's an awesome idea! I suggest you look for newsgroups or listservs dedicated to parrot enthusiasts. SemanticMantis (talk) 22:16, 7 June 2013 (UTC)
 * I know that it has been tried multiple times with dogs, but I'm not sure if it has been tried with parrots. ö   Brambleberry   of   RiverClan  22:20, 7 June 2013 (UTC)