Wikipedia:Reference desk/Archives/Science/2012 February 8

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February 8

Embryological Skeleto/muscular development

Hello. I've been looking to find out information on whether in a developing human embryo, does the skeleton/bones or the muscle develop first? My understanding is that both are produced simultaneously through differentiation of the mesoderm, but I have surprisingly been unable to find much on this. Any references (preferably online) that would shed light on this matter would be greatly appreciated. 114.77.39.141 (talk) 03:45, 8 February 2012 (UTC)

Hmmm. Both can emerge from somites, in limb bud development, or from branchial arches. Chondrogenesis involves the condensation of precartilage into cartilaginous structures. Muscle patterning involves a more dynamic process involving founder cells/muscle precursor cells. See [1] for a useful reference. Wnt (talk) 06:26, 8 February 2012 (UTC)

This reference [2] gives more about tendon development, the physical link between bone and muscle. It seems that bone, tendon, and muscle are independently specified during development from the somite stage onward; but there is cross-talk from bone to tendon and tendon to bone (at least, in the expansion of projections already present) and from muscle to tendon also. In a quick search of OMIM ("enthesis"; "tendon AND insertion") I didn't find any condition where muscles form independently of tendons (and thus perhaps bone), nor have I ever heard of it. Given Nature's fondness for cruel juvenile humor such as the imperforate anus I'm quite surprised really. The authors of the paper I cited remark on the absence of similar mutants in mice (at least for FGF-based mechanisms). But somites, bone, muscle, tendon - these are a large part of the overall vertebrate body plan, and so we should expect the situation to be complicated and well regulated. Wnt (talk) 14:18, 8 February 2012 (UTC)

OP here. Thanks for both responses; however I must admit I am lost by all the medical terminology. Especially with the second article, could someone direct me to where specifically it talks about the developmental stages of skeletons and muscle. 114.77.39.141 (talk) 11:09, 9 February 2012 (UTC)

That paper focuses on more on tendons, which to me seem a crucial conceptual and physical link; Figure 3 illustrates that at mouse E12.5 the differentiating bone and muscle are separated by a band of tendon progenitors which are still relatively unorganized until E13.5. Note: The "E" notation for mice is less sophisticated than it looks - it just means the number of days since a vaginal plug (evidence of mating) is observed, with the first day called "0.5" because it is assumed they mated sometime during the night. Sometime around day 19-20 birth occurs, but baby mice are even less developed than baby humans (mouse eyes open at 13 days after birth vs. humans in the 6-month fetus; I think epithelial stratification [an equivalent of amphibian metamorphosis] occurs around 3 months in humans vs. E11.5 or so in mice). Wnt (talk) 08:19, 10 February 2012 (UTC)

Brownian motion as perpetual motion

Could Brownian motion be actually considered the perpetual motion in a closed system?--46.204.55.76 (talk) 05:37, 8 February 2012 (UTC)

If you do, you might as well include planetary orbits, too. StuRat (talk) 05:41, 8 February 2012 (UTC)

When it comes to energy, there ain't no such thing as a free lunch. See Maxwell's demon and Brownian ratchet. Red Act (talk) 05:46, 8 February 2012 (UTC)

To make things a bit simpler: Perpetual motion is not an impossibility; there's lots of things in the universe which are essentially in perpetual motion; the molecules in the air around you are in perpetual motion. However you cannot use such motion to do work; any attempt to use a system in perpetual motion to do work will result in the system "winding down", and losing energy until it reaches some state of equilibrium and becomes unable to do more work. --Jayron32 05:50, 8 February 2012 (UTC)

Except that's not really true. The molecules in the air, or things illustrating Brownian motion in general, still have continual energy inputs, e.g., energy inputs from the sun continually add energy to the molecules in the air in the atmosphere. It's not a closed system operating indefinitely, which is required for perpetual motion. --jjron (talk) 11:53, 8 February 2012 (UTC)

My understanding of it, building on Jjron's comment: Real-life (as opposed to ideally-modeled) Brownian motion is usually something like the motion of very small particles of say, dust, as have molecules of gas (e.g. air) collide with them. The molecules are only colliding because they are themselves moving — they have kinetic energy in the form of heat. Every time they collide with the dust particle, they lose a little energy. If they were thermodynamically isolated from any additional temperature source, they would eventually expend all of their energy on colliding and it would stop moving. So it's not really perpetual — it runs down, like everything does, if there isn't a source of input energy (e.g. if it is in a closed system). In practice such systems probably never wind down to that stage, I speculate, because the amount of energy needed isn't much, and once you approach temperatures like absolute zero, all sorts of other weird things start to occur... --Mr.98 (talk) 12:51, 8 February 2012 (UTC)

To be clear, a closed system is one which can exchange energy but not mass with its surroundings; this is in contrast to an isolated system, which can exchange neither energy nor mass. A thermodynamically closed system will exchange energy with its surroundings as long as the system and its surroundings are at different temperatures; if you have a sealed container with a hot beverage in it, heat (energy) will be conducted through the walls of the container until the container (and the coffee inside) reach the same temperature as their surroundings. A thermodynamically isolated system, on the other hand, can't exchange energy with its surroundings. All the parts of the isolated system will reach equilibrium with themselves, but the total amount of energy present and the effective temperature of that system will remain constant. In practice, it's impossible to achieve complete thermodynamic isolation, as energy can even be conveyed across hard vacuum by electromagnetic radiation.

The closed system will 'wind down' only until it reaches equilibrium with its environment. (Note that this works both ways—a cold can of soda will also absorb energy from its surroundings until equilibrium is reached.) The isolated system, on the other hand, would – in principle – remain at a constant temperature forever.

Mr. 98's statement about Brownian motion running down is mistaken. While a gas molecule that collides with a dust particle may itself lose some kinetic energy, that energy is transferred to the dust mote, which in turn can transfer energy to another gas molecule in the future. In an isolated system, the total energy (and temperature) of the gas-dust mixture will remain constant forever. (In a merely closed system, the gas-dust mixture will exchange energy with its surroundings until they're both at the same temperature, and then the system will stay at that temperature.) If you wait long enough, you'll find that the highest concentration of dust will be near the bottom of the box and very few dust particles will be near the top, but the dust will never settle completely; there will gradually be an equilibrium established between Brownian mixing and gravitationally-driven settling. (This is a form of sedimentation equilibrium.) TenOfAllTrades(talk) 13:50, 8 February 2012 (UTC)

I was assuming that the energy would not be exchanged with 100% efficiency and some of it will be converted into a non-useful form, ergo the running down. Is this wrong? --Mr.98 (talk) 14:23, 8 February 2012 (UTC)

Gas collisions are generally elastic collisions. What form would collisions due to heat energy be converted to? Heat? 216.197.66.61 (talk) 15:41, 8 February 2012 (UTC)

I'd considered that, but wasn't sure. Good to be corrected! (Though the fourth paragraph of the elastic collision article does put somewhat of a limit on that if we are talking about molecules, no?) --Mr.98 (talk) 17:11, 8 February 2012 (UTC)

Once you get into situations that are more complex than monatomic gases, then you have to account for energy finding its way into other modes—that is, into things like rotational and vibrational excitation of the molecules. The energy is always conserved, though, and the equipartition theorem even means that at equilibrium each mode stores essentially the same amount of energy. TenOfAllTrades(talk) 19:05, 8 February 2012 (UTC)

Sun leaving main sequence between 1 and 5 billion years from now

How much bigger suppose the sun to get between 1 and 5 billion years from now. Our article said 10% luminosity in 1.1 Gyr, 3.5 Gyr is 40%. What is 10%, 20% mean by growing luminosity. Does sun get 10 times larger in size, every billion years, 20 times larger in size every billion years. Is sun's RGB 250xs current radius 5000 times more luminosity it means 5000 times brighter, or 2000 times brighter. If 5000 times brighter means habitable zone surface temperature everywhere in our solar system is too hot,even 100 AUs away. 2000 times brighter is habitable zone at Saturn system, Neptune system, or Pluto system? I am all messed up confused right now.--69.229.39.25 (talk) 06:06, 8 February 2012 (UTC)

I notice that neither this nor your previous query further up the page have yet been answered. To be honest, I started to yesterday, but then gave up because I found both queries too confusing. Each seems to have several intertwined questions, which makes the task of answering more daunting. Also, both are written in English sufficiently imperfect as to be difficult to understand. You might want to think a bit about exactly what you want to know, and then write one or more simpler questions, clearly separated. In the meantime, Section 5 'Life cycle' within our article Sun includes a graph which you might find helpful, though the concept of effective temperature is not wholly straightforward.

To address what I can: the Sun's radius will only increase to about 110% of its current value in 1 billion years from now, and to about 130% of today's value in 5 billion years from now. I'm sure that you can work out how much that will increase its surface area, which is the main cause of its gradually increasing luminosity during the main sequence part of its lifetime, during which its surface temperature will remain roughly the same. Such modest changes in size are of course trivial compared to the distance of the planets from the Sun – for example, the Earth orbits the Sun at a distance of about 214 times (21400% of) the Sun's current radius.

When the Sun, now with a little less mass after 5 billion more years of fusion, leaves the main sequence and becomes a Red giant, it will indeed grow to a size comparable to the size of the Earth's orbit (and will for this reason will become more luminous), but its surface temperature will also drop (lessening the increase in luminosity a little bit). Since the changes in mass and so on associated with these processes will, as you have already learned, cause changes to the orbits of the planets, it's difficult to calculate exactly where everything will end up, and I'm not familiar with the latest theories. Where the Habitable zone will be and whether any terrestrial-type planets will be in it depends partly on how you interpret that term: consider also that some moons of Jupiter and Saturn, for example are now thought potentially life-bearing right now, for reasons independent of Solar heating.

Hope this helps a little. {The poster formerly known as 87.81.230.195} 90.197.66.165 (talk) 00:32, 9 February 2012 (UTC)

nerves to size depiction chart required

I am trying to find a chart of the human body which depicts skin area size in proportion to the richness of nerve cells in that area. Thus, for example, eyes, lips, hands and feet are shown much larger than areas such as the forearms and thighs. I remember that genitals are not depicted at all, as the testes, for example, would be the size of cannonballs! Myles325a (talk) 10:58, 8 February 2012 (UTC)

I know the picture you mean, although in the version I recall the genitals were depicted, which is what made it so striking! The closest I have been able to find so far is the cortical homunculus, but I realize that's not quite what you're looking for.--Shantavira|^{feed me} 11:50, 8 February 2012 (UTC)

Try here. Bazza (talk) 13:43, 8 February 2012 (UTC)

As for the number of nerves in the genitals, it's not particularly high. Those nerves can trigger pleasure without being very numerous. More nerves are present where needed, such as the hands, for delicate work with tools, and the lips and tongue, for separating inedible things like pits and bone fragments from our food. StuRat (talk) 20:00, 8 February 2012 (UTC)

Op myles325a back live. Thanks guys. It's called a Motor / Sensory Homonculus. I needed it for an essay I'm writing. Oh, and StuRat is probably right about the genitals, leastways for MOST guys that is. My weiner is prehensile. Myles325a (talk) 02:47, 9 February 2012 (UTC)

Well I've lived on this earth for over 50 years and I've never seen or heard of a penis that can wind itself round a branch of a tree and hold on... --TammyMoet (talk) 10:09, 9 February 2012 (UTC)

Well, now you have: Hectocotylus. StuRat (talk) 05:56, 10 February 2012 (UTC)

Unusual fungus

I took this photo today at a park in Byron Bay, NSW, Australia. I'm wondering what type of fungus it is. http://tinypic.com/r/33ur9ft/5 180.181.84.225 (talk) 12:34, 8 February 2012 (UTC)

In a very broad sense, this looks like a type of fungus called a Puffball. Beyond that, however, we'll have to wait for a proper mycologist to come and identify which type of puffball. --Jayron32 14:52, 8 February 2012 (UTC)

I'm no mycologist, but it looks pretty similar to Lycoperdon perlatum. If you upload the shot to Mushroom Observer, you're likely to get a better ID. SmartSE (talk) 15:05, 8 February 2012 (UTC)

It's clearly this type of mushroom, which is labeled as an amanita, species not specified. Looie496 (talk) 02:16, 9 February 2012 (UTC)

Oh, wait, that's your picture, isn't it? Heh. Looie496 (talk) 02:19, 9 February 2012 (UTC)

Do you mind?! I don't resemble that fungus in the slightest, 'cepting I'm white.Myles325a (talk) 02:51, 9 February 2012 (UTC)

about electrical plug

why in a electrical plug, the earthing terminal is more thicker and longer than other two terminals? — Preceding unsigned comment added by 125.19.211.130 (talk) 13:00, 8 February 2012 (UTC)

So that it will fit in the socket. 180.181.84.225 (talk) 13:04, 8 February 2012 (UTC)

...in only one direction. --184.100.88.44 (talk) 03:07, 9 February 2012 (UTC)

It longer because if an electrical lead is over tensioned and pulls away from the terminals, the last conductor you want to go open circuit is the earth. It is thicker, because one wants the earth to have the lowest residence and so a thicker and longer conductor gives you that.--Aspro (talk) 13:13, 8 February 2012 (UTC)

Can I take it your are talking about this type of plug. Both ensure that on insertion into the socket the equipment is earthed before any current can flow and that the power circuit is disconnected before earth continuity is disconnected on extraction of said plug.--Aspro (talk) 13:34, 8 February 2012 (UTC)

And on UK plug sockets, at least, the longer prong of the earth makes contact with a simple mechanism which withdraws covers from the live & neutral terminal holes. Absent the earth prong, the live and neutral remain covered and thus pretty much inaccessible. --Tagishsimon (talk) 13:37, 8 February 2012 (UTC)

Think the OP is referring not to the UK but the old UK BS 546 standard which still in existence in many parts of the world that the US Empire din'nt reach. Perhaps he can come back and elucidate.--Aspro (talk) 14:20, 8 February 2012 (UTC)

There could be all sorts of "mechanical" explanations for various modern plugs, but I think at the basic level Aspro has it right in saying that "one wants the earth to have the lowest residence and so a thicker and longer conductor gives you that." HiLo48 (talk) 20:35, 10 February 2012 (UTC)

"Resistance". Whoop whoop pull up ^{Bitching Betty | Averted crashes} 18:37, 11 February 2012 (UTC)

Earth spin redux

sir, What will happen if the speed of rotation of earth about its own axis is doubled. The distance between the sun and earth will increase or decrease? — Preceding unsigned comment added by Tobyaickara (talk • contribs) 13:39, 8 February 2012 (UTC)

See the answers where you asked this question previously. — Lomn 13:50, 8 February 2012 (UTC)

Violating the 2nd law of thermodynamics leading to violating the 1st law?

Is this true that if you can violate the 2nd law of thermodynamics, it will eventually lead to violating the 1st law?

Please tell me if this is a valid example.

You have a river flowing downstream with a turbine extracting energy from it that is 100% efficient. You then have some mechanism that brings the water downstream to the top of the river that is 100% efficient at moving that water to the top in a closed system. The turbine and the mechanism are both examples of violating the 2nd law of thermodynamics. Extracting energy from the river with the turbine is essentially extracting energy from nothing thus violating the 1st law.

Correct or incorrect? ScienceApe (talk) 16:34, 8 February 2012 (UTC)

I think a properly implemented Maxwell's Demon should violate only the second, provided that the energy it extracts comes out of the hot or cold reservoirs it creates. Wnt (talk) 18:02, 8 February 2012 (UTC)

Speaking of which, someone scroll down that article around where it mentions Atomoscience and tell me if your BSometer is in the red also. Wnt (talk) 18:06, 8 February 2012 (UTC)

I don't think it is "BS" (the main researcher seems to be a reputable academic), I just think it is a very new field that isn't notable at this stage. Therefore, I have PRODed the article. --Tango (talk) 20:00, 8 February 2012 (UTC)

Actually I meant the Maxwell's Demon article, which has a section "In 2005, Raizen and collaborators showed how to realize Maxwell's Demon for an ensemble of dilute gas-phase atoms or molecules. The new concept is a one-way wall for atoms or molecules that allows them move in one direction, but not go back. The operation of the one-way wall relies on an irreversible atomic and molecular process of absorption of a photon at a specific wavelength, followed by spontaneous emission to a different internal state. The irreversible process is coupled to a conservative force created by magnetic fields and/or light. Raizen and collaborators proposed to use the one-way wall in order to reduce the entropy of an ensemble of atoms." On a closer look I think this is legit, but just sounds like something unlikely. I think the "prod" is unfortunate, though you might have it on the merits. Wnt (talk) 20:40, 8 February 2012 (UTC)

In your scenario, the first law isn't being violated as long as the only thing the turbine powers is the pump. But if some of the turbine's power is used to power something else in addition to the pump, and the system magically didn't slow down to a stop, that would be a violation of the first law. Red Act (talk) 19:10, 8 February 2012 (UTC)

The second law of thermodynamics is a statistical result about large systems of particles that are all behaving according to more fundamental laws of physics. As long as the particles are following the more fundamental laws, then they'll probably obey the second law of thermodynamics. In a hypothetical scenario where the second law is violated, either no laws of physics are violated and you're just proposing impossibly good luck, or something more fundamental is breaking. If the scenario is constructed by breaking conservation of energy, then the first law of thermodynamics is also being broken, but there are plenty of other ways you could decide to hypothetically break physics. Rckrone (talk) 04:02, 9 February 2012 (UTC)

the role of hormones

1. What are the specific roles of hormones in spermatogenesis in a human male?
2. How can the following processes give rise to genetic variation? -fertilization and -vegetative reproduction?
3. Which type of organism will exhibit the greatest genetic variability and why? -Asexually reproducing organisms and Self-fertilizing organisms — Preceding unsigned comment added by 41.205.4.87 (talk) 18:03, 8 February 2012 (UTC)

Pardon, but this sounds like a homework question, and if so people here prefer to have students work through them on their own, at least until they get stumped and have a question of their own to ask. I've taken the liberty of adding a few Wikilinks to your question above - tell us where they fall short. Wnt (talk) 18:09, 8 February 2012 (UTC)

asexual reproduction

one way of asexual reproduction is by vegetative propagation; this implies the offspring are gotten from the parent, according to me, there should be no genetic variation between the parent and the offspring and i am unable to find how that is possible. Any contribution will be of great help!! — Preceding unsigned comment added by 41.205.4.87 (talk) 18:35, 8 February 2012 (UTC)

When a plant undergoes vegetative reproduction, you are correct, there is no significant genetic variation, and plants that depend on vegetative reproduction (e.g. strawberries and bamboo) often form clonal colonies. As for "how that is possible", we can get into what physiological traits allow for such reproduction if you like (e.g. not all plants can be grown from cuttings), but the basic idea is that, if it's possible for a certain species, then the vegetatively grown "individual" must be genetically identical to the parent, because there has been no introduction of new genetic material, and no chance for recombination. There are a few edge cases. Some plants (e.g. spider plants) naturally form chimeras, and a cutting my only have some of the genotypes present. If your question is more about evolution in a clonal organism, note that very few things solely reproduce in this manner, and usually there is some opportunity for sexual reproduction. Fun fact resulting from clonal reproduction: every granny smith or red delicious apple you've ever eaten has come from a single individual. The same genetic material is maintained by cuttings and grafting :) SemanticMantis (talk) 19:00, 8 February 2012 (UTC)

(edit conflict) Vegetative reproduction, like many types of asexual reproduction, is basically a form of cloning, or just growth (for some plants). You're right that it doesn't add genetic variation. It's never the exclusive form of reproduction — it's something that happens under specific circumstances, often stressful ones where sexual reproduction would be riskier. There is usually (always?) some other form of reproduction that introduces in genetic variation, as your reasoning would lead you to conclude. Usually when we talk about vegetative reproduction is in the context of artificial reproduction, when humans are the ones doing the cloning, and have purposefully limited sexual reproduction (with seedless varieties being the ultimate extension of this — plants which cannot self-reproduce without being cloned or grafted). --Mr.98 (talk) 19:05, 8 February 2012 (UTC)

Except that reasoning is backwards. The general wisdom, and observation, is that organisms capable of both sexual and asexual reproduction utilize the asexual variant unless they are under stress. This is certainly the case for hermaphroditic nematodes and some species of rotifer. Vertebrates capable of asexual reproduction typically do so only when there are no mates available, at least in the case of parthenogenic lizards. Someguy1221 (talk) 22:49, 8 February 2012 (UTC)

Ah, you are right. How interesting. --Mr.98 (talk) 23:42, 8 February 2012 (UTC)

And now that you mention rotifers, the Bdelloidea are certainly an edge case. All individuals are female, and they only reproduce partenogenetically. The closest they ever come to sex is incorporating random DNA when they are reanimated from a dessicated state o.O SemanticMantis (talk) 01:45, 9 February 2012 (UTC)

That is some crazy sh*t. --Mr.98 (talk) 15:16, 9 February 2012 (UTC)

Also, mutation may come into play here. Let's say one cell mutates in a way that allows it to better retain water than the others. This cell is more likely to survive and reproduce than the others during dry periods. Over time, more of the plant will be composed of such cells, and more of the new individuals that survive will be, as well. Combine this with organisms being able to select their own rate of mutation (by only having one copy of a gene or many copies, for example, or exposing the DNA to UV in sunlight), and you get a viable form of reproduction with the mutation rate fairly high. StuRat (talk) 19:53, 8 February 2012 (UTC)

I really doubt individual cell mutation has too much to do with it in complex multicellular organisms. I think you overestimate how important any individual cell can be in a positive sense. --Mr.98 (talk) 23:44, 8 February 2012 (UTC)

Plutonium inventory

Is there a good estimate on how much plutonium was produced during the runtime of all nuclear power plants since the 1940s? --Stone (talk) 20:12, 8 February 2012 (UTC)

Do you mean civilian, military, or both? Do you mean plutonium that was separated or are you including plutonium that remains in a form of waste? There are fairly nice numbers for worldwide stocks of military plutonium that was separated. There are some hand-wavy figures for plutonium content in wastes (which could be separated, but isn't). Civilian-generated plutonium is only separated in reprocessing plants, in some countries, and very careful inventories of those exist. Depending on what you're asking for specifically there are more or less better estimates, but all of it is complicated and with heavy qualifications. (e.g.) The ranges I have seen for separated plutonium are between 300-500 tonnes. I've no idea about unseparated, but it's quite large too. --Mr.98 (talk) 23:40, 8 February 2012 (UTC)

Thanks! This is exactly what I was searching for! Perfect!--Stone (talk) 18:34, 9 February 2012 (UTC)

How long does ice in the Antarctic ice sheet last

Antarctic ice sheet article states that the ice sheets began 45-34 mya. Have they mostly covered Antartica continuously since this time? (Any evidence for major periods of decline?) Also how long does it take for ice to flow from the time it was originally deposited in the interior to the time it breaks up in the ocean. How old is the oldest ice to be found there? SkyMachine ⁽⁺⁺⁾ 22:14, 8 February 2012 (UTC)

I believe most of the ice only lasts for a small fraction of that period. That is, it flows to the sea and melts and is replaced by new ice. However, there may be spots where it is prevented from flowing to the sea, such as in a volcanic caldera, where the ice may be much older. StuRat (talk) 23:03, 8 February 2012 (UTC)

Indeed, even the lowest portions of the oldest ice cores are believed to be less than 1 million years old. Someguy1221 (talk) 23:09, 8 February 2012 (UTC)

Some of the oldest ice on the continent is believed to come from the Antarctic dry valleys, where claims of ice (usually mixed with soil) up to 8 million years in age have been made. Most of the ice on the continent is far younger though as the large ice sheets slowly flow towards the oceans and carry much of the oldest ice out to sea. The oldest reliably dated ice from ice cores on the ice sheet are about 800000 years old. There is speculation that some of the ice at the base of the ice sheet is older, perhaps 1.2 million, but basal ice tends to be highly disturbed by turbulent flow and/or basal melting, which makes it very difficult to date reliably. Dragons flight (talk) 21:05, 9 February 2012 (UTC)

Brain and learning

Is there a certain part of the brain responsible for human capability of learning? If so, does this part of the brain also affect other things? Thanks! 64.229.180.189 (talk) 23:47, 8 February 2012 (UTC)

More than one part of the brain, since there's more than one type of learning. Learning how to walk, for example, is quite distinct from learning the capital of North Dakota. Perhaps the better question would be if there are parts of the brain which don't learn, that is, which operate on instinct alone. I believe so, such as the brain stem, which regulates breathing and heartbeats, neither of which needs to be learned. Portions related to the senses are a mixed bag, as the parts that process the images, smells, sounds, etc., initially don't require learning, but the associations with events, objects, dangers, etc., do. StuRat (talk) 00:17, 9 February 2012 (UTC)

See long term potentiation for a major variety of learning; see the hippocampus for a major seat of memory. Wnt (talk) 15:00, 9 February 2012 (UTC)