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April 13

Minimum population required for the survival of a race.

The article on Angam Day currently states:

Upon eclipsing a population of 1,500, a number considered to be the minimum required for the survival of a race, Angam Day was declared.

Does a race really need a minimum population of 1,500 to survive? If true, why? If false, how many people does a race need to avoid extinction? Thank you in advance. --190.19.69.254 (talk) 04:33, 13 April 2013 (UTC)

Hmmmm. That's a pretty ugly part of that article. I would much prefer that the term ethnic group had been used throughout. Race is an unclear word with unfortunate connotations. The article Nauruan people, linked from Angam Day, avoids the term race completely. I note that the claim of 1,500 being the minimum number for a race to survive is unsourced. That's not good, and only makes things worse. I went hunting and couldn't find a source myself. You've got me thinking about what we should do with the article. HiLo48 (talk) 04:54, 13 April 2013 (UTC)

Reads like unmitigated bullshit to me. What makes an ethnic group (or race) a distinct unit is a shared culture. I'm not sure there's any arbitrary lower or upper limit on that, merely that the group has a certain level of cultural cohesion and distinctiveness, and I certainly can't find any literature that indicates that there's some official or "scientific" or whatever reason that would indicate that 1500 is some magic number. --Jayron32 05:00, 13 April 2013 (UTC)

The article clearly states that the number 1500 came from Brigadier General Griffith, the Australian administrator. It does not claim that the number has any deeper validity. It doesn't cite a source for that, but I don't see anything implausible about it. Looie496 (talk) 05:17, 13 April 2013 (UTC)

The article makes that assertion, but that assertion (nor the quote from Griffith) has any sources to support it. The big issue is if Griffith said directly, "if the Nauruans were to survive as a race, the population should be no less than 1,500.", then we would need to put quotes around that, as I have done, and provide a footnote to make it clear where the quote comes from. Without sources, the statement really shouldn't stand, however. --Jayron32 05:22, 13 April 2013 (UTC)

For what it's worth, I've managed to work out that the person referred to here is Thomas Griffiths (general). I'll add a wikilink to our article (and fix the spelling). Looie496 (talk) 16:46, 13 April 2013 (UTC)

The problem is extremely difficult for human populations because "survive" can mean "not all die" or "survive as a distinct culture". But if a group of people were cut off from the rest of humanity for some considerable time (either physically cut off - or culturally unwilling to take mates from outside of their cultural group) - then genetics and inbreeding would be the problem. The considerations in our Minimum viable population article would take effect. For large vertebrates, the accepted number is between 500 and 1000 individuals if the population is carefully managed (ie scientists decide who breeds with who!) - and more like 4,000 if not carefully managed. On that basis, you might think that 1500 people isn't enough - but it's in the right ballpark, and this isn't an exact science. But that kind of complete elimination of mating outside of that cultural group seems unlikely.

A classic example of how this can happen is the Pitcairn Islands - which was uninhabited until six men, eleven women and a baby arrived there after the infamous "Mutiny on the Bounty" incident in 1790. Since the island was hundreds of miles from any other land - and not of much interest to anyone, the hapless mutineers were left alone - and (inevitably) the population steadily grew to around 600 people. This is widely accepted as being the most inbred group of humans in the world. But even with such extreme in-breeding, the occasional outsider has managed to add enough genetic variation to keep the population viable - and according to most studies, they aren't suffering too badly.

Who says they aren't suffering too badly? Law enforcement in the Pitcairn Islands. Seems like they were raping children with impunity there till 1999. Sagittarian Milky Way (talk) 02:57, 15 April 2013 (UTC)

So we can conclude that there isn't some magical cutoff at 1500 people...at least not genetically. SteveBaker (talk) 13:16, 13 April 2013 (UTC)

Since the entire human race has an effective population size of probably around 5,000 (if not less) then no. Culture does weird things though. ~ Amory (u • t • c) 17:26, 15 April 2013 (UTC)

someone wrote a program to find that out. i just can't remember who, or the program name, or when. 70.114.248.114 (talk) 03:48, 14 April 2013 (UTC)

Is 2 centuries a long enough test to falsify the 1,500/4,000 individuals inbreeding rule? Sagittarian Milky Way (talk) 02:57, 15 April 2013 (UTC)

Seasonality of human hair growth

My friend, in her early seventies, is convinced that her hair grows more quickly in the Spring and more slowly in the Winter. Her evidence for this is the much shorter length of time it takes for white roots to appear after she has dyed her hair. (I have no reason to doubt her eyesight.) This sounds like folklore to me but I can find nothing to indicate that anyone has ever studied the matter. Thank you for your help. — Preceding unsigned comment added by 109.12.63.61 (talk) 07:24, 13 April 2013 (UTC)

This is an interesting question, as it is one of the few topics on which I think the written word does not match reality. If you google (google "rate of hair growth") or search in textbooks, you find almost all estimates lie in two categories: Those which say hair grows at a constant rate of 0.5 inch (13 mm) per month no matter what (the Wiki article human hair growth is one example), and those that say it varies depending on age, health, intake of certain vitamins, race, and a few other minor factors and is between 7 mm and 20 mm per month, which seems much more likely. What seems difficult to find is any refrence that says it varies depending on where on the head it grows from, and there's no reference that says it is seasonal, depite the fact that it most definitely IS seasonal for other mammals. Hairdressors are taught that it grows at a constant rate.

However, in my experience, it grows considerably faster on the back of my head and neck, and a lot slower on the top of my head. It also grows quite a bit faster in autum and slowly during winter. This is reflected in when I need to go to the hairdressor. I'm also in my seventies. I'm sure that it grew faster when I was younger, but suspect that the variation in growth rate was hidden when I had a younger thicker hair.

In my experience, cutting hair very short and cutting frequently casues it to react by growing faster. However hairdressors are taught that that is a fallacy. I had a friendly argument about it once with a hairdressor friend, so I experimented over a two year period, keeping records. I was right. However, I live in a hot climate, and cutting hair short probably raises skin temperature. If I lived in a cold climate, it may well be that cutting hair short would lower the skin temperature and therefore the growth rate. This suggests a conflict between two factors: skin able to grow hair faster when it is warm during warm weather, and the evolved capability of mammals to grow a thick winter coat in time for winter.

Wickwack 121.215.67.60 (talk) 08:41, 13 April 2013 (UTC)

You're in your seventies and it still grows on the top of your head? I'm jealous. HiLo48 (talk) 08:45, 13 April 2013 (UTC)

Don't fret too much. It grows so slowly on top, and so thinly, it might as well not bother. But I still need to have it cut from time to time. Wickwack 121.215.67.60 (talk) 08:54, 13 April 2013 (UTC)

Sorry Wickwack, although I defer to your superiority in age, I'm afraid hairdressers are taught that hair grows at different rates according to both position on scalp and time of year. Now if only I could find a reference for it. (I know they're taught it as I sat in on some of the sessions for the hair students when I was a therapy mature student about 5 years ago.) --TammyMoet (talk) 13:45, 13 April 2013 (UTC) I found this study which looks like a pretty neat exemplar of how to do citizen science! --TammyMoet (talk) 13:51, 13 April 2013 (UTC)

Very good Tammy! I only wish that age did bring superiority! Perhaps hairdressers are better taught in your country (the UK if I remember right), or perhaps knowlege has been updated since the hairdressors I've known did their training. I've found them adamant that it grows at a constant rate. The study you found has some limitations though - for instance they assert that temperature has little to do with it, but haven't proved it. One reasonably expects that hair growth rate is dependent on skin temperature, but the skin temperature relationship to climate would be confounded by the human practice of adjusting clothing to suit the season. They tested only one person. Did they check that she had the same diet/nutrition/calorific intake throughout? Wickwack 121.221.31.213 (talk) 14:34, 13 April 2013 (UTC)

You're indeed right to highlight the role played by diet and nutrition in hair growth: the study also failed to take blood samples to check on the endocrine status of the subject as I've found elsewhere that thyroid status affects hair growth as does oestrogen/progesterone status in women. It's not a complete study by any means, but an example of what can be achieved by someone wishing to follow the scientific method and make a difference. --TammyMoet (talk) 15:37, 13 April 2013 (UTC)

ques on tetrahedral and octahedral voids

A compound formed by two element a&b the anion b are located at the corner of the cube and face centres whereas cation a occupy all the tetrahedral void what is the simplest formula of the compound? — Preceding unsigned comment added by 70.39.184.248 (talk) 09:59, 13 April 2013 (UTC)

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. Roger (Dodger67) (talk) 11:59, 13 April 2013 (UTC)

What is a microstate?

Entropy is by definition $-k\sum _{i=1}^{\Omega }P_{i}\ln P_{i}$ where k is Boltzmann's Constant and $P_{i}$ is the probability of a particular state given our limited knowledge of the system. But, how is state defined? What fully characterizes a physical state?

150.203.115.98 (talk) 10:26, 13 April 2013 (UTC)

It is the complete information about the system. Suppose you have two systems in different physical states, then that means that there exists an experiment that you can do on the systems which will have a different outcomes, at least statistically. If on the other hand the two systems are in the same physical state, then no experiement can have (statistically) different outcomes.

You can then try to define the state of a system by specifying a list of experiments and what the outcomes of each of these experiments should be. In quantum mechanics, the outcome of a measurement is, in general, not pre-determined. Now, you do one experiment and then immediately repeat that same experiment you will get the same outcome (in the limit that the time between them is zero). If you do experiment A and then experiment B, you can compare that with doing this the other way around. If there is no difference, then measuring B will give you independent information than you get from measuring A. You can then add another such experiment C that doesn't interfere with A and B. If you try to make this list of experiments larger and larger, you will find that some point, you can no longer make this list larger. You will then have what is called a "complete set of observables" for the system. Then the state of a system is completely defined by specifying a list of the outcomes for each of the obsevables contained in such a list. The outcome of any other experiment can be predicted (in the form of a probability ditribution over the possible outcomes) when the state is specified. Count Iblis (talk) 12:27, 13 April 2013 (UTC)

That's really interesting, and I can see the article Complete set of commuting observables now. A state is basically characterized by its measurable properties, which makes sense, especially from a pragmatic point of view. It doesn't really make sense to call two states "different" if there doesn't exist any experiment, even in principle, to distinguish between them.

Now, suppose you have a physical system, and you want to change its state. How would you do this, in general?

150.203.115.98 (talk) 15:09, 13 April 2013 (UTC)

Changing state is already described in "general" terms. In various branches of physics, state change is described mathematically; for example, in quantum mechanics, physicists talk about "applying an operator" to the system. This is about the most precise and generalized way we can describe changing state for one variable, subject to physical constraint. Unfortunately, such generalization tends to be a bit obtuse, and some people find these decriptions difficult to intuitively connect to experimental physical systems. This is because the specific way you change a particular state for a particular system depends on what physical process corresponds to the change of that state variable. In other words, we write a very clean mathematical formalism to describe an operator; but it is not always immediately evident how that operator corresponds to an experimental procedure.

For example, in atomic physics, one state variable models the energy-level of the electron; you can change that energy level by (in general) applying an energy transform operator to the electron. In specific cases, that operation manifests as compton-scattering; or shooting laser photons at the atom; or colliding the atom with other warm atoms (thermal excitation); and so on; in each case, practical details arise; it may be impractical to change one state-variable without affecting thousands of other parameters. Nimur (talk) 16:57, 13 April 2013 (UTC)

An example of a particular state is an associated energy level, such as the ground state of a partice. Plasmic Physics (talk) 12:28, 13 April 2013 (UTC)

In thermodynamics, a microstate describes the position and momentum of every particle. It's the full description of the system. For example, with N particles, "particle 1 is at (3,2,5) and moving at 3/ms north, particle 2 is at (4,5,1) and moving at 9 m/s east, etc" counts as a microstate. A macrostate is something you care to measure on a macroscopic scale. For example, what's the density of the gas? How uniform is the gas? What's the velocity distribution of its particles?

There is an inherent arbitrariness in the definition of a microstate. If particle 1 is moved by 1 nm, does that count as the same microstate, or a different one? How about 0.0001 nm? First, this doesn't actually matter--entropy is defined as the logarithm of the number of microstates, so changing the precision with which you distinguish microstates only changes entropy by a constant. Differences in entropy would stay the same. Second, quantum mechanics sets a fundamental limit on how accurately you can measure phase space. dx*dp cannot be smaller than Planck's constant, because the uncertainty principle says you can't simultaneously measure position and momentum more accurately than that.

Over time, systems tend towards the macrostate with the most microstates. For example, their velocity distributions tend to become the Maxwell distribution. "A uniform gas" accurately describes many more microstates than "a gas in a container where half the container is empty". This isn't surprising--of course if every microstate is equally likely, and the particles randomly choose one, that microstate would most likely correspond to the most likely macrostate. This tendency towards the most likely macrostate is the second law of thermodynamics. --140.180.240.67 (talk) 18:34, 13 April 2013 (UTC)

Does that agree with the definition Count Iblis gave? And, don't you need to know other properties of the particles such as their mass, charge etc.? And

150.203.115.98 (talk) 20:10, 13 April 2013 (UTC)

You do. I was giving a simplified classical view of an ideal monoatomic gas, which I think is helpful for intuition. For such a gas, all the molecules can be considered point sources with no charge and the same mass. Sorry for not stating this explicitly. --140.180.240.67 (talk) 20:20, 13 April 2013 (UTC)

Eyesight

Can a teenagers social development be affected by poor eyesight? — Preceding unsigned comment added by 176.250.139.80 (talk) 11:15, 13 April 2013 (UTC)

Yes. (Strange question.) HiLo48 (talk) 11:21, 13 April 2013 (UTC)

Obviously anything that affects communication affects social development. However, what do you mean by "poor eysight"? Deficiencies that can be corrected with spectacles should not affect it, except to the extent that wearing spectacles may temporarily affect self esteem or may limit playing in team sports. Wickwack 121.221.31.213 (talk) 11:30, 13 April 2013 (UTC)

If you hadn't just admitted to being in your 70's, calling glasses "spectacles" would have told me. :-) StuRat (talk) 04:04, 14 April 2013 (UTC)

One tries to write for an international reader here. "Glasses" has multiple meanings, (e.g., magnifying glass) while "spectacles" has only two, and it's obvious which of the two meanings applies here. Wickwack 121.221.215.92 (talk) 09:49, 14 April 2013 (UTC)

...And of course it's a matter of degree. If the person's eyesight was sufficiently good that glasses were only needed for some specific task like driving or reading - then the effect should be very small indeed. On the other hand, I know an adult who's corrected eyesight is so bad that he can only read things a few inches from his nose - even with thick, heavy glasses. He can't drive, play video games or watch TV at all. Since those are all major teen social activities I'm sure that must cause significant social impairment in teenagers. On the other extreme, my son is mildly red/green color blind and sailed through most of his teenage years without even knowing it - which implies that there was no social impairment whatever. So the answer to our OP is obviously: Yes, it's possible for extremely poor eyesight to cause serious social impairment - but mildly poor eyesight does not cause impairment. It's not a very useful answer without knowing details about a specific case - but in that case we'd be unable to offer advice because it would constitute "giving a medical prognosis" - which we're strictly prohibited from doing. SteveBaker (talk) 12:48, 13 April 2013 (UTC)

While I don't disagree it's a matter of degree and quite variable depending on the imparity, I don't think it's as simple as you suggest particularly since the question was about 'social development be affected' which can be very broad. For example, depending on the person's interaction with peers, teachers and parents, I imagine it's entirely possible they will go through their teenage years with a mild myopia without really realising it, yet it will still affect them (e.g. they will avoid certain activities and be less good at them then they would be if it were corrected). Of course the same could happen for a whole host of other reasons. As Wickwack mentioned, even with perfect correction with glasses it can still have effects since it can affect self esteem, interaction with peers and in some cases the presence of glasses makes it more difficult to participate even without considering those effects. (Again these can also arise for a whole host of other reasons.) Contact lenses can help, but have their own issues. And depending on factors like whether the person is going to need glasses in addition (for times when they don't want to or can't where contacts), the level of the correction required (particularly astigmatism), how frequency the prescription changes and the price in the locale, contact lenses may not be financially possible. Of course for some people and in some places, corrective lenses of any kind may not be possible for financial reasons. Nil Einne (talk) 14:21, 13 April 2013 (UTC)

http://www.youtube.com/watch?v=ls2lC7DQFMI --Digrpat (talk) 23:06, 13 April 2013 (UTC)

In the case of uncorrected poor vision, there can be an interesting split in school. Some will move to the front of the classrooms, in order to see what the teacher is writing on the board, and tend to become "teacher's pets", while others will give up and fall behind in school. Either path could potentially negatively affect their social development. StuRat (talk) 04:12, 14 April 2013 (UTC)

Last spacecraft launch to orbit with *one* astronaut?

When is the last time that a spacecraft launch occurred which made at least one orbit that only had *one* astronaut in the capsule. If this was a private company, when is the last time that a National space agency did so. In either event, was the last launch in the Mercury program the last time the United States did so?Naraht (talk) 11:35, 13 April 2013 (UTC)

The most recent manned space flight with a single crew member seems to have been Shenzhou 5, the first manned space flight of the People's Republic of China, in 2003. Gandalf61 (talk) 12:23, 13 April 2013 (UTC)

The last U.S. single astronaut mission was Mercury-Atlas 9 in 1963. The last Soviet one may have been Soyuz 3 in 1968. No private company has yet done orbital flight. The company SpaceX is trying to do the first private manned orbital spaceflight in mid-2015 but it will carry a crew of three. Rmhermen (talk) 15:30, 13 April 2013 (UTC)

Cost of RNA vs protein

Hi Ref Desk,

I'm wondering what the energy cost to cell is for making an RNA molecule vs the protein for which it codes. Intuitively, I would say that the protein is much more expensive, but a study ([1]) suggests that RNA costs 5x more energy than a protein (49.3 phosphate bonds per nucleotide (x3!) vs 30.3 per amino acid)! I can't find any other estimates to compare this to - any tips?

Cheers,

Aaadddaaammm (talk) 12:16, 13 April 2013 (UTC)

It's not common for someone to come to us with a good reference in hand - thanks! You probably are aware already, but I should say a key thing to bear in mind here is the difference between total synthesis vs. polymerization of precursors. RNA and protein are both going to get degraded sooner or later back to amino acids and XMPs, so the total synthesis doesn't really apply except in growing populations of cells.

So far as I recall, the basic ratio for polymerization should be just one pyrophosphate released per charged amino acid in aminoacyl tRNA synthetase, with that energy being sufficient to power the ribosome, but EF-Tu/eEF-1 contributes another phosphate bond to improve accuracy. (Note that pyrophosphatase makes the PPi effectively count as two bonds split) Other elongation factors exist, for example EF-G at the end of the protein. I can't rightly recall at the moment where the other ~P the author of your reference comes from during elongation. So we're talking about 3 ~P I can count (ignoring the one extra at the end), 4 according to the author, plus parts. By comparison, I would count the "cost of polymerization" in the RNA as being a PPi per bond created (i.e. XTP to XMP). So to me the ratio that would seem to matter in steady-state metabolism would seem more like 2:3 with the amino acid being only a bit cheaper than a codon.

Anyway, what's interesting to me about this is that the selective pressure against having a high level of mRNA and protein per cell seems like it is going to be much less for an organism that remains in a stable state for a long period of time than one which is is exponentially growing. If an organism's whole ecology is geared toward putting on weight and splitting, that seems like it ought to lead to different overall gene expression level than if it is trying to hide for a long time and avoid getting eaten. Hmmm... Wnt (talk) 19:48, 13 April 2013 (UTC)

It's worth bearing in mind that a single mRNA molecule, once transcribed, can be translated multiple times. (Heck, multiple ribosomal complexes can attach to the same mRNA simultaneously, allowing translation of multiple copies of a protein at the same time from a single mRNA: [2].) What this means is that the energy 'overhead' cost of one mRNA molecule can – potentially – be 'amortized' over many, many translated protein molecules. In other words, even if transcription is 'expensive' on a per-base basis, it still accounts for a relatively small part of the entire protein biosynthesis energy budget because mRNA is reusable. TenOfAllTrades(talk) 03:23, 14 April 2013 (UTC)

Spatial Encoding

Since my question has been removed I post it here.

What are the typical computer video compressions algorithms names which use the human retina approach?2A02:8422:1191:6E00:56E6:FCFF:FEDB:2BBA (talk) 21:09, 13 April 2013 (UTC)

(I see where this was removed from Talk:Retina) - unfortunately, it is possible that this still isn't the best place, that Wikipedia:Reference desk/Computing would get you better answers. I'm certainly not aware of any video compression that attempts to follow the retina's approach literally. Figuratively... I can't tell. For example, if I do a Google search for "video compression" "edge finding" I get [3], but I can't really say whether that method of finding dominant edges to align stereo pairs has any relation to the biological scheme at all; certainly it is not a direct copy.

My gut feeling is that the two circumstances aren't comparable because we accept a huge loss of resolution from our retina. We aren't aware of individual rod and cone inputs on their own. So any computer algorithm that worked just like the retina would be seen as a really crummy way to store an image, until such time as the images are sooo high res that we really don't care. I think... Wnt (talk) 22:01, 13 April 2013 (UTC)

Why do you say there's a huge loss of resolution? As far as I know the eye's resolving power is pretty close to the cone spacing. -- BenRG 00:15, 14 April 2013 (UTC)

Our vision isn't nearly as good as it seems. We have lots of blind spots where we looked at something bright and burnt out a few cons and rods, or a blood vessel covers them, etc. Why don't we see black spots all over our field of view ? Out brain does an amazing job at filling in the missing spots. Unfortunately, this also means we aren't always seeing reality, but sometimes just what our brain makes up to fill in the gaps. StuRat (talk) 07:09, 14 April 2013 (UTC)

Perception is reality. 202.158.66.204 (talk) 09:56, 14 April 2013 (UTC)

Thanks for the quick answer I had thought to this. There are projects for getting 60TB per hard drive for the end of the decade. As it did for The GB step,there are reason to full the space. there will exist camera that would produce 25GB images with actuals compression techniques.

I can't imagine diffuser aren't planning the result for video download.I'm sure the algorithms are already written.

By the way I was thinking about the retina side only (no real care about the second eye) and not the decompression methods.

The method of "decompression" is always varying from person to person and time (optical nerves and human brain ). 2A02:8422:1191:6E00:56E6:FCFF:FEDB:2BBA (talk) 22:28, 13 April 2013 (UTC)

My knowledge of the spatial encoding in the optic nerve is based entirely on having read the article section just now, but it looks very similar to the wavelet transform, which is used in JPEG 2000, for example. The most popular video compression formats right now (e.g. h.264 and all versions of MPEG) don't use wavelets, but do use the discrete cosine transform, which is closely related. All image and video compression is based in one way or another on human vision. Even "uncompressed" images represent colors as RGB triples, a representation that's closely tied to human standard color perception. -- BenRG 00:15, 14 April 2013 (UTC)

• I don't really see how the retina can be compared to any image compression algorithm. The huge difference is that the retina has quite a small high-resolution zone, called the fovea -- it is roughly the size of your fist held at arm's length. The most important type of compression the retina uses is to represent only this very small region at high resolution. Nothing like that could work for a computer representation, because there is no way of knowing what part of an image will be the focus of attention. (I'm oversimplifying a bit, but I don't want to flood the board with verbiage.) Looie496 (talk) 03:15, 14 April 2013 (UTC)

Plaster of Paris as a structural material yet it is relatively water soluble, what gives?

Calcium sulfate dihydrate, the main component of plaster of Paris, has a solubility of 2 g/L. Yet this material is used to make all sorts of structural materials. So what I am trying to figure out is why doesnt this stuff dissolve? Perhaps the plaster components are relatively crystalline and have a low surface area, but still I would think that after a few years or decades (see Borujerdis House as one of many antiquities made of P of P) of rainy weather that it would be corroded away. Or, maybe this material is not used for exteriors very much except in dry climates.--Smokefoot (talk) 23:53, 13 April 2013 (UTC)

Paster of Paris is never used as a structural material, not in my country anyway. The term "structural" denotes a material that is load bearing. Plaster of paris is only used in non-load-bearing and decorative applications - someting else underneath (brick, concrete, framework, etc) takes the load - load being either static & dynamic downward forces due to gravity and/or wind loading. Actually, the ability of moisture to wreck plasterwork can be considered a virtue. It lets you know you have rising damp, or a leak in the roof, well before real structural damage is done, and it is easily repaired at mimimal cost. Where used as suspended ceilings where it must sustain its own weight, it is re-inforced with cellulose fibres or other semi-woven material.

I know nothing about the Persian building you cited, but none of the inticate work shown is structural. There's nothing wrong with using plaster work to decorate ceilings and other inside surfaces - this is extremely common in modern western buildings. Despite the labelling on the images, I expect the exterior decoration (which is applied, not structural) is all water-resistant stucco, not plaster. Wickwack 121.215.41.163 (talk) 02:56, 14 April 2013 (UTC)

Oh, good points. I used the wrong wording (structural). My question is simpler - why would anyone decorate the exterior of any building with a material that is fairly water soluble. --Smokefoot (talk) 03:04, 14 April 2013 (UTC)

Read Whitewash. Also note that Persia had (and still has) a rather dry climate, so water solubility wouldn't have been a big problem there. 24.23.196.85 (talk) 03:38, 14 April 2013 (UTC)

I thought so too, but fortunately I checked before writing my first post. It turns out that their annual precipitation (680 to 1700 mm) is somewhat greater than the precipitation where I live (Western Australia), hardly dry, and you certainly would not use plaster on an external surface here. That's why I think that the external decoration is not plaster but stucco. One of the characteristics of whitewash is that is a non-durable paint (once popular in the US) requiring regular re-application. If you used it for the sort of decoration depicted in the OP's link, you'd soon end up with a smooth surface and no decoration. Wickwack 60.230.245.70 (talk) 06:29, 14 April 2013 (UTC)

I think that stucco and plaster of Paris are the same thing (despite what is stated in stucco), calcium sulfate, which is fairly water soluble, so now what? --Smokefoot (talk) 12:32, 14 April 2013 (UTC)

There are various recipes for stucco. Stucco can indeed be made with plaster of paris. It can also be made with portland cement, which makes it completely waterproof, but with a lower quality finish. It also gives an ugly grey colour, but that can be fixed with pigments. There are a number of other water resistant mixes, eg lime-based (as in mortar used to stick bricks together), and you can also use a combination of plaster of paris with cement to give a degree of water resistance. Wickwack 124.182.15.108 (talk) 12:50, 14 April 2013 (UTC)

The answer might just be Relative humidity. Homes which use plaster are usually heated (which lowers the average RH). In older homes that have old fashioned larder rooms, the plaster in them (if they are plastered at all) often become crumbly. Plaster needs to be fairly damp in order to disassociate like this. In the tropics, were relative humidity is high and a artificial heat is not required, then plaster is seldom seen. If it is used, then a lime based wall coating is probably leaning towards hydraulic lime and that is not plaster of paris.Aspro (talk) 20:02, 14 April 2013 (UTC)

• Could plaster of Paris be used in Lath and plaster construction? --Jayron32 04:26, 15 April 2013 (UTC)
  • Certainly. By the 20th century, that's what it mostly was -- it dries much faster than the older lime-based plaster, and has fire protection qualities. --jpgordon^{::==( o )} 14:53, 15 April 2013 (UTC)

In common usage it seems that term Plaster of Paris (CaSO4·2H2O) is used mostly for its pure form but it is also known as gypsum. Its pure form could be used for plastering Lath but its setting time might be a bit too quick for a plasterer to get a good finish over a large surface. Builders gypsum is almost the same thing but it is modified to give a longer working time (i.e., Plaster of Paris multi-phased by the addition of lime etc). Pure lime plaster on the other-hand takes very much longer to cure. The latter, is only needed today for re-plastering some old buildings (especially stone and mortar dwellings) that where built without a damp-proof course. So yes. the white stuff one can buy from art & craft shops called Plaster of Paris will do the same same job. --Aspro (talk) 15:32, 15 April 2013 (UTC)

Lath and plaster was, of course, only used for indoor work, mostly in the USA. Wickwack 120.145.63.92 (talk) 00:50, 16 April 2013 (UTC)

April 14

What is this engine part?

What's the part in the red oval?

Shown is a picture of the engine of a 2004 Ford Escape. The silver cylindrical part in the red oval has a cable socket coming in on the left. I just repaired the cable and got the vehicle to work again, the problem being that it would start up fine but die within a second, unless I gave it gas, in which case it would keep running, until I took my foot off the gas, at which point it died. So whatever this part is seems to be related to the idling circuit. Like I said, the car works now. I'm just curious what the part is. Peter Michner (talk) 04:29, 14 April 2013 (UTC)

I'm pretty sure that's the oxygen sensor. But I'm not a mechanic. --Jayron32 04:46, 14 April 2013 (UTC)

Scanning some other stuff, it could also be part of the Exhaust gas recirculation (EGR) system. There's a bit called the "DPFE sensor" or "Differential Pressure Feedback (EGR) sensor" which looks like it is in about this location. I think this diagram is from a 2001 Ford Escape, and the DPFE sensor looks to be in about the location it is in your picture. But I'm just guessing here. --Jayron32 04:56, 14 April 2013 (UTC)

Thanks, looks like it's definitely called the idle air control valve Peter Michner (talk) 06:35, 14 April 2013 (UTC)

4D strorage device

How would one encode information onto a 4D crystal such as the example recently created? Plasmic Physics (talk) 07:20, 14 April 2013 (UTC)

Would there be any advantage over a conventional 2D storage device such as a USB stick? Plasmic Physics (talk) 10:04, 14 April 2013 (UTC)

I think you probably mean 3D, not 4D? If that's the case, see 3D optical data storage and Holographic data storage. Red Act (talk) 12:56, 14 April 2013 (UTC)

I think the question refers to this weird press release. As near as I can make it out they made a simple quantum system that has angular momentum in its ground state and for some reason called it a "4D crystal". Since it's in the ground state, you can't encode any information into it. -- BenRG 15:52, 14 April 2013 (UTC)

If anyone cares, here's the paper and here's the theoretical treatment it cites. The theoretical preprint, which is by Frank Wilczek, starts with a point particle confined to a circle through which there's a magnetic flux. He shows that the ground state has nonzero (orbital) angular momentum and seems to think that's surprising, having apparently forgotten that the ground states of a lot of atoms have that property. He discusses how this counterintuitive result can possibly be true. The answer, of course, is that the particle is uniformly smeared around the circle; it's a "clock" whose hand is in a uniform superposition of all directions at all times. It's rotating, but it doesn't tell time. He then introduces more particles to the loop and a mutually attractive force and shows that they clump together, and seems to argue that this clumping will counteract the smearing out. I don't know how a guy who won a Nobel prize for explaining the structure of hadrons could make that mistake, but as far as I can tell he did. In reality switching from a point particle to a clump changes nothing because the clump is a composite particle (like a hadron) whose position can be characterized by a single angular parameter, and the wave function in terms of that parameter is the same as before. It has to be because a ground state is a state of definite energy, and in a state of definite energy the probability density is time-invariant. He even mentions that fact at the start of the paper, but seems to believe he can circumvent it. Really bizarre. The experimenters have the same misconception about the state they created, but they're experimentalists so it's easier to understand. Wilczek's preprint is apparently unpublished, and maybe PRL accepted the experimental paper because of something interesting on the experimental side. They 2should have made them drop the crystal-power nonsense, though. -- BenRG 20:03, 14 April 2013 (UTC)

The thought occurs to me that Frank Wilczek may have been making an elaborate joke. He also speculates about iGlasses and iQuasicrystals (the "i" meaning "imaginary", possibly also a play on words). — Quondum 20:56, 14 April 2013 (UTC)

I think if it was a joke he would have said so by now. Imaginary time is an actual thing. Respectable physicists have written weirder preprints, like the ones coauthored by Holger Bech Nielsen claiming that the LHC exploded because of a Higgs-discovery-prevention mechanism in the laws of physics. -- BenRG 18:18, 15 April 2013 (UTC)

That is exactly what I'm talking about. So what did the experiment actually achieve? Plasmic Physics (talk) 13:10, 15 April 2013 (UTC)

I didn't read most of the paper, but they confined a number of charged ions to a circular path at very low temperature, so that they ended up in a ground state (effectively absolute zero). They threaded a magnetic field through the circle, which shifts the ground state into one where the ions have a fixed nonzero angular momentum. It's not a clock, though, because if you measure the position of the "hand" you'll get a random value that's uncorrelated with the time of the measurement. (One way of seeing that is the uncertainty principle: the angular momentum is exact so the angular position is totally indeterminate.) And it seems quite ridiculous to call it a crystal, much less a 4D crystal. I doubt this configuration of ions is useful for anything. Maybe it was an impressive experimental achievement to create it—I don't know.

By the way, I just now noticed that there's a Space-time crystal article. I can't critique Wilczek's paper in it, of course, because that would be original research. -- BenRG 18:18, 15 April 2013 (UTC)

If there truely existed such a thing as a codeable 4D crystal then it would circumvent the problem noted below by StuRat. All data is at the surface, just not all the time, so it should be possible to write as well as read. Plasmic Physics (talk) 22:42, 15 April 2013 (UTC)

Now that I've thought more about it, it still wouldn't be 4D - it would only be 3D (2D_L1D_T, not 3D_L), since the data is still only encoded onto a quantum surface. Plasmic Physics (talk) 08:09, 16 April 2013 (UTC)

However, 3D storage may make sense to replace 2D. Or, a convoluted surface like in the brain, designed to increase surface area. This would get by the problem of how to access and change data deep inside a 3D object (something like a CAT scan could conceivable read data inside a 3D object, but changing it is a bit more of a challenge). So, maybe 3D storage for read-only memory, with convoluted 2D storage for read/write memory. StuRat (talk) 18:08, 14 April 2013 (UTC)

If you have a "4D crystal" with a charged carrier moving in a circle (for sake of argument let's say that it's a 1-foot superconducting ring with a single electron going around and around) wouldn't it still emit some kind of electromagnetic energy into space over time until it comes to a stop or some kind of homogeneity? Wnt (talk) 21:51, 16 April 2013 (UTC)

In theory, no, because it supposed to be in its ground state, so it has no energy to lose, it can perform no work. Motion does not automatically imply energy. The only energy that it can lose would be potential energy, by physically decaying. Plasmic Physics (talk) 13:37, 17 April 2013 (UTC)

But is an electron moving in a ring in its ground state, before it is perfectly degenerate at all positions around the ring with no observable position? Wnt (talk) 15:07, 17 April 2013 (UTC)

Care to rephrase? Plasmic Physics (talk) 22:48, 17 April 2013 (UTC)

Compromised title

When searching for "Thin Layer Extraction" one is only redirected to the article "Liquid-Liquid Extraction" that refers to "Thin Layer Extraction" through a dead link. There exists apparently no article by the name "Thin Layer Extraction" to be edited. I have prepared an extended article on "Thin Layer Extraction" and I am unable to create it under this name. How else can one assign a title to a new article? RogerLie (talk) 14:23, 14 April 2013 (UTC)

Questions like this are better asked at the Help desk, but I'll answer anyway. The trick for bypassing a redirect is, after clicking on Thin Layer Extraction and being taken to the Liquid–liquid extraction page, note at the top a line saying Redirected from Thin Layer Extraction. If you click on the link in that sentence, you are taken to the redirect page. You can then edit it to turn the redirect into an article, or you can look at the Page History, which, to save effort, is here.

I note when I look at the page history that you already created a version of that article, back in 2009. It was turned into a redirect a few months ago because an editor felt that the article did not establish that the topic is sufficiently notable. In other words, it is not clear that the term is used in the literature to a significant degree. If you think you can resolve that issue, then you can either edit the redirect page to turn it back into an article, or else revert back to your earlier version and make improvements to it.

If you have further questions about how to edit articles, please ask them at WP:HELPDESK. Regards, Looie496 (talk) 15:09, 14 April 2013 (UTC)

RAST

Is RAST test an example of RAS syndrome?? My textbooks all say that "RAST" stands for "radioallergosorbent" (presumably the T is the final t in that word, which would make it more correctly RASt) and google doesn't show anyone referring to it as a RAS Test. 2.98.248.78 (talk) 15:35, 14 April 2013 (UTC)

The Department of Redundancy Department is definitely interested in this question. Looie496 (talk) 15:56, 14 April 2013 (UTC)

Yes. Affirmative. StuRat (talk) 18:12, 14 April 2013 (UTC)

Power-to-weight ratio: electric and combustion motors

What of both have a better power-to-weight ratio? Even not considering the storage (battery/tank), can an electric motor ever have a better power-to-weight ratio? OsmanRF34 (talk) 19:28, 14 April 2013 (UTC)

See Power-to-weight ratio. The Hi-Pa Drive electric motor has a (theoretical) power/weight ratio of 2.92 hp/lb, better than the Wankel engine at about 1.0 hp/lb, and much better than a conventional Otto engine. The advantage of IC is not so much the weight of the engine, but the weight of the fuel compared to the equivalent battery. Tevildo (talk) 22:10, 14 April 2013 (UTC)

Much lower percentages of waste heat can't hurt. Sagittarian Milky Way (talk) 03:33, 15 April 2013 (UTC)

But, what is the most common scenario when it comes to real life motors, like those found in cars? I have the impression that electric cars have smaller motors for the same HP, however, I thought it should be the opposite: an Otto or Diesel motor should be smaller by same HP. OsmanRF34 (talk) 00:20, 17 April 2013 (UTC)

Shouldn't this graph be periodic?

Why is the current/voltage diagram in Franck-Hertz experiment not actually periodic? Why is there an overall upward trend? Wouldn't you expect the function to be truly periodic according to the theory presented in the article?

150.203.115.98 (talk) 22:43, 14 April 2013 (UTC)

No. As voltage increases, electrons are drawn more quickly from the cathode and through the mesh, so current increases. This isn't surprising--if you increase the voltage across a resistor, current increases, and for similar reasons. --140.180.243.134 (talk) 23:27, 14 April 2013 (UTC)

A resistor isn't really the best comparison in this case, although the basic principle is correct. The null hypothesis for the experiment is that it should behave like a vacuum diode, so the curve would follow Child's law, I ∝ V^(3/2), if there were no interaction between the electrons and the gas. Tevildo (talk) 23:29, 14 April 2013 (UTC)

That certainly explains why the current increases between the peaks, but shouldn't the current drop down to zero at each multiple of 4.9 Volts, and start again? 130.56.234.8 (talk) 01:49, 15 April 2013 (UTC)

But it does drop down almost to 0 at each multiple of 4.9 volts. It doesn't get to 0 completely because some of the electrons don't encounter an atom before hitting the anode, and some of the electrons that encounter 1 atom don't encounter another, etc. --140.180.243.134 (talk) 05:34, 15 April 2013 (UTC)

Right, but that's not what the diagram shows; the diagram shows a long-run increase, an overall increase, as well.

150.203.115.98 (talk) 05:40, 15 April 2013 (UTC)

Are you perhaps confused by the fact the diagram is not current v time, but current v voltage? With higher voltages, electrons are more likely to be excited (or whatever the correct term is) even when the voltage is a multiple of 4.9v. The potential difference would be an average, but there would be fluctuations at the "particle" level so that some small portion of the electrons experience a potential difference not precisely a multiple of 4.9v. The higer the voltage, the larger the portion of electrons not precisely in that 4.9v region ergo the higher the current. Vespine (talk) 07:00, 15 April 2013 (UTC)

I don't think that per-particle KE variation is the principal reason for these effects. We never expect for the current to be 0: the only place we could have that is at na V (for a first excitation of a eV), but in that case the region (near the accelerating grid) in which the electrons can experience inelastic collisions is vanishingly small. The increase in the minimum for each "period" is then easily explained by the increased total flow of electrons. --Tardis (talk) 13:12, 15 April 2013 (UTC)

Yes I think I had it kind of backwards sorry, it's the absorbtion of electrons that reduces the current, so the fact there is a small current is explained by the fact that not all electrons are absorbed, even if they have the required energy to do so.. Vespine (talk)

April 15

The science (if any) of sunglass tints

I understand that glasses can usefully cut UV light (and that visually transparent lenses can do this perfectly well). And I understand that people may wish to reduce glare, to hide their eyes, or even to, uh, look at the world through rose-tinted glasses in order to tint the world rose.

I'm puzzled by the other claims for the benefit of various colors. This PDF from the American Academy of Ophthalmology tells readers that yellow is "optimum for object definition" and that amber "allegedly makes distant objects appear more distinct, especially in snow or haze" (my emphasis).

My understanding of color is very shaky but I do understand (or misunderstand) that filtering of visible light of some waveband may improve perception of light in other wavebands. Thus I suppose one could design a sort of experimental environment in which the definition of objects would be helped by yellow-tinted sunglasses. But in the larger, multicolored world, how could yellow, or any other color, be optimum for the definition of objects in general?

I've tried Googling for this but mostly just get retailers. Of course retailers want to shift product and have an interest in persuading novice anglers, skiers, etc. that experienced/expert anglers, skiers, etc. benefit from a certain tint of sunglasses. What I don't see is evidence or reasoning. Is there anything too this, or is it just old husbands' tales? (I'm guessing that it's more masculine than feminine.) Morenoodles (talk) 09:02, 15 April 2013 (UTC)

The problem with blue is that it seems to be defracted/reflected by everything, such as fog. So, if you block the blue, you can see more clearly in fog. On the other hand, on a perfectly clear day, I don't think it makes much difference. Then there's the negative effect of messing up color perceptions, making traffic lights look wrong, etc. StuRat (talk) 13:30, 15 April 2013 (UTC)

So, do you have any references to support your conclusions, or are you just giving the OP guesses, StuRat? TenOfAllTrades(talk) 14:17, 15 April 2013 (UTC)

What StuRat says are true statements...but you'd have to read a dozen different articles to pull together all of the disparate facts that make it so...hence, I'm not going to dig up all of the article names either! The atmosphere (by virtue of the Raleigh and Mie scattering mechanisms) takes the blue light out of sunlight and scatters it in all directions equally. That means that there is less sharpness to the blue light that we see because it's coming from absolutely everywhere. The problem is much worse at longer distances because the light from distant objects is also being scattered - making the blue part of the light "fuzzy". The complementary color of blue is yellow - and yellow-tinted glasses filter out much of that blue light. The result is a slightly dimmer image with less blue in it. Our eyes are able to adjust to the lesser amount of light coming in - so that effectively boosts our sensitivity to the colors that are not being scattered so badly - which makes everything look sharper - especially in the distance. SteveBaker (talk) 15:09, 15 April 2013 (UTC)

Thanks, Steve. I'm amazed that Ten doesn't know that blue light scatters more. That's the reason the sky is blue, after all, as the blue light coming from the Sun scatters the most, while the reds and yellows scatter far less. StuRat (talk) 17:34, 15 April 2013 (UTC)

No, StuRat's statements are inaccurate and misleading. It is true that atmospheric molecules scatter blue light more than red, due to the strong wavelength dependence of Rayleigh scattering. However, nowhere does StuRat use the word "scattering", and it's not true that objects generally "defract" (diffract?) or reflect blue light. For a fixed aperture size, diffraction has a larger effect for long wavelengths, as you can see from the first equation in the section on single-slit diffraction.

It is also not true that fog preferentially scatters blue light. If that was true, fog would appear bluish, but it's actually white. The theoretical reason for this is that Rayleigh scattering is an approximation of Mie scattering that only works when the scattering particles are much smaller than the wavelengths they scatter. For large particles, like the water droplets that make up fog, Mie scattering is not strongly wavelength dependent. See this link, for example: "Mie scattering is not strongly wavelength dependent and produces the almost white glare around the sun when a lot of particulate material is present in the air. It also gives us the the white light from mist and fog." --128.112.25.104 (talk) 01:09, 16 April 2013 (UTC)

Thank you all for your comments.As there's disagreement, I'm a bit lost. From one understanding of the relevant physics, it does seem that yellow tinting would be beneficial; from another, not. I distrust anecdotal evidence for this kind of thing, in that I imagine that competitive cyclists (for example) use unthinking imitation and hearsay for a lot of their decisions, and then come up with anecdotes and evidence to support these decisions. I wonder if there have been empirical tests for the value (or not) of tints for perception of distance, objects, etc. Morenoodles (talk) 05:53, 17 April 2013 (UTC)

To be clear, I don't think we are disagreeing that yellow lenses improve distance vision. There are details about fog and haze that are complicated...but overall, it's clear that these things should work, and for sound scientific reasons. User:128.112.25.104's comments are only about foggy conditions - we know that blue light is scattered by the atmosphere because that is why the sky is blue. SteveBaker (talk) 15:12, 17 April 2013 (UTC)

Blood Circulation

HI! I'm just studying about Blood Circulation and I need some clarification. 1. Why do RBC's pile up in blood vessels during blood circulation and what this process is called? 2. What is Haemocytometer? 3. What is Microcystic Anaemia? Please help me in clarifying my doubts. 114.79.141.44 (talk) 10:43, 15 April 2013 (UTC)

"Pile up" is a rather vague term, but you might find our articles on coagulation, hemocytometer and microcytic anemia helpful. Gandalf61 (talk) 11:01, 15 April 2013 (UTC)

Most populous species

Which is the most populous species in terms of total world population? Bacteria are not a single species. Human population is 7 billion. Which species has a world population that exceeds 7 billion? --Yoglti (talk) 12:12, 15 April 2013 (UTC)

Have a look here [4] for a good discussion on exactly your question. The answer seems to be krill, btw. Aaadddaaammm (talk) 12:40, 15 April 2013 (UTC)

Sorry, krill are probably the most abundant animal. I'd guess that pretty much any bacteria beats them. Some back of the envelope calculations: total bacterial cells on earth = 5x10^30 [5]. Number of bacteria species: more than 10 million (largest estimate) [6]. Let's say 10 billion to give the microbiologists some breathing room. Then the most abundant bacteria has at least 5x10^30/10 billion = 500 quintillion cells! This beats krill by 500 quitillion / 500 trillion = 1 million times. Wooo! Aaadddaaammm (talk) 12:50, 15 April 2013 (UTC)

(ec) It's estimated that there are 350 trillion krill out there. You might think that they win because of that - but not even close!

Consider that some species of cyanobacteria can double their population size in 6 hours...given enough space and nutrient, a single bacterium can produce:

• 2 bacteria in 6 hours.
• 65,000 in 3 days.
• 4 million in 5 days.
• 270 million in a week.
• ...and exceed the number of humans in just 9 days.

We don't stand a chance.

In a cup of yogurt, in your refrigerator, there are at least three billion bacteria per milliliter...although not from a single species. But if you killed all of the bacteria in a 10 gallon barrel of yogurt - then added one cyanobacterium and waited, then in a bit less than two weeks, they'd outnumber all of the krill on the entire planet by a comfortable margin.

Consider this - there are 10 trillion "good" bacteria in the gut of every single human being. Of those, about 50% come from just five species. So there are roughly 5% of each of those major species...which means that there are at least 500 billion bacteria of just one species in your gut right now. Our gut bacteria have the krill outnumbered by just the amount in the guts of a moderate sized football arena full of people.

So I don't know what the answer is - but it's not krill or humans...it's got to be some kind of bacterium or other uni-cellular organism.

...unless we decide to say that viruses are "alive" because if we count them, then the bacteria will be outnumbered to a crazily high degree.

SteveBaker (talk) 15:00, 15 April 2013 (UTC)

This is no kind of direct answer, but the query reminded me of a possibly apocryphal story: when asked what the study of nature could tell us about the Creator, J.B.S. Haldane supposedly replied only that one could conclude that He had, "an inordinate fondness for beetles." --Mr.98 (talk) 17:44, 15 April 2013 (UTC)

See "Lists of organisms by population".—Wavelength (talk) 17:52, 15 April 2013 (UTC)

What is the most populous macroscopic species other than humans? --Yoglti (talk) 00:34, 16 April 2013 (UTC)

What do you consider macroscopic? wiktionary:macroscopic says "Visible to the unassisted eye." Krill and insects are visible. And do you include plant species? Some of those are quite large and frequent in forests. PrimeHunter (talk) 01:35, 16 April 2013 (UTC)

Did you read the link or comment I posted above? Euphausia superba is the answer to your question. There are 500 trillion and they are visible to the naked eye (grow up to 6 cm). Aaadddaaammm (talk) 09:07, 16 April 2013 (UTC)

D-mannose

This substance works by letting E-Coli bacteria to attach to D-mannose and be "escorted" out of the body. The reliable sources about how it functions can be found on the WP:MEDRS discussion.

My question is, is that mechanism of action is absolutely unique? Is there any medicine on the market or in the development that works not by killing bacteria, but rather by allowing bacteria to attach to it? Thank you.

P.S. I'm asking this question, because it's a very interesting mechanism of action that may not result in bacteria resistance. Ryanspir (talk) 14:54, 15 April 2013 (UTC)

(1) Not unique - for example, proanthocyanidins in cranberry juice are thought to have a similar effect. In addition, the Tamm-Horsfall protein may inhibit uropathogens in the same way.

(2) Resistance to this mechanism was described at least 30 years ago (PMID 6105132). This is not surprising - adhesion mechanisms are quite mutable. -- Scray (talk) 20:26, 15 April 2013 (UTC)

Cranberry is not a medicine. My question relates "if there is any medicine..".

2) Thanks for correction. I meant to say evolving resistance. Ryanspir (talk) 13:53, 17 April 2013 (UTC)

quassia amara L. against glucose

In Brazil they use the tea of quassia amara-L to control the glucose. Do you know it? — Preceding unsigned comment added by 151.62.28.190 (talk) 15:07, 15 April 2013 (UTC)

Our article on quassia amara doesn't discuss that use, but there is a small amount of scientific literature on the topic, for example PMID 21480415. Looie496 (talk) 15:40, 15 April 2013 (UTC)

Searching on PubMed I found one article from a university in Uttar Pradesh. [7] They report lower glucose levels in rats and higher glucose tolerance. Another from Argentina seems focused on "preventing self-medication" to avoid what are apparently very rare risks (if only 15 adverse effects could be found in a pharmacovigilance program for this and two other herbs). [8] Unfortunately both of these are in obscure journals unlikely to be found at a local library. The degree to which research into herbal treatments has been neglected is just unbelievable, and often as not the emphasis of research seems to be toward spiking a competitor before there's any chance for benefit to be observed. Wnt (talk) 21:42, 16 April 2013 (UTC)

It's quite difficult to do rigorous research on herbal treatments unless there is a known active ingredient. Without that, there's no way of knowing whether doses prepared at different times and places are equivalent. That doesn't make it impossible, but it greatly increases the challenges. Looie496 (talk) 06:13, 17 April 2013 (UTC)

I don't agree at all! Most of biochemistry was worked out by people doing experiments with stuff like "fraction VII" and observing interesting effects, and none of those were pure compounds. Wnt (talk) 15:06, 17 April 2013 (UTC)

EKG words

Hey there, I have a question about the ElektroKardioGrama, the question is: Why Dr Willem Einthoven has used in the words p-q-r-s-t for the graph, precisely? what was his meaning in these words just (and not another like ABCDE)? מוטיבציה (talk) 15:24, 15 April 2013 (UTC)

From our article here, "Originally, four deflections were noted, but after the mathematical correction for artifacts introduced by early amplifiers, a fifth deflection was discovered. Einthoven chose the letters P, Q, R, S, and T to identify the tracing which was superimposed over the uncorrected labeled A, B, C, and D. [9]". That reference discusses your question quite thoroughly, let us know if you don't have access. Aaadddaaammm (talk) 15:31, 15 April 2013 (UTC)

Thank you, I have not paid attention to that. מוטיבציה (talk) 20:06, 15 April 2013 (UTC)

What is muscle stiffness and how does massage work?

What exactly is actually happening when we have stiff muscles? Wikipedia redirects to DOMS, which I don't mean (or maybe I do but I don't realize). I am talking about the stiffness which occurs after long periods of holding the same position, after sleep, or due to disuse of a muscle. How does massage help in anyway? Many of my friends have their joints cracked and muscles massaged, yet when I read wikipedia many of these treatments are treated as pseudoscience. What does massage actually do? 137.224.239.102 (talk) 17:09, 15 April 2013 (UTC)

I'm not sure the literature provides solid answers, but I'll give you my own thoughts. I believe there are at least three things going on: (1) overuse of muscles causes swelling, which means entry of fluid into the tissues, and massage moves some of the fluid around; (2) muscle tissue is full of sticky proteins and has a strong tendency to form glue-like adhesions -- massage breaks up the adhesions; (3) massage activates stretch receptors in the muscles and thereby causes effects on the nervous system. There is certainly a lot of pseudoscience in the field of massage therapy, and people sometimes overreact against it, but it doesn't seem to me that there is much doubt that basic massage is genuinely helpful for sore muscles. Looie496 (talk) 17:27, 15 April 2013 (UTC)

It might be as simple as temperature. That is, if you are in a cold environment, and haven't used your muscles recently, they may be below the ideal operating temperature (more so on muscles in the arms and legs than on the torso). All chemical reactions are highly dependent on temperature, and that includes those which cause our nerves to fire and muscles to contract. A massage might raise the temperature just enough, by friction and increased blood flow, to make them work properly. StuRat (talk) 17:26, 15 April 2013 (UTC)

I'm a fully trained Swedish masseuse. Muscle stiffness and soreness after exercise is due to a build up of lactic acid in the tissues, which a good sports massage will help to break down so that it can be eliminated: soreness can also be due to small tears in muscles. Massage aims to increase blood flow to tissues so that healing can occur quicker than if left. The sort of stiffness that occurs after a period of inactivity is different as there is no lactic acid to break down. I believe the problem lies in the shortening of certain muscle fibres and tendons which occurs in these circumstances. There is another problem which is that lymph is secreted constantly and circulates around the body - but has no pumping system of its own: it relies on muscle movement and the pumping of the blood around the body to promote the movement of lymph. If the body stays in one place for a long time, lymph gathers in much the same way as water does and tissues swell. Manual lymphatic drainage is one massage technique which gives some relief to people who suffer lymphoedema: other techniques involve strapping and compression. --TammyMoet (talk) 17:51, 15 April 2013 (UTC)

"seabrid" ?

What does the word "seabrid" mean? It is an adjective to refer to the morphology of leaves. --İnfoCan (talk) 17:17, 15 April 2013 (UTC)

I'm pretty sure that's a misspelling of "scabrid", which means slightly rough to the touch. Looie496 (talk) 17:35, 15 April 2013 (UTC)

advanced directives

when do you start implementing advanced directive? — Preceding unsigned comment added by Ucclemm (talk • contribs) 19:06, 15 April 2013 (UTC)

See Advance health care directive. The precise circumstances when it becomes active will depend on jurisdiction and the wording of the document, but it's basically when the patient lacks capacity to make (or communicate) decisions regarding his or her treatment. Tevildo (talk) 19:51, 15 April 2013 (UTC)

a book of blood tests (or with another medical laboratory tests)

Hello, I'm looking for two things, and I would like to get a help for that. The things are: 1. a book which includes the best matter about the blood tests (or tests of laboratory at all, but only medical tests -of course). This book should be with clear information about' like how is each tests made in laboratory, and what is the normal levels of the results etc. (Of course, It's very important to me that this book will be the most recent) 2. website that includes much as possible of the above. — Preceding unsigned comment added by מוטיבציה (talk • contribs) 21:18, 15 April 2013 (UTC)

Searching for "laboratory reference manual" will provide a lot of informative lists, like this one. Searching for "laboratory procedure manual" is less rewarding, but there may be some useful hits. -- Scray (talk) 23:59, 16 April 2013 (UTC)

Buffer Zone

What is a buffer zone? I've heard of a buffer capacity, but not of a buffer zone. On a graph, where is the buffer zone located?

Thank you.

--Jethro B 22:46, 15 April 2013 (UTC)

I normally hear the term buffer zone in a geographic or general sense, like "administrative assistants create a buffer zone between the executives and the public". Did you want it's meaning in a chemistry context ? I know you can add acids or bases to a buffered solution, up to the buffer capacity, before the pH changes substantially. Perhaps they are also calling this the buffer zone. StuRat (talk) 23:28, 15 April 2013 (UTC)

StuRat is correct in regard to buffered solutions. See http://uccpbank.k12hsn.org/courses/APBioI/course%20files/assignments/chapter2homework05.html. However, the term buffer zone has a more general use in graphs: It can be used to describe any straight line or approximate straight line portion of a graph between 2 points of inflexion, outside of which the graph slopes or curves quite differently, there being different processes happening on either side of the buffer zone. Ratbone 124.178.59.243 (talk) 00:03, 16 April 2013 (UTC)

The buffer zone is the region of the titration curve where the Henderson-Hasselbach equation applies. It is any point in the titration where both parts of a conjugate acid/base pair are present; for example where you have HC₂H₃O₂ molecules and C₂H₃O₂^1- ions in the same solution. --Jayron32 00:10, 16 April 2013 (UTC)

Thank you. Not a fan of the Henderson-Hasselbach equation. I prefer using the buffer equation, then using the [H+] value or [OH-] value to calculate the pH. But whatever you prefer! So you're saying it'd be the part of the titration curve from the beginning when the conjugate acid or base is added (mL>0), until the equivalence point (since past the equivalence point, you're just adding excess acid or excess base)? --Jethro B 01:25, 16 April 2013 (UTC)

Bingo. --Jayron32 04:49, 16 April 2013 (UTC)

The Great Apes

Hello, here's my question. If raised as an exotic pet, which would prove to be the least agressive and risky of the two: a bonobo, or an orangutan? — Preceding unsigned comment added by JadeGuardian (talk • contribs) 23:00, 15 April 2013 (UTC)

You might have a different problem with bonobos, when they try to mate with everything in sight. StuRat (talk) 23:32, 15 April 2013 (UTC)

Lol, that's what I thought. Maybe a tufted capuchin will do... --JadeGuardian (talk) 23:44, 15 April 2013 (UTC)

First, let's be very clear. Great apes make horrible pets, and there are serious ethical objections. Apes are today illegally poached from their native habitat, and they continue to rapidly approach extinction. Wildlife_trade just makes them go extinct faster. Read the articles. Here's some specific reasons, for orangs: ([10]) and for bonobos: ([11]). In fact, many people think that apes are persons, see Great_ape_personhood. Even if one could navigate (or criminally ignore) the financial and legal (CITES) hurdles of owning an ape, they would still make terrible pets. Now that that's out of the way, I'll note that some single wild animals can successfully be kept by amateurs, but they tend to be species that are not naturally gregarious or social. This is simply because it would be necessary to provide for dozens of animals to maintain any semblance of natural conditions. Make of that what you will. SemanticMantis (talk) 23:45, 15 April 2013 (UTC)

Oh, no, I'm just as much for animal rights as anyone, that was just more of a hypothetical question. I'm not looking for a pet or anything... --JadeGuardian (talk) 23:48, 15 April 2013 (UTC)

Hypothetically, either could become sexually aggressive towards humans, and be sold off as a research subject for experiments that would be unethical if performed on humans. Not so hypothetically, see the sad history of Oliver_(chimpanzee). The article recounts "Janet Berger herself claimed that Oliver was becoming attracted to her when he reached the age of 16.[4] He mounted her and tried to mate with her. After he tried it several times it became apparent that Oliver was a threat to Janet, and had to be sold." SemanticMantis (talk) 00:01, 16 April 2013 (UTC)

I don't think SemanticMantis has it correct. His cited references are about it being ethically wrong to acquire and keep primates as pets, not about whether they would make good pets once you've got one. Dogs are both gregarious and social - and millions of single dogs are kept as pets and companions by millions of individuals and families. However dogs have three important charecteristics built in: they assign their human master the role of Leader (the alpha male or alpha female), they instinctively want to help and protect both alphas and puppies (they seems to identify children as human puppies), and they are quite intelligent but not TOO intelligent. In addition, humans look and smell so different to dogs that I suspect that dogs just don't see humans in the least bit sexually attractive. These characteristics are not present in anywhare near the same degree in orangatangs and bonobos. One should also note the "randy teenager" phenomenon. We once got a male kitten and a female puppy at the same time. They played together and slept together and got on really well. The dog's growth rate way outstripped the kitten's, but that didn't seem to matter. One day though, when the cat got to it's equivalent to the human teenager years, it tried to have sex with the dog. (I assume that a dog makes, for a cat, a right uggly cat, but that cat was horny. It took a while to figure out what to do, but managed it) The dog made it VERY clear that penetration was not acceptable, and from then on their relationship was much cooler. It ended completely when the dog, now 10x the size of the cat, accidentally knocked the cat flying. One supects that if the cat was 10x the size of the dog, the dog would have had a very sorry life indeed, raped and beaten repeatedly. Wickwack 120.145.63.92 (talk) 00:43, 16 April 2013 (UTC)

Thanks Wickwack, I realize what I wrote was unclear. I thought about dogs and cats while I wrote, quite a bit. But I stand by what I said: dogs and cats are domesticated animals, not wild animals; thousands of years of artificial selection result in a number of behavioral changes. Even "as fast as possible" is ~12 generations, in the case of the dedicated Russian fox domestication experiment). So we can't really expect a wild animal to behave towards humans like a domestic animal might. It is true that sometimes a social instinct can be co-opted in favour of the humans, and it was likely a role in the domestication of dogs (e.g. Domestication_of_the_dog#Promise_of_food.2Fself-domestication). But I would still advise against a single wild wolf kept as a "pet," and I think my link to Oliver the chimp provides an example of "whether they would make good pets once you've got one." SemanticMantis (talk) 01:14, 16 April 2013 (UTC)

Ah! You have a point I overlooked - a very long period of domestication breeding undesirable characteristics out and desirable characteristics in. A wild dog native to Australia is the dingo. Keeping them has been illegal, and whether or not they make good pets is controversial. Many people have done so succesfully though, claiming they have a personality quite similar to dogs. Small numbers of Australians have kept kangaroos - a somewhat gregarious social animal with no history of domestication. Also quite physically capable of killing a human. My cousin had a pet kangaroo and always claimed it was good loving pet, but more difficult to house train than a dog. They have plenty of photos of roo and children cuddled up together. It's really only satisfactory if you have plenty of land area, which my cousin had (10 acres). We once had a neighbour who had a red kangaroo (they grow as high as a man and are downright dangerous in the wild) without any problems, except that it liked to go on long runs and could jump any fence - you need tolerant neighbours. Roos are cheap to keep as they get their own food (Grass and leaves. If you have any nice flowers in the garden, they eat them. If you catch them in the act and say sternly "Bad Roo!", they hop 3 or 4 m away and look at you as though you are weird). Wickwack 124.182.145.187 (talk) 01:48, 16 April 2013 (UTC)

Read The Murders in the Rue Morgue. Looie496 (talk) 23:54, 15 April 2013 (UTC)

Not a bonobo or an orangutan, but Project_Nim_(film) is an excellent doco. The impression that I got was that after a certain size / age, any of the apes become too unpredictable to be safe. I listened to a podcast recently with a primatologist, who did say that unlike all the other apes, a bonobo has never been observed to kill another bonobo, and they exhibit behavior that appears like remorse. In one particular case a bonobo would cower in the presence of a researcher whose finger it had "accidentally" bit off.. Not really comforting IMHO  :) Vespine (talk) 00:36, 16 April 2013 (UTC)

Bonobos will also happily tear monkeys apart and eat them! (see a recent question with a link). I realize now I've gone on way to much on this question, so I'm out now :) SemanticMantis (talk) 01:19, 16 April 2013 (UTC)

Just curious OP, why not gorilla?165.212.189.187 (talk) 12:54, 16 April 2013 (UTC)

I suggest that OP not to jump in at the sallow end. Instead start with a 3.5 day old Homo sapien (I use that phrase kindly – Neanderthal would be more descriptive). Note: Disregard the fact that they don't come with any reliably User Manual!!! Yet, after just the first 35 years, the OP will be ready to take on, not only Bono's and Orang-utans but realise and avoid, all those things that, that un-motherly control-freak Ellen Ripley did wrong. Also Jane Goodall's books are a very good read. --Aspro (talk) 19:47, 17 April 2013 (UTC)

Yes, young humans don't make good pets, for just the reasons I alluded to above: Especially when they become teenagers, they are just too darn independent, they assert their own will, and, dammit, they are most often smarter than their parents. Very well portrayed in Zits (http://en.wikipedia.org/wiki/Zits) Wickwack 120.145.20.216 (talk) 01:13, 18 April 2013 (UTC)

April 16

World population of brown rat

What is the global population of brown rat? --Yoglti (talk) 01:49, 16 April 2013 (UTC)

Brown rat doesn't seem to have totals, but you can infer some things from the article, i.e. the estimated ratio of rats to humans. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:14, 16 April 2013 (UTC)

How are subatomic particle conceptualized?

If they cannot be seen through the most advanced electron microscope, how are they discovered? How are their properties known? How atomic structure known when it cannot be seen? --Yoglti (talk) 02:37, 16 April 2013 (UTC)

See electron#Discovery, proton#History, and neutron#Discovery, for starters. Someguy1221 (talk) 02:52, 16 April 2013 (UTC)

If I hit you in the back of the head with a baseball bat, you know roughly what happened, even if you didn't see me do it. There are ways of extracting information from the world that do not involve your eyes. To answer the question a bit more seriously, the best way to think about this is a combination of geometry and quantum mechanics.

1) We know that atom consists of a dense, highly packed nucleus and a diffuse area occupied by electrons thanks to the contributions of Ernest Rutherford and his gold foil experiment. Rutherford had a theoretical basis in models developed by Hantaro Nagaoka.

2) We know that electrons cannot be physically orbiting the nucleus like a planet orbits the sun, because according to classical mechanics, such particles should be shedding energy all the time (per the Larmor formula), and thus spiraling in towards the nucleus. We know that the atom is stable (that is, electrons don't spiral into the nucleus), so they can't work like that.

3) We know that energy is quantized (that is, energy must exist in discrete amounts, not as a continuum of values) because of the ultraviolet catastrophe.

4) Thus we know that electrons must exist as a particle "smeared out" in space, and whose energy can only have certain values. Those values are based on a set of integer values known as the quantum numbers, and if you feed those integers into the correct equations (known as wavefunctions, or the Schroedinger equations) you get geometric shapes which define the regions in space around the positive nuclei which are where the electrons are. Now, conceptually, you can think of an electron as either a) a three-dimensional standing wave anchored at the nucleus and shaped like these orbitals or b) a probability distribution graphed on a three dimensional graph with the nucleus at the origin. Either or both explanations fit with the basic theory of what an electron is and how it behaves.

5) This mathematics is weird insofar as the kind of physics it describes does not in any way match how any object behaves that your senses are used to working with. That is, what happens at the atomic level simply does not work like anything your senses have experienced. We have various models of atomic-level behavior that attempt to make analogous pictures so we can tie in behavior to experience, but these are all to varying degrees wrong (but then again all models are wrong, some are useful.) These various models, such as VSEPR theory, hybridization theory, atomic orbitals, molecular orbital theory are quite useful in describing how atoms interact with each other to produce the geometric shapes that experiments tell us that they have when they do so.

Hope that helps some. --Jayron32 04:47, 16 April 2013 (UTC)

If somebody hits you on the back of the head with a baseball bat and you ever know what happens, he had better not get a place on the team! Wnt (talk) 21:28, 16 April 2013 (UTC)

Sub-atomic particles can be detected with equipment such as cloud chambers, bubble chambers and other devices listed in Category:Particle detectors. Gandalf61 (talk) 07:52, 16 April 2013 (UTC)

At some level, you also have to ask, "what's so special about seeing?" Seeing just means your eyes are receiving photons (yet another subatomic particle) bouncing off of other things. It's just another means of detection, one that itself has its downsides (you can only see in a very tiny range of the electromagnetic spectrum, for example). Does one completely lose the ability to perceive the world when one's eyes are closed, or when one is blind? --Mr.98 (talk) 11:49, 16 April 2013 (UTC)

As a general rule you can't really "see" most sub-micron particles either (everything from large colloids, to proteins and polymers, and most small molecules fall into this category). For reference 1 micron = 1000 nm = 10000 angstroms, where your typical atom is on the order of an angstrom, thus by definition a sub-atomic particle is at least 10,000 times smaller than the smallest thing we can resolve optically. There are however plenty of non-controversial methods for detecting things we can't see. (+)H₃N-Protein\Chemist-CO₂(-) 12:58, 16 April 2013 (UTC)

A necessary clarification is that I'm referring specifically to optically resolvable phenomena here. I wouldn't count scattering and diffraction as "seeing", but they are examples of "non-controversial methods for detecting things we can't see". (+)H₃N-Protein\Chemist-CO₂(-) 13:03, 16 April 2013 (UTC)

Inter-species sexual attraction

I noticed the discussion Wikipedia:Reference_desk/Science#The_Great_Apes, a thought came into my mind. We known some species are sexually attracted to another species, this makes hybrid animals possible. For example, a zebra may be sexually attracted to a member of another species. This makes Zebroid possible. A male donkey may be sexually attracted to a female horse. If inter-species attraction exists in nature, why humans are not sexually attracted to a gorilla or a chimpanzee? --Yoglti (talk) 08:18, 16 April 2013 (UTC)

They're not? --TammyMoet (talk) 10:22, 16 April 2013 (UTC)

Bestiality is what it's called. However normal people find non-humans distinctly unenticing. If you think you might like it with a gorilla, which would most likely think you are as ugly as you think he/she is, there's probably something in the DSM (http://en.wikipedia.org/wiki/DSM-5) to cater for you - if not, there should be. Wickwack 120.145.25.214 (talk) 10:28, 16 April 2013 (UTC)

As for the possibility of hybrid, see humanzee. --Mr.98 (talk) 11:56, 16 April 2013 (UTC)

I also don't think that mules or zebroids are common in nature; they primarily come about in captivity. Consider the teals. In captivity, a green-winged teal and a blue-winged teal can successfully breed, especially if they have no conspecific mates available. But in the wild they do not tend to not interbreed, presumably because sexual selection usually works to keep reproduction occurring only between very similar mates. So, to answer your question, I think you are inferring the general from the specific. Just because something can occur does not mean it is common. And I'm sure you could find at least one human person that reports sexual attraction to chimps. SemanticMantis (talk) 15:27, 16 April 2013 (UTC)

Do the chicks come out as teal-winged teals? --Trovatore (talk) 18:22, 16 April 2013 (UTC)

Ha, no, still green, at least this for this one [12]. But a clutch of hybrid siblings will show a lot of variety, so some might have more teal coloring. SemanticMantis (talk) 19:34, 16 April 2013 (UTC)

Who is that person? --Yoglti (talk) 15:51, 16 April 2013 (UTC)

Resembles a cow. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:31, 16 April 2013 (UTC)

Changing species through genetic engineering

Is it possible to change the species of an organism through genetic engineering? --Yoglti (talk) 08:19, 16 April 2013 (UTC)

You may be interested in the definition of species, "a group of organisms capable of interbreeding and producing fertile offspring". Naturally, two species are different if their members are unable to breed and produce fertile offspring with one another. Genetically engineering an organism to be incapable of interbreeding with its original species, but still capable of breeding with other genetically modified organisms, is given a theoretical treatment in this paper, specifically the section on "extreme underdominance". Such a thing could be considered a new species, by definition. Genetically modifying an organism to be capable of breeding with an existing and distinct species (such as creating a dog that can breed with a cat) is a much more difficult proposition. Such a feat would basically require overcoming reproductive isolation. For very closely related species, this may be doable, but for distantly related species, the reproductive barrier is likely near impassible. Someguy1221 (talk) 08:55, 16 April 2013 (UTC)

I would say yes. I can't provide a reference, but only personal experience. Humans regularly turn into Trolls. --Onorem♠Dil 16:02, 16 April 2013 (UTC)

Quick question: Is HeLa still a member of the Homo sapiens species? 64.56.89.2 (talk) 17:46, 16 April 2013 (UTC)

One method is by making paracentric inversions or balanced translocations. If you have enough of these in your new lineage, it should be difficult if not impossible for it to interbreed with the original. After that, you just have to make it look cool. :) Wnt (talk) 18:01, 16 April 2013 (UTC)

HeLa#Helacyton_gartleri specifically addresses the HeLa species question. Vespine (talk) 23:21, 16 April 2013 (UTC)

Orbit

According to Prime meridian, "Satellites changed the reference from the surface of the Earth to its center of mass around which all satellites orbit regardless of surface irregularities." Is that right? Would a satellite really orbit around the centre of mass of an irregular object? I understand that for perfectly spherically symmetrical objects the mass can be considered concentrated at the centre, but I thought there was no similar simplification for irregular bodies. 86.176.213.231 (talk) 11:46, 16 April 2013 (UTC)

See Center of mass, and Barycentric coordinates (astronomy). An orbiting body will be perturbed throughout its orbit by an irregular mass, but once you get far enough away, those irregularities in the gravitational field start to smooth out and the force is pretty much constant in the direction of the center of mass. 38.111.64.107 (talk) 11:54, 16 April 2013 (UTC)

In the context of that section, which is talking about centimetre-scale precision, I doubt that "pretty much" is good enough... 86.176.213.231 (talk) 11:58, 16 April 2013 (UTC)

Correct, which is why anything meant to stay in orbit for a long time has station-keeping abilities. However, the center of mass will certainly be the largest contributor to the orbit - the irregular distribution will perturb it from that orbit, but it makes a lot more sense to try to maintain an orbit around the center of mass than the center of the Earth. — Preceding unsigned comment added by 38.111.64.107 (talk) 12:07, 16 April 2013 (UTC)

Oh right, when it says "around which all satellites orbit" do you think it means that satellites are maintained in such an orbit using regular corrections, rather than that they will naturally maintain (exactly) such an orbit? If so, I think I will change the article to try to make that clearer. 86.176.213.231 (talk) 14:05, 16 April 2013 (UTC)

To first order, the satellite's orbit will naturally form an ellipse, one focus of which is at the centre of mass. Instability of the orbit is caused by second order effects which are due to the fact that the satellite is not actually a point mass. Gandalf61 (talk) 15:35, 16 April 2013 (UTC)

You meant that the Earth is not a point mass, not the satellite, right? --140.180.241.109 (talk) 16:25, 16 April 2013 (UTC)

Both. Tidal forces will apply to the satellite - consider that the far side of the satellite and the near side are forced to orbit at the same rate, even though a point in orbit at the far side should take slightly longer to complete an orbit than one on the near side. Interaction from other bodies such as the moon and sun also causes disturbances. 38.111.64.107 (talk) 17:49, 16 April 2013 (UTC)

Identification query: blue mushroom in the PNW

Here's a photo making the rounds on the interwebs, originally from a Seattle-area blogger. One tag might indicate it grows in the Pacific Northwest. I'd like to know its name, and also whether those blue-green colors are natural or were camera-enhanced. -- Deborahjay (talk) 14:17, 16 April 2013 (UTC)

It's a Trametes versicolor - and our article shows examples with all sorts of colors. SteveBaker (talk) 14:44, 16 April 2013 (UTC)

mathmetics

how we can say that 1 by infinity is equal to 0? — Preceding unsigned comment added by ARIF MIKAT (talk • contribs) 14:51, 16 April 2013 (UTC)

The limit of 1/x for x to infinity is zero. This means that for any small number epsilon, you can always find a number y such that for all x larger than y you are closer to zero than epsilon. You can easily that y can be chosen 1/epsilon. So, no matter how small you make epsilon, for large enough x, you will be closer to zero than that epsilon. Count Iblis (talk) 15:11, 16 April 2013 (UTC)

Or...you have one cake, using a very sharp knife you divide it equally amongst an infinite number of people, it's pretty clear that they each get no cake whatever. The tricky question is: "Where did the cake go?" SteveBaker (talk) 16:01, 16 April 2013 (UTC)

I wouldn't say that was in any way "clear"... 86.129.16.178 (talk) 17:00, 16 April 2013 (UTC)

I'll try to make it clearer for you. Your statement is incorrect - you mean to say that the limit of 1/x, as x approaches infinity, is zero. If you don't understand limits, i'll dissect each part for you. A limit is the value of an equation as the x variable approaches a specified number. If I say that x is approaching infinity, then I'm really asking, "What is the value of this equation as x gets larger and larger?" How large is it getting? Really large.

So let's say we plug in 10 for x. 1/10 is .1. Now let's say we increase X so that X is now 100. 1/100 is .01. Let's say that we increased x even more, so that x is 100,000. Well, 1/100,000 is .00001.

It can be seen that as we make x larger and larger (as x approaches infinity), the value for the equation is getting smaller and smaller - it's approaching zero. It doesn't become zero, but rather approaches zero. So the limit for 1/x as x approaches infinity is zero. --Jethro B 19:08, 16 April 2013 (UTC)

P.S. Limits are crucial for calculus and the definition of the derivative. Calculus itself is important for many fields of life, and can actually be a lot of fun if you understand the few basic concepts that it has (except some integrals, those can be killers). --Jethro B 19:10, 16 April 2013 (UTC)

I think the fact that they are killers IS what makes them fun. (never shy away from a puzzle). Dauto (talk) 20:01, 16 April 2013 (UTC)

Don't get me wrong - I love puzzles! One of the things I love about calculus is that you sometiesm need to piece together several concepts to answer just one question. If you're familiar with the AP Calculus AB course, for example, there are really only about 10 or so concepts in the calculus course, and the rest is just applying these concepts. For the Calculus BC Course, it's mainly applying these concepts some more, with about 2 new concepts.

However, there are year-long courses just on solving integrals, since there are so many types of integrals that have different ways to solve them. When you first learn just a few types, and you get an integral that you need to rearrange somehow or change the integrand somehow and then solve, it's a fun challenge. But when you need to recall which way out of so many different ways is necessary for solving that integral, it can get tedious! Or use Wolfram Alpha, shh!!!

That's a bit of a tangent though (see what I did there?) --Jethro B 01:26, 17 April 2013 (UTC)

One could say that 1 by infinity is an infinitesimal - some amount of cake that is less than any positive real amount of cake, but more than zero (which is where the cake goes). But this really should have been filed under WP:Reference desk/Mathematics ! Wnt (talk) 21:25, 16 April 2013 (UTC)

Prove that an infinitesimal is a nonzero number. Plasmic Physics (talk) 08:45, 17 April 2013 (UTC)

This just makes me think of people attempting to reject the idea that 0.999999999999999999999... is equal to 1. Nyttend (talk) 11:54, 17 April 2013 (UTC)

In case you're implying it: I'm not rejecting that idea. Plasmic Physics (talk) 12:03, 17 April 2013 (UTC)

Oh, no, I'm sorry; I meant that the limit-related explanations given to the original question sound like some of the proofs for 0.9999999, since both are proving that number A is equal to number B although none of the numerals in A are in B. Neither one sounds right, and I still have to fight my inclination to think of 0.9999999999 as being less than 1.00000000000. Nyttend (talk) 12:51, 17 April 2013 (UTC)

See here and here. Count Iblis (talk) 13:17, 17 April 2013 (UTC)

To be clear, I'm leaving this one up to the article. If you can resolve the point either way, by all means, cite your sources and add to it. Infinities are one aspect of mathematical philosophy that tend to arouse particular suspicion. There are so many things you can do with them that make perfect sense until they ... just ... don't. Wnt (talk) 15:04, 17 April 2013 (UTC)

In addition to the obvious mathematical flaw of "1 over infinity" as if infinity were a number... there is also the fact that there cannot possibly be an infinite number of people or of any organism... and that there is not an infinite quantity of molecules in any cake, no matter how large it might be. Even the standard phrase in limit theorems, "as x approaches infinity", is misleading. You can't "approach" infinity. It should be "as x gets larger and larger" or some equivalent phrase. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:08, 17 April 2013 (UTC)

Since maths, like geometric figures, are essentially abstractions, I don't think it matters whether or not there are infinite numbers of atoms or other objects. Perfect points, lines and circles can also be said to not exist in reality at all, yet these are very useful abstractions. Although infinitesimals are not comparable quantities (these are non- Archimedean), a sum of zeros is merely zero, but any sum of infinitesimal intervals can equal an interval: in the same sense that an infinite tree with one root can be subdivided into partitioned nodes of smaller fractional quantities an infinite number of times: {1,(a+b=1),(c+d+e+f=1),...}. With .999..., we have a very shallow tree with but one level of subdivision, although it has an infinite number of nodes: {1,(.9 + .09 + .009 + ... =1)}. It is a mistake, IMO, to claim that dividing any nonzero quantity an infinite number of times, as with the tree structure, that one will only obtain zeros though, which perhaps can be better understood with the Cantor set. With the construction of this set, there are two different entities; an infinite set of discrete points (each of these points has exactly zero width, of course, recall that any sum of zeros is zero) and a sum of excluded nonzero intervals which sum to the entire length of the original interval. -Modocc (talk) 22:09, 17 April 2013 (UTC)

1/infinity is typically undefined, but repeating the above answers: it can represent an infinitesimal and, moreover, it is only the limit of 1/x, as x approaches infinity, that is equal to zero. --Modocc (talk) 22:09, 17 April 2013 (UTC)

I think we did this one not long ago on the math refdesk. Here's one possible answer: Suppose you treat a cake as a subset of Euclidean 3-space (it isn't, of course, but if you want to make this into a math question you're going to have to make some accommodations.) Then what happens if you partition the cake into infinitely many identical pieces (say "identical" means one piece differs from the other only by a rigid motion)?

Well, if you cut it into countably infinitely many pieces, then the answer is, none of the pieces can be Lebesgue measurable. So the "pieces" are of such an unwieldy form that you cannot say how much cake is in a given piece. You can cut it into measurable pieces if you have an uncountably infinite number of cake-eaters, and in that case they might be measurable (depends on some other things), but the measure of each piece is zero. So each person gets some cake, but so little that it has precisely zero volume.

Hope this helps. --Trovatore (talk) 22:26, 17 April 2013 (UTC)

This does not make a whole lot of sense to me (I've a computer science background thus my use of a tree data structure). If you add volumes which are precisely zero volume, then certainly these sum to zero volumes which sum to a zero volume (of cake). Or not?-Modocc (talk) 22:56, 17 April 2013 (UTC)

Well, this mathematical cake is composed of points, right? Specifically, cardinality of the continuum-many points. $2^{\aleph _{0}}$ points. What's the volume of a point? It's zero. But put them all together, and you ahve the whole cake. --Trovatore (talk) 00:46, 18 April 2013 (UTC)

Let's suppose you have a cake, or whatever object, that's of finite size but is somehow "solid". Or, to conceptualize it more practically, image a finite volume of empty space, and say you're going to allocate the space to a number of persons as if it were a cake. If it's 1 person, he/she gets the whole thing. If it's 2 persons, they each get half (1/2). If it's 3, they each get 1/3. And so on. The larger "n" gets, the smaller each portion "1/n" gets. "n" can never "equal" infinity, but it can "approach" (so to speak) infinity, i.e. it can get larger and larger. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:37, 17 April 2013 (UTC)

If 1/0 = infinity (or negative infinity) then 0 * infinity = ? Well, this is why it's crazy philosophy. At least Trovatore gave us a link to read. And what he said makes some sense - if you pick a particular slice, even from an infinite number of slices, you're counting it, and if it is spread over an uncountably large number of recipients then there will be none of the infinitesimal left. Wnt (talk) 23:33, 17 April 2013 (UTC)

I heartily agree each slice is and should be counted. :-) I do not quite understand as to what is being counted though with zero volumes. To count "infinitesimal" zeros seems to be not very rigorous at all. Either we are adding together zeros or not (perhaps there is some alternate way of interpreting zero volume). In any case, counting the infinite number of infinitesimal nodes that result from an infinite partitioning, (as with (.9 + ,09 +...)), but where the numbers get infinitely small as one progresses into the tree... well at least I can comprehend a summation of such infinitesimals (because each node must become infinitely small by definition); this kind addition makes sense to me no matter what the data is representing, whether it be volumes, mass or an arbitrarily large number of nonzero likes. -Modocc (talk) 23:56, 17 April 2013 (UTC)

Here is a link to the previous recent discussion on a similar question (I think its the one Trovatore is referring to above). -Modocc (talk) 00:41, 18 April 2013 (UTC)

Main Battle Tank

How can the crews of Leclerc tanks extract the ammo which is not in the autoloader (from inside the tank or outside the tank like T-72) I asked this question before but I think the one who answered me did not notice that I was asking about Leclerc also not only T-72 so he answered : from outside Tank Designer (talk) 20:13, 16 April 2013 (UTC)

Here's a forum discussion (at the very bottom) that explains(?) the procedure from inside. On the top of the next page, it goes into a bit more detail, but the linked photos are blocked. Clarityfiend (talk) 00:59, 17 April 2013 (UTC)

Here's a more-convincing-sounding and easier-to-understand explanation[13] from someone claiming to be a French tank commander. Search for 09:37 (reloading from outside), and 09:39 and 09:44 (theoretically from inside). Clarityfiend (talk) 01:17, 17 April 2013 (UTC)

Thank you very much Tank Designer (talk) 08:00, 17 April 2013 (UTC)

Planck microwave background data

I notice that the Planck microwave background data shown in [14] isn't in our article yet (neither Planck (spacecraft) nor Cosmic microwave background radiation). There is an image at [15] but it is unsatisfying for a few reasons: the left edge is cropped off, and weirdly, when I click on "view image" (and presumably when I save it) I go from a reasonable-looking graphic to one that is slightly smaller with obvious jpeg damage. Above all, however... this time I want more than just one single Mollweide projection - I want the data itself, with the full spherical accuracy available, viewable from every possible perspective. That way if, say, I am hallucinating, say, a giant pentagram centered somewhere around 45N 5E, I can (in concept, at least, and ideally by some practical means) rotate to look straight up at it. So ... what options are available for actually seeing this data? Wnt (talk) 22:05, 16 April 2013 (UTC)

I haven't actually done it, but you should be able to download the data from here and then use a HEALPix viewer like SkyViewer. -- BenRG 00:31, 17 April 2013 (UTC)

The player works, and I found the map .. but the download is 1.7 GB! I may not actually look at it right this minute, but thanks! Wnt (talk) 15:02, 17 April 2013 (UTC)

April 17

Water ya doin'

some water on earth does not change into water vapor for hundreds or thousands of years what water is this--71.164.242.116 (talk) 00:54, 17 April 2013 (UTC)debbie smith

I would assume it's the water frozen deep inside glaciers and ice sheets? This sounds a little like a homework question... Brambleclawx 01:55, 17 April 2013 (UTC)

(edit conflict) There's also ground water (see hydrogeology) and lots of water which is trapped in rocks themselves, chemically bound up as water of hydration and could be very deep within the earth's crust. --Jayron32 02:32, 17 April 2013 (UTC)

Also, there might be locations deep underground where water is sealed in by impermeable rocks on the sides and bottom. StuRat (talk) 02:32, 17 April 2013 (UTC)

Fossil aquifers. Nimur (talk) 18:53, 17 April 2013 (UTC)

Magnolias in southern Illinois

Visited Metropolis, Illinois last week and spotted a tree that looks like a magnificent Magnolia grandiflora, but I get the impression from the article that this species doesn't get very big so far north. Are there other magnolia species that (1) resemble Magnolia grandiflora in appearance, and (2) would be likely to grow to full size in southern Illinois? I can upload a photo if you want it; besides the leaves, the photo shows a massive (and differently colored) version of one of these. See File:Curtis House Metropolis IL.JPG, if that helps at all; it's the same tree, as my photo was taken in front of the Curtis House. Nyttend (talk) 02:50, 17 April 2013 (UTC)

I don't see why it wouldn't be a cultivated Southern Magnolia. Sure, it's natural range doesn't extend as far north as Illinois, but the article you linked at Magnolia grandiflora notes a rather grand Magnolia in Nantes, which isn't exactly in its native range. --Jayron32 03:19, 17 April 2013 (UTC)

In short, if you thought it was a magnolia, it almost surely was. But keep in mind there are zillions of magnolia cultivars, and it can be difficult to ID down to the species/strain. I currently live in central IL, and can attest (WP:OR) that there are many beautiful magnolias around, but I don't think that many are pure grandifloras. For instance, Magnolia_×_soulangeana varieties are very common. They just started blooming last week or so. Some of them are quite old, and I think this year is giving a better than average display. There are a few magnolias in my neighborhood the size of the one in your link. SemanticMantis (talk) 03:59, 17 April 2013 (UTC)

The thing is that the article mentions magnolias getting farther north in the USA but says that they normally end up being stunted, not grand like this one; I can easily understand them flourishing in non-native climes that have weather similar to "home". But since SemanticMantis has them in central Illinois, I have to admit that I misunderstood something; Metropolis is just about as southern as you can get. Nyttend (talk) 11:58, 17 April 2013 (UTC)

I'm not sure what's really going on either. We definitely have some GIANT magnolias. But I'm thinking now that the biggest ones are not the wild-type grandiflora, but some cold-adapted hybrids or domestic strains... and central IL is certainly not much like the south! If you really want to get to the bottom of this, you might ask at the gardenweb forums, or contact a university extension in the region. SemanticMantis (talk) 14:06, 17 April 2013 (UTC)

We have "domestic" magnolias in the Detroit area as well - some of them as tall as two-story houses as not exactly stunted. A long drive (mostly north) from Metropolis and a bit colder in winter. Rmhermen (talk) 15:38, 17 April 2013 (UTC)

john s bergheim

this man was an oil man who lived in Belsize Court, Hampstead. He went to canada and started up a partnership with a Mr McCauley, together they found oil in germany, canada, russia and iran. He died in 1903 in a taxi cab accident. I cannot find any more information than this and would be grateful for your help. — Preceding unsigned comment added by Janeward (talk • contribs) 09:59, 17 April 2013 (UTC)

His partner appears to have been named either McGarvey or MacGarvey. The first article is more informative about their partnership. Searching for "John Bergheim" and "oil" brings up lots of useful hits (more than I can easily list here), although they can't seem to decide if he's a "Viennese banker" or a "British engineer". I may get around to writing a bio of one or the other or both. Clarityfiend (talk) 10:26, 17 April 2013 (UTC)

Focal length and "Focus" difference.

I know that focal length is the distance between the camera and the lens, changing it, will "zoom" the image, focusing will change the distance from the lenses which is being focused that can range from 3 ft to infinity, now what does focus exactly physically does to the lengths? Does it moves the length too? Changing focus will change the focal length?, Thanks. 190.60.93.218 (talk) 13:45, 17 April 2013 (UTC)

This question is not well written, so some guesses or assumption must be made about what you are really asking. The following points may be relevant:-

1. The focal length of a simple lens is a fixed property of that lens, is a measure of the lens focusing power, and is determined by the optical properties of the lens material (the refractive index) and the curvature of its surfaces. Focusing a camera does not therefore, and in fact cannot change the focal length.
2. When you focus a camera, you are moving the lens toward or away from the film/image sensor. When the lens is set for infinity, the distance to the film/image sensor is equal to the focal length - this means that incomming parallel light rays are brought to a point on the image sensor. For objects closer, such that focsing for them is needed, you move the lense further away from the film/image sensor, so that light rays for any point on the object still converge on a point on the image sensor, even though they don't get bent to the same angle after passing thru the lens.
3. In a zoom lens system, there is more than one actual simple lens present, and it is possible to alter the distance between lenses so that the aparent focal length of the lens system is changed. This alters the distance from the film/sensor that is required for focus, thus changing the image size. Zoom lens systems are designed so that when the focal length is changed, the whole lens system is moved as well, so as to maintain focus.

Wickwack 120.145.130.241 (talk) 14:20, 17 April 2013 (UTC)

I thought, the focal length was the distance between the length and the film, which changing makes the image "zoom", thanks for the clarification, but what I'm asking is how you "set" the lens to focus on something while keeping the same "zoom"/FOV. 190.60.93.218 (talk) 15:53, 17 April 2013 (UTC)

Focusing is done by moving the lens or lens assembly toward or way from the image plane, as I explained. However, an undesirable biproduct of doing this is a (generally small) altering of the field of view, as Nimur pointed out. It would be possible to construct a multi-lens system to automatically hold the field of view constant while focusing (just as zoom lens systems are constructed to hold the image in focus while the zoom ratio is changed), however I have never seen nor heard of such a thing - there is no commercial need. If the field of view is not as desired after focussing, move the camera and refocus as necesary. Your English is none too good, so I hope this answers the question you were trying to ask. Wickwack 120.145.20.216 (talk) 01:00, 18 April 2013 (UTC)

(ec) For very simple lens assemblies, changing the focus also changes the field-of-view. This works by moving the lens without changing its optical properties, which moves the focal plane; the effective focal length of the imaging system (not the lens) is changed. Because the field of view changes, this means that every focus change is also a slight zoom. That behavior is undesirable, which is why expensive camera lens assemblies have multiple lens elements. Some elements move during focus to counteract the focal length change due to the movement of the focal plane. As always, here's a pitch for the go-to reference for practical lens assemblies: Applied Photographic Optics, which is unfortunately still very expensive. Nimur (talk) 14:23, 17 April 2013 (UTC)

Caesarean

During a C-section, what is used to stitch the mother back up? Pass a Method talk 15:15, 17 April 2013 (UTC)

Surgical sutures and/or Surgical staples. Rmhermen (talk) 15:30, 17 April 2013 (UTC)

Non-black-body emission.

Our article on black-body radiation says that "...a black body is a diffuse emitter (its emission is independent of direction)". But that's an ideal black-body. Do non-ideal real-world materials also emit light independently of direction - and if not, is there any information about how directional that emission might be? (I know that they certainly reflect light in a directional fashion). Also, if it matters, I'm most interested in emission in the infra-red rather than the visual part of the spectrum. SteveBaker (talk) 16:11, 17 April 2013 (UTC)

I would expect the shape to have an effect, both on a macro scale and on a microscopic scale. That is, a direction with more material "pointed at it" should receive more radiation than others. For example, a long rod would presumably radiate less axially. StuRat (talk) 17:05, 17 April 2013 (UTC)

Steve, we use Lambert's cosine law for ideal materials, and variations on it for non-ideal materials. It can be used to model emission or reflection.

An integrating sphere nearly perfectly approximates a diffuse emitter, even though it is built from real-world material.

In computational imaging, you already know all the ways standard APIs model surfaces for reflection - and you know ambient and specular illumination.

You'll probably find tables and approximations of real-world illuminators; keywords that will help: radiation patterns, lambertian surface, antenna gain. When I learned all this stuff, I learned the theory for RF - and later applied it at visible/optical frequencies. As you know, infrared, optical, and radio light are all just electromagnetic waves of different frequencies - so the theory is identical. The practical parts - answers to questions like "how lambertian is a surface" vary quite a lot: at radio frequencies we almost always say "perfectly Lambertian."

Of course, the model for specularity is scaled by wavelength. If you're using very long wavelengths, every surface has roughness relative to the size of the wave! At infrared and optical wavelengths, this is less likely to be true.

Finally, keep in mind that an emitting or reflecting surface can be specular and non-specular independently of its lambertian or non-lambertian property.

As an example - humans are darned near perfect lambertian surfaces, even though some parts of them are more specular than others. This is (or ought to be) common knowledge amongst photographers; the mathematics are all over the internet, too. Here's one for optical models of human reflectivity, geared towards machine-vision applications - using physics to help robots identify human skin by sight!. From the standpoint of physical principles, if we reflect with that pattern, we probably emit our infrared according to the same law. Nimur (talk) 19:02, 17 April 2013 (UTC)

I thought the Lambertian stuff was about how objects reflect light - I'm interested in how they emit light...and specifically, IR light...due to their temperature. Are you saying that the radiation is also much greater in the normal direction than off at an angle?

Specifically: Suppose we have a heated cube, made of some uniform real-world material, out in the darkness of deep space. If I point an IR camera at it, will I see the various facets of the cube having different brightnesses due to their angle to the camera (which is what I'd see in reflected light) - or will I see a seemingly flat surface of uniform brightness as black body suggests? Could ask the same question of an object heated until it's white-hot, viewed in a conventional camera. SteveBaker (talk) 20:42, 17 April 2013 (UTC)

Correct, you can apply the cosine equation to emitted light in the same way you apply it to reflected light. That would be a perfectly diffuse reflector. The derivation of the lambertian equation is strictly from geometry - it has to do with the projection of the ray onto the unit-area of emitting (or reflecting) surface. Nimur (talk) 00:01, 18 April 2013 (UTC)

Better than a laser printer?

Can something be improved in a laser printer? (besides the price). It seems to me to be the perfect solution, both relating to quality and simplicity. Is there any new technology, with a complete new architecture being developed? OsmanRF34 (talk) 17:24, 17 April 2013 (UTC)

Well, you still have the potential problems from feeding paper in with rollers, which can lead to paper jams. And those moving parts are likely to wear out, eventually. Hopefully some steady-state solution will eventually become available, where you place paper on a flat bed, it prints to it, and you then remove it, with no paper feed mechanism required. (It could still have a paper-feed mechanism for multiple pages, but I typically print one page at a time, so would like this option.)

But printers themselves may become obsolete. In the future, a digital copy on your portable device may serve the same purpose. We already have some digital coupons, allowing us to skip the printing step. StuRat (talk) 17:30, 17 April 2013 (UTC)

Right, eventually there will be usable e-paper. Looie496 (talk) 17:35, 17 April 2013 (UTC)

Perfect solution for what? Laser printers are great for text and simple artwork like charts, graphs so therefore excellent for most documents, fliers are similar things. They aren't quite so good for reproducing photos or some types of artwork so with those, in cases where you care more about quality than cost or time (and possibly water resistance) they aren't really the perfect solution. In addition, while some laser printers can handle banners or continuous feed paper, it's more difficult to implement so is significantly less common then with a number of other forms of printing. Large format (I'm thinking A1 or larger) laser printers are also AFAIK a lot less common then inkjet ones I think for a mix of consumer demand and construction difficulty reasons. Laser printers are also still crap for very large scale jobs. P.S. I'm assuming by laser printer you mean one using toner not Digital printing#Digital laser exposure onto traditional photographic paper Nil Einne (talk) 18:13, 17 April 2013 (UTC)

Perfect for private and office use. For printing docs, not meant to be a big scale enterprise, like book printing and such. I'm not sure that inkejet printers are more common in this context. All people and companies around me user laser printers only since several years, as far as I am aware. OsmanRF34 (talk) 18:19, 17 April 2013 (UTC)

The examples you describe fit with the cases where laser printers work well, that doesn't change the fact laser printers aren't perfect for all uses. No one ever said inkjet printers were more common in the examples you describe although I think inkjets still have a reasonable market share in home use, probably more for printer purchase cost reasons then any of the ones I mentioned. Nil Einne (talk) 18:25, 17 April 2013 (UTC)

I didn't say anyone "ever said inkjet printers were more common in the examples [I] describe." OsmanRF34 (talk) 18:29, 17 April 2013 (UTC)

If the lasers were focused with perfect lenses to carve diffraction gratings into the paper that would act as structural color, so they never needed ink, I would be more impressed. Wnt (talk) 21:35, 17 April 2013 (UTC)

I think you are setting your expectations a little high - a printer that didn't regularly break down, jam or leak toner would be enough to impress me! Equisetum (talk | contributions) 00:01, 18 April 2013 (UTC)

.

Not only are laser printers not a good choice for large formats (e.g., A1 and A0 drawings for engineering) due to technical difficulties, inkjets are far cheaper and, for the last 10 years or so, offer resolution sufficient to make your own eye the limiting factor.

Laser printers are not generally acceptable for contract documents and drawings because their output is not archivable. All of us who have photocopied or laser printed (it's the same technology inside) a manual several years ago know that - the image is not permanent and comes off on adjacent pages. You can inkjet print with HP and Cannon technology printers and come back 200 years from now - if the paper has survived the image printed on it will.

A4 laser printers has become cheap enough, due to volume production (and the practice of manufactuers to sell at a loss and make money on the toner) to make them very common in homes and offices. But they are not built to last - you generally won't keep them more than just a few years. But the enginering/drawing office market is quite different - large format printers built to professional standards last a very long time.

I have an A0 inkjet in my office that has been turning out engineering drawings every day for 15 years (and, yes, we have a driver for it under the currently supported Windows). and the cost of ink (approx $500 a year) is far far below what laser toner would cost. I get to see lots of customer and co-contractor drawing/engineering offices - they all have inkjets, I have never seen a large format laser printer.

So, to answer Osman's question, what improvements are desirable in laser printers:-

1. Make them archivable - image stable for decades, not years
2. Either make them cheap in large formats or make them built to last
3. Reduce the cost of toner so they are competitive with ink for large format high volume applications.

I don't see any of this happening anytime soon.

Wickwack 120.145.20.216 (talk) 00:32, 18 April 2013 (UTC)

Did you move straight to inkjet from plotters? I've seen some quite old plotters still in service (indicating reliability), and to me their output for technical drawings still looks great. I can't imagine dot matrix technology doing well in large format vector graphics, but I don't know much about old printers, or what else might come in between. SemanticMantis (talk) 01:07, 18 April 2013 (UTC)

biology

Is acid rain and normal rain same?If not,then compare the climate before and after the acid rain. — Preceding unsigned comment added by Titunsam (talk • contribs) 18:09, 17 April 2013 (UTC)

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. Nil Einne (talk) 18:14, 17 April 2013 (UTC)

BTW, is it possible you could use a more descriptive title for your questions then the 'biology', 'chemistry', 'physics' you seem to use every time? As an example, in a case like this you could use 'Acid rain' or 'Acid rain compared to normal rain'. Nil Einne (talk) 18:16, 17 April 2013 (UTC)

Yet another Titunsam's question that looks like homework. OsmanRF34 (talk) 18:35, 17 April 2013 (UTC)

You do realise that Wikipedia has a very informative article on acid rain? It even has a very informative article on ordinary rain.--Shantavira|^{feed me} 19:53, 17 April 2013 (UTC)

Can you identify these Prunus species?

1. 16 and 17
2. 18

I would be very grateful. Surtsicna (talk) 19:54, 17 April 2013 (UTC)

For some reason 16 and 17 won't open for me but I think 18 might be Prunus cerasifera 'Atropurpurea'. Richard Avery (talk) 21:56, 17 April 2013 (UTC)

Thanks for your input! Can you open these: 16 and 17? If not, I'll have to try something else. Surtsicna (talk) 22:44, 17 April 2013 (UTC)

salt storing tissue?

Hi, I wondr if some organisms could have cells analogous to fat cells, but for salt instead of energy?thanks76.218.104.120 (talk) 23:52, 17 April 2013 (UTC)

How to destroy a planet in star completely

From i have learned the way scientist predicts inner planets to get swallowed up is to telltrace the chemicals, for example lithium and sodium. But if we get a hypothetical planet in the star how would I destroy it? I learned when a hypothetical rocky planet gets in the sun, they will not instantly get destroyed, they won't completely get destroyed until it gets to the sun's core. So when earth gets in the sun, will earth wait until it gets to hotter layers of the sun to get destroyed completely (only the crust to core) all at once, or it will first eat away the crust and erode the planet progressively (through the mantles to earth's core) as earth gets deeper in the sun. For scientist to predict the inner planets to get swallowed up to they try to find the missing planets and compare their solar system planets to our solar system's planets, or they always find the chemicals inside the star like sodium, lithium rocks which got evaporated into gas. Is this possible other sun-like solar systems might have planets closer to sun like Mercury or much closer to sun than Mercury, like 0.05 AUs away from their sun.--69.226.42.134 (talk) 00:39, 18 April 2013 (UTC)