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October 13

Floor tile material

I'm trying to determine the material some floor tiles are made of. At first, I thought they were vinyl, but after examining a few broken pieces, I now think it's something else. The tile pieces seem too heavy (dense) to be vinyl. They also feel cool to the touch, suggesting a higher thermal conductivity than familiar plastics. The tiles are about 1/8 inch thick (~ 3.2 mm). When I looked at the side of a broken piece, I noticed a rough texture that you're expect from broken earthenware. I also noticed a few sparkling (reflective) particles. What material could that be? Any educated guesses? --173.49.18.190 (talk) 03:06, 13 October 2013 (UTC)

Ceramic, just like you thought. Was that a bathroom tile? 24.23.196.85 (talk) 06:10, 13 October 2013 (UTC)

Ceramic is a possibility that I considered, but one thing I didn't mention was that the tiles seem at least somewhat flexible, as they seem to conform to and reveal the unevenness of the concrete floor below it. The location is not a bathroom. The tiles don't have any features that suggest they are designed for bathrooms. --173.49.18.190 (talk) 13:07, 13 October 2013 (UTC)

If it's from an older house, especially pre-1950's, it could be linoleum. Linoleum was made by mixing all manner of mineral powders, wood flour, etc, in a mixture of pine resin and linseed oil as a binder. The pine resin and linseed oil cured to a hard plastic, and the back side was often given a rough surface. Linoleum is extremely durable and you still sometimes find it. The fillers used, which probably account for >95% of the mass, do provide a higher thermal conductivity and considerably more thermal inertia that modern plastics. 121.221.33.239 (talk) 07:49, 13 October 2013 (UTC)

They could well be linoleum but a word of warning. Many vinyl floor tiles made between 1920 and 1990 contain asbestos and you should get professional advice before disturbing them see: here. Richerman (talk) 09:19, 13 October 2013 (UTC)

I don't know the vintage of the tiles, but they don't seem to have been laid during the period you mentioned (I think they're newer.) Do tiles that contain asbestos have markings or other telltale signs identifying them as such? --173.49.18.190 (talk) 13:07, 13 October 2013 (UTC)

No. In my country there are laboratories that will examine a sample and for a small fee tell you if there is asbestos. I guess there will be similar labs in other Western counries. 121.221.33.239 (talk) 15:08, 13 October 2013 (UTC)

No - if you look at the website I mentioned above it says "Vinyl flooring and wallpaper that contain asbestos cannot be recognized on sight" but it does tell you how to deal with them. However, it's not for me to say whether you should follow that advice or not - you must decide that for yourself. Richerman (talk) 19:21, 13 October 2013 (UTC)

It sounds like vinyl composition tile (VCT), which is a mixture of clays and other minerals in a vinyl resin binder. It's the ubiquitous 12" x 12" tile material seen in schools, large grocery and discount stores (Walmart uses square miles of the stuff), and institutional buildings all over North America. It replaced the more-durable vinyl asbestos tile (VAT), which used asbestos fibers as part of the composition, in the 1970s. It's not always obvious which is which, though VAT isn't especially dangerous unless it's been abraded or pulverized. Usually (but not always) VAT is more brittle than VCT, which will bend a little before breaking, and tends to come in 8" x 8" or 9" x 9" configurations as well as 12" x 12". There is no specific marking for asbestos tiles, since at the time they were being made and installed, asbestos was considered a good thing and was incorporated into a wide range of building products. Here's one manufacturer [1]. Acroterion (talk) 19:05, 14 October 2013 (UTC)

Vegetable identification

Hi guys. What is the vegetable behind the Apple? Thanks. Ben-Natan (talk) 05:39, 13 October 2013 (UTC)

It looks like a gourd. Plasmic Physics (talk) 06:26, 13 October 2013 (UTC)

Some variety of Cucurbita pepo, perhaps a yellow crookneck squash. μηδείς (talk) 20:32, 13 October 2013 (UTC)

Solution book of University Physics with modern Physics 13th edition

While solving problems of Sears and Zemansky's University Physics (by Hugh D. Young and Roger A. Freedman) 13th edition, I face two problems. First, answers of only odd-numbered problems (not the even-numbered problems) are given in the end of book. Whenever I solve even-numbered problems, I am not able to check whether my answers are right or wrong. Second, some problems are really very tough. Also, neither my teachers nor my friends use that book, and they often make excuses whenever I ask my unsolved problems to them. Therefore, I need a link to a website or any solution book. Thanks for helping me. Scientist456 (talk) 07:49, 13 October 2013 (UTC)

You need this booklet with answers to even numbered questions which should have come with the book. You can buy second hand copies from Amazon Marketplace (sorry, I can't post a link, the site seems to be on the blacklist) but most of them do not specify which edition they are for and I don't know how different the questions are between editions. SpinningSpark 10:41, 13 October 2013 (UTC)

What is a prepalate?

The prepalate is at 6.

I am contributing to the article on Kitab al-'Ayn, the first dictionary for the Arabic language. The author arranged the letters according to the source of pronounciation instead of alphabetically.
"Oh, that's a question for the language section of the reference desk."
No, ominous voice. I don't need to know about linguistics, I just need to know what a prepalate is. Is that another word for the hard or soft palate, for example? MezzoMezzo (talk) 10:33, 13 October 2013 (UTC)

This diagram comes from our article Places of articulation. The prepalate is at 6, between the very back of the alveolar ridge and the hard palate. The hard palate is at 7 and the soft palate further back still, at 8. It's a small area and often seems to be subsumed into the areas surrounding it for linguistics purposes. A Google search reveals that oral surgeons do often refer to it as a discrete area in the context of describing the extent of cleft palate. - Karenjc (talk) 12:10, 13 October 2013 (UTC)

What is the scientific explanation for this !

on link http://www.youtube.com/watch?v=jxOyST6gM_A — Preceding unsigned comment added by 37.237.196.193 (talk) 11:03, 13 October 2013 (UTC)

Very amatuerish camera trickery, eg stop motion shooting/editing. For arms shown projecting thru solid objects, chromakeying is the proffessional way to fake it, but this video is sufficiently rough and blurry that they could simply have made a hole in a sheet of fibreboard or similar. 121.221.33.239 (talk) 12:53, 13 October 2013 (UTC)

This is not amateurish camera trickery. The video quality isn't as good as one might expect under the circumstances, but the person involved is Criss Angel, a famous magician, and the video is apparently a (somewhat low quality) copy of an episode of his TV show Criss Angel Mindfreak, which presumably was broadcast with a much higher video quality. Criss Angel is easily rich enough to afford a high-quality custom built trick gate. Red Act (talk) 03:28, 14 October 2013 (UTC)

Your search keywords are "revealed" and "exposed". There are hundreds of videos trying to explain these magics tricks. Cacycle (talk) 17:47, 14 October 2013 (UTC)

A very rich dude acting as a boofhead and using professional staff and equipment to do work with a very amatuerish look then. 121.215.39.252 (talk) 23:51, 14 October 2013 (UTC)

Well, yeah, that's kind of his shtick. His genre is guerrilla magic, so it fits the style he's aiming for to look like an unpolished amateur "average joe" that you might happen to see walking down the street on an average day, except that he's doing something astonishing. I think the idea is that the "magic" is supposed to seem more amazing if it takes place under ordinary circumstances involving an ordinary guy, instead of taking place on a stage under the auspices of a guy in a fancy outfit, under circumstances that are clearly highly controlled. Red Act (talk) 01:28, 15 October 2013 (UTC)

Is there any picture of the mixed flow compressor in the pratt and whitney pw 600f?

hey guys do you know if any picture of the mixed flow compressor in the Pratt and whitney pw 600f exists? cause pratt and whitney mentioned this themselves and the wikipedia artickle says it but there is only one patent picture buzt it downt shows rhe mixed flow compressor..Saludacymbals (talk) 17:12, 13 October 2013 (UTC)

You've seen our Pratt & Whitney Canada PW600 article I take it? SpinningSpark 21:33, 13 October 2013 (UTC)

yes i saw the article but there is only the picture of the fan and not the compressor. so is there any picture of it?

amazing spider web bridge line (which type of spider?

http://www.youtube.com/watch?v=zubftSpCg2E in this video you can see an amazingly thick bridgeline of a spider web but there is a photo in the description of this type of spider. dguys do you know wich type it is? maybe darvins bark? Saludacymbals (talk) 18:36, 13 October 2013 (UTC)

Male and female variation, height and puberty

It is often said that men are taller than women; however, some women are taller than some men.

It is often said that girls begin puberty somewhat earlier than boys; is it also true then that some boys begin puberty earlier than some girls?--Whatdeanerwastalkingabout (talk) 23:57, 13 October 2013 (UTC)

While the logical link you are suggesting is fallacious, the answer is yes, some boys begin puberty at an earlier age than some girls. Puberty onset depends on a variety of factors, including sex, genes, nutrition and social circumstances. So boys with favorable factors for early puberty will experience it earlier than girls with unfavorable such factors. Effovex (talk) 01:56, 14 October 2013 (UTC)

It is often said that women are more fallacious than men. But some men are more fallacious than women. μηδείς (talk) 02:18, 14 October 2013 (UTC)

The trouble with women is that they all make sweeping generalisations :) Richerman (talk) 09:09, 14 October 2013 (UTC)

• People say men are cunning linguists. However, some women are more cunning linguists then men. — Crisco 1492 (talk) 09:15, 14 October 2013 (UTC)

Hmmm... I was going to say something about women being more fellatious but thought better of it. Richerman (talk) 09:24, 14 October 2013 (UTC)

What in the world did you think I was punning about? μηδείς (talk) 18:56, 14 October 2013 (UTC)

You could always try phallacious. -- Jack of Oz ^{[pleasantries]} 11:06, 14 October 2013 (UTC)

Note being one to engage in such puns and frivolity, let me try to give a straight answer. Things such as you describe generally follow a bell-shaped curve. I'm limited to what I can draw here, using ASCII text, but here's a rough idea of what it looks like:

  ^       _
  |      / \
N |     /   \
  |    / MEN \
  +------------>
       Height
  

That graph shows the number of men at each height. Note that there are more men of average height than very short or very tall men. If we did the same graph for women, we would find a similar pattern. although the average would be less than for the men:

  ^    _
  |   / \
N |  /   \
  | /WOMEN\
  +---------->
    Height

If we then graph both together, we get lots of overlap:

  ^    _  _
  |   / \/ \
N |  /  /\  \
  | /W /  \ M\
  +------------>
      Height

So, this shows that the average woman is shorter than the average man, but there are some women taller than some men. It's also likely that the tallest man will be taller than the tallest woman, and the shortest woman will be shorter than the shortest man, although not always, as the bell-shaped curve tends to become more variable at the ends. Now, you will sometimes find a pair of bell-shaped curves which don't overlap, like the weight of adult mice versus the weight of adult cats:

  ^    _        _
  |   / \      / \
N |  /   \    /   \
  | /Mice \  /Cats \
  +------------------->
         Weight

In that case, we could say that all adults cats are heavier than all adult mice. StuRat (talk) 13:05, 14 October 2013 (UTC)

Any two bell-shaped curves overlap by definition, a normal distribution does not have upper or lower limits. It's just that the overlap in some cases is negligible, so the chances of finding a cat smaller than a mouse are very small (assuming that their sizes really follow the bell-curve). - Lindert (talk) 14:06, 14 October 2013 (UTC)

Which of course brings us to the point of contention that most readily occurred to me, because they aren't necessarily likely to follow a bell curve at all. Stu's initial framing premise that "things such as the [the OP describes] generally follow a bell-shaped curve" is not necessarily at all true. It would depend greatly on the feature being considered (with considerable variation even amongst the obvious and superficial phenotypical features). Snow (talk) 22:06, 14 October 2013 (UTC)

Hippety Hopper. DMacks (talk) 14:10, 14 October 2013 (UTC)

Well no, it may not always be the best model, but I think he did a good job of showing how overlapping distributions lead to plenty of cases that happen differently than the average case. And because of the Central limit theorem, bell curves pop up all over the place in nature. In the case of height or start of puberty, it makes sense to expect a roughly bell-shaped curve, even though it obviously won't go off to infinity like an ideal one, and may have other deviations explainable by the properties of the things being measured. Katie R (talk) 14:46, 15 October 2013 (UTC)

Yes, it's not possible to have an infinite height or a zero/negative height. For puberty, I suppose it's possible for somebody to have some medical condition which causes them to live their entire life without hitting puberty. Puberty could also begin at, or even before, birth, due to some medical condition, but obviously can't start before conception. I have no idea whether such medical conditions actually exist, but they are theoretically possible. StuRat (talk) 17:48, 15 October 2013 (UTC)

Delayed puberty has many possible causes, some of which may "delay" it indefinitely. DMacks (talk) 03:40, 17 October 2013 (UTC)

October 14

Do fruit flies spontaneously generate?

I have seen and raised the maggots of Drosophila melanogaster in genetics lab in college. But although I have had briefly self-sustaining colonies of whatever teensy fruit fly is endemic to the NE US come into the house with fresh produce, why have I never seen one of their babies? (And please don't post pictures.) Thanks μηδείς (talk) 02:15, 14 October 2013 (UTC)

For the same reason you never see a baby pigeon - you're not looking in the right place! Richerman (talk) 09:19, 14 October 2013 (UTC)

Perhaps the best place to look is where fruit or their skins have been allowed to acidify, as might be suggested by the first answer in this link. While they may fly inside to lay their eggs on fresh fruit, they might be developing into maggots and then flies outside in the discarded compost and garbage. — Quondum 15:52, 14 October 2013 (UTC)

History of Animals, although it is not the latest scientific research on the matter, supports the theory of spontaneous generation. Thincat (talk) 09:59, 14 October 2013 (UTC)

Aristotle may have been a great philosopher, but as a scientist he was a bust. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:38, 15 October 2013 (UTC)

A great white marble bust. Plasmic Physics (talk) 02:42, 15 October 2013 (UTC)

As a serious note, Aristotle's science was excellent. He tried to induce principles based on observation. The problem with his science is that for the next millennium and a half people repeated his conclusions as dogma without using his method or testing his results. μηδείς (talk) 23:06, 15 October 2013 (UTC)

Fruit flies, humans and everything else we have here did in fact spontaneously generate from a cloud of Helium and Hydrogen gas. Count Iblis (talk) 02:57, 15 October 2013 (UTC)

'Everything' requires more than hydrogen and helium, what about the other elements? Plasmic Physics (talk) 03:18, 15 October 2013 (UTC)

The other elements can be spontaneously generated from hydrogen. Count Iblis (talk) 14:07, 15 October 2013 (UTC)

The same could be said of hydrogen - spontaneously generated from protons and electrons, et cetera ad absurdum. Plasmic Physics (talk) 00:32, 17 October 2013 (UTC)

Indeed, but what matters is that you can just start with some gas in a big enough box, sit back for a few billion years and out will come fruit flies, people, cities, cars, Wikipedia etc. etc., all by itself. Count Iblis (talk) 03:18, 17 October 2013 (UTC)

Spectral radiance/Planck's law

The article on spectral radiance, which I was linked to from the Planck's law article, defines spectral radiance as "the quantity of radiation that passes through or is emitted from a surface and falls within a given solid angle in a specified direction".

The Planck's law article states that the spectral radiance of a black-body, $B(\nu ,T)$, is given by

$B(\nu ,T)={\frac {2h\nu ^{3}}{c^{2}(e^{\frac {h\nu }{kT}}-1)}}.$

I'm trying to relate this law to the definition of spectral radiance above. I'm guessing the surface referenced to in the definition refers to the surface of the black-body, correct? But what solid angle are we talking about? Solid angles are defined with respect to a point (ie the origin of a coordinate system), but no such point is identified in the Planck's law article.

The reason I'm asking this question is that I'm confused about the derivation of the Stefan-Boltzmann law from Planck's law. I would have thought that, to use the notation from the article,

$j^{\star }=4\pi \int _{0}^{\infty }B(\nu ,T)d\nu$,

where the factor of 4π comes from the fact that there are 4π steradians in a sphere. But apparently,

$j^{\star }=\pi \int _{0}^{\infty }B(\nu ,T)d\nu$,

and I don't really understand why.

Finally, is the radiation emitted by a black-body at a particular point on its surface travelling perpendicular to the surface at that point? — Preceding unsigned comment added by 74.15.138.165 (talk) 02:36, 14 October 2013 (UTC)

A black body radiates in all directions from any part of its surface. A black body also absorbs radiation coming from any direction inpinging on any part of its surface. The law of reciprocity applies, and you can easily verify that all directions apply by looking at a hot enough black body surface from any angle. It does not appear dark at any off-normal angle. 121.215.39.252 (talk) 04:35, 14 October 2013 (UTC)

You can derive the Stefan-Boltzmann law from Planck's law as follows. Consider a box filled with thermal radiation in thermal equilibrium. This is described by Planck's law it is isotropic. The energy density as a function of frequency is some function u(nu) (so u(nu) dnu is the amount of energy per unit volume in the frequency interval between nu and n + dnu ). Then because the photons move at speed of c and are isotropic, the flux of photons with frequencies between nu and nu + dnu coming from a small solid angle dOmega is c u(nu)dnu dOmega/(4 pi). Now imagine a small black sphere of radius r inside this isotropic photon gas.

How much radiation will this sphere absorb per unit time? We don't need to calculate any integrals to find out, if we look at photons coming from any particular direction, then the intercepted flux by the sphere is the same as what a disk perpendicular to that direction of radius r would absorb. So, the sphere absorbs an energy per unit time of pi r^2 c u(nu)dnu dOmega/(4 pi) from the incident photons coming from photons from any solid angle range dOmega. Sice both the radiation and the sphere is isotropic, this doesn't depend on Omega, so we can integrate over all solid angles by multiplying by 4 pi. The total flux through the sphere from the photons from any direction is thus pi r^2 c u(nu)dnu = A/4 c u(nu)dnu where A is the surface area of the sphere. Since a black object at temperature T will emit as much radiation per unit time and frequency as it would absorb when placed inside a photon gas of temperature T, this means that a sphere will emit thermal radiation per unit frequency and unit area of c u(nu)dnu/4. This is then also valid for a black object of any arbitrary shape, because each emitted photon comes from some point on the surface and how much radiation each surface element emits per unit time, doesn't depend on the orientation of the other surface elements, as the emission process is a local process. Count Iblis (talk) 14:58, 14 October 2013 (UTC)

Another way to think about it: A piece of hot surface emits only into a half-space, so maybe the factor should be 2 π instead of 4 π. But if it really would be 2 &pi then it would have to emit the same energy into every direction of that half-space, and so if you start with a hot glowing sheet of some material being perpendicular to your line of sight, and then you tilt it, you should still receive the same amount of light from the surface, despite the fact that the surface's image on your retina is now smaller. I.e. the glowing sheet should actually look brighter if you tilt it. This obviously isn't true; the correction factor is equal to the cosine of the angle. Thus, we need an integral not only over the frequencies, but also over the angles:

$j^{\star }=\int _{\Omega }cos(\theta )\int _{0}^{\infty }B(\nu ,T)d\nu d\Omega$

Written out in full:

$j^{\star }=\int _{0}^{\frac {\pi }{2}}\int _{0}^{2\pi }cos(\theta )\int _{0}^{\infty }B(\nu ,T)d\nu sin(\theta )d\phi d\theta$

Thanks, I understand now. 74.15.138.165 (talk) 17:26, 15 October 2013 (UTC)

Icek (talk) 09:17, 15 October 2013 (UTC)

Are neutron star collision energies as large as supernova energies?

I've read that the nature of the energy emitted is mainly in gamma rays, and that unusual magnetic fields are created, so it's somewhat different than a supernova, but is the "pow" comparable in energy?76.218.104.120 (talk) 04:18, 14 October 2013 (UTC)

Well, a supernova certainly gives off more energy at once, when it explodes, but it's quite possible that the total energy given off from a neutron star, or even a normal star, over it's life, might be more. StuRat (talk) 12:41, 14 October 2013 (UTC)

I imagine that the OP was referring to the energy emitted at the time of a collision between two neutron stars, as might happen when they spiral into each other. This is one of the speculative sources of gamma-ray bursts. — Quondum 18:00, 14 October 2013 (UTC)

Yes, I certainly was. Stu misread my question.76.218.104.120 (talk) 08:15, 17 October 2013 (UTC)

Well, assuming that the proportion of gamma ray bursts observed attributable to neutron start collisions is not vanishingly small, that the number of collisions is not markedly larger than of supernovas (per unit time), that you are referring to the energy of each in the gamma ray spectrum, and that the spread over time of the emission is comparable for each, the logical conclusion is that the amount of energy is "comparable". This is essentially a ballpark conclusion; it would make sense to check the premises here a little more closely. There are other forms of radiation that can carry away enormous amounts of energy rapidly, especially neutrinos. — Quondum 18:36, 17 October 2013 (UTC)

Cytomegalovirus and HIV

This letter to Nature, dated 1990, suggests a relationship between cytomegalovirus (CMV) and Human Immunodeficiency Virus (HIV) infection where CMV increases susceptibility to HIV infection. I can't, for lack of google-fu, find any more recent discussion of this relationship between these two viruses. I don't really expect an answer to the question, but I'm looking for instruction that my google-fu might become stronger and am expecting that the masters at the reference desk will know how to find such things. Specifically, it'd be nice to have an actual paper that discusses this link, rather than just a letter. 71.231.186.92 (talk) 04:39, 14 October 2013 (UTC)

Have you searched Google Scholar, http://scholar.google.com/schhp?hl=en, rather than plain old Google? μηδείς (talk) 04:56, 14 October 2013 (UTC)

Yeah, a couple of ways. 71.231.186.92 (talk) 05:24, 14 October 2013 (UTC)

I have read the same, that there is a strong relation. Electron9 (talk) 07:30, 14 October 2013 (UTC)

Three things - firstly, you might not be aware that a "letter" in Nature is an actual, proper, peer-reviewed academic paper in it's own right, for presumably historical reasons Nature calls it's shorter papers "letters" and it's longer papers "articles". The difference is explained in more detail here [2]. Secondly you might want to have a look through these results [3], which are (most of) the papers which cite your paper (I got to this be searching for the title of your paper in google scholar and clicking the "Cited by" link below it). Google scholar doesn't have quite as good coverage as the proprietary databases that also do this, but those are really expensive. I find this search approach is normally the best for looking for more recent discussion on the topic of a paper. Finally you should keep in mind that the paper claims to have found a link between CMV and HIV infection in human fibroblasts, grown in vitro. This may or may not be in any way reflective of the situation in vivo. You should also bear in mind that fibroblasts are not the primary site of infection in HIV, although they can become infected. As far as I can tell from my quick read of the abstract this paper suggests one of the mechanisms by which this can occur, and would probably have no bearing on the primary site of infection which is the CD4 T cell (it would not affect these cells in the same way as the virus utilises the CD4 receptor to gain entry to these cells, rather than an Fc receptor, which is what is induced by the CMV in the McKeating et al. system). Equisetum (talk | contributions) 12:31, 15 October 2013 (UTC)

Is light from light-emitting diode emitted with same phase?

Does light from light-emitting diodes have the same phase ..? Electron9 (talk) 07:29, 14 October 2013 (UTC)

No, a normal LED is an incoherent source. SpinningSpark 07:34, 14 October 2013 (UTC)

...but then again, so am I. :-) StuRat (talk) 20:02, 16 October 2013 (UTC)

Not with a normal LED, but a laser diode is a closely related device which does produce coherent light. Red Act (talk) 15:24, 14 October 2013 (UTC)

What is the opposite of Wikipedia's List of mental disorders?

Is there a list of things that are unique to a healthy, able, sane mind? What is the study of ideal brains called? — Preceding unsigned comment added by 174.65.23.49 (talk) 11:42, 14 October 2013 (UTC)

Mental health and positive psychology study that sort of thing. Unique though, hmm, what is unique to a healthy animal? it can't be six legs like an insect or a trunk like an elephant. Dmcq (talk) 13:29, 14 October 2013 (UTC)

Yes, I would have said "things that are common to a ...", instead of "unique". One example might be having all parts of the brain be operational, such as can be shown on a blood-glucose utilization scan. However, some people have been amazingly functional with even large portions of their brains disabled or absent. StuRat (talk) 13:42, 14 October 2013 (UTC)

Thank you. — Preceding unsigned comment added by 174.65.23.49 (talk) 16:13, 14 October 2013 (UTC)

My brother-in-law wrote a book about that and titled it Optimal Human Being. It seems to get the idea across. Looie496 (talk) 20:23, 14 October 2013 (UTC)

Is he this guy, Kennon Sheldon? Must make for interesting dinner conversations. 220 of ^Borg 18:14, 18 October 2013 (UTC)

Can axon tracts travel *around* the internal capsule?

Can axon tracts travel *around* the internal capsule, or must all the axon tracts travel *through* the internal capsule thereby making the internal capsule a gateway canal-like thing between the cortices and rest of the body? I am having trouble visualizing the bigness of the internal capsule in 3D in my head, based on 2D myelin-stain representations. (Hey, it isn't easy, particularly if this brain sliced in coronally at one or a few locations!) 164.107.102.151 (talk) 17:59, 14 October 2013 (UTC)

If you are asking whether there are any direct pathways between the cerebral cortex and spinal cord that don't travel through the internal capsule, the answer as far as I know is no. But there are a number of indirect pathways that go by completely different routes. Our internal capsule article ought to be helpful to you for visualizing it. Looie496 (talk) 20:17, 14 October 2013 (UTC)

October 15

Overview of chemistry - book?

Can you recommend me a book that is an overview of chemistry? An overview as in it would have a short description of numerous sub-fields and some of their main results and references. --81.175.225.92 (talk) 00:22, 15 October 2013 (UTC)

Any high school or introductory college text will probably suffice. The Central Science by Brown, LeMay, and Bursten, or General Chemistry by Kotz and Purcell are two that I have used before. --Jayron32 00:54, 15 October 2013 (UTC)

Jayron, do you mean Chemistry and Chemical Reactivity by Kotz & Purcell, or General Chemistry by Kotz, Treichel, & Weaver? 121.215.39.252 (talk) 03:25, 15 October 2013 (UTC)

Both, actually. I've use the two of them, and was trying to recall by memory, and conflated the two. --Jayron32 10:45, 15 October 2013 (UTC)

ray of light theory of eyes

one of our articles says " The first theory, the emission theory, was supported by such thinkers as Euclid and Ptolemy, who believed that sight worked by the eye emitting rays of light."

Let's try to understand how the Greeks could have thought so. Why don't people see in a dark room? (cave etc)? Why does a 'source' of light need to be seen in this case, if eyes cast their own light? Most perplexingly - if eyes cast their own light, why can't we see the 'eyes' of other people glowing in the dark, for example? Could you explain a little the very loose kind of thinking that made this almost kind of make sense in a childlike way? 212.96.61.236 (talk) 00:30, 15 October 2013 (UTC)

Well, cat's eyes and some other animals reflect light, and that could be mistaken for emitting light. Perhaps they just thought human eyes emitted "invisible light" (what we might call infrared or ultraviolet), which changed to visible light under the right conditions. StuRat (talk) 00:49, 15 October 2013 (UTC)

But we clearly don't see in the dark... moreover, put someone in a darkish place and then put a whole chorus full of people in front of it, their eyes all shining into it: that person can't see any better. so....? I mean it just seems so unworkable... 212.96.61.236 (talk) 01:11, 15 October 2013 (UTC)

I see in the dark, and furthermore my eyes are sensitive to near IR (down to 800 nm) and near UV (up to 320 nm) -- the IR looks a dark reddish-brown, and the UV looks gray. 24.23.196.85 (talk) 05:04, 15 October 2013 (UTC)

That seems extremely unlikely, unless you are a bird, and even then you wouldn't be able to see IR. The visible spectrum is 390 to 700nm, no reference I've seen shows the outliers being anywhere close to 320-800. That's much further outside the realms of believable than human biology would permit. I would find some sources of true IR and UV light to really test yourself in a double-blind manner (you can start with the LED at the end of a remote control, with someone who isn't you pressing a button in such a way that you can't tell if they're pressing it). If real, go present your self to the Guinness record-keepers. — Sam 63.138.152.139 (talk) 14:24, 15 October 2013 (UTC)

People (like my mother) who had cataract surgery before the latest generation of implantable lenses became available are able to see a little way into the ultra-violet. The idea that you could see into the infra-red or in total darkness is ridiculous. If User:24.23.196.85 truly has these super-powers then (s)he should go find a reputable laboratory where these capabilities may be investigated. (...or WP:NOR...either way). SteveBaker (talk) 15:16, 15 October 2013 (UTC)

Biologists make a lot of generalizations. I will not believe the claim without proof, but see no unevadable reason why it couldn't be true. Wnt (talk) 04:18, 17 October 2013 (UTC)

For the record, I made the measurements myself using a spectroscope and lights (an incandescent light for the first measurement, and several LEDs for the second one), so I'm reasonably sure that my vision does in fact extend beyond the normal limits of the visual spectrum, but I cannot completely rule out experimental error. I'll be glad to have this independently verified, provided you folks tell me where I can have that done and how much it's likely to cost. As for night vision, I never said I could see in complete darkness -- what I said was that I could see in relative darkness (such as on a moonless night) better than most other people, even to the extent of being able to see (some) colors by the light of a full moon. 24.23.196.85 (talk) 05:41, 17 October 2013 (UTC)

Of course it's not possible to fully reconcile reality with the emission idea, which we know to be wrong. People have speculated on the reasons why this idea was so popular -- and there is even discussion on the question of why many people continue to believe it today. That comes down to thinking of ways that the emission theory has intuitive appeal. StuRat mentioned one reason (shiny eyes of animals). Another possibility is the subjective experience of heat or palpable pressure when someone is watching you; this matches the social understanding that a person who's staring at you is doing something to you, rather than you to them. As for the question about the loss of sight in darkness, that was explained either by some interaction of the sunlight with your eye's light, or by the idea that the eye doesn't create the light, but gathers it in and then sends it out again at whatever you're looking at. Here is a discussion of some of the past arguments for the emission idea: [4]. And a paper [5] and short article [6] discussing the question from the point of view of science education. --Amble (talk) 02:15, 15 October 2013 (UTC)

Are you looking for a source, or chat partners to tell you you are right? We can't tell you how correct you are, but we can recommend you read visual perception, emission theory, and intromission theory. μηδείς (talk) 02:19, 15 October 2013 (UTC)

I am offering some answers that have been given to the original question, and was slow in adding the sources from which I drew the information. --Amble (talk) 02:45, 15 October 2013 (UTC)

I am not the boss here, feel comfortable adding what you think appropriate. μηδείς (talk) 02:48, 15 October 2013 (UTC)

Superman's eyes emit light. But he's a strange visitor from another planet, where apparently things work differently. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:33, 15 October 2013 (UTC)

Resolved

See the transactional interpretation of quantum mechanics. You can say that eyes do emit a ray of light, which is propagated backward in time, and interacts with a source. As the ancients were ill equipped to measure the time of flight of the ray, positive or negative, this would have made little difference to them, and so their idea cannot be considered false. (If the ray of light travelling backward in time finds a bright light, star, etc., it is answered by another retracing the path in the opposite direction...) Wnt (talk) 04:16, 17 October 2013 (UTC)

Resolved? What? Who made the correct answer? The ancient belief in this ray theory operated like so: Your eyes emit rays that "feel" what is around you, reporting that information back to you as sight. What a "source of light" is actually doing is modifying the properties of air/glass/water so that such rays can transmit through them. Unaltered air does not permit your eye-rays to pass, resulting in a black appearance, a shadow, across your eyes. Such an idea was attractive to people long ago, as the concept of "action at a distance" simply did not sit well with them (they were far more comfortable with explanations of the senses that were reminiscent of how we feel things with our hands). It's easy to construct experiments to either disprove the idea or require ever-more-convoluted explanations. My source for this was the history book I read when I took history of science in college. I wish I could tell you that book's title, but I don't recall. Someguy1221 (talk) 04:51, 17 October 2013 (UTC)

binder related to textile.

Hi, I want to know that which chemical can decrease the strength or stickiness or can make it completely useless to work.. but I want to know a chemical name, addition of water do decreases its strength but I after a lot of research I havnt got any chemical which can help me out in decreasing the strength of binder.. Pleas help me out. — Preceding unsigned comment added by 182.180.45.104 (talk) 09:44, 15 October 2013 (UTC)

Can you be more specific? There are many different kinds of binder and many different kinds of textile. Water is a chemical, and it can be used to dilute many binders, as can many solvents.--Shantavira|^{feed me} 11:54, 15 October 2013 (UTC)

I have a hard time following your Q, but if you're trying to dissolve something, then most things which can be dissolved are water-soluble, oil-soluble, or alcohol-soluble. So, one of those will probably work. Peppermint oil, for example, can dissolve lots of adhesives. If none of those work, then a strong acid or a strong base might work. StuRat (talk) 17:38, 15 October 2013 (UTC)

i am using binder nameing UD BINDER of BASF for textile printing. i have discusses it with many chemist but non of them helped me out.. i had used a lot of acids to decreases its strength but non of them work out even though i had used strong base also but not succeeded but when I add strong base in the paste which is use in printing after 2 days it's make it like rubber but i want some thing like when i add that powder based chemical in that printing paste it become useless.. its strange but i want to make the printing paste totally unworkable and it happens only when binder losses its strength.. so I want powder based chemical which make binder totally use less..

It might help if you explained what you are trying to achieve. Why do you want to make the binder useless? Wouldn't that be the same as just not using a binder? SpinningSpark 22:25, 15 October 2013 (UTC)

I think the OP must have got some printing paste on his/her clothes, and is trying to find some chemical that will remove it. What I don't know is why he/she is using strong acids and bases, despite the danger of ruining the clothes in question altogether. 24.23.196.85 (talk) 23:27, 15 October 2013 (UTC)

Thermal radiation

I have read the articles on Thermal radiation and Black-body radiation, and I am still struggling to understand the actual mechanism that causes radiation to be emitted from energetic atoms. The explanation in Thermal radiation just says:

These atoms and molecules are composed of charged particles, i.e., protons and electrons, and kinetic interactions among matter particles result in charge-acceleration and dipole-oscillation. This results in the electrodynamic generation of coupled electric and magnetic fields, resulting in the emission of photons, radiating energy away from the body through its surface boundary

I have two conflicting models in my head, from forgotten Physics classes. One or both may be completely incorrect. They are

• If you take a dipole magnet and vibrate it, you will produce an EM wave. If you were able to vibrate it really really really fast, the frequency of that EM wave would be that of visible light, so it would emit visible light. In a warm body, each atom is like a tiny dipole magnet that vibrates, producing EM waves.
• In a warm body atoms are colliding with each other, occasionally causing electrons to jump energy levels. When they return, they may emit photons. Thermal radiation is caused by these emitted photons.

Is either explanation close to correct? — Sam 63.138.152.139 (talk) 14:08, 15 October 2013 (UTC)

The second statement is basically the quantum mechanical version of the first, but then specialized to electrons. The first picture is a classical picture of vibrating charges, but then if you describe this more precisely using quantum mechanics, each such vibrating charge is an (approximate) harmonic potential and there are then energy levels here too. So, it also emits radiation due to the system falling back to a lower energy level.

The relevant processes are spontaneous emission when making a transition to a lower energy level, excitation when absorbing a photon, and stimulated emission. Count Iblis (talk) 14:19, 15 October 2013 (UTC)

Hmmm, you say the second statement is a QM version of the first, but there seems to be a very critical difference: in my "vibrating magnet" explanation I can make my magnet produce *any* frequency by vibrating it faster or slower. In my QM explanation, my iron magnet could only produce those few precise frequencies defined by the energy differences in the electron shells of iron atoms (the "quantum" of quantum mechanics), right? — Sam 63.138.152.139 (talk) 14:35, 15 October 2013 (UTC)

If you look more precisely at e.g. the rotation of molecules mentioned by Gandalf below, then there are energy levels there too, but they are so densely packed that it looks like a continuum. Also, you have to take into account the interactions between the different molecules, an N particle system will have energy levels that for large N will be extremely densely packed. So, physically you putting a magnet in your hand and letting it vibrate at seemingly an arbitrary chosen frequency, or an atom emitting a photon are not distinct physical processes. The former involves many more particles and has a far larger number of degrees of freedom, so the emitted photons can have many more possible frequencies. But it is ultimateley the same quantum theory that explains everything (classical mechanics is only an approximation to quantum mechanics; unlike classical mechanics, quantum mechanics is always valid). Count Iblis (talk) 15:23, 15 October 2013 (UTC)

Both explanations are (more or less) correct, depending on the wavelength of the radiation. Infrared radiation and microwave radiation are caused by vibrations and rotations of molecules. Shorter wavelengths, such as visible light and ultraviolet radiation, are caused by transitions of electrons between energy levels within atoms/molecules. There is a table at Electromagnetic spectrum#Rationale. Gandalf61 (talk) 14:36, 15 October 2013 (UTC)

Wow. Thank you for that table -- my jaw just dropped. I had simply no idea that the continuum of the EM spectrum was caused by separate distinct processes, rather than a continuum of one process (like vibrating atom faster and faster). Thanks! — Sam 63.138.152.139 (talk) 14:41, 15 October 2013 (UTC)

Follow-up question, after seeing the table that Gandalf61 linked to. (please excuse me: my brain is trying to crush together two mental models that have always happily lived in separate bins and now need to be entangled together):

For the "vibrating dipole" model, my physics teacher always likened it to a whip: if your bar magnet is sitting on a table, there is a magnetic field line coming straight out of the North pole. Move the magnet and that field line shifts, but the displacement moves away from the magnet like a wave down a whip, traveling at the speed of light. Vibrate it back and forth and you get an EM sine wave. This was my model for thermal radiation, and a key point of this is that the wave has an amplitude in *physical space*, and that amplitude is the displacement of the magnet (or atomic dipole). That is, in magical-theoretical-world, if you put out metal filings and viewed the magnetic field lines like kids do in school, and your filings were absolutely weightless and frictionless etc etc., wiggling the magnet side to side would produce a sine wave of filings that you could even photograph (ignoring the speed of light).

In the QM model, an electron drops to an lower energy level and the energy is lost to a photon that is emitted with a specific frequency based on its energy. But this "frequency" has always seemed to me to be almost metaphorical -- the photon is a packet of energy with an associated wavelength, but it's not like a sine wave wiggling through space with an actual physical amplitude.

Now I find that both models are kind-of correct for different frequencies. Are both photons of exactly the same "kind"? Is the vibrating magnet actually producing a sine wave with an amplitude in physical space? How about the photon emitted by the electron? The two explanations seem so different, yet it seems they both produce the exact same thing. — Sam 63.138.152.139 (talk) 15:06, 15 October 2013 (UTC)

You need to note a couple of things. Firstly, merely vibrating a magnet DOES NOT produce electromagnetic radiation. If you mechanically rotate a bar magnet, you will get a rotating magnetic field, that is all, no matter how fast or slow you rotate or move it. To get EM radiation, you must have both a varying magnetic field AND a similarly varying electric field in the proper phase relationship. This is easily demonstrated as it is easy to produce very intense varying magnetic fields by passing large varying currents through a wire coil. However, by other means you can produce radio waves that embody significant energy yet the magnetic filed component may be quite small compared to that produced by a current in a coil.

Secondly, yes a warm body DOES radiate EM radiation (with a continuous spectrum albiet peaked at a given frequency). However, this does not require, and mostly does not involve, collisions between atoms or molecules (or collisions between any sort of particle. Collisions cannot occur in a solid or in a pure crystal. But all non-trasparent substances radiate. For instance, carbon, a solid, is a near perfect black body radiator at all temperatures in which it can exist as a solid, including up to the sublimation point, ~3900K, at which it will glow yellowish-white.

Collisions are relevant when considering gasses. Collisions transfer energy from one molecule to another, by the impact changing the translational and rotational velocity of the molecules concerned. Atoms and molecules must distribute their energy between translation, rotation, and electron orbital configuration. Only the spontaeous changes in orbital configuration contribute to black body radiation. The division of energy between translation & rotation, and electron orbitals, is governed by the emission laws.

[Special:Contributions/121.215.39.252|121.215.39.252]] (talk) 15:12, 15 October 2013 (UTC)

If you vibrate a magnet you will have a time dependent magnetic field and hence an electric field. Count Iblis (talk) 15:26, 15 October 2013 (UTC)

So, please Count Iblis, explain then why a radio transmitter needs an antenna, and does not radiate significant energy from its tank coil. After all, considerable energy goes into the tank coil, every half cycle of the carrier frequency, far more (typically 10 to several hundred times) than what leaves the antenna into space. That energy does not leave the coil by going off as EM radiation, it gets passed back and forth to and from that tank capacitor. And as I alluded to ealier, the magnetic component of the EM leaving the antenna my be considerably weaker than the magnetic field near the tank coil. Do not be confused by the fact that any time-varying magnetic field will induce a voltage in nearby conductors, and the electric field thereby created may result in some EM radiation as a secondary effect.

Lastly, consider this: A sinusoidaly varying current in an ideal coil absorbs no energy (as does a sinusoidal current in a capacitor) as the current is 90 degrees out of phase with the voltage. However, EM radiation contains/carries energy, lost to space, which is why an antenna presents an electrical resistance at its terminals (practical antennas may display reactance as well, but resiatnce is always present). Since an ideal coil, which of course does produce a sinusoidal magnetic field, absorbs no energy, there can be no EM radiation. Vibrating a magnet, and any other rythmic mechnical thing you can do to a magnet is not essentially diffrent to driving a periodic current through a coil. In vibrating a mass, you exchange kinetic energy between the mass and the driving device, twice each cycle. In vibrating a magnet in free space, some of the energy gets stored twice each cycle in the magnetic field but it always returns to the driving device, also twice each cycle.121.215.39.252 (talk) 15:45, 15 October 2013 (UTC)

Let's stick to one well defined example, let's consider the vibrating magnet modeled as an exact dipole magnet and work out this example from first principles in full detail. Here you can't a priori assume that a freely vibrating magnet will execute an exact harmonic motion and will therefore not radiate any energy, as you would then assume what you want to prove. An outline of this is is as follows. What you need to do is solve the Maxwell equations (taking e.g. the case of a frced harmonic motion of the magnet) which leads to an expression for the electromagnetic fields which are given in terms of the retarded potential, so the magnet at position r' and time t contributes to the field at position r at time t + |r-r'|/c, this time lag is going to lead to an 1/r contribution to the asymptotic behavior of the fields. If you ignore this time lag, then there is no 1/r behavior. Then the energy flux is proportional to the square of the fields which behaves as 1/r^2, therefore energy will leak away to infinity (the energy flux through a sphere of radius r is the proportional to r^2*1/r^2 = 1, so this stays finite in the r to infinity limit).

Another way to approach this, which is however not so practical for calculations, is to consider the problem of the self-force in electromagentism. If you consider the freely oscillating magnet, then it will oscillate according to a damped harmonic oscilator. But where does the damping force come from? This is, of course due to the emitted radiation, but the source of that is the magnet itself. How to properly deal with this was only solved recently. Count Iblis (talk) 17:56, 15 October 2013 (UTC)

Count Iblis, you cannot just ignore a logical argument and go off somewhere else in gibber-land. You need to show why my discussion above is wrong - and you haven't done that, because I have merely recited facts well known to graduates in electrical and electronic engineering world-wide. There is no difference between a magnetic field established by a current carrying coil (or a straight conductor for that matter) and a magnetic field established by a simple dipole magnet. In free space, an ideal coil or conductor absorbs no energy, and no EM radiation occurs. (In practice, of course, while we can have superconductors, we cannot have completely free space. There is always other (imperfect) conductors somewhere with closed loops. Current will be induced in the closed loops, setting up their own varying magnetic fields, which will do the same to the originating coil. By Lenz's Law (for which the proof is the impossible existence of perpetual motion machines) the induced voltage in the originating coil will always be in a direction/phase that will oppose the originating current, thus synthesising an electrical resistance.) I discussed sinusoidal exitation above to simplify it for the OP, however my argument does apply to any varying exitation, as any engineer will know (think in s-plane). 120.145.145.144 (talk) 00:41, 16 October 2013 (UTC)

Those text books will ignore the effects leading to radiation being emitted, but they will only tell that much later when they actually treat the subject of electromagnetic radiation, because they have not yet introduced the complete Maxwell equations before that.

Thing is that even an uncharged conducting metal sphere rotating in a perfect vacuum will emit electromagnetic radiation and slow down as a result of that. But this is due to quantum electrodynamical effects. Count Iblis (talk) 01:21, 16 October 2013 (UTC)

I'll take that as your subtle admission, Count Iblis, that any such EM radiation, if it in fact occurs, coming from a vibrating magnet or a wire/coil carrying a perioic current, is negligible. It has to be, or said textbooks, including what electrical/electronic undergrads have to study on Maxwells' equations (we got Maxwell in 3rd year of a 4-year course), would not have ignored it. Nor could practicing engineers get away with ignoring any such effects, which they universally do. Nor could they ignore it in the design/engineering of mechanical filter resonators, many of which achieve extremely high Q-factors (20,000 and better, which means the knietic energy is >20,000 times what is lost each cycle), well beyond what is practical in LC resonating circuits. They are carefully sized pieces of vibrating metal. And it is something that can be ignored with respect to the OP's questions too. His teacher was wrong; vibrating dipoles are not the source of black body radiation - electron orbital drops are. 120.145.145.144 (talk) 05:40, 16 October 2013 (UTC)

Infrared and microwave radiation is emitted and absorbed by changes in rotational and vibrational modes of polar molecules - see our articles infrared spectroscopy, vibronic spectroscopy, rotational spectroscopy and rotational-vibrational spectroscopy. Gandalf61 (talk) 08:13, 16 October 2013 (UTC)

True, but that is not black body radiation, and each applies to specific phases - eg the last 2 you mentioned apply only to the gas phase. The radiation and absorbance in these cases does not conform to the black body emission laws, and black body radiation applies to solids and liquids, and in theory, to gasses. In fact, the known atomic structure is not even required to derive the ideal black body emission curve. 120.145.145.144 (talk) 12:28, 16 October 2013 (UTC)

The OP asked about the "actual mechanism that causes radiation to be emitted from energetic atoms". The black body model is a theoretical abstraction based on thermodynamic principles. It does not posit a particular emission mechanism, and so it is something of a red herring in answering the OP's question. The OP's teacher was not wrong, although they may have given an oversimplified explanation. Gandalf61 (talk) 13:03, 16 October 2013 (UTC)

The OP was specifically asking about black body radiation - his/her first sentence is I have read the articles on Thermal radiation and Black-body radiation. And later in his/her question, he/she uses the terms "warm body" and "thermal radiation". So all this nonsense about dipoles and electric fields created by vibrating magnets is a side track. If we are talking about factors affecting the thermodynamic efficiency of gasoline engines, do we concern ourselves about oil drawn past the pistons, just because its calorific value has a tiny tiny theoretical impact? Yes, black body theory itself does not posit a particular emission mechanism - I said that myself. But that only means bodies must radiate with a tell-tale continuous spectrum (the other forms of radiation you mentioned have quite different discrete spectra) - we still need to understand what the actual mechanism is. The OP's teacher was wrong, and wrong in the same sense that you and I would be wrong by saying the energy of a gasoline engine comes from the lube oil burnt. Only more so. 124.178.48.59 (talk) 14:34, 16 October 2013 (UTC)

Surgical Caps and Shoe Covers

Hello. How do you visually distinguish between surgical caps and shoe covers? They look very similar. Thanks in advance. --Mayfare (talk) 16:13, 15 October 2013 (UTC)

Er, well, I'm not sure how to answer this. If you were physically presented with them, the difference would be obvious. If you're looking at a photo, it's hard to come up with solid criteria, because shoe covers are often crumpled and folded in a way that makes their shape hard to recognize. Basically hair covers are round, about a foot in diameter, and relatively thin; shoe covers are foot-shaped with the opening on one end, and pretty robustly constructed. Looie496 (talk) 16:44, 15 October 2013 (UTC)

It may depend on which part of the world you are living in (you don't give your county of origin) but I would say that visually 'shoe covers' are just large enough to encapsulate the foot and 'caps' are larger enough to cover the head, hair (and Tin foil hats for those quacks that feel they need ware need them). --Aspro (talk) 16:52, 15 October 2013 (UTC)

Head covers and shoe covers are generic medical supplies, used in vast quantities (along with gloves, masks, and gowns), and I think they're probably the same shape all over the world. In the veterinary facilities where I've worked, the most obvious difference was that the shoe covers were bright blue and the head covers were white. Looie496 (talk) 17:04, 15 October 2013 (UTC)

If you do a Google Image search for both items you will see there are big differences between the two. The shape to begin with, round for the head and narrow for shoes.Shoe CoverSurgical CapHope this helps! Mike (talk) 16:57, 15 October 2013 (UTC)

As a practical issue, there's no need to distinguish between them, as they come in labelled boxes. - Nunh-huh 02:39, 16 October 2013 (UTC)

Domestic waste solder

I have a handful of bits of solder, mostly crap sucked up with my desoldering tool and bits that ran off during tinning my soldering iron. I live in Edinburgh, Scotland. Should I make an effort to dispose of this in a special way or is that just for commercial enterprises producing large quantities of waste? --2.97.26.56 (talk) 20:12, 15 October 2013 (UTC)

Around here, (in California, in the United States), you would get in touch with your local county's Household Hazardous Waste program and determine the best way to dispose of those types of materials. If you're actually in Edinburgh, here's the website for your city government waste service. Nimur (talk) 20:39, 15 October 2013 (UTC)

It's WEEE, something that ideally you wouldn't put in the landfill waste stream. They do accept WEEE at Edinburgh's community recycling centres (it goes in the "small electrical"). But obviously a wee freezer bag full of WEEE (ahem) isn't worth driving out to e.g. Sighthill. Personally I keep a ziploc freezer bags of the little nasty stuff that they don't collect at the kerb (batteries, CF bulbs, WEEE, paint, etc.) and take it to the recycling place only when I'm taking something large. -- Finlay McWalterჷTalk 20:40, 15 October 2013 (UTC)

Okay, thanks. I'll hold onto it until my next visit to the recycling centre. 2.97.26.56 (talk) 21:22, 15 October 2013 (UTC)

By the way, you should no longer be using lead containing solder unless it is for maintenance of equipment that predates the ROHS directive. SpinningSpark 22:17, 15 October 2013 (UTC)

While it may come in scope of local regulations, I would not be concerned about a mere handfull. You need to keep things in perspective and understand the partly political motivation for the European Lead-Free Directive. Lead is ubiquitous in the environment. Those that frame laws and regulations seem not to understand how and why. Lead was used in all manner of things, including paint. That contributes to lead dust everywhere. Another source is the used of lead sheathing in power and telephone cables for about 80 years, until satisfactory plastic sheaths were developed in the 1970's. I was involved in the installation and testing of lead sheathed cables in the 1960's and 1970's. The sheath was about 3 mm thick and the cable pressurised with air, so as to enable detection of sheath damage and keep out moisture. Those cables still in use or just abandonned and left in the ground (which is most of them) have become porous, constantly leaking air. In many cases the lead has, over the intervening 40 to 80 years, become paper-thin. Where has the lead gone? Leached into the soil generally of course - where it can be further distributed whenever someone disturbs the soil for building construction or whatever. Authorities became concerned about the lead levels in the blood of childen 30 or so years ago. They thought that lead in gasoline was the problem, so various countries around the World banned lead in gasoline. That improved things a bit in the USA because of their high population densities, considerable use of private cars, and low use of diesel engines in busses and light trucks. But Australia and Europe, which have always used diesel engines in any sort of truck, didn't see much change in blood levels. So Europe decided to ban the use of lead altogether - at least that will mean lead levels don't get any worse, and help countries like Australia where some of the environmental contamination comes from dust released in the mining, processing, and transport of lead.

In any case, the lead in solder is pretty much trapped with the tin and rendered harmless. There has never been much concern about electronics technicians and electronics factory staff being affected by lead from solder - though it has always been standard to caution workers to wash hands before eating.

120.145.145.144 (talk) 01:07, 16 October 2013 (UTC)

Human mortality question

Based on known age-specific mortality rates, what is the expected time between successive deaths of the world's oldest inhabitant?→31.54.112.70 (talk) 22:42, 15 October 2013 (UTC)

A little over one year. You don't have to estimate it, since we know the true answer: World's oldest person#Chronological list of the verified oldest living person since 1955. Someguy1221 (talk) 22:48, 15 October 2013 (UTC)

You would have good luck asking this question at the Math desk. It's a basic stats question and the Oldest person page is a large enough dataset to get a good estimate. I don't know how to do the math for you offhand, but they will. I'm guessing a poisson distribution would be a good start. Shadowjams (talk) 02:29, 16 October 2013 (UTC)

October 16

Trackside thing

File:Trackside thing.jpg

What is this?

Over the past few years, thousands of these things have appeared alongside UK railways. What are they? They are about five feet tall and in groups of maybe 30-60 spaced about 20 feet apart. This one was quickly snapped on my phone near Milton Keynes.--Shantavira|^{feed me} 08:02, 16 October 2013 (UTC)

They are trackside lights for night inspections. SourceMike (talk) 13:53, 16 October 2013 (UTC)

Ah, that's interesting. Thanks.--Shantavira|^{feed me} 15:53, 16 October 2013 (UTC)

No problem! I found it just as interesting! Mike (talk) 15:54, 16 October 2013 (UTC)

Children crying because they can't do something?

Is it common for children to cry because they find something difficult? I recall crying about age 10 because I found it too hard to join up my writing (my cursive is now pretty neat IMO) which seems a strange thing to get upset about. --129.215.47.59 (talk) 10:43, 16 October 2013 (UTC)

The Wikipedia article titled Crying states "Crying is believed to be an outlet or a result of a burst of intense emotional sensations". The inability to complete a task can bring on intense stress, which would be an "intense emotional sensation". --Jayron32 10:48, 16 October 2013 (UTC)

If people around you are doing something effortlessly, and being praised for it, but you can't do it yourself, that's pretty frustrating. Happens to adults too. I'm in my sixties and still can't do joined up writing, not legibly anyway. Fortunately one develops a sense of perspective with time.--Shantavira|^{feed me} 11:06, 16 October 2013 (UTC)

A child might well cry because he does not understand some homework requirement such as finding the common denominator in order to add fractions, or writing a book report. Crying can also be a learned response, or a form of manipulation, to get a parent to do the homework for him, or to just avoid doing it at all. I did not see in our article about crying mention of crying as a learned or intentional tactic, or a form of manipulation,or a for of emotional blackmail to get something or to avoid something, although books say it sometimes is. Edison (talk) 21:48, 16 October 2013 (UTC)

I suggest that you pretend to cry, record yourself, and play it back to see how well you did. My guess is that you, like almost everybody else, would be laughably bad at it. --Bowlhover (talk) 05:10, 17 October 2013 (UTC)

I can cry on command, it's very lifelike and I doubt anyone who didn't know me extremely well would be aware it was fake. A lot of my ex-girlfriends, and a few ex-boyfriends (women seem better at this), could do the same with varying degrees of realism- but all on the believeable end of the spectrum. Then again, I know a lot of actors, and while not all of them were, this may bias things a bit. At any rate, it isn't that difficult to do consciously, and if it is a learned response, it might not even be being done consciously- in other words, it's neither implausible nor infeasible.Phoenixia1177 (talk) 06:47, 17 October 2013 (UTC)

Power used by mobile phone and radio towers

When a load is connected to the secondary of a transformer, the power drawn by the primary from the source increases because of the magnetic coupling. Will something similiar happen when a mobile phone is switched on? Suppose a thousand phones get switched on (and hence get 'connected' to the tower), will the tower use more power? The same question applies to radio transmission towers. Does a radio tower consume a more power when radios get tuned to it's frequency (and hence gets 'coupled')? - WikiCheng | Talk 10:53, 16 October 2013 (UTC)

From first principles of physics, we know that a transmitting antenna's effective impedance does change due to the presence of a receiving antenna, even if the receiver is many miles away. But that effect is tiny - you can do the math to verify. In the case of ordinary telecommunications, radio antennas operate in the far field (as opposed to near field). Definitionally, this means that the effects of the receiving antenna are too far away to matter.

A much more prominent effect is that modern digital telephones use a bidirectional protocol. Telephone transmitters are not broadcast towers: they are nodes in a many-node, asymmetric full-duplex communication. The transmitter has more work to do when multiple devices are attached. Perhaps the easiest protocol to intuitively understand is time-division multiplexing; adding more telephones would require a higher duty cycle; in other words, the transmitter is on for a longer part of each time interval, and therefore uses a higher average power.

Depending on where you are, and which company runs your mobile telephones, time-division multiplexing might be supplanted by more advanced digital communication protocols; but in principle, whichever scheme they choose will have the same general relationship between number of users and total transmitter power usage. (Thanks to the rule-of-thumb about circuit design, the gain-bandwidth product, we can relate the engineering tradeoffs between time- and frequency-multiplexing of the transmitter design back to first principles of physics, and the conservation of energy, and so on). Whether you spend the power over a wider frequency-spectrum during a short interval (typically, using complex digital codings); or if you use a narrow spectrum for a longer interval (using time-division scheduling); the same power-bandwidth product gives the same signal-to-noise ratio. In actual designs, practical details may shift the optimal choice in one direction or the other. So, this gives the engineers who design radio protocols a little room for flexibility, and lets them pick the best-available scheme that is implementable in today's electronics technology.

In closing, I should mention that the concepts of base load and variable load also apply to transmitters; it is plausible that for a large transmitter, the base load is so close to the variable-load that the transmitter's power supply cannot reasonably switch modes, or otherwise deliver a variable quantity of power. Such large power-supplies are difficult to design efficiently, and this is an active area for new engineering research and development. Now that software can switch transmitters on and off as fast as, say, once per millisecond (!), power supplies need to be designed that can toggle between peak and idle at rates very close to those software latencies. This seems trivial to the engineers with backgrounds in software and digital systems, but as the power supply designers need to build capacitors and inductors and so forth, they are constrained by device size and switching time. So, while controlling a digital signal at two gigahertz is very easy using today's computers, swinging a couple hundred kilowatts on and off at even one kilohertz is quite difficult. Compound this difficulty by the fact that your cellular tower is sometimes in a remote area that might not connect to a utility electric grid: it might have its own diesel engine or gas turbine... Nimur (talk) 13:37, 16 October 2013 (UTC)

A geometrical analyze of camera capture blur?

If one takes a picture with a camera like the Canon EOS 5D Mark III which has a image sensor with a size of 36 x 24 mm and 5760 x 3840 pixels. That captures an object that moves 0.178 meter sideways during the exposure time at a distance of 180 meters from the photographer. How many mm or pixels will the light from the object traverse during the image exposure? I suspect the distance from the middle of the lens to the sensor plays role here but don't find any data to calculate with. Electron9 (talk) 12:15, 16 October 2013 (UTC)

You have not supplied one vital piece of information. You need the focal length of the lens in use. The pixels traversed will obviously be greater if the lense is set for a higher zoom-in. 120.145.145.144 (talk) 12:43, 16 October 2013 (UTC)

I updated the distance to 180 m. And found this EXIF info which I hope completes the input data set:

Parameter	Value
ApertureValue	7,00 EV (f/11,3)
FocalLength	120,0 mm
FocalPlaneResolutionUnit	Inch
FocalPlaneXResolution	3942,5051
FocalPlaneYResolution	3950,617
XResolution	300/1
YResolution	300/1

Perhaps the EXIF "FocalLength" is another type of focal length ? Electron9 (talk) 14:51, 16 October 2013 (UTC)

Assuming that focal length is correct, the object's image would have moved 120(.178/180)=.1187 mm during the exposure time, which at 160 pixels/mm amounts to 19 pixels. The 36 x 24 mm sensor size is the same as the standard 35mm image size, so at least there's no distinction here between the real focal length and the 35 mm equivalent focal length. Red Act (talk) 17:16, 16 October 2013 (UTC)

It's occurred to me that your phrase "another type of focal length" might possibly be due to your finding the comma in "120,0" to be confusing, because it looks like two numbers separated by a comma, or a number in the thousands with an inadequate number of zeroes after the comma. It actually just means 120.0 ; a comma is used instead of a decimal point in many parts of the world, including most of Europe and South America. See Decimal mark. Red Act (talk) 21:01, 16 October 2013 (UTC)

Considering the camera dimensions are 152 x 116 x 76 mm, I find the 120 mm focal length rather large. Electron9 (talk) 06:10, 17 October 2013 (UTC)

In the picture in the link you gave, it looks like the camera's largest dimension is along the optical axis. And the dimensions don't appear to be for just the body of the camera without the lens, because 76mm would be an extraordinarily thick camera body. So the 120mm focal length seems quite plausible to me, because it's 32mm less than the 152mm total size of the camera along the optical axis. Red Act (talk) 11:57, 17 October 2013 (UTC)

Can natural remedies also be synthetic?

Among the natural occurring substances sold as pharmaceutical drugs (take for example, melatonin or 5htp), could it be that you find several synthesize substances? That would be funny, since some people take them because they want to avoid artificial substances. OsmanRF34 (talk) 15:34, 16 October 2013 (UTC)

Your terminology is wrong -- in the US those things are sold as dietary supplements, not as pharmaceutical drugs. My understanding is that in the US, if a chemical is synthesized, it is treated as a pharmaceutical drug, and the manufacturer has to provide proof of safety before it can be sold. If it is derived from a plant or animal, it is treated as a dietary supplement, and the burden of proof is in the other direction. Looie496 (talk) 15:50, 16 October 2013 (UTC)

I doubt that's correct Looie. There are synthesized "artificial" products that are not drugs, such as many "artificial flavors." There are specific definitions of "drug" and so I can't speak to them all, but at least some of those do not turn on whether a product is synthesized. I would need to see a good cite before I believed Looie's comment. Shadowjams (talk) 23:07, 16 October 2013 (UTC)

See the section about the DSHEA in [7], it discusses the shift in burden of proof to the FDA- the initial segment discusses that drugs must undergo stringent testing. Here's the actual text of the act (DSHEA), [8], see section 4 about the burden of proof issues; this, also from the FDA, [9] mentions that the FDA is required to take action after it is on the market. This from the FDA, [10], states that supplements do not require approval. For an FDA def. of a drug, see section 321(g)(1) of [11]- in that section, it mentions a distinction between drug and supplement relating to section 343(r), which can be found in this document, [12]Phoenixia1177 (talk) 09:08, 17 October 2013 (UTC)

By the way, this is in relation to the burden of proof claim- natural -vs- synthetic does not appear to enter into the issue, it appears to be related to what is being claimed. I haven't done the research on that specific aspect, but nothing I've read seems to draw a distinction, it is not directly in the definitions- indeed, the linked ones would appear to refute the claim, unless they were amended somewhere.Phoenixia1177 (talk) 10:09, 17 October 2013 (UTC)

But the lines gets blurry when the same chemical can either be produced by nature or in a lab. StuRat (talk) 19:57, 16 October 2013 (UTC)

This makes me think of 1080 poison, it is used to eradicate possums, which an introduced pest in New Zealand. If I'm not mistaken, being sodium fluoroacetate, it is a salt of a "natural substance", isolable from certain plants. So 'natural/organic/non-synthetic' are utterly useless terms when determining the toxicity of a substance. Plasmic Physics (talk) 00:29, 17 October 2013 (UTC)

If the absolute structure of a synthetic substance is exactly the same as that of the naturaly derived substance then it is considered bioidentical and as long as it is very very pure then it is as "good" as and as "healthy" as the purified "natural" one. This is essentially an economic desision, is it cheaper to extract from the natural source e.g. morphine or synthesize e.g. ephedrine and pseudoephedrine. Die Antwoorde (talk) 08:07, 17 October 2013 (UTC)

<rant>I find the "natural = good for you, artificial = bad for you" philosophy one of the strangest perversions of logic of modern times. Firstly an artificial substance that is chemically identical to a natural one is indistinguishable from it - it doesn't remember how it is made, it is, literally, the same thing. Secondly the statement is patently, demonstrably ridiculous - arsenic, mercury, uranium, snake venoms, hemlock, amatoxin, and all infectious diseases are entirely "natural", and not one of them is good for you. Paracetemol, aspirin and hundreds of other drugs are entirely synthesised and, if taken appropriately, cause little harm compared to the amount of good they do. Thirdly it is not even applied consistently - I have often seen vaccines disparaged because they are "artificial" when they are in fact one of the most natural therapies I can think of - priming the immune system to respond to previously encountered antigen is entirely in harmony with how the immune system naturally works. It is certainly more natural than many alternative therapies, take accupuncture - in what situation in nature are needles inserted in extremely specific locations on the body? This is not even getting into the strangeness of the philosophical position that regards humans and what they make and do as "not part of nature".</rant> Equisetum (talk | contributions) 11:24, 17 October 2013 (UTC)

For natural vs nature identicle)The difference resides in the impurities present!

For compouds that are "human designed"?)It is mainly a hstory of safe use thing. And it is not like we even know all of whats naturally in everything or if cretain "human designed" desigen compounds naturally occur in something! Die Antwoorde (talk) 12:55, 17 October 2013 (UTC)

Fair enough - if the impurities make a difference then they make a difference, but then the issue is the impurities, not the natural vs. artificial origin (if you could replicate the impurities as well the artificial stuff would be just like the natural). Likewise with the history of safe use - the issue is the history of safe use, not the origins, a newly discovered natural substance is more risky than an artificial compound with a long history of safe use. I accept that natural vs artificial can often broadly correlate with both these things, but I find the masking of the real issues behind the facade of natural vs artificial to be unhelpful at best and profoundly damaging to people's ability to make rational decisions at worst. Note that I'm not accusing anyone in this thread of this at all - in my opinion it's predominantly the mainstream media and the food and supplement industries that are responsible (along with the generally abysmal standard of school education in critical thinking and the assessment of evidence). Equisetum (talk | contributions) 14:40, 17 October 2013 (UTC)

What about enviromental etc differences between extraction of natural vs synthetic not just the bottom line $$. 122.111.240.138 (talk) 15:37, 17 October 2013 (UTC)

But, wouldn't the probabilities of impurities be lower in the case of artificial compounds? It seems intuitively easier to synthesize a pure compound than extract a pure one from some organic matter. OsmanRF34 (talk) 15:03, 17 October 2013 (UTC)

Yer but the impurities will likely be not natural stuff with no history of safe use.

Antibiotics in routine lab work

I was wondering how/why certain antibiotics are selected for use in lab work. Why penicillin and streptomycin and ampicillin and kanomycin? Is their use or disuse in medicine a consideration? --129.215.47.59 (talk) 16:17, 16 October 2013 (UTC)

I'm not sure what you mean by "lab work", but generally speaking the antibiotic effects of these drugs are a consequence of their chemical properties, which can make them useful in other contexts. For example, penicillin breaks down a component of the bacterial cell wall -- it also causes epileptic activity when applied to brain tissue in high concentrations. Looie496 (talk) 16:27, 16 October 2013 (UTC)

"Lab work" meant such work in a life science research facility, forensics lab or a myriad of other establishments employing such techniques as bacterial transformation and/or culture for production of plasmid DNA, among other things. --2.97.26.56 (talk) 21:39, 16 October 2013 (UTC)

Almost certainly price and availability factor in greatly, but there is also a lot of mindless rote tradition in biology. If someone does a demonstration once and it works, the next will tend to do the same thing, and the next, and the next... Wnt (talk) 04:11, 17 October 2013 (UTC)

More mindless than in chemistry and physics? 129.215.47.59 (talk) 10:35, 17 October 2013 (UTC)

I'd agree there is a lot of rote tradition in biology - but it isn't exactly mindless most of the time - if something works well you stick with it unless you have a good reason not to. This is for at least two very good reasons 1) It lets you more easily compare your experiments with others both in the same lab and outside it 2) you don't generally have to spend nearly so much time optimising protocols if they are already well used and characterised. I quite deliberately try to use "standard" techniques when I can because of this. It does often become mindless though when something doesn't work well for a particular system and people stick with it anyway because it is "what everyone does". With the antibiotics specifically, they are often used as a selection agent when transforming bacteria etc. (i.e. you include a antibiotic resistance gene in your construct so that you can select for those bacteria that have taken it up by plating them on antibiotic media). For this you need to use one which has a cloned, characterised and readily available resistance gene. In practice, since people don't tend to design their own vectors if they can use one "off the shelf" the choice is usually made for you when you choose the vector. I have never come across medical use as a specific contraindication for using an antibiotic (I presume you are thinking that you don't want to go around playing with resistance genes for medically essential antibiotics in case of accidental release). If you are using proper biosafety procedures it should not be to much of an issue in any case. I'm still not sure that I would be comfortable using a "last ditch" antibiotic such as vancomycin in the lab, although I have come across one protocol in the literature which used it (as a "quick and dirty" way to eliminate the gut microbiome of a mouse when you don't have access to germ free and gnotobiotic mice). Equisetum (talk | contributions) 10:58, 17 October 2013 (UTC)

I used to have a construct that used chloramphenicol as a control. It was the horrible cut-and-paste vector that had been spliced together from a number of different commercial plasmids, and passed down from lab to lab. No one even had a map of the whole vector, and it had duplicate restriction sites in completely illogical places, including several in the middle of the antibiotic resistance gene! Completely mind boggling that anyone used it. Part of why I'm glad I don't do much of any molecular biology these days.(+)H₃N-Protein\Chemist-CO₂(-) 11:15, 17 October 2013 (UTC)

Yes - that'll be the mindless part alright (not on your part - you recognised it was bad) - jesus, I can imagine using that, grudgingly, if I absolutely had to, but an incompletely mapped vector is entirely too much flying blind for my taste. Another thing I particularly "like" about molecular biology is the fact that no-one at all follows the protocols in the standard reference book (Molecular Cloning, A laboratory manual) because a PhD would take half your life if you did, but there is no standard reference for the quicker protocols and shortcuts that everyone actually uses! Equisetum (talk | contributions) 12:10, 17 October 2013 (UTC)

(edit conflict)What Equisetum said, more or less. - It's because you're using commercial vectors, so you pretty much have to use whatever antibiotic resistance is already built into the plasmid. Cloning out and replacing the antibiotic resistance gene in a bacterial expression vector is not particularly convenient, since the more useful restriction sites (places that restriction enzymes can cut the DNA) are near the multiple cloning site (where you put the gene), making it harder to actually excise the antibiotic resistance gene without accidentally ruining the construct. As a result, most people just stick with commercial pET vectors for expressing stuff in E.Coli, which means sticking with the more common antibiotics. If you accidentally damage the part of the plasmid with antibiotic resistance, then even the successfully transformed bacteria will die when you try to grow them on antibiotics. The whole reason for using these genes is that it forces your bugs (bacteria) to keep the plasmid you've given them or die, that way as long as you keep them on media with the appropriate antibiotic they have to express your protein of interest. (+)H₃N-Protein\Chemist-CO₂(-) 11:09, 17 October 2013 (UTC)

Bupropion: Elontril and Wellbutrin

Why has Glaxosmithkline two names for the same drug? I understand that Fluoxetine can be called Prozac or by other names, but these are from different companies. — Preceding unsigned comment added by 80.58.250.84 (talk) 17:24, 16 October 2013 (UTC)

It may be region specific. While GSK "owns" the drug it gets marketed by different partners which may offer it under different brand names. Mike (talk) 17:50, 16 October 2013 (UTC)

SourceMike (talk) 17:50, 16 October 2013 (UTC)

Right, it's region-specific. The name Wellbutrin is used in the US; Elontril is used in Europe. It might be worth noting though that Bupropion is actually sold by GSK under two different names even in the US alone: Wellbutrin and Zyban. The main difference is that the Wellbutrin formulation is intended as an antidepressant, whereas the Zyban formulation is intended to treat nicotine cravings. Looie496 (talk) 18:19, 16 October 2013 (UTC)

Lucid dreams

I'm quite interested in these sorts of things. Are there any particularly notable studies and/or papers I could read on lucid dreaming? Thanks! --.Yellow1996.^(ЬMИED¡) 18:21, 16 October 2013 (UTC)

Not exactly a reliable source however does have some good information: [13]Mike (talk) 18:48, 16 October 2013 (UTC)

Looks great (and anyone else is welcome to add what they find); thanks! :) --.Yellow1996.^(ЬMИED¡) 19:02, 16 October 2013 (UTC)

Omni Magazine published a Survey of lucid dreaming in April 1987 (Archived issue). This link summarises the results: [14]. --Auric talk 19:17, 16 October 2013 (UTC)

Cool - that one is really interesting. I'll read it in it's entirety soon. --.Yellow1996.^(ЬMИED¡) 19:28, 16 October 2013 (UTC)

is it true you can peer into the distant past?

is it true you can peer into the distant past by looking up at the stars? what does that mean? how far in the past? 212.96.61.236 (talk) 21:42, 16 October 2013 (UTC)

I don't even know how to answer this...no sorry! Mike (talk) 21:48, 16 October 2013 (UTC)

The speed of light is finite so when you look at the nearest stars you see them as they were about four years ago, and distant galaxies can be seen as they were billions of years ago.

What would be much more interesting is if they had huge mirrors and you could see what happened on earth eight or more years ago. They don't so we can't but hopefully aliens have recorded the Jack Benny Show or I Love Lucy or so we can enjoy them again. Even now aliens are recording and treasuring the The Rush Limbaugh Show or studying it in their equivalent media studies at university ;-) Dmcq (talk) 22:07, 16 October 2013 (UTC)

We recorded those shows ourselves, you know. StuRat (talk) 14:36, 17 October 2013 (UTC)

• We know the distance to various stars and galaxies in light years. If Sirius is 12 light-years away it takes its light twelve years to get here. So when you look at it you are seeing it as it would have appeared 12 years ago to somebody in the same solar system as it. This applies to the Alpha Centauri system, which is just over 4 light years away, to the Andromeda Galaxy, which is 2.5 million light years away. Betelgeuse, which is in the process of dying, is 642 light years away. It may actually already have gone nova, but we just haven't seen it yet. μηδείς (talk) 22:14, 16 October 2013 (UTC)

You can see into the very recent past by looking at your hand...the light that reaches your eyes is a couple of nanoseconds old - so you're seeing your hand as it was a teeny-tiny fraction of a second ago - not as it is "now". By extension, everything we see is somewhat delayed due to the time it takes the light from that object to reach us. Our other senses are delayed by even more than that. Sound waves travel at around 700 miles per hour - so if you can hear something happening a mile away, you're hearing it from about 5 seconds into the past. When the island of Krakatoa exploded, it was heard 3,000 miles away - and those people heard an event that had already happened four hours in their past! So yes, when you look out at the sky, you can see into the past. To pick a concrete example - on a dark night and with the naked eye, you can just about see the Crab supernova - and what you see is what was happening there 6,500 years ago when the pyramids were being build in Egypt. Nobody knows for sure what it looks like right now, and we won't know that for another 6,500 years. SteveBaker (talk) 22:43, 16 October 2013 (UTC)

More prosaically, every time lightning flashes, you see it nearly instantaneously (some very small fraction of a second), while you hear the thunder a few seconds later - a handy gauge for estimating how far away the lightning is. And if you're some distance from a ball game, it's almost unnerving to see the batter hit the ball soundlessly, and then hear the crack of the bat as he's running toward first base. Seeing into the past, hearing from the past. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:02, 17 October 2013 (UTC)

You may want to try to spot M81 with the naked eye see here for directions. You will then look 11.8 million years back in time with the naked eye. Count Iblis (talk) 23:36, 16 October 2013 (UTC)

Although you can't see it with the naked eye, the cosmic microwave background radiation was emitted around 380,000 years after the Big Bang. We study it to find out what was happening in the universe 13.8 billion years ago, before any stars or galaxies had formed. It's not possible to directly look back any farther than that, because the universe was not transparent at earlier times. --Amble (talk) 00:13, 17 October 2013 (UTC)

Can things interact faster than the speed of light? If not, does "now" have any real meaning for distant objects?  Card Zero  (talk) 02:43, 17 October 2013 (UTC)

That's kind of the "God viewpoint", i.e. somehow being in more than one place at once. But speaking in mortal terms, if light took 4 years to get from Alpha Centauri to us, then we're seeing it as it was 4 years ago... and conversely, if some cognizant being is there and can see our sun, they're seeing it as it was 4 years ago. Barring some catastrophe in the interim, their "now" should be just as meaningful to them as our "now" is to us. Would they be exactly the same "now"? If you could have magically plunked down a pair of clocks, set to the same time, in both places 4 years ago, and then magically retrieved them from both places now, would they still be in sync? Maybe, maybe not. But they should be close enough for government work. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:55, 17 October 2013 (UTC)

Andromeda paradox. Count Iblis (talk) 03:14, 17 October 2013 (UTC)

At least under the special theory of relativity, the concept of now (ie, events happening at the same instant of time) makes sense in a fixed inertial frame of reference. However observers in different frames of reference need not agree on whether two spatially separated events occur simultaneously or not; so the concept of now is not absolute. See relativity of simultaneity for further details. Abecedare (talk) 03:16, 17 October 2013 (UTC)

That's an oversimplification though. If one has the relative accelerations one can choose a frame of reference and calculate a now relative to it. Of course you won't be similtaneously aware of things outside you light cone. But existence and awareness are two different things. μηδείς (talk) 03:48, 17 October 2013 (UTC)

Yes, the universe is expanding. The rate of expansion and the speed of light is a Doppler phenomenon and is partly explained by the Hubble flow of the universe. Three dimensions is hard to visualize so a simpler model is to use a 2D model of the surface of a perfectly spherical balloon. If you image the light path between objects to great circles on the balloon, you will see that every point on the surface moves away from every other point as it inflates. The further the object, the faster it moves. As light has a constant velocity, this movement is reflected in a Doppler shift or commonly called the red shift. This is the way we measure distance to galaxies and stars as the frequency emmision of elements with zero relative velocity is known. The more the galaxy shifts to to longer wavelengths indicates that it is far away and moving away faster than nearer objects. The farther away it is, the older the system we see and therefore the farther back in time. It's fallacy, though to say we are "looking back in time" because there is no universal frame of reference (which point on the surface of the perfectly spherical balloon is the center?) We will never look back in time to our own sun, rather it is a measure of distance. It's 8 light-minutes away. For far away galaxies, it's more like saying the time difference and the spatial difference do not vary by the same amount through theories of relativity. They are moving away in time from the big bang just as we are but the speed and distance makes it look like they are closer to the big bang than we are., --DHeyward (talk) 09:55, 17 October 2013 (UTC)

If something happens on the sun, we see it 8 minutes later. Logic says we're looking back in time, i.e. we're seeing something that happened 8 minutes ago. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:14, 17 October 2013 (UTC)

Quantum Relative Entropy

Is the quantum relative entropy between two pure states always either zero or infinity? — Preceding unsigned comment added by 81.155.161.54 (talk) 21:58, 16 October 2013 (UTC)

Yes, if I'm understanding Quantum relative entropy#Non-finite relative entropy correctly. Red Act (talk) 00:00, 17 October 2013 (UTC)

October 17

Second opinion

Light can break Newton's third law – by cheating

Can I justify believing the veracity of the claims made by this experiment.? Plasmic Physics (talk) 00:49, 17 October 2013 (UTC)

You can read the claims made by Ulf himself in his paper. It's rather beyond me, honestly, but he makes no claims about violating the laws of physics. And I wouldn't trust anything you read on New Scientist anyway. Someguy1221 (talk) 01:02, 17 October 2013 (UTC)

I mean, how falsifiable are his claims, and do they stand up to scientific scrutiny? Plasmic Physics (talk) 01:10, 17 October 2013 (UTC)

So far as I can tell, his claims are eminently falsifiable. Unlike earlier theoretical works regarding diametric drives, Ulf's does not require any exotic materials to function (it also doesn't necessarily do anything useful). Anyone with the right expertise and resources should be able to build it, though since I do not have the expertise I have no idea how difficult that would prove. It's worth noting that this was published in Physical Review Letters, which is considered one of the most prestigious journals devoted to physics. So it is a given that this work was reviewed by several independent experts prior to publication. Someguy1221 (talk) 01:24, 17 October 2013 (UTC)

Yes, it's falsifiable, and I see no reason to doubt that the experimental realization was as reported. Note that even in the science-fiction scenario of a negative-mass diametric space drive, you're still not really violating Newton's third law. Instead, it's the consequence of applying Newton's laws to something with negative mass. The idea of breaking Newton's third law seems to have been introduced in the New Scientist report rather than the article itself. --Amble (talk) 05:42, 17 October 2013 (UTC)

I don't see how it happens. The objective appears to want to create a mass difference between two objects. But conservation of energy still applies. There is no such thing as a "rest mass of light." It's not zero. If there is a frequency, it has energy and mass. If it doesn't, it's not light. I can almost grasp a situation where a mass imbalance occurs between the front and rear of a spacecraft but not as a free energy + mass on one side and - mass on the other based on an interference pattern. Maybe a massive amount of light forced into a material withe significant dielectric differences fore and aft but that would just recenter the center of mass and it would return when the beam was stopped. --DHeyward (talk) 10:28, 17 October 2013 (UTC)

The overall conclusion seems to be "something that behaves mathematicaly similar to mass, but allows some probably impossible things (negative mass), behaves as we would expect that impossible thing to behave". As far as I can tell, the "drive" effect is only on the propagation speed of the light pulses, with no effect on the material itself. MChesterMC (talk) 12:33, 17 October 2013 (UTC)

Why do people tie off their arms when shooting up?

Thanks. μηδείς (talk) 01:03, 17 October 2013 (UTC)

The most obvious reason to me, would be to find a good vein. Plasmic Physics (talk) 01:08, 17 October 2013 (UTC)

Yes, it makes the veins pop up a bit. That's standard procedure at my clinic when they need to draw a blood sample. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:18, 17 October 2013 (UTC)

That makes sense. I had thought maybe it had to do with preventing the drug from entering the bloodstream while they were busy injecting it. μηδείς (talk) 02:22, 17 October 2013 (UTC)

They used to tell us in school that the addict would let some blood come into the syringe chamber to dilute the heroin slightly, before injecting the whole mess into the arm. Thankfully, I have no first hand (or arm) knowledge of that process. But it fits with tying off the arm to make the veins pop up and to initially draw blood before injecting it back into the vein. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:37, 17 October 2013 (UTC)

Intravenous therapy#Hypodermic needle mentions the practice of pulling up a bit of blood as a way to verify that the needle is actually in a vein. DMacks (talk) 06:10, 17 October 2013 (UTC)

Yer but just remember to release the pressure before you actually inject all you junky scumbags! :-) Die Antwoorde (talk) 07:35, 17 October 2013 (UTC)

"Only dopes use dope." ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:11, 17 October 2013 (UTC)

Apparently, [they don't always do it.] OsmanRF34 (talk) 11:16, 17 October 2013 (UTC)

Fish tank

Hi! I’m back again one more time… last days I pass by this little country hotel that have an awesome aquarium in the lobby and watching the fishes made me remember when I was a kid and have lot of fishes in tiny fishbowls… so one thing came after another and somehow I finished buying a couple of glasses and wow… it seems that I’m going to make a fish tank for my living room… of course it wouldn’t be as large as the one in the hotel, but I don’t know if, at my intended dimensions, the vertical water column pressure effect could be an important issue to consider.

my question is: how can I calculate the pressure that the glass and the glue/sealant will have to hold?

I know how to get the average pressure of the whole tank, but my principal concern is in the stress concentration at lower part of it

I’m thinking in something like 145cm width by 60 cm height by 50 cm depth more or less

thanks!!

201.220.215.14 (talk) 05:07, 17 October 2013 (UTC)

Go to your local pet supply shop and buy one that's already properly constructed. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:09, 17 October 2013 (UTC)

Seconding Bugs. Apart from any questions of sufficient mechanical strength, how do you know what glues and sealants, which will be in contact with the water, will or will not have a poisonous effect on the plants, fish etc in the tank? {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:50, 17 October 2013 (UTC)

Haha… no no I already bought the glasses, and besides let’s assume that here there isn’t anything like a “pet supply shop” plus building up the thing is part of the fun…

isn’t any physic or math formula that allow you to obtain the pressure in the edges of the tank?

the seller told me that the glass will hold up for that dimensions, my major concern is for the glue

the glue will be something silicon based

Iskánder Vigoa Pérez (talk) 13:59, 17 October 2013 (UTC)

P = ρgh. Where rho is defined as the density of water at a desired temperature, g is gravitational acceleration (choose standard or local), and h is the depth of water measured from the surface. This will yield the pressure as a function of depth. Plasmic Physics (talk) 14:09, 17 October 2013 (UTC)

While I agree that it seems odd to try to build an aquarium yourself, I will try to answer as best I can. Some thoughts:

1) You said you only bought 2 sheets of glass ? The usual aquarium has glass on 5 of the 6 sides. Do you intend to put something other than glass on the bottom and 2 of the sides ? Or do you intend to try to cut the glass yourself ? And do you have a lid ?

2) The pressure will be solely based on the depth of the water. However, you also need to consider that the glass will tend to bow out more, the greater the area over which the pressure is applied.

3) I suggest you add a physical support at the bottom, like a wooden frame to hold it all together. Then the load on the adhesive will be far less. Here's a top view of what I have in mind:

  +---+-----------------------+---+
  |   |         WOOD          |   |
  |   +-----------------------+   |
  | W |                       | W |
  | O |       AQUARIUM        | O |
  | O |                       | O |
  | D |                       | D |
  |   +-----------------------+   |
  |   |         WOOD          |   |
  +---+-----------------------+---+

You might also extend the wooden frame to have vertical posts along each of the 4 edges, and a repeat of the bottom wooden form at the top. Wood is far easier to work with than glass, and doesn't shatter if you mess up. StuRat (talk) 14:18, 17 October 2013 (UTC)

Not that it's any of my business, as it's your project - but isn't the kind of question an engineer would ask before buying the glass? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:18, 17 October 2013 (UTC)

Good scholarly sources

Are Razib Khan and Dienekes Pontikos blog good sources when it comes to human race classification? — Preceding unsigned comment added by 70.31.154.71 (talk) 08:57, 17 October 2013 (UTC)

Blogs are not considered as reliable sources on Wikipedia unless written by people who are acknowledged experts in the field or are under editorial control. See WP:RS. Dmcq (talk) 09:17, 17 October 2013 (UTC)

Dienekes and Razib Khan are both experts — Preceding unsigned comment added by 70.31.154.71 (talk) 09:29, 17 October 2013 (UTC)

You seem to have decided already that they are "experts". This is highly debatable - see also this. The idea that "human race classification" is a matter for a Science reference desk - when so much is based on social and cultural factors - is itself somewhat dubious. Ghmyrtle (talk) 10:04, 17 October 2013 (UTC)

Razib Khan seems to get a little bit respectability since his blog is hosted by Discovery Channel. He also has been cited thoroughly through out Wikipedia.OsmanRF34 (talk) 11:27, 17 October 2013 (UTC)

Drinking coke

As I understand correctly, 100 years ago, the favorite route of administration of cocaine was drinking it. Today it seems to be snorting it. Why the shift? OsmanRF34 (talk) 11:25, 17 October 2013 (UTC)

See nasal administration. It's faster, bypasses irrelevant organs that would try to digest the drug, and can also bypass the blood-brain barrier because the nose has a specially close connection to the brain. (This doesn't really answer why they didn't try snorting it in the first place, as was already done with snuff. Lack of imagination?)  Card Zero  (talk) 12:01, 17 October 2013 (UTC)

One important factor is that it was originally used as a medicine, not a recreational drug. (Coca-Cola was originally a weak concentration of cocaine mixed with cola, sold in syrup form, as a medication.) In that case, you want the slow release you get from the digestion process, not the quick release from snorting it. Indeed, if people didn't figure out that they could get high from refining it further and snorting it, cocaine might still be used as a med today. Also note that heroine and several other illegal recreational drugs also were used as medications originally. StuRat (talk) 14:25, 17 October 2013 (UTC)

Megawats, generating capacity and consumption

A small West African country is said to have 90-100 MW installed generating capacity. There is a proposed bio-fuels project which will grow suger cane, produce ethanol, and use the ethanol to produce 30 MW of electricity, offering 15 MW for sale back to the national grid, and using the other 15 MW for the ethanol plant and related local installations. If I understand, the entire country now uses less than 100 MW. One project can increase production by 30%, but requires 15% of what the entire national grid produces and consumes, just to run the one project (of 12,000 hectares) producing 85,000 cubic metres of ethanol for export. Does that make sense? Are these numbers credible? Thanks if you can make this more understandable. — Preceding unsigned comment added by 193.173.50.222 (talk) 12:09, 17 October 2013 (UTC)

One thing to keep in mind is that it always takes more energy to produce a fuel than you get from it. However, in this case, one of the biggest energy inputs is the sunlight used to grow the sugar cane, so it might be reasonable to expect that the rest of the refining process would take half of the energy produced. I am skeptical, though, that this process is the optimal use of the land and sunlight. Selling the sugar cane instead, or some other crop, might very well make more financial sense. You could also place solar panels there instead, to create electricity directly. However, solar panels are a rather low efficiency way to make electricity, too. StuRat (talk) 14:33, 17 October 2013 (UTC)