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September 29

One's Sexuality

If one is sexually attracted to regular women and to women with dicks (or men with breasts, long hair, and a feminine face, arms, stomach, and legs), then what would be the scientific classification for one's sexuality? I am not asking you to make a diagnosis, only asking if scientists have commented on the sexuality of people who are attracted to women and women with dicks. Futurist110 (talk) 01:58, 29 September 2012 (UTC)

That would at least partly depend on whether one was male or female. HiLo48 (talk) 02:15, 29 September 2012 (UTC)

Let's go with one being male in this scenario. Futurist110 (talk) 02:18, 29 September 2012 (UTC)

Please refer to Gynandromorphophilia. Sucks how Wikipedia:WHAAOE works for everyone else except for me; whenever I urgently need an answer the relevant article just vanishes. A8875 (talk) 02:39, 29 September 2012 (UTC)

What would be the chromosome arrangement for a so-called "she-male"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:20, 29 September 2012 (UTC)

Probably XY. Futurist110 (talk) 05:24, 29 September 2012 (UTC)

By definition XY. "Shemale" is a term which usually refers to mid-transition male-to-female transsexuals or, more commonly, genetic males who have decided to alter their bodies (surgically, hormonally or otherwise) to appear more feminine (up to and including breast implants and other plastic surgery) but without the intention of going through with a full sexual reassignment surgery. More than anything the term is used to describe (genetically male) pornographic actors or other sex workers emulating feminine traits who may or may not be transitioning -- it's also used derogatorily for transsexuals as a whole. Contrast this with intersexed individuals (hermaphrodites) who may have a mix of XX and XY throughout various tissues, or XXY (and other uncommon arrangements) throughout. Snow (talk) 06:29, 29 September 2012 (UTC)

You can name anything, but it is not clear to me that any special term for the OP's precise description would have been devised. Biologically, a term for male humans attracted to female humans with penises seems a bit pointless, since these have not actually been encountered except in the rarest instances, or within a recent timescale too short for significant evolution. Some term about this might be useful in describing the evolution of sexual selection in spotted hyenas, I suppose. A male is heterosexual if he selects female humans and not male humans as naturally encountered; once an artificial "sex change" is simulated, or some other model not normally available is presented, all bets are off. Wnt (talk) 15:46, 29 September 2012 (UTC)

I am quite sure there are terms in the sex community, "straight (pre-op) tranny chaser" sounds likely. I suggest posting the question to Craig's List. You'll get the bonus of answers with come-ons. μηδείς (talk) 22:33, 29 September 2012 (UTC)

Assume that hypothetically said male would not mind it if the woman kept her dick for the rest of her life. Would that still make said man straight? Futurist110 (talk) 03:03, 30 September 2012 (UTC)

Not when he had various sorts of contact with it? Don't worry, Futurist110, if God had meant men to give blowjobs he would have given them lips. Funny how they call me the troll. :) μηδείς (talk) 03:15, 30 September 2012 (UTC)

What's this "encyclopedia" I've been hearing so much about? Evanh2008 ^{(talk|contribs)} 03:32, 30 September 2012 (UTC)

There are some women with clitoromegaly (see File:Большой клитор.jpg), which is one extreme of a natural variation. The classic heterosexual male imperative is like that of the busy bee who visits every flower, even the oddly shaped ones. Any set of instinctive urges that would miss partners that potentially could be impregnated would fall short of this ideal. Wnt (talk) 15:02, 30 September 2012 (UTC)

The term for what you describe is heterosexual. If a person of male gender is attracted to people of the female gender, that's called heterosexual, regardless of the biological sex of the people involved. Kaldari (talk) 02:32, 3 October 2012 (UTC)

This isn't my field, and I wouldn't know where to begin to research the best sources, but I should just say my feeling is that that's going too far. I would think a heterosexual man should be defined to avoid sex with a man even if (s)he is wearing stereotypically female clothing, cosmetics and so forth and regards him/herself as a woman, because I think of it as a biological pattern recognition. But if the appropriate pattern is there - actual female buttocks, breasts, voice, etc. - then I would think that the instinct shouldn't really demand a lot of deep thought about whether the object of desire is "really" a woman in an intellectual sense, which indeed is a difficult and perhaps hopelessly subjective decision. Wnt (talk) 19:15, 3 October 2012 (UTC)

Wavelength

Let say I was given a picture of an object in space, cold be a star or anything that emit light or reflected light. And the question is what light wavelength is it in? The possbile answers are: "X-ray, UV, Optical, radio, IR". So how do I know which one is which? I meant like what are the features of each of the wavelength makes it stand out to the rest? (for the sake for not repeating the same word over and over lw = light wavelength) How can I distinguish if it's either X-ray lw or UV lw or Optical lw or radio lw or IR lw? Thanks!65.128.190.136 (talk) 03:22, 29 September 2012 (UTC)

The wavelength of light is its color. Those are analogous terms, though we usually preserve the word "color" to refer to wavelengths that human eyes can receive and interpret. If you are seeing the star with your eyes, unaided or with a simple optical telescope, the light's wavelengths you see are all in the visible range, by definition. There are also astronomical facilities like radio telescopes that receive light at non-visible wavelengths. Using some clever graphical processing, they frequently convert this data into a False color image so you can "see" what the radio telescope "sees", but your eyes and brain are not equipped to "see" light at those wavelengths. Does that help answer your question? --Jayron32 03:37, 29 September 2012 (UTC)

I'm not looking at anything with a naked eye. Ok let put it this way, someone takes a color picture of an object somewhere in the universe and that person can use any equipments to do it. After that give me the picture and asked: Which light wavelength is it in? I was given these choices:"X-ray, UV, Optical, radio, IR". So how do I know which one is which? What color would the object be if it is in X-ray? If it is in UV? If it is in Optical and so on... So I want to know how to distinguish X-ray light wavelength, UV light wavelength, Optical light wavelength, radio light wavelength, IR light wavelength. Hope I made my question clear this time.65.128.190.136 (talk) 04:43, 29 September 2012 (UTC)

If you are seeing it with your eyes, it is in the visible range, by definition. So, if you see a photograph, you're looking at visible light. Now, that is NOT the same thing as asking what wavelength was being used to produce the image. Take a look at the false color article I have already provided. It is possible to build devices which can "see" any wavelength of light at all, from high-energy X-rays and gamma rays down to low energy radio waves and everything in between. These devices are not your eyes. A picture which is made directly from those ranges of wavelengths would be invisible to you. So, in order to make it visible, what happens is they "translate" the wavelengths from the original image into "false colors" so you can see it. So the answer is, if you view an "untranslated picture" which contains only wavelengths of light from outside of the visible range, you would see nothing at all. If you're looking at a picture which you can see, it means it is in the visible range. Many astronomical pictures are translated from their original range of wavelengths to the visible range so you can actually see it. Does this make sense? --Jayron32 04:49, 29 September 2012 (UTC)

Ok let say after translation of the picture so that I can see it in the picture. What false color could "X-ray lw or UV lw or Optical lw or radio lw or IR lw" be?65.128.190.136 (talk) 05:09, 29 September 2012 (UTC)

It's completely arbitrary. The colors don't have any correlation from one picture to the other. Generally, a range of colors is chosen to make the contrast in the picture such that it is easy to show certain features within the picture, but there is no standard convention or anything. The actual colors don't have any meaning as to what the original wavelengths were. You'd need to get information from the original data as to what wavelength range the original picture was taken in. --Jayron32 05:14, 29 September 2012 (UTC)

The article False color, which Jayron had cited earlier, has some exmples of false color images which may help the OP visualize the matter. Obviously, they tinker with the invisible light to render it instead as visible light. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:16, 29 September 2012 (UTC)

If all you want are the actual numbers, see Electromagnetic spectrum. The conventional boundary between the X-ray and UV regions of the spectrum is at 10 nm, the boundary between the UV and the visibile is at about 380 nm, the boundary between the visible and the IR is at about 740 nm, and the conventional boundary between the IR and RF is at 300000 nm (300 μm). 80.254.147.84 (talk) 00:17, 30 September 2012 (UTC)

If this is a homework question, it's pretty poorly worded, a picture you are given could be any of those options, as discussed above. There is nothing that distinguishes a false colour x-ray image from a true colour optical image (unless you know the features of the object that would show up in each spectrum, which, if i understand correctly, you dont have any information about). We might be able to help further if you give us the exact question. (although we don't answer homework questions) --137.108.145.21 (talk) 11:52, 1 October 2012 (UTC)

[The contraction for "let us" is "let's" (wikt:let's).—Wavelength (talk) 14:49, 1 October 2012 (UTC)]

Is DNA always coiled up the same way in each of our cells ?

I found this quote:

"There is another sort of hairball as well: the complex three-dimensional structure of DNA. Human DNA is such a long strand — about 10 feet of DNA stuffed into a microscopic nucleus of a cell — that it fits only because it is tightly wound and coiled around itself. When they looked at the three-dimensional structure — the hairball — Encode researchers discovered that small segments of dark-matter DNA are often quite close to genes they control. In the past, when they analyzed only the uncoiled length of DNA, those controlling regions appeared to be far from the genes they affect."

It was in this article: [1]. For that to be the case, DNA would have to always coil up the same way, so that "slot A is near tab B", so to speak. Is this actually true ? StuRat (talk) 05:39, 29 September 2012 (UTC)

how DNA coils up inside the cell

Though our article is rather stubby, the concept you're grasping for is called the "quaternary structure" of the DNA. See Nucleic acid quaternary structure. Nucleic acid structure is divided into different levels of organization: primary structure is the code itself (GATC). Secondary structure is the way that the two strands of DNA interact to make a single "ladder". Tertiary structure is how the "ladder" coils up into the "double helix". Quaternary structure refers to how that 10-foot-long strand of DNA gets crammed into the nucleus. It's complex, and involves more than just the DNA. There's a lot of protein molecules called Histones that help organizes and hold the DNA in place. The DNA strand coils around Histones to form structures called Nucleosomes, which creates a sort of "string of pearls" type structure along the DNA strand. This is bound up into a larger structure called Chromatin. However, as complicated as it is, it definately isn't random. Each identical DNA strand in your different cells should coil up in essentially the same way. This is analogous to how proteins work: just as every identical molecule of hemoglobin coils up in exactly the same way (it needs to so that every one of those billions of molecules will work the same way in your body), every one of the billion identical copies of your DNA should coil up in exactly the same way. I've added a pic above that I found that should illustrate the levels of organization here. --Jayron32 05:54, 29 September 2012 (UTC)

Thanks. StuRat (talk) 00:07, 30 September 2012 (UTC)

Resolved

It should be noted that the DNA in mitochondria (and other non-eukaryote cells) is not bound in chromosomes as it is in eukaryotes. μηδείς (talk) 03:10, 30 September 2012 (UTC)

Distance to a star

How do I do this problem? And this is NOT homework as some people may say so. It is a problem from an astronomy event in Science Olympiad. I used able to do it but I forgot. I need some refreshing here. Thanks!Pendragon5 (talk) 05:59, 29 September 2012 (UTC)

I think this is refering to Cepheid variables, whereby the period of pulsation of the Cepheid is directly correlated to its luminosity. These are used as "standard candles" for estimating distances. I forget the exact method for using a Cepheid to do so, but that'd give you a lead. --Jayron32 06:27, 29 September 2012 (UTC)

Actually, the calculation of the luminosity from the period is one piece of information this chart does give. But somewhere in question 21, 20, etcetera must be the important detail of what the period of this star was. If I assume the pencil line through "5" on the graph is accurate, then I think it is probably 2000 times the luminosity of the sun (those lines don't look straight...). Since the Sun has absolute magnitude +4.83 (another piece of information the question gives) and "visual brightness" (which I shall assume is comparable to the "apparent magnitude" on this chart) of -26.74, and is 1.5 x 10⁸ km away ... we know that if we knew the apparent magnitude of the star, we would know how far away it was. But without some indication of that, this isn't coming to an answer.

Incidentally, while this is a pretty simple chart, the combination of question text and specific formatting is probably copyrightable. Commons takes forever to delete stuff adversarially, but I suggest that once the question is resolved (if not sooner) you delete this file on your own. For now I'll call it "fair use", but that's not Wikipedia policy - they don't give any credit for Refdesk uses, and they don't want fair-use material on Commons. Wnt (talk) 14:09, 29 September 2012 (UTC)

Sorry I forgot to give more information regarding this problem. From earlier problem, we know that the star has 5.37 days of period. I also have the answer key number 22. The answer is 240-290 parsecs distance to star G. Any number falls in that range is acceptable. But I don't know how to get the answer. Since we already know the period is 5.37. We can just look at the graph and give rough estimate of the luminosity of star G, which is about 2000 luminosity solar. (I drew the pencil line, which is unaccurate) And I think even if the rough estimate we still end up with acceptable answer. Anyway I have calculated to be more exact base period we got. The luminosity of star G is 2111 luminosity solar and the absolute magnitude of star G is -3.48. You're right if we can just figure "apparent magnitude" somehow then we can find the answer. Pendragon5 (talk) 19:59, 29 September 2012 (UTC)

When I use the answer key provided to find apparent magnitude (let just pick 260 parsec), I got 3.616 for apparent magnitude. But how do we find 3.616 without knowing the distance already?Pendragon5 (talk) 20:04, 29 September 2012 (UTC)

WOW never mind, my bad! I know how to do it now lol. I was given the apparent magnitude in problem 20 all along without knowing it. I guess this could end here. Thanks anyway for the help!Pendragon5 (talk) 21:22, 29 September 2012 (UTC)

Fruit ripening

I'm pretty sure there are two types of fruit - those that continue to ripen after being picked (like a banana or tomato) and those which do not (apple or cherry). What is the technical term for these types? And if that term doesn't link to an article here, where can I find a listing of which is which? Thanks! Franamax (talk) 06:11, 29 September 2012 (UTC)

I'm not sure there is is any general categorization of those types of fruits, as cherrys and peaches are both drupes, but while cherries are picked when ripe, peaches can do significant ripening off the tree. Likewise apples and pears are both Pome-type fruit, but while apples are usually picked ripe, pears often need to sit for a day or two on the counter to get over that "hard" stage and become soft and flavorful enough to eat. I did find two articles you may find interesting: [2] and [3]. The ripening process in nearly all fruits is controled by the production of ethylene. The amount that a fruit ripens "off the vine" or "off the tree" probably depends a lot on how ethylene production works in the fruit. If the fruit stops making ethylene when it is picked, it won't continue to ripen, instead it will just "rot". If the fruit continues to make ethylene after being picked, it can be picked fairly early and ripen on its own. I know from experience that bananas need to be kept seperate from other fruit: ripening bananas apparently outgas so much ethylene that they can cause other fruit to overripen just by sitting in the same bowl with them. The apple that'd last a week by itself can get unpalatably mushy if kept next to a banana for a few days. --Jayron32 06:22, 29 September 2012 (UTC)

The two types that do or do not undergo the process Jayron has described are climacteric and non-climacteric; see Climacteric (botany). μηδείς (talk) 17:39, 29 September 2012 (UTC)

Eyes rolling back

In TV, if someone gets shot in the head and their head is not destroyed then their eyes usually roll back into their head. Is this grounded in reality? Please elaborate. (I just watched the Mayday/Air Crash Investigation episode about Pacific Southwest Airlines Flight 1771, which is why I'm posting this question very early in the morning). Whoop whoop pull up ^{Bitching Betty | Averted crashes} 06:59, 29 September 2012 (UTC)

I think the key words in your question are "on TV". In my experience almost all TV depictions of real life in fictional scenarios are inaccurate. This includes portrayals of death in various forms. The eye is kept in forward looking position by several muscles that pull in a balanced tension. I have never seen a person who has died whose eyes turn up, down or sideways.(and I have seen many) At death, however it arrives, the muscles will relax and the eye will take up a neutral, forward looking position with the eyelids closed or open or usually partially open. The ability of the ordinary human eye to "roll back" in its socket is very limited in most people. Richard Avery (talk) 07:43, 29 September 2012 (UTC)

Which raises the question of where that idea came from in the first place. It's actually a long time since I've seen that depiction of death on TV. I couldn't find anything on TV Tropes: these days, stary eyes wide open seems to be the usual way to indicate termination.--Shantavira|^{feed me} 08:53, 29 September 2012 (UTC)

I grew up on a farm, and have seen a few animals die, either from natural causes (disease, old age), or killed (as in killed for the meat). I think there are three principles to grasp here: First, Richard Avery is correct - an animal (including humans) that dies peacefully will die with muscles relaxed and eyes forward. Second, an animal that dies suddenly from head trauma (eg gunshot, striking with blunt object) may die with some muscles contracted from nervous spasm. I've never seen this roll the eyes up, but in priciple it could happen. Thirdly, when you see an animal die right in front of you, the moment of death is pretty obvious (and traumatic to experience the first time you see it - I witnessed my first large farm animal death from disease while assisting the vet when I was 12 and will never forget it even though the animal did not suffer) - a sigh as the breathing muscles "let go", ceasing of chest movement, and, most significantly, you see the life go out of the eyes - an event hard to describe but unmistakable when you see it. These days this could be faked in movies by digital effects, but on TV traditionally there's been no easy way to fake it, and in many parts of the world it would be culturally unacceptable anyway. So, with a gentle sigh not obvious, loss of chest movement not obvious, and the loss of "eye shine" not possible, producers need a way to symbolise death. Asking the actor to roll back his/her eyes is easy. Wickwack121.215.59.111 (talk) 10:02, 29 September 2012 (UTC)

There was a rather disturbing picture showing the dead eyes of a girl who died trapped in a mudslide in Latin America published in National Geographic in the 1980's. "Rescuers" could photograph her eyes before and after death but not save her. There is also this picture of the recently assassinated ambassador Chris Stevens: http://www.latimes.com/news/local/readers-rep/la-me-rr-us-ambassador-killed-why-editors-put-photo-on-front-page-20120912,0,4420095.story μηδείς (talk) 17:46, 29 September 2012 (UTC)

Is the photo in Omayra Sánchez the one you mean? According to the photographer, it was taken a few hours before her death. I can't find a record of one taken after she died. For those of you unfamiliar with the photograph, be advised that is very powerful. Bielle (talk) 00:21, 30 September 2012 (UTC)

Great find, but that foto has haunted me since I saw it, so forgive me if I won't look again. μηδείς (talk) 00:30, 30 September 2012 (UTC)

Regarding dimension of physical quantities

During school years, we were taught of the two-dimensional and three dimensional co-ordinate systems. The Three dimensional one, as I understood, had length, width and depth with respect to an origin. A few days ago, a friend asked me about "Dimensional Analysis". I began conversing with him about this and the more so I did, the more I got confused. I could not understand how Length, Mass and Time (L,M,T) are "dimensions", and the radian is a dimensionless quantity. I googled, but found nothing to aid my understanding. My confusion is : Why are the quantities Length, Mass, Time regarded as dimensions and how do these dimensions differ from the 3 Dimensional objects (Cubes, prism, etc.) that we were taught during school years? Also, what is the application, real life, of a dimensionality calculation? — Preceding unsigned comment added by 210.4.65.52 (talk) 07:53, 29 September 2012 (UTC)

Well, there are fundamental dimensions, like length, and derived dimensions, like area and volume (which in this case we get by multiplying 2 or 3 lengths). StuRat (talk) 08:34, 29 September 2012 (UTC)

Did your Googling not find our comprehensive article on dimensional analysis? That would seem to address your questions. A dimension is not necessarily only spatial.--Shantavira|^{feed me} 08:41, 29 September 2012 (UTC)

What's missing in the OP's understanding as he stated it, is (1) that everything that can be measured, can be measured in terms of fundamental units, that is for any measurable quantity, the units of that quantity can be expressed in terms of fundamental units, and (2) by first working out what the fundamental units should be for some quantity you are trying to work out the formula for, the formula often becomes obvious without having to do a whole lot of math, or you can at least check that you made no errors in your math. Or, dimensional analysis may give you a likely looking formula that you can't work work out analytically but you can test against laboratory measurements.

An example: The unit of energy is the joule. Energy is mass x length squared divided by time squared. If you, for some reason, have mathematically derived a formula for energy in some weird system, and the units in your formula don't cancel out to mass x length squared over time squared, you know you must have made an error.

While our WP article Dimensional Analysis covers this, it's like a lot of WP physics articles - it's poorly written. The info is burried in a mass of detail. The author seems to have wanted to impress rather than inform. There's no introductory paragraph or "executive summary" at the top that sets out the fundamental merit that I've just given, so that a lay person can quickly look to see if it's what he's after, whether it's worth ploughing thru the rest of it.

Wickwack121.215.59.111 (talk) 10:27, 29 September 2012 (UTC)

• It's really very simple. The word "dimension" has several distinct meanings, and these are two of them. See Wiktionary:dimension. Looie496 (talk) 16:28, 29 September 2012 (UTC)

In other words, there are several dimensions to this problem. StuRat (talk) 17:45, 29 September 2012 (UTC)

so do h, w, l, t just happen to be the most obvious?GeeBIGS (talk) 03:44, 30 September 2012 (UTC)

If, by h, w, l, t, you mean height, width, length, and time, you haven't grasped it right. Height, width, and length are all of dimension type length - you can meassure them all with a tape measure or ruler. The fundamental units are length, mass, and time, as the OP said. You cannot measure mass with a ruler, nor can you measure time with a ruler. Over the years, a few additional "fundamental units" have come and gone. For instance, electric current (measured in amperes) has been considered, for convenience and practical reasons in maintaining a lab reference ampere, a fundamental unit, but in fact as a current flowing in two parallel conductors sets up a magnetic force between them, the ampere can be defined in terms of force (derived from the fundamental unit mass, and the distance between the conductors (the fundamental unit length). Wickwack124.182.129.22 (talk) 10:19, 30 September 2012 (UTC)

.

That mass, length and time are assigned dimensions is actually an arbitrary choice. There is nothing fundamental about these dimensions, it's an arbitrary convention. You can do physics without units working with only dimensionless quantities. Dimensional analysis is ultimately nothing more than invoking scaling relations of certain equations (in some appropriate limit). I explain a special case of this here. Count Iblis (talk) 03:59, 30 September 2012 (UTC)

So, if you use natural units, you can interpret that as considering everything to be dimensionless. Then you can put hbar, c and G back, but not as dimensionful quantities, rather as dimensionless parameters. Clearly, everything is still consistent if you do that. Now, the interpretation of what you are doing is simply a rescaling of the equations. Expressed in SI units, c is very large while hbar is very small, so this corresponds to (almost) some scaling limit. If you then take the original equations and explore the exact scaling limit, you would lose certain relations that involve hbar, c and G. The relation between mass and lenght (e.g. the equation for the Compton wavelength), the relation between energy and mass (E = m c^2, but c tends to infinity), the relation between frequency and energy (E = h f, but h tends to zero).

Since we happen to live in (almost) the scaling limit, we don't have (easy) access to the relations between length, time and mass, and they look like independent quantities. In the equations of classical physics you can arbitrarily rescale these quantities. There is then no way to compare time to length and length to mass, that's why you have 3 independent "dimensions". But in reality they are related to each other.

This then also means that dimensional analysis without any assumptions is completely useless. Indeed, if you do dimensional analysis, you always make assumptions about whether or not you can use one or more of the constants hbar, c and G, otherwise you can convert any quantity into any other quantity. The assumption that you e.g. can't use c, hbar and G ammounts to working in the scaling limit that leads to classical mechanics. Count Iblis (talk) 04:14, 30 September 2012 (UTC)

That may be so, Count Iblis, but how does that help the OP, that is inform him as distinct from impressing him? Wickwack124.182.129.22 (talk) 10:19, 30 September 2012 (UTC)

The OP asked "I could not understand how Length, Mass and Time (L,M,T) are "dimensions", and the radian is a dimensionless quantity". The answer is that these dimensions are not fundamental, you can always assign different dimensions to different quantities, defining completely arbitrary unit systems. The question then becomes why we end up with (L, M, T), or at least why this is useful and some other choice is not. That has to do with scaling properties of equations in classical physics. And then one can think about where those scaling properties come from, the answer is that classical mechanics is the scaling limit of more fundamental theories.

So, in the end what you see is that something rather trivial is going on. You have some set of mathematical equations that do not contain any dimensional quantities. Certain phenomena that are described by these equations exist in some extreme scaling limit. E.g. when considering the air flow near surfaces, you'll have a boundary layer. If you want to study those phenomena it is useful to rescale certain varables in your equations. You then end up with very small of very large constants. As a first approximation, you can then obtain some idealised equations in which these constants are exactly zero or infinity (which is the exact scaling limit).

In the case of our unit system, the relevant constants are hbar, c, G, k_B etc., their small or large values when expressed in terms of meters, seconds and kilograms made them invisible to classical physicists, which causes Length, Time and Mass to appear as if they are independent, incompatible quantities. Count Iblis (talk) 16:02, 30 September 2012 (UTC)

Well, I cannot know just what was in the OP's mind, but it seems to me that the following simple answer would meet his needs for understanding why an angle is dimensionless and length, mass, and time are dimensions. It's simply that an angle is measured by the ratio of arc to radius, i.e., the ratio between two distances, so the L dimension cancells out. It is quite typical and understandable that lay persons think of angles are different to linear distances - it does not necessarily occur to lay persons to think of an angle as a ratio. You have gone off on a $100 tangent when a 10 cent straightforward answer would have done. Wickwack124.178.42.216 (talk) 01:53, 1 October 2012 (UTC)

So why do they seem interconnected: time and length seem to be mutually dependent. you can measure mass with a ruler if you know the density. You can measure time with a ruler if you know the speed of something.GeeBIGS (talk) 02:50, 1 October 2012 (UTC)

If all you have is a ruler, you can only measure length. You can't use just a ruler to measure mass, and without something to measure mass you cannot know density. Density is a derived thing - it is dimensionaly Mass / Length cubed. Similary, you cannot know speed unless you know both time and distance. Wickwack124.178.47.203 (talk) 06:19, 1 October 2012 (UTC)

Extreme cold weather clothing

Do they ever use silica gel or other desiccants to absorb moisture inside extreme cold weather clothing ? (I realize that breathable fabrics somewhat keep the heat in while letting the moisture out, but there has to be a limit to this approach. For example, a space suit or an underwater dry suit can't just let the water vapor escape into the environment.) StuRat (talk) 21:19, 29 September 2012 (UTC)

I've never heard of that, and I think it would be a really bad idea. Cotton is actually an extremely good absorber of moisture, and it is avoided like the plague in cold weather clothing for exactly that reason. In a space suit or dry suit it would make more sense, but it would only work for a limited time. Looie496 (talk) 23:21, 29 September 2012 (UTC)

How about Antarctica in winter ? You really wouldn't want much air exchange there. StuRat (talk) 00:01, 30 September 2012 (UTC)

The moisture will just freeze on the outside providing extra insulation Count Iblis (talk) 03:35, 30 September 2012 (UTC)

A first-hand explanation here. Zoonoses (talk) 07:10, 30 September 2012 (UTC)

Good link. Modern "base layers" (ie thermal underwear) have the property of "wicking" moisture away from the surface of the skin and into the outer layers of clothing. The outermost or "shell" layer of modern mountaineering kit is breathable, Gore-tex was the first in the field. See our article; Layered clothing. I don't really know, but I suspect that space suits don't have this property; they just hold the moisture away from the skin until you get a chance to take it off and dry it out. Alansplodge (talk) 11:54, 30 September 2012 (UTC)

Actually, astronauts wear a Liquid Cooling and Ventilation Garment to draw moisture away and recycle it into the space suit's cooling system.    → Michael J Ⓣ Ⓒ Ⓜ 05:22, 1 October 2012 (UTC)

Phase

What is phase is this graph means? Does it mean the period of the star?Pendragon5 (talk) 21:51, 29 September 2012 (UTC)

Yes, it looks like they are using it to mean the period, with a phase of zero being when it is at it's minimum magnitude (and phases of 1, 2, 3, etc., one being when it is at minimum magnitude the next few times in the cycle). StuRat (talk) 22:09, 29 September 2012 (UTC)

The terminology is getting a bit mixed up here. In anything that goes through a repetitive cycle, the period is the time that each cycle lasts, and the phase is a way of indicating a specific point within the cycle. Phase is commonly measured either as an angle (if you think of the repetition as a point going around a circle over and over again), or, as in this example, as a number between 0 and 1, with 0 indicating the start of the cycle, and 1 indicating the end, which is identical to the start. Looie496 (talk) 23:14, 29 September 2012 (UTC)

Ah yes, they do seem to start over at 0 when they hit 1, on the graph shown. StuRat (talk) 23:52, 29 September 2012 (UTC)

When were tracking chips invented?

By tracking chips, I mean those things that one wears in order for others to track down his/her exact location later on--such as if an FBI operative managed to infiltrate a mafia "cell" and then needs to alert his co-workers what location he's at. Also, what is the technical term for tracking chips? English isn't my first language, so personally I don't know what the technical term for them is. Futurist110 (talk) 22:42, 29 September 2012 (UTC)

You don't mean RFID chip, do you? μηδείς (talk) 22:57, 29 September 2012 (UTC)

If those are the ones that could be used, for instance, to infiltrate mafia "cells", then Yes, those are the ones that I'm talking about. Futurist110 (talk) 23:07, 29 September 2012 (UTC)

They couldn't. You seem to be thinking of something like a miniature GPS receiver. Looie496 (talk) 23:23, 29 September 2012 (UTC)

Yeah, I guess so. When were miniature GPS receivers invented? I mean the really small ones that you can simply put inside your clothes/pockets and easily hide them from others. Futurist110 (talk) 23:29, 29 September 2012 (UTC)

But RFID's can be used to track people, just not give their location within a decimeter. I am not sure why knowing where a mafioso is within 6 inches matters. μηδείς (talk) 23:34, 29 September 2012 (UTC)

It really woulda helped with Jimmy Hoffa. Clarityfiend (talk) 23:41, 29 September 2012 (UTC)

Didn't they just find him? μηδείς (talk) 23:43, 29 September 2012 (UTC)

The following doesn't quite amount to "found him": On September 26, 2012, Roseville, Michigan police announced that it will take soil samples from the ground under a suburban Detroit driveway after a person called and told police he believed he witnessed the burial of a body around the same time as Hoffa's 1975 disappearance. No evidence of a body was found in samples taken September 28, 2012, but tests for decomposition of human remains are being conducted. -- Jack of Oz ^[Talk] 00:01, 30 September 2012 (UTC)

I don't quite understand that last part. What "tests for decomposition" ? After 37 years, would there be anything left to show up in a test, other than bone ? StuRat (talk) 00:05, 30 September 2012 (UTC)

It depends on the conditions of the ground and etc. where the body is. Some conditions will reduce bodies to bones or less in that amount of time; some will keep them relatively well preserved. Some can even basically "mummify" the body to an incredible degree. Presumably they are just looking for any tell-tale chemicals of human decomposition on the off-chance they are preserved. --Mr.98 (talk) 02:04, 30 September 2012 (UTC)

Michigan is neither a desert nor a peat bog, and doesn't have permafrost, so I don't know why they expect to find anything other than bones. StuRat (talk) 04:23, 1 October 2012 (UTC)

RFID chips can only be tracked if they pass within a few yards of an RFID reader. To the best of my knowledge RFID readers are not standard equipment in Mafia hideouts. Looie496 (talk) 23:59, 29 September 2012 (UTC)

I have no idea, but the article says they can be used to track people, and they are obviously smaller than GPS devices. Perhaps someone should tag the RFID article. μηδείς (talk) 00:01, 30 September 2012 (UTC)

Today is would likely be some kind of GPS receiver/transmitter, though in theory you could do this with a regular radio transmitter as well if you had the right setup. I vaguely recall that using radio transmitters was possible even fairly early on the 20th century — the technology is not terribly complicated for localized tracking (that is, not anywhere in the world, but, say, anywhere within a fixed geographic area). They had portable transmitter tracking technology by World War II, which puts some kind of boundary on it. Whether it was used for this purpose, I don't know. (These days this can be fairly easily done by just tracking cellular phones.)

RFID requires you to be very close to an RFID reader, which would require you knowing in advance where people are going to be traveling. It would not be very practical, and there are better options. --Mr.98 (talk) 02:04, 30 September 2012 (UTC)

To be precise, being cheap and short-range, the application for RFID chips is to track the movement of many people in a restricted area with the appropriate infrastructure. As an example, a supermarket chain could find out which premisses somebody visits how often, or a company could track everybody in a sensitive building, or a very oppressive government could track everybody inside city limits. But that requires a network of RFID readers in many places. For tracking a few things (like e.g. a mafiosi) with little fixed infrastructure in a large area, current technology would use a GPS tracking unit with some kind of wireless data communication. The classical James Bond technology would use a simple radio transmitter transmitting at a known frequency, and a (pair of) radio direction finders to locate the source of that transmission. --Stephan Schulz (talk) 05:51, 30 September 2012 (UTC)

• I think (but I don't know) the key for tracking "mafiosos" (more likely political dissidents) with RFID chips is that the readers turn up in unexpected locations. For example, in computer printers to read what cartridge is present (image) - the question is, has the company arranged a way for the printer to "phone home" the data, and does this "unknowingly" get sold to an organization that has placed a special cartridge chip in something they want to trace that might end up near a printer somewhere? Wnt (talk) 14:33, 30 September 2012 (UTC)

Violets

I have read the article on violas but am trying to determine the type of violet that grew in a vacant lot in Poughkeepsie, NY in the 1950's. They had thick stems coming up between leaves close to the soil, were self seeding perennials. Were they Viola Sororia or Viola Odorata? Where can I buy them to plant in the spring? What type of soil do they require?67.241.225.159 (talk) 22:44, 29 September 2012 (UTC)

Do the pics at Viola sororia or Viola odorata match your memory ? The sororia article says they are stemless, which seems to conflict with your description. StuRat (talk) 23:54, 29 September 2012 (UTC)

Could they be Pansies? I've found that these self-seed. --Jayron32 18:33, 2 October 2012 (UTC)

What this paragraph on tetany mean?

This could be a question for the language desk, but I thought I might find more people familiar with the medical terminology here. Could someone please put the following from Tetany into plain English?

Low calcium levels in the bloodstream increase the permeability of neuronal membranes to sodium ions, causing a progressive depolarization, which increases the possibility of action potentials. If the plasma Ca2+ decreases to less than 50% of the normal value of 9.4 mg/dl, action potentials may be spontaneously generated, causing contraction of peripheral skeletal muscles.

Thanks, Bielle (talk) 23:07, 29 September 2012 (UTC)

There's probably no way to put it into plain English without losing some of the content, but the thrust is this: Under normal circumstances, skeletal muscles only contract when they receive command signals from motor neurons in the spinal cord. If calcium levels in the bloodstream drop to less than half their usual value, though, muscles may begin to contract spontaneously, in an uncontrollable way. Is that any better? I'll be happy to do a bit of editing on that paragraph if you think it would be useful. Looie496 (talk) 23:35, 29 September 2012 (UTC)

I think it would be very useful, as would be links to technical terms like "action potentials", for example. Thanks for the translation. Bielle (talk) 23:53, 29 September 2012 (UTC)

That's not really a translation, though. The point here is that the calcium levels outside the neuron affect what voltage is needed to open a voltage-gated sodium channel in its membrane. Opening the channel, allowing sodium ions to pass into the cell, which carry a positive charge, causes a reduction in the normal electrical charge difference (i.e. an electrical current) between the two sides of the membrane (depolarization). Note that the membrane potential of a cell is usually negative (which means, the inside is negative) so when sodium comes into the cell with a + charge it reduces this potential; and the way an action potential works is that once the potential is decreased in one part of a neuron, the rest also allows in ions so that the change passes in a wave from one end to the other. Wnt (talk) 14:48, 30 September 2012 (UTC)

September 30

pink nebula

In Apple's splash screen, is that pink thing a real nebula or aurora or what? —Tamfang (talk) 08:08, 30 September 2012 (UTC)

Well, it's called "Aurora Leopard" in the sceensaver preferences on OS X Mountain Lion. So it probably is an aurora. I suspect its "real" in that it is based on a real photo, but I suspect that either the photographer or the designers at Apple, or both, have worked with real and digital filters to enhance the colours. --Stephan Schulz (talk) 08:56, 30 September 2012 (UTC)

Make that OS X 10.5 Leopard. hydnjo (talk) 21:29, 30 September 2012 (UTC)

There is some discussion of it here which I found interesting. The star pattern is duplicated in the background which suggests that the very minimum that it's a manipulated photograph or that it's been entirely generated anyway. It seems not unrelated to whatever they used to generate the intro sequence. I suspect it's entirely generated. --Mr.98 (talk) 14:58, 30 September 2012 (UTC)

abbreviation question

In this cite, what does "CC" stand for?

"Figs. B I, B II, B III. Three sections of a Pristiurus-embryo. B I is through the heart, B II through the anterior part of the dorsal region, and B III through a point slightly behind this. Drawn with a camera. (Zeiss CC ocul. 2.)"

69.138.178.234 (talk) 11:20, 30 September 2012 (UTC)

That parenthetical phrase refers to components used in microscopy: a specific Zeiss objective (see example here), and a specific ocular (eyepiece). For those familiar with the terminology, this phrase would describe the microscopic method (of course, it's jargon to the rest of us). -- Scray (talk) 12:33, 30 September 2012 (UTC)

Pancreatin use

Re:http://en.wikipedia.org/wiki/Pancreatin

Are these supplements meant merely to supply deficient enzymes? Is there a supplement which will decrease the body'w own production of amylase and lipase, as by a negative feedback mechanism? Is there a difference in this in regards to pancreatin vs. pancrealipase, pre-enzymes vs. active enzymes? I'm unsure how passage through the stomach affects these enzymes before they reach the small intestine. — Preceding unsigned comment added by 173.28.222.74 (talk) 15:42, 30 September 2012 (UTC)

Definitely these digestive enzymes can destroy some food allergens if used outside the body, before eating. [4]

unsourced speculation

The downside is that (I would say - the paper doesn't) in order for this to be effective, you pretty much have to reduce the food to some sort of amino acid supplement pap, unless, that is, you devise some extraordinarily clever enzyme that can seek out and destroy the specific epitopes responsible and not much else, which I think can be done, but drawing you a blueprint is another matter again. I would view other uses with considerable skepticism. Note that pancreatin itself can cause hypersensitivity to repeated exposure.[ PMID 1134882] I would have some suspicion that extensive exposure to non-human digestive enzymes, especially in persons prone to allergy, would be a Bad Thing, and that there would even be some risk of subsequent allergic rejection of the person's own digestive enzymes, but I have no proof for this, and admittedly, people have been exposed to pancreatin and some other enzymes in freshly butchered kills for millions of years, and regulatory agencies approve that these products are handled incidentally as contact lens cleaners by large numbers of people without obvious drawbacks. Wnt (talk) 17:24, 30 September 2012 (UTC)

cool melting

is there any explaining about cool melting in wikipedia? --Akbarmohammadzade (talk) 17:06, 30 September 2012 (UTC)akbarmohammadzade--78.38.28.3 (talk) 17:04, 30 September 2012 (UTC)

Can you explain your question more fully? In the meantime, see NaK which is molten and cool in both senses. μηδείς (talk) 17:10, 30 September 2012 (UTC)

Perhaps, he means to say sublimation - whereby a solid changes phase to a gas without passing through the liquid phase. Alternatively, he could be talking about the pressure dependence of a melting point. I agree, he needs to either rephrase the question, or provide a meaningful description of what he means to say. Plasmic Physics (talk) 22:50, 30 September 2012 (UTC)

I'm melting! Melting! Oh, what a world! Clarityfiend (talk) 00:33, 1 October 2012 (UTC)

Does our article on melting not answer your question?--Shantavira|^{feed me} 07:10, 1 October 2012 (UTC)

thanks!ok , i couldn't find any thing about cool melting there.Akbarmohammadzade — Preceding unsigned comment added by 78.38.28.3 (talk) 05:00, 2 October 2012 (UTC)

cool melting may occur by effect of radio waves .three phases of matter have common point named triple point in thermodynamic ,the solid matter can pass from liquid phase direct to vapor case .This process is in thermodynamic for amounts of pressure and temperature and volume ,but radio waves can melt solid matter in very cool temperature.akbarmohammadzade--78.38.28.3 (talk) 04:09, 2 October 2012 (UTC)

I am not familiar with this concept, but you may be interested to read Laser ablation, Induction heating, and Dielectric heating. Plasmic Physics (talk) 05:26, 2 October 2012 (UTC)

Based on your field of study, I assume that you may be most interested in dielectric heating. The methods above are examples of non-contact heating, which is to say, they are examples of electromagnetic heating. Plasmic Physics (talk) 05:44, 2 October 2012 (UTC)

All right ,so — Preceding unsigned comment added by 78.38.28.3 (talk) 06:14, 2 October 2012 (UTC)

theoretical extent of hydroplaning -- how to calculate?

Given water thickness h, water viscosity η, water density d, wetted tire surface area A, and vehicle velocity v, how do I find the force slowing down the vehicle, if the tires do not make contact with the road?

To solve this homework problem I've used my professor's cited (empirical? N-S derived?) relation of skin drag coefficient = 1.33 / sqrt(Re), where Re is Reynold's number. Then I used the drag equation to compute the force. For example, if the mass of the vehicle is 1000 kg, A = 0.1 m^2, h=0.1mm, and v = 10 m/s and dynamic viscosity of water is 1.002 * 10^-3 N*s/m^2 and water density 0.9982 g/cm^3, I get a stopping distance of 206m, assuming the water plane thickness h and wetting area A do not change.

However, something doesn't sit right with me (for example, I don't think *all* of the drag is skin drag) and I'm looking for an alternate way to solve this problem. 71.207.151.227 (talk) 17:32, 30 September 2012 (UTC)

I see a couple problems there. One is that air resistance is ignored. That might make sense in normal braking, where it's not very significant compared to the much larger friction force against the road, but, in this case, it may be significant. The second issue is that, when you slow to a certain speed, the vehicle will cease to hydroplane, at which point you must switch calculation methods. However, if you want to get an A, I suggest you ignore reality and do as your Prof suggests. StuRat (talk) 07:20, 1 October 2012 (UTC)

Are these images useful?

I stumbled across two images, File:AWaveEquation.gif and File:AWaveEquation2.gif, that apparently describe some kind of wave equation. I don't know what they mean, and I can't tell if they are meaningful or useful. I've listed them for deletion because they aren't used anywhere; see Wikipedia:Files for deletion/2012 September 30#File:AWaveEquation.gif. If someone here can see that these images are potentially useful for some encyclopedic purpose, please contribute to the deletion discussion there. —Bkell (talk) 18:40, 30 September 2012 (UTC)

Does the Vagainal Mucos and Vagainal Lubrication are same?

except urine, female-semen, and lubrication, what else is released by the fluid-releasing vaginal parts? Thx. 58.11.229.10 (talk) 21:26, 30 September 2012 (UTC)

I'd be surprised if they synthesised semen. AndyTheGrump (talk) 00:37, 1 October 2012 (UTC)

Please answers.— Preceding unsigned comment added by 58.11.113.153 (talk • contribs) 04:13, 1 October 2012

I don't understand the question, but the following corrected links may help (many will consider these links NSFW): Vaginal mucus, Vaginal lubrication -- Scray (talk) 04:17, 1 October 2012 (UTC)

(ec) First let me spell them correctly so you can find our articles: vaginal mucus & vaginal lubrication. StuRat (talk) 04:18, 1 October 2012 (UTC)

Vaginal mucosa is the vaginal tissue which produces mucus. By vaginal semen the OP may mean female ejaculation. μηδείς (talk) 04:22, 1 October 2012 (UTC)

October 1

Prevent superheating in microwave

How exactly does a spoon prevent superheating of liquids in a microwave. Does it matter whether it is a wooden/plastic/metal spoon? bamse (talk) 07:34, 1 October 2012 (UTC)

By providing nucleation sites. A rougher material is better at that, so a well-polished metal spoon might not work. Wooden spoons are always rough, I believe. Plastic I'm not so sure about. StuRat (talk) 07:56, 1 October 2012 (UTC)

I know there was a Mythbusters episode that debunked the myth that a microwave oven would explode if a metal spoon was put int it, but nevertheless I thought putting any metal object in a microwave oven was not a good idea because it could damage the magnetron and shorten the lifespan of the oven. Am I out of date ? Gandalf61 (talk) 10:33, 1 October 2012 (UTC)

Maybe the metal spoon is meant to be completely submerged in the water although that isn't as much fun. Sean.hoyland - talk 11:08, 1 October 2012 (UTC)

My understanding of the advice is to put the spoon in after the microwave has finished, so that, if the liquid is going to boil over when disturbed, it does so before you pick it up and you don't get scalded. --Tango (talk) 17:00, 1 October 2012 (UTC)

Per StuRat, the goal of the guidance is to provide nucleation sites. The "spoon" part of "wooden spoon" is irrelevant for this purpose; the real question is one of material. Wood is excellent because it is rough and it is an insulator (so that it won't in turn be burning hot when you take it out of the boiling water). Some plastics might work, but as you can superheat water in a plastic vessel, I wouldn't count on it to be rough enough. Metal, per Gandalf, should be considered bad due to the potential for unpleasant interactions with the microwave, plus it still might not be rough enough and would certainly become dangerously hot. Tango's understanding is incorrect; the object must be inserted before the potential superheating occurs; otherwise, all you'll do is trigger the explosive boilover when you insert the object or otherwise disturb the water, and that will burn your hand. In a laboratory environment, the role of the wooden spoon is filled by boiling chips. So, wrapping up: wood is the material of choice because it provides nucleation to prevent superheating, is insulative to protect your hand, and does not interact negatively with the microwave. Other common household kitchen options generally fail at least one of those three criteria. — Lomn 17:29, 1 October 2012 (UTC)

My understanding is that you insert the spoon carefully, at arm's length. I wouldn't say the boilover from superheating is "explosive" - when people get significant burns from it, it's usually from actually holding the cup at the time (you might get splashed a little otherwise, but not enough to cause serious harm). --Tango (talk) 11:13, 2 October 2012 (UTC)

While you could create a wooden object smooth enough to avoid nucleation sites, by applying a lacquer, I don't believe such lacquers are used on wooden cooking spoons, as they could come off when stirring boiling liquids (especially if they contain hard objects, like bone). StuRat (talk) 18:23, 1 October 2012 (UTC)

Thank you all for the explanations. On what length scale should be the roughness? (Strangely enough, all the microwave oven manuals I've seen only mention a "spoon", saying nothing about its material.) bamse (talk) 18:33, 1 October 2012 (UTC)

The manuals will have only mentioned "wooden spoon" specifically because it's the only sufficiently rough object that most people are likely to have in their kitchen that they don't mind putting in their food. Someguy1221 (talk) 23:18, 1 October 2012 (UTC)

Well, it's a fairly large scale, since you can feel the difference between wood and metal. Metal looks rough under a powerful microscope, but apparently that's not enough. StuRat (talk) 20:50, 1 October 2012 (UTC)

Thanks. I had hoped for an answer in terms of some fundamental constants. Do I understand correctly that this length would depend only on properties of the liquid and not on the microwave or the container? bamse (talk) 22:44, 1 October 2012 (UTC)

Yes, I imagine there's a bell-shaped curve showing the ideal scale of roughness, but I haven't found it. The properties of the liquid certainly matter, but the characteristics of the microwave and container also play a role. Obviously, a rough container will promote nucleation directly. Also, the microwave and container control how evenly the liquid is heated, which is an important consideration when super-heating a liquid. If heated unevenly, parts may get hot enough to boil, even without nucleation sites. To maximize the possibility of super-heating the liquid, you want it to be evenly heated and to avoid all sound/vibration. StuRat (talk) 23:09, 1 October 2012 (UTC)

for the claim a metal spoon isn't rough enough. Lomn has suggested it may not be, but I looked before anyone replied (I didn't reply because I couldn't find any good sources), and couldn't find anything suggesting that would be the case. I'm not even convinced the roughness matters much, simply the shape of the object and disruption of the surface may be enough. Many sources simply say a 'non metallic' object, but the reason for specifying non metallic is likely for the reasons highlighted above, not because it may not be rough enough. Otherwise they wold likely also caution to avoid something made of glass (in fact I even came across some sources which suggest a glass rod). Some of the examples I came across don't give a wooden spoon as an example at all, more commonly a skewer or stir stick. I can't speak for how things are in the US or elsewhere, but I would say it's rare to have a wooden spoon suitable for these purposes in most households in NZ, you may have wooden spoons for stirring pots but they will often be too long to fit in the microwave and even if not, often too large to fit in a cup so I would question the claim people are likely to have one in their kitchen. I.E. It's likely a bad idea to read too much in to the fact some sources suggest a wooden spoon. Plastic spoons are more likely, they've often not mentioned I presume because of concerns they will melt or at least leech rather then the believe they won't work. Nil Einne (talk) 08:55, 2 October 2012 (UTC)

I'm skeptical about a glass rod working. After all, if glass worked, then the interior of a glass cup would presumably also work. StuRat (talk) 08:59, 2 October 2012 (UTC)

The rod will have a sharp(ish) edge which will include nucleation sites even if most of the rod is too smooth. I don't think you need much area over which bubbles can form to prevent superheating. --Tango (talk) 11:13, 2 October 2012 (UTC)

I was thinking of glass rods with hemispherical ends. I think "more is better" when it comes to nucleation sites. StuRat (talk) 18:06, 2 October 2012 (UTC)

This fish prefers deep waters and it is illiophagus

Is illiophagus even a word? I can't find it in any online dictionary. Ebaychatter0 (talk) 15:53, 1 October 2012 (UTC)

It's spelt "illiophagous", and it means that the fish in question ingests mud. Dominus Vobisdu (talk) 16:07, 1 October 2012 (UTC)

• You beat me to it! I'm glad to see the OP is paying attention - I once found a vandalism "glucojasinogen" that was left in an article so long it was plagiarized to two different scientific journals... :) Wnt (talk) 16:12, 1 October 2012 (UTC)

I can't find illiophagous either. Google suggests oligophagous. Ebaychatter0 (talk) 16:31, 1 October 2012 (UTC)

On Google, under where it says "showing results for oligophagous", click on "search instead for illiophagous". That will show you the results for "illiophagous". Dominus Vobisdu (talk) 16:40, 1 October 2012 (UTC)

As to the possibility of "ingesting mud", it could be true, if it then filters out it's food from the mud. I believe there are some crabs that do this. StuRat (talk) 18:06, 1 October 2012 (UTC)

That would be the reason that catfish are not kosher. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:05, 2 October 2012 (UTC)

Is this in a WP article somewhere? If so, perhaps it needs to be restated in plain English, or a translation provided. Alansplodge (talk) 12:33, 2 October 2012 (UTC)

Waves going toward or away from shore

I'm on a Caribbean island with a westward-pointing pier on the western shore. In the morning as I walk out the pier, I see that the wind is blowing toward the sea from land (i.e. from east to west, so the land-sea breeze augments the prevailing trade winds); and the waves appear to be going in the same direction--away from shore. This fits with my understanding that waves are normally wind-driven. Yet waves are also lapping at the shore, coming west-to-east. What drives them against the wind? Duoduoduo (talk) 17:23, 1 October 2012 (UTC)

While wind can create waves, it's not very effective and cancelling waves. So, those waves may have formed out at sea, where the wind direction is different. StuRat (talk) 18:04, 1 October 2012 (UTC)

I don't think that's it. Farther out to sea, the wind direction certainly from east-to-west (the direction of the tropical trade winds), so that doesn't explain waves coming in west-to-east and hitting the west shore. In any event, let me ask a related question: why is it that at any given time waves are coming into the shore on all sides of the island--i.e., in every possible direction? Duoduoduo (talk) 19:14, 1 October 2012 (UTC)

There's an inherent asymmetry between motion toward and away from shore. Waves can be travelling in all directions out at sea. Indeed, I have never seen only coherent unidirectional waves without some very strong extrinsic reason. But as any wave which happens to be moving toward the shore approaches, it will slow down, rise up, and break. This also has the tendency of refracting waves moving obliquely along the coast so that they bend to move in paralleling the coast. Those are the waves we see as they rear up and come in face on to the coast. Depending on the steepness of the shore, you can also see waves reflected back out coherently, causing a zipper effect as incoming and outgoing waves intersect. μηδείς (talk) 19:24, 1 October 2012 (UTC)

You say that waves can be travelling in all directions out at sea. What happens when waves arrive at the same place from opposite directions at the same time? Do they both just keep right on going unless there's some relation between their frequencies or wavelengths? Duoduoduo (talk) 19:49, 1 October 2012 (UTC)

Yes, waves pass right through each other. This is true even if they have the same frequency/wavelength. However, you can get interesting effects in these cases, like a standing wave or a null point. StuRat (talk) 20:47, 1 October 2012 (UTC)

I recently learned about seiches, which are resonant standing waves in enclosed bodies of water, like lakes or even some seas. Pfly (talk) 22:44, 2 October 2012 (UTC)

Russian loudspeakers

I buy a couple of loudspeakers, brand “Radiotehnika” and the enclosoure say “4 Om”… the receiver I currently have is only 6 Ω… I just pluggued the loudspeakers this morning and and the system sound fine to me but…

what are the risks to the new loudspeakers blowout or burn to the hell or do any other electric bad thig to my receiver?? — Preceding unsigned comment added by Iskander HFC (talk • contribs) 17:42, 1 October 2012 (UTC)

It should work OK as long as you do not drive your receiver close to its limit. Keep the volume backed off 50% and the chances of transisters going up in smoke is much reduced. Graeme Bartlett (talk) 20:51, 1 October 2012 (UTC)

And they should put a label on the volume dial, or physically block it, if possible, to prevent anyone else from turning it to max. StuRat (talk) 23:57, 1 October 2012 (UTC)

Ok… thankyou very much! Iskánder Vigoa Pérez 00:55, 2 October 2012 (UTC) — Preceding unsigned comment added by Iskander HFC (talk • contribs)

There's no need to worry. In the early days (up to early 1960's)of transistor circuitry, transistor prices increased dramatically with power rating, so design engineers would cut things a bit fine. This issue went away with the introduction of low cost silicon parts in the late 1960's. Certainly in the last 30 years, no design engineer of any merit would design a reciever or amplifier circuit that critical - after all, the impedance of a loudspeaker is well understood to be only a nomimal value. In any case, it became the norm from the 1970's onward to include automatic protection circuits in recievers and amplifiers. With modern integrated circuits, this is always done.

In any case, marking the volume control to avoid turning it up is just plain silly. How hard the circuit works is primarily set by the amplitude of the bass, including the very deep bass that is barely audible, but loudness as percieved by the ear is a complex function of the bass, mid-range, and treble components. This means that the power level encountered by the circuitry varies considerably from musical item to item, even when the volume, as percieved, and as set, stays fairly constant. If you have a copy of the CD "Buddy Holly Story (London Cast)", play it on your stereo at a lowish volume setting while monitoring the loudspeaker voltage with an analog voltmeter. You will see a dramatic variation in voltage from track to track even though you aren't changing the volume control setting. (This particular CD is notorious for showing up amplifier weaknesses due to the deep bass in some tracks only).

Keit60.230.201.133 (talk) 01:18, 2 October 2012 (UTC)

Connecting the dots in a graph

If you obtain through direct measurement the points 2,2; 3,3; 4,4 in a x-y graph. Is it wrong to connect them with a line? Actually, you don't have the measure 2.5, 2,5, but your graph with connected dots would be showing them, and you could not rule out that y was 3 when x was 2.5. Isn't that a little bit like inventing stuff? OsmanRF34 (talk) 18:24, 1 October 2012 (UTC)

Creating a line or curve to connect graph points is fine. The connection between graph points is an interpolation of the data, and the line or curve beyond the end points is an extrapolation of the data. Interpolation is more reliable than extrapolation. While only 3 data points may very well be insufficient to draw a line or curve reliably, you will never have an infinite amount of data, so some extrapolation is required in order to determine any trend. StuRat (talk) 18:30, 1 October 2012 (UTC)

I understand that in certain scenarios that makes sense. But shouldn't such graphs have an indication of the density of the points and how much interpolation (or extrapolation) was done? OsmanRF34 (talk) 18:35, 1 October 2012 (UTC)

Yes. This is normally done by showing both the data points and the line/curve, on the same graph. Extrapolation is sometimes shown as a dotted or dashed line/curve, to show that it is less reliable. StuRat (talk) 18:38, 1 October 2012 (UTC)

I would expect to see error bars as a indicator of probability density. Also, there would be no justification for drawing a straight line unless there was a reasonable assumption that a linear (or regionally near-linear) model could be used to explain the trend. That is not always the case. Dominus Vobisdu (talk) 18:51, 1 October 2012 (UTC)

Indeed. "But...the line must be a good fit; I used Excel" is the bane of first-year laboratory lecturers. Do you have a model? Did you look at the data? Anscombe's quartet is probably my favorite cautionary illustration for linear regression. TenOfAllTrades(talk) 20:50, 1 October 2012 (UTC)

Indeed - just as first years (and even final years) taking a reading with an instrument and believing that's all there is to it because the intrument has a digital readout or a famous brand name on it. The reality is that you learn more, and detect mistakes, if before you take any readings, you know what to expect - that is you develop a theory that predicts what the readings will be. And if the readings fall where your theory says they will, your theory is confirmed (to a reliability that is dependent on circumstances and the number of readings), and you know how the dots should be joined. Soemtimes you cannot know the theory, but as far as possible, you should work out the theory before coming near any instrument. Ratbone23:45, 1 October 2012 (UTC) — Preceding unsigned comment added by 124.178.43.23 (talk)

If you want to connect your points with lines but need the individual data points to stand out, the usual approach is to mark them, using circles or squares or some other symbol, it doesn't really matter what as long as it is visible. Looie496 (talk) 03:54, 2 October 2012 (UTC)

It's not directly an answer to your question, but the mathematics for producing the best line to fit a given set of data is linear regression. If the experimental uncertainty in the data is known, there are formulas that can be used to help decide whether the graph is a good fit or not. With your three-item dataset, you couldn't rule out the possibility that the next point would be (2.5,3.0), however as the dataset gets larger the confidence one can have in the result goes up.--Srleffler (talk) 17:51, 2 October 2012 (UTC)

Beta carbon nitride

The article Beta carbon nitride says that the substance is expected to be harder than diamond, but the diagram implies a planar, rather than a solid structure. What am I not understanding here? μηδείς (talk) 19:12, 1 October 2012 (UTC)

The diagram doesn't do the model justice (although ironically this is just a colored variation of the diagram put forth by Cohen himself). Rather, bonding is tetrahedral. It's described in greater detail in [5], if you have access. Someguy1221 (talk) 20:43, 1 October 2012 (UTC)

No, instead of buying the parents of my niebles a one-year's subscription to Science, I bought them a lifetime subscription to National Geographic for their wedding present. Any chance you can link to an image available at Google Images? μηδείς (talk) 22:10, 1 October 2012 (UTC)

If I knew of one, I'd give it to you. What I can do is quote the caption that accompanied the original figure, which is identical to the one in the article but in black and white:

Structure of beta-C3N4 in the a-b plane. The c-axis is normal to the page. Half the atoms illustrated are located in the z = -c/4 plane, the other half are in the z = c/4 plane. The structure consists of these buckled planes stacked in AAA... sequence. The parallelogram shows the unit cell.

Someguy1221 (talk) 22:21, 1 October 2012 (UTC)

Assuming I take that right, it means that the atoms are in a crumpled plane, sort of like an egg crate. But still in a sheet. That still doesn't seem to get us to a solid 3D structure like diamond. Do some of the pictured carbons have bonds that are not shown? Arent all the bonds where the carbon and nitrogen atoms are shown as touching, rather than linked, double bonds? It seems to me every carbon has two single and one double bond in the crumpled plane, while every nitrogen has one double and one single. μηδείς (talk) 02:08, 2 October 2012 (UTC)

The paper describes the nitrogen atoms as being sp2 hybridized and the carbon atoms as being sp3 hybridized, with each carbon atom being linked to four nitrogens, so yes, there must be bonds in the model that aren't shown. Someguy1221 (talk) 02:18, 2 October 2012 (UTC)

Ah, and so the bonds are actually intermediate between those implied in the diagram? Each carbon shown is bonded to one not-shown nitrogen, and most of the nitrogens shown to a carbon not in the plane? Can you edit the image in the original article accurately to fit that, so future readers are not as flummoxed as I was? μηδείς (talk) 03:12, 2 October 2012 (UTC)

I would, but I still don't know what it actually looks like! With that image, the caption, and what I just told you, you now know as much as I do about the structure of beta carbon nitride. I might look into some of the references Cohen provides to see if any of them are enlightening. Someguy1221 (talk) 02:34, 2 October 2012 (UTC)

Well, at least you can see the source. perhaps you could at least add that certain bonds not in the plane are not indicated? μηδείς (talk) 03:12, 2 October 2012 (UTC)

I also have access to the source, but it really provides no further visual information except as the above. The black-and-white original provides slightly more depth (because it's more evident which bonds are coming up or going down relative to the viewer) but the missing C-N bonds (the third bonds on the smaller N atoms, the fourth bonds for the larger C atoms) are not drawn. Adding them is not simple - I'm not sure what angles they would take (probably perpendicular to the sheet). Absent a reliable source, accurately drawing this would require a 3-dimensional model with multiple layers (i.e., a fair amount of original research). -- Scray (talk) 04:17, 2 October 2012 (UTC)

No, I wouldn't expect you to draw the bonds. I just thought you could update the caption text to mention them in a way you believe is accurate from the source. μηδείς (talk) 17:26, 2 October 2012 (UTC)

Clouds and pressure

Why does a sudden reduction in pressure cause clouds (or vapor) to form? 74.15.136.9 (talk) 22:04, 1 October 2012 (UTC)

Because this implies a low pressure front has moved in, which generally means lower temperatures, too. If the temperature drops below the dew point, clouds and then precipitation occur. StuRat (talk) 22:08, 1 October 2012 (UTC)

See PV=nRT. μηδείς (talk) 22:10, 1 October 2012 (UTC)

Here's a more detailed answer. Generally speaking, air closer to the suface has a larger amount of water vapor in it (in terms of absolute humidity, that is the grams of water per cubic meter of air) because it is warmer (and warmer air can hold more water vapor) and it is of a higher pressure, which means there's more of everything in a given unit of volume. What a low pressure area indicates is a trend of rising air (see Vertical draft for a short explanation or Low-pressure area for a fuller explanation), which means there is a general flow of ground air up to the higher areas of the atmosphere. If you lift a lot of warm, moist, higher pressure air into the upper atmosphere, it cools, spreads out, and releases all of its water vapor as little droplets. Hense, clouds. --Jayron32 22:45, 1 October 2012 (UTC)

StuRat basically has part of the right answer, and Jayron's explanation is also part of the answer, but the full story involves some additional complexities. A sudden reduction in pressure usually means that a low pressure system has moved in. Low pressure systems spin cyclonically (clockwise in the northern hemisphere), which means that they bring in air that is often warm, moist, and unstable. Also, as the low pressure systems move eastward (the usual direction), they tend to create frontal boundaries, which are particularly unstable. Looie496 (talk) 01:38, 2 October 2012 (UTC)

Thanks for the answers everyone. I have two more related questions: when a nuclear weapon goes off, there will often be a condensation cloud that accompanies it. As the article explains, the clouds form because of a reduction in temperature, which in turn is caused by the low pressure that follows a shock wave. My questions are 1) why does this sudden rarefaction of air produce a reduction in temperature? (The answers given above don't seem to work, because the low pressure evidently isn't caused by a influx of cold air. 2) why is there a low pressure zone after the shock wave? Thanks again. 74.15.136.9 (talk) 21:37, 2 October 2012 (UTC)

For #1, see adiabatic cooling which is how a refrigerator works. Energy is a zero sum game, which means that rapid changes in pressure can cause equally rapid changes in temperature if there is minimal energy exchange with the surroundings. That means that a rapid pressure drop, which happens too fast to allow energy to properly equilibrate with the surroundings, will result in an equally rapid temperature drop. This is how both a refrigerator and a diesel engine work, in opposite directions. The refrigerator works by taking a compressed gas and allowing it to expand rapidly, the resulting expansion cools the refrigerator. The compressor in the refrigerator re-compresses the gas to it can be allowed to expand again. In a diesel engine, the pistons generate enormously high pressures, and the massive increase in pressure causes the fuel-air mixture to spontaneously combust. With a nuclear bomb, you've essentially got the refrigerator effect happening: as the air rushes away from the blast site, you create an area of rapidly forming low pressure, which results in a near instantaneous temperature drop. The shock wave situation is the same thing: As a shock wave moves away from its origin, the origin is left with less stuff there, and that rapid pressure drop causes a rapid cooling. --Jayron32 21:52, 2 October 2012 (UTC)

To help visualize why a blast creates both high and low pressure, consider these particles at rest:

XXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXX

Now a blast wave comes along and moves some of those particles into the crests, leaving troughs where they were removed:

X    XX    XX    X
XX  XXXX  XXXX  XX
XXXXXXXXXXXXXXXXXX

The number of particles remains the same (air molecules in this case, or water molecules during a tsunami). The peaks represent high pressure, in the case of an air blast, and the troughs represent low pressure. So, just like you get a receding waterline between tsunami waves, you also get low pressure during a nuclear explosion. StuRat (talk) 02:08, 3 October 2012 (UTC)

October 2

Kinetic reclamation to your phone due to bodily movements.

I've heard of watches that recharge just by the movement of your wrists. It's piezo mechanics, right?

Why can't we put that in phones so that when they move with your body while in the pocket, your bodily movements help recharge them too?

If they're on their way, how far away is that technology, and why isn't it here already? Thanks. --129.130.237.27 (talk) 03:59, 2 October 2012 (UTC)

The power drain of a wrist watch is minuscule compared to a smartphone. Think about it: A little button battery can run a watch for 5 years, and that technology is like 50 years old. You can use your smartphone for what, like 8 hours before it needs a charge, and that's on supermodern batteries that didn't exist 5 years ago. The difference is like the difference between shooting a bullet with a gun (the smartphone) and throwing it (the watch). Not even a comparison. --Jayron32 04:15, 2 October 2012 (UTC)

Our article, orders of magnitude, claims a quartz watch uses about a microwatt, without a source. That's about one million times less power, on average, than a modern computerized mobile telephone (at least, while it is in use). While looking for sources, I found a fantastic detailed overview of the Seiko 7S26 mechanism; and Mike Murray's Everything You Ever Wanted To Know About Mainsprings (except, of course, a quantitative estimate of their potential energy content!) I seem to recall, though I'm unable to cite a source, that quartz digital watches consume more power than a mechanical spring-driven watch; but a quartz watch battery contains significantly more potential energy than a spring... which is why digital watches last longer than mechanical watches, between winding. Let the race begin to find a reliable reference! Nimur (talk) 04:24, 2 October 2012 (UTC)

OK, we've established that movements of the wrist won't be enough, but how about if we put a crank on the phone ? I have a portable radio that runs off a crank, and that uses a comparable amount of energy to a cell phone, I bet. Obviously cranking your phone to charge the battery isn't something you'd want to do often, but you might on occasion, like if your car breaks down and you then discover that your cell phone battery is dead. StuRat (talk) 04:52, 2 October 2012 (UTC)

They exist, though mostly they are advertised as "emergency" chargers: Crank like crazy for 5 minutes and you can get enough charge to call a tow truck. Maybe. Not enough to be practical to keep a constant charge, but enough to put a few minutes of call time on the phone. --Jayron32 04:57, 2 October 2012 (UTC)

Virtually all automatic watches have been mechanical - a swinging weight rewinds a spring, as with the Sieko cited by Nimur. I very much doubt that windup cellphones would catch on, for three reasons: Firstly, the typical radio frequency output of a hand held cell phone is 200 milliwatts (200 mW). The typical maximum electrical power into the speaker in the sort of transistor radio that you can get with a crank generator is 250 mW. That sounds about the same, but that's not the whole story. The cell phone's RF output is continous throughout each call. Assuming a typical call duration of 3 minutes, that's 36 Joules of energy, assuming the circuitry is 100% efficient at converted battery DC into radio frequency output (which it won't be). However, the ratio of average to peak power in voice and music is very low - a transistor radio may have a max output of 250 mW but the battery drain under typical programme conditions wil be more like 20 mW, or 1.2 Joules per minute. But there's more: The second reason: When you've had enough of listening to the news and the latest silly nonsense from the politicians, you can turn the radio off and energy consumption is then zero. But a cell phone must be kepton, in standby mode, so you can recieve calls. It's hard to find reliable data for phone standby drain, but 10 mW would not be unreasonable. That means a consumption, above the call consumption, of 0.6 joules per minute, 144 joules each 4 hours. Thirdly, a generator and crank of the necesary size would increase the volume and weight of a cell phone by about a factor of 10. Keit60.230.201.133 (talk) 05:14, 2 October 2012 (UTC)

Jayron's answer above includes pics that appear to about equal the size of the cell phone they charge, so not 10X. You might want to take one with you camping, for example (away from electrical outlets but still within cell tower range). Also, you don't need to leave your phone in standby mode. You can just wind it up, make a call, and turn it back off again. When you next wind it back up and turn it on, you should get any messages left for you. Many people in the older generation don't even like to leave them on, given the choice. StuRat (talk) 05:31, 2 October 2012 (UTC)

You must have magic fingers as when I tried Jayron's link, it didn't work. However Jayron makes it clear it's not very practical - he said "crank like crazy for 5 minutes...and make one (quick call) ...maybe". Yes, you can turn the phone off, but to catch on ie be a market success the phone has to work normally - stay on standby and let you make decent length calls. Orthwise only a few nutters will buy it. Don't forget that every time you turn a cellphone off, and everey time you turn it on, it enters into an automatic dialog with the network, so the network knows which base stations to route the call to, should it be worthwhile. This is so that the network can operate efficiently - each time a call (or text) comes in, the network doesn't try every base station in the country (and any other countries you can roam to) - the network only tries base stations at and adjacent to where they last found you, and doesn't try at all if it knows your phone is off. It means the sequence turn it on - make a quick call - turn it off is very inefficient energy-wise. Keit124.182.178.117 (talk) 13:12, 2 October 2012 (UTC)

...which is because modern mobile telephones are cellular phones, not general-purpose radio telephones. Cellular mobile telephones require an elaborate digital communication protocol, and must remain in contact with a cellular base-station, in order to operate. Contrast this to, for example, a conventional civilian aviation handset, whose RF transmitter is on exactly only when transmitting voice signal; and whose receiver amplifier requires very little power. Nimur (talk) 16:23, 2 October 2012 (UTC)

I'm certainly not suggesting that the crank would be used normally, you'd go with the usual battery operation and wall outlet recharging, then. And the crank charging unit would be separate, so you don't have to carry it around with you (although you could, in a pocket or purse, say). StuRat (talk) 18:02, 2 October 2012 (UTC)

Infant mortality rate and birth rate

Is it true that if the Infant mortality rate goes down in an area (i.e. child survivability goes up), the birth rate usually goes down more so that the population declines? Bubba73 ^{You talkin' to me?} 05:07, 2 October 2012 (UTC)

Damn skippy. See Demographic-economic paradox for a fuller treatment. --Jayron32 05:35, 2 October 2012 (UTC)

I don't know what "damn skippy" means, but in any case the statement is not true. The literature on the relationship between infant mortality and fertility struggles to find any consistent effect at all, and certainly not a large enough effect to counteract changes in infant mortality. It's hard to even imagine how that could come about. Looie496 (talk) 05:39, 2 October 2012 (UTC)

You could read the article I provided a link to. Or you could provide your own links or references. See [6] for your other question. --Jayron32 05:45, 2 October 2012 (UTC)

Well, as you point out, there is a lot of evidence that increases in prosperity can reduce birth rates to the extent of causing a population decline. But that article doesn't say that changes in infant mortality alone can do it. A Google Scholar search for articles on the topic finds a number of them, none of them supporting such a result as far as I can see, but none that is recent and authoritative enough to be worth citing; see for example http://www.nber.org/papers/w1528. Looie496 (talk) 06:13, 2 October 2012 (UTC)

I suppose part of the problem is teasing out a specific correlation. There's a melange of factors which leads to modern development, and the things which lead to decreased infant mortality tend to get all wrapped up in the same sorts of things (education, industrialization, improved access to health care) that leads to "development" generally speaking. What you'd need is some sort of society where somehow there was access to fully-modern prenatal care, but with no other development at all. It's hard to imagine such a place existing, so there isn't really a great way to run the experiment. What we're left with is the broad trends, that show that as a population becomes more "developed" in an economic sense, the birth rate goes down (as does infant mortality), but I'm not sure there's a causative or directly correlative effect which could be isolated for those two AND ONLY those two variables. --Jayron32 06:34, 2 October 2012 (UTC)

It's false. See Qatar, UAE, and Bahrain for counter-examples. A8875 (talk) 07:54, 2 October 2012 (UTC)

See outlier. Come back when you have a question. --Jayron32 13:58, 2 October 2012 (UTC)

They certainly look correlated, but that doesn't mean that one is the cause of the other. Like Jayron pointed out, the two are probably both just small parts of overall development. Here is a graph showing the two values plotted against each other: [[7]] 209.131.76.183 (talk) 11:48, 2 October 2012 (UTC)

The (loose) association is known as the demographic transition. Itsmejudith (talk) 13:20, 2 October 2012 (UTC)

Those graphs are quite interesting, and the type of information I was looking for. Bubba73 ^{You talkin' to me?} 14:00, 2 October 2012 (UTC)

I'm in favor of helping children in underdeveloped countries live, but is that making the problem worse in the future? Bubba73 ^{You talkin' to me?} 17:12, 2 October 2012 (UTC)

Good question. like it could explain the genocide that occurs in Africa. those that were "supposed" to be dead a long time ago are eventually killed by the militias fighting for food, etc.165.212.189.187 (talk) 17:33, 2 October 2012 (UTC)

It's a complex problem. One the one hand, compassion dictates that we don't let people starve. On the other hand, long-term continuous foreign aid in the form of basic necessities may also be what is keeping these countries from developing their own native food and clothing industries. Here is just one article on the detrimental effect of clothing donations on the domestic clothing industry in Nigeria. here is a similar paper which poses the same sorts of problems related to food aid and farming. However, issues noted in the D-E paradox and Demographic transition articles noted above point to the solution likely coming from development and education in general. I've seen some studies which show a marked improvement in living conditions in areas with properly applied Microcredit systems that allow development of native industries instead of blanket food aid. Which is not to say that food aid isn't needed in some dire cases, but it isn't the end of the solution. --Jayron32 17:42, 2 October 2012 (UTC)

There is also breastfeeding infertility, the tendency of women breastfeeding live children for a few years not to ovulate during that period. μηδείς (talk) 00:44, 3 October 2012 (UTC)

derivation of lensmaker's equation for a thick lens

What is the derivation of the lensmaker's equation for a thick lens. It seems hard to find on the internet. (Why isn't it on Wikipedia?) 137.54.11.202 (talk) 05:44, 2 October 2012 (UTC)

Does Lens_(optics)#Lensmaker.27s_equation answer your question? --Jayron32 05:46, 2 October 2012 (UTC)

By googling "derivation lensmaker's equation" I found the following two derivations[8][9]. I personally don't think derivations belong on Wikipedia(unless the derivation warrants its own article), since they add unnecessary bulk to the articles. People looking for an equation and people looking for a derivation of the same equation are on completely different skill levels. A8875 (talk) 07:20, 2 October 2012 (UTC)

I had always presumed that the lensmaker's equation is strictly an empirical first-order approximation. This is why it doesn't hold up very well to modern, complicated materials like compound glasses. The incredibly over-priced, but totally-without-equal, textbook Applied Photographic Optics, has no substitute: it thoroughly runs through the physics and the actual engineering specifications for many common lens glasses and compound lens groups. Nimur (talk) 16:18, 2 October 2012 (UTC)

The reason why I need a derivation is that I am solving a problem for an exotic lens, so I'm trying to use the same technique to derive the thick lens equation to create an equation for my exotic lens. 199.111.224.96 (talk) 18:21, 2 October 2012 (UTC)

what is the resistor for?

Hello, in this circuit, what is the 1MOhm resistor for? Also, shouldn't there be a series resistance in series with the potentiometer? Thanks in advance! Asmrulz (talk) 14:09, 2 October 2012 (UTC)

The 1M resistor sets the time constant (and the scaling factor) for the differentiator. An extra series resistance in line with the potentiometer wouldn't help or hurt the measurement of the time-derivative of current, because it is constant; it might be a good idea to prevent accidental shorting of the battery. Many potentiometers don't span all the way to zero ohms, so it's not necessary in practice. To fully analyze the role of the resistor, you should write the circuit equations in terms of a complex impedance, which will allow you to solve the circuit in the Laplace domain, permitting a straightfoward accounting for the time/frequency effects as well as the differentiation. Nimur (talk) 14:25, 2 October 2012 (UTC)

I haven't thought of this as an RC element *slaps himself on the forehead.* Thanks again. Asmrulz (talk) 15:01, 2 October 2012 (UTC)

Out of curiosity, how would I go about writing the circuit equations? Asmrulz (talk) 15:59, 2 October 2012 (UTC)

Kirchoff's circuit laws, appropriately using complex impedance instead of simple resistance. A typical first course in circuit analysis goes over the common techniques to write out equations for each node and then uses the techniques of linear algebra to solve simultaneously, giving the voltage at each node, and the current in each branch. Nimur (talk) 16:14, 2 October 2012 (UTC)

Like this, just in complex numbers? Asmrulz (talk) 18:10, 2 October 2012 (UTC) not quite, probably... Asmrulz (talk) 23:39, 2 October 2012 (UTC)

Morphine/Dilaudid conversion

Does anyone know what 20 mg of Kadian converts to in terms of hydromorphone? This is simply a factual question; I am not seeking any kind of medical advice. Joefromrandb (talk) 14:50, 2 October 2012 (UTC)

Anyone?... Nevermind...too late.165.212.189.187 (talk) 17:29, 2 October 2012 (UTC)

Some kind of Wikispeak? Joefromrandb (talk) 17:50, 2 October 2012 (UTC)

I think the OP is suggesting this is a homework question. Nil Einne (talk) 20:27, 2 October 2012 (UTC)

Our Hydromorphone article, while fairly poor, ('and it can be said that hydromorphone is to morphine as hydrocodone is to codeine and, therefore, a semi-synthetic drug' - is it a copyvio or copied from a public domain source without talk page attribution or something?) says this:

Hydromorphone's oral-to-intravenous effectiveness ratio is 5:1 and equianalgesia conversion ratio (hydromorphone HCl to anhydrous morphine sulfate, IV, SC, or IM) is 8:1. The oral equianalgesic conversion rate (hydromorphone HCl to morphine SO4) can vary between 5:1 to 8:1. Therefore, 30 mg of immediate-release morphine by mouth is similar in analgesic effect to about 4–6 mg of hydromorphone by mouth (requiring extra care during conversion & titration), 10 mg of morphine by injection, and 1.5 mg of hydromorphone by injection.

Given the state of the article, I can't vouch for these figures. But it does indicate an unsurprising issue, this isn't a simple factual question and there's no simple conversion. These are related but different drugs so don't have any perfect correlation in effect. (Our article also says other things which indicate this.)

Also your question is fairly unclear. In the subject you mentioned 'Dilaudid', in the question you mentioned 'Kadian'. The later is apparently an extended release form of morphine sulfate in capsules and the former a immediate-release form of hydromorphone hydrochloride in tablets or liquid. From this it sounds like you're referring to oral ingestion (obviously an important consideration) but the lack of consistency and generally limited information makes this unclear. Notably, if you're referring to an extended release form of morphine and an immediate release form of hydromorphine, this wasn't clearly specified and is unlikely to be obvious to anyone unfamiliar with the specific brands you mentioned in the subject or in the question.

Nil Einne (talk) 20:15, 2 October 2012 (UTC)

BTW I've added one link above from the article as again while not a great article, it'll give you an idea of how to begin to look for answers (plural intentional) Nil Einne (talk) 20:24, 2 October 2012 (UTC)

Thank you very much for the help! And although I am perpetually learning, I can assure you my "homework" days are decades behind me. Joefromrandb (talk) 20:33, 2 October 2012 (UTC)

And perhaps I was more vague than I needed to be. Specificallly, I was comparing an 8mg immediate-release Dilaudid to a 20mg extended-release Kadian. Joefromrandb (talk) 20:40, 2 October 2012 (UTC)

Bowel flora

What happens to the bowel flora if a person only receives IV nutrition? Does it "starve" to death? If not, how does it obtain sufficient nutrients? Thanks in advance.--Leptictidium (mt) 14:56, 2 October 2012 (UTC)

Do people only receive IV nutrition? I'm pretty sure that for any nutrition is dealt with via Feeding tube. Intravenous therapy is used for fluid or electrolyte replacement, but not generally for caloric needs, at least on a long term basis. --Jayron32 16:34, 2 October 2012 (UTC)

Yes, check out "Total peripheral nutrition", for example.--Leptictidium (mt) 16:55, 2 October 2012 (UTC)

Google is your friend. This list came from Google Scholar. Use it wisely. --Jayron32 17:05, 2 October 2012 (UTC)

what is the formula for the angular magnification for a single lens?

Like say, a magnifying glass? Everywhere I look on the internet, the formula is always given for microscopes or telescopes with an "eyepiece", which is totally inappropriate to my problem. 199.111.224.96 (talk) 18:22, 2 October 2012 (UTC)

It sounds like you want a textbook introduction to geometric optics! Our article does have a formula for magnification for a simple lens, which is suitable for a high-school-level approximation. (This equation, which is commonly used in simple lenses, expresses magnification as a magnitude, in terms of focal-length and object distance). Whether that formula applies to your lens, or not, is entirely what makes optics a not-very-easy subject. If you've never studied optics formally, a decent introduction is found in Tipler's Physics for Scientists and Engineers, (in the second volume, Chapter 30-something in the 2nd edition). If you really really want to study optics, you should start with formal analysis of geometric optics and then study generalizations of electromagnetic wave propagation; so that you can appropriately model the lens or optical path you care about. Nimur (talk) 18:30, 2 October 2012 (UTC)

I think the problem is that a single lens can give you magnification that is so distorted and dim as to be useless. So, the question becomes "what is the useful magnification", which depends on the application and is subject to opinion. StuRat (talk) 18:33, 2 October 2012 (UTC)

Animal eyesight and the electromagnetic spectrum

I was thinking about how awesome it would be to be able to see radio waves directly and not needing them to be interpreted by television sets, wireless receivers, etc. (watching TV and browsing the Internet directly with your eyes just by looking at open air!), which led me to the following questions:

• Why did terrestrial animals evolve eyesight focused toward the infrared, visible, and/or ultraviolet parts of the electromagnetic spectrum, instead of evolving sensitivity toward other parts of the spectrum such as radio waves, microwaves, x-rays, or gamma radiation?
• Under what sorts of environmental conditions might we expect animals to have instead evolved sensitivity toward those other regions of the spectrum?
• How would such hypothetical animals perceive the world? For instance, radio waves can penetrate right through walls, with distortion being minimal enough that wireless receivers read them just fine. Does that mean a theoretical animal that sees only radio waves would be unable to see walls?

—SeekingAnswers (reply) 18:59, 2 October 2012 (UTC)

Yes, and that's the problem. All they would see is the source of the radio emissions, so things like stars and lightning. Animals need to see what's right around them, so visible light, ultraviolet, and infrared are ideal, as they reflect off nearby objects, and some are actually produced by certain organisms (like mammals producing IR). Sound and vibrations, while not part of the EM spectrum, similarly react with, and are produced by, the local environment, so are useful. Similarly, the ability to "see" electrical fields is useful. StuRat (talk) 19:10, 2 October 2012 (UTC)

There are environments where there is no light, and blind organisms evolve there. (While some organisms can give off their own visible light, most do not, and sufficiently murky water would make even that approach unusable.) An organism living in space might not be able to use sound and vibrations, and, if inside a dark cloud of gas, might not be able to see, either. I'm not sure if being able to detect those other wavelengths of EM would be of much benefit, though. StuRat (talk) 19:30, 2 October 2012 (UTC)

A picture is worth a thousand words. I'll let this one do the speaking. --Jayron32 19:22, 2 October 2012 (UTC)

(ec with Jayron) The solar spectrum and the opacity of the atmosphere to electromagnetic radiation have a lot to do with the wavelengths to which the eyes are sensitive. The Sun's output peaks at ~550nm and so does the sensitivity of the eyes. The articles on eyes has some general information on this, and Color vision has quite a lot of information. Astronaut (talk) 19:28, 2 October 2012 (UTC)

Cellular Renewal

I have heard that every seven years, all the cells in a human body will be replaced. I am quite skeptical of this claim, so I wanted to know about it's factual accuracy. Is it true? Also, aren't there some cells, especially neurons in the brain, that are not replaced?128.227.85.113 (talk) 19:57, 2 October 2012 (UTC)

No, that is not true. But it does seem to have a grain of truth, or was based on a true claim. According to the website for Stanford's Institute for Stem Cell Biology [10], "Every single cell in our skeleton is replaced every 7 years." (emphasis mine). Granted, that web page does not link to a specific reference for that claim, but I'm willing to trust them on this one. SemanticMantis (talk) 20:24, 2 October 2012 (UTC)

Also, some cells are replaced much faster, like red blood cells, which only last a few months. StuRat (talk) 20:27, 2 October 2012 (UTC)

This is a decent link on the subject: [11]. --NorwegianBlue ^talk 22:28, 2 October 2012 (UTC)

The way I heard this one a long time ago was that every seven years the atoms would be replaced because of how the (electrons? protons?) swap places with each other so much. Is that totally wrong? Would there be a viable equation or something to determine the atoms version? ~ R.T.G 00:17, 3 October 2012 (UTC)

No. Electrons can bop around, but protons and neutrons stay with the atom (barring nuclear fusion, nuclear fission, and radioactive decay). StuRat (talk) 01:55, 3 October 2012 (UTC)

Entire atoms are exchanged to. Much of the molecules in your body are constantly being repaired and regenerated on a molecule-by-molecule basis; a carbon atom that was part of a fat cell yesterday could be part of hemoglobin next week, and be breathed out as CO2 in a few weeks. I have no idea on the time scales involved, but it isn't just the electrons that shuffle around. The "renewal of the body" thing, taken on an "atom-by-atom" basis is a classic example of the Ship of Theseus/George Washington's Axe paradox... --Jayron32 03:08, 3 October 2012 (UTC)

Jayron is right. That's why cells have nuclei, to produce new protein molecules by genetic transcription, ultimately from chromosomal DNA. Red blood cells die within about a month because they cannot transcribe from DNA, lacking cell nuclei. One can't give a seven year expiration date, but all living cells obviously regenerate their molecular structure or die. μηδείς (talk) 03:20, 3 October 2012 (UTC)

The fossil part of Fossil fuels

How can we know that fossil fuels are originally from fossils? Before life appeared on Earth, there should have been plenty of carbon around, so, couldn't the fuel been formed be it? OsmanRF34 (talk) 22:09, 2 October 2012 (UTC)

While we wait for an answer to your question, I give you Abiogenic petroleum origin for the nay-sayers ;) --Tagishsimon (talk) 22:14, 2 October 2012 (UTC)

I know that there is such a kind of fringe theory about oil, but it doesn't explain the other side of the equation. Why is it regarded as common wisdom that oil's origin is from fossils? OsmanRF34 (talk) 22:19, 2 October 2012 (UTC)

Well, from direct observation we can see that plants and animals produce oils and methane (hopefully not too directly on that one). Methane is also produced by natural processes, but we don't know of any inorganic process which produces oil or coal. StuRat (talk) 22:27, 2 October 2012 (UTC)

In the case of anthracite (hard) coal, you sometimes find the fossils right in the coal: [12]. We also have intermediate steps, like peat bogs, around today. StuRat (talk) 22:20, 2 October 2012 (UTC)

"fossil fuel" does not mean "fuel made of fossils", it means "fuel that is a fossil", where "fossil" means "of the ancient past". That's all it means - fuel from long ago. -- Finlay McWalterჷTalk 22:21, 2 October 2012 (UTC)

Sure, but the question is why the biogenic origin theory is favoured over the abiogenic in the cases of liquid and gaseous fuel. Oddly, the best we have on this seems to be at Abiogenic_petroleum_origin#State_of_current_research which summarises arguments in favour of the biogenic origin theory. --Tagishsimon (talk) 22:25, 2 October 2012 (UTC)

One of the things to consider is that we've got examples of every stage along the mechanism from living things to coal. Consider things like Peat which is just very young coal, Lignite, Bituminous coal, anthracite, etc. You can pretty much find all of the steps along the mechanism right now. What we don't find is large quantities of all of the steps of so-called "abiogenic coal". --Jayron32 22:32, 2 October 2012 (UTC)

Fossil, according to Wikipedia, means something which is fossus, dug up from the ground. Fossil fuels are made of stuff that plants produce when they decompose and are found in places where plants seem to have been decomposing. Scientists can not only theorise how oil occurs, they can/could (it's all gone remember) could predict whereabouts it would be and how much would be there, even under the ocean, so they know something. Household garbage can be compressed down some way to squeeze petrol out of it sort of like coal can be squeezed into diamonds in a pressure machine and those things are probably about as direct as any evidence we could ever get without time travel. Sap from some trees, for instance of doubt, drips and pours in large amounts. It hardens and becomes amber with little million year old insects in it. Maybe it's not tree sap after all, But it's made of tree sappy stuff and has little tree insects stuck in it. But don't worry about that because the oil is all gone away to a better place now with the copper and other useful stuff. ~ R.T.G 00:00, 3 October 2012 (UTC)

Have I missed where we have an article on abiogenic coal? Thomas Gold seems to have suggested that some bituminous coal may have a non-biological origin. I am not aware of any serious, detailed, broadsweeping theory that all coal can be explained without reference to decaying plant matter. μηδείς (talk) 03:13, 3 October 2012 (UTC)

Rating rechargeable battery input and output

I think most people get cheaper electricity at night and I wanted to work out if it would be viable to buy large batteries, such as those used in solar energy systems, charge them at night and then run some home electrical devices from them. Okay so working out, I understand wattage. KWh just means kilowatt per hour. My heater here beside me is 2kWh and that means while switched on it uses 2 per hour chared to me at 32cent each. Now, try to figure out how many kWh it takes to charge a battery and how many kWh it will return is not so straightforward and there isn't much explaining it on the internet from what I see. It's just a pie in the sky but if you could get back much more than 50% of the energy expended charging etc., no reason not to work that out.. There is some discussion board stuff on the net and I probably work it out after a while but might take me a few hours reading and frowning... Anybody on here just kind of know? ~ R.T.G 23:27, 2 October 2012 (UTC)

I can't see that working out. There's the inefficiency in charging and discharging the batteries, and the initial cost of batteries, plus maintenance costs, since they don't last long. And, from an environmental POV, there's all those old batteries to dispose of. A better approach would be to heat an insulated tank of water at night, then use that hot water to heat the home during the day. StuRat (talk) 23:36, 2 October 2012 (UTC)

It's more for the electricty itself. Water heating and conversion would be impractical for me (Ireland climate, small apartment), but if you could charge one of these extremely efficient new cells and discharge enough for the PC, the kettle, or even oven etc.. I know probably unlikely but also kind of frustrating not to do the equations very easily. I have a torch powered by 2 CREE batteries about mid size between AA and D cell, light as softwood, but it's bright enough to dazzle and goes for a couple hours, I've no idea however how much wattage it takes to charge and how much it releases, only that it seems powerful and that large size batteries can be made of the same stuff. I know if it could be done people would probably be doing it already but how close we are I can't tell. ~ R.T.G 00:14, 3 October 2012 (UTC)

There's a lot of discussion out there about storing energy from off-peak times. This is a very reasonable idea, and can potentially aid in the efficiency of the entire network, as well as save money for users. The cost/benefit analysis is tricky, but you may be interested in the idea of using a flywheel to store energy. I can't sort through them right now, but /home flywheel energy storage/ presents several interesting results on google, and some are commercial products for home use: [13]. See also our article on flywheel energy storage. SemanticMantis (talk) 01:40, 3 October 2012 (UTC)

BTW, you said your heater is 2 KwH. I think you mean it's 2 Kw, which means, if you use it for an hour, that makes 2 KwH. The main problem with batteries is that they are expensive and don't last, with inefficiency being a minor concern. The flywheel suggestion may work, because, unlike batteries, it shouldn't need to be replaced every few years. If you want electricity, rather than just heat, another option is to pump water into a water tower at night, and use that gravitational potential energy to run an electricity generator as the water flows back down to a lower tank, during the day. StuRat (talk) 01:43, 3 October 2012 (UTC)

The most common way that energy is stored from off-peak hours, at least residentially, is a Storage heater, which basically heats up some bricks at night, and allows the heat to escape into the room during the day. Storing heat is nice because it is, pretty much by definition, 100% efficient - any electricity you use will be converted into heat, and the design is such that most of it can be directed when and where you want it. If you want to get energy back in a usable form (to power your computer, or whatever), it's a little harder. On a municipal level, it's probably most common to pump water up, and then let it fall back down to reclaim the energy: Pumped-storage hydroelectricity. This is what is done at the Robert Moses Niagara Hydroelectric Power Station: They generate more power at night (because they don't have pushy tourists who want to look at the falls), but they have higher demand during the day. They therefore pump water up into a man-made reservoir at night, and let it come down during the day to provide supplemental electricity. Not practical on a residential level, to say the least. One of the ways being looked at to store power during cheaper times (again, mostly on a larger scale, though possibly adaptable to a household) is a flow battery [14]. The general term for this sort of thing, by the way, is Load balancing. Sorry I'm not providing much specific help, but I thought I'd point out some of the things that are done. Buddy431 (talk) 04:21, 3 October 2012 (UTC)

October 3

Motherboard oscillators in the GHz..

How does the oscillator circuit that generate 2.0 .. 4.2 GHz on ordinary motherboards for the CPU look like?, seems hard to find the "anonymous chip" among all other components. It would be interesting too see how wire paths has been done to deal with RF-issues. Electron9 (talk) 02:25, 3 October 2012 (UTC)

In any case, you might be interested to know that most high-frequency digital logic chips are driven by fairly low-frequency clock sources. These frequencies are stepped up to high frequency, including the microwave range, on the silicon die, where the processes and parasitic effects can be controlled more carefully. You might want to read about frequency multipliers and phase locked loops.

For example, Intel's reference design for their 82583 10-Gigabit Ethernet Controller (which internally uses one of the highest frequencies present anywhere on many computer main logic boards) is driven by a 25 MHz (megahertz) crystal.

Once you've mastered low-frequency design, you can migrate to microwave engineering; and ultimately reach Planar Microwave Engineering, or, the art of putting very high frequency circuits together in a way that can be built into a silicon wafer or printed circuit board. Nimur (talk) 03:17, 3 October 2012 (UTC)

I believe most processors on "ordinary motherboards" use a simple 14.318 MHz crystal which the processor inernally multiplies to acheive the GHz clock rates, as the above replies describe. You can find the crystal by doing a google image search of clock crystal motherboard. But I don't think you'll find anything fancy about it, all the "RF issues" would be dealt with inside the processor it self. Vespine (talk) 03:40, 3 October 2012 (UTC)

Audio waveform graphs

What is the official name for these sort of graphs? Is there a Wikipedia article about them?

What do the numbers on the Y axis correspond to? I gather they refer to amplitude, but what sort of unit are the values in? I've seen graphs where the values go from: 1 to 0 to -1 (like the one above); 30000 to 0 to -30000[15]; and -1 to -infinity to -1 (some audio software). Why the heck are these numbers so random? Do they actually mean something? Kaldari (talk) 02:41, 3 October 2012 (UTC)

These are line graphs of waveforms. I'm not aware of any "official" name for them; it looks like you took a screen shot of Audacity (software). The numbers can be just about anything; if they range from -1.0 to +1.0, they are normalized; if they range from about -30,000 to about +30,000, the axis is probably directly displaying the value of the signed 16-bit PCM sample data. (Even if the audio-file originally started as an encoded file, like an MP3, its decoded signal may be represented by PCM data internally by the software). Other times, axes will be labeled logarithmically; or in normalized decibel levels. (Logarithmic graphs often represent a "zero" signal-level as "negative infinity", which is a "correct" mathematical representation for the value of log(0); though there are various other conventions used for signal-processing, such as a logarithm of a moving average). As with any graph, if the axis isn't labeled with units, the data format is ambiguous, but we can draw reasonable conclusions based on common practice. Nimur (talk) 02:55, 3 October 2012 (UTC)

Thanks for the explanation. A follow-up question: If it is a normalized logarithmic graph, what would be the "correct" values for the top and bottom of the chart? Would they both be -1, both be 1, or would one be 1 and one be -1? And if it's not too much trouble: Why? Kaldari (talk) 04:13, 3 October 2012 (UTC)

Selective dissolution

What solutions will dissolve calcite (calcium carbonate), but not sphalerite (zinc sulfide), pyrite (iron sulfide) or galena (lead sulfide)? 203.27.72.5 (talk) 04:17, 3 October 2012 (UTC)

Water? --Jayron32 04:19, 3 October 2012 (UTC)