Science desk
< September 28	<< Aug \| September \| Oct >>	September 30 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

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)[reply]

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

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

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)[reply]

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)[reply]

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

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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

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)[reply]

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)[reply]

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

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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

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

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)[reply]

.

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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

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

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

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)[reply]

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)[reply]

Phase

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

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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

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)[reply]

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

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)[reply]

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)[reply]

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

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

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) [reply]

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) [reply]

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)[reply]

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) [reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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

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)[reply]

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)[reply]

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)[reply]

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)[reply]