Wikipedia:Reference desk/Archives/Science/2012 March 17

= March 17 =

Meaning of ground state chemistry notation
I have a paper which apparently uses the notation 3P to identify oxygen atoms in the ground state, as distinct from 1D and 1S for oxygen atoms in an excited state. The wikipedia page for oxygen says that the (presumably) ground state oxygen electron configuration is 1s22s22p4, as do other web sites (the superscripts are the number of electrons in each mode), such as http://periodictable.com/Elements/008/data.html. How does the notation 3P identify the ground state, or, how does it relate to the notation given in the websites? Wickwack124.182.39.88 (talk) 04:34, 17 March 2012 (UTC)
 * That's the term symbol which is used in addition to the electron configuration to indicate the total angular momentum in the particular configuration. The superscript number is the value 2S+1, where "S" is the sum of all ms values for all electrons.  Thus, for an oxygen atom in the ground state, you have 1s2 (a +1/2 and a -1/2 spins) 2s2 (a +1/2 and a -1/2 spins) and 2p4 (3x +1/2 and only one -1/2 spins).  That gives S=1 (all s values cancel except in the 2p orbital, where one +1/2 cancels a -1/2, but there are 2 +1/2 spins left over).  So that makes the superscript 2S+1=3.  The big letter P is the value "L" in the term symbol, where "L" is the sum of all "ml" values.  For s orbitals, ml=0, and for p orbitals ml=+1, 0, -1 for each p orbital.  So for oxygen, for all 8 electrons, you have L 0+0(1s) +0+0 (2s) +1+1+0-1 (2p) = 1, so L = 1, which is P.  (basically, Capital letters are the sum of the individual lowercase letters in the Term Symbol).  The rules for constructing a term symbol for the ground state of an atom are described by Hund's rules.  Excited states have electrons in different sets of quantum numbers, so have different term symbols.  It is possible for two atoms to have the same notional electron configuration and have different term symbols; for example there are multiple ways that 2p4 could be organized into the three degenerate p orbitals, and only those with the term symbol 3P are considered the "ground state".  Organizations that give different term symbols are considered excited states.  -- Jayron  32  05:19, 17 March 2012 (UTC)

Are the concepts of closed space and sliders real concepts?
So I am a big fan of The Melancholy of Haruhi Suzumiya, which is a science-fiction series. In that anime, there are alien, time travelers and ESPers. Obviously, aliens are an established concept in science, as well as time travel, and ESP is being researched by some people. However, in that series, there is mention of so-called "closed space", where ESPers can travel to, and "sliders", who apparently can switch between dimensions. I think the "closed space" concept is made-up by Tanigawa Nagaru, but what about sliders? Has there ever been scientific theories or conspiracies about their existance? Asking this in the Science RefDesk instead of the Entertainment one since I am more interested in Haruhi Suzumiya's scientific basis. Narutolovehinata5 tccsdnew 10:04, 17 March 2012 (UTC)
 * Essentially all serious scientific proposals involving spacelike dimensions beyond the three dimensions of everyday life contemplate that such dimensions would be subatomic in size, so no person would ever be directly aware of them. They are also usually closed in the sense that the two dimensional surface along a very long pipe is closed along the circumference of the pipe's cross sections but not along its length. The reason for those attributes is usually to accommodate the unification of the physical forces, which is motivated by (what could be a merely coincidental) fact that all physical forces appear to be very similar at high energies. However, the prospect of multiple timelike dimensions is sort of an open question which would allow for all kinds of interesting physics. In general though, it is unlikely but there are a number of possibilities around the basic objections. Npmay (talk) 10:35, 17 March 2012 (UTC)
 * That's not the answer to my question. My question is, are the terms "closed space" and "sliders" made-up or not, or are there actual scientific theories about them that call them as such. Narutolovehinata5 tccsdnew 11:00, 17 March 2012 (UTC)
 * Closed space is an actual mathematical attribute of spatial dimensions which has scientific theories about it calling it such; it is usually called a closed manifold. Sliders are entirely fictional concepts which are certainly not possible without dimensional attributes that are almost never considered seriously in science. Npmay (talk) 11:20, 17 March 2012 (UTC)
 * Opon review of the fictional literature cited in the original question, I find the Yuki Nagato character most believable, although the most persuasive evidence of extraterrestrial life on Earth is invariably dismissed by serious scientists, but not, in my opinion, for good reasons.
 * Furthermore, I would say the "closed space" concept is probably less similar to a closed manifold and more similar to a macroscopic brane intersection between multiverses, which is, well, let's just call it fringe science. When branes as scientists theorize them collide, they do things like cause big bangs more often than they open dimensional portals from which one can fight monsters with psionic powers. Npmay (talk) 12:06, 17 March 2012 (UTC)


 * I'm tempted to think that "sliders" is a reference to Sliders rather than any real physics. Wnt (talk) 20:03, 17 March 2012 (UTC)

how do bridge makers model stresses
in general it seems easy enough to imagine things that support compression or pull, and so there must be software where you can just combine rods and suspending things at all angles you want, specify their attributes and see if the whole thing collapses or how it acts. so what is it? --80.99.254.208 (talk) 11:33, 17 March 2012 (UTC)


 * Physical modeling with finite element analysis CAD software is usually very accurate, but is almost always checked in practice with physical scale models for new structures of nontrivial complexity. Npmay (talk) 11:53, 17 March 2012 (UTC)


 * You seem like you know a bit about this subject. Could you explain it.  --80.99.254.208 (talk) 12:10, 17 March 2012 (UTC)


 * Have a look at that article and this video. Npmay (talk) 12:39, 17 March 2012 (UTC)


 * Not quite professional grade, but I recommend anyone interested in learning the basics try out the bridge builder series of games (some are free or free trial). It lets you visualize the stresses, and you will very quickly get better at building bridges :) SemanticMantis (talk) 14:41, 17 March 2012 (UTC)


 * I was about to say the same thing, online there's "Bridge Thing" and "Cargo Bridge". Also, sites about building bridges from toothpicks give good info, and there's the bridge design software West Point Bridge Designer, free to download. 84.197.178.75 (talk) 14:49, 17 March 2012 (UTC)


 * The basics of bridge building have been known for centuries, but some considerations, like wind-loading, resonance, and metal fatigue, have only been fully understood in the last few decades. See Tacoma Narrows Bridge (1940) for a case where the first two issues caused a collapse. StuRat (talk) 21:10, 17 March 2012 (UTC)

Software to draw schematic diagrams?
Hey, is there any software that can be used to draw schematic diagrams of machines or any device for that matter? And I don't mean CAD software, they're used for engineering drawings only. What I mean is something that can be used to draw stuff like this See, I'm reduced to uploading my horrible drawings to Wikipedia. Thanks!  Lynch 7  16:53, 17 March 2012 (UTC)


 * If you're just looking for a free package to make diagrams for Wikipedia, then Inkscape is good and it is in Wikipedia's preferred SVG format.  Spinning Spark  17:27, 17 March 2012 (UTC)


 * If Inkscape has too high a learning curve, LibreOffice Draw might do. Npmay (talk) 21:01, 17 March 2012 (UTC)


 * You wouldn't want to blow $5000 and many hours of leaning to use on professional CAD programs like Autocad, but purchasing a consumer grade CAD product like DesignCAD ($200 or so) is well worth the ease in which you can make very nice drawings with very little learning effort. With a few hours practice it becomes quicker than hand sketching.  I find it is very nice for doing custom graphs with special axis too.  For example I used it to graph viscosity of mineral oil versus temperature - this requires a [log of (log + K)] scale, not possible in Excel.  Keit58.170.182.237 (talk) 04:24, 18 March 2012 (UTC)

crypto rands automatically good for monte carlo?
Is any random number source that's good for crypto automatically good for a monte carlo simulation? (i.e. the monte carlo converges on whatever you would see in the wild with those natural conditions/percentages/whatever, rather than ever converging on some fluke of the RNG.

to illustrate what I'm talking about, int rand % x is not a good way to monte carlo random integers betwen 0 inclusive and x exclusive, because lower ones tend to come up more than higher ones. Likewise it would be a terrible choice for a crypto secure random integer.

So, my question is about the general case: if something is good enough for cryptography, is it good enough to monte carlo nature with? (i.e. all i have to worry about is finding a crypto library of random numbers, and I can go on my merry way assuming each random number is as good as forking to a random universe to continue, with equal distributin in each random universe...) forgive me if this belongs on the comp sci desk. --80.99.254.208 (talk) 18:55, 17 March 2012 (UTC)


 * Well, cryptography is pretty notorious for not being as good as claimed - it's hard for the user to tell, after all. It's not my field, but I should think that if your monte carlo acts aberrantly, you're already well on the way to cracking the encryption.  So I'd ask ... would it be newsworthy that the encryption that you're using had just been cracked by accident? Wnt (talk) 20:01, 17 March 2012 (UTC)


 * The needs of cryptography, and those of Monte-Carlo methods, are somewhat different. In principle, for example, a bitstream PRNG used for cryptography in certain ways (say, to get initialization vectors) could tolerate some slight bias (say, 50.1% 1s and 49.9% 0s), because bias per se is unlikely to help an attacker much.  However, for Monte-Carlo applications, you don't want bias.
 * That said, as far as I know, cryptographic PRNGs are all unbiased.
 * The main downside of using a cryptographic PRNG for Monte Carlo is likely to be speed. Monte-Carlo methods typically need random values in huge torrents; getting those from RC4 or something may be a bit slow.
 * Then there's a different issue: Are you sure you really want pseudo-random numbers at all?  Many Monte-Carlo type algos work better when you give them self-avoiding sequences (let's see if subrandom comes up blue), because you don't waste time exploring points of the space that have already been explored.  There's a good practical treatment of some of these in Numerical Recipes in C. --Trovatore (talk) 20:12, 17 March 2012 (UTC)
 * Well, Numerical Recipes is blue. DMacks (talk) 08:03, 18 March 2012 (UTC)

Why is the urinalysis called also: "Routine and Microscopy"?
I would like to understand it, thank you. — Preceding unsigned comment added by 176.13.203.54 (talk) 20:21, 17 March 2012 (UTC)


 * You don't say where you saw this, but it was likely on a lab slip where someone places a check-mark by the tests they want to order. One might want to order a routine urinalysis, or an examination of the urine under a microscope, or both. If you want both, you'll check off "routine and microscopy". The reason these are separated is that a routine urinalysis consists of chemical tests, and can be done very simply with a urinalysis dipstick, and it can be completely automated, making that part of the test cheaper than a microscopic examination, which requires spinning the urine in a centrifuge and examination by an actual person with a microscope. Our urinalysis article is a little misleading, because "Routine and Microscopy" is not a synonym for urinalysis, but rather an abbreviation of "routine urinalysis and microscopy". A routine urinalysis would include chemical tests for pH, specific gravity, glucose, ketones, protein, nitrite, blood (red blood cells (RBCs)), and leukocyte esterase (from white blood cells (WBCs)) - bilirubin or urobilinogen or other tests may also sometimes be included. But because there can be false positive chemical tests for blood and WBCs, so these would ordinarily be confirmed by microscopic examination, where one can actually see RBCs or WBCs (or other abnormal urine contents) if present. - Nunh-huh 20:51, 17 March 2012 (UTC)
 * Thank you for help. 176.13.203.54 (talk) 21:42, 17 March 2012 (UTC)
 * You're more than welcome. By the way, the combination of a routine urinalysis with a microscopic examination of the urine is sometimes called a "complete urinalysis". - Nunh-huh 21:58, 17 March 2012 (UTC)


 * Thank you. By the way, you're a good explainer and I wish to meet yuu here a lot in the down the road.176.13.203.54 (talk) 23:06, 17 March 2012 (UTC)


 * Yes, thanks for your analysis of urinalysis. StuRat (talk) 02:28, 18 March 2012 (UTC)

Why is the Urine culture called also Diaslide?
I don't understand it. thank you for help. 176.13.203.54 (talk) 20:49, 17 March 2012 (UTC)


 * Diaslide is a trademark for a specific brand of urine culture test. Just like "Bic" is the trademark for a specific brand of pen. - Nunh-huh 20:53, 17 March 2012 (UTC)


 * Youtube has a video showing it in use.--Aspro (talk) 20:56, 17 March 2012 (UTC)


 * And I imagine it's short for "DIAgnostic microscope SLIDE culture". StuRat (talk) 20:59, 17 March 2012 (UTC)

The relativity of time.
Could time be the big and small force? — Preceding unsigned comment added by 192.148.117.95 (talk) 23:11, 17 March 2012 (UTC)

vanessa1234394! tahliabrehm — Preceding unsigned comment added by Tahlia1234 (talk • contribs) 23:22, 17 March 2012 (UTC)


 * Dunno. Give up! What’s the answer?--Aspro (talk) 00:05, 18 March 2012 (UTC)


 * If you mean the strong nuclear force and weak nuclear force, then no, absolutely not, not any more than time can be the tomato in your salad. StuRat (talk) 01:59, 18 March 2012 (UTC)
 * According to Gary Larson, Einstein proved that time is actually money. ←Baseball Bugs What's up, Doc? carrots→ 04:20, 18 March 2012 (UTC)