:[[Barnacle]]s?-- <small>[[User:Obsidian Soul|<font color=0>'''O'''</font><font color=gray>BSIDIAN</font>]]</small><font size="3" face =times new roman>†</font><small>[[User talk:Obsidian Soul|<font color=0>'''S'''</font><font color=gray>OUL</font>]]</small> 01:47, 5 February 2012 (UTC)
:[[Barnacle]]s?-- <small>[[User:Obsidian Soul|<font color=0>'''O'''</font><font color=gray>BSIDIAN</font>]]</small><font size="3" face =times new roman>†</font><small>[[User talk:Obsidian Soul|<font color=0>'''S'''</font><font color=gray>OUL</font>]]</small> 01:47, 5 February 2012 (UTC)
== Cure for fetishes ==
What's the cure/treatment for a foot fetish? --[[User:Jafkldajsfkejwo|Jafkldajsfkejwo]] ([[User talk:Jafkldajsfkejwo|talk]]) 02:25, 5 February 2012 (UTC)
Revision as of 02:25, 5 February 2012
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Our article doesn't seem to suggest that the Mirage was developed entirely using CATI. Do you have some reason to think it was? Considering CATI was renamed to CATIA in 1981, it seems easily possible nothing was entirely developed using CATI. Presuming you do have some reason to think a Mirage was developed entirely using CATI, well our article suggests it was developed in 1977. In that case, you can narrow the range down significantly using Mirage (aircraft) and Dassault Aviation as it seems there are only a few Mirages developed post 1977 (Mirage 2000 and variants, Mirage 4000, Mirage 50 and Mirage III NG although there may be other variants that are missed. If it's the Mirage 4000, it's questionable if you can say if it was developed entirely using CATI since it never got past prototype stage.) Nil Einne (talk) 15:32, 2 February 2012 (UTC)[reply]
[1] mentions CATI. It doesn't mention what it was used for but from the description there, I'm not sure there's any reason to think things were developed entirely using it when first released (depending on your definition of 'entirely' I guess). In fact looking at the ref our article uses to support the early history of CATI [2], it looks like the first use was to design the wing, which concurs with what the earlier ref suggests. I presume it was used for other things soon after but the same ref supported by [3] suggests digital mockups wasn't even possible to the 90s (it also mentions the first to use that feature was the Rafale and the Falcon 2000). Also a quick search of the obvious place, the dassault-aviation website for 'CATIA mirage' finds results such as [4] which suggests the Mirage 2000 may have been the first to use CATI (but probably not developed entirely in it). This of course seems themost likely candidate from the earlier list (since the others were more variants of existing designs and the Mirage 4000 as I said wasn't completed). Nil Einne (talk) 15:52, 2 February 2012 (UTC)[reply]
Name of a sunset...measure-y...thing.
Hello!! This should be simple if what I'm looking for exists; if not, well it could be more tricky. I know that the position of sunset on the horizon swings from due west (I am talking northern hemisphere) during the equinoxes to the north and south for the solstices, and if one studies and records the position of said sunsets they can use it as a kind of calendar. Now I heard that one of the many theories of the existence of stone circles is to do just this; is there an actual name of such a built structure to help one measure the sunset locations instead of relying on hills or forests? My mind is saying 'Gnomon', but that's a sundial. Thank you!! LadyBlahDeBlah10:51, 1 February 2012 (UTC)[reply]
Henge is the general name for structures such as The Stonehenge and other stones henges, created to honor the dead. There were also wood henges, created for the living, which have since rotted away. StuRat (talk) 19:01, 1 February 2012 (UTC)[reply]
Been there. ^^ Recommended visit even if you can't get too close to the stones. But I think I'm more looking for if there's a name of the instrument/structure rather than the name of a place - unless I'm looking in the wrong places I might have to make one up... LadyBlahDeBlah11:35, 1 February 2012 (UTC)[reply]
I've seen references to "unbleached" flour and sugar, so the common white varieties must be somehow "bleached." How are food ingredients bleached? When a food ingredient is bleached, is the main constituent chemically altered or just the impurities? Chemically what does food bleaching do? Is it an oxidation process? If so, how does oxidation make something lose its color? — Preceding unsigned comment added by 71.185.179.180 (talk) 11:14, 1 February 2012 (UTC)[reply]
Bleach has a bit of info on the chemical processes. Oxidizing bleaches (such as chlorine and its compounds, azodicarbonamide, atmospheric oxygen, dinitrogen tetroxide) break up coloured molecules (and colourless ones), while reducing bleaches turn double bonds into single bonds, changing the frequencies of light absorbed. (See also chlorination.)
As to the effects on the main consitutents of flour, bleaching tends to reduce levels of gluten and other proteins[5][6][7]; however the precise effect depends on the type of bleach (air bleaching seems to be better than some chemicals). Bleaching may also reduce Vitamin E levels[8] though flour is often enriched with vitamins to counter this. --Colapeninsula (talk) 16:02, 1 February 2012 (UTC)[reply]
And note that, in general, "bleaching" is a rather vague term, and can mean any process that lightens the color, such as "sun bleaching". StuRat (talk) 18:14, 1 February 2012 (UTC)[reply]
Also note that bleaching flour sold for human consumption is actually illegal in a lot of countries nowadays. You geolocate to the US, so I imagine it varies by state. Bleaching flour does change how it behaves when used in baking, but just leaving the flour alone for a few weeks has much the same effect. 86.166.41.126 (talk) 22:27, 2 February 2012 (UTC)[reply]
How fast is iron metabolised into haemoglobin?
Due to ferropenic anemia, my doctor injected me with 500 mg of iron half an hour ago. Just out of curiosity, how long will it take for all this iron to be metabolised into haemoglobin? And how many grams of haemoglobin will my body produce with it? Thanks. Leptictidium (mt) 16:05, 1 February 2012 (UTC)[reply]
Every person is different, and since this deals with a treatment you have received, you should contact your doctor for information. --Jayron3218:10, 1 February 2012 (UTC)[reply]
This paper suggests a biological absorption half-life for iron in the blood of about half an hour - every half an hour, the body will metabolise 50% of the iron left - but that's based on an oral dose, not an intravenous one (which will start much faster) and like Jayron32 says, it'll vary from person to person, so if you're asking out of anything other than idle curiousity, ask the doctor. According to the paper, 500 mg of blood iron corresponds to 15 g of haemoglobin, assuming that all of it is converted.Smurrayinchester19:27, 1 February 2012 (UTC)[reply]
If *all* of the iron is incorporated in hemoglobin (which it isn't), it would correspond to about 143 g of hemoglobin (MW of hemoglobin tetramer = 64000, atomic weight of iron = 55.845, four atoms of iron in a hemoglobin molecule),
Note that a largish dose of iron will be absorbed largely to ferritin storage, at least in the short term. [9] says that radiolabelled iron is 90% incorporated into hemoglobin in about a week's time. But the kinetics might well be quite different if someone is deficient of iron to start with, and/or if a large dose is taken at once. One brand name of 500 mg iron sucrose injection is Venofer, which provides some data [10]; if you know the exact product you received you might likewise find interesting information online about it. (I wouldn't assume all formulations work the same way for sure) The easiest thing to answer is the hemoglobin weight per iron atom; per these articles Hb (human, presumably intact with heme present, not sure about glycation, bound CO2 etc.) has molecular weight 64458 g/mol, whereas iron is 55.842 g/atom, so take 500 mg * (64458/(4*55.842)) = 144.29 grams of hemoglobin. (While doing this I accidentally discovered Google's calculator function takes units. Now I should see what happens with ergs and statcoulombs...) Wnt (talk) 21:43, 1 February 2012 (UTC)[reply]
The 15 g figure given by Smurrayinchester is too small by a factor of 10. In someone not suffering from hemochromatosis, more than half of the body's iron is contained in the hemoglobin of the blood. If only 10% of the injected iron is incorporated into hemoglobin (as the 15 g figure would suggest), where does the rest go? It is not excreted in the urine - the iron content of urine is low [11], as the kidneys actively retain iron. The paper linked to above contains the following statement "Iron is present in blood in two forms (1) as hemoglobin, in red blood cells; 1.5 g of hemoglobin per 100 mL blood corresponds to 50 mg of iron ...", which appears to be the source of the 15 g figure above. Well, the quoted sentence contains a typo, 100 ml of blood contains approximately 15, not 1.5, grams of hemoglobin. It is correct, however, that 100 ml of blood contains approximately 50 mg of iron, corresponding to 250 mg in a blood unit (derived from 0.5 litres of donor blood), see [12], corresponding to approximately an iron content of about 0.5 g/L of whole blood. And the hemoglobin content of whole blood is approximately 145 g/L, which further confirms my (and Wnt's) calculation. --NorwegianBluetalk22:38, 1 February 2012 (UTC)[reply]
Ah, thanks for that. I was going to work it out with atomic masses, but assumed (wrongly, as it turns out) that it would have been quicker to just use the figures quoted in the paper. Smurrayinchester23:34, 1 February 2012 (UTC)[reply]
Pre-Einstein relativity
Before Einstein, how were the Lorentz equations arrived at? Were they guessed at in an attempt to reconcile Maxwell's equations with the failure to detect an ether? Or could they have been derived *from* Maxwell's equations.
For example, length contraction of a metal bar in motion can be explained by looking at the electrical forces in the metal and seeing how they transform when the bar goes into motion. But does Maxwell's equations include everything you need to show that the forces transform "in the right way", or do other assumptions need to be introduced. 74.15.137.145 (talk) 23:34, 1 February 2012 (UTC)[reply]
We have a rather long article on History of Lorentz transformations, and one on the Lorentz ether theory, which is what Lorentz was getting at with them. Shorthand version is that Lorentz comes up with this after Michelson-Morley, decides that an ether+length contraction makes philosophical sense and mathematical sense, and jibes fine with observation. That doesn't quite answer every bit of your question; if nobody has come along with a better answer by tomorrow I'll try to remember to check Helge Kragh's Quantum Generations and see what he says on this; it's a great resource for just-technical-enough discussions about the history of physics. --Mr.98 (talk) 23:51, 1 February 2012 (UTC)[reply]
Maxwell's equations could motivate the Lorentz transform, but they can't account for all of special relativity, because they don't include any statement about mass, inertia, or momentum. Looie496 (talk) 00:53, 2 February 2012 (UTC)[reply]
I've been curious about this one for a while myself. The best thing I can find on google is this forum thread, which seems reasonably useful, but of course is not a reliable source. Nakurusil's post there sounds credible, and he says that Lorentz fiddled with the transforms in order to make Maxwell's equations invariant. As far as I understand it, the upshot was that the Michelson-Morley null result now made sense. So that would make it a yes, to deriving from Maxwell's equations, with the property of invariance added. It is still considered ad hoc, mind you. IBE (talk) 16:41, 2 February 2012 (UTC)[reply]
Copper doorknobs
EPA, Environmental Protecting Agency, Washington DC has declared tat copper and its alloys are germicidal against bacteries, fungi,trichomonades and even against viruses.
Proposal: To reduce the contamination with pathologic germs and subsequent infections e.g. in hospitals the application of e.g doorknops of alloys containing more than 60% of copper is recommended.The germicidal properties of copper and other metalls like Zinc and silver are well known in history of mankind.
Our evaluation shows that probably the cupric ion is the active agent. We could find no description how the metallic ions interfere with the metabolism of the respective germ.
Also it is extremely important to find the way e.g. copper interferes with the energy production in the respiratory chain of the mitochondrium in the sperm which are immobilized in the presence of copper. — Preceding unsigned comment added by 93.203.60.179 (talk) 23:48, 1 February 2012 (UTC)[reply]
The use of brass fittings for their antimicrobial properties has been previously proposed and apparently recently subjected to considerable testing, with what sounds like a good amount of success. See Brass#Germicidal_and_antimicrobial_applications. You may rest easily knowing that folks have been looking into this for a few years now. --Mr.98 (talk) 23:55, 1 February 2012 (UTC)[reply]
However, in order to keep the doorknob from turning itself and any hand that touches it green, aren't they normally coated with clear lacquer, making the copper biologically unavailable ? (On the other hand, perhaps green gunk on your hand might make you wash it, thus sanitizing the hands the proper way. Perhaps doorknobs should be made of graphite. :-) ) StuRat (talk) 01:09, 2 February 2012 (UTC)[reply]
Any doorknob or lever that is used much is polished by contact and protected from extensive oxidation by hand oils. A green patina is actually fairly hard to transfer by casual contact. Factory-polished hardware is frequently protected by a lacquer to keep its shine, so it would lose any antimicrobial action. Acroterion(talk)04:44, 2 February 2012 (UTC)[reply]
... but it would regain it's microbial properties on areas under constant use where it would quickly lose its lacquer. Dbfirs07:54, 2 February 2012 (UTC)[reply]
I don't think brass buttons or silverware have killed many people, though allergies and bizarre genetic syndromes do make it occasionally conceivable. I think that brass doorknobs are a pretty standard decor. Wnt (talk) 19:53, 2 February 2012 (UTC)[reply]
Mustn't space be quantized for scale to make any sense?
If space is not quantized, i.e. there is no smallest volume or length, then isn't any arbitrary object (or length) infinitely large? Could scale even make sense? Everything would be infinitely large if a given volume of space could be infinitely small and we would have to allow for the possibility of entire other universes tinier than a plank length. --TimL (talk) 23:52, 1 February 2012 (UTC)[reply]
if there is no smallest length, then I am infinitely large. In fact any object is infinitely large since you can make a ruler of any arbitrary size with an infinite number of divisions, that has no finite length, because the divisions on the ruler can be made arbitrarily small. Anything could be said to be infinitely large no matter how tiny. It's a matter of scale. How does scale make sense if one cannot define a limit on how small something can be? --TimL (talk) 01:44, 2 February 2012 (UTC)[reply]
Your suggestion reminds me of Zeno's paradox. And what's the problem with universes smaller than a plank length? Certainly, it would have to either exist in some exotic environment, or be made of some exotic type of particles, as the laws of physics would not allow such a thing to exist with known particles (although such universes have been suggested by theoretical physicists to exist inside singularities). But what's the problem with it? There is no requirement that the consequences of physical law be intuitive. Someguy1221 (talk) 01:21, 2 February 2012 (UTC)[reply]
Well I guess if space is not quantized there could be an infinite number of universes in, say, one billionth of a plank volume. I guess I'll just have to deal with that possibility. --TimL (talk) 01:44, 2 February 2012 (UTC)[reply]
Thanks. Thought I had read all the articles on Planck units, but never found that one. Very interesting! (Incidentally it was Greene's program that led me to think of this "problem".) --TimL (talk) 02:05, 2 February 2012 (UTC)[reply]
That stuff about "sub-Planck physics" is not generally accepted physics, it's just random speculation by Brian Greene, almost certainly wrong. -- BenRG (talk) 07:11, 2 February 2012 (UTC)[reply]
I find your comment confusing; however, it might be relevant to consider that atoms have a characteristic size and nearly everything we know about is made of atoms. We can't shrink physical things by arbitrary amounts because we can't shrink the atoms, rather you would have to build the same object with fewer atoms and eventually that will become impossible if you go small enough. So materials of the kind that we have around us in everyday life can't be made arbitrarily small. Dragons flight (talk) 02:17, 2 February 2012 (UTC)[reply]
The appearance of scale in quantum field theory is a topic of serious study among particle physicists; it's called the breaking of conformal invariance. Conformal symmetry includes scale invariance as well as a lot of other transformations. I don't know much about this except that having particles with mass in a theory breaks conformal symmetry and establishes a length scale. Particle mass is a coupling between fields of opposite handedness. One way of looking at it, which is not too inaccurate, is that the left-handed particle turns into the right-handed particle and vice versa at a rate proportional to the strength of the coupling, and when the handedness changes, the particle reverses direction, so instead of moving in one direction at the speed of light, a particle with mass follows a zigzag path, with an overall (averaged) speed slower than light. The zigzag path has a width, and the more frequent the changes of direction, the narrower it is. So higher masses are associated with smaller distances. The characteristic size of atoms is determined by the mass of the electron and the strength of the electromagnetic force. (See this old thread.) -- BenRG (talk) 07:11, 2 February 2012 (UTC)[reply]
What I take the original question to be getting at is that if object positions in the universe are completely non-quantized, then the position of anything is a real number of infinite precision, and thus a hypothetical computer system running it would need an infinite amount of memory. (Yes, objects are all fuzzy, but the dead center of the fuzz still has a precise position) But I don't think anyone truly has a good explanation of exactly why a numeric value of this sort takes on physical reality, or whether there is a computer running the world or some more capable instrument. Wnt (talk) 07:32, 2 February 2012 (UTC)[reply]
Going back to the original question - "Mustn't space be quantized for scale to make any sense"? The answer may well be 'yes', but only if you assume that 'making sense' is necessarily a characteristic one might reasonably expect from a universe. Given the limited sample I've had the chance to look at in any detail (one), I'd have to say that this is somewhat presumptuous... AndyTheGrump (talk) 08:04, 2 February 2012 (UTC)[reply]
Agreed. In addition to measure theory, I think the OP's ideas are touching upon the Banach-Tarski paradox. Paraphrased heavily, it states that you can take a ball (made up of points represented by real numbers, which are 'not' quantized), cut it up into pieces, glue them together, and end up with two balls with the same radius as the original, or a ball with e.g. 10 times the radius of the original. SemanticMantis (talk) 14:58, 2 February 2012 (UTC)[reply]
That paradox seems like it's cheating to me. In Banach-Tarski_paradox#Step_1 the idea is that by "concatenating" (even "multiplying") strings, you turn one segment into three. Yet this is not regarded as a stretch in the same way that simply multiplying real numbers by three would be? Why not? Wnt (talk) 16:55, 2 February 2012 (UTC)[reply]
You appear to be balking at the definition of the free group on two generators. The proof in the article starts with a 'paradoxical' decomposition of this group, but the paradox does not become apparent until you've moved through the isomorphic group of rotations, and thence to the decomposition of the unit sphere. If there's any 'cheating' going on, it's probably in the axiom of choice :) The fact that we get to a group of rotations means there's no stretching going on. As to your "why not?" question specifically: the simplest answer is that the free group on two generators is not the field of real numbers. In fact, in many groups, 'multiplication' of group elements is identified with a size-preserving isometry, such as rotation. Hope that helps. But really, If you want to question/discuss this paradox, it's probably better to start a new question. SemanticMantis (talk) 18:13, 2 February 2012 (UTC)[reply]
February 2
I'm baffled!
What's the difference between a baffled and an unbaffled flask? And why would someone be motivated to use one over the other? Only after typing that did I see how much that sounds like a homework question. I'm reading a protocol and it calls for the use of baffling in one part, and to avoid it in another. But I don't know what the damn flask is, or why the writer cares. Someguy1221 (talk) 05:04, 2 February 2012 (UTC)[reply]
See the third item here, which was the first entry found on a Google search of "baffled flask". Our article Laboratory flask describes them as a "culture flask", with an explanation of their purpose, and they also seem to be called a Fernbach flask. Long story short, when you swirl liquid around in a baffled flask (which has baffles on the inside) the liquid is aerated more than would occur in an unbaffled flask. {The poster formerly known as 87.81.230.195} 90.193.78.57 (talk) 05:22, 2 February 2012 (UTC)[reply]
hi, what happens to a plastic biliary stent after the stent's expiry date, say 8 months after placing it in a patient? Will that be removed or it gets degraded by itself? — Preceding unsigned comment added by 199.224.149.10 (talk) 05:11, 2 February 2012 (UTC)[reply]
I'll assume this is a serious question. You need to ask yourself to what does the term expiry refer. To the stent or to the integrity of the sterile packaging it is in before insertion. Richard Avery (talk) 08:27, 2 February 2012 (UTC)[reply]
To the stent after insertion. Plastic stents are for temporary purpuse unlike metallic ones. So, I wanted to know what happens to it after the purpose served or after maximum duration a plastic stent serves. Should that be removed surgically from the patient or will the stent be degraded? — Preceding unsigned comment added by 199.224.149.10 (talk) 11:24, 2 February 2012 (UTC)[reply]
This site [13] suggests that biodegradable stents were being developed as of 2002, but were still pretty experimental. Also [14] from 2006, [15] from 2011. It looks like they're often poly-L-lactate. There are more refs out there. I didn't see any indication patients are actually getting these yet, but I may well not have looked hard enough. Wnt (talk) 19:33, 2 February 2012 (UTC)[reply]
What a fascinating subject. Here is a relevant site which talks about the likelihood of clogging of 'plastic' stents and the need to remove them within 8 months. There is also a more delicate issue about their use in patients who may have limited life expectancy and 8 months may not be achieved. Richard Avery (talk) 19:44, 2 February 2012 (UTC)[reply]
This anonymous editor is being pointy but is making a good point: [16]. I've repositioned my tinfoil, as 1000 km is way too low for a perigee and I have stuff in the basement. Presumably this is height above the mean surface of the Earth, so let's go look at the underlying article on the ISO. There, the infobox definitely says the "orbital height" perigee is 1000 km - but if I put "orbital height" into the internal search engine, I get nuthin'. Am I reading this all wrong, or do we have a potentially big problem? This is a concrete example of confusion (or incomplete definition of terms) between orbital distance and height, but I don't know how to fix it without an article to wikilink for the term used. And more widely, how many Earth-orbit figures have been mixed up between centric and surface distances? Thanks! Franamax (talk) 05:47, 2 February 2012 (UTC)[reply]
Oh, so the problem is just a little worse than my nightmare scenario? This would be a good opportunity for the more space-minded of the SciDesk regulars to get one of those rarely used {RD collaboration} thingies for improving articles, or just throw up some more sources so I can try to figure this out. It looks like an embedded problem, how many other NASA-sourced figures use the same assumptions? Franamax (talk) 08:41, 2 February 2012 (UTC)[reply]
This woke me up with a start last night. Given a universe in which time is a dimension, what would happen if for some reason that dimension disappeared, and there were still humans around to experience it? --TammyMoet (talk) 10:53, 2 February 2012 (UTC)[reply]
It's not really clear what you mean by time "disappearing". Nevertheless, time is a vital part of the way the human brain works - when we think, our brain is effectively bouncing from one energy state to another according to the laws of physics and the structure of the brain as chemical and electrical signals bounce through the brain cells (much the same way a computer works by sending electrons through a series of transistors). Without time, our brains wouldn't be able to think or perceive anything, and so we wouldn't be able to experience a universe without time in any way that we currently think of as experience, so the question's kind of moot. If you want fictional explorations of the idea, Kurt Vonnegut's books Slaughterhouse Five and Timequake (and to a lesser extent The Sirens of Titan) are about how humans might experience various oddities in the flow of time (S5 is about a man who becomes "unstuck in time", TQ is about people being forced to relive a decade, SoT features a character who flies his spaceship into a point of space where all times and places co-exist), and they're all good reads*, but they're not scientifically accurate unless you suppose our thoughts and memories are controlled by an external soul instead of the brain. * Lets not get into a debate about the literary value of Timequake. Smurrayinchester11:08, 2 February 2012 (UTC)[reply]
You are completely wrong in your suggestion of this work, Von Restorff. Flatland is not about dimensions. It is about social classes. It's just a boring book with mere historical value. 88.14.194.205 (talk) 14:45, 2 February 2012 (UTC)[reply]
Lol. It is also about social classes, but also about dimensions. Did you read it? I wouldn't describe it as boring, but I do not know what kind of books you like. Most of the related works have little to do with social classes btw. Von Restorff (talk) 00:24, 3 February 2012 (UTC)[reply]
(I'm 88.14). I didn't say anything about the related books, which appear to be much better. And no, Flatland is no good work for someone trying to understand something about dimensions. Flatland is so much about dimensions as Terminator is about time travel. Neither has made any contribution to the topic or have anything to say about the physical side of it. Both have a different leitmotiv. WKB52 (talk) 13:29, 3 February 2012 (UTC)[reply]
Exactly, that is what I mean, we've basically redefined the word dimension and added a new meaning to it when people came up with the idea of a temporal dimension, but time is not a dimension like the others, we just use the same word for something completely different because time is closely related to the spatial dimensions. I wish I could explain this better Von Restorff (talk) 13:22, 2 February 2012 (UTC)[reply]
Nay, check out the special theory of relativity. Two events separated widely in space can appear to occur in a different order depending on your motion in the "physical" dimensions. An object falling into a black hole has the singularity in its future, which is close to what the OP has in mind. But the thing is, our theory of time is generally continuous and well-behaved - when it comes to an end like that, who knows what really happens? Wnt (talk) 19:48, 2 February 2012 (UTC)[reply]
Time is not at all "something completely different" from space. "Space" and "time" are inextricably connected. Which direction in spacetime you consider to be the "time" direction is an arbitrary choice, except that the choice of forward-in-time direction from an event has to lie somewhere strictly interior to the event's future light cone. That's very much like how what direction in a Euclidean space you consider to be the "z" dimension is an arbitrary choice, except that the choice of "time" direction is a little more restricted. Similarly, 3-dimensional Euclidean space does not physically exist, except as a submanifold of (4-dimensional) spacetime. What 3-dimensional submanifold of spacetime counts as "space" depends entirely on that arbitrary choice of how you choose to define "time". Red Act (talk) 07:09, 3 February 2012 (UTC)[reply]
The first thing I thought of was Flatland too, or rather its interpretations by Martin Gardner. His The Colossal Book of Mathematics (Ch. 12 The Church of the Fourth Dimension) touches briefly on multi-dimensionality but I'm sure I've seen either he or Hofstadter go on at greater length, so a collection of the Mathematical Games columns from Scientific American might have more. And as it turns out, the book I cite has Ch. 40. Does Time Ever Stop?. :) In that, Gardner mentions several fictional works and discusses an academic paper on the topic: S.S. Shoemaker (1969). "Time Without Change". 66: 363–381. {{cite journal}}: Cite journal requires |journal= (help). If you really want to stay awake at night though, consider this: as the universe expands, it cools and we suspect it has undergone several phase changes. From the Big Bang forward, the quark soup "condensed" into elementary particles, which later condensed into atoms, which cooled down enough to form molecules. So what happens if we cross another "freezing point" and molecules start condensing into something else? Franamax (talk) 19:16, 2 February 2012 (UTC)[reply]
I don't think that should worry me. Two hydrogen atoms in the solar plasma would live to settle down and get together; they just don't have the chance because everything happens so fast. Likewise someday our protons and electrons might decay and "neutrino nuggets" might start stably form, but it'd take a ridiculously long time, just as our time scale is ridiculously long compared to those early Big Bang eras. (And theirs, likewise, is probably ridiculously long compared to some era we can't even guess at) Wnt (talk) 19:45, 2 February 2012 (UTC)[reply]
Time doesn't exist, it's an unobservable fictitious parameter that can be entirely eliminated from the known fundamental equations of physics. Count Iblis (talk) 00:07, 5 February 2012 (UTC)[reply]
Over the last couple of months (since early December), I've noticed a very bright object in the western sky, visible for the first couple of hours after sunset. It appears to move slowly northwards, before disappearing (although I've never managed to track it completely).
I'm in south east England.
I assumed it was Venus, but I would have thought that would have moved to a different part of the sky by now. Any ideas? Rojomoke (talk) 15:55, 2 February 2012 (UTC)[reply]
Jupiter has also been up. It's nearly impossible to pinpoint what you've been seeing unless you can be more specific; even an approximate setting time would help narrow down the possible options. Nimur (talk) 16:15, 2 February 2012 (UTC)[reply]
Could be Vega or (less likely) Altair. Messing about in Stellarium suggests both have been in the west (from London) over this winter, visible from sunset, with Altair setting between 8 and 10 and Vega setting between 10 and midnight (though if you live in a hilly or built up area, they may appear to disappear much earlier). Vega is the 5th brightest star in the sky and 2nd brightest in the northern hemisphere, so it can really stand out, especially if light pollution drowns out the rest of its constellation (Lyra). Smurrayinchester16:51, 2 February 2012 (UTC)[reply]
Well, I'm in SW England, and right now there are two really bright 'stars' in the western sky. I think the most westerly is Venus and the other is Vega. Chris (talk) 19:20, 2 February 2012 (UTC)[reply]
Venus has been in the evening sky towards the setting Sun over the winter. Jupiter has been the brightest object in the rest of the sky, but it has been almost overhead and visible most of the night. So you probably saw Venus. --TammyMoet (talk) 20:42, 2 February 2012 (UTC)[reply]
If you have a smart phone you should check out Google Sky Map or similar software. It allows you to just point your phone at the sky and see what you're looking at. --Sean14:36, 3 February 2012 (UTC)[reply]
how does stylus work
Can anyone explain to me how a electronic stylus works? Will anything that is magnetic work as a stylus? Can I use a metal pen or a paperclip — Preceding unsigned comment added by 208.83.61.203 (talk) 16:21, 2 February 2012 (UTC)[reply]
It depends on the type of touchscreen#Technologies involved. Some only sense pressure, so it doesn't really matter what you use to press on them. Some involve some sort of a circuit that involves the person or instrument touching it. In some cases, a magnet may suffice for pressure and position-sensing, but also interfere with other electronics in the touch-screen. DMacks (talk) 21:17, 2 February 2012 (UTC)[reply]
strange temperature changes
Can anyone explain to me what the heck is going on with the weather? How come one day it's below zero and the next day it's 40°. I read this seesawing temperature changes is a signal that an Ice Age is approaching is this true?
History says you're User:208.83.61.203, geolocating to Philadelphia. I'm north of Philadelphia and I don't think it's gone under 12 F or so all winter. So you have to tell us more about where you are or we don't have a hope of answering you.
This story mentions that the cold weather from the continental U.S. and southern Canada is apparently shifted north to Alaska, or even over the pole to places like Odessa and Europe. I've noticed that it seems like there's some kind of inverse relationship between the two sides of the northern hemisphere, but haven't seen much about it. Looking at a map the U.S. by rights is level with southern Europe and you'd think it would be very mild indeed, and I always had trouble believing that one little Gulf Stream would be enough to change weather across Europe. Are there other jet-stream level mechanisms that can explain the difference between the continents, which might fail for some reason? Wnt (talk) 16:30, 2 February 2012 (UTC)[reply]
Human life span is short. A person born in to a period of wildly fluctuating temperatures may well have said in the past (and maybe in the future) – what the heck has happened to the weather all of a sudden – it hardly ever changes. Remember too, the dust bowls – it was good farming land when the settlers first arrived and then native Americans said – did we not tell you so?!!!--Aspro (talk) 16:46, 2 February 2012 (UTC)[reply]
Hmmm, cite for that? I ask because usually the Dust Bowl has been blamed on extensive farming of a type that - I might wrongly presume - the Native Americans wouldn't have managed with their smaller populations. But North America has been colder than Europe since the days of the "Pilgrims". Wnt (talk) 18:25, 2 February 2012 (UTC)[reply]
Dust Bowl discusses this, and both are right. The farming practices were terrible and ill suited to the environment, but there was also a prolonged period of wetter than average condition in the decades before the 1930s drought hit. Those wetter conditions gave settlers a false set of expectations about what to expect from life on the plains. When the drought finally did come, the false expectations compounded the problems created by poor land management and made an already severe situation into a catastrophe. Dragons flight (talk) 19:58, 2 February 2012 (UTC)[reply]
The main cause of the cold weather in Europe and above-average temperatures and below-average snowfall in North America is the positive phase of the North Atlantic Oscillation. La Nina is also contributing to warm temperatures across the United States. Last year, we had an arctic dipole anomaly for the second winter in a row, in a combination of a negative NAO and a negative AO. ~AH1(discuss!)01:49, 5 February 2012 (UTC)[reply]
The middle to bottom-right is obviously fake (to my eyes). Someone suggested this is camera blur, but on the left and top, the individual coins are clear and not blurred. It looks like some or all of this picture is photoshopped. What do you think?
For further evidence: I consider this comparison photo unshopped (http://i.imgur.com/KGd5R.jpg). You can count the number of coins in it quickly, without any "fractional" coins or weird ones. Now count the number of coins in the one I call a shop. You can't, because there's all sorts of cruft, coins splitting and melding, etc. It's totally unclear in the section I'm talking about, while being perfectly clear in the top-left, and there is no camera-jerk "blurring" right of the stack of coins. It just seems obviously photoshopped to me. 78.92.81.13 (talk) 16:36, 2 February 2012 (UTC)[reply]
I just don't see it. The "cruft" you mention to me looks like just a tiny jiggle in the camera. I don't see any similarities in the patterns of the coin stacks. And just in terms of credulity, this photo is a very simple spiral even I could make given enough time and money, whereas that other thing is, well, a masterpiece of some sort or other. Sometimes shopped .jpg images can be spotted with error level analysis, but the site everybody linked to for that[17] is "temporarily shut down for a move", which is Internetese for dead beyond all possibility of resuscitation. Wnt (talk) 16:43, 2 February 2012 (UTC)[reply]
"Error level analysis" is pretty much pure pseudo-science. BenRG posted a pretty good debunking last April; I vaguely recall User:SteveBaker similarly debunking it. I'd offer up my own debunking of the error-level analysis technique too, if I believed it had any bunk to begin with - but it doesn't, so I won't.
Determining whether a photograph has been "forged" requires a very very careful definition of what "forgery" means. Image processing experts armed with powerful analysis tools can tell you whether an image is bit-identical to another; and they can often spot image artifacts that appear to be the result of amateurish use of common image-processing tools; but unless there's an authoritative reference for comparison, it's provably impossible to determine whether a pixel in a rendered JPEG file is "digitally altered," or if it's actually what the camera image-sensor recorded. The individual pixels contain no additional information, other than their color value.
As I said, the problem devolves into a matter of definition of "forgery." Suppose somebody constructs an elaborate, photorealistic painting of a scene, and then digitally photographs the painting. The painting may contain any image characteristics I wanted to paint on it - any possible combination of pixels. The camera may perfectly capture the photo, but the scene is "phony." Statistical analysis of the image will show whatever, but without knowing how those statistics compare to the actual scene, they're useless for analysis - no matter how improbable any metric may be in a "normal" scene. Is that a "forged" digital image? Nimur (talk) 18:01, 2 February 2012 (UTC)[reply]
Why can I clearly count and delineate with my eye each coin in the background (not foreground); each coin at the left of the image; each coin in the comparison (up-down arrow) image (up-close). But when you zoom in real close on the center, you suddenly see that you an individual coin photorealistically (no blurring) splits apart, or is photorealistically (no blur) cut as though it were an impartial, shattered coin, and photorealistically see coins that bend up and over one above them, as though they were bent out of shape just to go to the trouble of occluding something they wouldn't if they were straight? All of these effects are photorealistic: they are not blur. There is no blur that makes the coins difficult to discern or dilineate elsewhere in the image; nor is there any blur outside the stack of coins: the whole image is photorealistic. I'm asking you to click up close, magnify and zoom in, and then explain the photorealistic (non-blurred) effects you see. 78.92.81.13 (talk) 17:03, 2 February 2012 (UTC)[reply]
The only splitting I see is that the camera was pretty clearly jiggled up/down during the exposure. That's why there are double highlights and why the grooves in the edges of the coins are so much sharper than everything else (because they run up/down and superimposed on themselves) Is that what you mean or something else? Wnt (talk) 18:21, 2 February 2012 (UTC)[reply]
Carbon 14 half life
I understand that carbon 14's half life is approximately 5730 years. Are there any conditions that affect the amount of carbon 14 in a fossil; i.e. heat, pressure etc? Thus, affecting accurate dating. What are the presumptions, if any, that affect carbon 14 dating. If carbon 14 decays to nitrogen in approximately 5730 years; how can anything that contains carbon 14 be older than 5730 years?
209.243.5.164 (talk) 16:34, 2 February 2012 (UTC)[reply]
Half-life means the time it takes for half of it to decay, not all of it. If there were 1,000 atoms of C-14 in the organic matter when it died, there will be about 500 after 5,730 years, then 250 atoms after 11,460 years, 125 atoms after 17,190 years, etc.. It would take a very long time before all the C-14 was gone. Nothing is going to affect the rate at which C-14 decays. The main problem with carbon dating is contamination with more recent organic matter. The main assumption behind carbon dating is what the proportion of C-14 in the environment was at the time the organism died was. The C-14 levels were pretty constant until we started doing nuclear testing, but you need to be very careful with using any kind of radioactive dating on things after nuclear testing started. --Tango (talk) 16:51, 2 February 2012 (UTC)[reply]
After you get down to two carbon 14 atoms, and 5730 years later you then have one lonely carbon 14 atom and immediately start the stopwatch, how long until that one turns? 5730 years? But then 100% would have gone in that period. 20.137.18.53 (talk) 18:29, 2 February 2012 (UTC)[reply]
Half life (especially when dealing with quantum things like radioactive decay) is a statistical property. It's more accurately stated as "the time after which there is a 50% probability that any given nucleus would decay". According to the law of large numbers that's equivalent to "the time it take for half of it to decay" when you have a large number of atoms. However, that breaks down when you have a small number of atoms. So for a single atom, flip a coin - if it comes up heads, the atom will still be around in 5,730 years. Flip it again: 11,460 years, etc. Even for something like 10 atoms of C-14, you can't say that there will be exactly 5 of them in 5,730 years - you would effectively flip 10 coins, and might get 5 atoms, but may get 6, or 8 or even (with small probability) all 10 decaying over the 5,730 years. -- 140.142.20.101 (talk) 18:56, 2 February 2012 (UTC)[reply]
(edit conflict)You can't know how long it will take any individual atom to turn. It's a probabilistic process. Imagine that every day you roll a six-sided die. You have a 1/6 chance of getting a 6 each day. Maybe you'll get one the first day, but probably not. Maybe you'll go two weeks without getting even one six. On average you'd expect to have rolled a six on or before the sixth day, but there are no guarantees. Radioactive decay is like that. Imagine that every atom has its own little die, and each day it rolls it to determine whether it will decay. Except in stead of having 6 sides, this die has 2 million sides. So there is only a 1 in 2 million chance that the atom will decay on any given day. You'd expect that the typical carbon-14 atom will have rolled the magic number that causes it to decay after 2 million days have passed (5730 years to be precise), but some will take longer, and some will decay right away. Because it is probabilistic we can predict how the population will change in aggregate but you can't make any such predictions for individual atoms. Dragons flight (talk) 19:08, 2 February 2012 (UTC)[reply]
As we currently understand it, the half life of spontaneous fission of a radionuclide is the same everywhere in the universe, regardless of external stimuli like heat or pressure. A 2008 edition of Science News contained a story where someone suggested that there might be small changes in half life when in the proximity of a sun (it's subscription only, unfortunately). I mention this only for nebbish completeness - even if this is the case, it might affect the long-term power output of space probes, but the effect will be much too small to have any bearing on radiocarbon dating. -- Finlay McWalterჷTalk18:19, 2 February 2012 (UTC)[reply]
Just in case we've missed it, the key concept to keep in mind here is that atoms, like flipped coins, don't have a memory. An atom of C-14 doesn't know when it was born, doesn't know if it's been 5000 or 50000 years. If you go for a half-life, half the atoms are gone, but the other half don't know they're the other half. To their perspective they're a brand spanking new sample of C-14 and they've got their whole half-life ahead of them, at the end of which half will be gone - i.e. only half of the first half will be left, which is 1/4. And so on. Now 1/2, 1/4, 1/8, 1/16, 1/32, 1/64 ... the sequence does grow fast. So if you go out ten, twenty, thirty half-lives the number of remaining lucky atoms gets very very small indeed, too small to measure. Our article says 60,000 years, i.e. about ten half-lives = 1/1024 of the original sample, is the practical limit. Wnt (talk) 19:37, 3 February 2012 (UTC)[reply]
Well, let's start by redlinking ethene-1,2-disulfonic acid, which subtly helps to indicate demand. Normally you'd go to WP:RA to request the article next, but maybe we can move things along... Next I go to PubChem and see what turns up. Term not found, curses. Tried PubMed for the heck of it... nada. Alright, now I'm thinking there's a more common name so I just plain Google it. Top hit is in Wikipedia - for ethanedisulfonic acid, a.k.a. ethane-1,2-disulfonic acid. At this point, I have to actually think for a moment. I've put the graphic up at the beginning of the section - we see there are two and only two carbons; each has a sulfonate and a bond to one other carbon so they have two hydrogens also. We could have one hydrogen and one double bond between the carbons. So the compound you suggest is reasonably possible, though I don't know how stable it is - what's clear though is that with only two carbons we don't need the 1,2. Which means back we go to Google, and voila, there are results. [18] One of them looks like exactly what we want (ChemSpider, forgot them the first time!): [19] But it doesn't have much data - it links an inside front cover and thousands and thousands of patents, and I doubt any of that is real. Tried PubChem again and nothing.[20] Nothing from PubMed: [21] Google Scholar turns up one hit, to a patent, [22] but this is as a long list of groups claimed including methanedisulfonic but excluding ethanedisulfonic. Oops, somebody filed a patent with a hole in it - if it wasn't from 1981 this might be worth something. ;) Now despite much discouragement, I try Google Books, and voila! 131 hits for ethenedisulfonic! [23] A lot of these are derivatives but right off the top I find [24] "Ethenesulfonic acid polymerizes in aqueous solution (32-3*0, under the influence of hydrogen peroxide, potassium persulfate, or ultraviolet light." But it's all locked up under copyright and you'd have to interlibrary loan it (at best) to get at the gooey center. Certainly an ethene polymerizing is not the most shocking idea I've heard, though. [25] says, "Preparation Salts of ethenesulfonic, also known as ethylenesulfonic or vinylsulfonic acid," and oh lord here we go again. PubMed: 12 and 35 hits and 12 more for "vinyl sulfonic acid" [26]. PubChem 3 hits and 18 hits and 2 hits but alas none sulfonic at both 1 and 2. The PubMed results may well be similar. So alas, I've fallen into the "Where did Google want me to go today?" trap and hit on their "synonym" of ethenesulfonic for ethenedisulfonic, likewise all the rest. (Should have looked at the chemical formula in the first book hit and I would have realized) But in the process I've thought of a term "ethylenedisulfonic" which works in Google for a bunch of hits. [27] But that, alas alas, gets me back to ethanedisulfonic hits again. This ambiguity matches that for ethylene chloride - there could be good hits in that Google mass somewhere, or not.
So far I really have is one ChemSpider hit, which for all I know is about an entirely hypothetical compound. Now the one thing I haven't done is to search Chemical Abstracts, or Beilstein for that matter, which might give some more useful direction, because unfortunately we have not made the same strides to liberate chemistry as we have with biology. Wnt (talk) 18:11, 2 February 2012 (UTC)[reply]
For future reference, you can put single quotes around a word to stop Google using synonyms. See here for details and other similar tricks. (Oddly, I thought it was a + sign you were meant to use... I guess that explains why that never seemed to work properly!) --Tango (talk) 18:22, 2 February 2012 (UTC)[reply]
This is very interesting and has produced a number of useful connections. Thanks! Your finding the reference [29] that says, "Preparation Salts of ethenesulfonic, also known as ethylenesulfonic or vinylsulfonic acid," was very good, because I am looking for a sulfonate analogue of maleic acid. I used the term, "ethene-1,2-disulfonic acid" because that's what comes directly out of ChemDraw; and it distinguishes what I am seeking from, say, ethene-1,1-disulfonic acid. Ethene-1,1-disulfonic acid is very likely unstable. Oh, and I am not looking for ethanedisulfonic acid (as mentioned above), which we already have an article about. User:Colgator4—Preceding undated comment added 20:22, 2 February 2012 (UTC).[reply]
I checked SciFinder (CAS) for the substructure S-CH=CH-S and none of the hits had any oxygen on the sulfur. The parent compound (dithiol) is known as are a bunch of salts and simple alkyl (including dialkylsulfonium on one of the sides). DMacks (talk) 20:37, 2 February 2012 (UTC)[reply]
Molecules
Few questions that I have been pondering.
1) Is there a limit to the number of different kinds molecules that can exist?
2) If there is a limit, do we know of all of the different kinds of molecules that exist in the universe?
3) Is it possible to engineer a molecule that doesn't normally form in the universe? ScienceApe (talk) 21:05, 2 February 2012 (UTC)[reply]
Since molecules can be arbitrarily large, it follows that the number of different molecules that can exist is a very, very large number, much as the number of possible spoken sentences that can exist is a very, very large number. Comet Tuttle (talk) 21:25, 2 February 2012 (UTC)[reply]
Lignin biosynthesis
Yes, but it is immensely large. Some molecules are immensely complicated - lignin is produced by small molecules with free radicals reacting with a much larger molecule. The process is completely random, so each molecule produced will be large and unique. There are probably many other possible reactions similar to the only thing limiting the number of different types of molecules, would be the amount of matter in the universe.
No and we may never know, since mass spectrometry can only detect small molecules.
I think that proteins are a great example for all these things. Using the genetic code you can make a pretty much arbitrary sequence. Sure, sometimes it'll misfold into inclusion bodies and be a general pain in the rear, but actually that doesn't even matter for your abstract question. Every three basepairs of DNA gives 20 different possible ways to extend the molecule, for more or less as long as you want - thousands of amino acids in a row. And the weirdest thing is sometimes it seems to take hundreds of amino acids to get a specific property you want. Wnt (talk) 00:04, 3 February 2012 (UTC)[reply]
Alcohol and steam from drain gates
In the movie Perfume: The Story of a Murderer, Dustin Hoffman's character warns the protagonist to be cautious when he hastily grabs a large container of pure alcohol and asks him if he wants to blow up the entire building.
Can alcohol explode?
My other question is why does steam comes from drain grates in cold mornings?
Nearly pure alcohol has a very low flash point, and fire marshals treat it as a very dangerous combustible liquid on account of its easily-ignitable vapor: so yes, it's far more dangerous than you might think. However, 190-proof alcohol is not widely found outside of distilling operations, pharmaceutical plants and perfume manufacturing plants. But explode? No, not really. It'll just make a really nasty fire if it's got an ignition source.
Steam that comes from drainage grates is water vapor from the relatively warm underground stream/drain that condenses when it hits the colder air above the surface. Acroterion(talk)21:27, 2 February 2012 (UTC)[reply]
Everclear (alcohol) is available in 190 proof, and is commonly used by amateur perfume makers. It is sometimes used in making "Rocket fuel" punch for parties, along with ginger ale, sherbet, and dry ice. When moviemakers wish to depict a street scene in a large old US city such as New York, they cause steam to come from the street grates. Now York has steam heating pipes under the streets. I once saw makers of a movie about New York use another US city as a substitute to save money, but they made sure to cause steam to come out of the street grates. Edison (talk) 00:59, 3 February 2012 (UTC)[reply]
I'd forgotten about Everclear. But it's not an explosive, except where your brain cells are concerned. And yes, in some cities with central steam heating plants like New York, Baltimore and others, you can get actual steam (or at least genuinely warm water vapor) from street vents; there are pressure relief valves down there. In New York you'll see chimneys set up to keep it from affecting visibility. Acroterion(talk)02:34, 3 February 2012 (UTC)[reply]
Note that while not explosive under normal conditions, alcohol can be made into an explosive by increasing it's surface area and possibly the oxygen percentage in the air. The surface area can be increased by spraying it in a fine aerosol, as is done in an internal combustion engine run on ethanol or methanol, or as could be done in an thermobaric weapon. Even something like wheat dust can be made into an explosive in this way. StuRat (talk) 18:59, 3 February 2012 (UTC)[reply]
There are probable a few unfortunate people sleeping in the gutters along the streets of large cities whose fondest dream would be getting "alcohol from drain grates. " Edison (talk) 20:17, 3 February 2012 (UTC)[reply]
Let say there is a star i have to identify it on the Hertzsprung–Russell diagram. How can i identify it base on its apparent magnitude (in other word its brightness)? Basically i need someone to explain for me how to use the diagram and how to interpret it. Ok i have an example problem, i already know the correct answers but i don't understand them. Where would Mira variable be locate on the Hertzsprung–Russell diagram? The answer is V. I was given the Mira variable's brightness. Pendragon5 (talk) 01:05, 3 February 2012 (UTC)[reply]
Yea that's what i don't really get. There are many things around the HR diagram to determine where the star should be on there but they only give me like 1 info. Let say they do give me the absolute magnitude then how do i do it? The answer was V so i would guess all they want is just a basic answer. This letter V would represent something on the HR diagram which i don't know.Pendragon5 (talk) 12:43, 3 February 2012 (UTC)[reply]
If you look at the big picture at the top of that article, you'll see that V refers to the main sequence (if that's the only answer they gave, then they must be asking you for just the general category of star, rather than anything more detailed). You'll also see that the different categories only overlap between about -3 and +5 in absolute magnitude (although dimmer than +10 could be a white dwarf, if you are counting those). If the absolute magnitude you are given is outside that range, then you can be pretty sure about which group it will fall into. If it's in that range, then you need more information (firstly, colour, but if it's blue-white you would need to know its size to distinguish between a giant, sub-giant or main sequence star). --Tango (talk) 13:12, 3 February 2012 (UTC)[reply]
That's the B-V colour. It is one of the measures of color that can be extracted under the UBV photometric system. To measure the B-V color, one photographs a star through a B (blue) filter, and again through a V (visible, actually a slightly yellowish green) filter. The B-V color is the difference in apparent magnitude when seen through the B and V filters. If the star's light output is more blue (smaller B magnitude) the B-V value will be smaller (or even negative) and the star will fall further to the left on the HR diagram. If the star is more red (less blue, and therefore greater B magnitude), B-V will be more positive and the star will sit further to the right on the HR diagram. TenOfAllTrades(talk) 22:01, 3 February 2012 (UTC)[reply]
Does decay heating and nuclear fission generate the same amount of energy in the end?
Suppose I have a certain amount of HEU and want to harvest the greatest amount of energy from it in the form of heat. There are two possible methods:
1. Decay heating over an infinitesimal amount of time.
2. Construct and detonate a fission bomb. (assuming all the uranium is consumed in the fission process and that the fissile products contain a negligible amount of untapped radioactivity energy)
Would the two methods generate the same amount of heat in the end? I'm guessing yes but I don't know enough about the subject matter to justify it.
And no, I'm not a terrorist. This is just a thought experiment to see whether it's feasible to use nuclear weapons to geologically reactivate Mars's core.99.245.35.136 (talk) 09:49, 3 February 2012 (UTC)[reply]
I think you'd have to explode something like a Hiroshima type bomb every ten minutes to equal the amount of heat generated in the Earth's core by fission. I think we'd have huge problems trying to do that even using fusion bombs never mind the problem of getting it near the centre. Plus I don't see the point. Dmcq (talk) 12:47, 3 February 2012 (UTC)[reply]
No, they wouldn't release the same energy because you won't end up with the same results. The decay products will, after a while, mostly end up as lead. The fissile products will be all sorts of things. Your problem is that the radioactivity of the fissile products isn't negligible to your calculation. If you include the decay heat from the fissile products, you should end up with approximately the same total energy because they will all decay into lead eventually as well. (It might not be exactly the same because there are different isotopes of lead they might decay into, and you may have to wait billions of years before they actually get to lead if they decay to something else stable first). The important thing is to compare what you have at the beginning with what you have at the end. If they are the same, then the energy released must be the same. However, I don't think your plan to heat up Mar's core would work - you would probably destroy most of the planet in the process, even if you could find enough fissile material to do it. --Tango (talk) 13:18, 3 February 2012 (UTC)[reply]
I wouldn't think it will be the same. From a thermodynamics point of view, a fission process would be irreversible adiabatic (nearly), while the decay process would probably be reversible isothermal (because it takes place quasi-statically). The reversible isothermal process would probably generate more energy. I have no background in Nuclear Physics, but only thermodynamics, so excuse any inconsistencies please. Lynch714:49, 3 February 2012 (UTC)[reply]
This should be pretty easy to quantify. The amount of energy released by an average U-235 fission is around 200 MeV. What's the energy released over the entire course of a U-235 decay chain? According to this chart, it's at most 46.4 MeV by the time it gets to lead. Comparing masses of them directly of course assumes 100% efficiency in the bomb. If my understanding is right, they would be equal if the bomb is only 23.2% efficient, and the decay would win out if the bomb was less efficient than that. The Little Boy bomb was around 1% efficient, the Fat Man bomb was about 17% efficient, but later bombs were much more efficient than either of those. (If I've made some sort of idiotic assumption or error, someone please correct me!) Again, this neglects fission products, which are pretty radioactive, and would tip the balance quite decisively in the direction of the bomb. --Mr.98 (talk) 19:14, 3 February 2012 (UTC)[reply]
Out of curiosity, I ran through one set of common fission products, strontium-94 and xenon-140. They give off a total of about 24 MeV from their respective decay chains. So that's over half of the total energy from the total U-235 decay chain by itself, without even including the fission yield. --Mr.98 (talk) 21:09, 4 February 2012 (UTC)[reply]
is any encryption other than OTP physically secure
I mean in a physical-universe sense (including quantum mechanics or anything else that could be discovered). I don't consider "hey it would take a while to compute with the best-known current algorithms on the best-known current physical non-quantum mechanical computers". --78.92.81.13 (talk) 13:19, 3 February 2012 (UTC)[reply]
It depends. What do you mean by secure? Many algorithms are secure enough for any practical purpose. But, you seem to be asking in a hypothetical sense if an encryption could be completely secure under any theoretical circumstance. WKB52 (talk) 13:36, 3 February 2012 (UTC)[reply]
A one-time pad is unique in that, properly executed, cryptanalysis is not only practically but theoretically impossible (I think this is what you mean by "physically secure"). Cryptographer Bruce Schneier is fond of noting, though, that modern cryptographic methods are plenty secure, both now and for the foreseeable future, and that other factors (that tricky "properly executed" clause above) are far more likely to cause cryptographic failure -- even (or particularly) in the case of OTP. — Lomn16:04, 3 February 2012 (UTC)[reply]
The security of a OTP shouldn't be exaggerated - you have to get those numbers from somewhere. For example, you might use a random number generator which is easily reverse engineered. Or you can use a service like HotBits,[30] which I assume has its entire output archived to some handy-dandy NSA decoding disk somewhere in transit. More to the point, that sticker on your computer that says "Intel inside" isn't really talking about the brand of chip they used... Wnt (talk) 17:27, 3 February 2012 (UTC)[reply]
Well, you could generate them from a physically random source (say, use diode noise to fill an entropy pool, and take out only as much entropy as you put in), and unless NSA has invented magic, it's hard to see how they could get at that. The difficulty, of course, is key exchange — somehow you have to get the same random values to both parties.
But if you know in advance with whom you want to exchange secure messages, this can certainly be done. Just fill up some DVDs with the random bits, and transfer the DVDs in such a way that they never leave the physical custody of trusted parties. It's a lot less convenient than public-key methods, but it can be done. --Trovatore (talk) 17:37, 3 February 2012 (UTC)[reply]
Are there actually any cases of people being able to crack modern, strong encryption schemes because of insufficient pseudorandomness? (I'm not counting cases like VENONA where they accidentally duplicated the same random number sheets more than once which was a lucky typo, not a case of the algorithm being wrong. I'm also not counting toy cases where people demonstrate how pseudorandomness can be misleading — I mean actual cases of intelligently designed systems with intelligently used pseudorandom or quasirandom number generators.) --Mr.98 (talk) 03:24, 4 February 2012 (UTC)[reply]
I don't think that's the question at issue. I think Wnt was assuming a one-time pad based on a PRNG, which as far as I know is not a commonly used encryption scheme, though in principle it should work given a sufficiently strong PRNG. The classical one-time pad is based on true randomness rather than a PRNG. --Trovatore (talk) 04:19, 4 February 2012 (UTC)[reply]
I think it's worth adding that, in addition to the randomness (or lack thereof) issue raised above, the one-time pad also needs to be "as large as or greater than the plaintext, never reused in whole or part, and kept secret" (to quote our article) in order to be as impervious to cryptanalysis as Lomn initially suggested. Jwrosenzweig (talk) 06:55, 4 February 2012 (UTC)[reply]
The hard part of cryptography is key management. Encrypting something with an OTP is like locking it in an uncrackable safe. But now what are you going to do with the key to the safe? Lock it in another safe? What are you going to do with the key to that safe? Keep in mind that the key is as large as the thing it's protecting. So the safe gains you very little—you're trading the security of one item for the security of another item of the same size. You can leave the key unlabeled and hope nobody figures out which safe it goes with—that's one kind of security through obscurity.
People talk above about using a pseudorandom number generator to make an OTP. That's impossible because it's part of the definition of an OTP that it uses truly random bits. Using pseudorandom bits in the manner of an OTP has a different name: a stream cipher. -- BenRG (talk) 19:48, 4 February 2012 (UTC)[reply]
Strictly speaking that might be true, but I think the meaning is clear to anyone who understands what a one-time pad is in the first place. --Trovatore (talk) 23:42, 4 February 2012 (UTC)[reply]
When you say "understands what a one-time pad is" you must mean "understands what it means to exclusive-or two bit streams together". Some explanations of OTP seem to spend almost all of their time on that minor detail. Since the output of a stream cipher is also exclusive-ored with the plaintext, someone with that "understanding" of OTP might have a head start on "understanding" stream ciphers too. What OTP is actually about, though, is having as many possible keys as possible plaintexts. -- BenRG (talk) 00:50, 5 February 2012 (UTC)[reply]
Oh, responding to your first paragraph: The key is the same size, but it doesn't need to be generated at the same time. You can exchange the key in advance (by exchanging physical artifacts such as DVDs), and then when the time comes that you know what secret message you want to send, you're good to go, and you can transmit the message faster at that time than you could get a DVD to the recipient. Obviously this isn't convenient enough for, say, online banking, but for certain applications it could be workable. --Trovatore (talk) 23:48, 4 February 2012 (UTC)[reply]
That's true, and OTPs have been used in that way by major governments (and they've screwed it up and their messages have been cracked). I think this is one of those if-you-have-to-ask things. Only in very specific circumstances is using an OTP a good idea, and people in those circumstances are not going to ask the likes of me for advice on the subject. So if someone does ask me, I can safely tell them they shouldn't do it. -- BenRG (talk) 00:50, 5 February 2012 (UTC)[reply]
about mechnical force
what is easy to pull a stationary thing or to push it? what takes less force to pull or to push a thing whereas the idle conditions are considered such as friction is same for both pulling and pushing? — Preceding unsigned comment added by 27.124.12.98 (talk) 13:37, 3 February 2012 (UTC)[reply]
With the standard assumptions of an idealized physics problem, pulling or pushing an object requires the same force. In the real-word however, consider an example such as an adult human moving a 1 m cube of wood. Pushing often introduces a downward component of force. This can increase friction, making the object harder to move. Likewise, pulling might be done using a rope, which could introduce an upward force, reducing the friction, and making the object easier to move. SemanticMantis (talk) 14:07, 3 February 2012 (UTC)[reply]
There's more, isn't there? For pushing, isn't the best location for a vantage point somewhere such that you can lean your own weight against the wood, say at such a distance away that your body forms a 45 degree angle with it? Whereas, for pulling, you can only lean away from the wood as far as your arms go (or put another way, the same 45 degree angle would put your feet INSIDE the block of wood, with you leaning outwards and pulling). If you have a piece of rope, you can lean as far away as you like... I would say for this reason in an ideal world it's far easier to push than to pull anything, except when there is a rope or the like attached of sufficient length for you to lean however you like, in which case it's roughly the same... 188.156.144.183 (talk) 15:47, 3 February 2012 (UTC)[reply]
And note that pushing is unstable, and the object will want to "fish tail", as in a rear-wheel drive car, while pulling is inherently stable. Pushing some objects without wheels or skis also doesn't work well, since they will want to dig into the ground at the front. StuRat (talk) 19:02, 3 February 2012 (UTC)[reply]
that's interesting (and same as the friction answer given earlier, isn't digging in just increasing friction :)). Do you think the push/pull distinction above is valid StuRat? 79.122.90.56 (talk) 21:01, 3 February 2012 (UTC)[reply]
"Digging in" can go beyond just increasing friction. The usual def of friction is that the only work it does is to create heat. But if the object plows into the ground, it may also do work moving dirt. Or, consider a case where you push or pull a brick along a sidewalk. At the seam between two slabs, the brick may dig in, and then any pushing force is trying to move the entire slab of sidewalk. Note that this all assumes that you push above the center of gravity. Pulling above the center of gravity will also tend to make the front edge dig in, but, since you likely need to attach a rope or chain to pull an object, you can just as easily attach it below the center of gravity. StuRat (talk) 21:09, 3 February 2012 (UTC)[reply]
In the case of pulling, much depends on the presence of a handle or other device to pull onto. Consider also the case of pulling vs. pushing up an inclined ramp. ~AH1(discuss!)01:40, 5 February 2012 (UTC)[reply]
[See Inverter (electrical)#Basic designs One way is by switching the DC back and forth so that it follows two different directions through the transformer primary. A distorted AC output is produced from the secondary of the transformer. The output can be at a different voltage from the input, depending on the turns ratio and frequency of the switching. In automobiles years ago, an electromechanical vibrator circuit did the switching, to produce high voltages via a transformer and then a rectifier to operate vacuum tube radios. In modern circuits used to step up DC to high DC voltages or to convert DC to AC, transistor switches or other solid state devices such as thyristors are used in place of the vibrator. Edison (talk) 14:53, 3 February 2012 (UTC)[reply]
Did Homo sapiens get their pale skin and red hair from Neanderthals?
Someone told me that sapiens got pale skin and red hair from interbreeding with neanderthals which already possessed these traits. I seem to recall in my Human Evolution class that neanderthals did indeed have these traits, but they were coded for by different genes so it was just an example of parallel evolution. Who is correct? ScienceApe (talk) 14:54, 3 February 2012 (UTC)[reply]
For context consider that just about any mammal has red-haired members with some mutation or other in MC1R. Making redheads, genetically, is no big deal. Wnt (talk) 17:21, 3 February 2012 (UTC)[reply]
Autofluorescence isn't very much for most things, and neither is photobleaching; in fact, as mentioned in that article, advanced glycation end-products produce much of the fluorescence - in other words, damage done by other means already. So it's part of the normal wear and tear, but not that much considering, and of course evolution will have tended to lead to the marking of any particularly susceptible proteins for rapid degradation and replacement. See ubiquitination, proteasome, autophagy, endosome, lysosome ... no doubt I'm forgetting lots of biggies. To survive and thrive, cells have to be almost as good at recycling and replacing proteins as they are at making them to start with. Wnt (talk) 19:14, 3 February 2012 (UTC)[reply]
computer screens
Sorry, but for a rather bad pun/joke on another site, can anyone tell me what the letters shown on the computer screens are actually made of, what is within the part of the screen they take up that makes them different to the surroundings or whatever is going on in there?
It depends on the type of monitor being used. On an old style CRT, it's just particles (electrons) being beamed on to a screen that begins to glow due to fluorescence I believe. ScienceApe (talk) 17:52, 3 February 2012 (UTC)[reply]
The letters, as well as everything else on the screen, are made up of pixels. Those are actually each a dot or square, but when tiny dots are placed close together, you see them as letters or pictures, as in a dot matrix printer or in Pointillism paintings. If you look closely you may see the dots. A magnifying glass or a drop of water on the screen may help. TVs use similar technology, but often have bigger pixels, which are easier to see up close. StuRat (talk) 18:18, 3 February 2012 (UTC)[reply]
You may be interested in these magnified images of text, shown on ipad and kindle screens [31]. Of interest is the fact that neither one uses uniform placement of square pixels. SemanticMantis (talk) 18:35, 3 February 2012 (UTC)[reply]
The pixels on the iPad and Kindle in that article are arranged in a square grid. They aren't perfect squares, but that's as close to perfect squares as you'll ever see. Most CRTs used a triangular/hexagonal grid (File:CRT pixel array.jpg). -- BenRG (talk) 19:30, 4 February 2012 (UTC)[reply]
Can Potassium nitrate (KNO3) be used to supply oxigen for breathing in close quarters?
Note that with overheating the remaining potassium nitrite decomposes to produce nitrogen oxide, i.e. concentrated smog. The same might be true if it is impure, mixed with other cations. I wouldn't count on the oxygen to be "suitable for breathing" except in some specific, well designed application. Wnt (talk) 19:21, 3 February 2012 (UTC)[reply]
The propensity that potassium nitrate has for decomposing explosively would be a very real problem. If it happens in close proximity to the user the need for breathable oxygen may be ended. Short version: The stuff explodes rather easily! Roger (talk) 19:31, 3 February 2012 (UTC)[reply]
The article Microwave oven contains this sentence: In turntable-equipped ovens, more even heating will take place by placing food off-centre on the turntable tray instead of exactly in the centre.
Can anyone either give me a reference for why this is so, or offer an explanation comprehensible to a someone who is not even an amateur scientist? Thanks, Bielle (talk) 20:51, 3 February 2012 (UTC)[reply]
The heating of a stationary object will be uneven, with some spots getting more heating and others getting less. By rotating it, you average out all the spots at that radius, which is bound to give a heating amount closer to the overall average. The farther from the center, the more spots are averaged out, while at the very center, there's only one spot, so, whatever heating level the center would get if stationary, it will still get when rotating. If your microwave oven happens to heat the average amount in the center, you will be OK, but, if not, rotating won't improve things at the center. StuRat (talk) 21:03, 3 February 2012 (UTC)[reply]
From the article "Children and adolescents are particularly sensitive to the early and late extrapyramidal side effects of haloperidol. It is not recommended to treat pediatric patients." I would like to know where I can read more about this. If there isn't a citation available, perhaps someone can direct me to a specific person i could contact? Thanks198.189.194.129 (talk) 21:47, 3 February 2012 (UTC)[reply]
It's going to depend on a lot of things. Light certainly helps prevent crime, but so do potential witnesses. If there are a lot of people around at 5pm and not many people around at 8:30pm, crime could be higher at 8:30pm despite it being lighter. --Tango (talk) 22:56, 3 February 2012 (UTC)[reply]
That might be true of an area where people work (approximately 9-5) but don't live, for example. The assumption being that the question is asking solely about safety from crime. As for safety from traffic accidents, full light is better, but sunset and dusk can be even worse than total darkness, since people's vision may be obscured by the Sun and some may not have their lights on yet. StuRat (talk) 23:15, 3 February 2012 (UTC)[reply]
It's difficult to figure this out, because even knowing the crime rate isn't enough. For example, this analysis finds crime in San Francisco to be highest from 4 to 8 p.m. But what that omits is that to a particular person walking late at night, the lower overall number of crimes is little comfort when he has so few people to share them with. I think that despite the increase in crime rate per time of day, the best guide is still the instinctive feeling that when you're one of just a few passersby, the whole criminal element has the chance to put you in their sights. Wnt (talk) 23:24, 3 February 2012 (UTC)[reply]
Certain studies have found that street lighting only reduces the fear of crime without having any noticeable impact on actual crime rates[32]. Sunshine can cause other problems, like traffic-disrupting glare in the early mornings and late evenings. ~AH1(discuss!)01:34, 5 February 2012 (UTC)[reply]
Very doubtful. What would be the point of having that extra strength? The extra muscle mass would mean they need to eat more, which would decrease their chance of survival. Evolutionary pressure is very strongly towards flying creatures being as light as possible and no stronger than they need to be to get off the ground (and perhaps to pick up prey, but according to pterodactylus only had a wingspan of 1.5m, so they weren't large enough to eat human-sized prey). --Tango (talk) 00:41, 4 February 2012 (UTC)[reply]
Pterosaurs in general grow to be much larger, up to a 10m wingspan (see Pterosaur size). They seem to have a lot of tricks that help keep them aloft at that size, including internal air sacs to reduce their density as much as possible. The article of one of the largest pterosaurs, Quetzalcoatlus, talks about their weight (70-200 kg), them needing to vault themselves to get airborne, and includes an illustration of them doing their feeding on the ground. Most of the mighty predatory birds that need to do some impressive lifting feats (like the mighty eagles dropping goats off of cliffs) start lifting mid-flight, having a lot of momentum built up to work with, but is not sustainable flight - they lose altitude continuously.
To answer your question, at the high-end estimated weight of a Quetzalcoatlus, it may have more room to spare in terms of carrying capacity than one would think, but a 200kg flyer could certainly never haul a 100kg person with any lift. I can't give a calculated estimate without years of incredible engineering research as these scientists have employed, but I can tell you immediately that each downbeat of the wings has to be at least 25% more powerful than normal and 50% more frequent. That's like me jogging to the grocery at a comfortable 8-minute mile, but then having to carry food back at an impossible 4:30. SamuelRiv (talk) 01:22, 4 February 2012 (UTC)[reply]
(e/c) No. The largest pterodactyls (suborder Pterodactyloidea) are the members of the family Azhdarchidae, the azhdarchids. Azhdarchid flight is relatively poorly known, but like SamuelRiv said, they are believed to engage only in limited anaerobic (flapping) flight, and be predominantly soaring/flap-gliding animals that utilized columns of rising air to keep aloft. They launched by a running/flapping start and the addition of half to a third (a human's weight) of their current estimated body weight (~200 kg (440 lb) for an azhdarchid with a wingspan of 10 to 11 m (33 to 36 ft)) would make that quite impossible. Not to mention the aerodynamic drag and balance problems produced by a human rider. Azhdarchids are also believed to be stalkers, hunting their prey on foot like modern storks, not skimmers like some of the more commonly known marine pterosaurs (e.g. Pteranodon). They can not pick up prey while in flight because of the drag produced. A human riding them would produce similar if not even more catastrophic drag.-- OBSIDIAN†SOUL01:43, 4 February 2012 (UTC)[reply]
But according the article, many of those claims of large-animal flight, consistent with today's birds, are under dispute for pterosaurs. Surprisingly to me, there are apparently models for flight that is athletic and dynamic like a swallow, not soaring like an owl. As an analogy this might be improper, but one might consider in human flight, the size and shape of a plane varies greatly with what it has to carry - in no sense can one make a plane "scale up". So to make a small one-person recreational airplane carry 20 people, you can't simply make the wingspan 20 times bigger and/or the engine 20 times stronger - you have to redesign it. SamuelRiv (talk) 18:45, 4 February 2012 (UTC)[reply]
Swallows are dynamic soarers actually. They do not engage in much anaerobic flapping. While azhdarchids are more likely to be such, given their shape and the velocities they can achieve, and not like the heavy poor flyers of today (like pelicans); also consider the fact that the faster they fly, the greater the effect of parasite drag. An extraneous human clinging on its back would produce such a drag. The paper points out the inappropriateness of the comparison with birds. The shape, lack of feathers, bend location, muscle structure, wing membrane (with matted pycnofibers that give it additional structural integrity) and bone strength of azhdarchids are too different from birds for any accurate comparisons. Thus the older estimates of azhdarchids only having an estimated weight of 80 kg (180 lb) for an individual with a 36 m (118 ft) wingspan used for the flying model is now considered wrong. But that argument is really only useful in refuting the assertions that azhdarchids were flightless. 70 to 100 kg (150 to 220 lb) human is still a third to half of the largest pterosaur's weight. Unless they had propellers, they wouldn't even be able to launch, much less keep aloft.-- OBSIDIAN†SOUL01:34, 5 February 2012 (UTC)[reply]
Cycloaddition Mechanism
Hello. What is the reaction mechanism for the addition of dichlorocarbene to cyclohexene? Cited sources are appreciated. Thanks in advance. --Mayfare (talk) 06:35, 4 February 2012 (UTC)[reply]
We have an article about dichlorocarbene, with a section entitled "Reactions" that tells you the product but not the mechanism. But it also suggests that the "dichloro" and the "cyclohex" details might not be important (they are not altered by the change taking place in the given reaction). So take a look at the more generic carbene article and maybe in particular the "Reactivity" section. DMacks (talk) 15:18, 4 February 2012 (UTC)[reply]
Most numerous vertebrate species
I recently heard a naturalist claim that humans are the most numerous vertebrate species. Is this true? If so, which other vertebrate species have populations in the billions? I would have thought that the brown rat and some domesticated animals would challenge humans for numbers. Warofdreamstalk13:47, 4 February 2012 (UTC)[reply]
I don't think anyone really knows. He's wrong, but probably not by much, we'd probably be in the top 50 or something, few species are really readily adaptable to a wide range of ecological conditions like humans are. And to be fair, the most likely candidates (domestic and synanthropic animals) only attained their population sizes and distribution because of humans. On the opposite end of the spectrum, passenger pigeons which was believed to have once reached an estimated population of 3 to 5 billion were singlehandedly decimated to extinction within a century by humans.-- OBSIDIAN†SOUL14:34, 4 February 2012 (UTC)[reply]
The brown rat article claims there are 1.3 rats in the UK per person (which, if it's true, would obviously push the rats ahead of the humans). But it cites an hysterical piece in, of all sources, The Sun, which takes its info from Rentokil (Britain's largest ratcatcher, in whose interests it surely is to embiggen the "rat threat"). Snopes cites rather better sources for New York City claiming a ratio of only 1:36. -- Finlay McWalterჷTalk15:00, 4 February 2012 (UTC)[reply]
Rodents aren't limited to cities, they also do quite well in farm fields. In the U.S., we have around 220 million acres just under corn, soybeans, and wheat, and, even at a conservative estimate of 40 rodents/acre, U.S. grain field rodents are more populous than humans. (They also love fruit orchards and grass, e.g. alfalfa fields.) However, most of them are not brown rats, they are meadow voles.--Itinerant1 (talk) 19:56, 4 February 2012 (UTC)[reply]
Rodentia, however, is not a single species. Few rodent species are truly cosmopolitan, and the ones that are are synanthropic species that stay close to human habitations. Field mice in Pakistan, for example, will be most likely to be a different species than field mice in Iowa. In contrast, a Norway rat in the Hong Kong sewers would be the same species as a Norway rat in New York.-- OBSIDIAN†SOUL00:56, 5 February 2012 (UTC)[reply]
back muscles
When I lean backwards whilst standing, my abs and (to a lesser extent) chest muscles flex to help me maintain position. When I lean forwards my back muscles do the same. So why, after carrying a heavy backpack all day, do my back muscles hurt and not my abdominal/chest muscles? This seems counter-intuitive. The Masked Booby (talk) 14:43, 4 February 2012 (UTC)[reply]
Both muscle groups would have to act with each other to stabilize your backpack, so both would be working. A backpack is fairly efficient, though, so the group to feel the most soreness would be the group that is least used to this type of heavy work. For me at least, my that mid-lower-back area doesn't see a lot of heavy or long-term exertion, even in any sport I play. SamuelRiv (talk) 18:52, 4 February 2012 (UTC)[reply]
Is it possible to improve vision with eye exercises
I personally used to use the Bates method, because my initial experience with it was surprisingly good. I tried palming, and afterwards my vision was noticeably clearer for a little while (less than a minute). I started believing the claims, but no matter what, it doesn't do much in the long term. Once I did manage to shave about a diopter off my prescription, but there is no way of knowing if that was just because my eyesight was unnaturally bad due to stress, or whether it was some other effect of the treatment. Also, the eyesight eventually went back to what it was. When I finally read the research, I gave up pretty quickly, regardless of the initial experience. IBE (talk) 15:54, 4 February 2012 (UTC)[reply]
If the Bates method is of any value at all, is it that it reminds one that the eyes focus by the means of muscles and if they don't get enough exercise they weaken. I can understand IBE's comment because I can't say that his (Bates) exercises appeared to do me any good when I tried them. Yet, I noticed after I stopped working in an office (where every-day I was only focusing 10 – 15 ft at the most and most of the time a lot shorter and a similar amount in the evening glued in front of the TV) that my eyesight improved to the point where I forgot to wear my specs because I could see well enough without them. Maybe also, because I then needed to take notice of vertical line as well as horizontal that my bad astigmatism became negligible. Thus, I think that just doing a few exercises from time to time it not really enough to make a major improvement, as they don't exercise the muscles enough. Also, as one grows older, atrophy of muscles, due to lack of exercise, takes less time to occur. Extended Bed Rest Accelerates Muscle Deterioration In Older Adults. Some might consider this last comment trite, but older friends of mine that have only spent a few hours in the Pub, focusing no further than the bar-maid, come out, unable to see their way home – and back to the wife. I tell you -this is the truth. Old age is not very kind – so don't go there. --Aspro (talk) 19:59, 4 February 2012 (UTC)[reply]
Weakening of the ciliary muscle with age, which regulates the accomodation reflex, tends to result in presbyopia, or reduced ability to focus on near objects. There is definitely variation in ciliary muscle strength between individuals of the same age, so any valid eye exercises may focus (no pun intended) on these muscles. ~AH1(discuss!)01:25, 5 February 2012 (UTC)[reply]
Why can animals be classified as vertebrates or invertebrates if vertebrates only make up one phylum?
I simply don't understand why scientists have to classify animals as vertebrates or invertebrates. Invertebrates make up several phyla, while vertebrates are in only one phylum? Yes I know humans are vertebrates, and that fact can lead to bias (like the Old World and New World stuff) but remember, not all chordates are vertebrates. Was it done for the sake of convenience, or just because chordates are somehow special? And what current phylum has the most similarities with chordates? Narutolovehinata5tccsdnew15:23, 4 February 2012 (UTC)[reply]
Scientists classify things in whatever ways they think will be useful. Vertebrates have a lot of similarities to each other that they don't have with invertebrates, which makes it a useful classification. You won't find scientists talking about invertebrates much since, as you say, they are so varied - you would want to talk about a specific subset of invertebrates. The word only exists to distinguish them from vertebrates, rather than as a classification of its own. --Tango (talk) 15:54, 4 February 2012 (UTC)[reply]
(WP:EC)See Invertebrate#History and Invertebrate#Significance_of_the_group. The term was coined by Lamarck, who himself is responsible for making further taxonomic subdivisions (Linneaus apparently divided all invertebrates into insects and worms). The article goes on to say "the (invertebrate) grouping has been noted to be "hardly natural or even very sharp."" Suffice it to say, it is a useful term for casual conversation, and does reflect some bias, but is not really used with much scientific weight. Also, just to clarify: "invertebrate" is not a "classification", it has no place in taxonomy or phylogeny, and as you point out the group is highly paraphyletic. It has the same scientific level of rigor as a term like "Non-ant insect". In short, the term is still used because it is useful, and is fairly well-defined. SemanticMantis (talk) 16:09, 4 February 2012 (UTC)[reply]
Right. Classifying animals as vertebrates and invertebrates is a bit like classifying people as Americans and foreigners. If you live in America the classification is useful, but it is not a very meaningful distinction from a global point of view. Looie496 (talk) 23:57, 4 February 2012 (UTC)[reply]
It's a very old classification system, back when people didn't truly appreciate the vast differences between groups of organisms and were still a bit anthropocentric in that they consider vertebrates to be more important than anything else (after all, they are usually the largest organisms). Today, Invertebrata is not a formal taxonomical rank (note its article does not have a taxobox in contrast to subphylum Vertebrata). It's merely a colloquial grouping meant to quickly distinguish vertebrates from non-vertebrates.-- OBSIDIAN†SOUL00:51, 5 February 2012 (UTC)[reply]
Basic iTunes question
Sorry, this is really basic, and please transfer it to Entertainment RD if that's more appropriate. I am gradually ripping all my CDs and putting them onto an iPod, using iTunes. It is taking up more space than I would like on my hard drive. If the music is safely on the iPod, how can I easily take them off the hard drive, or compress them, or whatever? ITunes seems to want me to have everything on both the hard drive and the iPod, "synchronised". Thanks. Itsmejudith (talk) 18:31, 4 February 2012 (UTC)[reply]
(ec)You might do better at the Computing desk than either! Not having used it, my hazy understanding of iTunes is that it is mostly for copy-locked (DRM) music files rather than for the all-purpose files from a ripped CD, and so a simple general purpose sound playback program might do better. But the extent of my musical forays nowadays is YouTube running Video DownloadHelper (with NoScript to block the VEVO ads ;) ) Wnt (talk) 19:04, 4 February 2012 (UTC)[reply]
This is not true at all. You can use iTunes to manage any MP3s or other media files. They don't have to be DRMed at all, and usually aren't if you are ripping them from your own CDs (which you can do within iTunes easily). They are only DRMed if you get them through the iTunes store, which you're under no obligations to do. I don't think anybody cares about how you pirate music and I'm not sure why you offered that up as an answer. --Mr.98 (talk) 20:59, 4 February 2012 (UTC)[reply]
You can set iTunes to "Manually Sync" your iPod. That way, it won't attempt to automatically make the two libraries match every time you plug it in. You can then safely delete music from your computer's hard drive, without affecting the iPod as long as you don't try to sync the whole music library manually. Usually, I prefer to set it to Manual and only select specific playlists to sync to my iPod. As long as you keep that music on your computer's hard drive, it won't have any problems. — The Hand That Feeds You:Bite19:15, 4 February 2012 (UTC)[reply]
You can also just set it to manually manage (not sync at all). Set up in this way, you move music to the iPod by dragging it within iTunes. You can then delete it off of the main computer if you want. --Mr.98 (talk) 20:59, 4 February 2012 (UTC)[reply]
Parrots (e.g. Amazon)
Is it true that male Amazon Parrots usually get on better with women and that female Amazon Parrots get on better with men? Something to do with pheromones? Thanks.
Can someone give the formula including 3 numbers: solar mass of both stars, separation distance, period. So if i was given 2 out of the numbers i can figure out the other one. So a formula that including all of 3 info above. Thanks!Pendragon5 (talk) 22:50, 4 February 2012 (UTC)[reply]
The deviation of an elliptical orbit from perfectly circular is known as its orbital eccentricity, where a value of 0 is a circle and 1 is a parabola. The average distance between two objects is the semi-major axis, and the centre of gravity between a system of gravitationally-bound objects is its barycenter. You may try finding some 2-body simulators online, as the mass of either object does affect the shape of the orbit, or compare some real-life examples such as Capella versus Epsilon Aurigae. ~AH1(discuss!)01:15, 5 February 2012 (UTC)[reply]
Note that the rapidly moving water will also rapidly enlarge the hole, so they wouldn't need to get bored waiting to die. :-) StuRat (talk) 00:10, 5 February 2012 (UTC)[reply]
Hi. One day while glancing over the surface of the water in a partly-full water bottle in a room with windows at the back and fluorescent lights over top, I noticed an unusual spectrum. At least part of the spectrum was likely from the fluorescent lights, but probably not the part you'd expect, since I observed the fluorescent spectrum in water to be very similar to the natural white light spectrum. I will list the colours of this spectrum in order, but keep in mind that italic text signifies what I call "narrowband", bold what I wrote down as the thickest part of the spectrum, taking up almost half of the entire spectrum, and underline for colours seen very narrowly at the edge of some transition, possibly into fluorescent lighting or ambient ceiling.
Now, any idea what this spectrum may consist of? There did not be any objects directly contributing, unless there was a ubiquitous green backpack or other container within my line of sight. Thanks. ~AH1(discuss!)01:04, 5 February 2012 (UTC)[reply]
Resolved