Wikipedia:Reference desk/Archives/Science/2012 February 1

= February 1 =

First aircraft developed using CATIA?
What was the first aircraft designed entirely using CATIA? From the CATIA article it sounds like one of the Mirage fighters, but I'm not sure which one.99.245.35.136 (talk) 07:04, 1 February 2012 (UTC)
 * Chinese Xian JH-7A is the first aircraft developed by CATIA V5, when the design was completed on September 26, 2000. I am not sure if it was entirely designed using CATIA. Von Restorff (talk) 07:09, 1 February 2012 (UTC)
 * "FAI developed the first full-scale digital mock up and virtual model of an entire aircraft in China using CATIA V5 and ENOVIAVPM." ENOVIAVPM is based on the components of the CATIA Data Manager. Von Restorff (talk) 07:10, 1 February 2012 (UTC)
 * Sorry I wasn't clear, guys. I meant using the very first version of CATIA, back when it was known as CATI.99.245.35.136 (talk) 08:19, 1 February 2012 (UTC)
 * 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)
 * 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, 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 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  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)

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!!  Lady  Blah De Blah  10:51, 1 February 2012 (UTC)


 * I wanna say Stonehenge... --Ouro (blah blah) 11:30, 1 February 2012 (UTC)


 * 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)


 * As did the humans that built them, which might be the point they were making. ←Baseball Bugs What's up, Doc? carrots→ 08:36, 3 February 2012 (UTC)


 * Yes, that was the point, although they seemed to practice cremation, so they didn't get a chance to rot. StuRat (talk) 23:40, 3 February 2012 (UTC)


 * 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...  Lady  Blah De Blah  11:35, 1 February 2012 (UTC)
 * You can "walk" through them on Google Earth. Dismas |(talk) 11:47, 1 February 2012 (UTC)


 * There doesn't seem to be a specific name for such a structure, but the study of them is called archaeoastronomy. Smurrayinchester 11:35, 1 February 2012 (UTC)


 * Would it not be called a calendar? The word can mean both the system used, as in Gregorian Calendar, or the instrument itself, as in solar calendar and desktop calendar. - Cucumber Mike (talk) 12:13, 1 February 2012 (UTC)


 * Observatory appears to be the name of the structure that fits the bill.--Aspro (talk) 18:07, 1 February 2012 (UTC)


 * Analemmatic sundial.--Srleffler (talk) 18:37, 1 February 2012 (UTC)

"Bleached" food ingredients
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)


 * There is an article Flour bleaching agent which provides some of the answers you are looking for (though not for your technical ones). --Saddhiyama (talk) 11:18, 1 February 2012 (UTC)


 * 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; 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 though flour is often enriched with vitamins to counter this. --Colapeninsula (talk) 16:02, 1 February 2012 (UTC)


 * Here and Here are explanations of the chemistry of bleaching. --Colapeninsula (talk) 16:10, 1 February 2012 (UTC)


 * 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)
 * Hence the term Bleachers. ←Baseball Bugs What's up, Doc? carrots→ 20:05, 1 February 2012 (UTC)


 * 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)

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)
 * Every person is different, and since this deals with a treatment you have received, you should contact your doctor for information. -- Jayron  32  18:10, 1 February 2012 (UTC)
 * 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. Smurrayinchester 19:27, 1 February 2012 (UTC)
 * 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),
 * 0.5*64000/(4*55,845)
 * or did I make a silly mistake? --NorwegianBluetalk 20:26, 1 February 2012 (UTC)
 * Note that a largish dose of iron will be absorbed largely to ferritin storage, at least in the short term.  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 ; 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)
 * 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, 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 , 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. --NorwegianBluetalk 22:38, 1 February 2012 (UTC)
 * 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. Smurrayinchester 23:34, 1 February 2012 (UTC)

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)


 * 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)

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)


 * 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)

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)


 * 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. 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)


 * 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)


 * 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)


 * ... but it would regain it's microbial properties on areas under constant use where it would quickly lose its lacquer.   D b f i r s   07:54, 2 February 2012 (UTC)


 * Copper is also a Homo-sapiens-cide .. ie poisonous for humans. Silver and Zinc might have their sides too thou. I hope one is cautious with its use in direct contact with human flesh and doesn't see it as an wonder cure. Electron9 (talk) 18:27, 2 February 2012 (UTC)


 * 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)

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)
 * I think you must be making some unstated assumptions, because none of that seems like valid reasoning to me. Looie496 (talk) 00:47, 2 February 2012 (UTC)
 * 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)
 * Do you know any calculus? It's a good way to discuss how infinitely many arbitarily small things can add up to finite areas and volumes. Staecker (talk) 13:01, 2 February 2012 (UTC)
 * 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)
 * 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)


 * You may be interested in Sub-Planck. hydnjo (talk) 01:52, 2 February 2012 (UTC)


 * 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)


 * 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)


 * 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)


 * 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)


 * 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)


 * 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)

So I'm a bit late, but it might be a good idea to take this from physics to mathematics and specifically to the concept of measure.--Rallette (talk) 10:56, 2 February 2012 (UTC)
 * Agreed. In addition to measure theory, I think the OP's ideas are touching upon the Banach-Tarski paradox. Banach-Tarski_Paradox.svg 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)
 * That paradox seems like it's cheating to me. In Banach-Tarski_paradox 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)
 * 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)