Wikipedia:Reference desk/Archives/Science/2011 March 8

= March 8 =

Blood erythritol
The polyol erythritol is used as a sugar substitute. Although it is absorbed by the body and passed through the kidneys, it is not metabolized. It does not increase "blood sugar", i.e. blood glucose, it is a sugar alcohol. Even so, it actually has anti-oxidant effect. Even so, I have to ask: is erythritol also a kind of "blood sugar" -- i.e., does erythritol have any properties that duplicate those of an equal amount of glucose? For example, does it increase blood viscosity, cross-link proteins, or add to strain on the kidneys? Wnt (talk) 01:37, 8 March 2011 (UTC)

Gear trains
actually i have solved a gear train questions which is giving negetive value for number of tooth for one of the gears.what could i interpret from that. should i take absolute value of the number of tooth. 59.93.130.41 (talk) —Preceding undated comment added 06:42, 8 March 2011 (UTC).


 * We would need more information about what great train question you solved (i.e. what the math was). A negative number could mean you have an error, or perhaps it means the gear is rotating in reverse. It's impossible to say without knowing what formula you used. Ariel. (talk) 11:01, 8 March 2011 (UTC)

Q. The annulus A in the gear shown in the figure rotates at 400 rpm about the axis of the fixed wheel S which has 80 theeth.The four armed spider is driven at 180 rpm.Determine the number of teeth required on wheel p. —Preceding unsigned comment added by 59.93.134.20 (talk) 12:46, 8 March 2011 (UTC)


 * I've tweaked the image to make it viewable. --Tagishsimon (talk) 12:49, 8 March 2011 (UTC)

Thanx for tweaking, Here when we solve we get number on tooth on annulus gear(red one ) to be -24.82.to solve remaining problem should we take modulus value of number of gears.Or it is having any significance. —Preceding unsigned comment added by 59.93.134.20 (talk) 13:07, 8 March 2011 (UTC)


 * Don't you worry about the fractional number of teeth as well? Dauto (talk) 15:26, 8 March 2011 (UTC)


 * Which gear is S and which one is p ? Gandalf61 (talk) 15:29, 8 March 2011 (UTC)


 * Typically "S" is the "Sun" (center) and "P" is the "Planet" gear (by analogy to orbits). See Sun and planet gear.  In this case, we have one sun, four identical planets, and an outer-ring that the OP is calling the "Annulus" (A).  Nimur (talk) 17:15, 8 March 2011 (UTC)


 * And can you show us your math ? StuRat (talk) 15:58, 8 March 2011 (UTC)


 * Ariel seems to be right. Epicyclic_gearing says that a negative result means rotation in the opposite direction. --Heron (talk) 19:17, 8 March 2011 (UTC)
 * I might be wrong, but I think the funny result is due to the given velocity ratio being impossibly high. By my reckoning it cannot exceed 2 and the question requires it to be 20/9.  Sp in ni  ng  Spark  01:00, 11 March 2011 (UTC)
 * I'm not sure there's an upper bound on the velocity-ratio between the annulus and the drive-shaft. I think I solved this problem the day it was posted and obtained a reasonable, integer number of gear-teeth for the planet-gears (36).  I can dig out my math on a scrap of paper out of my recycle-bin, if anyone's still interested in the worked solution. Nimur (talk) 14:58, 11 March 2011 (UTC)
 * Don't forget that the normal situation with planet gears is that the annular gear is fixed and the sun gear drives the planets. This question requires the sun to be fixed and the planets driving the annular ring.  This is a completely different case.  My reasoning is as follows: In one revolution of the spider, if the planets were not free to move independently, the annulus would be carried round one revolution also.  However, since the planets are free to move, the annulus will be driven forward from this position (of exactly one revolution) by the turning of the planets.  How far forward? - that would be the number of teeth on one planet times the number of times it rolls as it turns one revolution of the sun.  If the sun (S) is n times the teeth of planet (P) then the forward position is nP or, with a little thought, equal to S.  So the total roatation of the annulus for one rotation of the spider is 1+S/A.  Since it is a physical requirement that S<A then 1<RotA/Rotspider<2.  A doubling of speed is the limiting case of infinitely large sun gear and annulus.  I got a different numerical answer to the OP, but like the OP it was fractional and negative.  Sp in ni  ng  Spark  15:33, 11 March 2011 (UTC)

Autotrophic respiration
We don't seem to have an article on root respiration (autotrophic respiration), although it seems to be a fairly mainstream topic. I am curious about the interaction between scion and rootstock on tolerance to waterlogging and couldn't even find the relevant mechanisms defined here. DId I miss it or could someone who has a clue (unlike me) start one? --BozMo talk 09:59, 8 March 2011 (UTC)


 * Perhaps the articles Autotroph or Photoheterotroph may help? - 220.101 User talk:220.101.28.25\ 15:08, 8 March 2011 (UTC)


 * Basically there is zilch on Wikipedia on this rather major topic. I found a decent apparently RS elsewhere though which answered my questions --BozMo talk 16:36, 11 March 2011 (UTC)

Flight angle
An accident occured in which the vehicle was twisted at flight angle. What does the term "flight angle" mean technically and also how is it used on day to day basis? aniketnik 16:26, 8 March 2011 (UTC) — Preceding unsigned comment added by Aniketnik (talk • contribs)


 * Probably, "flight angle" refers to either the angle of attack (the angle of elevation of the wing surface, relative to horizon, as a rotation along the pitch-axis); or to the pitch angle (the angle of the aircraft airframe, measured relative to the horizon, along the axis designated as the "pitch axis"). In the case of a catastrophic accident, those two angles might not be identical!  See our diagram for the conventional layout; and on most fixed-wing aircraft, note that pitch and angle-of-attack of the wing surface are fixed relative to each other.  Other important "angles" are described in our aircraft flight dynamics article, with animations.  Your exact quote, "twisted at flight angle", sounds very ambiguous - it is possible that the intended meaning is that the aircraft was within its normal operating orientation limits and should not have stalled.  If you provide a source for your exact quote, we may be able to interpret the intended meaning a little better.  Nimur (talk) 17:00, 8 March 2011 (UTC)

spin
How can they force the spin axes into a horizontal alignment by imposing an electric field that alternates at radio frequencies like it says in this article http://findarticles.com/p/articles/mi_m1200/is_n11_v133/ai_6507705/ — Preceding unsigned comment added by Lufc88 (talk • contribs) 17:55, 8 March 2011 (UTC)


 * It would help us to better answer this question if you were to explain what exactly you are having difficulty with in that article. You might find what you are looking for in magnetic moment and Electron magnetic dipole moment.  Simply put, a spinning electron is equivalent to a circulating loop of electric current and consequently has a magnetic field identical to a small dipole magnet.  For this reason, the electron will be acted on by external magnetic fields and, in particular, will tend to align the axis of spin with the field.  At least, this is the situation with classical field theory, to get the full picture quantum mechanics must be applied.  When this is done it is found that the dipole moment can take on only certain quantised values.  Sp in ni  ng  Spark  00:07, 11 March 2011 (UTC)

Elements which make life possible
Which element or elements makes life possible? I am also wondering if life can be inorganic instead of organic? Matthew Goldsmith 19:08, 8 March 2011 (UTC) — Preceding unsigned comment added by Lightylight (talk • contribs)


 * This is covered in some detail in the article Hypothetical types of biochemistry. Short answer: there may be all sorts of different chemical configurations that can make life happen, but we haven't observed them yet. (Except maybe GFAJ-1, but that's a small modification of the general template, if it is real.) --Mr.98 (talk) 19:58, 8 March 2011 (UTC)


 * I added a better (sub)title; please try to make your title more useful in the future. Also, a question: Do you mean chemical elements, or "elements" like light, heat, water, and gravity ? StuRat (talk) 22:15, 8 March 2011 (UTC)


 * Carbon, hydrogen, oxygen, nitrogen, (phosphorus or arsenic), and sulfur are all necessary. --75.15.161.185 (talk) 01:10, 9 March 2011 (UTC)

Why wouldn't silicon based computer technology not qualify as life when it become self supporting? E.g., in the near future we may have robots that maintain themselves and the infrastructure that sustains them. Count Iblis (talk) 15:11, 9 March 2011 (UTC)


 * Some might argue that to be life it must be self-replicating rather than self-supporting, which goes to show that whether or not a machine is considered alive depends on ones definition of life.  Sp in ni ng  Spark  08:31, 11 March 2011 (UTC)

efficiency
how efficient are steam power plants like coal in converting heat to electricity in percentage? how efficient are antennas in converting em waves to electricity in percentage? — Preceding unsigned comment added by Lufc88 (talk • contribs) 19:39, 8 March 2011 (UTC)


 * The answer is, of course, "it depends." Practically, a coal power station is about 40% efficient, per carnot efficiency and engineering practicality.  Antennas can be very close to 100% "efficient," if your amplifier and signal path are impedance-matched to free space (377 Ω), if you count all power out in any direction.  Read thermal power station efficiency, and antenna gain.  Do you need help understanding those articles?  Nimur (talk) 21:28, 8 March 2011 (UTC)

Thanks i think i understand — Preceding unsigned comment added by Lufc88 (talk • contribs) 17:49, 9 March 2011 (UTC)

Standardization in Redox Titrations
Hello. Is standardization of KIO3 necessary before titrating against ascorbic acid if I am preparing KIO3(aq) from its solid? Thanks in advance. --Mayfare (talk) 21:42, 8 March 2011 (UTC)
 * Hi Mayfare. I think you have to ask yourself what reasons might mean that weighing solid KIO3 might not accurately tell you the molarity of the solution. Here are a few to consider...


 * Purity of solute (KIO3) as sold. Was the solute intended for use as a primary standard or is it just a ground-up radiation pill, etc?
 * Storage. Has the solute been kept in an airtight container so that it can't react with atmospheric gases around the lab? Would that be an issue?
 * Humidity. Is the solute totally dry? If not, how might you dry it before use?
 * Purity of solvent (H2O). You might get an extra mark for mentioning this!
 * Accuracy of weighing. How much solute are you weighing out? What is the precision of the weighing device?
 * Accuracy of dilution. What errors might you expect here?
 * Hope this helps. Try estimating the cumulative effect of the last two (Accuracy) points. - Pointillist (talk) 22:31, 8 March 2011 (UTC)

Inheritance traits and DNA
Is it possible to determine the skin tone, hair/eye color and blood group after studying the inheritance traits during DNA analysis? --89.76.224.253 (talk) 22:33, 8 March 2011 (UTC)


 * It certainly is in the DNA somewhere (barring the use of hair dye, colored contacts, and such), but I'm not sure if we know exactly where. It's sometimes vastly more complex than just one chunk of DNA which sets each trait.  There might also be certain diseases or environmental factors which might have an effect (like sun-bleached hair). StuRat (talk) 23:06, 8 March 2011 (UTC)


 * (ec)There are some claiming to do this. This is fairly embryonic, and I would keep an eye out for chicanery.  Genetic testing to determine the blood type shouldn't be difficult, but I can't think of many situations in which it would actually be useful.  After all, if you have blood, might as well go for a DNA match. Wnt (talk) 23:07, 8 March 2011 (UTC)


 * The Daily Mail article is (no surprise) extremely misleading. It says that theoretically in the future you could reconstruct certain details about a person's face from DNA. (Granted in theory you could do this to some degree — but we're a long way away in practice, and it's unclear if those details you could extrapolate would actually be useful in identification.) Then it says something like this was already done... because they used DNA to determine that a suspect was Black rather than white. That's not the same thing at all; it's relatively easy to guess what ethnicity/racial category someone would fall in based on their DNA (it's probabilistic, but you can say things like, "you carry genes are extremely prevalent in people from this part of the world as opposed to this part of the world" — which, in some situations, is probably enough to say, "this guy is probably pretty white looking or Asian looking or Black looking" — which is not terribly precise, but could be useful in identifying a suspect). It's totally different — one is modeling development (which is hard), the other is tracing origins (which is not as hard). --Mr.98 (talk) 23:21, 8 March 2011 (UTC)


 * It's not easy to say exactly where this line is crossed, because any statistical fact is meaningful. We shouldn't expect that one day the genetic information is worthless and the next you can draw the suspect's face - rather, there is a period when it can rule out some possible suspects and provide "most likely" values for some features. Wnt (talk) 23:38, 8 March 2011 (UTC)


 * Note that even ruling out suspects (or matching DNA) is (under currently used practices) still probabilistic. They do not currently sequence entire DNA sequences (though someday they may do this, once it gets really cheap), just a finite series of markers within them. The odds of two different sets of DNA being seen as identical under these procedures is small but not impossible. (And calculating those odds depends on what assumptions you make about the target populations.) It is to my understanding still quite rare to use DNA testing to say something about what your suspect should look like — usually DNA analysis is useful after you already have samples to compare against. --Mr.98 (talk) 00:36, 9 March 2011 (UTC)

Speed of back-and-forth motion
How to measure the speed of continous back-and-forth motion? One b&f move per second? -) —Preceding unsigned comment added by 89.76.224.253 (talk) 22:56, 8 March 2011 (UTC)


 * How about dividing the total distance traveled per cycle by the time for each cycle ? This will give you the average speed.  However, if you want the instantaneous speed, which would be expected to be zero at the furthest extensions and (normally) at maximum in the center, that gets trickier. StuRat (talk) 23:03, 8 March 2011 (UTC)


 * If I continously make for example 0,5 m back and forth per 1 s, that would be 0,5 m/sec per cycle, I guess? But what about instances where speed is inequal? --89.76.224.253 (talk) 23:08, 8 March 2011 (UTC)


 * If it goes half a meter one way, then half a meter back, that's 1 meter total. If that happens in one second, then that's an average of 1 meter per second.  However, the speed WILL be uneven.  That is, it must stop and turn around at the end of it's motion at each end.  This is what I was getting to with "instantaneous velocity", which is the speed at any given time.  If we make some additional assumptions, like constant acceleration/deceleration and no rest time at each end, we might even be able to come up with a graph of the instantaneous velocity at each point in the cycle, from the data you supplied. StuRat (talk) 23:19, 8 March 2011 (UTC)


 * Do you mean Hertz? You could say that the motion has frequency v and then calculate the position = K sin (2 pi vt) and therefore velocity = 2 pi K v cos (2 pi vt) [the derivative].  (K is half the total distance moved; the 2 pi factor converts cycles per second to radians per second, which can be multiplied by seconds and input into the sin function)  But only if it moves sinusoidally.  It could just bounce back and forth at constant velocity, for example.
 * To elaborate, suppose you have a piston that is driven by something that circles 0.25 m away from a central pivot once per second. Therefore the piston moves 0.5 m back and forth once per second.  (Depending on the linkage I don't think this is precisely sinusoidal, but it could be)  Time zero is the piston half extended, moving outward.  The position of the piston is simply 0.25 m (2 pi t).  When t = 0.25 it is 0.25, 0.5 it is 0, 0.75 it is -0.25, 1 it is 0.25 again.  The velocity of the piston is (2 pi radians/cycle) (0.25 m) (1 cycle/second) cos (2 pi radians/cycle * 1 cycle/second * t).  At t=0 this is 0.5 pi "radians" m/s = about 1.57 m/s.  The decision to use radians in the velocity is momentarily confusing (both radians and cycles are in a sense "dimensionless") but radians signify the actual distance traveled, whereas cycles are merely a count of events.  Wnt (talk) 23:24, 8 March 2011 (UTC)


 * Only a massless object could do that. Any real world object takes some time to accelerate and decelerate.  However, the instantaneous velocity profile isn't necessarily sinusoidal, that's only true under constant acceleration.  In the case of a ball being batted back and forth by a cat, for example, this wouldn't be the case. StuRat (talk) 23:23, 8 March 2011 (UTC)


 * I just edited the above a little, but to address your point, yes, there is at least some period of acceleration. But if the impact is elastic at either end, it would be a very small amount of time. Wnt (talk) 23:26, 8 March 2011 (UTC)


 * So, we should ask, what's driving this object to move back and forth ? This may help us to determine what type of motion and acceleration we're dealing with. StuRat (talk) 23:28, 8 March 2011 (UTC)


 * We have an article on the simple harmonic oscillator. This is the simplest type of "back and forth" motion modeled in physical systems.  More complicated models deal more accurately with other types of motion.  Nimur (talk) 23:37, 8 March 2011 (UTC)
 * You may need a stroboscope to measure it. 92.28.254.54 (talk) 13:38, 10 March 2011 (UTC)