Wikipedia:Reference desk/Archives/Science/2013 September 8

= September 8 =

Monoethanolamine membranes?
Hello, I've been reading about CO2 scrubbing systems and I'm curious as to whether there is a way to pipe gas through monoethanolamine without percolating it through. I thought there might be some membrane which is permeable to CO2, but not to monoethanolamine. Does any such material exist? If so, what is it called? Thank you. 71.41.39.2 (talk) 04:00, 8 September 2013 (UTC)

Understanding calculus in non-geometric terms
I was studying thermodynamics recently and I noticed that I understand calculus, but only in geometric terms, and I couldn't justify (intuitively, but rigorously) the correctness of equations unless I thought about surfaces or lines (or color/density coded 3D space). So I was wondering is there a way to understand calculus in a more general way that doesn't need geometry, so that when I try to understand what happens in say, a gas in a tube, I think of a gas in a tube, not surfaces. And I know that the representation is essentially equivalent mathematically, but it still bugs me. A while ago I had (and still do have) the same kind of problem with integrals. I understand why the area under a curve is calculated by the anti-derivative of that curve, but I don't understand why the more general notion of integrals, especially multi-varibale ones (which roughly speaking is a form of "summation")is related to derivatives. I can understand limits in a general, non-geometric view, but not the things I just mentioned. So is there any book, or article or anything in which these subjects are discussed in more general ways than a geometric view?--Irrational number (talk) 08:30, 8 September 2013 (UTC)


 * It sounds like all you need is just practice/experience. When I was in 1st and 2nd year at university doing electrical engineering, we had subjects taught by the School of Engineering where we studied fundamental electrical components, whose behavior can be explained, sort of, with physical models (eg the rubber tube analogy for inductance) but can be clearly and precisely understood with calculus.  With just those subjects it doesn't really settle in.  But from the Math Department we studied calculus using a textbook that had copious examples from all branches of science and engineering.  Once you had worked your way through that book, you were alright, and understanding electrical stuff was real easy.  1.122.160.213 (talk) 10:58, 8 September 2013 (UTC)


 * Try reducing it to qualitative visualisations. A derivative describes how a dependent variable changes with respect to the independent variable. That means that whenever the derivative is positive for a certain range of the independent variable, the dependent variable will be increasing as you transition through that range, the converse is also true, and it is true for both points and ranges.
 * An example, if you have a parabola (y=x2), then its derivative is dy/dx=2x. The derivative is negative for any value of x<0, and positive for any value of x>0. This means that y decreases for any value of x<0, and increases for any value of x>0. Keep in mind that this is only true if you transition in the positive direction for x.
 * When you take the integral of z(x,y) with respect to x, and then y, you'll get a function which will yield a 3D graph also called a surface. Plasmic Physics (talk) 13:39, 8 September 2013 (UTC)


 * Understanding things in only geometric terms is actually not such a limiting thing I have found - since almost everything (at least that I have encountered) can be mapped in some way to a visual concept, and humans are such visually oriented creatures. In fact I struggle to think of anything that I don't think about visually. To give some examples: statistics (venn diagrams, distributions and decision trees), logic (flow chart-like things) and foreign languages (vocabulary in categorised and subdivided spaces/bins, sentences constructed by slotting together parts of speech like jigsaw puzzle pieces). You may find that if you are a visual thinker like me it may be easier to work on your confidence in robustly mapping any situation back to the geometric case so you can always say "I can show this is true for the geometric case, and I can show that the geometric case is equivalent to my case, therefore this must also be true in my case". Maybe I'm misunderstanding you, but it appears to be the second step that is tripping you up (i.e. it might not bug you so much if you could demonstrate that a geometric representation is exactly equivalent, rather than simply "know it is essentially equivalent"). Learning to think about it non-geometrically is also a sensible approach, but personally I wouldn't even know where to begin thinking about anything at all without a visual metaphor. Equisetum (talk &#124; contributions) 14:08, 8 September 2013 (UTC)

Why does salt amplify flavors in food?
When you add anything else to food it just makes the dish taste more like whatever you added yet salt makes other things taste more strongly, why is that?Bastardsoap (talk) 12:50, 8 September 2013 (UTC)


 * I'm not entirely sure that it does. However one suggestion I've seen in a few cook books is that salt pulls liquids from inside of cells to the surface by osmosis and that this brings more flavor to the surface where it's more easily tasted.
 * Of course it's not just salt, Monosodium glutamate (MSG) has a reputation for enhancing whatever flavor the food already has - but that too is a somewhat dubious claim because MSG has an innate umami flavor of its own. SteveBaker (talk) 13:10, 8 September 2013 (UTC)

Wouldn't sugar have an equal osmotic effect in equal concentrations?Bastardsoap (talk) 13:17, 8 September 2013 (UTC)
 * Perhaps it does? We add it to foods in similar ways. SteveBaker (talk) 13:42, 9 September 2013 (UTC)


 * I found National Center for Biotechnology Information - Taste and Flavor Roles of Sodium in Foods: A Unique Challenge to Reducing Sodium Intake which says; "Added salt improves the sensory properties of virtually every food that humans consume, and it is cheap. There are many reasons for adding salt to foods. The main reason is that, in many cases, added salt enhances the positive sensory attributes of foods, even some otherwise unpalatable foods; it makes them “taste” better. For people who are accustomed to high levels of salt in their food, its abrupt absence can make foods “taste” bad." It continues; "One understood mechanism by which sodium-containing compounds may improve overall flavor is by the suppression of bitter tastes.". Alansplodge (talk) 13:39, 8 September 2013 (UTC)

Suppression of bitter tastes is not a mechanism, doesn't tell you anything about how it does thisBastardsoap (talk) 15:51, 8 September 2013 (UTC)

I'm almost certain that McGee will have something to say on this subject in On Food and Cooking (how much detail he will go into I cannot say - it's a big book, but the guy has a lot of ground to cover). I will have a look in my copy when I get home in about 8 hours. If I don't post back here within 12 hours feel free to bug me on my talk page because that will mean I've forgotten. Equisetum (talk &#124; contributions) 14:17, 9 September 2013 (UTC)
 * I'm afraid that McGee gives no more information than the review article above, and certainly no attempt at mechanism. 46.37.160.194 (talk) 07:48, 10 September 2013 (UTC). Sorry, forgot to sign in. Equisetum (talk &#124; contributions) 07:50, 10 September 2013 (UTC)


 * Sugar, salt and fat are the essence of tasty cooking. We have a particular reaction to sweetness that is so distinct the word for pleasure and sweet are often the same--compare the word hedonism the root of which is cognate to the English sweet.  Note that fat is very different from sugar, in that it has a mouth feel more than a separate taste.  Sugar on the tip of your tongue is sweet; fat on the tip of your tongue is inert.  Salt seems to enhance the taste of fatty foods.  Slat by itself, say on a cracker or pretzel, has a distinct taste.  And while salt can be extremely unpleasant; for instance, if you unknowingly find salt, instead of sugar, in the sugar bowl; you can also use it as an abrasive to brush your teeth with with little objection.  In cooking salt seems to enhance flavors, especially fat.  Steak without salt is almost flavorless.  Salt brings out the flavor immensely without really tasting salty at all in the way a salted cracker does.  The next time you have a really bad, dry tasteless steak, try spreading a tiny bit of butter or a fatty spread with just a little salt and the taste will improve immensely.
 * The science of taste is hugely interesting, but it doesn't yet seem mature. One source I found on the internet said there are seven tastes: sweet, sour, bitter, salty, umami, hot, and metallic.  I saw a science of cooking show that adds fat, called "richness", as another flavor. The question is not just chemical, but also psychological. μηδείς (talk) 00:28, 10 September 2013 (UTC)


 * None of those responses actually gets at the most important part of the story. Our flavor perception system faces a serious engineering challenge, in that most of the complexity of flavor actually comes from the sense of smell.  So why don't we perceive everything that we smell as a flavor?  The answer seems to be that flavor perception is "gated" by taste perception -- the brain needs to have some activation of taste detectors located in the mouth in order to generate a percept of flavor.  Sweet and salty tastes are more effective than sour or bitter. Looie496 (talk) 19:57, 9 September 2013 (UTC)


 * To me, salt makes food "not bland", but there are many other things which can do that, like peppers (capsaicin), in the proper proportion, of course. StuRat (talk) 07:59, 10 September 2013 (UTC)

Coriander
Which aldehyde is responsible for the foul flavour of coriander, variously likened the smell of gym-socks, stink bugs, or dishwashing water, only perceptible by a fraction of the populace? Plasmic Physics (talk) 13:00, 8 September 2013 (UTC)
 * This paper gives details of the genetic component. It cites this paper, which states "The most important odorants in C. sativum were found to be Z-2-decenal, a co-eluting odour-cluster (E-2-dodecenal, E-2-dodecen-1-ol, and 1-dodecanol), beta-ionone, eugenol, and E-2-decenal." Tevildo (talk) 15:02, 8 September 2013 (UTC)


 * Thanks. Plasmic Physics (talk) 23:20, 8 September 2013 (UTC)

If evolution doesn't exist ...
Moved to the Reference_desk/Humanities

An Indisputable, Cheap DNA/Genetic Test For Jewish Ancestry/Descent
For the record, this question is not meant to be offensive to anyone. Anyway, is there any indisputable, cheap DNA/genetic test which can test someone's DNA/genes for indisputable Jewish ancestry/descent? The reason that I am asking is that my family members (my mom, my uncle, et cetera) are suspecting that my maternal grandfather might have had some Jewish ancestry, but the thing is that my maternal grandfather has already died in January 2005. I was not even a teenager when he died, and thus I was unable to ask him these types of questions myself. What is really annoying is that my maternal grandfather (who, only in my opinion, did look Jewish to some extent/degree) was an only child, and finding cousins from him from both of his parents is much harder or maybe even (almost) impossible for my case, considering that he died in and his family members live in the former U.S.S.R., while I and my family live in the United States. In addition, my family has not kept in touch with any of my maternal grandfather's cousins for decades by this point in time, so there is no guarantee of us being to find them right now. Thus, I was thinking, if possible, to convince my mom to take a cheap DNA/genetic test to see if she has any indisputable Jewish ancestry if such a test is currently available here in Orange County, California, where I and my family currently live. (For the record, in case anyone is wondering, there is zero dispute that my dad has Jewish ancestry--we know for sure that my paternal grandfather was Jewish; it's my maternal grandfather's ancestry which I and my family are not completely sure about). Thank you very much. Futurist110 (talk) 19:43, 8 September 2013 (UTC)
 * No such 'indisputable' test can possibly exist. There are no alleles unique to individuals of Jewish descent. AndyTheGrump (talk) 20:09, 8 September 2013 (UTC)
 * On the other hand, given the tendency of people to mingle their genes, a simple card that says "Yes" will be 99.9999% correct, or better. --Stephan Schulz (talk) 20:16, 8 September 2013 (UTC)
 * Is there such a cheap test with/to 99.99% accuracy? This kind/type of test would be fine with/by me. And for the record, my maternal grandmother was not Jewish (I know this for a fact, unless there is something about her which I do not currently know; and for the record, she has already passed away as well in September 2009, so I cannot ask her about her and her husband's ancestry/descent as well anymore), so any Jewish ancestry which my mother would have would almost certainly come from my maternal grandfather's side of the family. Futurist110 (talk) 20:21, 8 September 2013 (UTC)
 * Also, in regards to a "simple card," if you mean a document/record which states this, then as far as we know, no such document exists. My maternal grandfather's documents/records (or at least the ones of them which we have and which state his ethnicity/nationality) state that he is a "Russian." Of course, keep in mind that in the Soviet Union, children of mixed Jewish-Russian ethnicity could have Russian written on their documents/records (for example, my dad and his sister both have "Russian" written on their documents/records from the U.S.S.R./Russia, but my dad also has documentation/records for his father which explicitly state that his father was "Jewish"), so having his documents state that he is a "Russian" doesn't necessarily mean that he didn't have any Jewish ancestry. Also, there is the matter of the Nazis occupying the city of Oryol, where my maternal grandfather lived with his family back then, during World War II. It is possible that if my maternal grandfather and one or both of his parents (likely one of his parents, though) had some Jewish ancestry, then they would have destroyed such documentation during World War II so that the Nazis could not see and find it. As for my maternal grandfather's parents' documentation/records (the ones which survived and/or which were re-made after World War II, I mean), neither I, nor my mother, nor my uncle (mother's brother) has seen these documents/records, so we do not know if they state that either of his parents had Jewish ancestry or not. Futurist110 (talk) 21:43, 8 September 2013 (UTC)
 * As Stephan Schulz suggests, such a test would probably be unnecessary given the low degree of probability that your maternal grandfather had no Jewish ancestry. Anyway, the answer is still no - for the reason I have already explained. AndyTheGrump (talk) 20:40, 8 September 2013 (UTC)
 * If Stephan Schulz is talking about a "simple card" which states this, then my family does not have and has never seen anything of that sort which either explicitly confirms or necessarily denies Jewish ancestry for my maternal grandfather and/or for either of his parents. If we had (found/seen) something like this by now, then I would not be asking this question here right now. Futurist110 (talk) 21:43, 8 September 2013 (UTC)
 * Futurist110 my interpretation is that if you sent my your DNA and I didn't bother analysing it, but just replied yes, I would be right 99.9% of the time.-- Gilderien Chat&#124;What I've done 21:51, 8 September 2013 (UTC)
 * Do you genuinely work for some company that does this, or are you simply joking/messing with me here? I honestly can't tell. Also, for the record, my mom's DNA would need to be the one to be analyzed, since my DNA would obviously hint at Jewish ancestry through my dad and through his side of the family regardless of whether or not my mom has any Jewish ancestry. Futurist110 (talk) 22:42, 8 September 2013 (UTC)
 * Well, I was half joking, half making a point. Chances are extremely high that you, and your grand parents, have at least one Jewish ancestor. Starting with the Jewish diaspora, there are about 80 generations of gene mixing. Assuming perfect non-incest, you would have about 2^80 ancestors back then, and (2^80)-1 conception events (about 1.2 million million million million). If one of them involved a Jew,  you'd have Jewish ancestry. Of course in reality there is plenty of inbreeding (obvious because the population of the world was only around 300 million 2000 years ago), but chances that you (or I, or anyone alive who has roots in areas influenced by the Mediterranean classical cultures) have no Jewish ancestors are pretty close to zero. Note below that 23andme claims they can reliably identify Ashkenazi ancestry if one grandparent was Jewish. That's 4 candidates. Going only 200 years back, you have around 250 candidates. --Stephan Schulz (talk) 05:30, 9 September 2013 (UTC)


 * Jewish descent is reckoned through the mother's line. So, no. μηδείς (talk) 22:08, 8 September 2013 (UTC)
 * DNA does not obey Halachic law. Futurist110 is clearly asking about 'descent' in the biological sense. AndyTheGrump (talk) 22:17, 8 September 2013 (UTC)
 * Exactly. Andy is correct here. I was asking about descent in the biological sense, not according to Jewish religious law. I know that according to Jewish law, I am not Jewish, since neither of my grandmothers were Jewish, and since I did not convert. I also eat things which are not kosher, so yeah. (As a side note, I do have Israeli citizenship, in large part due to the fact that my paternal grandfather was indeed Jewish and had documents/records to prove his ancestry/ethnicity). Futurist110 (talk) 22:42, 8 September 2013 (UTC)
 * If you want to look at it that way, Jews were estimated to comprise up to 20% of the Persian Empire and 20% of the Roman Empire's population, and not just limited to the Levant. Presumably there are Saami peoples without Jewish extraction, but no guarantee. μηδείς (talk) 23:21, 8 September 2013 (UTC)
 * 23andme.com testing can identify Ashnkenazi Jewish ancestry by finding sections of your DNA which match people self-identifying as Ashkenazi. Despite statements above about 99.99% of the people having Jewish ancestry, if that is what is semi-humorously being claimed, many people show no such Ashkenazi gene sequences. See  a blog at 23andme which  says that the Ashkenazi are "genetically unique and distinct from the European population at large" .  A research paper in Genome Biology,  a refereed journal stated that 'even subjects with a single Jewish grandparent can be statistically distinguished from those without Jewish ancestry."  See also "Finding a family's Jewish ancestry."The cost of 23andme testing was $99 (US) the last time I looked. That seems "cheap" by my standards, but nothing is "indisputable," as seen when a "nonpaternity event" is shown by such genetic testing and the individual's parents say the test must be mistaken, or when a "pureblooded" southern US caucasian turns out to have 1%  Subsaharan African ancestry and can't accept it. Edison (talk) 01:42, 9 September 2013 (UTC)

Zero ohm resistor
Zero ohm resistors apparently do exist in special applications. But in the form shown in Electronic color code, added sans sources by anon, is that real or a joke? Colour me citation needed. 88.112.41.6 (talk) 20:24, 8 September 2013 (UTC)
 * We have an article on the so-called Zero-ohm link. At least the latter two of the sources cited seem to check out. AndyTheGrump (talk) 20:47, 8 September 2013 (UTC)
 * They sell them! --Stone (talk) 20:48, 8 September 2013 (UTC)


 * It's certainly not a joke.


 * There are certainly places where a zero ohm resistor makes sense. For example, my laser cutter has stepper motors that are driven by a controller module.  That module has a current limiter (so it cuts out if the motor stalls or something) - and you "program" that limit with a resistor.  The value of the resistor determines the current limit - and there is an equation that they provide to calculate what value of resistor you need for what stepper motor.   Well, for a 1.5 amp limit, the equation says that you need zero ohms.  If you buy your stepper motors from LinEngineering, you need 1.5 amps (and zero ohms) - if you buy from NanoTech, you need 2.5 amps - and a 220 ohm resistor.


 * The circuit board has two pads for you to solder the appropriate resistor into - so if you want a 1.5 amp limit, you solder in a piece of wire - otherwise you solder a resistor between those two pads. Now, you might think that you don't need actual zero ohm resistors when a simple piece of wire will do.  But consider some automatic manufacturing system - it might look at whether the customer ordered a system with 1.5 amps or one with 2.5 amps - and insert a resistor of either zero or 220 ohms.   In those circumstances, there would be enormous benefit to having the physical properties of the "zero ohm resistor" be identical to a 220 ohm resistor so that the machine can easily bend the leads, insert the resistor and solder it in place without human intervention.  In those circumstances, being able to buy a bandolier of zero ohm resistors would be tremendously useful.  Since normal resistors only cost pennies each - the extra cost of buying a zero ohm resistor instead of using a piece of wire might well be completely negligable compared to the convenience.


 * SteveBaker (talk) 22:09, 8 September 2013 (UTC)


 * Some clarifications, the name "zero ohm resistors" would indicate some superconducting device since all other conductors have resistance. To my knowledge no "zero ohm resistors" are superconducting, this would be very costly due to the low temperatures needed. In reality "zero ohm resistors" is normal wires with an insulating "resistor body". They have a non zero but low resistance that usually are negligible.
 * They are usually used when conductor paths need to cross each other on a single sided printed circuit board. The advantage over a conventional wire are that they can be handled with some automated mounting equipment that have problem mounting normal wires. The insulating resistor body also means that the wire is lifted from the circuit board so the wire does not short circuit any printed conductor traces on the surface of the circuit board. Gr8xoz (talk) 22:35, 9 September 2013 (UTC)


 * I mentioned that "not truly zero ohm" thing to a friend of mine and he said that they probably only make them in the 5% precision range...think about it! :-)  SteveBaker (talk) 23:50, 9 September 2013 (UTC)
 * *facepalm* OTOH, IIRC, the lowest color code possible is 10–2 = .01 ohms, so anything below .005 ohms would pass as zero ohm resistor, at least by engineering standards. - ¡Ouch! (hurt me / more pain) 09:34, 10 September 2013 (UTC)
 * Nope. The lowest value colour code possible is black-black-black, depicting zero-zero followed by zero noughts, i.e., 0.0 ohms, as I said.  As is traditional, where all three colours are the same, manufacturers often use a single wide band.  Hence the commom marking of a single wide black band, depicting zero ohms.  They dont use a code such as brown-black-gold on zero ohm links, depicting 0.01 ohms, as that would depict an actual 0.01 ohm resistor. And in SMT parts, zero ohm links are stamped with a single numeral "0". 121.215.54.95 (talk) 04:56, 11 September 2013 (UTC)
 * A carefull look at my Kamaya. Tyco, Arcol etc catalogs shows that they are listed under the through-hole styles and SMT physical sizes (402, 1206, etc) - but those sizes are used for 5% and 1% tolerance resistors. That is, they are not stated to be within 5% (or 1%) of nothing, they are sold as made in the standard resistor physical sizes.  The through hole types are marked with a single black band, which under the standard code means zero zero times 100 with no tolerance.  SMT types are marked with a single zero.  So, nothing humorous to think about. 1.122.160.213 (talk) 04:03, 10 September 2013 (UTC)
 * The problem is that within the standard resistor coding system, to get a zero ohm device that's not perfectly zero ohms (which we know it can't be) - you'd have to say it had a realistically small valued resistance with a 100% error tolerance in order to allow use in situations where the circuit designer demanded a zero ohm device. But then you'd fall afoul of all sorts of specificational problems - such as when NASA and the military have a blanket requirement for 1% resistor tolerances for all in-flight or mission-critical equipment.  Fortunately, I very much doubt that this is a "real" problem in practical engineering.  People generally just have a laugh and move on. SteveBaker (talk) 15:22, 10 September 2013 (UTC)
 * Well, no, not amongst electronic engineers anyway - only among the amatuers and the ignorant. You have missed my point.  Zero ohm links are not sold as having any tolerance.  You don't get to buy a "0-ohm 5%" resistor.  You get to by a "0-ohm" link in 1206 or CR37 (or whatever) resistor size.  That is, they are sold as having the same physical dimensions as standard resistors.  And standard resistors have a tolerance, which may be 5% or 1% in the same sizes.  The fact that you cannot have a perfect conductor in a physical specimen is a non-issue, as NO electronic parts sold are perfect.  1.122.160.213 (talk) 15:41, 10 September 2013 (UTC)
 * Well, the tolerance surely applies to the resistor, not to the leads leading up to it, or else you'd spoil the tolerances by cutting them shorter. :) Wnt (talk) 18:57, 11 September 2013 (UTC)