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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)[reply]

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)[reply]

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)[reply]

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)[reply]

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 | contributions) 14:08, 8 September 2013 (UTC)[reply]

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)[reply]

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)[reply]

Wouldn't sugar have an equal osmotic effect in equal concentrations?Bastardsoap (talk) 13:17, 8 September 2013 (UTC)[reply]

Perhaps it does? We add it to foods in similar ways. SteveBaker (talk) 13:42, 9 September 2013 (UTC)[reply]

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)[reply]

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)[reply]

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 | contributions) 14:17, 9 September 2013 (UTC)[reply]

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 | contributions) 07:50, 10 September 2013 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

Thanks. Plasmic Physics (talk) 23:20, 8 September 2013 (UTC)[reply]

If evolution doesn't exist ...

Moved to the Wikipedia: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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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|What I've done 21:51, 8 September 2013 (UTC)[reply]

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)[reply]

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)[reply]

Jewish descent is reckoned through the mother's line. So, no. μηδείς (talk) 22:08, 8 September 2013 (UTC)[reply]

DNA does not obey Halachic law. Futurist110 is clearly asking about 'descent' in the biological sense. AndyTheGrump (talk) 22:17, 8 September 2013 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

They sell them! [1] --Stone (talk) 20:48, 8 September 2013 (UTC)[reply]

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)[reply]

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)[reply]

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)[reply]

*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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

September 9

6d transition metals

Has anyone ever published predictions on the melting and boiling points of the 6d transition metals? Double sharp (talk) 03:50, 9 September 2013 (UTC)[reply]

From some simple searching of each article, Rutherfordium has both a predicted melting point and a predicted boiling point although I haven't checked the sources. If you include it, Lawrencium also has a predicted melting point although I don't know where the figure came from as there's no citation in our article, may be you can work out from the history. Nil Einne (talk) 17:02, 9 September 2013 (UTC)[reply]

Anything for the others? (I can imagine the region around Sg and Bh having insanely high melting and boiling points!) Double sharp (talk) 05:34, 10 September 2013 (UTC)[reply]

To be clear, for all our articles those were the only 2 that mentioned a predicted melting or boiling (at least under the search terms 'melti' and 'boil' or something similar). One more Hassium, mentioned the relatively high melting point of other group 8 elements but that a melting point had not been precisely calculated (whatever it means by that). I think pretty much every one was mentioned as a predicted solid which isn't surprising but does suggest there's some estimation of the melting point even if it's simply that it's higher than room temperature. (I have no idea what's published outside our articles, I would guess the sources used in our articles would be a start.) Nil Einne (talk) 13:17, 11 September 2013 (UTC)[reply]

I had a look at the paper they were citing (I should know, I wrote that part!) and they only say that the elements are solids. That's not a terribly interesting estimate, especially for these transition metals, for which I can think of no reason why they should not be solid at STP! Cn would interest me more. Except that I've seen predictions for it being solid, liquid, or gaseous at STP (and never with associated melting and boiling points!) Double sharp (talk) 11:57, 13 September 2013 (UTC)[reply]

Stability of Technetium

Just a quick question: exactly why is Technetium radioactive despite its low atomic number? Based on a search I did in the Reference desk, our article on it used to have a section which explained why, but for some reason no longer does so. Could someone explain or link to an article/page which explains why Technetium is radioactive? Narutolovehinata5 ^tccsdnew 11:33, 9 September 2013 (UTC)[reply]

Isotopes of technetium#Stability of technetium isotopes, Mattauch isobar rule. Double sharp (talk) 12:09, 9 September 2013 (UTC)[reply]

But ⁹⁷Tc⁴³⁺ (fully ionized) should be stable as ⁹⁷Tc can only decay via electron capture. Double sharp (talk) 12:12, 9 September 2013 (UTC)[reply]

For a more detailed look at it, see this. Double sharp (talk) 12:35, 9 September 2013 (UTC)[reply]

Well, technically every element from niobium onwards is susceptible to at least spontaneous fission (see List of nuclides), so maybe that answers your question? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 19:33, 12 September 2013 (UTC)[reply]

Medication and the angle of the head

I've noticed that some people (no idea if it's common or not) when taking medication pop the pill in their mouth, take a sip of liquid and then tilt their head backwards. I assume that this is a belief that the pill will be easier to swallow. Is there any reason why tilting the head backwards would assist in taking pills? CambridgeBayWeather (talk) 12:47, 9 September 2013 (UTC)[reply]

Logic suggests that it provides a steeper slope off the tongue, and hence the pill would go down more easily 217.158.236.14 (talk) 12:51, 9 September 2013 (UTC)[reply]

This is entirely original research (well, not quite - I was given this tip by a friend when I had to take some large tablets), but I think the idea is that you want the medication to be swallowed with the liquid, not after the liquid. Tipping the head back makes a tablet sink to the back of the mouth, where it is swallowed at the same time as the bulk of the liquid. Conversely, for capsules, tipping the head forwards means they float to the back of the mouth with a similar effect. Since my friend gave me the tip I've always done it this way (tablets back, capsules forward) and found it significantly easier. I have observed that far fewer people use the head forwards trick with capsules than the head back trick with tablets - perhaps because it is slightly counterintuitive. Equisetum (talk | contributions) 14:06, 9 September 2013 (UTC)[reply]

More ObPersonal, based on experimenting with my cup of coffee and lunchtime baguette immediately on reading this question.

I, and I assume many if not most people, find it somewhat easier to swallow when my head is tilted back rather than in a normal sitting posture or looking downwards (e.g. in a keyboard-wards direction); this seems to be related to relative compression of the tongue and throat in these postures.

Pills/capsules are generally harder and sometimes larger and more angular than typical (masticated) food boluses (boli?) or particles that are swallowed, and combined with one's heightened consciousness in swallowing pills (as opposed to the semi-unconscious actions of normal feeding) are in any case harder than normal to swallow: tilting the head back therefore helps to counteract this added difficulty. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 14:49, 9 September 2013 (UTC)[reply]

Thanks. I find, to my annoyance, that I am now doing it as well. CambridgeBayWeather (talk) 00:10, 10 September 2013 (UTC)[reply]

On rare occasions I find I have not taken enough water for a large or set of pills, and rather than gag while pouring more water, I will tilt my head back and swallow. This happened only last week taking a C supplement. I don't think it's necessary with small pills or sufficient water, I very rarely find I need to do it. μηδείς (talk) 00:26, 10 September 2013 (UTC)[reply]

Unless you're using a straw, you're pretty much compelled to tilt your head backward when drinking something. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:28, 10 September 2013 (UTC)[reply]

That's blatently, obviously, CLEARLY false! Do you even think a tiny bit before answering questions here?

It depends entirely on the vessel you're drinking from. Suppose we take an idealized situation, a hemispherical bowl that's utterly full of some liquid. When you tilt the bowl in any direction, by even the tiniest amount - liquid spills out. So long as you can place one edge of the bowl to your lips and tilt it even a tiny fraction - you can easily drink without tilting your head. The same is true of a cylindrical container - which has most normal drinking vessels covered.

Moreover, by creating some suction and using the flexibility of one's lips, it's easily possible to drink from a flat liquid surface without even tilting either head or container.

Only if the container is very small - and far from full, might you may be unable to tilt it sufficiently to get liquid out without the opposite rim hitting your face and then you'll have to tilt your head backwards - or if the container flares outwards (like a conical flask) then you might have to tilt your head forwards to avoid your chin hitting the bottom part of the container. But for something like a glass, it's very easy to drink without tilting your head so long as it's reasonably full.

Just try something once before making such ridiculous pronouncements. SteveBaker (talk) 15:02, 10 September 2013 (UTC)[reply]

Just take your personal attacks and stick 'em where the moonshine don't shine. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:37, 10 September 2013 (UTC)[reply]

And when you're finished with that task, go to google images and search [chugging], and then send notes to all those folks tilting their heads back and inform them that they're drinking the wrong way. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:53, 10 September 2013 (UTC)[reply]

Well, if you search for "chugging" I'd expect that - it means "drinking rapidly" - and to do that, you need to tip your head back. But that's not what you said. You said: "...pretty much compelled to tilt your head backward when drinking..." - so if I search Google images for pictures using the more reasonable search term "drinking" - then I see a good mix of people tilting their heads back and not tilting their heads back. So, it doesn't appear that people are in any way "compelled" to do that - and I'm sure you now realize that which is why you try to deflect the criticism by searching other terms to find one that might somehow support your ridiculous claim. Indeed if you look closely at the "drinking" photos where people are tilting their heads back while drinking, you'll see that most (but admittedly not all) are drinking from bottles and cans and other narrow-mouthed containers - or are emptying the last drops from something - exactly as I said above. The ones who are merely taking a mouthful of water (as one would to swallow a pill) are much less likely to be tipping their heads back. So what you said was incorrect. You can't have even stopped for a moment to think about what happens when someone drinks before you answered because even a 10 second test of your claim shows that it's bullshit. So just man-up and admit that you were wrong...it happens all the time to all of us here - there is no shame in it. SteveBaker (talk) 14:03, 11 September 2013 (UTC)[reply]

Surely SB was being ironic? His comment must have been a joke. No sane person uses five apostrophes around allcaps. μηδείς (talk) 18:04, 10 September 2013 (UTC)[reply]

Let's hope so, for his sake. And I must remind you that we don't do medical diagnoses here. If there are concerns about his mental health, he needs to see an appropriate professional. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:06, 10 September 2013 (UTC)[reply]

Here's a little something I found by googling the subject.[2] It's evident that tilting the head back is pretty common. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:00, 10 September 2013 (UTC)[reply]

So if that link you provided is correct then what I originally thought was right. Look at #7 which says don't tilt your head back. By the way I use #10 and have done since I was a kid. It ensures that you don't get to taste the pill which is what happens if you put it in your mouth first. CambridgeBayWeather (talk) 00:30, 11 September 2013 (UTC)[reply]

So I think we have an answer now. It's evident that some people do tilt their heads back when swallowing pills - and other don't. It's neither necessary to do that - nor advised - and some advice says not to because there is some scant evidence that it may actually make the "gag response" worse. SteveBaker (talk) 14:03, 11 September 2013 (UTC)[reply]

wasp 2

What time of the year do queen wasps hibernate in the UK? I had one in my house today flying around and now and it seems to have gone somewhere and hidden. Would this be the right time of year for such behavior? I had one last year as well which emerged in May after sleeping the winter in a cupboard, could it be the same one? Waspgirl03 (talk) 15:03, 9 September 2013 (UTC)[reply]

Queen wasps normally come out of hibernation in the middle of April. However, due to abnormal temperatures in the UK in 2012, wasps in 2013 came out of hibernation later than normal. Up until July population rates of wasps were below normal however the UK is now being plagued by wasps due to the long hibernation.Jenn859 (talk) 20:19, 11 September 2013 (UTC) ^[1] ^[2] ^[3][reply]

Three-masted merchantman tonnage discrepancy

According to this painting by Samuel Walters, the Thames, of 454 tons, was built in London in 1829 for the West India trade. Originally owned by Hibberts of London, she later passed into the ownership of Thompson of London and was in service for over thirty years.

Section 1 in this information about the convict ship Thames gives the tonnage as 366.

I suspect both links are about the same ship. Are they? If they are about the same ship, what, if anything, is the difference between the term tons and tonnage? Why is the apparently same ship given a different value (454 and 366 respectively) for something I suspect should be the same?

--Senra (talk) 16:24, 9 September 2013 (UTC)[reply]

See Ship measurements. The tonnage of a ship is a measure of the _volume_ (not weight) of cargo it can carry. Describing a ship as "450 tons" might be expressing its maximum cargo volume using a different metric, or it might be expressing its maximum cargo weight, _or_ it might be expressing the displacement of the ship. The numbers you give (without any more precise definition) aren't inconsistent, and probably do refer to the same ship. Tevildo (talk) 17:33, 9 September 2013 (UTC)[reply]

It's possible that the ship was refitted for these different kinds of service - that could easily affect the tonnage. Of course there are many measures of tonnage too. Read Displacement (ship) for a few possibilities. SteveBaker (talk) 17:34, 9 September 2013 (UTC)[reply]

Thank you both. Useful input. Yes indeed. She could have been refitted between the two dates. The first link suggests the painting was completed in 1839, ten years after she was built. The second link indicates a voyage (the maiden voyage?) occurred between London and Van Diemen's Land (now Tasmania) between 31 July 1829 and 21 November 1829. --Senra (talk) 18:52, 9 September 2013 (UTC)[reply]

Religious people and Alzheimer's disease

Is there a correlation between actively religious people (people who attend weekly religious services and mingle with fellow congregants) and occurrence of Alzheimer's disease? 164.107.103.9 (talk) 20:54, 9 September 2013 (UTC)[reply]

Our article says: "At present, there is no definitive evidence to support that any particular measure is effective in preventing AD" - so going to church doesn't prevent the disease. It also says "People who engage in intellectual activities such as reading, playing board games, completing crossword puzzles, playing musical instruments, or regular social interaction show a reduced risk for Alzheimer's disease." - so if attending religious services counts as "regular social interaction" - then maybe, but it's not specifically being religious that does it - doing intellectually difficult things in a social environment is good - so you could join a musical group, take a degree course in particle physics or play Dungeons and Dragons (heretical!) and get the same kinds of benefits. SteveBaker (talk) 21:06, 9 September 2013 (UTC)[reply]

I once heard a story about the correlation between Alzheimer's disease and the occurrence of it in American nuns. 164.107.103.9 (talk) 21:20, 9 September 2013 (UTC)[reply]

I would also add that physical activity and education may also contribute to Alzheimer's. It's not just intellectual stimulation. So, going to church - if a person enjoys the experience of going to church, meeting new people, and thinking about thought-provoking biblical topics and verses - may not be so bad, after all. 164.107.103.9 (talk) 21:45, 9 September 2013 (UTC)[reply]

You may be thinking of the famous Nun Study, which was a study of which nuns developed Alzheimer's, rather than a finding that nuns are generally susceptible. You may find the article enlightening. Someguy1221 (talk) 21:38, 9 September 2013 (UTC)[reply]

The only relevant academic study I could find is PMID 17470754, which found that the rate of cognitive decline in Alzheimer's patients tends to be slower if they are high in religiosity or spirituality. Looie496 (talk) 23:01, 9 September 2013 (UTC)[reply]

Similar to Looie496 source, there's PMID 20088813, which also found a slower rate of decline in Alzheimer's patients with high religiosity. Unfortunately, both studies deal with patients who have already been diagnosed with Alzheimer's. They don't address the question of whether religiosity is correlated (positively or negatively) with an Alzheimer's diagnosis in the first place. (The latter study is much more difficult to do.)

Boyle et al. have carried out a number of what appear to be good-quality prospective studies that found a correlation between between greater "purpose in life" and significantly reduced risk of developing Alzheimer's (PMID 20194831), as well as greater resistance to the effects of physical, pathological changes in the brain (PMID 22566582) among individuals who do have the disease. Note that "purpose in life" is not the same thing as "religiosity" or "theism", however. (There's a good summary of these types of tests at [3].) Boiled down, there seems to be less cognitive decline in individuals who feel useful, who feel their lives have meaning, and who feel that they still have worthwhile things to do. Commenting purely out of my own opinions, I can see how spirituality or religiosity might be avenues that encourage those types of feelings, but would be far from the only ones. TenOfAllTrades(talk) 15:00, 10 September 2013 (UTC)[reply]

Stoichiometry for explosion of Nitroguanidine

I recently expanded Nitroguanidine, a popular explosive that is apparently being introduced into air bags. Anyone have a suggestion for a balanced equation for the gas forming reaction?

(NH₂)₂CNNO₂ → ??? CO₂, NH₃, N₂...

Thanks, --Smokefoot (talk) 22:51, 9 September 2013 (UTC)[reply]

That would depend on whether the N-N bond cleaves first in the nitroaminodiyl group. If it does, then you'd not get dinitrogen, but nitrogen dioxide which nitric oxide and oxygen which then oxidises the guanidinyl radical to carbon dioxide and ammonia. Plasmic Physics (talk) 00:49, 10 September 2013 (UTC)[reply]

[4] — Preceding unsigned comment added by 128.226.130.145 (talk) 16:59, 10 September 2013 (UTC)[reply]

why do knots weaken ropes?

Our article, Rope_splicing, says "Splices are preferred to knotted rope, since while a knot typically reduces the strength by 20-40%,[1] a splice is capable of attaining a rope's full strength." Why is it that a knot reduces the strength of the rope to such a significant degree? 178.48.114.143 (talk) 22:57, 9 September 2013 (UTC)[reply]

My guess (and it's only a guess) is that when a large diameter rope goes around a tight (compared to the diameter) curve - as it does in a knot - the fibers on the outside of the curve are in tension and the fibers on the inside are in compression. When you pull on the knot, all of the force goes on the outside fibers and none whatever on the inside ones. It makes sense that with all of the force being applied to only a few of the fibers will cause them to break before the entire rope could have done if it was straight. As a few fibers snap, the tension transfers to the layer beneath - they get all of the force - so they break. And so on, and so on until the entire rope snaps. A classic cascade failure.

Think of it like the trick of tearing a phone book in half. You can't possibly do it when you try to rip the whole thing - the trick is to bend the book into a U-shape and then you're effectively only tearing one page at a time.

But this is just a guess - I'm sure someone here will come along with an "official" answer. SteveBaker (talk) 23:45, 9 September 2013 (UTC)[reply]

So is there some special knot that does not require untwisting or braiding/splicing per that article, and instead, while treating each rope as a single strand, 'knots' them together end-to-end but without very tight curves? 178.48.114.143 (talk) 00:18, 10 September 2013 (UTC)[reply]

Very strong bends include the Carrick bend, the Flemish bend and the blood knot. Tight curves are not the problem, it's about where the curves are, and how they are loaded. E.g. the blood knot has very tight curves, but they are not loaded much, and it is one of the strongest known bends. Hitches can generally be stronger than bends. The "dressing" of the knot also affects its strength. SemanticMantis (talk) 15:55, 10 September 2013 (UTC)[reply]

Knot#Strength has some details and cites. And bend knot has lots of styles for joining ropes end-to-end, including some especially suited for single-strand (though lots for multistrand that retain strength. DMacks (talk) 05:32, 10 September 2013 (UTC)[reply]

In addition to the above, I've noticed that certain types of knots become hard and brittle before the remainder of the rope. I have the think the uneven stresses on the knots cause this result. StuRat (talk) 08:53, 10 September 2013 (UTC)[reply]

The weakening effect of knots in ropes is well known, but the details are still poorly understood. Steve's basic guess above covers it generally: it is all about the non-uniform stresses and strains introduced by knot geometry. However, translating that into specific mechanisms is quite difficult, and different mechanisms are involved for different knot types and rope types. See e.g. this well-referenced blog post [5]. Take special note of the several intuitive descriptions that that author rejects. This science article has some pretty good analysis, but is limited to monofilament line [6]. Any given cord is strongest under uniform tension. Note also that the failure mode of knots will depend on the rope type. Sheathed climbing rope will break differently than 3-ply twisted rope, which will break differently than monofilament. The US coast guard takes a more empirical approach, and simply loads and breaks several ropes with knots. They have a classic study on the topiuc, but right now I cannot find it, only references to it. Finally, a great resource for all-things-knot is the International Guild of Knot Tyers, igkt.net. One of their threads discusses the issue here [7]. SemanticMantis (talk) 15:48, 10 September 2013 (UTC)[reply]

September 10

Physics Practise Exam Question - Can't Get it!

I'm currently doing a past paper for a physics exam. Would anyone be able to enlighten me on how to answer this!? Thanks guys.

Advertising for a plasma screen television that operates on a 240V electricity supply has a page of fine print which is reproduced below.

• Operating cost for electricity consumption = $30.00 per year • cost based on 2000 hours of operation • cost based on electricity charged at $0.15 per kWh

(a) What is the power consumption of this television? (b) Given your answer find the current drawn. 220.233.20.37 (talk) 03:13, 10 September 2013 (UTC)[reply]

We don't do homework for you (doing sample exams is a form of homework - pointless if we do it for you), but we help if you are stuck. As you have provided no evidence that you have made a start but got stuck, I'll give only an outline. As you have pricing data, you can work out the energy in kilowatt-hours consumed in 2000 hours of operation. You can then convert the kilowatt-hours in 2000 hours to watt-seconds in one second. Why one second? Your knowlege of SI should tell you that. The second part is a trivial relationship of power, voltage, and current. Ignore power factor for a question at this level. [0.417]1.122.160.213 (talk) 03:43, 10 September 2013 (UTC)[reply]

... unless you are specifically asked to work in SI units (joules), you can stay with hours. There's no need to make things more complicated by working in seconds. You need to find out the total number of kWh used over a year, then just divide by the number of hours to give an answer in kW. You could convert this to watts, which is how most most power consumptions are expressed. For (b) you just need an equation connecting power, current and voltage (as mentioned above). You probably should know this equation, so I won't give it here. Dbfirs 08:01, 10 September 2013 (UTC)[reply]

Of course, this being a advertising statement, the result will be a lower limit ("will under no circumstances use less than..." ;-). --Stephan Schulz (talk) 08:43, 10 September 2013 (UTC)[reply]

Oh, yes, the calculation gives the average current. In practice there will be a higher current at switch-on, and, as mentioned by 1.122.160.213, there are the complications of power-factor, but at this level is it safe to assume a purely resistive load (or corrected power factor), and that the average value of RMS current is being asked for. I hope the OP has worked out the answer by now. Dbfirs 16:51, 10 September 2013 (UTC)[reply]

Astable oscillator/multivibrator with logic gates

Hello,

How are astable square-wave oscillators built using NOT gates (or other gates configured to act as NOT gates) typically "initialized" and powered? I'm aware that, in practice, the ICs containing the gates require power, but is this enough to start the oscillator going? Is its initial output state (high or low) random? It seems that, if for no other reason, there should be source and ground connections to set the logic levels.

Some examples:

Diagram (located under the heading "NAND Gate Astable Multivibrators" on this page)
Part (b) of this figure (located on this page)

Any information on this subject would be appreciated! 142.20.133.199 (talk) 14:08, 10 September 2013 (UTC)[reply]

The resistors bias the gates into the active region. While logic gates are designed to give an all or nothing output, that is, an output that is clearly logic 0 or ligic 1, there is always, unless there is internal positive feedback to give a snap (termed "schmitt") action, where the gate functions as a more or less linear amplifier. Since the capacitor(s) or crystals return the output to the input so as to reinforce any change (positive feedback), any small change that arises, whether form thermal noise, supply rail noise, or ranmp up upon switch-on, will be self amplified until the output is driven hard into clipping. The capacitor(s) or crystal then charges to the clipped voltage. This stops the resinforcement, upon which there is gate input change in the other direction (toward the bias point), which snaps through again hard over in the other polarity. And so it goes on....

Because amplification is the key to getting oscillation started, lowering the resistors until the linear loop gain is less than unity will result in no oscillation if the power supply ramps up slowly upon switch-on, although if the circuit is then "shocked" into limitting (by say momentarily shorting the output to ground), oscillation may then start. The same applies to the traditional 2-transistor, 2-FET, or twin triode astable multivibrator oscillator. Biasing to give at least a small linear gain is key to reliable starting. Powering up is not alone sufficient for oscillation. For slow power up (meaning theh power supply ramps up slowly compared to teh oscillator capacitor(s), startup is somewhat random due to its origin in noise. If the power supply is snapped on rapidly, the oscillator will always start in the same output condition (logic 0 or 1), but which it is depends on the design of the gates and production variation. This is because all practical gates will pull more strongly in one direction or the other.

1.122.160.213 (talk) 15:25, 10 September 2013 (UTC)[reply]

The idea behind these devices is to create a kind of logical paradox - so a NOT gate could (theoretically) have it's output connected to it's input - so the NOT gate is asserting that the output is NOT the input - and the bit of wire going from output to input says that output and input are identical. Mathematically, you have a paradox.

The result should be that the gate continually changes it's mind about what the output should be and because the speed of the logic gate is finite, it ought to oscillate at a frequency that's the reciprocal of the delay through the gate.

The practical problem is that logic devices are not the perfect 0/1 binary devices we kinda imagine them to be - so in practice, the circuit settles down to some voltage between zero and three volts (or whatever the logic level for '1' is) and doesn't oscillate at all.

So practical multivibrators are all about reinforcing that essential paradox by using multiple gates and that kind of thing. Getting the device started is another ikky problem since it's essentially indeterminate which state it would initially power up into. Hence you need a solid way to initialize the device to a known state before it starts vibrating. Then of course, you usually want control over how fast the device oscillates - and that drags you back into ikky analog territory. For those reasons, it's hard to view these devices as strictly digital contraptions - and you have to fall back to understanding them as strictly analog devices. SteveBaker (talk) 15:46, 10 September 2013 (UTC)[reply]

Thank you both for your comments. Do you think another method of generating a square wave (e.g., an appropriately configured 555 timer) might be a better choice? From what you've said, it seems like using the logic gate approach introduces a number of factors that aren't easily accounted for. 142.20.133.199 (talk) 19:18, 10 September 2013 (UTC)[reply]

What is "better" depends on the circumstances. A 555 timer will deliver a cleaner better defined squarewave and its frequency is more easily predicted by calculation based on the R and C values. But the one- and two gate circuits will often be quite good enough. A Mercedes is a better car than a small Toyota, but if what you do is deliver pizzas, what are you going to buy? A given circuit design might have, after all other functions have been taken care of, have one or two NAND, NOR, or invertor gates, or even a flipflop that can be wired to perform an invertor function, left over. In such cases it will be cheaper to use the left over gates to make the clock oscillator, and not use a 555. As a practicing electronic engineer, I can tell you that success in large scale and even medium scale manufacturing involves shaving a few cents here and there wherever you can, without affecting performance too much. Another factor in reducing cost is to not have too many different parts in your inventory. If you design in a part, say a 555, and yours is the only one of many products your company makes that uses a 555, you may loose friends in the procurement section.

There are many occasions that require better frequency stability and accuracy than what astable multivibrators (whether gates or 555's) can provide, but the stability and accuracy required does not justify the cost of a crystal. In such cases an oscillator tuned by an inductor-capacitor combination will do the job. One can make a very good LC oscillator in the Colpitts configuration using a NAND, NOR, or invertor gate.

In a factory production environment, adjustments are avoided like the plague. Adjusting adjustments, whether done by a human or by some robotic machine, are expensive. Often crystal oscillators are used for that reason alone. But if you are building a one-off for a lab special or a home project, it may be no big deal to use a crummy 2-gate oscillator with a 30% frequency error on first switch-on, and adjust it as necessary.

An advantage of LC oscillators over astable multivibrators is that they are quite immune to interference. I can remember a timing oscillator based on a two-gate multivibrator that worked perfectly on the bench. But when installed it ran erratically at around 2 to 3 times the correct frequency, as hash from nearby DC electric motors made the gates "flip" early in each cycle. Changing to a colpitts LC circuit solved the problem completely. Never use a 2-gate astable oscillator in a switch mode power amplifier for the same reason, unless you can thoroughly shield it and thoroughly test a lot of prototypes. The switching spikes from the power stage are likely to couple into the oscillator and drive it nuts.

121.215.54.95 (talk) 00:41, 11 September 2013 (UTC)[reply]

Those are good points to consider (also, I've never previously encountered a Colpitts oscillator, so I'll look into that). This is for a one-off circuit, so thankfully economic considerations aren't a priority, although your point about using leftover gates rather than adding another IC makes sense even in that context. I think I'll try the oscillator based on logic gates, see if it's sufficient for my application, and then perhaps try a circuit using a 555 timer or a Colpitts oscillator if not. Thanks for your help! 142.20.133.199 (talk) 16:02, 11 September 2013 (UTC)[reply]

See Colpitts oscillator (and electronic oscillator) for our relevant articles. Tevildo (talk) 21:29, 11 September 2013 (UTC)[reply]

ISOLATION OF CELL COMPONENTS .

How are components of cell isolated ??? are there some techniques to isolate components of cell ??? what is the method to isolate cell ?? kindly reply me soon as possible ...(139.190.155.177 (talk) 14:25, 10 September 2013 (UTC))[reply]

This is actually an enormous question. The short version is—yes, there are techniques to isolate many different components and structures from many different types of cells. Google and PubMed are your friends here. Search using phrases like isolation of mitochondria or protocol for isolation of nuclei for your chosen organelles and components.

Beyond that, the Wikipedia Reference Desk isn't here to do your homework for you, but we will often try to help you if you get stuck with specific questions (and you show us how you've tried to answer them yourself). TenOfAllTrades(talk) 15:07, 10 September 2013 (UTC)[reply]

(ec) We don't even know what kind of cell you're talking about here! A prison cell? An electrochemical cell - like in a battery? A plant or animal cell? An Excel spreadsheet cell? A mobile phone reception area? A part of a spy network? All of those things might reasonably need to be "isolated". The best guess might be a plant/animal cell - but I'm far from sure that's what we're being asked here. SteveBaker (talk) 15:33, 10 September 2013 (UTC)[reply]

Oops. That's a good point, Steve—I'm looking at the question through the lens of my own current work. It could just as easily be a question about an electrochemical cell, couldn't it? TenOfAllTrades(talk) 20:54, 10 September 2013 (UTC)[reply]

We are not talking about space, but something emerged from no existence and exist that the space

We are not talking about space, but something emerged from no existence and exist that the space ? Even if nothing is opposite thing, why the two found why such a system exists? — Preceding unsigned comment added by 37.238.82.114 (talk) 20:50, 10 September 2013 (UTC) [reply]

I understand that you are probably not a native speaker of English, but this question is very hard to understand. Will you put a little more effort into explaining what you want us to answer? --Trovatore (talk) 20:56, 10 September 2013 (UTC)[reply]

That's probably the same guy from Baghdad who asked "Why did not remain nothing nothing?" on September 6, and possibly another, similar question. In short, he's seeking a logical explanation for why or how the Big Bang would have occurred. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:06, 10 September 2013 (UTC)[reply]

Using Google Translate, translate back to Arabic:

نحن لا نتحدث عن الفضاء، ولكن شيئا ظهر من لا وجود له وجود أن الفضاء؟ حتى إذا ليس هناك ما هو الشيء المعاكس، لماذا وجدت اثنين من سبب وجود مثل هذا النظام؟

Click on some of the words to choose an alternative translation back to Arabic that looks a bit better, e.g. this one:

نحن لا نتحدث عن الفضاء، ولكن لا شيء ظهر من غير موجودة، وهناك تلك المساحة؟

حتى إذا لم تكن هناك ما هو الأمر المعاكس، لماذا وجدت مدة من لماذا لا يوجد مثل هذا النظام؟

Then translate this back to English and you then click on the words that don't make sense to get alternative translations, e.g. I got this:

"We're not talking about space, but nothing emerged from the non-existent, and there is that space? Even if there were not, the opposite is something, why any duration of the Why is there no such a system?"

Count Iblis (talk) 00:14, 11 September 2013 (UTC)[reply]

I’m not convinced there could even be such a thing as absolute “nothing”. And if there really IS such a thing as “nothing” then even God couldn’t exist there. Answer the question “Where did god exists before there was "somewhere"?” The answer is "Nowhere". Nothing can “exist” and “not exist” at the same time, it’s the law of non contradiction. Positing some "supernatural" realm where God could exist is purely ad hoc reasoning, and it's not "nothing". Vespine (talk) 03:41, 11 September 2013 (UTC)[reply]

The short answer is that nobody knows. — kwami (talk) 05:40, 11 September 2013 (UTC)[reply]

I'm not 100% sure what exactly you're asking, but there are some articles that might be related (and might exist on other language forms of Wikipedia, which might serve you better). Our article Ex nihlo goes into detail about various positions related to "creation from nothing". Parmenides may be of interest to you, as might Nothing comes from nothing. On a more physics related side, Zero-energy universe, Vacuum genesis, and Hartle–Hawking state; relating to the last one, [8].Phoenixia1177 (talk) 08:14, 11 September 2013 (UTC)[reply]

Asking what happened before the Big Bang is like asking what land lies above the horizon. Asking where the Big Bang came from is like asking what is beyond the horizon. The horizon - like the singularity of the Big Bang - is a limit on what we can see from our perspective. From the first microsecond to the next is the same as from the first billion years to the next billion. Wnt (talk) 16:32, 11 September 2013 (UTC)[reply]

Why do you love God if he does not love you and you're a nobody for him

we do notanswer requests for personal opinions

The following discussion has been closed. Please do not modify it.

Why do you love God if he does not love you and you're a nobody for him Why live then account you on life and your situation and you did not ask him to create you, He does not need you and you do not need him before create you. So What?Why?37.238.93.248 (talk) 21:09, 10 September 2013 (UTC)[reply]

Your basic premise runs counter to standard theology. God loves everyone, and He does "need" us, which is why we were created. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:14, 10 September 2013 (UTC)[reply]

Requests for people's personal reasoning for their relationship with their God do not belong at the reference desks. μηδείς (talk) 21:18, 10 September 2013 (UTC)[reply]

It does belong at the Humanities desk, but the people reading this one won't be as likely to know. There is scarcely an argument in relation to God that hasn't been proposed, named, rebutted, and most likely fought over at some point in history. Wnt (talk) 21:23, 11 September 2013 (UTC)[reply]

That we live in a computer screen on the face likening or simulator or why we discovery if that was all you discover is the information illustrated in space , So How crash this screen that was all of this illusion.

That we live in a computer screen on the face likening or simulator or why we discovery if that was all you discover is the information illustrated in space , So How crash this screen that was all of this illusion. Controlled by the laws of the invisible So, Why try to discover the image from nothing embodied in a space — Preceding unsigned comment added by 37.238.93.248 (talk) 21:27, 10 September 2013 (UTC)[reply]

Please clarify your question. 163.202.48.126 (talk) 07:23, 11 September 2013 (UTC)[reply]

It sounds like you might be talking about the Simulation hypothesis, or something related to it. Your question makes me think of the following related topics as well: Allegory of the Cave, Brain in a vat, Cogito ergo sum, René Descartes, and Gnosticism- if this is a relation, perhaps taking a look through them could help to clarify what you are asking:-) The phrase, "information illustrated in space" brings to mind, Holographic principle.Phoenixia1177 (talk) 08:22, 11 September 2013 (UTC)[reply]

Yes, and in layman's terms, perhaps he is thinking of The Matrix. StuRat (talk) 13:04, 11 September 2013 (UTC)[reply]

My guess is by vote. Those running the simulation probably recognize they're doing something ethically dodgy, but if the denizens get together and make a clear statement calling for its discontinuation the ethics committee might get off their ass and do something about it. It occurs to me that with society racing toward a Singularity (the absolute disparity between rich and poor) this might be an interesting political tactic - probably more legal though perhaps less effective than ordinary biowar. Wnt (talk) 18:54, 11 September 2013 (UTC)[reply]

I think by "screen" they are referring to a theory I saw touched upon briefly during a space/physics documentary of sorts (I watch a lot of those.) Basically the theory was that all of reality was just a projection... though it didn't elaborate much further on that. Sounds a little more farfetched than the theories presented on the simulation hypothesis page (or maybe it's on there? I didn't have time to read through it all.) As for how the screen could "crash" and the illusion be lost, I don't think anyone can really know. --.Yellow1996.^(ЬMИED¡) 03:26, 12 September 2013 (UTC)[reply]

That sounds a lot like the Holographic principle, see the second paragraph of the lede there. I guess this, see the 2nd section, could be a "screen crash", kind of reminds me of a BSOD:-)Phoenixia1177 (talk) 04:53, 12 September 2013 (UTC)[reply]

Hydrolysis of PET with 30% ammonia

Some month ago I poured a few centiliters of 30% concentrated ammonia in an empty coca-cola bottle. I didn't know that concentrated ammonia hydrolize PET, so after a few days the bottle turned opaque and a white powder was formed. I verified that the white precipitate was terephthalic acid (not ammonium terephthalate) and I tried to get more using 36% H₂SO₄ as the hydrating agent. I waited for more than a week buth the PET is still intact. So my question is: why does ammonia corrode the PET, being a weak base, and the sulfuric acid doesn't although is a strong (and more concentrated) acid? Bokuwa (talk) 22:43, 10 September 2013 (UTC)[reply]

I'm not sure, but perhaps you're getting sulfonation reactions instead of hydrolysis? Also, sulfuric acid is a very efficient dehydrating agent, so maybe the water is not even getting to the PET in the first place because the acid is tying it up. FWiW 24.23.196.85 (talk) 06:34, 11 September 2013 (UTC)[reply]

I don't think so: the acid is mixed with 64% of wather by weight. This means that there are 40 mol of wather per 3,63 mol of sulfuric acid. I read the article about that acid and there isn't any explanation about the dehydrating proprieties of H₂SO₄, so I have no certainty but I think that in these proportion the acid can't act as dehydrating by itself, and it might occur hydration reactions. Furthermore, my first decomposition reaction of PET was made with 94% sulfuric acid; did I dehydrate that compound? And what did it become?

I haven't tried other concentrated acids yet, but I will, to verify all the hypothesis. Thanks for answering :D Bokuwa (talk) 19:31, 11 September 2013 (UTC)[reply]

September 11

Arrhenius base

To be defined as an Arrhenius base, does the molecule have to release hydroxide ions, or can it rather generate hydroxide ions?

Compare elemental sodium: 2 Na + 2 H₂O → 2 Na⁺ + 2 HO⁻ + H₂,
With sodium hydroxide: NaOH (s) → Na⁺ (aq) + HO⁻ (aq). Plasmic Physics (talk) 01:46, 11 September 2013 (UTC)[reply]

See Acid-base reaction: sodium metal would be defined as a Bronsted-Lowry base, but not an Arrhenius base. 24.23.196.85 (talk) 06:38, 11 September 2013 (UTC)[reply]

Really? I've never heard of sodium accepting a proton to become NaH⁺ under ordinary conditions. What about NH⁻
₂?

NH⁻
₂ + H
₂O → NH
₃ + HO⁻

Even though the amide accepts a proton, it also generates hydroxide; is just a BL base or is it also an A base? Plasmic Physics (talk) 07:08, 11 September 2013 (UTC)[reply]

It is also an Arrhenius base. The definition of an Arrhenius base is that it generates excess OH- ions in water solution. It can either generate those ions by adding them directly (i.e. NaOH) or by reacting with the water to extract a hydrogen ion from it, leaving the OH behind (i.e. NH3). What makes something an Arrehenius base is the generation of excess OH- when added to water. Or, if you prefer, if a water-based solution of it has a pH greater than 7 (which is functionally the same). --Jayron32 14:43, 11 September 2013 (UTC)[reply]

Once this all gets sorted out here, please make sure Acid-base reaction#Arrhenius definition and Acid#Arrhenius acids match it. One of those defines it as "dissociates in water to form hydroxide" and the other as "decreases the concentration of hydronium ions when dissolved in water". The first of those sounds restricted to only those that themselves contain hydroxide rather than also possibly causing water to dissociate to give it by some other means. This issue really needs to be resolved via high-quality cited references. Some leads (thanks IUPAC!) might be: Arrhenius, S., J. Am. Chem. Soc. XXXIV, 4 (1912)Bates, R.G. and Guggenheim, E.A., Pure Appl. Chem., 1, 163 (1960) DMacks (talk) 15:03, 11 September 2013 (UTC)[reply]

Evaporation before formation

If the time stops around event horizon, a black hole to us would never collapse into a singularity; not only, if we accept the Hawking's radiation a black hole would evaporate in a FINITE TIME, even to us; so any object falling into a black hole would evaporate with the black hole itself without ever crossing the event horizon; even if there were primordial black hole with a singularity would be for the same reason impossible for an infalling oblject (or people) cross the event horizon. So, the final point is: it is impossible to cross event horizon, because the infalling observer observer would evaporate before crossing it (as part of black hole). This would mean that is impossible, even for the infalling observer, to surpass the event horizon? 95.239.192.130 (talk) 11:29, 11 September 2013 (UTC)[reply]

From whose perspective?

The whole thing you are missing here is that all frames of reference are equally valid - there is no "right" or "true" or in any way "special" frame of reference.

Sure, from my perspective as an observer far from the black hole, an infalling object gets squished into an infinitely thin splat on the event horizon and stays there forever.

From the perspective of the infalling object, (aside from likely being shredded by tidal forces and irradiated into oblivion), they sail through the event horizon with graceful ease while the outside universe goes on fast-forwards to it's eventual demise.

From the perspective of the black hole itself...who knows? Things get weird because it's a singularity.

From the perspective of a different object that's falling into the same black hole a few seconds later...yet different things.

So it's all about which frame of reference you pick. What's worse is that every fundamental particle within the in-falling object has it's own frame of reference. Usually, it's a fair approximation to say that for something the size of a human being, the frames of reference for all of our atoms are about the same...but with the crazy tidal forces and steep gravitational gradients near to a black hole, every atom is running on it's own clock - so even more crazy stuff happens because of that. What does it mean for chemical reactions when the rate of time's passage is radically different between the atoms taking part in it? Predicting outcomes under such extreme conditions is exceedingly difficult.

SteveBaker (talk) 12:29, 11 September 2013 (UTC)[reply]

My thought was another. I simply said that if a black hole evaporates, even an infalling observer would never cross the event horizon because the black hole would disappear (by evaporation) before it happens. 95.239.192.130 (talk) 13:23, 11 September 2013 (UTC)[reply]

In which frame of reference? The question (and answer) is meaningless without specifying that. SteveBaker (talk) 13:37, 11 September 2013 (UTC)[reply]

For us (external observer) a black hole would evaporate in a FINITE amount of time (that varies with the size of a black hole) and on object falling into a black hole would (ever for us EXTERNAL OBSERVER) take an INFINITE amount of time to cross event horizon; so we would see black hole evaporating before any object could enter (and maybe ever reach) the event horizon. But even an infalling observer would see black hole evaporating before he crosses the event horizon (obviously for the gravitational time dilation for him the black hole would evaporate in a tiny fraction of second but howewer BEFORE CROSSING event horizon); so what i wanted to say was that it's impossible, if exists Hawking's radiation, to enter into a black hole; would be possible only if a black hole doesn't evaporate. This simply because a black hole would evaporate before any external thing could falling into (I think that the feeling for an observer falling into would be to cease to exist in the moment he reaches event horizon). 95.239.192.130 (talk) 14:25, 11 September 2013 (UTC)[reply]

You want to take into account the effects of black hole evaporation, but you can only do that that in a fully self-consistent way. This means that you need to write down the Schrodinger equation for the matter fields and space-time metric (the wavefunction is a "functional" of the fields, i.e. it assignes to each field configuration a probability amplitude). This is done in this article, and they reach the conclusion that there two possibilities, one is similar to what you claim here, the other is the conventional view. Count Iblis (talk) 13:57, 11 September 2013 (UTC)[reply]

I understood the first possibility (the one similar to my thought) but I didn't understand the other (the conventional view): what does it mean?95.239.192.130 (talk) 14:25, 11 September 2013 (UTC)[reply]

The conventional view (which by the way is the one that is most likely correct and that's why it is conventional) states that from the point of view of the infalling observer NOTHING special happens at the event horizon and the observer reaches the singularity after a finite amount of time. 64.56.89.67 (talk) 14:47, 11 September 2013 (UTC)[reply]

How the conventional view can conciliate with the Hawking's evaporation theory? 95.239.192.130 (talk) 15:02, 11 September 2013 (UTC)[reply]

Without too much difficulty (The only real sticking point is the information paradox. 64.56.89.67 (talk) 16:06, 11 September 2013 (UTC)[reply]

It's worth mentioning that from the point of view of an outside observer, black holes of any reasonable size take vastly longer than the life of the universe to evaporate...so this may not be a practical problem because from the perspective of the in-falling observer, the universe ends before they reach the event horizon anyway.

No, that's not right. from the point of view of the infalling observers they reach the singularity after a finite amount of time and NOTHING particularly interesting happens at the horizon. 64.56.89.67 (talk) 16:51, 11 September 2013 (UTC)[reply]

What's the idea of the antigravity engine and how it works

What's the idea of the antigravity engine and how it works — Preceding unsigned comment added by 37.238.81.178 (talk) 13:25, 11 September 2013 (UTC)[reply]

The idea is that it can generate anti-gravity, or be shielded from gravity. How it works is whatever you want, because it is fictional. 217.158.236.14 (talk) 13:34, 11 September 2013 (UTC)[reply]

There is no such thing as "an antigravity engine" (nor is there ever likely to be) - so it doesn't "work". If you're talking about some fictional device (E. E. "Doc" Smith used such a device in his "Skylark" series, for example) - then, um, the unobtainium flange remodulator disencabulates the phase differential of the graviton-muon interaction cycle which in turn de-mitigates the...ok...look, just make up your own B.S explanation and enjoy whichever book/movie/video-game/serious-theatrical-production you're interested in. SteveBaker (talk) 13:35, 11 September 2013 (UTC)[reply]

I can think of a couple theoretical ways to counter gravity, while stationary, on Earth:

1) Put a very large, dense mass directly above you. The attraction towards that mass will cancel the Earth's gravity. Ordinary matter wouldn't work, as you would need a mass equal to Earth if at the same density as earth. However, some super dense matter, like in a neutron star, would allow you to use far less, since it would be far closer, on average.

2) If something is found which repels mass, rather than attracting it, then you can gather a larger amount of that below the person, to counter the gravity from the Earth. Dark energy appears to do this, but is extremely diffuse. I'm not sure if it can be concentrated.

And of course, in either case, you'd have the problem of how to contain those materials.StuRat (talk) 13:57, 11 September 2013 (UTC)[reply]

So "No" then? SteveBaker (talk) 14:30, 11 September 2013 (UTC)[reply]

Yes, "no" then. 64.56.89.67 (talk) 14:38, 11 September 2013 (UTC)[reply]

No confirmed. 217.158.236.14 (talk) 14:58, 11 September 2013 (UTC)[reply]

Well, certainly no today. But in the distant future, maybe. StuRat (talk) 09:54, 12 September 2013 (UTC)[reply]

Negative mass is an interesting read. Two objects of equal but opposite mass would continually accelerate towards the one with positive mass - the gravitational force will have a negative sign, making it a repulsive force for the positive mass object. The negative mass reacts oppositely (pushing it causes it to accelerate towards you), so the "repulsive" force actually attracts it. They will have opposite mass, momentum and energy, so the mass, momentum and energy of the system is zero. If you could create something with negative mass and use it this way, I guess you could call it an antigravity engine. Katie R (talk) 15:09, 11 September 2013 (UTC)[reply]

Too bad negative mass objects don't seem to actually exist. 64.56.89.67 (talk) 18:13, 11 September 2013 (UTC)[reply]

The anti-gravity article is interesting. The idea seems unlikely, but we should never exclude the possibility that there are flaws in current theories. Remember, we're using a model of the universe in which there is no preferred frame, even though there is cosmic microwave background and practically everything in any given region of space is moving at 0.01c or less relative to it. And even within entirely legitimate, accepted relativity there are gravitomagnetic effects, such as the attraction of two wheels to one another depending on which way they are spinning, which potentially modify ordinary gravity as we know it. (Though making them big enough to be measurable, let alone usable, is not so simple) Wnt (talk) 18:50, 11 September 2013 (UTC)[reply]

There don't need to be significant flaws in current theories, just incompleteness. The Standard Model of quantum physics is not assumed to describe every particle that might exist in the universe, so there is always the possibility that something may yet be discovered with exotic properties. On the same note, there is no reason to suspect that we will discover a useful exotic particle any time soon. Someguy1221 (talk) 10:14, 12 September 2013 (UTC)[reply]

Power supply problems.

(Not 100% sure that the science desk is the right place for this - but people with big brains and electrical knowledge hang out here so...)

I have a small 24 volt, 3.2 amp, switched-mode power supply for my number-two laser cutter (The data sheet is here). The machine has been giving me trouble ever since I first built the it - and it turns out that the problem may have been that the power supply was not generating the 24 volts that my machine needs. The data sheet linked above says that the output can be adjusted between 22 and 27 volts - and there is a prominent blue potentiometer marked "ADJUST". So I assumed that I just needed to tweak the potentiometer and all would be well. I know that the under-load voltage may be different than the no-load volts on a switched mode supply - so I set the laser cutter off working and put a multimeter onto the terminals of the power supply. Lo and behold, the meter read 22 volts - so I slowly turned the pot and got it up to 25 volts (because I wanted a volt or two over 24 to allow for voltage drop though the circuitry - and the stepper motor controller that it's powering is happy up to 80 volts). But just as the multimeter reached 25 volts, there was a burning smell, the green LED on the power supply went out and my laser cutter stopped moving.

:-(

I have another power supply on order (they only cost $25) - but I don't want that one to undergo the same fate!

So here is the question: It seems like the power supply must have been faulty because it could not be adjusted up to the maximum 27 volts that the manufacturer claims. But what kind of failure mode would have caused this to happen - and could that explain why it only produced 22 volts in the first place? It's hard to imagine why it would do that. The two motor controllers that it's powering pull at most 1.5 amps each - so I wasn't exceeding the current limits - and it had been running for weeks (presumably at 22 volts) without any obvious problems other than that my motors were somewhat lacking in torque.

Any ideas?

SteveBaker (talk) 13:28, 11 September 2013 (UTC)[reply]

Lambda makes very nice power supplies, although we tend to use almost identical-looking Meanwell supplies here. In my experience they're usually very stable at the set voltage through all sorts of load conditions, and the Meanwell ones (and presumably the Lambdas) are factory-set to the advertised voltage. If it was running low in the first place, then I think it is likely that you simply had a faulty unit. I would run the new supply with no or light load to make sure it shipped at 24 volts, then run your full load. Tweak the potentiometer with the meter as close to the load where you need the 24V as possible to compensate for the voltage drop along the way rather than putting the meter on the supply and guessing at how much to push it up. The little bit you pushed it past 24V certainly shouldn't have been an issue - they expect you to push it a bit for exactly the reason you did. We've had another manufacturer's supplies get stuck in a low-voltage failure mode that requires a power cycle to clear, and could sometimes get spuriously triggered, but it would have dropped far lower than 22V if it had that "feature". Katie R (talk) 13:54, 11 September 2013 (UTC)[reply]

The power had been cycled many times - and the machine has had marginal motor power since we first built it - so I doubt that it had gotten stuck in some resettable failure mode. But I'll take your advice to measure the voltage up by the motor controller - I was indeed measuring at the terminals of the power supply just because it was easier to juggle two multimeter probes and a screwdriver in the cramped electronics bay while keeping all body parts well away from the 40,000 volt laser power supply!

What I'm curious about is the nature of a fault that could have the thing operating well at 22 volts and self-destructing at 24. SteveBaker (talk) 14:25, 11 September 2013 (UTC)[reply]

You need to get yourself some nice probes with clips! You should be able to hook up the probes, sit the meter somewhere convenient (or stick it somewhere if you get a case with a magnet on the back), and then have your hands free for adjusting the pot. Hopefully your post-mortem teaches you something - I don't know enough to be able to speculate on the failure. I am surprised it made it through their QA process. Katie R (talk) 14:48, 11 September 2013 (UTC)[reply]

Do you use the same supply on your other laser cutter? It would be interesting to see what voltage it's putting out under the same conditions. Katie R (talk) 13:59, 11 September 2013 (UTC)[reply]

Sadly, no. The other laser cutter is an older version with a completely different power supply setup. SteveBaker (talk) 14:25, 11 September 2013 (UTC)[reply]

I'd want to do a postmortem and find where the burned spot is in the power supply. That spot was probably also the reason for the low voltage to begin with. I'd also complain to the company. They may or may not replace it, but they should know they are making defective equipment, in any case. (Was it made in China, by any chance ?) StuRat (talk) 13:50, 11 September 2013 (UTC)[reply]

TDK (and TDK-lambda) is a Japanese company. I don't know where the power supply was made - but TDK have a fairly solid reputation. When I pull the old power supply out of the machine, I'll dismantle it and look to see where the Magic smoke got released from. It has a three year warranty from TDK - so we'll definitely send it back...be we needed a replacement in a hurry - and having a spare doesn't hurt. SteveBaker (talk) 14:25, 11 September 2013 (UTC)[reply]

A Japanese company might still farm out production to China, and get lower quality products as a result. I'd look specifically for a label saying where it was manufactured. StuRat (talk) 07:44, 12 September 2013 (UTC)[reply]

The datasheet says the supply has overcurrent protection. Nevertheless, there might be some value in setting up a meter to measure the output current, in case it isn't what you think it is. Jc3s5h (talk) 15:56, 11 September 2013 (UTC)[reply]

I'm not sure how it would cause your particular failure, but I suggest using a scope to check a questionable power supply, since a multimeter's reading does not typically disclose brief sags/surges/spikes which could be caused either by the power supply itself or by the load. In other words, there may be more to it than the average power level. Edison (talk) 16:07, 11 September 2013 (UTC)[reply]

Purely speculative, but your mains voltage might be a bit low. This could give you a current through the main rectifier / transformer primary / main switching transistors that's above the design maximum - the output current limit may be working OK, but there probably won't be anything more than a thermal fuse on the input, and the semiconducting elements will burn out before that trips. But finding the burnt out component will give you a better idea of where the problem was. Tevildo (talk) 19:55, 11 September 2013 (UTC)[reply]

Population before human bottleneck

According to the Toba catastrophe theory there was a bottleneck of human population, with numbers reaching as low as around 10,000 individuals. What was the human population just before this event? Staecker (talk) 16:27, 11 September 2013 (UTC)[reply]

I'd be surprised if such estimates don't exist, but any such number would be hugely speculative. It would depend on how you define human, since in adition to Homo spaiens sapiens there were other species and subspecies existing at that time. The 10,000 figure is derived from working backwards from genetic assumptions. More recent discoveries on Y-chromosome lineages that weren't known in 1998 would expand the number that passed through the bottleneck. Sorry if that doesn't strictly give the answer you are looking for. μηδείς (talk) 20:41, 11 September 2013 (UTC)[reply]

Obesity baloon treatment

I have heard that Gastroanterology offer a baloon treatment to Obese people. Could someone please elaborate on it's mechanism? Thanks guys. — Preceding unsigned comment added by 95.35.55.212 (talk) 17:03, 11 September 2013 (UTC)[reply]

I think you're interested in Adjustable gastric band. Wnt (talk) 17:13, 11 September 2013 (UTC)[reply]

Or gastric balloon. DMacks (talk) 20:57, 11 September 2013 (UTC)[reply]

A little more information at NHS - How weight loss surgery is performed - scroll down to "Intra-gastric balloon" at the bottom of the page. Alansplodge (talk) 08:27, 12 September 2013 (UTC)[reply]

Standing on a Vauxhall Corsa

I'd like to stand on the roof of a car to get a better vantage point for a photograph of a building. I'm a 5'2" female and I weight about 9 and a half stone. (You could say that makes me chubby but I prefer curvy with good muscle tone... :P ) The vehicle I have at my disposal for this purpose is a newish Vauxhall Corsa. Will it hold my weight? Will I dent it/damage it? Julia\^talk 17:23, 11 September 2013 (UTC)[reply]

This isn't answerable with the information given. What matters is the pressure. If you're wearing gigantic foam snowshoes, maybe. (I disclaim all responsibility...) If you're wearing cleats or stiletto heels, not so much. Wnt (talk) 18:38, 11 September 2013 (UTC)[reply]

I'll take my shoes off and just wear socks. My feet are a UK size 5. Does that help? ;) Julia\^talk 18:41, 11 September 2013 (UTC)[reply]

I'm pretty sure you'll dent it.

What usually works is to buy and install a suitable roof rack - then screw either planks or half-inch plywood across it. That produces a nice stable platform that you can walk on comfortably with no risk of damaging the car. This site suggests a limit of 75kg for a Vauxhall Corsa roof rack. Since 9.5 stone is 60kg - then even with the weight of the planks/plywood, you should be OK. You could probably get away with more than that if you're only doing this while the car is stationary because that 75kg number must include the dynamic load while cornering, etc. (Please tell me it's stationary!) SteveBaker (talk) 19:27, 11 September 2013 (UTC)[reply]

(ec) You don't want to stand on the roof of the car unless you know there is support under the part of the roof panel you're standing on. The edges are safe, but it's easy to lose your balance. Socks or shoes won't make a difference when it comes to denting it. Shoes may scuff up the top, but socks are a lot more slippery, especially on a waxed curved roof. If you can borrow a ladder it would be a much better idea. Something like the Little Giant Ladder System folds down enough to fit in the Corsa, but sets up much taller than the roof you would be standing on. Katie R (talk) 19:36, 11 September 2013 (UTC)[reply]

I'd be very surprised if I couldn't damage the roof of a modern car with mere hand pressure while standing on the ground. Don't risk it, buy a roofrack. Or hire a car. Greglocock (talk) 00:08, 12 September 2013 (UTC)[reply]

I used to use the roof of my (old) car instead of a ladder, but that was in the days when car steel was thicker. (It flexed a bit, but bounced back.) I wouldn't risk it on my present car. Dbfirs 12:01, 12 September 2013 (UTC)[reply]

Since you mentioned it and this is the science desk, with a height of 5 feet 2 inches (1.575m) and a weight 9.5 stone (60.3kg) this gives a body mass index of 24.3, which for someone of predominantly European descent (which from your user page I think you may be) is generally considered in the normal weight range (albeit at the upper end since the boundary is 25). BMI has it's problems as our article attests but given the figures you provided were height and weight, it's probably the best way to analyse them and it suggests people shouldn't consider you 'chubby' based on those figures anyway. Nil Einne (talk) 15:11, 12 September 2013 (UTC)[reply]

Diode as radioactive detector - detecting energies?

Will a diode setup in reverse bias indicate the difference in energy from ionizing radiation? ie not only detect events but also give precision on the energy of the same event? Electron9 (talk) 18:59, 11 September 2013 (UTC)[reply]

It certainly will - see Semiconductor detector. Tevildo (talk) 21:22, 11 September 2013 (UTC)[reply]

If you are considering some sort of home made project, see a series of articles on making a particle detector featured in the magazine Elektor recently. They ran a construction project and some follow up articles within about the last year or so. 120.145.207.247 (talk) 23:41, 11 September 2013 (UTC)[reply]

Is there a scientific definition of "shake well"?

Many canned or bottled bottled products inform the user to "shake well" before using. (I assume to blend ingredients that have a tendency to seperate when stored.) All things being equal, how much shaking is expected when a product is labeled as such? --208.185.21.102 (talk) 19:17, 11 September 2013 (UTC)[reply]

As for your header, check out chaotic mixing. Basically, what you want might be called a "homogenous" mixture, though that term can be misleading, what you really want is a uniform distribution of each material in the heterogeneous mixture. See also homogenization. For you final question, I can't imagine much serious scientific investigation has been done for consumer goods, but mixologists usually aim for 30 seconds, e.g. here [9] SemanticMantis (talk) 19:27, 11 September 2013 (UTC)[reply]

I think SemanticMantis possibly meant Homogenization (chemistry) when linking to homogenization which redirects to Homogeneity (disambiguation) --220 of ^Borg 11:10, 12 September 2013 (UTC)[reply]

"My salad dressing label said I should shake well before using, so I shook it up last week in anticipation of using it today." :-) StuRat (talk) 07:41, 12 September 2013 (UTC) [reply]

And when you went to get it, it cried, "Close the door! I'm dressing!" ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:19, 12 September 2013 (UTC)[reply]

If it said "Shake well before using", then StuRat should have vigorously shaken himself before using it. Stu's getting on in years, perhaps he shakes a bit anyway. 120.145.207.247 (talk) 16:34, 12 September 2013 (UTC) [reply]

I would imagine that the viscosity (informally 'thickness') and perhaps particle size (for powders) of the material/s being mixed needs to be taken into account. A very thick liquid would need a longer time to re-mix properly (homogenously). Perhaps even the density of the various materials in a mixture, as some liquid mixtures may settle out rather quickly (oil and water for example), and require to be 'well shaken' for longer. Whereas if the various components are of similar density then they would likely remain in a 'mixed' state far longer, and be easier to re-mix quickly. (Martini? "Shaken, not stirred"?) A mixture of powders, like a cake mix for example could be expected to stay mixed, once 'homogenised', but may separate if subject to vibration during transport. In that case the larger particles would tend to rise to the top. I think that these would be somewhat harder/ take longer, to re-mix than a liquid.

Looking at a jug of pancake mix it says "Shake bottle to loosen dry mix", so some foods may tend to stick in the container without a shake. (And after a shake the powder is indeed moving more freely. wp:OR). Hmm, pancakes!

Thus to the question, it depends to some extent on what is in the container you are 'shaking well'. Experience will tell if you've shaken it enough. --220 of ^Borg 11:10, 12 September 2013 (UTC)[reply]

If in doubt, get one of those machines they use at hardware stores to shake paint cans. That should do it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:20, 12 September 2013 (UTC)[reply]

In case anyone is interested, this is similar to the question "How many times should I shuffle the cards to make the deck random?", dealt with at Shuffling#Randomization. Duoduoduo (talk) 20:11, 12 September 2013 (UTC)[reply]

What is the radiation dose (Sv) from a CME when in commercial flight?

During a commercial flight at 10 000 m (30 000 ft) the annual radiation rate 20 mSv. But what is the radiation rate when a CME occurs? Electron9 (talk) 20:23, 11 September 2013 (UTC)[reply]

The question seems to relate to Coronal mass ejection (as opposed to Chicago Mercantile Exchange or [Continual Medical Education ). Dozens of news articles just refer to "increased" or "intense radiation" without even giving an approximation as to the extra dose. 22:50, 11 September 2013 (UTC) — Preceding unsigned comment added by Edison (talk • contribs)

I'll noticed that too :-) Electron9 (talk) 23:03, 11 September 2013 (UTC)[reply]

This NASA internal presentation might possibly be useful, particularly the example graphs on page 8 of the PDF: http://ccmc.gsfc.nasa.gov/support/SWREDI/Decision_Dashboard_YZheng.pdf -- The Anome (talk) 11:41, 12 September 2013 (UTC)[reply]

Bald Eagle flock...

How common is a scene like this? I was under the impression that the Bald Eagle is a fairly solitary species. --Kurt Shaped Box (talk) 23:04, 11 September 2013 (UTC)[reply]

The American Eagle Foundation writes: "The only time the bald eagle tolerates the presence of other bald eagles is during winter migrations when large groups of bald eagles gather in one place to share an available food source" ("Eagle Survival - Habitat or Environment"). Another reason for gathering in larger groups during winter migration might be "to scout out potential partners" ([10]) ---Sluzzelin talk 23:20, 11 September 2013 (UTC)[reply]

Perhaps relevant: the Bald Eagle population has been growing rapidly in the recent 10-15 years, see Bald_eagle#Population_decline_and_recovery. The species is now registered as "of least concern". SemanticMantis (talk) 01:55, 12 September 2013 (UTC)[reply]

Homework

two particles of masses 4kg and 6kg are at rest separated by 20m.if they move towards each other under mutual force of attraction the position of the point were they meet is. — Preceding unsigned comment added by 117.213.217.180 (talk) 05:51, 12 September 2013 (UTC)[reply]

I added what I assume is an appropriate title to your question. Please change it if I'm wrong. BTW, we don't do people's homework for them Rojomoke (talk) 06:47, 12 September 2013 (UTC)[reply]

F = ma. d = t(υ₀ + Δυ/2), υ = υ₀ + at. Both masses will accelerate as they approach the common coordinate. Combine these formulae for each mass, remembering that force and time are equal in magnitude for both masses, and substitute into the other. using the constraint that both masses must travel a total distance of 20 m. Plasmic Physics (talk) 07:35, 12 September 2013 (UTC)[reply]

You should find that, this procedure of combining the formulae should yield a simple ratio. Plasmic Physics (talk) 07:46, 12 September 2013 (UTC)[reply]

... or you can use the fact that in the absence of external forces the centre of mass of the two particle system will remain at rest (since it is initially at rest). Gandalf61 (talk) 09:06, 12 September 2013 (UTC)[reply]

... yes, Gandalf61's method is ~~much~~ easier! (If you want to do it the algerbaic way, you can choose any force you wish [F>0] between the two masses and you will get the same answer in the end.) Let is know how you get on and if you need further help. Dbfirs 11:54, 12 September 2013 (UTC)[reply]

Eh? If you follow my method, you don't even need to find value of Ft². It cancels out under the substitution part. Plasmic Physics (talk) 12:23, 12 September 2013 (UTC)[reply]

Since υ₀ = 0, υ = at, and d = tυ/2. Thus υ = Ft/m, and thus d₁ = Ft²/(2m₁), d₂ = Ft²/(2m₂). Get the idea now? Plasmic Physics (talk) 12:30, 12 September 2013 (UTC)[reply]

OK, only a bit easier if you do the cancelling first in your method. I've striken my "much". It all depends on what the OP knows and whether their algebra is as good as yours. Dbfirs 12:40, 12 September 2013 (UTC)[reply]

Body weight

I have heard that, if you weigh yourself daily, it is best to do so in the morning (since a person's weight will be lowest in the morning). Is this true or just a myth? If true, why would it be the case that you weigh less in the morning? Thanks. Joseph A. Spadaro (talk) 15:16, 12 September 2013 (UTC)[reply]

Mostly because you haven't drank anything in eight hours. But you've still lost moisture to sweat, breath, etc. APL (talk) 15:45, 12 September 2013 (UTC)[reply]

(edit conflict)I don't have my sources on hand right now. But one of the reasons people record lower weights in the morning is that it's typically done after urinating and before eating. Also, it's about 9 - 10 hours since your last meal so you would have lost some weight due to perspiration and the fast since yesterday's cup of tea.

Btw, I think the reason the morning is the best time to weigh yourself is due to the morning weight being the least volatile from day to day. Your weight at say 13:00 may vary from day to day due to your eating / expulsion habits changing each day. Zain Ebrahim (talk) 15:49, 12 September 2013 (UTC)[reply]

Thanks. That all makes sense. On a related note, what would be the expected variation in weight that one would see from a morning weighing versus another time of day or night? Perhaps a pound or two? The variation will not be particularly high, correct? Thanks. Joseph A. Spadaro (talk) 19:03, 12 September 2013 (UTC)[reply]

It can be quite a bit. That's why you should weigh yourself daily - but calculate about a ten day "moving average" to see what the trends are. But yeah - morning weights (after first pee - before first drink) are the most reliable - particularly if you're someone who poops on a fairly regular schedule (ie once per day). I strongly recommend The Hacker's Diet - which goes into this in the kind of detail that only a geek could love!

For an average human, each day, 2.5 lbs of food, 9.2 lbs of water and 1.8 lbs of oxygen enter your body and 0.3lbs of poop, 11 lbs of water (pee, sweat, etc) and 2.2 lbs of CO2 leave your body. So, as you can see, to get consistency, you need to have not drunk a lot recently and have just emptied your bladder. Hence first thing in the morning is the best time. It's not just that your weight is the lowest - but it's definitely when it's at it's most consistent from one day to the next.

SteveBaker (talk) 20:30, 12 September 2013 (UTC)[reply]

Cats and Dogs

Can someone please tell me why, in nature, varieties of cat, like lions and tigers, are so much larger than varieties of dog like wolves. Is there an inherent limit, I wonder, to how large a 'wild' dog can be? I was also thinking of the various monsters, say in 18th Century France, that turned out to be enormous wolves. — Preceding unsigned comment added by 109.12.64.88 (talk) 15:18, 12 September 2013 (UTC)[reply]

Well, the simple answer is that all dogs and wolves are basically the same species. A species with a surprisingly diverse number of breeds, but still one species.

Cats actually show less variation if you only consider the ones that are the same species as a house-cat.

For example, a house-cat and a lion share the same family (Felidae), but not the same species.

So where are the giant, more fearsome members of the Canidae (dog-like) family? Extinct mostly. Check out the Dire Wolf. APL (talk) 15:40, 12 September 2013 (UTC)[reply]

Still, as far as I know, the largest Canids are smaller than the largest Felids, even counting all known extinct species. As for "inherent limits" -- I think not. I think the size difference has more to do with adaptive radiation and ecological niches, perhaps influenced by other factors, such as how sociality tends to be a little different between the Felid and Canid clades. SemanticMantis (talk) 16:12, 12 September 2013 (UTC)[reply]

From the evolutionary standpoint, the largest "dogs" are seals and bears. Indeed, the split between Feliformia and Caniformia occurred earlier than the split between Canidae and Arctoidea. Large size of largest seals, bears, and cats is almost certainly an adaptation to being a solitary apex predator, as SemanticMantis has already noted. --Dr Dima (talk) 18:54, 12 September 2013 (UTC)[reply]

Another factor contributing to the large size, at least in some of these, is a Sexual selection. Species in which solitary dominant males fight for reproductive rights, tend to have much larger males than females. However, the trend towards progressively larger males can drive the average female size up, as well (both because of the shared genes and because of the evolutionary pressure to produce and care for larger offsprings). --Dr Dima (talk) 20:46, 12 September 2013 (UTC)[reply]

Polyhedron-polyhedron intersection?

Is there a simple algorithm for detecting whether or not two polyhedra intersect? I don't necessarily need to know HOW they intersect (ie: the resulting polyhedron of intersection) so much as THAT they intersect. Any tips or links would be much appreciated! 64.134.148.66 (talk) 19:29, 12 September 2013 (UTC)[reply]

This might be one for the math desk - but here goes anyway:

For convex polyhedra - it's relatively simple - for arbitrary concave ones - and especially the really nasty ones with holes and such, it's much harder. Generally, it's easier to try to split a non-convex polyhedron into a bunch of convex ones and to test the resulting debris.

The Hyperplane separation theorem is the key here. It says that if two (convex) polyhedra do not intersect then there is an infinite plane that lies between them. In this case, such a plane can always be found fairly easily because it can always be the plane containing one of the faces of one of the two polyhedra. So for two polyhedra, A and B, then naively:

Calculate the plane equations of every plane in polyhedron B.
Substitute all of the vertices of polyhedron A into all of the plane equations from polyhedron B to get the signed distance between each vertex of A and the planes running though each of the faces of B.
If any plane of B is positioned such that ALL of the vertices of A lie on the outside of it (ie have a positive distance from it) - then there is no intersection and you can stop testing.
If you didn't find any separation plane in B, swap A and B and repeat.
If neither polyhedron contains a separating plane - then they either intersect or one is entirely inside the other (you can test for the latter case separately by checking that all of the vertices of one of the polyhedrons lie inside all of the planes of the other).

You can save time by computing one plane and one set of distances at a time - and doing an "early out" if one of the vertices has a negative distance to that face. If you know the surface normals for each face then there are possible optimisations there too.

If performance matters to you, you'll want to compute the bounding sphere of each polyhedron and check to see if those overlap first - if they don't, then you're done. That's a spectacularly fast test and allows you to only have to compute the more difficult algorithm when the two objects are relatively close to touching.

Another approach for concave polyhedra is to test whether any edge of one polyhedron penetrates any face of the other. Again, you calculate the plane equations for each face, but now you test the signed distance for the vertices at the ends of each edge of the other. If the edge straddles the plane (one positive and one negative result) then you have to find the intersection point of plane and edge and determine whether it lies inside or outside of the face...which is easier if you first decimate your polygonal faces into triangles. If any edge straddles any plane and intersects the face - then it's a collision.

In all of these algorithms, there are ikky special cases when two faces or two edges just touch and are parallel - when one object is entirely inside the other of if two polyhedra with the topology of a torus are linked into a chain...and so forth. Numerical rounding errors are also out there to bite you...so you have to take special care with how you decide things like "inside and outside" to be highly consistent.

SteveBaker (talk) 20:10, 12 September 2013 (UTC)[reply]

Doesn't the edge-penetrates-face test err if one polyhedron is totally inside the other, falsely reporting there's no intersection? -- Finlay McWalterჷTalk 20:16, 12 September 2013 (UTC)[reply]

Yes, it does...but are we testing the surfaces or the volumes? SteveBaker (talk) 20:18, 12 September 2013 (UTC)[reply]

(ec) This page lists various papers which give algorithms and/or code for calculating intersections of various objects, and gives several sources for polyhedron/polyhedron intersections. I'd imagine most real-world scenarios will first attempt to trivially reject cases with bounding-box intersection tests; many will also try to limit expensive tests using a more sophisticated spatial partitioning like octrees or binary space partitions. -- Finlay McWalterჷTalk 20:12, 12 September 2013 (UTC)[reply]

Yes - in something like a computer game - those are all good strategies. Also, things like "if A and B were X units apart last time we checked and neither of them has moved more than X units relative to the other - then they still don't touch." - temporal checks and caching plane equations and things like that can speed things up immensely. Also, many of these calculations can be done on the GPU instead of the CPU - which speeds things up by at least one or two orders of magnitude. This is a topic of study all to itself. There are people who make careers out of nothing but collision detection tests! SteveBaker (talk) 20:22, 12 September 2013 (UTC)[reply]

Transmission of blood groups

How is the heredity of blood group determined, is it matriarchal or patriarchal? If, for example, my mother's blood group was B positive, what would mine be? --TammyMoet (talk) 20:33, 12 September 2013 (UTC)[reply]

Like all normal genes, inheritance is from both parents, so it depends on the father as well. Neither A or B is dominant over the other (they are codominant), and can both be expressed. If the father is A or AB, any combination is possible. O or B in the father and only O or B are possible for the child. Rhesus inheritance (the 'positive' part) is simpler, rhesus factor in either parents will normally lead to the child being positive too. As another example, I myself am AB-, so any children I have can have any of the combinations of blood types, but can only be rhesus positive if their hypothetical mother is rhesus positive. Fgf10 (talk) 20:52, 12 September 2013 (UTC)[reply]

If you're AB than you cannot have children with blood type O. Dauto (talk) 21:13, 12 September 2013 (UTC)[reply]

[1] ttp://www.bbc.co.uk/news/magazine-23356578

[2] ttp://www.dailymail.co.uk/news/article-2404598/Wasps-plague-Britain-cold-winter-late-spring.html

[3] ttp://blackpool.gov.uk/NR/rdonlyres/B0EC7A93-64B5-4778-92A8-E0DC0A268F1D/0/WaspsFactsheet.pdf

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