Content deleted Content added

Inline

Revision as of 13:42, 11 September 2013

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

Shortcut

WP:RD/S

Want a faster answer?

Main page: Help searching Wikipedia

How can I get my question answered?

Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
Post your question to only one section, providing a short header that gives the topic of your question.
Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
Don't post personal contact information – it will be removed. Any answers will be provided here.
Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
Note:
- We don't answer (and may remove) questions that require medical diagnosis or legal advice.
- We don't answer requests for opinions, predictions or debate.
- We don't do your homework for you, though we'll help you past the stuck point.
- We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

September 7

Largest volcano on earth discovered?

Re: Tamu Massif, as mentioned on the main page - how exactly could scientists not have known for decades that something of that size was down there? I mean, finding a 260,000 square kilometre volcano... it's not like finding a set of car keys, is it? Did they just miss it? I'm confused. --46.208.75.245 (talk) 00:26, 7 September 2013 (UTC)[reply]

It doesn't have an obvious caldera, and it's over a mile down, and 145 million years old. They determined it is just one volcano by studying the lava flows, which all originate from one center. That's not an easy feat given the physical and time depth and erosion and deformation over that period. μηδείς (talk) 00:31, 7 September 2013 (UTC)[reply]

For decades they had assumed that Tamu Massif was formed from several volcanoes that had grown together. Think of the Hawaiian islands for comparison. Each island is a separate eruption center, and hence those islands were formed from a group of related volcanoes. The surprise with Tamu Massif is that the entire feature now appears to have been created by a single volcano. Dragons flight (talk) 01:24, 7 September 2013 (UTC)[reply]

Light emitting black hole

As we know black hole emit a Hawking radiation and the smaller the black hole, the more powerful the radiation. Is it possible that there is a sweet spot for a black hole size so its emitted radiation is in the visible light spectrum not just in usual gamma ray? 140.0.229.26 (talk) 01:07, 7 September 2013 (UTC)[reply]

As explained in the article, the temperature of black hole Hawking radiation is inversely proportional to mass. To get a sun-like spectrum (e.g. 5000 K), you'd need a mass of about 2×10¹⁹ kg (about twice the mass of Ceres), which implies a event horizon radius of about 30 nanometers. Dragons flight (talk) 01:34, 7 September 2013 (UTC)[reply]

Note the evaporation rate according to the article is 3.562 x 10³² W / M² (with M in kg); for the mass given above it should be 8.9 x 10^-7 W. I think that if magnified under a microscope about 4000x it should seem like an incandescent bulb in brightness, but with an arc just (under the scope, appearing to be) 0.12 mm in size the filament would seem a little thin and bright by comparison. Wnt (talk) 06:17, 7 September 2013 (UTC)[reply]

Yellow–brown stains on marble

Is this true? Thanks, 84.109.248.221 (talk) 17:08, 7 September 2013 (UTC)[reply]

It certainly looks like it. You can see similar stains on the arms - but not on other protruding parts. This source says that oils leave a dark brown stain on marble - and that's what we're seeing here. It's hard to imagine any other source of oil being selectively deposited there. The image at right here shows similar staining on places where people's hands are most likely have reached. SteveBaker (talk) 20:06, 7 September 2013 (UTC)[reply]

Also, this blog shows a photograph of a bronze sculpture where the breasts were worn shiney bright while the rest was a more typical tarnish. SteveBaker (talk) 20:16, 7 September 2013 (UTC)[reply]

I'm not saying it's not true, but there is in fact at least one imaginable other source of oil being selectively deposited there: A combination of linseed oil and beeswax that used to be "applied as a polish, permeating the structure and, over time, forming an oxalate skin which invariably discolours the crystalline structure. Oxalate skins are complex and almost impossible to remove." ("Cleaning Marble", Victoria and Albert Museum). ---Sluzzelin talk 20:28, 7 September 2013 (UTC)[reply]

OK - but why would someone use the wrong kind of polish for cleaning marble...and do it selectively only on that specific part of the statue - and not at all on the male statue standing right next to it? I have presented evidence that other statues have their boobs groped on a regular and selective basis - how could that not be the case here? SteveBaker (talk) 00:15, 8 September 2013 (UTC)[reply]

Apparently, some owners or their employees did use to apply this kind of polish, maybe out of ignorance, I don't know. Yeah, I have no good explanation for the selectiveness, except that those surfaces might have looked more smudged, or that some caretakers perhaps polished these surfaces more vigourously, but I'll gladly concede that point. I just wanted to make sure no one came to believe that yellow stains on marble in general always came from human oils. ---Sluzzelin talk 19:37, 9 September 2013 (UTC)[reply]

See also this photo of the bronze boar outside the Deutsches Jagd- und Fischereimuseum in Munich. Note which parts are highly polished... Tevildo (talk) 00:14, 8 September 2013 (UTC)[reply]

Kidney transplant location

My grandmother had a kidney transplant (in the UK) around 1990. Mum says that her functional kidney is positioned over her stomach, at the front. Could this be correct or mum full of crap, as usual? --89.241.237.164 (talk) 18:09, 7 September 2013 (UTC)[reply]

See Kidney transplantation. According to the article, the new kidney is usually positioned in the iliac fossa (just above the top of your leg). It wouldn't be near the actual _stomach_ (which is much further up your abdominal cavity), but using "stomach" as a general term for "abdomen", your mum is approximately right. Mothers tend to be. Tevildo (talk) 19:22, 7 September 2013 (UTC)[reply]

A quick Google confirms that this is the case, although it may possibly have been different in 1990 (?). Alansplodge (talk) 14:28, 8 September 2013 (UTC)[reply]

My mother was frequently wrong before 1990... MChesterMC (talk) 08:31, 9 September 2013 (UTC)[reply]

Legality of spectrum analyzer use?

Is there any legal challenges to the use of a spectrum analyzer in the US ..? Electron9 (talk) 20:53, 7 September 2013 (UTC)[reply]

Are you sure you don't mean a radio scanner ? -- Jheald (talk) 21:15, 7 September 2013 (UTC)[reply]

A simple spectrum analyzer should be OK. There was a ban on scanners that could receive the analogue mobile phone system after some politician's phone call was publicized. If your spectrum analyzer can decode a signal into audio it may be subject to the same ban, and therefore have frequencies blocked. Usually equipment is made for an international market, so there will be a simple way to make it into a device suitable for a different country. Graeme Bartlett (talk) 21:48, 7 September 2013 (UTC)[reply]

Among the relevant places to check are the website of the Federal Communications Commission - http://FCC.gov - and Title 47 of the Code of Federal Regulations, e.g. 47 C.F.R. §18, regulating equipment for industrial and scientific use. I am not aware of any spectrum analyzer that requires operator licensing or regulation, (e.g., you do not need a HAM license to operate a radio receiver with spectrum analyzer attached), because most of them do not transmit any meaningful quantity of signal or interference. On perusal of http://justice.gov, I found numerous court case dockets with the search term "spectrum analyzer," but almost all of these referred to allegations of intellectual property infringement; a few legal battles involved import and sale of spectrum analyzers and other equipment in violation of tax and import regulations. Nimur (talk) 21:55, 7 September 2013 (UTC)[reply]

I saw this comment at slashdot:

strong cryptography on mobile phones (Score:1)

by fustakrakich (1673220) writes:

Shit, the FBI and NSA, et al put the kibosh on that before the damn things hit the streets. Instead they made a law that prohibits the sale of full spectrum scanners to the public, like was supposed to make them secure...

*

Re: (Score:1)

by Anonymous Coward writes:

Instead they made a law that prohibits the sale of full spectrum scanners to the public

Is that to outlaw bug sweepers and counterintelligence in general?

This in combination with TI:s sub 1 GHz spectrum analyzer MSP430 that covers 300-348, 383-464, 779-928 MHz made me wonder if there's something hiding in the open of the spectrum somehow. Electron9 (talk) 00:09, 8 September 2013 (UTC)[reply]

Some electronics test equipment is ITAR-restricted. That doesn't mean it's illegal; it just means that it's restricted. Chances are very high that if you knew what to do with such equipment, you'd already be on your way to being well-paid and securely employed by a company or organization with access to that type of equipment. Nimur (talk) 00:49, 8 September 2013 (UTC)[reply]

You'd have gotten a better answer at Humanities - off the top of my head, the problem was ECPA, which at the time stood out to me as the first case of banning a radio receiver in certain frequencies like in the Soviet Union. My impression is that the de facto outcome is that people import these products from other countries (I think it was Britain) instead of making them here. In theory I think they might be subject to be stopped at Customs, or perhaps damaged by a meteorite impact during shipping... Wnt (talk) 05:26, 8 September 2013 (UTC)[reply]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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". 209.131.76.183 (talk) 13:42, 11 September 2013 (UTC)[reply]

Revision as of 13:42, 11 September 2013 edit 209.131.76.183 (talk) →‎Power supply problems. ← Previous edit		Revision as of 13:42, 11 September 2013 edit undo 209.131.76.183 (talk) →‎Power supply problems. Next edit →
Line 286:		Line 286:
	[[User:SteveBaker\|SteveBaker]] ([[User talk:SteveBaker\|talk]]) 13:28, 11 September 2013 (UTC)		[[User:SteveBaker\|SteveBaker]] ([[User talk:SteveBaker\|talk]]) 13:28, 11 September 2013 (UTC)

	::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". [[Special:Contributions/209.131.76.183\|209.131.76.183]] ([[User talk:209.131.76.183\|talk]]) 13:42, 11 September 2013 (UTC)		: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". [[Special:Contributions/209.131.76.183\|209.131.76.183]] ([[User talk:209.131.76.183\|talk]]) 13:42, 11 September 2013 (UTC)