Wikipedia:Reference desk/Archives/Science/2013 February 15

= February 15 =

Lists of textbooks
The MAA has "a list of books recommended by the Association for purchase by college and university libraries". Where are the lists for topics other than math? I know many universities have lists of their course books online, but those aren't that comprehensive. --83.84.137.22 (talk) 00:43, 15 February 2013 (UTC)

Perthes disease
perthis diseases — Preceding unsigned comment added by 115.249.81.251 (talk) 01:41, 15 February 2013 (UTC)


 * See Perthes disease. Ariel. (talk) 02:09, 15 February 2013 (UTC)

Research access to data in the New England Journal of Medicine
I am not familiar with the usages that prevail in medical journals. When an article published in the New England Journal of Medicine reports conclusions of a statistical analysis of data, without explicitly giving the data itself, does the journal provide access, via the web or otherwise, to the actual data? Michael Hardy (talk) 12:10, 15 February 2013 (UTC)


 * Different journals have different standards and requirements. Within a particular journal, the specific requirements may depend on the type of data and type of analysis.  NEJM makes specific demands for accessibility to raw clinical trial data and raw microarray data: NEJM manuscript submission requirements.  Many medical journals, NEJM included, follow the ICMJE's Uniform Requirements for Manuscripts Submitted to Biomedical Journals. TenOfAllTrades(talk) 13:47, 15 February 2013 (UTC)
 * Interesting, but it only applies to studies with human subjects and to microarray data, and not necessarily to public health data, which is closer to what I'm looking for. Michael Hardy (talk) 02:02, 16 February 2013 (UTC)
 * Depending on the nature of the data that you're looking for, and the degree of 'raw'-ness, there may be issues with converting the data into a properly anonymized form that would be suitable for release (and permitted by ethics committee of the institution or organization that generated the data in the first place). TenOfAllTrades(talk) 15:55, 16 February 2013 (UTC)


 * It would be impossible for a journal to provide raw data -- the variability in formats would be impossible to handle in a reasonable way. Even if the journal requires the data to be available, you would have to contact the corresponding author of the paper to get it. Looie496 (talk) 22:04, 15 February 2013 (UTC)


 * Experimenters often spend years accumulating a dataset (and tons of grant money) and can be pretty reluctant to lend the data to somebody else who is essentially in competition with them for grant money, and can get points for publising some analysis without spending the time/money to put the data together. Outside from Congressmen who are hostile to the conclusions of the researchers, most folks don't expect them to hand over the data until they've finished wringing any possible publications out of it. So, basically, if you want access to it, you contact the researcher and make your case; if they figure you're not in competition or something you'll probably get it. On the other hand are people who analyze public datasets put together by the government; public health, meteorology, etc., so anybody can access the same data. Gzuckier (talk) 07:37, 18 February 2013 (UTC)

Fluorine Swallowing
TenOfAllTrades(talk) 13:29, 15 February 2013 (UTC)

Air pressure
Hi,

I would like to know why in different heights only the ears feel the pressure, and not some other organs.

Exx8 (talk) 12:19, 15 February 2013 (UTC)


 * The thin tympanic membrane bulges inward or outward. The eustacian tube is supposed to equalize pressure, but is easily blocked.  The nerves in the area are quite sensitive, in order to protect the ear from damage (if you do something which would cause a hearing loss, you feel pain and hopefully stop).  Most of the other organs aren't as sensitive to pressure, but the eyes might be the next most sensitive.  However, people with rheumatism often report their pain varies with atmospheric pressure.  StuRat (talk) 13:07, 15 February 2013 (UTC)


 * The bends can cause pain and injury elsewhere, but the pressure change involved is much greater. Ears are designed to sense pressure changes (sound), even vibrations on the scale of a single atomic diameter. Wnt (talk) 16:32, 15 February 2013 (UTC)

The difference between Fjord and Gulf?
Hi,

I would like to know what is the difference between a Fjord and a Gulf? Exx8 (talk) 12:23, 15 February 2013 (UTC)


 * A fjord is an inlet carved by a glacier. A gulf is just a general term for a large inlet. Dauto (talk) 14:32, 15 February 2013 (UTC)
 * To quote our own article, a fjord is "a long, narrow inlet with steep sides or cliffs, created in a valley carved by glacial activity". It isn't just any small inlet. Gulfs are arms or bays of oceans or seas. In fact the Gulf of Mexico is larger than most seas. (Aside, why can't I find a list of water bodies by size on Wikipedia?) Rmhermen (talk) 18:45, 15 February 2013 (UTC)


 * Wnt please go away from my sections. You are right buy you annoy me.I had a mistake okay, English IS NOT my mother tongue such as modesty is not your main attribute. Thanks for the rest who resisted their desire of making fun of spelling mistakes and for answering my answer.Exx8 (talk) 21:03, 15 February 2013 (UTC)


 * Hey man, don't let it get to you. Humor is a good thing. I though the jokes were OK. What's not OK is for you (or whoever did it) to erase other people's posts (even if they were just jokes.) Dauto (talk) 21:56, 15 February 2013 (UTC)


 * Here's a link to the deleted posts since none of this makes any sense otherwise: diff. μηδείς (talk) 02:41, 16 February 2013 (UTC)


 * It sounds like Exx8 got my statement backwards here - I was not making fun of him and indeed do not even regard saying "a Golf" as a mistake when you are speaking of a map of Sweden. Wnt (talk) 21:23, 16 February 2013 (UTC)

Note that the tern "fjord" is a technical term used by geographers, but in general speech specifically refers to these features in Scandinavia. In Scotland, they are generally called "sea lochs", an example is Loch Goil, and in the rest of the English speaking world (someone will correct me if I'm wrong about this) "inlet" is used, an example is Burrard Inlet in Canada. However, because these are general terms, they are sometimes applied to features that are not technically fjords. Alansplodge (talk) 11:42, 16 February 2013 (UTC)
 * The region of New Zealand where the inlets are very similar in both look and geology to those of Norway is "correctly" called Fiordland. However, the fjords themselves have names containing the word sound, e.g. Milford Sound./Coffeeshivers (talk) 15:12, 17 February 2013 (UTC)

The role of splitter plates in jet engine inlet geometry
I started the article Splitter plate (aircraft) thinking I knew I how they worked, otherwise I wouldn't have started the article, but looking for citations on the net has led me to doubt my understanding of the topic. I had thought that what the splitter plate did in supersonic flight was that in breaking up the boundary layer air, it tipped turbulent air into the stream of air entering the intakes creating an air dam that slowed the ingested air sufficiently that a simple pitot intake, without the need for intake ramps or inlet cones, was sufficient to insure air entering the engine was within its operational range. Am I very mistaken? One source I found stated that the purpose of the splitter plates was to prevent slow boundary layer air entering the intakes since the engine would work at their most efficient by maximising the intake of fast travellin free air. I know that these things are compromises and trade offs, are different effects at play at different speeds/altitudes --KTo288 (talk) 14:42, 15 February 2013 (UTC)


 * I don't fly jets, so I'm not very familiar with supersonic technology; but fast piston-powered aircraft use cowl flaps to control airflow for cooling and air-intake, at the expense of extra drag. Complex aircraft can open and close the cowl flaps as needed.  Nimur (talk) 15:33, 15 February 2013 (UTC)
 * I don't design or fly jets either. I did carry out a quick Google search, however, using the term "boundary air control above mach 1" which resulted in this: It may be of help -- Senra (talk) 19:55, 15 February 2013 (UTC)
 * Also My bold-italic emphasis -- Senra (talk) 20:32, 15 February 2013 (UTC)


 * Perhaps this will help: Diverterless supersonic inlet talks about diverting the boundary layer with some sexy grooves and bumps, and the photo in that article contrasts it with the F16's conventional intake. More explicitly, that article cites as a reference this Lockheed Martin article, which talks about different ways of dealing with boundary layer effects in supersonic jet intakes. That seems to be differentiating between a "diverter" and a "splitter plate".  This says "Splitter plate not required with proper diverter design". So I'm not sure that what Splitter plate (aircraft) is talking about isn't really a diverter, of which a splitter plate is an optional element (rather than a synonym). But anyway, all of that differs from your "breaking up the boundary layer" idea, but rather at preventing the boundary layer air from entering the intake at all. -- Finlay McWalterჷTalk 21:27, 15 February 2013 (UTC)

Entropy
Is the following the correct equation to use to find the entropy generation when iron is quenched?

S(water)= mclnT/T S(iron) = mclnT/T Total S generated = S(water) + S(Iron)

Thanks Clover345 (talk) 17:59, 15 February 2013 (UTC)

Entropy production
I know that dS=(Q/T)out - (Q/T)in + S(produced in the system). But how do you find dS so that you can find S(produced in system). For some reason my calculation works if I set dS to 0 but I don't know why. My system is a building wall and I calculated the entropy generated by it given the temps outside and inside, it's conductivity & convection heat transfer coefficients from wall to environment and wall to inside. Why is dS 0? Clover345 (talk) 19:04, 15 February 2013 (UTC)
 * Because no entropy is produced in the wall except for one related to heat transfer through the wall. Ruslik_ Zero 19:21, 15 February 2013 (UTC)
 * isn't that contradictory? If entropy is produced by heat transfer through the wall, shouldn't dS be over 0?  Clover345 (talk) 19:47, 15 February 2013 (UTC)
 * $$\Delta S=0$$ for the wall over any period during which the temperatures on the two sides are (taken to be) constant, because entropy is a state function and the wall's state is constant. The entropy changes from the heat transfer occur on the two sides: a negative change on the warm side and a (larger) positive side on the cold side.  --Tardis (talk) 03:58, 16 February 2013 (UTC)
 * thanks but this confuses me. If dS=0, why is the entropy produced by the wall higher than 0. Clover345 (talk) 19:43, 16 February 2013 (UTC)
 * The entropy produced "by" the wall (that is, because the wall isn't a perfect insulator and heat is flowing through it) can be non-zero even though the entropy produced in the wall (that is, because of any change in the wall's state) is zero.
 * We can associate with any heat flux an entropy flux: $$\vec s:=\frac1T\vec q$$ (recall that we usually do not define division (as in $$\Delta S=\frac QT$$) for vectors), and in direct analogy to the first law, we may write $$\frac{\partial\rho_S}{\partial t}=\rho_{\dot S}-\vec\nabla\cdot\vec s$$ (the change of entropy density is equal to the entropy (density) generation rate minus the divergence of the entropy flux). (The difference between the first and second laws is that $$\rho_{\dot Q}$$ must be balanced by some change in the internal energy of the system, whereas $$\rho_{\dot S}\ge0$$ but is otherwise unrestricted.)  For every point in the wall, $$\frac{\partial\rho_S}{\partial t}=0$$, so $$\rho_{\dot S}=\vec\nabla\cdot\vec s$$.  The only kind of process occurring is heat flow (no chemistry, work, compression, etc.), so this entropy production is entirely due to the heat flow.
 * Assuming a linear temperature profile in (say) x, as for a wall of uniform material and small temperature changes, this rate is $$\frac{\partial s_x}{\partial x}=\frac d{dx}\frac qT=q\frac{-1}{T^2}\frac{dT}{dx}=\frac k{T^2}\left(\frac{dT}{dx}\right)^2$$ (the thermal conductivity times the square of the logarithmic derivative of temperature over space). Letting the wall extend from 0 (where the temperature is $$T_1$$) to X (where the temperature is $$T_2$$), this is $$\frac k{(T_1/m+x)^2}$$, where $$m=\frac{T_2-T_1}X$$ is the thermal gradient.  So the entropy is produced throughout the wall, most intensely at the colder side ($$x=0$$ for $$m>0$$), but it is all emitted at that side and none is retained in the wall.  (I won't claim to have proven this point, since I derived $$\rho_{\dot S}$$ from the statement that $$\frac{\partial\rho_S}{\partial t}=0$$, but I hope that it's easier to accept given this context and explanation.)  --Tardis (talk) 19:25, 17 February 2013 (UTC)