Wikipedia:Reference desk/Archives/Science/2012 December 11

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December 11

Medical degrees

Is it possible to do MS (surgery) or MD without MBBS? With MCAT score and without MBBS is it possible to do MD or MS (surgery)? — Preceding unsigned comment added by 199.224.149.10 (talk) 08:21, 11 December 2012 (UTC)

Is a masters in pediatrics course without MBBS considered a specialization in that field? after completing masters in diagnostics radiology without MBBS, is it possible to be considered as a professional radiologist? — Preceding unsigned comment added by 199.224.149.10 (talk) 08:22, 11 December 2012 (UTC)

In which country or countries? --Dweller (talk) 11:37, 11 December 2012 (UTC)

The OP's IP geolocates to Hyderabad, in case that helps. Marnanel (talk) 13:52, 11 December 2012 (UTC)

Rocks

How this type of rock (on the foreground) is called? Thanks.--93.174.25.12 (talk) 18:41, 11 December 2012 (UTC)

I think that's just a series of sedimentary layers that are very radically tilted. Looie496 (talk) 19:19, 11 December 2012 (UTC)

It bears some resemblance to Devils Tower. Bus stop (talk) 19:28, 11 December 2012 (UTC)

The Devil's Tower is an example of columnar jointing in an igneous rock, but Looie496 is right, these are layers of sedimentary rock tilted to nearly vertical. They look like alternating thin layers of sandstone and shale, with the sandstone layers possibly being turbidites, deposited from turbidity currents, as part of a flysch sequence. Mikenorton (talk) 21:20, 11 December 2012 (UTC)

Flow rate

I should be able to find the formula for this...but I can't seem to find the right one...argh!

I have a small vessel that's pressurized to around 20psi with nitrogen gas from a large cylinder with a regulator valve. The gas is flowing out to atmosphere through a 5mm diameter circular hole. Everything is at room temperature. I'm trying to find out roughly how long an 80 cu.ft cylinder will be able to maintain that pressure before I run out of gas.

Thanks in advance. SteveBaker (talk) 18:59, 11 December 2012 (UTC)

This can be solved approximately by a multi step process:-

1. Assume the flow out the orifice will be turbulent

2. Use standard fluid dymanics tables to convert the orifice to an equivalent pipe or 5 mm diameter. If the hole has abrupt edges (no chamfering) the equivalent length is roughly 10 x diameter

3. Add a length equal to the thickness of the material the hole is in

4. Add an equivalent length to represent the abrupt interface on the inside of the pressurised vessel

5. Apply the Fanning-Darcy equation to the total equivalent pipe length.

6. With the flow rate calculated in step 5, calculate the Reynolds Number

7. Use the Reyolds Number to verify that the flow is indeed turbulent.

If the flow is not turbulent, do Step 5 again using teh laminar flow version of the Fanning Darcy equation.

Fanning Dracy for turbulent flow is F = 0.718 Π [ ΔP/L x D¹⁹/(μρ³) ]^1/7

where F is flow rate m³/s; ΔP is pressure drop; L is equiv pipe length, m; D is pipe diameter, m; μ is viscosity of air, mPa.s; ρ is density of air, kg/m³.

Ratbone 124.178.135.56 (talk) 02:00, 12 December 2012 (UTC)

Depending on what assumptions you're making, this problem can more easily be solved by one of the Bernoulli equations. I would try the one for adiabatic compressible flow even though the adiabatic assumption may not jive with your request of Everything being at room temperature. Dauto (talk) 04:09, 12 December 2012 (UTC)

Neither of the above seems to notice that you have asked for the impossible, as soon as you let some gas out the pressure will drop below 20 psi and according to your question that's the end of that. Flow through orifices is well known at an engineering level, I can't say that Bernouilli or t'other stuff would actually even enter into my approach, once you have decided what you want. Incidentally is the tank insulated? (clue). Incidentally you are aprroaching and probably over the pressure ratio for Mach choked flow (second clue). Greglocock (talk) 23:42, 12 December 2012 (UTC)

Not correct. While a 5 mm orifice is quite significant, providing the pressurised chamber is large enough so that the percentage of gas released in the time frame of interest is low, a steady state pressure can be assumed. And if the throttling between the gas cylinder and the chamber is such that the gas cylinder can replace the gas let out of the chamber, steady state is maintained in the chamber until the cylinder drops to 20 psig. There must be a regulator between the cylinder and the chamber, in order to set the pressure to 20 psig. The OP didn't specify the time required to drain the cylinder - that's what he wants to calculate. Ratbone 124.178.41.96 (talk) 23:58, 12 December 2012 (UTC)

Sorry, yes you are right. oh well, he needs to specify the amount of gas in the supply tank as well, obviously. http://lss.fnal.gov/archive/d0-en/fermilab-d0-en-173.pdf is relevant. Greglocock (talk) 00:25, 13 December 2012 (UTC)

He did - it's an 80 cu ft cylinder. Ratbone 121.215.68.145 (talk) 01:31, 13 December 2012 (UTC)

Yeah - this isn't a theoretical arrangement - I know several people who have such systems operating. I just don't have any numbers on estimated gas consumption - and neither do they because they use the same gas cylinder for operating other equipment. The actual arrangement is a "80-size" nitrogen gas cylinder (which holds 80 cubic feet of gas, suitably compressed), with a "regulator valve" feeding into a couple of meters of 6mm tubing and then into an 8cm long by 2cm diameter cylindrical chamber with a 5mm diameter hole leading out to ambient air. The pressure regulator keeps the pressure at 20 psi as the air leaks out of the hole. I'm not even looking for exact numbers. Will the tank empty in 10 minutes, an hour, a day or a month? Gut feel says a couple of hours...but that's a lot less than some people are claiming. SteveBaker (talk) 14:20, 13 December 2012 (UTC)

Well, I've given you one method to get a rough answer, and Greglocock has given you another. Now you can calculate it for yourself and see. I agree with Greg that you need to calculate the velocity and check that it is not mach limitted - I should have thought of that before. We are here to help but not do all your work. Ratbone 120.145.60.154 (talk) 15:49, 13 December 2012 (UTC)

how much power does humanity consume with respect to the amount of solar power it receives?

I read from Dyson sphere that the Sun would provide only an order of a trillion times more energy than the power consumption of humanity. This makes humanity's power consumption seem quite large, as I would have expected it to be on the order of 10^15 or more. This means that humanity doesn't seem to have a lot of space to expand even within the solar system, energy-wise. 71.207.151.227 (talk) 23:02, 11 December 2012 (UTC)

Incoming solar power is 174PW [1]. World average power use is 15TW [2]. 15TW/174PW = 0.0086%. Sun's total output is 380YW[3], which is 2.5*10^13 times mankind's current energy usage. I doubt anyone can even make educated guesses on what the energy consumption of a civilization capable of building a dyson sphere would be like. Dncsky (talk) 23:35, 11 December 2012 (UTC)

We can't of course use all the solar power the Earth recieves. We need to leave much land and sea clear. A more practical view is this: The peak insolation at the Earth's surface is about 1 kW/m². over the 24 hour cyle it is approximately a half sine curve, integrating and allowing for weather and conversion efficiency (PV panels about 20%, other metthods about the same), you can generally extract an average of about 100 W or so. Taking the average roof plan area of a house as 400 m², Solar power is good for about 4kW, barely enough for an advanced western lifestyle. And it is far far too expensive. Floda 120.145.197.96 (talk) 01:30, 12 December 2012 (UTC)

Yes, under those circumstances it'd be insufficient. However, looks like a combination of wind & solar could be financially viable by 2030 to supplant a regional power grid. — The Hand That Feeds You:^Bite 20:49, 15 December 2012 (UTC)

Astronaut Lifestyle

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

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Are (male) astronauts allowed to masturbate while in zero gravity? If not, due to, well, basically the mess it could create, would the prohibition have an impact upon their mental health? 86.13.97.144 (talk) 23:54, 11 December 2012 (UTC)

One of the Apollo 12 astronauts did that very act, and was gently critisized for it by the flight surgeon for using up too much oxygen, but not seriously reprimanded. See the Flight Journal at 092:07:53. Tevildo (talk) 00:47, 12 December 2012 (UTC)

It should be noted that they were provided (as a bit of a joke) material for that exact purpose, as noted in the Apollo 12 article you linked. --Jayron32 00:55, 12 December 2012 (UTC)

Indeed. :) And, incidentally, when it comes to creating a mess, going to the lavatory in zero gravity is far more of a problem, and something that no amount of self-control can prevent. Apollo 8 had particular issues in this area. Tevildo (talk) 00:58, 12 December 2012 (UTC)

At the risk of feeding a troll OP, I think the transcipt has been misinterpreted. While the bit about eels is clearly a reference to masturbation, it is a joke reference. It is extremely unlikely that Pete Conrad would have, he was 39 and had been married since 1953; Richard Gordon was 40; Alan Bean 38 and married. At that age they were well and truely past the the teenage urge stage, and even if not married, were quite unlikely to be virgins. From personal experience, I know that when I had my first girl it was so far and away better than any tug, there was thereupon absolutely no interest in tugging ever again. Floda 120.145.197.96 (talk) 01:20, 12 December 2012 (UTC)

Happily married men don't masturbate?. --Jayron32 01:22, 12 December 2012 (UTC)

I can't speak for you, Jayron. However, from personal experience, normal men who have sexual access to a female, whether maried or not, happy or not, have something so superior to tugging, its like eating cheap hamburgers with bad meat, only more so, - if that's all you have, those hamburgers taste fine, but if you get regular perfectly cooked meals made from fresh ingredients, you won't ever bother with those smelly burgers. And folk in their middle ages, as the astronauts were, don't have the urges of teenagers. Floda 120.145.197.96 (talk) 01:38, 12 December 2012 (UTC)

I think what you mean to say there is that you stopped masturbating. It is important to remember not to generalize from singular experiences. --Jayron32 04:04, 13 December 2012 (UTC)

I'm glad you said "singular" and not "one-off". I wonder if NASA had any contingency plans if the Apollo capsule were involved in a high-jacking. DMacks (talk) 04:39, 13 December 2012 (UTC)

Chortle. --Jayron32 14:50, 13 December 2012 (UTC)

Approximately 70% of married people masturbate at least occasionally.[4] The reference I cited doesn't say so, but my presumption is that the percentage for married men alone would be higher than the 70%, since more men than women masturbate in general (92% vs. 62% according to our article). Red Act (talk) 02:10, 12 December 2012 (UTC)

In a study cited by the Kinsey Institute web site[5], 85% of men who were living with a sexual partner reported masturbating within the past year. Red Act (talk) 02:19, 12 December 2012 (UTC)

This is the first time I've ever heard it called feeding the troll. μηδείς (talk) 02:13, 12 December 2012 (UTC)

"Feeding the troll" means posting in response to a post made by a troll - that is, someone who posts a question to see what we all do about it, rather than because they need an answer. Ref Desk is unfortunately infested with trolls. The OP question ij this case could be a troll question. Floda 120.145.163.32 (talk) 02:24, 12 December 2012 (UTC)

The concept even has its own semi-nifty illustration, which you can see in Wikipedia:Deny recognition. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:25, 12 December 2012 (UTC)

Am I the only one who took Medeis' (Medeis's?) comment as a joke? Evanh2008 ^{(talk|contribs)} 04:30, 12 December 2012 (UTC)

Oops, you're very likely right. I'm slow (as is the IP just below, perhaps). But I still insist that the illustration is semi-nifty. I would call it flat-out nifty except it took me about a year to figure out what was going on in that illustration. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:13, 12 December 2012 (UTC)

Like always, Ref desk volunteers are not open-minded enough to assume good faith, and denounce every question which they themselves aren't mature enough to legitimately ask as "trolling". --140.180.249.194 (talk) 06:46, 12 December 2012 (UTC)

This is not actually a troll question - it demonstrates the conflict between astronauts as an exercise in public symbolism and conventional morality versus the scientific question of whether free-fall has any effect on this process. I would be prone to think that the sensation of constant falling might have some far-reaching instinctive effects (actually, it amazes me that astronauts can adjust to the point of being able to sleep) but I don't know. Looking up briefly, I don't know if anyone has actually gotten mice to breed in space for example [6] - actually, the things they are described in breeding in that article are all things that can be done more or less "in vitro" with sperm and eggs. Until I see actual evidence that an astronaut can ejaculate in free fall I don't know it will happen. Wnt (talk) 03:43, 12 December 2012 (UTC)

I'm bemused by this whole conversation... particularly the notion that anyone over 20 and married ceases to masturbate, especially when at least part of that notion's based on the fact that they have wives... which is of course very relevant when one is in outer space for weeks on end. Shadowjams (talk) 03:53, 12 December 2012 (UTC)

A related question is someone is certain to brag about being the first to be conceived in space, and someone is going to be able to brag about being the first to be born in space. Both a certainty. Apteva (talk) 04:22, 12 December 2012 (UTC)

That Wired reference casts some doubt on whether embryos will develop properly. (But mouse and human embryos develop very differently) Nothing is certain in biology until the experiment is done. Wnt (talk) 16:56, 13 December 2012 (UTC)

Apollo astronauts were not in space for weeks on end - they were only in space for a few days. The reference to eels in the transcript came at 3.8 days into the flight and refered to an oxygen anomaly that happened some hours before. Not that the flight time would matter much. Floda 121.215.48.204 (talk) 07:08, 12 December 2012 (UTC)

I guess it is a good thing I am not an astronaut cause it appears I am not normal! lol I am 50, have been happily married for many years, have an amazing sex life yet still manage to masturbate at least once ot twice a week! 99.250.103.117 (talk) 04:29, 12 December 2012 (UTC)

Indeed. It seems that men who never masturbate, or claim never to do so, regardless of marital status or ready access to sexual partners, are the ones who are way outside what is statistically "normal". But I rather think that Floda didn't mean "normal" in that sense. -- Jack of Oz ^[Talk] 21:48, 12 December 2012 (UTC)

My buddy used to tell me about the times he would date "Rosy Palm and her Five Sisters". Seriously, the Apollo Command Modules were not much bigger than your typical subcompact car on the inside; with two crewmates sharing the space with you, getting a little time alone was impossible. Hemoroid Agastordoff (talk) 17:30, 12 December 2012 (UTC)

Nowadays, probably few boys graduate from high school still a virgin, but back in the 1960's (in my country at any rate) that was not the case. Back then, drinking alchohol was illegal until you were 21, illicit sex was a lot less culturally acceptable, and folk left high school at 16 instead of 18 now.

When young 16 year olds started employment back then, the old guys at work would often try a few tricks and pranks to put the younguns in their place, or to try them out. A not uncommon initation workplace exchange was something like this:-

Old tradesman: "Are you a wanker?"

Young apprentice: "Of course not." - spoken with an indignant expression.

Old tradesman: "Are you married?"

Young apprentice: "No."

Old tradesman: "Do you live with a girl, then?"

Young apprentice: "No."

Old trademan: "Well, you must be a wanker!"

At that point, the young guy was usually red in the face and speechless. That pretty much sums the matter up. Floda 124.178.41.96 (talk) 00:34, 13 December 2012 (UTC)

That is a fantastic story, that I didn't actually read. And I think is long overdue to close up this stupid question. Shadowjams (talk) 03:56, 13 December 2012 (UTC)

Resolved

Now should someone with a "That is a fantastic story, that I didn't actually read" attitude close a topic? As much as I think he shouldn't, the question about mental issues is absurd. The sheer length of the topic is even more absurd, given that humans can go for a decade without masturbation. so, this is as resolved as possible. - ¡Ouch! (^{hurt me} / _{more pain}) 12:01, 13 December 2012 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.