Wikipedia:Reference desk/Archives/Science/2007 December 26

= December 26 =

reactions to drugs
Is a person's reaction after smoking cannibis at all genetic (e.g. Red, eyes, paranoia, sense of floating). Only asking because a friend of a friend of a roommate of one of my distant cousins said he noticed this. Thanks, schyler (talk) 00:30, 26 December 2007 (UTC)


 * Of course I can't speak for any specific symptoms, but according to this study, certain individuals have a genetic predisposition toward becoming psychotic as a result of cannabis use; so yes, genetics can affect your reaction to cannabis. And you might want to tell your "roommate's friend's friend's distant cousin" to stop hitting the stuff or see a doctor if the effects are starting to worry him. Someguy1221 (talk) 03:00, 26 December 2007 (UTC)

Ill make sure to tell him ;) Thank you. schyler (talk) 03:11, 26 December 2007 (UTC)

Sex - Related
medical question removed

I'm sorry, but you are, by the definition of the word, requesting a diagnosis. And so I must apologize, but this is precisely the kind of question that the reference desk guidelines prohibit asking or answering. Someguy1221 (talk) 02:53, 26 December 2007 (UTC)
 * Fact check. The question was not asking for a diagnosis. The request seemed to be for links to relevant medical information. --JWSchmidt (talk) 15:02, 26 December 2007 (UTC)
 * The question related some symptoms and then said "What could be the cause of this?" - that is clearly a request for a diagnosis - and is therefore not an acceptable question for the reference desk. The fact that the questioner asked for a reply in the form of some links rather than some inline explanation doesn't change that in the slightest.  It is the question that is disallowed - not the form of the answer.  If the questioner had asked for a reply in the form of an interpretive tapdance routine, that wouldn't be OK either.  Please take further discussion to the talk page. SteveBaker (talk) 15:25, 26 December 2007 (UTC)
 * I find it disruptive when reference desk participants assume bad faith and bite new visitors. If we intend to interpret any description of personal health issues as not being welcome here then we should list that as a rule at the top of this page where people can see it before they edit the page. "Please take further discussion to the talk page" <-- I'm trying to repair the damage that has been done here, on this page, to a Wikipedia visitor. I do not see how that can be done effectively on some other page. If the person who started this thread comes back I want them to see that it is Wikipedia policy to welcome and help new visitors. --JWSchmidt (talk) 16:20, 26 December 2007 (UTC)
 * Taken to talk page. Nil Einne (talk) 16:45, 26 December 2007 (UTC)
 * To the question asker - you should seek the advice of a doctor for medical/health issues you have as they are the people who are qualified and trained to help you in such matters. If you are too shy, you may want to seek out a female doctor or whoever you will feel comfortable asking. Bear in mind that in nearly all cases doctors are ethically bounded to keep any thing you tell them confidential. Nil Einne (talk) 16:57, 26 December 2007 (UTC)

It's that time of the year again... (science edition)
Ok, I'm bored, on vacation and my pending image projects don't look very exciting at the moment. Do you guys have any suggestions for cool science images, especially animations, for me to create? Especially physics, but any suggestion is welcome. Drop them here and I'll see what I can do. :) By the way, merry belated xmas! &mdash; Kieff | Talk 06:03, 26 December 2007 (UTC)
 * The Atom page is the the science COTM and would probably be great with some sort of animation. maybe some sort of energy in --> excited state --> return to ground state with emission of a photon or a matter/antimatter annihilation? Cheers! Furmanj (talk) 09:38, 26 December 2007 (UTC)
 * Interesting. But how far can artistic freedom go with such a thing? It can't be too conceptual, or there would be misunderstandings. &mdash; Kieff | Talk 14:06, 26 December 2007 (UTC)


 * Have you seen Greenspun illustration project? --JWSchmidt (talk) 14:56, 26 December 2007 (UTC)


 * Personally I think the Tokamak page could use some nicer illustrations. Currently there is only one low-res explanatory graphic and it's not all that explanatory in my opinion. --24.147.86.187 (talk) 17:47, 26 December 2007 (UTC)


 * I'm still hoping for a geology and biome map of the the terrain underneath North Carolina. I had hoped I would be skilled enough to create this diagram but I am not.  I'm thinking a nice isometric cutaway to reveal the soil and rock forms of the three regions of the state (Appalachian Mountains, Piedmont, and Coastal Plain); then, on top, a sort of schematic representation of the flora and fauna for each region.  Post on my Talk Page if you're interested - I can expound in great depth!  Nimur (talk) 19:35, 26 December 2007 (UTC)

Take a look at all the wonderful varieties of diffusion at Diffusion! Animations of these topics could clarify the mechanisms and differences between each one. &mdash; Scientizzle 00:53, 29 December 2007 (UTC)

Winter Solstice
If the shortest day is in December, why is the coldest time of the year in January & February? —Preceding unsigned comment added by 67.177.229.163 (talk) 06:48, 26 December 2007 (UTC)


 * The average temperature continues to fall as large bodies of air and water radiate heat into space. Not until those later months to they start gaining net heat. As Cecil Adams put it in this edition of The Straight Dope which I found as an external link in Season, "The period of max temperature in the mid-latitudes always lags about 25 to 30 days behind the period of max daylight, due to the fact that the earth heats up and cools off relatively slowly." MilesAgain (talk) 08:18, 26 December 2007 (UTC)


 * January and February is the warmest time, not the coldest... And the longest day is in December, not the shortest... :-P Nil Einne (talk) 15:38, 26 December 2007 (UTC)


 * You must live in the southern hemisphere. It's cold in January in the northern hemisphere. NYCDA (talk) 16:34, 26 December 2007 (UTC)


 * I'm aware of that. I was pointing out the OP may not know. Hence the :-P Nil Einne (talk) 14:12, 28 December 2007 (UTC)


 * The OP clearly said "IF the shortest day is in December..." - so this is quite clearly a hypothetical question which (in practical terms) relates only to the Northern hemisphere. SteveBaker (talk) 17:00, 26 December 2007 (UTC)


 * Well, this is of no such importance to start a discussion, in any case. If we go logical, though, the shortest day is in December is an undecidable proposition, if a point of reference is not adjointed. I think this is an issue that relates to the whole planet, for in the Southern hemisphere a similar situation arises, with cold being replaced by warm, I guess. Pallida  Mors  18:56, 26 December 2007 (UTC)


 * Yes but does the OP there is a difference? Some people don't and the OP gave no clear indication he or she does in his or her question so I saw no harm in pointing that out. Note that if could be taken in two ways. It could be taken to mean 'if the shortest day is in December' (like it is in the Northern hemisphere) or 'if the shortest day is in December' (i.e. Since we all know the shortest day is in December). Both are easily as likely. For example, in my above sentence I presumed at the time that it would be clear I knew the difference between the southern hemisphere and northern hemisphere since I included the smiley. NYCDA clearly didn't understand that though and rereading my sentence it was easily posible I was using the smiley because I was poking fun at what I thought was a mistake on the part of the OP rather so it was perfectly resonable for NYCDA to assume I might not know the difference (although I think the a far greater of people in the southern hemisphere particularly those from English speaking countries are since they are exposed to the northern hemisphere a lot) Nil Einne (talk) 14:11, 28 December 2007 (UTC)


 * This has nothing to do with the Winter Solstice, but the shortest day of the year in the United States is actually the second Sunday in March. This is the day on which we "spring ahead" from Standard Time to Daylight Saving Time.  It has only 23 hours. Thomprod (talk) 03:10, 27 December 2007 (UTC)

Digital to analog convertor IC sampling Vs settling time confusion
HI everybody, I am not sure if this is the right place to ask this but just asking with hope.If anybody knows then please just reply. I have seen a DAC IC(DAC 9238) indicating that it gives 125MSPS(million samples per sec) or 125MHz speed in updating the digital data to analog signal in its datasheet. But for dac's, the settling time is important(time taken to convert digital data to analog signal). For this dac the settling time is 30ns(I found this value somewhere inside). So this gives a data update rate of only 33 MHz. So what does 125MHz here mean?.The adds show this 125MHz in huge size fonts but looking at the settling time,it can't even exceed 33MHz.I hope you can understands what I'm trying to say.If anybody gets a click in their mind,plz do reply. Thanks for your time. —Preceding unsigned comment added by 122.164.63.100 (talk) 10:55, 26 December 2007 (UTC)


 * Settling time should be quoted to a certain accuracy. So it may settle to within 1% @ 33 MHz, but to within 10% @ 125 MHz. Therefore it can still be used at 125 MHz but with reduced accuracy. BTW 125MPS is equivalent to 62.5 MHz.--TreeSmiler (talk) 11:21, 26 December 2007 (UTC)


 * 62.5 MHz is the maximum bandwidth of a bandwidth-limited signal that can theoretically be reproduced faithfully given a sampling rate of 125 MHz. However, uses of DACs are not limited to reproducing sampled waveforms. I don't think it is strictly correct to equate 125 MSPS to 62.5 MHz without considering the application. --71.162.233.225 (talk) 16:57, 26 December 2007 (UTC)
 * OK Say you had a sine wave at 62.5 MHz. THis can be digitized (just about) By taking 2 samples per cycle (ie a sampling rate of 125MS/s). DA conversion followed by a low pass filter with a cutoff just above 62.5 MHz would reconstitute the sine wave. Agree?--TreeSmiler (talk) 22:44, 26 December 2007 (UTC)

Thanks for your replies. I understood. Anyway, how can we reconstruct using just 2 samples using a LP filter?...I thought that I may gonna need atleast some 20 samples of digital data for one sinewave inorder to reconstruct using a dsp or mcu through dac... —Preceding unsigned comment added by 122.164.61.94 (talk) 11:31, 27 December 2007 (UTC)

Return protocol for Michael Collins
If during the Apollo 11 mission, there had been an accident which would have left Armstrong and Aldrin stranded on the Moon with no chances of being rescue, would it have been possible for Michael Collins to make it back to Earth alone? Was there even any special plan prepared for such an eventuality? -- Danilot (talk) 13:35, 26 December 2007 (UTC)
 * The recent film "In The Shadow Of The Moon" includes the text of a speech for Nixon, in case Armstrong and Aldrin were stranded on the moon. Collins would have returned to Earth. I remember the Apollo 11 mission well.  A few days before, the Soviet Union lauched Luna 15 but the West didn't know that it was a robot sampler.  The press speculated it might have been a lifeboat to enable the Apollo astronauts to return in case there was an accident.--80.176.225.249 (talk) 14:34, 26 December 2007 (UTC)
 * The press also speculated that Luna 15 was sent to sabotage the US landing effort. SteveBaker (talk) 15:14, 26 December 2007 (UTC)

loaded question
I have been reading on nasa's web site about stellar evolution and some questions have came up that I could not find an answer for. I am currious but not well educated so if you can answer my questions please use small words. Q- if iron evolves inside stars and the end result of this star is a black hole, that not even light can escape, then how do we have iron on our tiny little planet? Q- what is the process that causes gas to colapse into a star. I thought that a gas would dissipate evenly into its surroundings.

cris —Preceding unsigned comment added by 68.209.69.103 (talk) 16:55, 26 December 2007 (UTC)
 * You can find answers in our articles on star formation and planet formation. Cheers, Ouro (blah blah) 17:13, 26 December 2007 (UTC)


 * Answer 1: Black holes are not the only possible end for a star. It can also become a white dwarf or a neutron star. Both can trigger a supernova in different ways, therefore spreading iron and many more elements into space.


 * Answer 2: Gravity is the key. An initial smooth distribution of matter will eventually collapse and cause the hierarchy of structures, such as clusters of galaxies, stellar groups, stars and planets. So gas stays in clouds until other forces are unable to compensate for gravity, and mass starts to collapse inwards. -- Danilot (talk) 17:16, 26 December 2007 (UTC)


 * Most of the iron in the universe comes from supernova nucleosynthesis (specifically, Type I supernovae), not stellar nucleosynthesis (Carroll & Ostlie, Modern Astrophysics). Regarding star formation through self-gravitation, see Jeans instability, which has nothing to do with Plumber's Crack. -- Coneslayer (talk) 17:31, 26 December 2007 (UTC)

Athletic Performance
On the behalf of every high school athlete out there - does "saving yourself" ; ) before a game or meet actually do anything? If so, how long should one hold off? I've gotten so much conflicting advice, and I think the RD is the place to put this to rest. Thanks. - Anonymous


 * For the avoidance of ambiguity, you mean avoiding sexual activity (specifically orgasm) before athletic activity, right? Marnanel (talk) 23:03, 26 December 2007 (UTC)

Yeah. Hence ; ) - OP
 * This is just my opinion: I have no experience of such matters. BUT, if one were not to expend much energy during the act (ie making it an extreme quickie), I dont see how it could affect your performance in the sport. In fact it might be beneficial, because it gets those feelings out and allows you to concentrate on the game etc.--TreeSmiler (talk) 03:24, 27 December 2007 (UTC)


 * I was going to ask TreeSmiler if the absence of experience is referred to sexual or athletic activity. But then I refrained. That is so personal. The amount of athletic activity he/she has is none of our business. ;) Pallida  Mors  14:32, 27 December 2007 (UTC)
 * I am not an athlete so I wouldnt know the effect of pre performance sex! The important point is that if you spent all night lovemaking, it takes a lot of energy and you are going to be tired in the morning. I assume the original questioner is male so I think pulling off a 1 minute quickie just before (not during) the game would not affect performance unduly.--TreeSmiler (talk) 17:12, 27 December 2007 (UTC)


 * Most of what I can find online (e.g. ) seems to say there is no direct link. However, a more important factor is being well-rested and avoiding extra psychological stress.  So, if sex causes you anxiety and/or is keeping you from sleeping, then perhaps you should abstain.  If instead you find sex is satisfying and it is timed not to interfere with sleep, then perhaps it is a good thing to continue.  In either case, I would encourage you and other high school athletes to consistently practice safe sex when you choose not to abstain.  Dragons flight (talk) 15:59, 27 December 2007 (UTC)

anatomy
I'm trying to find out what ligament holds/supports the aorta in place. —Preceding unsigned comment added by 71.172.220.245 (talk) 22:07, 26 December 2007 (UTC)


 * Unless we have a doctor/nurse to answer, the best shot is to Google aortic supporting tissues I suppose--TreeSmiler (talk) 22:49, 26 December 2007 (UTC)


 * Or possibly somebody who knows where to look. Have a bit of a wander round here and there is a fair bit about the anatomy of the chest and what the aorta is attached to. You might even be able to find some pictures.Richard Avery (talk) 23:09, 26 December 2007 (UTC)


 * Is it supported?--TreeSmiler (talk) 23:17, 26 December 2007 (UTC)


 * Too bad those images are so low res I can't read all of the text. Should be vector graphics, btw. —Bromskloss (talk) 23:23, 26 December 2007 (UTC)


 * Gray's Anatomy is free at Bartleby. This link takes you to a page that describes the attachments. It seems that the deep fascia of the neck hold the whole business up, and that a pair of ligaments, the superior and inferior sternopericardiac ligaments, anchor the pericardium in front. There's more.  --Milkbreath (talk) 00:15, 27 December 2007 (UTC)

Stainless steel, nickle, pulled by magnet
Is it true if an alloy stainless steel has no nickel, it is pulled by a magnet, whereas if an alloy of stainless steel has nickel in it, then it is not pulled by a magnet? William Ortiz (talk) 23:15, 26 December 2007 (UTC)


 * The article Stainless steel should answer this. But it says here that only austenitic ss is non magnetic--TreeSmiler (talk) 23:20, 26 December 2007 (UTC)


 * It is my understanding that austenitic stainless steel, which is normally nonmagnetic, can be magnetic if it has been "cold worked". Billtobill (talk) 15:53, 27 December 2007 (UTC)


 * Yeah thats what my link says. Did you see it?--TreeSmiler (talk) 17:03, 27 December 2007 (UTC)