Wikipedia:Reference desk/Archives/Science/2014 April 9

= April 9 =

Chemical Test
How is a chemical test developed and/or discovered.Please explain with an example.117.194.234.95 (talk) 03:22, 9 April 2014 (UTC)

StuRat (talk) 04:51, 9 April 2014 (UTC) I am not a student of school college university.I asked you question that has nothing to do with homework.I disapprove prejudiced notions.I dont think it will be a good thing to go to school/college in thirties.I soloicit your answer to my query and not these malicious conjenctures.117.194.249.163 (talk) 13:32, 9 April 2014 (UTC)
 * What chemical test did you have in mind? Wikipedia has an article titled Chemical test that discusses many wet chemistry chemical tests.  There's a long list of them.  If you read articles on any one of them, it may discuss how that test came to be.  -- Jayron  32  14:14, 9 April 2014 (UTC)
 * I think the OP is thinking about a "chemical test" like the pH paper that you find so often in Chemistry labs. In that case, we may have to look up the history of the pH paper. But it all depends on whatever "chemical test" you're talking about. 140.254.227.100 (talk) 22:02, 9 April 2014 (UTC)

Skin cream gun control study
Hello, maybe you've heard of the study in which participants had to assess the results of a (fake) study about the efficacy of either skin cream or g*n c*ntr*l laws (with exactly same numbers), which purportedly showed that peoples' math reasoning ability declined when the math problem in question had to do with a politicized issue. I'm interested in the (fake) problem itself: After that the participants had to "indicate whether the experiment shows that using the new cream is likely to make the skin condition better or worse." It says on the internet that it's not enough to compare the numbers, one has to do the ratios. But what ratios? I see two ways of going about solving this: Which way is the correct one and why? (If I'm ever recruited for a similar study:) And is it incidental that in this example they devised, the conclusion is the same either way or is it mathematically inevitable?
 * Of those who used the cream, 223/(223+75)=75% got better, vs 107/(107+21)=84% of those who didn't => ergo, cream sucks
 * Of those whose rash got better, 223/(223+107)=68% used the cream, vs 75/(75+21)=78% of those, whose rash got worse =>cream still sucks

Asmrulz (talk) 05:37, 9 April 2014 (UTC)
 * I'm not an expert, but it seems to me that the 1st method is correct. The 2nd group is your control group, you are comparing the effectiveness of the treatment vs the control group, which can be "no treatment" as in this case, or can be the current best available treatment (especially where withholding treatment all together would be unethical). So yes, put simply with the treatment 75% got better, without it 84% got better, so the treatment actually performed WORSE then no treatment at all. Vespine (talk) 06:02, 9 April 2014 (UTC)


 * You can only use the second method if you extrapolate the numbers ("normalize"?) to make the population sizes equal. The first group has 298, the second only 128. Multiply the second row by 2.328 and you get 249 and 49. That makes it clearer that using the cream has no particular effect. In fact, it appears that letting the body's own immune system handle it seems to be better than using the cream. But as to whether it "sucks" or not, you would have to do some kind of statistical analysis to see whether the 249 and the 223 are statistically different across the given population. ←Baseball Bugs What's up, Doc? carrots→ 08:25, 9 April 2014 (UTC)


 * Why the asterisks on "gun control" ? Is it considered an obscene term in your part of the world ? StuRat (talk) 08:33, 9 April 2014 (UTC)
 * It's from the Jargon file of hacker slang which I read long ago (link) It's funnier this way :) Asmrulz (talk) 10:16, 9 April 2014 (UTC)
 * The first method where one comparess the ratios of improvement in two unrelated populations is a rational test of the cream. The second method conflates the ratio of interest with the ratio of test and control populations, which is arbitrary, and cannot justify its conclusion. In this data the cream demonstrated less improvement 75% than whatever else (unspecified) other people did that improved 84% of them. The cream really sucks but the lesson here will not be welcomed by g*n r*ghts l*bby*sts with kn**-j*rk th*nk*ng st*ck *n 1791. 84.209.89.214 (talk) 13:08, 9 April 2014 (UTC)

Thanks to all of you for your answers. Asmrulz (talk) 14:43, 9 April 2014 (UTC)
 * I agree with others that the first method is the correct one. But let me just add a note that the differences are not actually statistically significant (p = 0.0574 using Fisher's exact test, calculated using this tool, so the conclusion in a published paper would be that the data don't establish that the cream has any effect. Looie496 (talk) 14:02, 9 April 2014 (UTC)

Heat and magnetic fields.
As I understand it, heat destroys magnetism. So why then, does the magnetic field of the earth survive when the core of our planet which is hot enough to create a molten core? — Preceding unsigned comment added by 86.6.96.72 (talk) 09:59, 9 April 2014 (UTC)
 * Your understanding is wrong. --DHeyward (talk) 10:12, 9 April 2014 (UTC)

Explain?

Heat can stop a magnet being magnetic, this is true. Read the following to understand why we have a magnetic field around the Earth. http://en.wikipedia.org/wiki/Earth's_magnetic_field#Physical_origin 217.158.236.14 (talk) 11:29, 9 April 2014 (UTC)
 * A Magnetic field is produced by electric charges in motion i.e. Electric current. The way that works was explained by Maxwell in his elegant set of differential equations which hold true at all temperatures that we experience. 84.209.89.214 (talk) 12:09, 9 April 2014 (UTC)
 * Just to clarify, I am aware of the above and I am not debating it, however it is also true that ferromagnets can lose magnetic properties when heated to above the Curie temperature.217.158.236.14 (talk) 12:23, 9 April 2014 (UTC)
 * Yes, but that isn't because "heat destroys magnetism". It's because heat alters the crystal structure of the iron so it no longer has ferromagnetism.  Different ideas.  -- Jayron  32  12:31, 9 April 2014 (UTC)
 * Agreed, which is why I said "Heat can stop a magnet being magnetic", and not "destroys magnetism". — Preceding unsigned comment added by 217.158.236.14 (talk) 13:14, 9 April 2014 (UTC)


 * To add detail to the answers above: ultimately magnetism arises from the movement of large numbers of electric charges in a synchronized way.  In a ferromagnet (an ordinary solid iron magnet), the synchrony comes from the fact that large numbers of atoms are frozen into alignment with each other.  If you heat a ferromagnet to near the melting point, the atoms lose their alignment and the magnetic field disappears.  But the Earth is not a ferromagnet.  Its magnetic field arises from electric currents flowing coherently through the magma on a vastly larger scale.  The reason why that happens, incidentally, is not very well understood -- but clearly it does happen. Looie496 (talk) 13:52, 9 April 2014 (UTC)
 * Vast energies are stored in the Earth's magnetic field and evidence in the Geologic record that it has periodically reversed polarity is evidence that it is part of a resonant system. As yet no simple global model of Earth's resonant modes, that may be linked with resonances in other bodies, has emerged because the short time span of collected data is plagued by Heteroscedasticity of local anomalies. 84.209.89.214 (talk) 16:02, 9 April 2014 (UTC)
 * (Hey, you seem to be giving some good responses/refs here recently... or at least I think so, but it's hard to keep track of IPs... any chance we can convince you to register? It is less anonymous and more pseudonymous than signing with an IP, but it may actually increase your privacy too :) SemanticMantis (talk) 22:58, 9 April 2014 (UTC)
 * I'm pretty sure the editor behind the IP has had multiple accounts and are technically WP:block evading. People are just turning a blind eye because they aren't harping on about its/it's and other grammar and spelling issues. However registering another account is still probably not a good idea, instead requesting an unblock under one of their blocked accounts, preferably the main one. Nil Einne (talk) 05:01, 10 April 2014 (UTC)
 * (Thank you for those kind comments. Nil Einne can identify me easily. "Its" and "it's" mean different things. A registered user pointed that out a while ago.) 84.209.89.214 (talk) 12:52, 10 April 2014 (UTC)


 * Many factors establish the earth's magnetic field. It's not constant and rotation and heat affect it.  If you want an extreme case, look at the sun.  It has no iron core.  It's created by heat and rotation.  It flips N/S polarity every 11 years and often has a weak quadropole during maximum sunspot activity.  The resultant magnetic field is very strong at sunspot minima.  The earth has a different mechanism, but it's not correct to simply associate heat with the destruction of the magnetic field.  There are solid magnetic properties as well as rotating, conducting fluids.  See Dynamo theory to see how the Earth's magnetic field is created and changes.  A ferromagnetic solid may reflect the magnetic field imprinted on it, but it's not necessarily the force that is responsible for the magnetic field.  --DHeyward (talk) 05:42, 10 April 2014 (UTC)

Institutional dependence
Hi there. I am interested in a phenomenon whereas an individual who spends many years in a restrictive environment, e.g. prison, becomes dependent on the institution and develops unhealthy reactions sabotaging normal release process for instance. I am also interested if the phenomenon like this has ever been coded, if there is a corresponding ICD-9 or ICD-10 code describing it. Thank you --AboutFace 22 (talk) 20:01, 9 April 2014 (UTC)
 * Stockholm syndrome came to my mind. Brandmeistertalk  20:07, 9 April 2014 (UTC)

Oh lordy! I just was about to get back and add that in my understanding the phenomenon I am looking for or the code thereof is NOT the same as Stockholm syndrome. It should be distinct from it. Thanks.--AboutFace 22 (talk) 20:10, 9 April 2014 (UTC)

I think Learned_helplessness is relevant, since it describes the effect that a punitive environment has on individual volition. OldTimeNESter (talk) 20:17, 9 April 2014 (UTC)


 * So, you are asking about individuals who become institutionalised? 86.146.28.229 (talk) 21:21, 9 April 2014 (UTC)

Thank you. The last two suggestions are quite valuable. I have to think about it, especially the institutional syndrome. --AboutFace 22 (talk) 01:50, 11 April 2014 (UTC)

Quadruple axels and beyond
What actually prevents a figure skater from making quadruple or even quintuple axels and similar feats? And what capabilities should (s)he theoretically have to perform them and similar stuff? Is it just a muscular force of legs during the jump-off, adequate jump height giving more time and a good sense of balance? --93.174.25.12 (talk) 20:04, 9 April 2014 (UTC)
 * The article on Jumping mentions the force-velocity ratio for muscles, which establishes the biomechanical limits on jumping height. OldTimeNESter (talk) 20:29, 9 April 2014 (UTC)


 * Basically you have to do it "just right", or you'll be either over or under rotated and will land with the skate blade not pointing in the right direction, and will probably fall. You also have to keep your center of gravity "just so", or you'll land at the wrong angle... and will probably fall. The more spins you have in a given jump, the harder it is to do. But it will happen eventually. The double axel was once considered tough to do. And lots of skaters fall on triple axels. As the commentators said at the Olympics recently, "It's really hard!" But someone will eventually succeed in doing the quad axel (4 1/2 times around) and that will set the bar higher. ←Baseball Bugs What's up, Doc? carrots→ 20:54, 9 April 2014 (UTC)


 * Maybe we'll see it done some day. But there are limits to the torque a skater can apply to himself, as well as (perhaps softer) limits to the ability to control. I'm confident there's some n for which humanity will never see an n-tuple axel, but what that n is is probably best investigated by watching competitions and waiting, rather than trying to model it from first principles. In other words, I think the answer to your last question is "yes"; it's "just" those three things that would have to improve. Maybe replace "sense of balance" with kinesthetic intelligence. SemanticMantis (talk)
 * It probably varies per-person, given the above comments. But the basic thing is that you must have enough angular velocity to complete those axels in the time you remain in the air. A quantitative analysis would require the maximum impulse the skater could deliver using the muscles in question, and how quickly (so the time for spinning can be calculated). The axis of rotation should be close to vertical for balance purposes, you do not want any torque components other than the vertical component to deal with (torque is a pseudovector).--Jasper Deng (talk) 07:48, 10 April 2014 (UTC)
 * One technical point: If you intend "axels" to mean "rotations", note that the jump known as the "Axel" is named for a guy, Axel Paulsen or some such. It's the only one of the jumps that starts facing forward. Hence a single Axel is 1 1/2 revolutions, a double Axel is 2 1/2, and so on. ←Baseball Bugs What's up, Doc? carrots→ 05:07, 11 April 2014 (UTC)


 * This is purportedly Keegan Messing unsuccessfully attempting a 4A in practice. 70.36.142.114 (talk) 00:02, 13 April 2014 (UTC)