Wikipedia:Reference desk/Archives/Science/2015 March 26

= March 26 =

STAR*D
Where can I find the complete text of the study STAR*D (Sequenced Treatment Alternatives to Relieve Depression)? --151.41.185.32 (talk) 04:58, 26 March 2015 (UTC)
 * A study is not a text object, it is a project that (hopefully) produces one or more text objects as a result. So there is no such thing as "the complete text of the study".  You can find a comprehensive review of the results at https://www.madinamerica.com/wp-content/uploads/2011/11/The-Star-D-Project-Results.pdf. Looie496 (talk) 12:52, 26 March 2015 (UTC)

Electronics problem


I don't really understand what's going on here. What does the text in the boxes mean? I suspected something to do with power factor initially, but I'm sceptical as the real power of inductors and capacitors is zero. Can someone help me out?--Leon (talk) 10:13, 26 March 2015 (UTC)


 * It looks like the "VAR" values in the boxes are the reactive power in volt-ampere reactive. If that's what the VAR values mean, the loads are not purely reactive--they have resistive components. --173.49.16.112 (talk) 11:27, 26 March 2015 (UTC)
 * I suspect that the small ind. and cap. beside each box indicates that the first two are pure inductors and the third is a pure capacitor. — LongHairedFop (talk) 13:02, 26 March 2015 (UTC)
 * But a pure inductor has a real power of zero, as does a pure capacitor.--Leon (talk) 14:18, 26 March 2015 (UTC)
 * Okay, with the help of 173.49.16.112 I think I understand what the terms in the boxes mean. But, what I'm ultimately interested in finding the resistance R, and I still don't know what to do. I know nothing other than the diagram and that the voltages and currents written down are RMS values. Can anyone help?--Leon (talk) 19:49, 26 March 2015 (UTC)
 * The impedance of each of the loads has a resistive and reactive component, and can be represented as a complex value $$Z = R + jX$$, where $$R$$ is the resistance, $$X$$ is the reactance, and $$j$$ is the unit imaginary number. The difference between capacitive reactance and inductive reactance is that the value of $$X$$ is positive for one and negative for the other (off the top of my head I don't remember which is which). Impedance can be combined using the same formulas for combining resistance in series and parallel connections. Ohm's law applies to impedance too, when resistance is replaced by impedance. What you have now is a circuit analysis problem, much like one for a DC circuit except that you're now dealing with complex values. The power measured across a load is still $$V\cdot I$$, except that it has a real and a reactive component (which are given to you). You can solve for $$R$$ by solving a system of linear equations. --173.49.16.112 (talk) 02:12, 27 March 2015 (UTC)
 * What 173. said, except that you don't really need a system of equations, just a few algebraic steps. First work out the left-hand impedance using $$S=I^2 Z$$, $$S$$ being apparent power (a complex number, with watts being the real part and inductive VARs being the negative imaginary part). Then work out the combined impedance of the other two loads by adding the apparent powers, remembering that capacitive VARs are positive and inductive ones negative, and using $$S=I^2 Z$$ again. Now add those two complex impedances and you can work out the voltage at the right-hand side of $$R$$. --Heron (talk) 11:19, 28 March 2015 (UTC)
 * Okay, I think I've got it now. Cheers!--Leon (talk) 11:28, 28 March 2015 (UTC)

What type of mixture is smoke?
Smoke is homogeneous or heterogeneous mixture? Just a word plz. This is not my homework.

Learnerktm 13:47, 26 March 2015 (UTC)


 * Usually heterogeneous, because smoky air is usually turbulent. Looie496 (talk) 13:58, 26 March 2015 (UTC)
 * Looie496, but smoke isn't itself homogeneous when two or more gases are mixed in it without considering air?

Learnerktm 14:58, 26 March 2015 (UTC)


 * It really depends on how careful you want to be, and what exactly you're talking about. One the one hand, we can say smoke is clearly heterogeneous. Start a fire, freeze time, and examine a sample a liter of smoke. Parts of it are solid particles, parts are gas, and parts are liquid. Since we have different things in different places, we could say that it is heterogeneous.
 * On the other hand, looking at that same liter of smoke, we could look at the distribution of each particle size and type in any given cc volume. Unless you have highly sophisticated, accurate and precise measurements, you would find that the properties of any given cc are indistinguishable from any other cc. In that case, you could say that the mixture is homogenous, sometimes we would say well-mixed. So the "correct" answer really depends on why you are trying to answer the question, what you want to do with that info, and how you operationalize the concepts of homo/heterogeneity. For example we could use Mean_field_theory to analyze smoke, under the assumption that it is close enough to homogenous. Or, if we are interested in vortex dynamics of a specific plume, we could consider the anisotropic features, etc. SemanticMantis (talk) 15:13, 26 March 2015 (UTC)
 * Under the standard definition of homogeneous/heterogeneous as taught in most chemistry classes, smoke is clearly and unambiguously heterogeneous. The definitions are of course a bit "fuzzy" depending on context, but under the normal understanding, homogeneous mixtures feature molecule-sized particles evenly distributed with each other.  Heterogeneous mixtures feature distinct particles of a clearly different phase from each other.  The surface effects of the phase distinctions are clearly demonstrated through the Tyndall effect, which is often used as the main "test" for distinguishing a homogeneous solution from a heterogeneous suspension.  Under that formal definition, smoke is unambiguously heterogeneous, as smoke particles scatter light, no matter how "well mixed" they are.  -- Jayron 32 15:54, 26 March 2015 (UTC)


 * Yes, but smoke is rarely well-mixed -- as the picture illustrates. Looie496 (talk) 15:57, 26 March 2015 (UTC)
 * I think we all agree that smoke is heterogeneous, except for in rather non-standard situations and interpretations. Just wanted to allow for that possibility in my post above. SemanticMantis (talk) 18:55, 26 March 2015 (UTC)


 * It's hard to tell without a color picture, but white "smoke" is almost always steam, and one can assume they use electric heating and water cooling at a steel mill, neither of which generates smoke. The smelting process itself generates carbon dioxide. For real smoke you need to see an old coal-burning plant or locomotive or the like. μηδείς (talk) 17:50, 26 March 2015 (UTC)
 * "The largest single use of coal in the steel industry is as a fuel for the blast furnace" - see also blast furnace and Bethlehem Steel. Apparently there are at least some electric powered blast furnaces, but our article says they are only used in countries that have low access to coal. SemanticMantis (talk) 18:55, 26 March 2015 (UTC)


 * There is a column, barely visible, of what looks like smoke in that picture, on the mid-right background. The rest is steam that has condensed to water vapor. μηδείς (talk) 19:35, 27 March 2015 (UTC)


 * Well, to be strictly speaking, the white smoke also isn't steam, it is fog. Steam is invisible and homogeneous in air, whereas the white stuff you see in what we commonly call "steam clouds" is actually condensed water droplets, which is fog, which is heterogeneous.  The first paragraph of the article steam deals with these linguistic inaccuracies.  -- Jayron 32 18:53, 26 March 2015 (UTC)


 * Coal used to run a blast furnace will produce black smoke, which it is possible one may see in the distant background of the picture given. (The image is of low quality, but I have no reason to insist the right center background plume is not actual smoke.  AS far as my informants tell me, coal blast furnaces in the US are a thing of e distant past, even from the 1970 view.)  But the clean white plumes are obviously steam, and CO2 is invisible.


 * The claim that white "smoke" is actual smoke (partially oxidized carbonaceous particles) is about as well-founded as saying that the steam that is sometimes released from nuclear containment plants is "smoke".


 * We simply can't judge certainly whether the fourth background plume from the given image is actual smoke (it very well may be) but the white plumes certainly aren't.


 * Fog is a weather phenomenon; Jayron32 may have meant smog, which in the US is nowadays usually caused by a combination of atmospheric inversions and automobile exhaust. Chinese smog is a different issue, given the "crony capitalist" oligarchy there can do as it pleases. μηδείς (talk) 02:50, 27 March 2015 (UTC)


 * Fog, mist, cloud, it's all the same stuff. Little droplets of water.  Still not steam.  I didn't mean smog, which isn't purely water droplets, but contains a lot of particulate matter of other stuff as well.  Big puffy white plumes of water are still fog/cloud/mist etc and still not steam regardless of their source.  -- Jayron 32 12:48, 27 March 2015 (UTC)
 * The image is not helpful. The OP asked about smoke. There are more generators of smoke than coal. How about car exhaust of badly tuned engines, volcanic smoke, wood/forest fire smoke, tobacco smoke, explosives smoke etc. Are they all the same in terms of physical homogeneity/heterogeneity. Richard Avery (talk) 10:01, 27 March 2015 (UTC)
 * Yes, any of these "clouds" are heterogeneous for most considerations and purposes. SemanticMantis (talk) 14:12, 27 March 2015 (UTC)

Colloid
See colloid and you will see that smoke is listed as a colloidal dispersion of solid particles in gas. Any colloid is heterogeneous in that it consists of the dispersed substance and the medium in which it is dispersed. Whether the smoke particles themselves are homogeneous or heterogeneous is another question, which would depend on the source of the smoke. Robert McClenon (talk) 17:49, 27 March 2015 (UTC)


 * Regarding the picture, I spoke with an engineer who's built refineries, chemical, and nuclear plants. The two most obvious white exhaust plumes are condensed steam, the most distant tower in the right-mid background is giving off smoke, and the other tower may be giving of smoke, but the quality of the image makes it difficult to determine.  I have changed the caption to reflect this.  My expert suggested the fourth tower may also be a scrubbing tower which injects steam into a stream of smoke, allowing much of the particulate matter to condense out within the tower. μηδείς (talk) 21:37, 27 March 2015 (UTC)

Condoms
I read the Wikipedia page on Condoms, but I have some more questions about the article's assumptions and implications.


 * Why does the (male) condom have to go on an erect penis? This seems counter-intuitive from what I learned in previous health classes, because an erection indicates a man is having an orgasm, and if a man is having an orgasm, then he wouldn't be entirely conscious of what he's doing and therefore cannot stop sexual intercourse, wouldn't he? Or perhaps, I am getting an incorrect understanding of the use of condoms or erection and male orgasm? Wouldn't it make more sense to put on the condom prior to erection and orgasm instead of during sexual intercourse?
 * When a man is putting on his condom, does that involve his partner, especially when the partner is of the opposite sex, to look at his penis? For the sake of body modesty, it would make sense to cover up the genitalia with a blanket, so during the act of sexual intercourse, the sex act and the genitalia are never seen.
 * Since the male condom seems to be covered in some sort of slimy, oily substance, can the slimy, oily substance be washed away? Or will that lower its effectiveness? I don't think the oily substance can be washed away, because if it is indeed oil, then that means it's non-polar and thus hydrophobic.
 * Is the female condom oily too?
 * Can the male condom be stretched to cover a man's penis, scrotum, and testicles? How much of the penis does the condom cover?
 * How many times does a man have to change condoms during sexual intercourse? How long does it take to put the condom on and to take it off? How many condom-covered penile penetrations can a single condom hold?
 * Can a man use a female condom instead of a male condom, since it's basically just a barrier, and the opening of the female condom may have a wider cirumference than the opening of the male condom?
 * Can cotton fabric and rubber bands be used as a condom? 140.254.226.237 (talk) 14:03, 26 March 2015 (UTC)
 * Read human sexual response cycle and condom. We can't provide health advice here, but in general, the answer to most of your questions is "no," "don't do that," "why would you even want to do that," "seriously, no, don't do that," and "differs from couple to couple." --OuroborosCobra (talk) 14:26, 26 March 2015 (UTC)
 * The condom needs to go on an erect penis because erection gives the penis the necessary rigidity. Erection does not indicate a man is having an orgasm (although it is a prerequisite for orgasm to occur), but only that the man is sexually excited and the penis is physically ready for intercourse.  It is common (though not universal) for the partner to assist with putting on the condom as part of sex play, and participants in sexual intercourse usually do not suffer from body modesty.  It would certainly be possible for a man to put his condom on where his partner could not see, although this might offend the partner.  The slimy, oily substance on the condom is lubricant.  Removing it may irritate the vagina or rectum and may also cause the condom to tear, so it should not be washed away.  A female condom also has lubricant.  The male condom should cover the head of the penis and part or all of the shaft; it should not cover the testicles, which if tried would probably be quite painful.  Usually a man does not change condoms during sexual intercourse.  The length of time required to don the condom varies considerably, and an inexperienced man may be expected to take longer; a condom can be removed in a few seconds.  A condom should not be re-used.  Female condoms are not constructed to go on the penis; if a normal male condom is too small, there are larger sizes available (sometimes purchased by men who wish to pretend that their penis is larger than it really is).  Cotton fabric and rubber bands would make a most unsatisfactory condom, as germs and sperm could go through the cotton, and cotton would provide less pleasant sensations for both participants.  John M Baker (talk) 14:58, 26 March 2015 (UTC)
 * Thanks for the detailed answer. Now, I have a few more questions.


 * Is the condom used in oral sexual intercourse?
 * Is sexual excitement the same as sexual arousal?
 * Is sexual foreplay required to make a man sexually aroused or sexually excited in order to erect the penis and slip on the condom? Does that mean that a man cannot have an erect penis at will? Which part of the nervous system controls the erection of the penis?
 * Why must there be rigidity in the penis in order to slip on the condom?
 * How does a man know that he is having an erection or an orgasm or that he is sexually aroused or excited? Is he fully conscious and alert during sexual intercourse?
 * So, is sexual intercourse a time where body modesty does not exist at all?
 * Why would covering up the testicles be painful? Are there condoms that are designed to cover the testicles?
 * Why doesn't a man change his condom during sexual intercourse? If he ejaculates, then wouldn't the volume of the semen be located at the tip of the condom? Can the condom overfill, if it is not changed after every erection, penetration, and ejaculation?
 * Can a condom still be re-used, if it had been sterilized and then soaked in an oily lubricant?
 * Why do some men pretend that their penises are larger than they really are?
 * Can a piece of polyethylene fabric prevent leakages? 140.254.136.178 (talk) 16:17, 26 March 2015 (UTC)


 * Note that the testicles are used to keep the sperm cool, by evaporation of sweat, etc., hence covering them with a waterproof material would be extremely uncomfortable. Also, the scrotum is larger than the penis, even when erect, meaning you would have to stretch the condom, resulting in high forces on the scrotum, a broken condom, or both. StuRat (talk) 17:22, 26 March 2015 (UTC)


 * Male sexual arousal does not require foreplay, at least in younger men. Visuals (a naked partner, video, or magazine) are usually enough or maybe just sexual thoughts.  Sometimes nothing at all is needed, since erections occur periodically so that ejaculation can take place to clear out old sperm. StuRat (talk) 17:25, 26 March 2015 (UTC)


 * "Changing a condom during sexual intercourse" makes no sense. That would mean while the penis is inserted into the vagina.  If you mean between closely spaced periods of sexual activity, yes, that might very well happen, during the refractory period.  Note that after anal or oral intercourse a condom change is required before vaginal intercourse, for hygiene reasons. StuRat (talk) 17:36, 26 March 2015 (UTC)


 * Body modesty still exists for many, particularly if they fear they might be unattractive naked. Turning the lights out is usually enough to deal with this. StuRat (talk) 17:40, 26 March 2015 (UTC)


 * I have heard of the phrase that "spooning leads to forking", meaning that when a male and a female cuddle in bed, that will lead to sexual intercourse. But then, wouldn't sexual intercourse require the removal of clothing? Or perhaps, the clothes would act like a condom-barrier, even though it may ineffective at preventing pregnancy.
 * If the condom is used in oral sexual intercourse, then that implies that it is chemically non-toxic to the flesh or the digestive system, right?
 * If the lights are turned off, and the male and female are both wearing condoms, would the female condom serve as an aid to locate the vagina? 140.254.136.157 (talk) 17:58, 26 March 2015 (UTC)
 * Why don't younger men require sexual foreplay to experience sexual arousal? How young is "young"?
 * Do sexually mature men wear condoms every day? Do men sexually stimulate themselves by masturbation, make sure the penis is erect, put on the condom, put on the underwear and trousers, and then go about the day wearing condoms? Do sexually mature men have to take off their condoms every time they need to urinate? 140.254.136.157 (talk) 18:04, 26 March 2015 (UTC)
 * I think we're dealing with a troll... --OuroborosCobra (talk) 18:13, 26 March 2015 (UTC)
 * Probably true, given trolls lack penises. μηδείς (talk) 21:30, 28 March 2015 (UTC)
 * Think? I would have thought it was obvious by the poster's implied knowledge of the issue which clashed with the naivety of the questions. But as usual on the Ref Desk if sex is mentioned everybody weighs in. Richard Avery (talk) 07:27, 27 March 2015 (UTC)


 * Nobody should ever use male and female condoms at the same time, that is much less effective than either one used correctly and separately . If you are actually in Columbus, OH as your IP seems to indicate, you can go to your local planned parenthood here and get answers to all these questions. SemanticMantis (talk) 18:41, 26 March 2015 (UTC)
 * We're getting questions that seem straight out of a South Park episode. --OuroborosCobra (talk) 18:44, 26 March 2015 (UTC)
 * I don't watch South Park. I am just curious about condoms, because AIDS/HIV is a serious pandemic, and I want to be informed so that I understand what people are talking about when they are talking about sex-related issues. 140.254.136.178 (talk) 19:49, 26 March 2015 (UTC)
 * Anyone who seriously has such outlandish questions, how many, two-dozen? should be asking a professional or their high school guidance counselor or college health service, not asking volunteers to entertain wild "thoughts". μηδείς (talk) 19:30, 27 March 2015 (UTC)

parallel universes, rainbow gravity, different color photons moving at different speeds, gravity leaking between dimensions, MAKING black holes in the lab, say what?
I'm seeing some crazy talk in the news about all this stuff. Now, I'd like to say I applaud recent progress toward marijuana legalization, but ......... can someone talk some sense about this? Like, why does the second source claim light of different colors moves different speeds, what does that have to do with "rainbow gravity", what does that have to do with parallel universes, how does gravity leaking into parallel universes make it easier to make a mini black hole. Etcetera. Somebody throw me a clue here. Wnt (talk) 15:53, 26 March 2015 (UTC)


 * Here's the clue: Real science is esoteric, arcane, and boring. In order to make new discoveries either accessible to the lay reader, OR more interesting to the lay reader, people will use language, often borrowed from science fiction, which makes discoveries more interesting than they really are.  "Scientists communicate with a parallel universe!!!" sounds much more exciting than "So, there's this stuff called "quantum mechanics" and it's really confusing, and we're not entirely sure how it works, but we know it does.  We have lots of weird explanations for why it might work (see interpretations of quantum mechanics) and just recently, one group of scientists found one piece of evidence which looks like it supports one of the myriad explanations (the Many-worlds interpretation)."  Explaining exactly what the "many-worlds interpretation" means is far less exciting than what we picture a "parallel universe" to mean from Science Fiction, and it also requires a lot of arcane mathematics and jargon and concepts most people are 5-10 years of heavy education away from understanding.  So we say shocking things like "Scientists contact a parallel universe!" rather than "Scientists perform an experiment which seems to indicate that one of the many interpretations of quantum mechanics may have some empirical validity."  Which is closer to the truth, but far less likely to get clicks.  -- Jayron 32 16:53, 26 March 2015 (UTC)


 * Some real science seems fascinating to me. There's particles/waves seeming to behave differently when an observer is present, for example, as in the double-slit experiment.  Then there seems to be faster-than-light transfer of info via quantum tunneling, despite that being theoretically impossible. StuRat (talk) 17:02, 26 March 2015 (UTC)


 * The "faster-than-light" quantum tunneling experiments agree with theory, and the theory doesn't need any faster-than-light process to explain them, so there's no excuse for making such claims to the press. -- BenRG (talk) 18:00, 26 March 2015 (UTC)


 * See this post by Sabine Hossenfelder. Summary from the last paragraph: "The authors work in a framework that combines rainbow gravity with a lowered Planck scale, which is already ruled out. They derive bounds on black hole production using existing data analysis that does not apply in the framework they use. The main conclusion that Planck length effects should suppress black hole production at the LHC is correct, but this has been known since 10 years at least. None of this has anything to do with parallel universes."
 * I'd never even heard of "rainbow gravity" before this, but if different frequencies of light have different speeds in the vacuum (which is a prediction of some versions of quantum gravity) then white light will separate into a rainbow after traveling long distances, and that's reason enough to call it "rainbow gravity", I suppose. I doubt it deserves a Wikipedia article.
 * In theories with large extra dimensions, gravity is fundamentally much stronger than it appears to be, and seems weak at larger scales only because it falls off like 1/rd−1 instead of 1/r3−1 at small distances (which someone might call "leaking into the extra dimensions" if they were feeling silly). That means it's easier than you'd expect to make black holes smaller than the scale of the extra dimensions. The extra dimensions are not "parallel universes", although in some of these theories our 3+1 dimensional world might be a brane and other branes could be called "parallel universes". This has nothing to do with the many-worlds interpretation. -- BenRG (talk) 18:00, 26 March 2015 (UTC)


 * Never heard about gravity rainbow? It is actually Gravity's rainbow. I wonder how renowned scientist like Faizal got it wrong. Senteni (talk) 01:25, 27 March 2015 (UTC)


 * If I got the details wrong, at least the general idea was right; it is just sensationalism and oversimplification. -- Jayron 32 18:49, 26 March 2015 (UTC)
 * Thanks for that great analysis by Hossenfelder. He ripped Faizal so many new ones that if this physics thing doesn't pan out he can always find a job as a church organ. :)  The obvious problem I had with "rainbow gravity" is that people have observed abrupt, high energy events from very long distances and never a word about them changing colors in some set sequence; according to this I take it the paper simply assumed this contrafactual.  Which is why the media went beyond what I perceive as their usual limits of sensationalism this time. Wnt (talk) 20:17, 26 March 2015 (UTC)
 * Theorists are quite good at evading experimental bounds. A speed difference comparable to frequency × planck time may be ruled out (I think it is), but there can be smaller effects. I think Hossenfelder (who is a she, by the way) believes there might be, so I don't think she'd criticize rainbow gravity on that basis. -- BenRG (talk) 21:10, 26 March 2015 (UTC)


 * Sometimes I feel that what reporters say is rather like quantum mechanics - what you get out is related to what you put in only by some probability distribution and fixing any one point will make everything else completely unreliable. Dmcq (talk) 10:32, 27 March 2015 (UTC)