Wikipedia:Reference desk/Archives/Science/2016 January 31

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January 31

Alkanes

What is the lowest viscosity alkane available, and would it be ok as oil for a sewing machine?--213.205.192.13 (talk) 01:17, 31 January 2016 (UTC)

Presumably the literal answer is methane, and no, it won't work.

If you mean the lowest-viscosity paraffin that's a liquid at room temperature, I expect that would be one of n-pentane, isopentane, or neopentane. Our article gives the viscosity for n-pentane but not for the other two. I doubt they would work as sewing-machine oil, but then I don't really know the requirements, so I can't say for sure. --Trovatore (talk) 02:51, 31 January 2016 (UTC)

I found the value for isopentane (it's less than that for n-pentane) in PubChem and added it to the article. PubChem doesn't have the value for neopentane. DMacks (talk) 03:52, 31 January 2016 (UTC)

Found some data about neopentane, but given it is a gas at room temp, it's probably not useful for your context (and also explains why our article doesn't list it). DMacks (talk) 04:53, 31 January 2016 (UTC)

KY

Can it have a laxative effect if swallowed in quantity?--213.205.192.13 (talk) 01:34, 31 January 2016 (UTC)

What do you mean by "KY"? Our KY page lists a bunch of topics, including a bunch of non-swallowable ones such as Kentucky and the Kyrgyz language. Are you perhaps asking about K-Y Jelly? Nyttend (talk) 02:26, 31 January 2016 (UTC)

A lubricant laxative coats the stool with slippery lipids and retards colonic absorption of water so that the stool slides through the colon more easily. It also increase the weight of stool and decreases intestinal transit time. Handbook of Nonprescription Drugs by the American Pharmaceutical Association mentions mineral oil which may decrease the absorption of fat-soluble vitamins and some minerals. In case of Constipation get qualified medical advice from a doctor and/or the directions given with an approved treatment because laxative abuse can lead to potentially fatal fluid and electrolyte imbalances, see Laxative#Problems_with_use. K-Y Jelly is a brand name rather than a specific formulation and it is not approved for laxative use. To do so amounts to medical advice that Wikipedia does not give. AllBestFaith (talk) 15:48, 31 January 2016 (UTC)

Cats and dogs

What causes cats and dogs to be mutually hostile? Is it body language? pheromones? or something else? 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 03:52, 31 January 2016 (UTC)

Body size of cats.
Sleigh (talk) 06:12, 31 January 2016 (UTC)

One suggestion is body language. The dog waves its tail happily, while the cat whips its tail in anger. Easy to confuse the two. Star Lord - 星爵 (talk) 14:21, 31 January 2016 (UTC)

Dogs are predators whose natural behavior is to chase and try to kill anything that isn't a dog. Cats naturally recognize a dog as an animal that is dangerous to it. Socializing these species by exposing them to each other from a young age can overcome these tendencies, but they often continue to some degree. In dogs that have not been exposed to cats, and cats that have not been exposed to dogs, the natural behaviors generally manifest with full strength. Looie496 (talk) 15:43, 31 January 2016 (UTC)

I strongly agree on the body-language thing.

• A friendly dog will often greet others with a 'play bow' (front end flat on the floor - back end up in the air) - but that's the posture a cat adopts when it's about to pounce.
• The contented purr of a cat probably sounds like an agressive growl to a dog.
• A wagging tail means "happy" to a dog and "angry" to a cat.
• Cats arch their backs in order to look larger when they feel the need to be agressive - dogs arch their backs like that when they are frightened.
• Cats extend their claws when there is danger around - dogs can't retract their claws - so cats may well see extended doggy claws as a perpetual danger.
• Dogs are pack animals - and if introduced to a cat as a member of the family "pack", they should be OK with that. But cats are much more likely to be highly individual - and the dog's immediate desire to understand who is a part of the pack and who isn't (and who is the 'alpha' pack leader) gets misinterpreted as getting too familiar too soon for the cat.

It's no wonder that they find it hard to get along. But dogs and cats that are introduced carefully - and preferably at a young age - they do seem to learn these differences and adjust accordingly.

When I recently introduced 'Drake' (our yellow lab) to a couple of cats whom we had to stay in the same house with for a few days - Drake wagged his tail, did a play-bow and then went towards the cats to sniff them out - that's what dogs do when they first meet. Both cats immediately took a bee-line to the most distant room in the house - where they hid for two days before venturing out a little at dead of night to investigate - again, very typical of cat behavior in the face of a gigantic threat animal invading their space. By the time the cats were ready to sneak out for a quick investigation, Drake had evidently decided that this was not the reasonable behavior of pack members - and all of that sneaking around was more likely the behavior of intruders. So, unsurprisingly he no longer saw them as potential friends and chased these non-pack-members back into hiding.

I'm not so sure about the 'predator' thing. Most breeds of domesticated dogs have evolved and been engineered by humans to be much more docile and relaxed around the house. When faced with another animal (or even a small child) - their reactions are more often curiosity and a desire to play than aggression. Cats are still fairly close to their wild counterparts - so they are more concerned about risk to themselves and opportunities to hunt.

SteveBaker (talk) 16:25, 31 January 2016 (UTC)

And that might be because the domestic dog is at least 33,000 years old while the cat is only 10,000, and even then the purpose was agricultural rodenticide first and cute later. Sagittarian Milky Way (talk) 01:17, 1 February 2016 (UTC)

Wikipedia articles: Cat behavior, Dog behavior. AllBestFaith (talk) 17:25, 31 January 2016 (UTC)

Our article at dog–cat relationship notes that it's the more generalized behaviour of the animals: cats are easily spooked and dogs like to chase things. A dog is going to be confused by cat purrs? Seriously? Matt Deres (talk) 17:36, 31 January 2016 (UTC)

Thanks, everyone! So it's not just the tail, but the whole spectrum of behavioral differences, right? 2601:646:8E01:9089:F88D:DE34:7772:8E5B (talk) 02:06, 1 February 2016 (UTC)

It is not only about behaviour. The psychology is different, quite opposite, difficult for them to find a common ground. In a word, Dogs are social, cats are solitary. Social hunters VS. lone hunters. Dogs pride is all about getting along well with the herd, being able to join forces and organize helpfully with the others. Cats pride is all about being self-sufficient without needing any help to deserve her food. Quite opposite mentalities. Akseli9 (talk) 14:57, 2 February 2016 (UTC)

• You may also enjoy reading Tolkien on the theme of Sauron--"Tevildo" in the form of a cat--and the speaking hound "Huan". μηδείς (talk) 04:18, 1 February 2016 (UTC)

Clashing colors.

We have an article complementary colors, but I haven't been able to find an article on clashing colors or any good google results. By clashing I mean something subjectively judged as unattractive, such as mixing brown and blue in your wardrobe, or such as at this blog. Thanks. μηδείς (talk) 04:29, 31 January 2016 (UTC)

Color_analysis_(art) is one article on a similar topic of wardrobe color matching, closest I could find quickly. DMacks (talk) 04:44, 31 January 2016 (UTC)

Yes, thanks, DMacks, that's closer in theme to the article I found. But what I was hoping for was an article or source that gave specifically clashing clothes--say--a pale, blue-eyed redhead wearing a charcoal shirt, a green vest, a navy jacket and an peach tie, that would explain why the colors clashed, and gave an example of explaining how changing one of the colors alone would bring the ensemble into harmony. μηδείς (talk) 06:12, 31 January 2016 (UTC)

Can you upload a picture of you wearing that combination? I'm having difficulty imagining it! Dbfirs 11:19, 1 February 2016 (UTC)

I don't think we have an article... we do have an articles on e.g. dissonance, so maybe we should. Then again Consonance_and_dissonance can be formalized in a way that matching and clashing usually aren't. Color theory is hard (and nobody will ever admit that's not really art or science, though it can be informed by both ;)

I think blogs may be your best bet for info. Outside of fashion, color clash also is discussed a lot with respect to print design [1], so you might use printing to narrow future searches. Here [2] is a freely accessible scholarly article that has some interesting empirical findings related to color clash. This one [3] is all about how single colors are interpreted in marketing, but the deconstruction into saturation,hue etc. make it a nice companion to the previous, I think. SemanticMantis (talk) 16:12, 1 February 2016 (UTC)

I believe what is interpreted as color clashes are to a great extent cultural. I have seen preferences for which colors clash change during my lifetime. If anyone starts an article with one theory or opinion about which colors clash, one should probably make early allowance for alternative opinions so that the article does not overly influence the subject it is trying to describe. Star Lord - 星爵 (talk) 21:31, 1 February 2016 (UTC)

Chemotherapy, Radiotherapy, Colorectal cancer and Ileus

Unfortunately I got a bad news just now. My friend told me that his father seems to have a Tumor, he asked me to search about "Radiotherapy, Chemotherapy and Colorectal cancer" to find out "could there be a cure for a level 4 Colorectal cancer and could Chemotherapy or Radiotherapy treat Ileus"? But his message is not clear and I don't understand, and unfortunately he does not answer my call. He previously told me that his father was a heavy cigarette smoker. This is all I know. Could you please help me? -- Bkouhi (talk) 07:21, 31 January 2016 (UTC)

Tell your friend that he should take his father to a doctor. We are unable to give medical advice.-- Jack of Oz ^{[pleasantries]} 07:33, 31 January 2016 (UTC)

Oh, I didn't notice that. Actually they are now in a hospital, in another city. I was so anxious that I didn't notice that there is an article for Colorectal cancer, I'm reading now. Thanks anyway. -- Bkouhi (talk) 07:50, 31 January 2016 (UTC)

Geodesics near a black hole

I have a question about matter in "freefall" near a black hole (timelike geodesics). First, an analogy. Suppose I take the surface of an ordinary round, positively curved, sphere, and I pinch off a small region into a bottle. This involves introducing a negatively curved region in the neck. The effect on the space of geodesics is rather dramatic: originally, geodesics were fairly boring, non-ergodic objects. But now a geodesic might fall into the bottle, becoming trapped there for a very long time (affine parameter), and then emerge much later.

Now, in the vicinity of some very high curvature region of space-time, it is conceivable that something similar might happen. One can consider (probably very non-physical) space-times which have precisely such bottles built into them, and matter can get stuck in the bottle for a long time before emerging from the other side. The twin paradox in such a scenario could allow a pair of twins A and B in freefall, such that twin A falls into the bottle and becomes trapped there for a very long proper time (in his rest frame), while twin B remains safely outside the bottle and sees twin A emerge just a few moments later. One can, amusingly, imagine a scenario where twin A will appear to have aged longer than the total age of the universe (from twin B's perspective).

Obviously, if such a scenario could hold in a physically reasonable universe, one would expect a black hole to form. I'm guessing the bottle would need to be something like the ergosphere. Assuming no physical principle rules this out (e.g., positive energy density), could matter whizzing about in the ergosphere of a black hole ever appear to be blueshifted? Also, is it ever possible for matter to appear blueshifted in a black hole without an ergosphere (i.e., Schwarzschild)? (Maybe this last is not quite the right question: I should ask, can a timelike geodesic acquire arbitrarily large proper time, relative to a static observer, by passing close enough to a black hole, and then coming back out again?) Sławomir
Biały 16:03, 31 January 2016 (UTC)

The ergosphere is a region located outside a rotating black hole in which it is theoretically possible to extract energy and mass from the black hole. The maximum radius of the ergosphere corrresponds to a non-rotating black hole's Schwarzschild radius at which the escape velocity is the speed of light, suggesting that no Doppler shift of light can be observed externally. Theories (for amusement?) about the Ultimate fate of the universe generally imply that all non-reversible entropy-increasing events, such as separated twins reuniting, shall have played out before the final curtain. AllBestFaith (talk) 17:59, 31 January 2016 (UTC)

None of this answers the question, however. This is a specific question about the behavior of timelike geodesics in Schwarzschild or Kerr. Obviously, the twin could not pass within the event horizon and reunite with the twin that remained static. What might be called the standard response is that the twin that become precipitously close to the black hole would appear redshifted relative to the the static twin. Thus, if the twins ever were to be reunited, the static one would be the older one. I'm asking if there is a scenario in which this standard response is actually wrong, whether because of something happening in the ergosphere, or some other global effect owing to the curvature of the spacetime. Certainly, the situation in Riemannian geometry is such that even tiny regions where the curvature becomes negative appear to have rather dramatic effects on the entropy of the geodesic flow. So it's not unreasonable to wonder whether such behavior is typical of the singular regions in a Lorentzian manifold. (Apologies, I am a mathematician...) Are there any "anomalous" blueshifts in light from quasars? Sławomir
Biały 19:50, 31 January 2016 (UTC)

Generally non-straight worldlines in spacetime are shorter, not longer as they'd be in a positive-definite space. My intuition (based on thinking about the metric in stationary coordinates) is that "most" worldlines (not just geodesics) that approach and then leave a black hole will be shorter than those of someone who hovers or orbits at a fixed distance, and none will be dramatically longer. I'm not sure what the spacetime analogue of your bottle would be exactly. I'm almost sure that it would be ruled out by standard energy conditions, but again that's just intuition, based on the fact that ordinary mass gives you gravitational time dilation and "time compression" would seem to require negative mass. There are geodesics that approach a black hole, circle it arbitrarily many times, and then leave again, but they take a long time (from the faraway stationary perspective) to do it.

Objects near a Schwarzschild black hole can appear blueshifted for a fairly uninteresting reason: if they're moving outward fast enough then the special-relativistic blueshift will overwhelm the gravitational time dilation. -- BenRG (talk) 21:45, 31 January 2016 (UTC)

Yes, this more or less agrees with the "standard response" scenario. I have heard that the energy density is negative in the ergosphere of Kerr, although perhaps that's not immediately relevant to your intuition regarding negative mass. (Of course Kerr, being vacuum, has vanishing Einstein tensor, so "energy" is possibly used in a different sense.) Sławomir
Biały 22:08, 31 January 2016 (UTC)

Here's an attempt to be more precise about my intuition. In a Kerr–Newman background you can write any causal worldline outside the event horizon as a function of t (even inside the ergosphere). If you write the metric as ds/dt = f(r, θ, dr/dt, dθ/dt, dφ/dt) and maximize it over dr/dt, dθ/dt, dφ/dt for fixed r, θ, you get (ds/dt)_max = g(r,θ). This function approaches 0 at the event horizon and 1 at infinity and I'm pretty sure it has no critical points. If that's true, then a stay-at-home twin that moves at nonrelativistic speeds far from the hole will be younger by at most a tiny GPS-correction factor than a travelling twin that goes closer to the hole where g is smaller.

For bottles in general, I really don't know. The best I can come up with is something like: if the twin that enters the bottle can return extremely old, it seems likely that they can return arbitrarily older for initial conditions approaching some asymptote. There would then (maybe?) be a causal diamond containing all of those geodesics and (maybe?) it would be noncompact, which would mean the spacetime is not globally hyperbolic. But that may be nonsense. Try asking at Stack Exchange or Physics Forums. -- BenRG (talk) 00:54, 1 February 2016 (UTC)

I am having a hard time picturing a "neck of a bottle" in the universe. I think there's something in the wormhole article about stabilizing a wormhole with negative mass, which I think might give that negative curvature, but I really don't understand this stuff enough to say, so just count that as a request: doesn't negative curvature require negative mass? Which is of course unknown, but even if it were known, I wonder if you only get your reverse effect if you use enough negative mass to outweigh the positive mass of the black hole, at least in terms of its effect on the passing twin ...? Wnt (talk) 00:17, 1 February 2016 (UTC)

What is World Health Organization's guidance on the longevity of Bti mosquito abatement strains?

I remember when Bti treatments for mosquitos were announced; they were supposed to live for five years in the wild, where presumably they would have a chance to flourish in ponds and lakes. But recently when I bought some on Amazon, they said they needed to be reapplied every month. I can't tell from e.g. [4], [5], or [6] what the expected environmental persistence of the live cells and spores (not the mosquito toxin which is often also shipped) is. Does anyone know? 75.166.29.132 (talk) 16:09, 31 January 2016 (UTC)

Five years was the original guidance? 50.203.182.130 (talk) 13:17, 3 February 2016 (UTC)

AIDS in the middle east

Why is AIDS less prevalent in the Middle East than in western countries? — Preceding unsigned comment added by I just registered a new account (talk • contribs)

This has some background material. At least part of the answer will be due to under-reporting. AIDS is still largely seen as a "homosexual problem" by many people, and so unworthy of broader concern. LGBT in the Middle East has a bit on that, with links. Those links often also deal with HIV/AIDS in particular countries. For example, here is the section on HIV in Saudi Arabia. There are also references there to follow to deeper answers. Matt Deres (talk) 18:04, 31 January 2016 (UTC)

Map of HIV prevalence. Grey means "no data".

• The map on the right there dates back to 2009... but even 7 years later, many Middle Eastern countries aren't reporting HIV/AIDS data. The most recent UNAIDS report for the Middle East might help you - if you see page 85 you'll see that as Matt Deres says, many countries ignore (or actively repress) the LGBT population, and many also don't attempt to engage with drug users or female prostitutes either. So it's difficult to say for sure that it is less prevalent (per the report, "Given the gaps in HIV data, particularly related to key populations at higher risk, it is likely that the scope of the HIV epidemic and its impact in the region continues to be underestimated."). A more minor factor, which is also mentioned in the report, is "Nearly universal male circumcision in MENA could also act as an important biological factor which has potentially contributed to a reduced heterosexual transmission of HIV in the region." Smurrayinchester 14:59, 1 February 2016 (UTC)

LIST OF FAMOUS PEOPLE WITH MELANCHOLIC DEPRESSION

Hi, wikipedians i`m writing a novel, about a woman who is a personification of melancholic depression and want to know where on the internet i can find a list of people who suffer from it to say in the novel she made suffer from the disease. If any of you can also list some people who suffer from it that would also be helpful. THANKS — Preceding unsigned comment added by 96.250.231.111 (talk • contribs)

Your best bet would be List of people with major depressive disorder -- that's the clinical name for severe melancholic depression. Looie496 (talk) 17:57, 31 January 2016 (UTC)

Measuring the universe – Henrietta Leavitt

Seeing Silent Sky, a play about Henrietta Leavitt, I had two questions:

Why was it so hard to find the connection between frequency and distance?

According to Silent Sky, Leavitt pondered for years over the data she had already collected until she realized that frequency and brightness were related by a simple power law. This seems to be reflected in her paper, where the periods are mentioned almost merely in passing. That seems strange to me. Just like waves, any regularly variable phenomenon exhibits three characteristic quantities: The maximum, the minimum or the range, and the period. Why was that not an idea everyone had from the onset? — Sebastian 23:05, 31 January 2016 (UTC)

Lots of things that seem obvious in retrospect weren‘t so at the time … Without a set of measurements that were all from the same approximate distance, there was no way to compare the true luminosities of cepheids, even though the class had been recognized for quite some time. Most (if not all) of the members Leavitt identified in the Magellanic Clouds were being observed for the first time. Moreover a century ago practically nothing was known about astrophysics, stellar evolution, or galactic structure, so there was little context for any patterns that might have been perceived.—Odysseus1479 01:23, 1 February 2016 (UTC)

I'm not asking about the 100-year view, but why Leavitt took so long, after she already had the data. And the truism that hindsight is 20/20 is just what I wanted to preclude with the sentence "Just like waves ...". — Sebastian 02:17, 1 February 2016 (UTC)

I can only speculate from a position of ignorance, but the fact that most of the periodic behaviour observed in ‘classical’ astronomy is orbital, rather than intrinsic to the objects involved, and therefore quite independent of mass or luminosity, might have something to do with it.—Odysseus1479 05:43, 1 February 2016 (UTC)

Yes, that makes it somewhat harder to find. Maybe the answer is not as profound as I thought. — Sebastian 05:45, 3 February 2016 (UTC)

How was the actual distance determined?

The 24-inch Bruce Telescope has a diffraction limit of about 1/3″, and the Magellanic clouds are over 50 kpc away, far more than could be measured by parallax. Consequently, the cepheids could only be used to provide relative distances. The absolute distance was apparently provided later by Hubble, but I don't see how he did that in the section The universe goes beyond the Milky Way galaxy or at the Science Oddysey referenced there. How did he determine the basic distance? — Sebastian 23:05, 31 January 2016 (UTC)

Is there a typo around "candles only provided gave relative" ? I can't parse it. StuRat (talk) 23:47, 31 January 2016 (UTC)

Yes, thanks for asking: The "gave" was redundant. It seems that even with that correction, the sentence was a bit to flowery, so I reworded it and the next one. — Sebastian 00:01, 1 February 2016 (UTC)

Harlow Shapley seems to get most of the credit for fixing the distance to one or two nearby Cephids, which is a start towards fixing them all, though even this doesn't make it clear to me. Anyway Cephids need not be well aligned in the cosmic distance ladder to understand that those seen in globular clusters are more distant than most, and those in M31 are many times more distant. Jim.henderson (talk) 00:15, 1 February 2016 (UTC)

Calibration of the distances was made possible by the identification of cepheid variables in our own Galaxy that are near enough for their distances to be measured by parallax (geometrical or statistical—see Ned Wright’s tutorial). These stars are not terribly common, so it was a quite a while before enough data were obtained. I guess an incomplete revision, where only one of “provided” and “gave” was intended to be kept. P.S. I should have got an edit-conflict here, but for some reason didn’t. Please ignore any consequent redundancy.—Odysseus1479

Thanks, guys, that going in the right direction, good links, and the term "calibration" is of course what I should have used. Unfortunately, the numbers still don't add up yet: According to cosmic distance ladder, the closest globular clusters seem to be around 1kpc from us, which just recently gets into the range where we can use parallax. The cepheids near the center center of our own galaxy are even 10 kpc away. Not sure if there are some stray ones closer to home; unfortunately I couldn't find out which ones Shapley looked at. I checked a few candidates: Delta Cephei: 244 ± 10 pc, Eta Aquilae: approx. 400 pc. — Sebastian 02:17, 1 February 2016 (UTC)

The secular and statistical parallax methods applied to star-clusters have somewhat longer range than the geometrical parallax as used by terrestrial surveyors; the precision of radial-velocity measurements doesn’t fall off with distance like that of positional measurements, although the difficulty of obtaining individual spectra from a cluster must increase with its distance. I just browsed some of our articles like Astronomical spectroscopy, and could find nothing about the history of radial-velocity measurements aside from cosmic red-shift, but I believe it was all pretty new at the time. Ejnar Hertzsprung did a lot of the early work on cepheid ranging.—Odysseus1479 05:18, 1 February 2016 (UTC)

The problem I have with that is that those, too, require calibration. But I just found that there are several intermediate steps: http://www.astro.washington.edu/users/anamunn/Astro101/LecturesBennett/DistanceScale/expansion.html#scale. Could it be that Shapley went through the whole "stairstepping" process? — Sebastian 05:45, 3 February 2016 (UTC)

The sixth satellite of Saturn

This question doesn't fit under the headline "Measuring the universe", but it's something I found incidentally: The same Harvard Annals, on page 33, also contain a very different mention of Miss Leavitt: "The required measurements [of the sixth satellite of Saturn] and their reduction were assigned to Miss Leavitt. It then appeared that in examining some of these plates on December 10 1904 she had already marked and measured the sixtli satellite but had concluded that it was probably an asteroid near its stationary point." Is that Phoebe, which is described at Moons of Saturn#Early observations as the ninth moon found? (The first to be discovered after the eight that had been found by direct observation.) If so, why does the Harvard paper credit Perrine at Lick, not Pickering or Leavitt, with the discovery? — Sebastian 23:05, 31 January 2016 (UTC)

I don’t know the specific history WRT Phoebe, but discovery credit generally requires that an object’s nature be identified, not just its existence. Galileo recorded a couple of observations of Neptune, but since he didn’t recognize it as non-stellar these aren‘t considered to constitute the discovery of the planet per se.—Odysseus1479 01:37, 1 February 2016 (UTC)