Wikipedia:Reference desk/Archives/Science/2015 December 17

= December 17 =

sodium iodide catalysis of SN2 reactions of diols on dichloromethane
I have an acid-sensitive catechol (which I believe is vulnerable to oxidation in acidic conditions) which I plan to methylenate under basic conditions. Reacting catechols with dichloromethane is discussed in the literature, but one way for me to increase yield would be to convert the dichloromethane into a more active form using an iodide catalyst. However, sodium iodide is not very soluble in dichloromethane. For various reasons, I plan to run the reaction in cyclohexanol with DCM dissolved in it, because the first step that leads to my catechol derivative relies on a ~1% catalytic impurity found in technical grade cyclohexanol (cyclohexenone). I shouldn't expect sodium iodide to be very soluble in cyclohexanol either.

If I produce diiodomethane using the Finkelstein reaction by dissolving DCM and sodium iodide in acetone, the problem is that even if I evaporate the acetone and any leftover DCM (leaving just the diiodomethane) I think the acetone will form an azeotrope with the diiodomethane, and this acetone will act as a surfactant and interfere with acid-base extraction during workup. (The octanol/water logP is -0.042, or an octanol/water partition coefficient of 0.9). At what points would diiodomethane and acetone form a zeotrope? (The liquid range of DIM is 6-182C, acetone -94 to 57C) Yanping Nora Soong (talk) 07:55, 17 December 2015 (UTC)


 * Diiodomethane is itself available (or can be made and isolated separately ahead of time). Why are you trying to make it in situ, with resulting complications from acetone? But thinking about separation process, I don't quite see why the data you have would necessarily leave acetone present. At say 60°C, most of it should evaporate easily. However, if it is a problem, there are azeotropes of acetone with cyclohexane and with hexane that could be used to drive out the acetone and leave instead a hydrocarbon that is much less water-soluble. DMacks (talk) 10:37, 17 December 2015 (UTC)


 * DIM is expensive, 5-10 times more expensive than dichloromethane.
 * NIST reports Antoine constants for DIM : p(in mmHg) = 10^(7.16 - 1715.7/(218.17 + T(in deg C)) -- these constants are however based on very low pressure points however (0.67 to 7.53 mmHg) plus the BP data


 * selected points for DIM:
 * 57C => 8.4 mmHg (0.011 atm)
 * 100C => 0.077 atm
 * 130C => 0.225 atm
 * 160C => 0.55 atm
 * 182.7C => 0.998 atm
 * 183C => 1.005 atm


 * (the "max deviation" and "standard deviation" reported for this regression are 0.005 atm and 0.001 atm respectively)


 * based on the Antoine curve for acetone, acetone reports a vapor pressure of 3.7 atm at 100C, so from this data, should I predict against the formation of an azeotrope? I'm not sure how to put an upper bound on azeotrope formation based on "common sense" or ab initio assumptions. Yanping Nora Soong (talk) 23:15, 17 December 2015 (UTC)


 * The other question I have is -- what would be the concentration of acetone required (given a partition coefficient of 0.9) to "fuck up" the acid-base extraction workup process? I'm not sure how to model that either. For example, knowing acetone's partition coefficient, and assuming our organic layer has similar lipophilicity to octanol, how much of a problem in acid-base extraction would 0.01%, 0.1% and 1% acetone in the reaction pot be respectively? Yanping Nora Soong (talk) 23:21, 17 December 2015 (UTC)

black holes, space physics stuff
(I don't really know how to word what I want to know properly and I'm a complete astrophysics layperson, so I apologize in advance if it's not clear and I'll try to clarify if need be.)

Been reading black hole and related articles because I want to understand how black holes "work", in a sense. One thing that's mentioned in the main black hole article here is that black holes don't actually suck in all objects around them unless those objects are within their "horizon" (I assume this means the event horizon); from a distance, it has the same gravitational field as normal objects of the same mass. At least, that's my understanding of what's written. What confuses me about this statement though, is that black holes have an enormous amount of gravitational pull (I think because of its incredibly high, dense mass, if I understood correctly?), and I would think that anything caught by its pull would get pulled in eventually. Galaxies are basically a ton of stars being slowly-but-surely pulled in by a black hole at the center, aren't they. Doesn't that mean that black holes do slowly suck in everything around them, or am I just misunderstanding something about how bodies orbiting a significantly greater mass works? Thanks, Drapsnagon (talk) 12:50, 17 December 2015 (UTC)


 * No, an object can orbit around a black hole in the same way as around a smaller object such as a star or planet. Basically if an object is not moving directly toward a black hole it has angular momentum, and needs to lose it in order to fall in.  The usual way for an object to lose angular momentum is by collisions with other objects moving along different trajectories. Looie496 (talk) 13:15, 17 December 2015 (UTC)


 * No, not really. Black holes operate under normal gravity, not magical "suck everything in" gravity.  Consider the following thought experiment:
 * Q? What would happen to the earth if we replaced the Sun with a black hole of the exact same mass in terms of the Earth's motion?
 * A? Not a damned thing. Everything would work the same.  All objects have a center of mass, which is the imaginary point to where its gravitational pull attracts other objects.  If you replace one object with a different object of the same mass in the same location, its gravitational effects would be identical.
 * The ultimate fate of the universe depends greatly on the exact effects of attractive forces (mostly gravity) and repulsive forces (mostly the metric expansion of space due to inertia left over from the big bang. Again, since black holes don't have magical gravity, just normal gravity; taken in the bulk their gravitational effects are not greater on the whole universe than other objects.  While there has been historically some debate over what will ultimately happen to the universe (it really depends on small differences in assumptions between how much various kinds of "stuff" exists that a) we don't know if it really exists and b) if it does, we're not entirely sure how much exists and what it does.), things like dark matter and dark energy.  Consensus today is roughly that the universe will keep expanding forever, but evidence is not strong in any direction.  Hope that all helps.  -- Jayron 32 13:25, 17 December 2015 (UTC)


 * To pick a nit: a spherically symmetric body has a g-field equivalent (outside itself) to that of a point mass. —Tamfang (talk) 01:13, 18 December 2015 (UTC)


 * (ec)"Galaxies are basically a ton of stars being slowly-but-surely pulled in by a black hole at the center, aren't they?" No they are not. Just like the moon is not falling onto the earth (in fact, it is getting further ), objects can orbit each other for all of eternity.


 * Thanks for the answers (and take it easy on me-- as I mentioned, astrophysics (and physics in general really) is a little difficult for me to wrap my head around, and I did mention having a feeling I had it wrong about how orbiting objects work...) Drapsnagon (talk) 13:50, 17 December 2015 (UTC)


 * Let me add a footnote that a black hole is not exactly the same as a smaller attractor, because for objects orbiting near it, the gravitational field can be so strong that general-relativistic effects come into play. In particular orbiting objects can radiate energy in the form of gravitational waves, and thereby fall into gradually lower orbits.  But this effect is only significant for objects lying very close to the black hole. Looie496 (talk) 14:35, 17 December 2015 (UTC)
 * Not really that much of a footnote. General relativity (the modern theory of Gravity) operates on all objects equally, not just on objects near black holes.  In close proximity to black holes, the effects of general relativity are more pronounced, but that's not different from saying that "near black holes, gravity is more pronounced" because for our purposes general relativity = gravity, and it's still not magic created by the black holes, simply expected increase of effects that happen everywhere.  For example of general relativity effects showing up in a "smaller attractor", see Perihelion precession of Mercury.  -- Jayron 32 14:47, 17 December 2015 (UTC)
 * Yes -- but the rate of energy loss via gravitational wave radiation only becomes significant when the field is extremely strong. It's true that the effect exists for smaller attractors, but it is too weak to be meaningful. (I don't think we are disagreeing, just emphasizing different aspects of the situation.) Looie496 (talk) 14:56, 17 December 2015 (UTC)
 * Or just say that the surface of the body interrupts the nice increase of the gravity and prevents the field from getting any stronger. Sagittarian Milky Way (talk) 15:30, 17 December 2015 (UTC)

I think you might find Crash Course Astronomy interesting. Here's the episode on black holes. --71.119.131.184 (talk) 04:55, 18 December 2015 (UTC)


 * Let me contradict with some of what you said above. In some sense, black holes do suck in objects that orbit very close to them.  There are locations around a black hole where the gravity is so strong that no matter how fast you orbit, you can't stay there.  This actually applies not only to black holes, but to objects that are almost as dense as black holes.  It does not apply to ordinary non-sense planets or stars though.  If you don't collide with the atmosphere or other objects, you can orbit a spherical planet arbitrarily close.  (You could count this phenomenon as black hole magic, because it happens only in relativity, not in Newtonian gravity.)
 * But it is true that this applies only to regions of space very close to the black hole, to a distance comparable to the event horizon. So indeed stars in a galaxy aren't "slowly-but-surely pulled in by a black hole at the center", because they are far from the black hole where they can have a periodic orbit.  &#x2013; b_jonas 11:32, 18 December 2015 (UTC)

Cloud seeding to prevent floods
Recently there was severe flooding in Cumbria caused by a storm. With weather forecasts giving a few days warning of a big storm's approach, would it be practical to seed clouds while they were still over the sea, and prevent dangerous levels of rain falling on land? I have read the cloud seeding article which doesn't seem to rule this out, but doesn't mention it happening either. 94.1.53.114 (talk) 15:19, 17 December 2015 (UTC)


 * Hey, it's December - the week of the American Geophysical Union Fall Meeting! If ever there were a group of respectable and informed scientists who could take this kind of question seriously, it would be them.  A few years ago - 2013, I think - the entire "theme" of the fall meeting was developing new science to support geoengineering as a response to climate change.  Here's their policy statement: Geoengineering Solutions to Climate Change Require Enhanced Research, Consideration of Societal Impacts, and Policy Development.  "Three proactive strategies could reduce the risks of climate change: 1) mitigation: reducing emissions; 2) adaptation: moderating climate impacts by increasing our capacity to cope with them; and 3) geoengineering: deliberately manipulating physical, chemical, or biological aspects of the Earth system (emphasis added).
 * Here's another workshop from 2014 - Refilling California’s Reservoirs—The Roles of Aerosols and Atmospheric Rivers, presented by Scripps from San Diego. Again, the take-away is that serious scientists have actually investigated this kind of idea.
 * And here's a 2009 blog, A Cold Drip: Emergency Water from the Air, which presents the more dismal view that "there isn’t much scientific evidence that cloud seeding actually works well enough to be useful." So, not everyone is enthused by the idea!
 * You can scour their publications - here's a search query for GRL - to see what has been studied specifically with respect to cloud seeding; mostly, the best scientific answer we have today is that we need more research.
 * Nimur (talk) 15:48, 17 December 2015 (UTC)


 * China is the world's leader in attempting cloud seeding for weather modification. Most of the time they are trying to increase rainfall for crops, but at least occasionally they do something more like what you have in mind.  During the 2008 Olympics, they announced an effort to use cloud seeding on weather fronts approaching the Beijing Olympics in an effort to get them to rain out before they got to Beijing.   I am unaware of any effort to try and determine how effective these or similar efforts actually are at reducing downstream rainfall.  Dragons flight (talk) 10:40, 18 December 2015 (UTC)

Glaciers on Pluto


That article talks about water ice "mountains" on Pluto up to 1.5 miles high. On Earth, those wouldn't last more than a few thousand years, because gravity would cause the ice to flow as glaciers and flatten out.

1) Does the same process work on Pluto ?

2) Does the lower gravity slow it down proportionately ?

3) Do colder temps slow it down ?

4) Any other reason it would differ on Pluto ? StuRat (talk) 16:03, 17 December 2015 (UTC)


 * Yes! There is an emergent system-property called the critical angle of repose that is studied in geology, in the study of granular materials, and in related fields.  This property determines how steep and how tall mountains can be - and it is widely studied in planetary science, because it depends on the gravity and the material composition of the world, and lots of other factors.  Ice is an even more complicated scenario, because it's not quite a perfect solid material (it deforms in a non-elastic fashion).
 * As always, I defer to my favorite planetary science book, de Pater and Lissauer, which does have a chapter on the geological process that shape a planet - including its highest and steepest geologically-sustainable mountains. We have only just begun to have high-resolution data for Pluto, so it'll probably be a while before we have great geophysical models for it; but to answer everything StuRat asked in one shot: yes, all these parameters contribute to the sustainable mountain heights and slopes.  You might also want to read our article on orogeny, which regrettably has a decidedly Earth-based bias.
 * Nimur (talk) 16:21, 17 December 2015 (UTC)


 * As to your third question, the lower the temperature the slower ice will deform under its own weight. Glaciers flow because for the temperatures we experience on Earth, ice is always not too far from its melting point. Compared to other materials, this is a high homologous temperature and makes crystalplastic processes more likely. At the surface temperature that we think is likely on Pluto (~44 K), such processes are unlikely to be active, so the interesting question is, how did the mountains form in the first place? Mikenorton (talk) 11:32, 18 December 2015 (UTC)


 * My bet for how it formed is a water volcano. That is, water squirted up and froze immediately when it hit the surface.  Now that poses the question of where the heat came from to produce liquid water in the first place.  Of course, Pluto would have been plenty hot when it formed, along with the solar system, some 4.3 billion years ago.  So ice volcanoes could have formed after the surface cooled but the interior remained warm.  But how long would the interior remain warm ?  Well, it gets little solar heating to seep down to the interior, but it does have a rather large moon, Charon, along with some smaller moons, and that might provide enough tidal heating to have kept the interior warm (along with radioactive decay).  So this all relates to my Q.  Could those ice mountains be billions of years old, or only millions or thousands ?  If not billions, then that implies that the interior of Pluto is still warm.


 * Another possibility is that Pluto wasn't always where it is now. That is, it was captured from somewhere else in the solar system or even outside.  The capture process might have generated the heat required.   StuRat (talk) 15:22, 18 December 2015 (UTC)
 * Evidence for cryovolcanism - here and possible explanations. Mikenorton (talk) 11:05, 19 December 2015 (UTC)
 * As to the age of the mountains - NASA reckon about 100 million years. Mikenorton (talk) 11:09, 19 December 2015 (UTC)


 * Also, of course, Pluto isn't really a planet, and its surface gravity is a measly 0.063 g. So a 1.5 mile high mountain of ice on Pluto weighs the same as 500 feet of ice on Earth. Wnt (talk) 14:26, 18 December 2015 (UTC)


 * Does the curvature of the surface play a role? Contact Basemetal   here  14:40, 18 December 2015 (UTC)


 * As far as I can see, the biggest difference is that the reduced pressure at the base of the glacier due to lower gravity, combined with lower temperatures - would combine to make it difficult (and maybe impossible) for liquid water to form under the ice as it does here on Earth. That water lubricates the flow of the glacier - and without it, everything happens much more slowly.


 * The Pluto-Charon system is the only known double planetary system, although the barycenter of our own Solar System lies Jupiterward of Sol. μηδείς (talk) 02:59, 19 December 2015 (UTC)


 * You didn't explain how that would affect glaziers. Pluto is tidally locked to Charon - so Charon doesn't cause periodic tidal effects - and the sun is too far away to have a significant tide.  So there would be only the smallest of tidal forces on the glaciers. SteveBaker (talk) 03:32, 19 December 2015 (UTC)


 * About the tidal locking, do we know if there is still "tidal rocking" ? That is, do the two still rotate with respect to each other a bit, then go back the other way, and repeat ?  If so, I would expect that this would still generate significant tidal heating. StuRat (talk) 07:00, 19 December 2015 (UTC)


 * You mean libration? Whoop whoop pull up Bitching Betty &#124; Averted crashes 03:04, 20 December 2015 (UTC)


 * Yes, thanks, that's the term. StuRat (talk) 03:40, 20 December 2015 (UTC)


 * I think glaziers would be pretty much out of luck on Pluto. Not too many people are going to go that far to buy a window pane. --Trovatore (talk) 03:34, 19 December 2015 (UTC)


 * Yes, anyone living on Pluto would have to be highly eccentric. But, reflecting on that paneful typo, rather than making light of it, I wonder how warm you could get it inside an ideal greenhouse on Pluto.  Would anyone care to do the math, and illuminate me with your brilliance ? StuRat (talk) 06:55, 19 December 2015 (UTC)


 * Thanks for the recommendation, User:Nimur. My alma mater has just instituted an ILL self-serve system, and my order for Planetary Sciences is their inaugural request. μηδείς (talk) 19:35, 18 December 2015 (UTC)

Infrastructure asset management
Do engineers who manage infrastructure assets ever go out on site? — Preceding unsigned comment added by 2A02:C7D:B901:CC00:7527:BB74:28CB:C5A3 (talk) 17:55, 17 December 2015 (UTC)
 * ObPersonal, but in my 20 years of experience working in the fields of Facilities/Asset Management and Engineering Administration, I would say that almost all such Engineers would go out on Site occasionally, regularly or very frequently. One who did not would in most instances be carrying out mere administration (as I do) that would not usually require engineering qualifications (which I myself do not have). An exception might be a qualified Engineer unable to work in the field due to injury or illness, who might then revert to a purely office-based role. (A Structural Engineer who works as a consultant in my office makes no Site visits, because he's 84 years old and has Parkinson's disease, but his expertise and knowledge is still valuable.) Of course, it's impossible to give a completely definitive answer to such a sweeping question about a broad field: there are bound to be exceptions. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 18:27, 17 December 2015 (UTC)