Wikipedia:Reference desk/Archives/Science/2014 November 12

= November 12 =

Bird identification
I'm cycling into my office every day, and I picked my flat to have a nice ride through several of our beautiful parks. In the last few days, I've met a largish grey bird, sedately stalking around the grass. Can anybody identify it? Its a bit hard to see in the image, but it does have a rather large beak.--Stephan Schulz (talk) 00:05, 12 November 2014 (UTC)
 * Looks like the familiar great blue heron to my eyes, but the filename says Stuttgart so maybe a grey heron? Wnt (talk) 00:42, 12 November 2014 (UTC)
 * Definitely a heron, and just a little small (perhaps immature) for a great blue, which I have had the misfortune to see face to face. The grey heron seems to be stouter, and to have a yellow beak and a whiter neck than this bird. There's always BIRD at which to enquire. μηδείς (talk) 01:07, 12 November 2014 (UTC)
 * Thanks. Yes, I should have specified the location (Stuttgart, Germany) explicitly (in fact, I planned to, but then forgot - it was just past midnight ;-). Heron is a very plausible suggestion (and in Germany then likely a grey heron). It was a bit small, but it might be a young one. --Stephan Schulz (talk) 13:09, 12 November 2014 (UTC)
 * Must be a grey heron unless it escaped from Stuttgart zoo. It looks exactly like the grey herons that we have here in London. Alansplodge (talk) 11:45, 15 November 2014 (UTC)

Where have all the slugs gone?
I have an issue with slugs crawling through my window at night. I find mucus trails over all sorts of surfaces in the morning, but I can't find the culprit(s). Where am I most likely to find them hiding during the day? Usually, slugs hide in moist, dark places to conserve body moisture, but I don't have any moisture in my room other than the barometric humidity. Are they going to feast on my paperwork or laundry, for lack of a suitable alternate food source? Plasmic Physics (talk) 00:56, 12 November 2014 (UTC)


 * You say they're crawling through your window, so wouldn't they be outside during the day? They can get through very small gaps. Do you have houseplants in your room? They may be coming in to feed on leaves and moisture dropping from the plants. Putting moistened slug pellets on your window sill should stop them.--Shantavira|feed me 08:18, 12 November 2014 (UTC)


 * I'm more interested in the slugs which are already inside, as opposed to the ones who have yet to crawl in. I don't keep plants in my room. Plasmic Physics (talk) 08:45, 12 November 2014 (UTC)


 * Slugs like plants. They'll eat wet and rotting paper, but I don't think you need to worry about the crunchy stuff. Almost certainly not clothes. Even if they're starving, they just aren't built for it. They will slime them, of course. If they can get back out your window, they probably will. If not, check the corners. There are many kinds of slugs, though. And snails, which are also slimy. Maybe some have acquired a taste. InedibleHulk (talk) 09:30, 12 November 2014 (UTC)


 * How likely am I to be sharing a bed with one of them? I don't want to roll over right on top of one. Plasmic Physics (talk) 09:41, 12 November 2014 (UTC)
 * See window screen. The pores in one of those should be sufficiently small as to prevent slugs from making into your bedroom at night.  -- Jayron  32  13:23, 12 November 2014 (UTC)
 * Also see apophallation. Better to share a bed with just one of them. If it's Limax maximus, don't worry; these things would rather hang above your bed on a slimeline to work on their night moves. Like a baby mobile (but different). InedibleHulk (talk) 14:12, 12 November 2014 (UTC)


 * Think that the OP's slugs are just looking for pastures new. Since his home is in the way, they explorer it too. As a kid, I loved making slug traps (they also provided tasty nibbles for my vivariums). There is much advice on google such as this. Example:[]. Reduce the local population and the lower peer pressure negates them from being forced to explore ones home. The other thing I found, is that if one burns off the varnish from fine copper wire ( which I salvaged from army surplus headphone coils) and laid those out, the slugs and snail did not like to cross them.  Gastropoda such as theses can metabolise many plant toxins, but in the 1960's we could just paint on a little dilute DDT over the glass-house threshold,  non could not cope with that. Anti-seize-lubricant was also good as it too contains copper.   Gastropoda know if the local population is too high and so emigrate – in this case into the OP's home.  Houses are not their natural environment. Just reduce the local population with slug traps.--Aspro (talk) 14:52, 12 November 2014 (UTC)

Thank you to all. Plasmic Physics (talk) 20:31, 13 November 2014 (UTC)

Laundry detergent as dish soap
If someone uses powdered laundry detergent to do the dishes, is it safe? Anna Frodesiak (talk) 05:22, 12 November 2014 (UTC)
 * (EC)Make sure you rinse off the excess soap. Soap is not that toxic, otherwise soap packets would have warnings on them. But what do you think people used before dish-washing detergent? Graeme Bartlett (talk) 05:29, 12 November 2014 (UTC)
 * Not toxic, okay. Before dish-washing detergent? I never thought about. Bar soap? Some sort of plant? Anna Frodesiak (talk) 07:49, 12 November 2014 (UTC)
 * Sodium carbonate was cheap and commonly used. Laundry detergent is different from soap, by the way.  I wouldn't use any scented product to wash dishes, but I'm fussy about residual scents.  I guess it's OK if you rinse it off.    D b f i r s   08:10, 12 November 2014 (UTC)
 * Sodium carbonate, eh. I'd never heard of that. Anna Frodesiak (talk) 21:42, 12 November 2014 (UTC)
 * It might be toxic. For example it contains Optical brighteners and other things. But then again dishwashing machine powder is also toxic, and they use that all the time. It's really all about rinsing it off thoroughly afterward. Ariel. (talk) 10:16, 12 November 2014 (UTC)
 * Fair enough. Thank you, all. :) Anna Frodesiak (talk) 21:42, 12 November 2014 (UTC)
 * Handlevwith care. I find the dishes to be much more slippery. Jim.henderson (talk) 23:20, 12 November 2014 (UTC)

petroleum engineers in USA
How many petroleum engineers USA want in 2030?

I learnt there's a growing demand for natural gas and oil
 * The United States Department of Labor projects about 48,000 petroleum engineers will be employed nationwide in 2022. Petroleum engineering employment is growing faster than the national average for other occupations, and demand is projected to continue growing "much faster" than the average.  Do you specifically need predictions for 2030?  Nimur (talk) 06:31, 12 November 2014 (UTC)


 * 2030 is a very long way ahead for this kind of prediction. Will robotics and automation reduce the need to nearly zero?  Will the demands of the industry mean that they need a ton of computer geeks but hardly any petroleum experts?  Will the world finally come to it's senses about global climate change and drastically cut back on the demand for oil, and decimate the industry?  Will the demand for oil continue to increase and require increasingly clever techniques to extract it from ever more difficult sources - pushing the demand for new engineering techniques through the roof?  Will new oil discoveries in (...picking a place at random...) Outer Mongolia swamp the market with cheap Mongolian oil - driving the US  industry into bankruptcy?  We really can't answer any of those questions...nobody can.   So we can't possibly come up with a good prediction...it's a wild assed guess at this point.


 * In the news right now, today, Saudi Arabia is deliberately selling its' oil at rock-bottom prices in an attempt to drive US domestic production out of profitability and into a death spiral. Will they succeed?   Clearly they think so - and clearly the US industry doesn't think so or they'd shut down their operations right now and cut their losses.  If those two sets of undoubted experts are dualling for such insanely high stakes rewards - then we know that they don't agree on what the outcome will be.   If those experts don't agree on what the future of the US oil industry is...what chance do we stand?


 * SteveBaker (talk) 14:57, 12 November 2014 (UTC)
 * Steve, you make excellent points across the board. But, to be fair, the Department of Labor projections are a little better than a wild-assed guess.  You can read about their projection methodology, which does specifically take into account the uncertainties that are inherent to each industry.  The Department of Labor can arguably make the case that its projection is intended to be accurate - neither optimistic nor pessimistic - unlike the projections of a corporation involved in that industry.  As a government agency, their projections do not positively affect their own profit-and-loss outlook or shareholder valuation.  They employ statisticians and industry experts.  There is a plausible case that they do have some biases that are difficult to overcome; but their role is to inform policy.  If realistic evaluation of uncertainty implies that employment numbers for some specific American industry are on the verge of a catastrophic collapse, the Department of Labor wants to inform policy-makers and citizens about that issue.  (As an excellent example, look at the textile industry, for which DoL projects a nearly 50% reduction in current employment over the next ten years.  America's textile industry has shrunk for reasons too numerous to mention, but overseas competition is a very real contributing factor).
 * The petroleum in particular has a tendency to be very volatile, prone to sharp changes because of technology, politics, and outside economic factors. But even if E&P moves out of the United States, it is very probable that American petroleum engineers will continue to be very highly employable, inside and outside our borders.
 * Nimur (talk) 17:19, 12 November 2014 (UTC)
 * To add: Here is BLS's evaluation of its own 10 year projections made in 1996 (for year 2006). My takeaway:
 * As Nimur says, the BLS projections are likely to be close to the best that can be done, and are certainly better than a seat of the pant approach, naive extrapolation, or just throwing up ones hands at the problem.
 * As Steve says, one should be aware that the error bars on the projections can be pretty large, especially for jobs employing a small number of people (like the petroleum industry).
 * Abecedare (talk) 00:33, 13 November 2014 (UTC)

Transitional dipole moment
How do I find the transitional dipole moment of a particular carbon atom within a PAH according to the zero-overlap approximation. All I have, are the normalised SALCs, and the relative atomic positions. I'm trying to interpret equation 17 in the article. Plasmic Physics (talk) 09:33, 12 November 2014 (UTC)

What is the relationship between lambda/nu and l/m, where l/m refer to the carbon atoms that define bond Rk? Plasmic Physics (talk) 09:54, 12 November 2014 (UTC)

Schiehallion experiment — determining mountain density
The accuracy of the Schiehallion experiment is dependent on a good estimation of the density of the mountain Schiehallion. The article doesn't state how this was determined. According to http://www.sillittopages.co.uk/schie/schie90.html, Hutton assumed that the exposed rocky outcrops were representative of Schiehallion as a whole. Is this what he did? CS Miller (talk) 11:37, 12 November 2014 (UTC)
 * CS Miller: Nothing quite as sophisticated as that. Here you have Hutton's own explanation. He assumed the mountain to be a mass of solid rock, and thus judged the density to be the same as "common ſtone". הסרפד  (call me Hasirpad) 20:00, 12 November 2014 (UTC)
 * BTW That's not a typo of "ftone", that a Long s. Ariel. (talk) 00:03, 13 November 2014 (UTC)
 * ♪♫ "Where the bee ſucks, there ſuck I..." ♫♪♫ --Shirt58 (talk) 07:55, 13 November 2014 (UTC)

Philae (spacecraft)
Are the signals between the Philae probe and our planet (Earth) traveling at the speed of light? Bus stop (talk) 18:13, 12 November 2014 (UTC)
 * Strictly speaking the signals from Philae do not travel to Earth - Rosetta is used as a relay to reduce the power needed aboard the lander. Ignoring the minor delay in relaying, yes - radio waves are a type of electromagnetic radiation and like all other electromagnetic waves, they travel at the speed of light. WegianWarrior (talk) 18:51, 12 November 2014 (UTC)
 * Great, thank you for that. Does the signal take almost 1/2 hour to traverse the distance one way between Rosetta and Earth? Bus stop (talk) 18:59, 12 November 2014 (UTC)
 * It is 0.471 light-hours from Earth, so the transit time is 28.26 minutes. CS Miller (talk) 19:11, 12 November 2014 (UTC)
 * Great, thank you very much for that information. Bus stop (talk) 19:31, 12 November 2014 (UTC)


 * Of course, both time and distance are currently shrinking as the comet heads in towards the earth's orbit...so these numbers will gradually become smaller, then larger again. SteveBaker (talk) 15:12, 13 November 2014 (UTC)


 * Thanks. That is an interesting point, that I had not considered. I understand the rate of water spewing off the comet increases as it nears the Sun. If that is the case, wouldn't it have lost all its water by now? Bus stop (talk) 21:00, 13 November 2014 (UTC)


 * Some comets do eventually do that. But they are actually pretty big objects (kilometers across) - and they are shedding material relatively slowly, even close to the sun.  Ice is a rather good insulator - so the comet may not be close enough to the sun for all that much of it to melt and evaporate/boil away.  But they do eventually lose all of their volatile materials and either break up, or continue to orbit as loose collections of rocky material.  We have an article about them: Extinct comet.   A case in point is 5D/Brorsen which was discovered in 1846, returned about every five and a half years - but got harder and harder to spot until it vanished completely towards the end of the century and didn't return on-cue in 1901.  Many other comets disappear or break up because they get too close to a large planet - and of course Comet Shoemaker–Levy 9 is the classic and spectacular example of that.  Even good old reliable Halley's Comet will eventually break up and disappear, perhaps within a hundred more orbits.   The Leonids meteor shower is actually a bunch of debris that was shed by comet 55P/Tempel–Tuttle over many trips around the sun that has gradually spread out around the entire length of it's orbit, and which peppers the earth quite spectacularly every November as we pass through it.


 * Shorter period comets like 5D/Borsen boil away quickly because they re-visit the sun more often than longer period comets like Halley. 67P/Churyumov–Gerasimenko has a period of only 6.5 years - so it's probably not going to be around for very long either.  SteveBaker (talk) 21:55, 13 November 2014 (UTC)


 * Update on the Rosetta mission, including status of the Philae lander. Bus stop (talk) 16:09, 14 November 2014 (UTC)