Wikipedia:Reference desk/Archives/Science/2019 January 24

= January 24 =

Firing up a train
What's the procedure for firing up (from cold and dark) a steam train fitted with a mechanical stoker (in particular, the Russian P36 engine)? How is it different from firing up a hand-stoked engine? 2601:646:8A00:A0B3:C513:DCE6:D87B:6555 (talk) 03:27, 24 January 2019 (UTC)
 * "It is preferable that the fire should be started and maintained by hand in the usual manner until the locomotive has been coupled up and the train has started on its journey". See Railways of the World - Firing the Locomotive Mechanically. Alansplodge (talk) 12:02, 24 January 2019 (UTC)


 * Coal or oil?
 * For mechanical stokers with coal, there was always a small firedoor above the stoker. This could be used for lighting up by hand, or for emergency firing if the mechanical stoker jammed (not too uncommon). The reduced size of this made firing on the line very difficult though. Andy Dingley (talk) 14:21, 24 January 2019 (UTC)


 * So, same procedure until they built up steam? (And yes, I did mean coal, not oil.) 2601:646:8A00:A0B3:C513:DCE6:D87B:6555 (talk) 03:01, 25 January 2019 (UTC)
 * Yes, exactly the same. Although the firing technique was sometimes different with mechanical stoking, as it tends to add coal in the same place and rely on it shaking forwards. The layout of the firebox might thus be re-arranged to cope with that.  One reason why some UK locos didn't adapt very well to it.
 * Also remember that of course the mechanical stoker is steam-powered, so that just won't work until there's pressure. Andy Dingley (talk) 12:18, 25 January 2019 (UTC)

Are large gulls closely related?
I have been watching youtube videos about seagulls recently and it seems to me that in coastal areas in most parts of the world, there are to be found at least one local species of gull that fits the 'standard basic large seagull' description. Chicken sized, white body and head, wings that are various shades of gray/black, yellow beak, communictes with squawks and squeals, has a trumpeting territorrial call, etc. A bunch of them look like palette swaps. Considering their global distibution I was wondering if they evolved from their shared ancestor fairly recently and then spread across the globe quickly, as they don't seem to have changed much in appearance in various locations. This may also be the case with the small hooded gulls (the other common 'design') but I didn't look at them that closely. Thanks. — Preceding unsigned comment added by 146.200.128.175 (talk) 11:02, 24 January 2019 (UTC)
 * Gull, European herring gull, Lesser black-backed gull, Larus, and Herring gull may be of interest. Notably Nil Einne (talk) 11:32, 24 January 2019 (UTC)
 * Pinging, who I haven't seen in a while, but is our resident gull expert. -- Jayron 32 04:07, 25 January 2019 (UTC)
 * KSB hasn't edited since 2016.--Shantavira|feed me 10:32, 25 January 2019 (UTC)
 * Holy shit. Has it been that long?  Fun flies when you're doing time... -- Jayron 32 01:54, 26 January 2019 (UTC)

magnetic moment
magnetic moment is product of pole strength and magnetic length.atom is a magnetic dipole of magnetic moment equal to product of electric current and area of current loop.if magnetic length is less than 1.4 fm then resulting moment is of di or monopole? — Preceding unsigned comment added by 42.110.136.86 (talk) 15:20, 24 January 2019 (UTC)
 * No, a dipole is different than a monopole, no matter how small its moment arm becomes. If you're interested in the mathematical explanation, read about multipole decomposition to express a pure function.  If you're interested in a physical explanation, read about Maxwell's equations as they relate to magnetic point-particles, and recognize that no scientific experiment yet devised has ever reliably detected magnetic monopoles.
 * As you push farther into the microscopic regime, you will start to require more and more complicated math and physics to describe particle behaviors, so it's very important that you have a very solid understanding of the basic physics and math. A dipole cannot ever be expressed as any combination of monopoles: this is a mathematical fact because multipole expansion uses an orthonormal basis: you can never rearrange terms to turn a dipole into a monopole.  There is no "equivalent" monopole for a very small pure dipole: it will always be a very small dipole, and can not ever be correctly re-expressed as a simple sum of two-extraordinarily-closely-spaced-monopoles.
 * This math is rigorously worked in Griffiths Electrodynamics, §5.4.3 Multipole Expansion of the Vector Potential... which makes a great early-morning read on a day that feels like it's below freezing.
 * Nimur (talk) 16:01, 24 January 2019 (UTC)
 * The one of Maxwell's four equations sometimes attributed as Gauss's law for magnetism expressed in differential form


 * where $∇ ·$ denotes divergence, and $B$ is the magnetic field implies non-existence of free magnetic poles. If magnetic monopoles were ever discovered, then Gauss's law for magnetism would need to be modified to make the divergence of $B$ proportional to the magnetic charge density $ρ_{m}$, analogous to Gauss's law for electric field. DroneB (talk) 23:28, 24 January 2019 (UTC)

This article, based on this paper describes the case of quasiparticles which can be separated from dipoles into monopoles. While these aren't real monopoles, it seems like the math can accommodate shifting from one to the other somehow. I mean, how do we know that all our real particles aren't quasiparticles in some other system beyond at least my comprehension, though perhaps known to some bright physics professionals out there? Wnt (talk) 19:26, 29 January 2019 (UTC)

Economically viable garbage recycling without subsidies
What financial gain can be obtained from household garbage? Without the gov forcing it to be profitable, either by subsidies or regulation, without causing some collateral damage, like burning some toxic material and without cheating (like starting with a pile of already sorted plastic). Can something be mined from a pile of random garbage? --Doroletho (talk) 17:49, 24 January 2019 (UTC)
 * well garbage often involved throwing out perfectly functional but unwanted items. See reuse and recycle. Compost is possible but will require the source to separate. Graeme Bartlett (talk) 22:42, 24 January 2019 (UTC)
 * Bottles are readily suitable for recycling which can be encouraged by providing Reverse vending machines. See the article about History of bottle recycling in the United States. Plastic recycling can be increased when manufacturers of packaged goods minimize mixing of packaging materials and eliminate contaminants. Japan's plastic waste utilization rate rose to 83% in 2014. Trash pickers are those who practice Dumpster diving for subsistence or even profit. DroneB (talk) 23:06, 24 January 2019 (UTC)
 * "The UK recycling rate for Waste from Households (WfH; including IBA metal) was 45.2% in 2016".
 * The EU "recycled 6.8m tonnes, 40.9%, of its 16.7m tonnes plastic packaging waste in 2016". I suspect European recycling is heavily subsidised.
 * "Of 30 states (including Switzerland and Norway), ten have reached a recovery rate of over 90%".
 * Meanwhile across the pond, U.S. Plastic Recycling Rate Projected to Drop to 4.4% in 2018. Alansplodge (talk) 11:54, 25 January 2019 (UTC)
 * Alansplodge (talk) 11:59, 25 January 2019 (UTC)