August 18, 2017 at 02:38AM

Today I Learned: 1) You can put incredibly thin coats of stuff onto other stuff using a process called "vacuum sputtering". You be tempted to say "stuff to other stuff? That's pretty vague." And you'd be right. Because it's a pretty general technique. That's part of the awesomeness of it. Deposition techniques in general take advantage of the ability of most materials to easily form reactive species on surfaces. Under most conditions, those surfaces react immediately with oxygen -- that's why metals rust and why many plastics age. In vacuum, though, reactive species will just sit on the surface of whatever material they're on until they get hit with something. So if you want to coat a surface with, say, titanium, you just have to get that (very clean) surface into a vacuum and introduce a "few" titanium atoms into the vacuum. Vacuum sputtering is a technique for getting the coating substance into the vacuum. You set up the substrate (the thing you want to deposit onto) across from a target (a block of the material you want to coat with). Then you hit the target with high-energy gas or plasma (typically argon). The impact of the gas sends atoms/molecules of the target flying off into the vacuum... where they hit the substrate and stick. It's a bit like MALDI, but with ionized gas instead of lasers (for those who know what MALDI is). So, next time you want to coat a wasp with gold, this is how! 2) ...how to use Lie derivatives to determine system identifiability. I'm not going to go into much depth on this, because I'm still in the early, fuzzy stage of understanding Lie derivatives, but basically there's a technique using Lie derivatives that helps you figure out what parameters of a system you can, in principle, figure out by looking at some output of a system. A schematic example -- say you have a car driving along a road, and you want to consider a bunch of variables (parameters) like a) what kind of gas it's using, b) what temperature it is outside, c) what kind of road it's driving on, and d) how hard the gas pedal is pushed down. Now say you have some equations that tell you, given all of those parameters, how fast the car goes. Now say you *only* have a record of the speed of the car, and, say, the temperature of the engine (and say that engine temperature also appears somewhere in the equations you have). From that information, can you figure out parameters a-d? A Lie derivative will tell you at least some things about what parameters you can and can't back out, given the variable you observe. 3) Carbide is steel with little crystals of carbon in it. For some reason, this makes carbide very hard. That hardness makes carbide a good material for drill bits, which wear out quite quickly when used in industrial assembly lines. Apparently wearing out drill bits contributes a surprising amount to the cost of manufactured goods?