Jim Melcher diffusion-as-electric-circuit anecdote

Tom's welding/copper-steel current flow problem with the Curie transition; Melcher (MIT) drew an infinite series of parallel resistors instead of thinking atomistically. Used to make the lecture's closing point that engineers from different disciplines speak different languages.

I had a problem once which was a problem in current flow through copper and steel when we were doing welding. The steel would go past the Curie temperature and become non-ferromagnetic, and that's going to really affect the way the current flows through the thing. I went to see Jim Melcher, one of the great scientists at MIT, who passed away about 15 years ago. We started talking diffusion. To me, diffusion is: you have a vacancy, an atom moves into the vacancy, and they change places. Jim Melcher started talking diffusion, and he drew me an infinite series of parallel resistors. He thought of everything as an electric circuit. I thought of diffusion in terms of atomistics. Mike Mousakas thinks of the flow in Stamixco as a boundary layer problem. I think of it as inhomogeneous deformation. Even though we're all engineers, we speak different languages. That's one of the lessons for today. I'll see you on Tuesday.