Particle-Mobility

Particle mechanical mobility for aerosol single-particle dynamics. Migrated from Aerosol.jl@c8c640bb src/single_particle_dynamics.jl:230 (`ParticleMobility` @component). Computes the particle mobility B, which relates an external force on a particle to the steady drift velocity it produces; via the Einstein relation D = B k T it also fixes the Brownian diffusivity (Seinfeld & Pandis 2006, Chapter 9, Eq. 9.78).