 Justin M. Brown

Justin M. Brown is the first author, with Pascale Garaud and Stephan Stellmach, of a study of chemical mixing by fingering convection in stars. The 2013 paper developed a physically motivated transport model, tested it with three-dimensional direct numerical simulation, and supplied a method for incorporating the results into one-dimensional stellar calculations.^[ref]

Fingering convection is a form of double-diffusive convection: heat and composition affect buoyancy but spread at different rates. A background that resists ordinary overturning can therefore admit smaller-scale mixing when the compositional arrangement is destabilizing. The paper also investigated when layered structures could form, rather than assuming that every unstable region develops a staircase.^[ref]

A simple scaling comparison helps explain why unequal diffusion matters. In time $t$, a diffusing disturbance spreads a distance proportional to $\sqrt{Dt}$. If the thermal diffusivity is one hundred times the diffusion coefficient for composition, thermal changes spread roughly ten times farther in the same time. The calculation is illustrative, not a measured universal ratio for stars. Brown's coauthored work connects such local processes to the much larger problem of predicting chemical transport through a stellar interior.