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M. Bober is an author of Plutonium redistribution in fast reactor mixed oxide fuel pins by M. Bober and others. The study uses autoradiographs of irradiated fuel to examine how plutonium redistributes, considering thermal diffusion, evaporation–condensation and oxygen chemistry. The contribution is a spatial measurement of fuel evolution rather than an assumption that its starting composition remains uniform.^[ref]

Stephan Stellmach is a researcher in geophysics and fluid dynamics. His University of Münster profile records work on density stratification, convective turbulence and magnetic field generation, alongside publications on rotating convection.^[ref]

His 2013 work with collaborators on fingering convection connects small-scale fluid dynamics to chemical transport inside stars. A stabilizing temperature gradient and an opposing composition gradient can have a stable combined mass density profile while still permitting fingers, because thermal diffusion and molecular diffusion act at different rates. Their paper develops a transport model supported by three-dimensional direct numerical simulations, with a prescription usable in one-dimensional models of stellar evolution.^[ref]

The bridge between dimensions is the practical point: a one-dimensional calculation of a star's evolution cannot explicitly resolve every three-dimensional finger. Estimating their average transport from local numerical simulations supplies a model for that unresolved motion. It is a physically tested approximation within the modeled parameter regime, not a direct observation of all mixing inside a star.

Here thermal diffusion means the spreading of temperature by thermal conduction. In a stationary homogeneous material with constant thermal conductivity $k$, mass density $\rho$ and specific heat capacity $c$, energy balance and Fourier's law give the heat equation ${\partial }_{t}T=\alpha {\nabla }^{2}T$, where $\alpha =k/(\rho c)$ is the thermal diffusivity.

A disturbance spreads over a length of order $\sqrt{\alpha t}$, so equilibration across thickness $L$ takes a time of order $L^2/\alpha$. This is the heat-transport sense of the term; temperature-gradient-driven separation of components in a mixture is a distinct transport effect.