Diffusivem

Diffusivem is a term that appears in some diffusion-related discussions to denote an effective, generalized measure of how a quantity spreads through a medium under complex conditions. It is not a standard physical constant but a modeling construct used to capture combined effects such as heterogeneity, anisotropy, and temporal memory.

In different works, diffusivem can be defined as a scalar, a tensor, or a function of state variables and time. It often arises when extending classical Fickian diffusion to non-Fickian regimes, porous media transport, or diffusion in structured or evolving media.

Applications include materials science, environmental engineering, and theoretical biology, where researchers simulate diffusion processes with spatially varying diffusivem that reflects microstructure, external fields, or reaction terms. In simulations, diffusivem is typically calibrated from experiments or microstructure data to reproduce observed spreading rates.

The term has no single, universal definition, and its use varies by author and domain. As a result, diffusivem should be interpreted in context of the underlying model and accompanying equations.

See also diffusion, diffusion coefficient, anisotropic diffusion, non-Fickian diffusion.