Difuusivus

Difuusivus is a term used in theoretical discussions of transport phenomena to denote a diffusion-like process in which a quantity spreads through a medium mainly by random motion, but with potential deviations from classical diffusion arising from nonlinearities, anisotropy, or nonlocal interactions. In its common mathematical usage, a difuusivus process is described by a governing equation of the diffusion family, typically ∂u/∂t = ∇·(D(u, x, t) ∇u) + S, where u(x,t) is the field of interest, D is a diffusivity that may depend on the field, position, or time, and S represents sources or sinks.

Distinctions: The term is often reserved for diffusion that departs from Fick's linear law in one or more ways: nonlinear diffusivity D(u, x, t), anisotropic diffusion with a diffusivity tensor, or nonlocal diffusion operators such as fractional Laplacians that allow long-range interactions. Difuusivus thus covers a range of models including porous-media diffusion, image-processing diffusion filters, and certain ecological or biological transport problems where the spreading rate varies with concentration or environment.

Usage and context: The term is used in multidisciplinary contexts where a general diffusion-like framework is useful but precise modeling choices vary. As a label, it emphasizes the diffusion character of transport while acknowledging departures from idealized, homogeneous, linear diffusion. See also diffusion, nonlinear diffusion, anisotropic diffusion, nonlocal diffusion.