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Three-dimensional rendering of diffusion of purple dye in water. Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical potential.
In anisotropic media, the diffusion coefficient depends on the direction. It is a symmetric tensor Dji = Dij. Fick's first law changes to it is the product of a tensor and a vector: For the diffusion equation this formula gives The symmetric matrix of diffusion coefficients Dij should be positive definite.
Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of the particles. Diffusion explains the net flux of molecules from a region of higher concentration to ...
The diffusion equation is a parabolic partial differential equation. In physics, it describes the macroscopic behavior of many micro-particles in Brownian motion, resulting from the random movements and collisions of the particles (see Fick's laws of diffusion ). In mathematics, it is related to Markov processes, such as random walks, and ...
diffusion takes place on many different scales, chapter three focuses on the various models of individual or micro-level diffusion, urban diffusion, regional diffusion, and macro-level (or national and international) diffusion. Chapter four discusses the frontiers of diffusion research. Also included'is a list of further readings and
Mass diffusivity. Diffusivity, mass diffusivity or diffusion coefficient is usually written as the proportionality constant between the molar flux due to molecular diffusion and the negative value of the gradient in the concentration of the species. More accurately, the diffusion coefficient times the local concentration is the proportionality ...
Keywords: diffusion, leaving exam, pre-service teacher, osmosis, Slovenia INTRODUCTION Diffusion and osmosis are very important basic science concepts, especially for understanding cell physiology (Odom, 1995; Odom & Barrow, 1995). Diffusion is the primary system of short-distance transport in cells.
The convection–diffusion equation is a combination of the diffusion and convection ( advection) equations, and describes physical phenomena where particles, energy, or other physical quantities are transferred inside a physical system due to two processes: diffusion and convection. Depending on context, the same equation can be called the ...