While MRI is merely a means to visualize diffusion, molecular diffusion itself (of water or other molecules, metabolites, neurotransmitters) has a life of its own and remains a powerful, genuine multidisciplinary concept at our disposal to understand cell physiology and life.
DTI parameters, including fractional anisotropy (FA), which is sensitive to white matter integrity, and mean diffusivity (MD), which quantifies water molecular diffusion at levels approximating cellular dimensions, were determined for aggregate 3D volumes of interest.
The features of this reactor are shown by means of mathematical modelling of molecular diffusion and viscous flow combined with an instantaneous, reversible reaction inside the membrane.
Molecular diffusion is evidently unimportant as a means of atmospheric transport and mixing at sea level.
By exploiting regularities in molecular diffusion barriers, QSI can estimate the average barrier spacing such as the mean axon diameter in white matter (WM).
Our research suggests that spatial heterogeneities can be well captured and modeled by means of time delayed processes with specific delay distributions, stemming from molecular diffusion profiles and the geometry of the cell and/or compartment analyzed.
Waves transfer their energy and momentum to the mean flow via breaking and dissipative processes, such as radiative damping, eddy viscosity, nonlinear diffusion, molecular diffusion and thermal conduction, and ion drag (Yiğit et al. 2008).
Molecular diffusion induced by turbulent mixing is described by the simple interaction by exchange with the mean (IEM) mixing model.
At this boundary the pressure falls to less than 5 × 10 7 bar and the mean free path of air molecules approaches 1 m, at which point bulk turbulent motion starts to break down and molecular diffusion dominates.
2. At what altitude does molecular diffusion become more important than turbulent diffusion as a mechanism for atmospheric transport?
