Emulations of a Diffusing Fluid

Alternatively to the methods involving propagation of individual ion trajectories (4.1.1), one may treat evolving ion cloud as a diffusing homogeneous compressible fluid. This process is governed by second Fick s law of diffusion  

Equation 4.5 may be solved using finite-difference methods of fluid dynamics, and C at the j-th time step in the y-th radial cell of span Ax is  

The approaches based on trajectory dynamics and discrete cells are fundamentally equivalent, providing a valuable cross-check. Excellent agreement between the results of these models in various scenarios testifies to their accuracy (below). These simulations and mathematical derivations have been applied to explore the dependence of FAIMS performance on instrumental parameters that we shall now review. 

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