Quality of approximating a mass-emitting object by a point source in a diffusion model

Peng, Q.; Hille, S.C.

doi:doi:10.1016/j.camwa.2023.10.034

For the sake of computational eﬃciency and for theoretical purposes, in mathematical modelling, the Dirac
Delta distributions are often utilized as a replacement for cells or vesicles, since the size of cells or vesicles is much smaller than the size of the surrounding tissues. Here, we consider the scenario that the cell or the vesicle releases the diﬀusive compounds to the immediate environment, which is modelled by the diﬀusion equation. Typically, one separates the intracellular and extracellular environment and uses homogeneous Neumann boundary condition for the cell boundary (so-called spatial exclusion model), while the point source model neglects the intracellular environment. We show that extra conditions are needed such that the solutions to the two models are consistent. We prove a necessary and suﬃcient condition for the consistency. Suggested by the numerical results, we conclude that an initial condition in the form of Gaussian kernel in the point source model...Show moreFor the sake of computational eﬃciency and for theoretical purposes, in mathematical modelling, the Dirac
Delta distributions are often utilized as a replacement for cells or vesicles, since the size of cells or vesicles is much smaller than the size of the surrounding tissues. Here, we consider the scenario that the cell or the vesicle releases the diﬀusive compounds to the immediate environment, which is modelled by the diﬀusion equation. Typically, one separates the intracellular and extracellular environment and uses homogeneous Neumann boundary condition for the cell boundary (so-called spatial exclusion model), while the point source model neglects the intracellular environment. We show that extra conditions are needed such that the solutions to the two models are consistent. We prove a necessary and suﬃcient condition for the consistency. Suggested by the numerical results, we conclude that an initial condition in the form of Gaussian kernel in the point source model compensates for a time-delay discrepancy between the solutions to the two models in the numerical solutions. Various approaches determining optimal amplitude and variance of the Gaussian kernel have been discussed.
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Quality of approximating a mass-emitting object by a point source in a diffusion model