Matthieu Mangeat, Heiko Rieger
The stochastic motion of particles in living cells is often spatially inhomogeneous with  a  higher  effective  diffusivity  in  a  region  close  to  the  cell  boundary  due  to  active  transport  along  actin  filaments.  As  a  first  step  to  understand  the  consequence  of  the  existence  of  two  compartments  with  different  diffusion  constant for stochastic search problems we consider here a Brownian particle in  a  circular  domain  with  different  diffusion  constants  in  the  inner  and  the  outer  shell.  We  focus  on  the  narrow  escape  problem  and  compute  the  mean  first passage time (MFPT) for Brownian particles starting at some pre-defined position to find a small region on the outer reflecting boundary. For the annulus geometry we find that the MFPT can be minimized for a specific value of the width of the outer shell. In contrast for the two-shell geometry we show that the  MFPT  depends  monotonously  on  all  model  parameters,  in  particular  on  the outer shell width. Moreover we find that the distance between the starting point  and  the  narrow  escape  region  which  maximizes  the  MFPT  depends  discontinuously on the ratio between inner and outer diffusivity.
|    The narrow escape problem in a circular domain with radial piecewise constant diffusivity  | 
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| J. Phys. A 52, 424002 (2019) | [pdf], [arXiv] | 
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