Abstract
In this paper we study continuous time random walks such that the holding time in each state has a distribution depending on the state itself. For such processes, we provide integro-differential (backward and forward) equations of Volterra type, exhibiting a position dependent convolution kernel. Particular attention is devoted to the case where the holding times have a power-law decaying density, whose exponent depends on the state itself, which leads to variable order fractional equations. A suitable limit yields a variable order fractional heat equation, which models anomalous diffusions in heterogeneous media.
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Ricciuti, C., Toaldo, B. Semi-Markov Models and Motion in Heterogeneous Media. J Stat Phys 169, 340–361 (2017). https://doi.org/10.1007/s10955-017-1871-2
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DOI: https://doi.org/10.1007/s10955-017-1871-2
Keywords
- Semi-Markov processes
- Anomalous diffusion
- Continuous time random walks
- Volterra equations
- Fractional derivatives
- Subordinators