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Time-fractional Diffusion of Distributed OrderDepartment of Physics, University of Bologna, and INFN, Via Irnerio 46, I-40126 Bologna, Italy, francesco.mainardi{at}unibo.it
Department of Physics, University of Bologna, and INFN, Via Irnerio 46, I-40126 Bologna, Italy
Italian Agency for New Technologies, Energy and the Environment (ENEA), Via Martiri di Monte Sole 4, I-40129 Bologna, Italy
Department of Mathematics and Informatics, Free University of Berlin, Arnimallee 3, D-14195 Berlin, Germany The partial differential equation of Gaussian diffusion is generalized by using the time-fractional derivative of distributed order between 0 and 1, in both the Riemann-Liouville and the Caputo sense. For a general distribution of time orders we provide the fundamental solution, which is a probability density, in terms of an integral of Laplace type. The kernel depends on the type of the assumed fractional derivative, except for the single order case where the two approaches turn out to be equivalent. We consider in some detail two cases of order distribution: Double-order, and uniformly distributed order. Plots of the corresponding fundamental solutions and their variance are provided for these cases, pointing out the remarkable difference between the two approaches for small and large times.
Key Words: Anomalous diffusion fractional derivatives Mittag-Leffler function Laplace transform Fourier transform
Journal of Vibration and Control, Vol. 14, No. 9-10,
1267-1290 (2008) |
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