There are two types of time-fractional reaction-subdiffusion equations for two species. One of them generalizes the time derivative of species to fractional order, while in the other type, the diffusion term is differentiated with respect to time of fractional order. In the latter equation, the Turing instability appears as oscillation of concentration of species. In this paper, it is shown by the mode analysis that the critical point for the Turing instability is the standing oscillation of the concentrations of the species that does neither decays nor increases with time. In special cases in which the fractional order is a rational number, the critical point is derived analytically by mode analysis of linearized equations. However, in most cases, the critical point is derived numerically by the linearized equations and two-dimensional (2D) simulations. As a by-product of mode analysis, a method of checking the accuracy of numerical fractional reaction-subdiffusion equation is found. The solutions of the linearized equation at the critical points are used to check accuracy of discretized model of one-dimensional (1D) and 2D fractional reaction–diffusion equations.
Object-Based Image Enhancement Technique for Gray Scale Images
