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Renjun Duan

2007-06-28
10:30:00 - 11:30:00

103 , Old Mathematics Building

Although the decay-in-time estimates on the semigroup generated by the linearized Boltzmann operator without forcing have been well established, there is no corresponding result for the case with general external forces. This talk is mainly concerned with the optimal decay estimates on the solution operator in some weighted Sobolev space for the linearized Boltzmann equation with a time-dependent external force. No time decay assumption is made on the force. The proof is based on both the energy method through the macro-micro decomposition and the Lp-Lq estimates from the spectral analysis. The decay estimates thus obtained are applied to the study on the global existence of the Cauchy problem to the nonlinear Boltz-mann equation with time-dependent external force and source. Precisely, for space dimension n ≧ 3, the global existence and decay rates of solutions to the Cauchy problem are obtained under the condition that the force and source decay in time with some rates. This time decay restriction can be removed for space dimension n ≧ 5. Moreover, the existence and asymptotic stability of the time periodic solution are given for space dimension n ≧ 5 when the force and source are time periodic with the same period. Some recent improvements on the solution space will be also mentioned. This is a joint work with Professors Seiji Ukai (CityUHK), Tong Yang (CityUHK) and Huijiang Zhao (WuhanU). attractor bifurcation theory and the center manifold reductions.