2017年国际青年学者东湖论坛数学中心分会场

报告人：陈晨

报告题目：The boundary conditions of multi-scale models

报告摘要：Multiscale modelling aims to systematically construct macroscale models of materials with fine microscale structure. However, macroscale boundary conditions are typically not systematically derived, but rely on heuristic arguments, potentially resulting in a macroscale model which fails to adequately capture the behaviour of the microscale system.

We derive the macroscale boundary conditions of the macroscale model for longitudinal wave propagation on a lattice with periodically varying density and elasticity.We model the macroscale dynamics of the microscale Dirichlet, Robin-like, Cauchy-like and mixed boundary value problem. Numerical experiments test the new methodology.

Our method of deriving boundary conditions significantly improves the accuracy of the macroscale models. The methodology developed here can be adapted to a wide range of multiscale wave propagation problems.

报告时间：2017年12月28日下午2:30-3:00

报告地点：恩明楼813室

报告人：刘凯

报告题目：Thin-film hydrodynamic effects at cell-cell interfaces

报告摘要：T cell is a kind of lymphocyte (leukocyte subtype), which plays a key role in cellular immunity. The surface of T-cells is covered by long and hard molecules, like phosphatase CD45, which hinders the combination of the T cell receptor to the target antigen. We used a stochastic immersed boundary method to simulate the hydrodynamics of transient cell-cell contact. We examine the thin-film hydrodynamic effects at cell-cell interfaces, and our results suggest a role for plasma membrane permeability and optimal active protrusion length for T cell receptor triggering.

报告时间：2017年12月28日下午3:00-3:30

报告地点：恩明楼813室

报告人：柴利慧

报告题目：Frozen Gaussian Approximation based Seismic Tomography

报告摘要：We present a systematical introduction to the Frozen Gaussian Approximation (FGA) for high-frequency seismic tomography in 3-D earth models. In the frozen Gaussian approximation (FGA) we approximate the seismic wavefield by a summation of frozen (fixed-width) Gaussian wave-packets propagating along ray paths. One can use a relatively small number of Gaussians to get accurate approximations of the high-frequency wavefield. Meanwhile, FGA algorithm can be perfectly parallelized, which speeds up the computation drastically with a high-performance computing station.

In order to apply FGA to the computation of 3-D high-frequency seismic tomography, first we reformulate the FGA so that one can efficiently compute the Green's functions; and second, we incorporate Snell's law into the FGA formulation, and asymptotically derive reflection, transmission and free surface conditions for FGA to compute high-frequency seismic wave propagation in high contrast media. We successfully apply FGA in the local earthquake inversion and cross-well inversion using travel-time tomography and full-waveform inversion. Our numerical tests show that FGA has a huge advantage in comparison with the classical direct solver such as spectral element method in improving the computational efficiency, parallelizability, and accuracy in the high-frequency regime and large domain simulation.

报告时间：2017年12月28日下午3:30-4:00

报告地点：恩明楼813室