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Event(s) on April 2010


  • Monday, 12th April, 2010

    Title: DLS: Nonlinear evolution of ablative Rayleigh-Taylor instability
    Speaker: Prof. Xian-Tu He, Institute of Applied Physics and Computational Mathematics, China
    Time/Place: 16:00  -  17:00 (Preceded by Reception at 3:30pm)
    RRS905, Sir Run Run Shaw Building, HSH Campus, Hong Kong Baptist University
    Abstract: Evolution of the ablative single-mode Rayleigh-Taylor instability in the present of preheating is investigated numerically. It is found that the evolution depends strongly on the preheating length L in front of the ablation-front interface. For weak preheating (L/L_{SH} <= f_0, where LSH is the Spitzer-Harm length and f_0 ~ 20 is a critical value), the linear growth rate has a sharp maximum, and a secondary spike-bubble pattern is generated. Interaction of the growing secondary pattern with the master spike-bubble pattern leads eventually to rupture of the latter. However, for strong preheating (L/L_{SH} > 20), the linear growth rate has no sharp maximum and there is no secondary spike-bubble pattern. Instead, the master spike-bubble pattern evolves into an elongated jet. These results are interpreted in terms of the evolution and interaction of the instability generated harmonic modes.


  • Friday, 16th April, 2010

    Title: Efficient Numerical Solution of Acoustic Scattering Problems in Layered Media
    Speaker: Dr. Jari Antero Toivanen, Institute for Computational and Mathematical Engineering, Stanford University, USA
    Time/Place: 11:30  -  12:30
    FSC1217, Fong Shu Chuen Library, HSH Campus, Hong Kong Baptist University
    Abstract: We study time-harmonic acoustics scattering in layered media with a piecewise constant speed of sound. This leads to the solution of the Helmholtz equation with jumps in wavenumber. The problems can include sound-hard, sound-soft, or elastic scatterers. A finite element discretization is performed using an orthogonal meshes which can be locally adapted to the interfaces. For the iterative solution of resulting large indefinite linear systems, domain decomposition preconditioners are constructed using a fast direct solver. The iterations can be carried out in small subspaces related to interfaces. The numerical experiments demonstrate the capability to solve very large scale two-dimensional and three-dimensional problems with up to billions of unknowns.


  • Thursday, 22nd April, 2010

    Title: Two-Player Evasion-Interrogation Games with Uncertainty
    Speaker: Prof. Banks, H.T., Center for Research in Scientific Computation, North Carolina State University, USA
    Time/Place: 11:30  -  12:30
    FSC1217, Fong Shu Chuen Library, HSH Campus, Hong Kong Baptist University
    Abstract: We first consider electromagnetic interrogation in the context of evader-interrogator games where each player has uncertain information about the adversary’s capabilities. The mathematical formulation results in a static minmax problem over spaces of probability measures. The minmax cost functional is based on reflected fields from an object such as an airfoil or missile. To investigate theoretical, computational and approximation issues for these problems, it is necessary to put a topology on the space of probability measures. A natural choice for this is the Prohorov metric topology. One can then develop well-posedness and approximation results for the associated minmax problems. Efficient computational methods that correspond to Von Neumann’s finite mixed strategies can readily be developed in this context. Our efforts on static two person non-cooperative games demonstrate the feasibility and the potential usefulness of developing counter-interrogation (CI) and counter-counter-interrogation (CCI) theories for problems with uncertainty. We will also present our initial efforts on a conceptual, theoretical, and computational framework for CI/CCI dynamic games with uncertainty. This eventually involves allowing both the evader and interrogator to make dynamic changes to their strategies while each has only partial information (stochastic in nature) of the other’s changes. We will describe a number of different formulations among possible stochastic approaches. The framework we describe makes essential use of much of the important theoretical and computational results involving feedback control for partial differential equations as developed during the past several decades. We illustrate some of the technical ideas in the context of an evader’s formulation to thwart detection in the presence of dynamic interrogation with uncertainty.


  • Tuesday, 27th April, 2010

    Title: 隨機無窮維動力系統
    Speaker: Prof. Guo Boling, Beijing Institute of Applied Physics and Computational Mathematics, China
    Time/Place: 11:30  -  12:30
    FSC1217, Fong Shu Chuen Library, HSH Campus, Hong Kong Baptist University
    Abstract: 主要介紹隨機無窮維動力系統出現於大氣物理、金融系統、等離子物理 等領域以 及非線性波在隨機介質中的傳播,對當前該領域的研究新進展及某些存在的問題也作簡要的評述。


  • Wednesday, 28th April, 2010

    Title: Penalized maximum likelihood and its application
    Speaker: Prof. Zhang Yuanming, College of Agriculture, Nanjing Agricultural University, China
    Time/Place: 15:00  -  16:00
    FSC1217, Fong Shu Chuen Library, HSH Campus, Hong Kong Baptist University