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Event(s) on April 2010
- 12/4/2010
| 題目: |
DLS: Nonlinear evolution of ablative Rayleigh-Taylor instability |
| 講員: |
Prof. Xian-Tu He, Institute of Applied Physics and Computational Mathematics, China |
| 時間/地點: |
16:00 - 17:00 (Preceded by Reception at 3:30pm)
RRS905, Sir Run Run Shaw Building, HSH Campus, Hong Kong Baptist University
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| 摘要: |
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.
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- 16/4/2010
| 題目: |
Efficient Numerical Solution of Acoustic Scattering Problems in Layered Media |
| 講員: |
Dr. Jari Antero Toivanen, Institute for Computational and Mathematical Engineering, Stanford University, USA |
| 時間/地點: |
11:30 - 12:30
FSC1217, Fong Shu Chuen Library, HSH Campus, Hong Kong Baptist University
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| 摘要: |
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.
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- 22/4/2010
| 題目: |
Two-Player Evasion-Interrogation Games with Uncertainty |
| 講員: |
Prof. Banks, H.T., Center for Research in Scientific Computation, North Carolina State University, USA |
| 時間/地點: |
11:30 - 12:30
FSC1217, Fong Shu Chuen Library, HSH Campus, Hong Kong Baptist University
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| 摘要: |
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.
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- 27/4/2010
| 題目: |
隨機無窮維動力系統 |
| 講員: |
Prof. Guo Boling, Beijing Institute of Applied Physics and Computational Mathematics, China |
| 時間/地點: |
11:30 - 12:30
FSC1217, Fong Shu Chuen Library, HSH Campus, Hong Kong Baptist University
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| 摘要: |
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。
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- 28/4/2010
| 題目: |
Penalized maximum likelihood and its application |
| 講員: |
Prof. Zhang Yuanming, College of Agriculture, Nanjing Agricultural University, China |
| 時間/地點: |
15:00 - 16:00
FSC1217, Fong Shu Chuen Library, HSH Campus, Hong Kong Baptist University
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