You are welcome to attend the following talk.

Date: May 17th(Thursday), 10:00-12:00am
Place: National Institute of Informatics, 12F, Lecture Room 1 (1212)
Title: A Novel Multigrid Based Preconditioner For Heterogeneous Helmholtz Problems
Speaker: Professor Cornelis W. Oosterlee
(Delft University of Technology, Delft, the Netherlands, and, CWI, Center for Mathematics and Computer Science, Amsterdam.)

This is joint work with Y.A. Erlangga, C. Vuik, A. Kononov and Chr. Dwi Riyanti.

Abstract:
In this presentation an iterative solution method, in the form of a preconditioner for a Krylov subspace method, is presented for high wavenumber Helmholtz problems in heterogeneous media.
The preconditioner is based on the Helmholtz operator, where an imaginary term is added. This preconditioner can be handled by one iteration of the multigrid method. This may be somewhat surprising as multigrid, without enhancements, has convergence troubles for the original Helmholtz operator at high
wavenumbers. The choice of multigrid components for the corresponding preconditioning matrix with a complex diagonal is validated with Fourier analysis.
Multigrid analysis results are verified by numerical experiments. High wavenumber Helmholtz problems in 2D heterogeneous media are solved indicating the performance of the preconditioner. The method is parallelized and generalized to three dimensions. We will include a 3D example.

The research is financially supported by Dutch Ministry of Economic Affairs project BTS01044.

You are welcome to attend the following seminar.

Mr Picard (FT R&D) will present his research on the automatic construction of knowledge resources at France Telecom R&D and at the National Institute of Informatics, under the supervision of professor Aizawa.

Schedule: Thursday 17th of May 2007 (14:30-15:30)
Location: National Institute of Informatics (Tokyo), 20F, Room 2006
Language: English
Registration fees: None
Seminar page: http://horizons.free.fr/his/eng/seminars.htm

*Automatic Extraction from Web Corpora of Characteristic Properties of a Concept by Mr PICARD Etienne

Abstract:
The goal of our project is to automate the construction of knowledge resources. Our framework starts with a concept (e.g. museums, singers), and extracts from web corpora properties linking this concept to other ones. The initial concept is described by its name (e.g. museum) and by the name of instances (e.g. The Louvre). Based on this information, we use search engines to build texts corpora from the web, and apply text mining techniques to extract properties from those corpora. Our aim is to build resources usable by information retrieval dialoguing agents.

Speaker:
Mr Picard is a doctor student at Jospeh Fourier University of Grenoble (France). He conducts his research at France Telecom R&D's laboratory in Lannion (France), and joined the National Institute of Informatics for a 3-months internship under the supervision of AIZAWA Akiko. His current research topics deal with text mining, web content mining, and knowledge extraction.