Seminar information archive

Seminar information archive ~11/09Today's seminar 11/10 | Future seminars 11/11~

2009/03/02

GCOE Seminars

15:00-16:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Bernd Hofmann (Chemnitz University of Technology)
Convergence rates for nonlinear ill-posed problems based on variational inequalities expressing source conditions
[ Abstract ]
Twenty years ago Engl, Kunisch and Neubauer presented the fundamentals of a systematic theory for convergence rates in Tikhonov regularization
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/gcoe/activity/documents/hofmann.pdf

2009/02/26

Lectures

17:00-18:30   Room #270 (Graduate School of Math. Sci. Bldg.)
Freddy DELBAEN (チューリッヒ工科大学名誉教授)
Introduction to Coherent Risk Measure

GCOE Seminars

15:00-16:00   Room #470 (Graduate School of Math. Sci. Bldg.)
Jijun Liu (Southeast University, P.R.China)
Reconstruction of biological tissue conductivity by MREIT technique
[ Abstract ]
Magnetic resonance electrical impedance tomography (MREIT) is a new technique in medical imaging, which aims to provide electrical conductivity images of biological tissue. Compared with the traditional electrical impedance tomography (EIT)model, MREIT reconstructs the interior conductivity from the deduced magnetic field information inside the tissue. Since the late 1990s, MREIT imaging techniques have made significant progress experimentally and numerically. However, the theoretical analysis on the MREIT algorithms is still at the initial stage. In this talk, we will give a state of the art of the MREIT technique and to concern the convergence property as well as the numerical implementation of harmonic B_z algorithm and nonlinear integral equation algorithm. We present some late advances in the convergence issues of MREIT algorithm. Some open problems related to the noisy effects and the numerical implementations are also given.

2009/02/24

Colloquium

16:00-17:00   Room #002 (Graduate School of Math. Sci. Bldg.)
神保道夫 (東京大学大学院数理科学研究科)
相関関数の構成要素
[ Abstract ]
2次元の可積分な格子模型や、それと等価な1次元量子スピンチェインは、ベーテ、オンサーガー以来多くの研究が重ねられ、詳細に調べられている。ハミルトニアンのスペクトルと並ぶ重要な物理量に相関関数がある。イジング模型や共形場理論では相関関数自身が微分方程式で特徴づけられるがこのような簡明な結果はそれ以外の場合には知られていない。イジング模型を超える代表的な例として1次元のXXZ模型がある。相関関数は多重積分であらわされ、その長距離漸近挙動の研究が近年フランスのグループにより大きく進展している。
講演の前半では、相関関数に焦点をあててこれまでの研究の歴史を概観する。結合定数や温度などのパラメータの関数として見た場合、相関関数は2つの要素的超越関数から原理的には有理的に決まっていることがわかる。後半ではこの話題を紹介したい。

2009/02/23

Lectures

13:30-14:30   Room #123 (Graduate School of Math. Sci. Bldg.)
長田 博文 (九大数理)
TBA

Lectures

14:40-16:10   Room #123 (Graduate School of Math. Sci. Bldg.)
Herbert Spohn (ミュンヘン工科大学)
Some problems from Statistical Mechanics linked to matrix-valued
Brownian motion

Lectures

16:20-17:50   Room #123 (Graduate School of Math. Sci. Bldg.)
Stefano Olla (パリ第9大学)
Macroscopic energy transport: a weak coupling approach

2009/02/19

Lectures

17:00-18:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Freddy DELBAEN (チューリッヒ工科大学名誉教授)
Introduction to Coherent Risk Measure

Algebraic Geometry Seminar

15:50-18:00   Room #128 (Graduate School of Math. Sci. Bldg.)
O. F. Pasarescu (Romanian Academy)
・Linear Systems on Rational Surfaces; Applications (15:50--16: 50)

・Some Applications of Model Theory in Algebraic Geometry (17:00 --18:00)

2009/02/18

Seminar on Mathematics for various disciplines

10:30-11:30   Room #056 (Graduate School of Math. Sci. Bldg.)
野原勉 (武蔵工業大学)
Non-existence theorem of periodic solutions except out-of-phase
and in-phase solutions in the coupled van der Pol equation system
[ Abstract ]
We consider the periodic solutions of the coupled van der Pol equation system $\\Sigma$, which is quite different from the ordinary van der Pol equation. We show the necessary and sufficient condition for the periodic solutions of $\\Sigma$. Non-existence theorem of periodic solutions except out-of-phase and in-phase solutions in $\\Sigma$ is presented.

thesis presentations

17:00-18:10   Room #122 (Graduate School of Math. Sci. Bldg.)
清野和彦 (東京大学大学院数理科学研究科)
Finite group actions on spin 4-manifolds(四次元スピン多様体への有限群作用)

2009/02/14

Infinite Analysis Seminar Tokyo

10:30-14:00   Room #117 (Graduate School of Math. Sci. Bldg.)
藤健太 (神戸理) 10:30-11:30
野海・山田系におけるタウ関数の関係式
[ Abstract ]
野海・山田系は, A型のドリンフェルト・ソコロフ階層の相似簡約から得られる高階
の常微分方程式系である.
本講演では, ドリンフェルト・ソコロフ階層を波動作用素を用いて考察することによっ
て, 野海・山田系のタウ関数の双線形方程式を求める.
鈴木貴雄 (神戸理) 13:00-14:00
ワイル群の regular な共役類に付随するドリンフェルト・ソコロフ階層とパンルヴェ型微分方程式
[ Abstract ]
ドリンフェルト・ソコロフ階層はKdV階層のアフィン・リー代数への一般化で, ワイ
ル群の共役類(またはハイゼンベルグ部分代数)によって特徴付けられる可積分系で
ある.
本講演では, ワイル群の共役類のうち特に regular と呼ばれるものに注目し, それ
に対応するドリンフェルト・ソコロフ階層の定式化について, F.Kroode-J.Leur, Kik
uchi-Ikeda-Kakei 等の仕事を紹介しつつ解説する.
また, パンルヴェ型微分方程式との関連についても述べる.

2009/02/13

GCOE lecture series

15:00-16:00   Room #370 (Graduate School of Math. Sci. Bldg.)
Vladimir Romanov (Sobolev Instutite of Mathematics)
ASYMPTOTIC EXPANSIONS FOR SOME HYPERBOLIC EQUATIONS 第3講
[ Abstract ]
For a linear second-order hyperbolic equation with variable coefficients the fundamental solution for the Cauchy problem is considered. An asymptotic expansion of this solution in a neighborhood of the characteristic cone is introduced and explicit formulae for coefficients of this expansion are derived. Similar questions are discussed for the elasticity equations related to an inhomogeneous isotropic medium.

GCOE Seminars

14:00-14:45   Room #270 (Graduate School of Math. Sci. Bldg.)
Johannes Elschner (Weierstrass Institute)
Direct and inverse problems in fluid-solid interaction
[ Abstract ]
We consider the interaction between an elastic body and a compressible inviscid fluid, which occupies the unbounded exterior domain. The direct problem is to determine the scattered pressure field in the fluid domain as well as the displacement field in the elastic body, while the inverse problem is to reconstruct the shape of the elastic body from the far field pattern of the fluid pressure. We present a variational approach to the direct problem and two reconstruction methods for the inverse problem, which are based on nonlinear optimization and regularization.

GCOE Seminars

16:15-17:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Wenbin Chen (Fudan University)
New Energy-conserved Splitting Finite-Difference Time-Domain Methods for Maxwell's Equations
[ Abstract ]
In this talk, two new energy-conserved splitting methods (EC-S-FDTDI and EC-S-FDTDII) for Maxwell’s equations are proposed. Both algorithms are energy-conserved, unconditionally stable and can be computed efficiently. The convergence results are analyzed based on the energy method, which show that the EC-S-FDTDI scheme is of first order in time and of second order in space, and the EC-S-FDTDII scheme is of second order both in time and space. We also obtain two identities of the discrete divergence of electric fields for these two schemes. For the EC S-FDTDII scheme, we prove that the discrete divergence is of first order to approximate the exact divergence condition. Numerical dispersion analysis shows that these two schemes are non-dissipative. Numerical experiments confirm well the theoretical analysis results.

2009/02/12

Lectures

17:00-18:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Freddy DELBAEN (チューリッヒ工科大学名誉教授)
Introduction to Coherent Risk Measure

2009/02/10

GCOE Seminars

15:00-16:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Piermarco Cannarsa (Univ. degli Studi Roma "Tor Vergata")
Carleman estimates for degenerate parabolic operators with application to null controllability
[ Abstract ]
From the controllability viewpoint, the behavior of uniformly parabolic equations is by now well understood. On the contrary, fewer results are known for degenerate parabolic equations, even though such a class of operators arise in many applied, as well as theoretical, problems.

A fairly complete analysis of the null controllability properties of degenerate parabolic equations in one space dimension was completed in a series of recent works by the speaker and coauthors. The aim of this talk is to review the above theory and present some recent results obtained in collaboration with P. Martinez and J.Vancostenoble for higher dimensional problems. Essential tools of such an approach are adapted Carleman estimates and Hardy type inequalities.

GCOE Seminars

16:15-17:15   Room #270 (Graduate School of Math. Sci. Bldg.)
Yurii Anikonov (Sobolev Institute of Mathematics)
Constructive methods in inverse problems
[ Abstract ]
New representations for solutions and coefficients of evolutionary equations are presented. On the basic of these representations theorems of solvability for inverse problems are obtained. This direction develops constructibility in the theory and applications of inverse problems to differential equations

2009/02/07

Monthly Seminar on Arithmetic of Automorphic Forms

13:30-16:00   Room #123 (Graduate School of Math. Sci. Bldg.)
河村隆 (成蹊大学) 13:30-14:30
次数2のモジュラー群の基本領域における行列式の最小値
早田孝博 (山形大学・工学部) 15:00-16:00
Siegel's fundamental domain of degree 2 and Groebner method

2009/02/06

GCOE lecture series

15:00-16:00   Room #370 (Graduate School of Math. Sci. Bldg.)
Vladimir Romanov (Sobolev Instutite of Mathematics)
ASYMPTOTIC EXPANSIONS FOR SOME HYPERBOLIC EQUATIONS 第2講
[ Abstract ]
For a linear second-order hyperbolic equation with variable coefficients the fundamental solution for the Cauchy problem is considered. An asymptotic expansion of this solution in a neighborhood of the characteristic cone is introduced and explicit formulae for coefficients of this expansion are derived. Similar questions are discussed for the elasticity equations related to an inhomogeneous isotropic medium.

thesis presentations

09:45-11:00   Room #118 (Graduate School of Math. Sci. Bldg.)
中岡 宏行 (東京大学大学院数理科学研究科)
Brauer Groups,Mackey and Tambara functors on profinite groups,and 2-dimensional homological algebra(Brauer群、プロ有限群上のMackey及び丹原関手と2次元ホモロジー代数)

thesis presentations

11:00-12:15   Room #118 (Graduate School of Math. Sci. Bldg.)
廣惠 一希 (東京大学大学院数理科学研究科)
Generalized Whittaker functions for degenerate principal series of GL(4,R)(GL(4,R)の退化主系列表現の一般Whittaker関数)

thesis presentations

13:00-14:15   Room #118 (Graduate School of Math. Sci. Bldg.)
阿部 紀行 (東京大学大学院数理科学研究科)
On the existence of homomorphisms between principal series of complex semisimple Lie groups(複素半単純リー群の主系列表現の間の準同型の存在について)

thesis presentations

11:00-12:15   Room #122 (Graduate School of Math. Sci. Bldg.)
中村 伊南沙 (東京大学大学院数理科学研究科)
Surface links which are coverings of a trivial torus knot(自明なトーラスの被覆の形をした曲面結び目の研究)

thesis presentations

13:00-14:15   Room #122 (Graduate School of Math. Sci. Bldg.)
山下 温 (東京大学大学院数理科学研究科)
Compactification of the homeomorphism group of a graph(グラフの同相群のコンパクト化について)

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