Seminar information archive

Seminar information archive ~02/17Today's seminar 02/18 | Future seminars 02/19~

Seminar on Probability and Statistics

15:00-16:10   Room #128 (Graduate School of Math. Sci. Bldg.)
Ilia NEGRI (Department of Management and Information Technology, University of Bergamo, Italy)
Some problems related to the estimation of the invariant measure of an ergodic diffusion.
[ Abstract ]
We consider a one dimensional ergodic diffusion process solution of a stochastic differential equation. We suppose that the diffusion coefficient is known whereas the drift coefficient $S$ is unknown. Our interest is the invariant measure of the process denoted as $\\mu $. We denote by $f_S$ and $F_S$ the invariant density and the invariant distribution function of $\\mu$ respectively. We present the problems of finding efficient estimators when we observe the trajectory of the diffusion in continuos time over $[0,T]$ and we study asymptotic properties of the estimators when $T$ goes to infinity.
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2006/12.html

PDE Real Analysis Seminar

10:30-11:30   Room #128 (Graduate School of Math. Sci. Bldg.)
Tan Yongji (School of Mathematical Science, Fudan University )
A case study in petroleum industry: Mathematical modeling and numerical simulation in spontaneous potential well-logging
[ Abstract ]
Spontaneous well-logging is an important technique in petroleum exploitation. The potential field is of strong discontinuity on the interface since the spontaneous potential differences. It causes difficulty in mathematical analysis and numerical computing.

New mathematical model and numerical method is designed to overcome the difficulty and good results is obtained.
[ Reference URL ]
http://coe.math.sci.hokudai.ac.jp/sympo/pde_ra/index.html

2006/10/31

Lie Groups and Representation Theory

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
大島利雄氏 (東大数理)
ルート系の部分系の分類
[ Abstract ]
ルート系 Ξ からルート系 Σ へのCartan整数を保つ写像の分類を考える(像は Σ の部分系と見なせる).
Σ のWeyl群(Σ の内部同型)で移りあうものを同値とみたときの分類をまず行い,
同値の条件をさらに Ξ の自己同型(部分系の分類に対応),Ξ の既約成分の自己同型の直積,
Σ の自己同型などを許すものに広げた場合の分類や像が放物型かどうかの判定も与える.
ルート系の dual pair の概念を定義し,同値類への Ξ の自己同型の作用の考察に用いる.
[ Reference URL ]
http://akagi.ms.u-tokyo.ac.jp/seminar.html

Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
中村 信裕 (東京大学大学院数理科学研究科)
Unsmoothable group actions on elliptic surfaces
[ Abstract ]
Let G be a cyclic group of order 3,5 or 7.
We prove the existence of locally linear G-actions on elliptic surfaces which can not be realized by smooth actions with respect to specific smooth structures.
To prove this, we give constraints on smooth actions by using gauge theory.
In fact, we use a mod p vanishing theorem on Seiberg-Witten invariants, which was originally proved by F.Fang.
We give a geometric alternative proof of this, which enables us to extend the theorem.

2006/10/30

PDE Real Analysis Seminar

16:30-17:30   Room #128 (Graduate School of Math. Sci. Bldg.)
Matti Lassas (Helsinki University of Technology, Institute of Mathematics)
Inverse Problems and Index Formulae for Dirac Operators
[ Abstract ]
We consider a selfadjoin Dirac-type operator $D_P$ on a vector bundle $V$ over a compact Riemannian manifold $(M, g)$ with a nonempty boundary.

The operator $D_P$ is specified by a boundary condition $P(u|_{\\partial M})=0$ where $P$ is a projector which may be a non-local, i.e. a pseudodifferential operator.

We assume the existence of a chirality operator which decomposes $L2(M, V)$ into two orthogonal subspaces $X_+ \\oplus X_-$.

In the talk we consider the reconstruction of $(M, g)$, $V$, and $D_P$ from the boundary data on $\\partial M$.

The data used is either the Cauchy data, i.e. the restrictions to $\\partial M \\times R_+$ of the solutions to the hyperbolic Dirac equation, or the boundary spectral data, i.e. the set of the eigenvalues and the boundary values of the eigenfunctions of $D_P$. We obtain formulae for the index and prove uniqueness results for the inverse boundary value problems. We apply the obtained results to the classical Dirac-type operator in $M\\times \\C4$, $M \\subset \\R3$. The presented results have been done in collaboration with Yaroslav Kurylev (Loughborough, UK).
[ Reference URL ]
http://coe.math.sci.hokudai.ac.jp/sympo/pde_ra/index.html

2006/10/26

Operator Algebra Seminars

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Remi Leandre (Univ. Bourgogne)
Introduction to Brownian surfaces

2006/10/25

Number Theory Seminar

17:00-18:00   Room #117 (Graduate School of Math. Sci. Bldg.)
平之内 俊郎 (九州大学)
Extensions of truncated discrete valuation rings ( 田口雄一郎先生との共同研究 )
[ Abstract ]
局所体の拡大とその付値環の或る商である"truncated" dvrの拡大の圏を比較する. 不分岐拡大と剰余体の拡大が一対一対応するのと同じ様に, 分岐に関する条件を加えれば,局所体と "truncated" dvr の拡大の圏が同値になる (Deligne).
今回は, 古典的な(上付き)分岐群の代わりにAbbes-斎藤による分岐群を用いて分岐に関する条件を与える. そして,この分岐群の Rigid 幾何的解釈を踏襲する事でDeligneの定理の剰余体が非完全な場合への一般化が得られる事を述べる.

Lectures

16:30-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Heinz W. Engl (Industrial Mathematics Institute, Kepler University, Linz and Johann Radon Institute for Computational and Applied Mathematics, Austrian Academy of Sciences)
Regularization of nonlinear inverse problems: mathematics, industrial application fields, new challenges
[ Abstract ]
Motivated by some of the industrial examples presented in the first talk, we outline the theory of regularization methods for the stable solution of nonlinear inverse problems. Then, we turn to some new problem fields of possible future industrial relevance in systems and molecular biology.

2006/10/24

Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Marco Zunino (JSPS, University of Tokyo)
A review of crossed G-structures
[ Abstract ]
We present the definition of "crossed structures" as introduced by Turaev and others a few years ago. One of the original motivations in the introduction of these structures and of the related notion of a "Homotopy Quantum Field Theory" (HQFT) was the extension of Reshetikhin-Turaev invariants to the case of flat principal bundles on 3-manifolds. We resume both this aspect of the theory and other applications in both algebra and topology and we present our results on the algebraic structures involved.

Tuesday Seminar of Algebraic Analysis

16:30-18:00   Room #052 (Graduate School of Math. Sci. Bldg.)
吉野 邦生 (上智大理工)
Asymptotic expansions of solutions to heat equations with genelarized function initial value (岡康之氏との共同研究)
[ Reference URL ]
http://agusta.ms.u-tokyo.ac.jp/alganalysis.html

2006/10/23

Geometry Seminar

14:40-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Naichung Conan Leung (Chinese University of Hong Kong) 14:40-16:10
Toric geometry and Mirror Symmetry
[ Abstract ]
We first review the geometry of toric varieties. Then we will explain the SYZ mirror symmetry conjecture and how toric geometry plays an important role here.

Xiaowei Wang (Chinese University of Hong Kong) 16:30-18:00
Balance point and stability of vector bundles over a projective manifold
[ Abstract ]
In this talk, we will start with some basic theory of GIT and symplectic quotient, then introduce various kind of stability of a holomorphic vector bundle over a projective manifold. As an application of the general theory, we will answer a question raised by Donaldson by showing that GIT stable vector bundle produces a sequence of balanced embedding of the underlying projective manifold to the Grassmanian.

Seminar on Geometric Complex Analysis

10:30-12:00   Room #128 (Graduate School of Math. Sci. Bldg.)
泊 昌孝 (日本大学文理学部)
Classification of hypersurface simple K3 singularities -- 95 and others

Lectures

16:30-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Heinz W. Engl (Industrial Mathematics Institute, Kepler University, Linz and Johann Radon Institute for Computational and Applied Mathematics, Austrian Academy of Sciences )
Mathematical modelling and numerical simulation: from iron and steel making via inverse problems to finance
[ Abstract ]
We first describe the industrial mathematics structure in linz, extending from basic research via graduate education to industrial collaboration. We then present a few projetcs from our experience, ranging from aspects of iron and steel processing via mathematical simulation and optimization in car industry to robust and fast pricing methods for financial derivates. Since some of the projects involve inverse problem, we give a first introduction into this field, which will be deepened in the second talk.

2006/10/21

Infinite Analysis Seminar Tokyo

13:30-14:30   Room #117 (Graduate School of Math. Sci. Bldg.)
国場敦夫 (東大総合文化)
組合せベーテ仮説とタウ関数
[ Abstract ]
組合せベーテ仮説ではベーテ根とベーテベクトルの代わりにその組合せ論的類似物として rigged configuration と highest pathを対象物とする.
これらは Kerov-Kirillov-Reshetikhin (KKR)全単射により1対1対応する.
今回のお話では rigged configuration に付随した超離散タウ関数を導入し,以下の性質,結果について(時間の許すところまで)紹介します.
アフィン・クリスタルのエネルギー関数に一致する.
超離散双線形方程式をみたす.
KKR全単射の明示公式を与える.
箱玉系の角転送行列に相当し,一般Nソリトン解を与える
周期的 highest pathでは超離散リーマンテータ関数になる.
(坂本玲峰氏,山田泰彦氏との共同研究)

Infinite Analysis Seminar Tokyo

15:00-16:00   Room #117 (Graduate School of Math. Sci. Bldg.)
小森 靖 (名古屋大学) (名古屋大学多元数理)
ルート系に付随した多重ゼータ関数とベルヌーイ多項式
[ Abstract ]
ルート系に付随した多重ゼータ関数とは E. Witten によって導入された半単純リー代数の既約表現に関するゼータ関数を松本氏が多変数化したものである. この視点から見るとリーマンゼータ関数は A_1 型であり, Euler-Zagier 多重ゼータ関数は A_n 型で適当な変数を 0 にしたものであるといえる.
講演では, 特殊値とその間の関係式, 関数関係式, 母関数および付随するベルヌーイ多項式の性質を紹介する予定である.
(松本耕二氏, 津村博文氏との共同研究)

2006/10/20

Colloquium

16:30-17:30   Room #123 (Graduate School of Math. Sci. Bldg.)
新井 仁之 (東大・数理)
視覚科学における数学的方法

[ Abstract ]
眼球から入った視覚情報は,網膜から始まり LGN,そして脳内で処理が行われる.この講演で扱うのはこのうち網膜から主として大脳皮質の V1 野で加えられる視覚情報処理である.研究のキーワードは「錯視」.錯視は視覚の解明のための一つの重要な鍵と考えられており,100年以上前からさまざまな方法で研究されてきた.しかし未だ不明な点が多い.本講演では,視覚情報処理の離散ウェーブレットを用いた新しい非線形数理モデルを作り,それを用いて行った色や明暗の錯視発生のメカニズムに関する研究結果を述べる.
[ Reference URL ]
http://faculty.ms.u-tokyo.ac.jp/~seminar/colloquium.html

Infinite Analysis Seminar Tokyo

16:30-17:30   Room #118 (Graduate School of Math. Sci. Bldg.)
Petr Kulish (Steklov Math. Inst.)
Spin systems related to Temperley - Lieb algebra

2006/10/19

Operator Algebra Seminars

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
酒匂宏樹 (東大数理)
A unique decomposition result for HT factors with torsion free core (Popa の論文の紹介)

2006/10/18

Number Theory Seminar

16:30-18:45   Room #117 (Graduate School of Math. Sci. Bldg.)
Fabrice Orgogozo (東大数理・Ecole Polytechnique de Paris) 16:30-17:30
p-dimension of henselian fields: an application of Ofer Gabber's algebraization technique
Kim Minhyong (Purdue大学・京大数理研) 17:45-18:45
Fundamental groups and Diophantine geometry

Seminar on Probability and Statistics

16:20-17:30   Room #128 (Graduate School of Math. Sci. Bldg.)
松田 安昌 (東北大学大学院経済学研究科)
Fourier analysis of irregularly spaced data on R^d
[ Abstract ]
1970年代にはじまった時系列解析の研究は、1変量時系列からはじまり、多変量時系列、空間系列、時空間系列へと対象が拡張されてきている。近年の空間系列、時空間系列の文献を調べてみれば、時系列と同じく等間隔に観測されたデータ(regularly spaced data) を前提としている場合が多い。しかし時系列とは異なり、空間系列ではランダムに散らばった地点で観測されたデータ (irregularly spaced data)を仮定する方が、応用範囲がひろい。そこで本発表では、irregularly spaced dataによる空間相関の推定問題を扱う。具体的にはデータを周波数領域に変換してスペクトルを推定する方法を提案し、推定量が一致性、漸近正規性を持つための条件を示す。本方法による東京地価データ分析例も紹介する。本研究は、矢島美寛教授(東京大学大学院経済学研究科)との共同研究です。
[ Reference URL ]
http://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2006/11.html

Algebraic Geometry Seminar

16:00-18:15   Room #122 (Graduate School of Math. Sci. Bldg.)
E. Esteves (IMPA) 16:00-17:00

Jets of singular foliations and applications
to curves and their moduli spaces

F. Zak (Independent Univ. of Moscow) 17:15-18:15
Dual varieties, ramification, and Betti numbers
of projective varieties

2006/10/17

Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Arnaud Deruelle (University of Tokyo)
Networking Seifert Fibered Surgeries on Knots (joint work with Katura Miyazaki and Kimihiko Motegi)
[ Abstract ]
We define a Seifert Surgery Network which consists of integral Dehn surgeries on knots yielding Seifert fiber spaces;here we allow Seifert fiber space with a fiber of index zero as degenerate cases. Then we establish some fundamental properties of the network. Using the notion of the network, we will clarify relationships among known Seifert surgeries. In particular, we demonstrate that many Seifert surgeries are closely connected to those on torus knots in Seifert Surgery Network. Our study suggests that the network enables us to make a global picture of Seifert surgeries.

2006/10/16

Seminar on Geometric Complex Analysis

10:30-12:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Sebastien Boucksom (東大数理 JSPS研究員)
Differentiability of the volume of divisors and Khovanskii-Teissier inequalities

2006/10/12

Operator Algebra Seminars

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
酒匂宏樹 (東大数理)
保測同値関係の Haagerup property

2006/10/11

Seminar on Probability and Statistics

16:20-17:30   Room #128 (Graduate School of Math. Sci. Bldg.)
石川保志 (愛媛大学)
Optimal stopping problem associated with jump-diffusion processes
[ Abstract ]
We study an optimal stopping problem of some performance function with respect to a jump-diffusion process.

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