過去の記録

過去の記録 ~05/21本日 05/22 | 今後の予定 05/23~

2006年11月14日(火)

トポロジー火曜セミナー

16:30-18:00   数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
高瀬将道 氏 (信州大学理学部)
High-codimensional knots spun about manifolds
[ 講演概要 ]
The spinning describes several methods of constructing higher-dimensional knots from lower-dimensional knots.
The original spinning (Emil Artin, 1925) has been generalized in various ways. Using one of the most generalized forms of spinning, called "deform-spinning about a submanifold" (Dennis Roseman, 1989), we analyze in a geometric way Haefliger's smoothly knotted (4k-1)-spheres in the 6k-sphere.

2006年11月13日(月)

複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 128号室
小野 肇 氏 (東京工業大学)
Sasaki-Futaki invariant and existence of Einstein metrics on toric Sasaki manifolds

代数幾何学セミナー

16:30-18:00   数理科学研究科棟(駒場) 126号室
青木昌雄 氏 (京大数理研)
Hom stacks and Picard stacks

2006年11月10日(金)

東京幾何セミナー

16:00-17:30   数理科学研究科棟(駒場) 056号室
中島啓 氏 (京都大学大学院理学研究科)
箙多様体のベッチ数の計算
[ 講演概要 ]
箙多様体の S^1 作用に関する固定点は, 次数付き箙多様体と呼ばれる. そのベッチ数の母関数は, 量子ループ代数の q-指標の t-類似と呼ばれ, 表現論的に大切な対象である. このベッチ数を, 仮想ホッジ多項式と, 箙多様体の stratified グラスマン束の構造を用いて計算するアルゴリズムを紹介する. 時間があれば, 大型計算機による計算結果についても紹介する.

トポロジー火曜セミナー

17:40-19:00   数理科学研究科棟(駒場) 118号室
樋上和弘 氏 (東京大学大学院理学系研究科 物理)
WRT invariant for Seifert manifolds and modular forms
[ 講演概要 ]
We study the SU(2) Witten-Reshetikhin-Turaev invariant for Seifert manifold. We disuss a relationship with the Eichler integral of half-integral modular form and Ramanujan mock theta functions.

2006年11月09日(木)

作用素環セミナー

16:30-18:00   数理科学研究科棟(駒場) 126号室
水田有一 氏 (東大数理)
Operator-algebraic superrigidity for SL_n(Z) II(Bekkaの論文の紹介)

講演会

16:20-17:50   数理科学研究科棟(駒場) 123号室
S. Bloch 氏 (シカゴ大学)
<連続講演> Graphs and motives

2006年11月08日(水)

諸分野のための数学研究会

10:30-11:30   数理科学研究科棟(駒場) 056号室
Fredric Flin 氏 (Hokkaido University)
Crystal growth in dry deposited snow: experiment, theoretical modeling and simulation
[ 講演概要 ]
Snow, from its fall until its full melting, undergoes transformations of its microstructure with time. This process, named “metamorphism”, drastically influences its physical, thermal and mechanical properties and is of great interest in snow and ice sciences.
The recent possibility of acquiring 3D images of small snow samples opens new opportunities for investigating snow in details. For this purpose, we developed specific algorithms in order to extract the relevant geometrical and physical parameters from the imaged samples (e.g. normal and curvature fields, specific surface area). We then used these estimators to develop 3D models that simulate the time-lapse transformations of snow directly from an experimentally observed microstructure. These models, which can be checked with experiments in cold room, offer new outlooks for the study of snow metamorphism.
[ 講演参考URL ]
http://coe.math.sci.hokudai.ac.jp/sympo/various/index.html

講演会

16:20-17:50   数理科学研究科棟(駒場) 123号室
S. Bloch 氏 (シカゴ大学)
<連続講演> Graphs and motives

東京幾何セミナー

14:40-18:00   数理科学研究科棟(駒場) 056号室
梶原 健 氏 (横浜国立大学大学院工学研究院応用数学) 14:40-16:10
代数多様体の退化とトロピカル幾何
[ 講演概要 ]
トロピカル幾何について説明しながら,多様体の退化等との関係や既知の応用について,簡単に紹介します.また,具体的にトロピカル超曲面で記述される退化として,射影トーリック多様体の退化について説明します.ここで現れる退化トーリック多様体は,Alexeev 氏がアーベル多様体のモジュライ空間のコンパクト化の研究において導入した,安定トーリック多様体です.
西納 武男 氏 (京都大学理学研究科数学教室) 16:30-18:00
Counting problem in tropical geometry
[ 講演概要 ]
この講演ではここ数年進展したトロピカル曲線を用いたトーリック多様体上の正則曲線の数え上げについて解説したいと思います.
はじめにトロピカル曲線と正則曲線の関係について,正則曲線のアメーバを介して(Target spaceが複素2次元の場合に)直感的な説明を試みます.トロピカル曲線は実1次元のグラフ状の集合ですが,複素構造のような幾何学的対象の退化を考えると自然に現れます.その考えに基づき,トロピカル曲線がトーリック多様体の退化と自然に関わることと,その事実の数え上げへの応用についてお話ししたいと思います.時間があればディスクの数え上げの場合について,閉曲線の場合との関係などにも触れたいと思います.

統計数学セミナー

16:20-17:30   数理科学研究科棟(駒場) 128号室
蛭川 潤一 氏 (早稲田大学)
LAN Theorem for Non-Gaussian Locally Stationary Processes and Their Discriminant and Cluster Analyses
[ 講演概要 ]
This talk is concerned with asymptotic inference for non-Gaussian locally stationary processes. Lucien LeCam established the most important and sophisticated foundation of the general statistical asymptotic theory. He introduced the concept of local asymptotic normality (LAN) for the likelihood ratio of general statistical models. Once LAN is proved, the asymptotic optimality of estimators and tests is described in terms of the LAN property. The techniques of statistical inference for stationary time series have been well established. However, stationary time series model is not plausible to describe the real world. One of the difficult problem when we deal with nonstationary processes is how to set up an adequate model. Otherwise, the observation in the future will bring no information for the present structure. Recently, Dahalhaus has proposed an important class of nonstationary processes, called locally stationary processes. Locally stationary processes have the time varying densities whose spectral structures smoothly change in time. In this talk, we first show the LAN results for locally stationary processes under the assumption of the non-Gaussianity. Then, we apply the LAN theorem to estimation and testing theory, non-Gaussian robustness and adaptive estimation. Our LAN theorem elucidates various non-Gaussian asymptotics. Next, we develop asymptotic theory for discriminant and cluster analyses of non-Gaussian locally stationary processes. We discuss about non-Gaussian robustness of our classification statistic. Furthermore, we execute the clustering of stock returns in Tokyo Stock Exchanges. Consequently, we observe that the clustering results well extract features of relationships among companies.
[ 講演参考URL ]
http://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2006/13.html

2006年11月07日(火)

講演会

16:20-17:50   数理科学研究科棟(駒場) 123号室
11月7日(火)-11月9日(木)の連続講演です.
担当者: 斎藤 毅

S. Bloch 氏 (シカゴ大学)
<連続講演> Graphs and motives

2006年11月06日(月)

複素解析幾何セミナー

10:30-12:00   数理科学研究科棟(駒場) 128号室
Mihai Paun 氏 (Université Henri Poincaré Nancy)
On the extension of twisted pluricanonical forms

2006年11月02日(木)

作用素環セミナー

16:30-18:00   数理科学研究科棟(駒場) 126号室
水田有一 氏 (東大数理)
Operator-algebraic superrigidity for SL_n(Z) I(Bekkaの論文の紹介)

応用解析セミナー

16:00-17:30   数理科学研究科棟(駒場) 056号室
Messoud Efendiev 氏 (ミュンヘン工科大学)
On attractor of Swift-Hohenberg equation in unbounded domain and its Kolmogorov entropy
[ 講演概要 ]
The main objective of the talk is to give a description of the large-time behaviour of solutions of the Swift-Hohenberg equation in unbounded domain.This will be done in terms of the global attractor. Here we encounter serious difficulties due to the lack of compactness of the embedding theorems and the interplay between the different topologies will play crucial role.We prove the existence of the global attractor and show that the restriction of the attractor to any bounded sets has an infinite fractal dimension and present sharp estimate for its Kolmogorov entropy.Spatio-temporal chaotic dynamics on the attractor will also be discussed.

2006年11月01日(水)

代数学コロキウム

16:30-18:45   数理科学研究科棟(駒場) 117号室
2講演です
G.Bayarmagnai 氏 (東大数理) 16:30-17:30
Essential dimension of some finite group schemes
Jacques Tilouine 氏 (パリ北大学) 17:45-18:45
Overconvergent Siegel modular forms
[ 講演概要 ]
We recall what is known and what is conjectured on p-adic families of overconvergent Siegel modular forms. We show how this relates to a Fontaine-Mazur type conjecture on the classicality of certain overconvergent Siegel forms of genus 2. We explain few results known in this direction.

統計数学セミナー

15:00-16:10   数理科学研究科棟(駒場) 128号室
Ilia NEGRI 氏 (Department of Management and Information Technology, University of Bergamo, Italy)
Some problems related to the estimation of the invariant measure of an ergodic diffusion.
[ 講演概要 ]
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.
[ 講演参考URL ]
http://www.ms.u-tokyo.ac.jp/~kengok/statseminar/2006/12.html

PDE実解析研究会

10:30-11:30   数理科学研究科棟(駒場) 128号室
Tan Yongji 氏 (School of Mathematical Science, Fudan University )
A case study in petroleum industry: Mathematical modeling and numerical simulation in spontaneous potential well-logging
[ 講演概要 ]
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.
[ 講演参考URL ]
http://coe.math.sci.hokudai.ac.jp/sympo/pde_ra/index.html

2006年10月31日(火)

Lie群論・表現論セミナー

16:30-18:00   数理科学研究科棟(駒場) 126号室
大島利雄氏 氏 (東大数理)
ルート系の部分系の分類
[ 講演概要 ]
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.
[ 講演参考URL ]
http://akagi.ms.u-tokyo.ac.jp/seminar.html

トポロジー火曜セミナー

16:30-18:00   数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
中村 信裕 氏 (東京大学大学院数理科学研究科)
Unsmoothable group actions on elliptic surfaces
[ 講演概要 ]
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年10月30日(月)

PDE実解析研究会

16:30-17:30   数理科学研究科棟(駒場) 128号室
Matti Lassas 氏 (Helsinki University of Technology, Institute of Mathematics)
Inverse Problems and Index Formulae for Dirac Operators
[ 講演概要 ]
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).
[ 講演参考URL ]
http://coe.math.sci.hokudai.ac.jp/sympo/pde_ra/index.html

2006年10月26日(木)

作用素環セミナー

16:30-18:00   数理科学研究科棟(駒場) 126号室
Remi Leandre 氏 (Univ. Bourgogne)
Introduction to Brownian surfaces

2006年10月25日(水)

代数学コロキウム

17:00-18:00   数理科学研究科棟(駒場) 117号室
いつもと時間が違います
平之内 俊郎 氏 (九州大学)
Extensions of truncated discrete valuation rings ( 田口雄一郎先生との共同研究 )
[ 講演概要 ]
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.

講演会

16:30-18:00   数理科学研究科棟(駒場) 122号室
Heinz W. Engl 氏 (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
[ 講演概要 ]
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年10月24日(火)

トポロジー火曜セミナー

16:30-18:00   数理科学研究科棟(駒場) 056号室
Tea: 16:00 - 16:30 コモンルーム
Marco Zunino 氏 (JSPS, University of Tokyo)
A review of crossed G-structures
[ 講演概要 ]
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.

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