過去の記録

過去の記録 ~02/21本日 02/22 | 今後の予定 02/23~

2013年03月11日(月)

作用素環セミナー

09:45-12:00   数理科学研究科棟(駒場) 123号室
Tristan Bice 氏 (York Univ.) 09:45-10:45
Traces and Ultrapowers (ENGLISH)
David Penneys 氏 (Univ. Toronto) 11:00-12:00
Constructing subfactors with jellyfish (ENGLISH)

作用素環セミナー

13:30-18:15   数理科学研究科棟(駒場) 123号室
Danny Hey 氏 (Univ. Toronto) 13:30-14:30
Classification and the Toms-Winter Conjecture (ENGLISH)
Stephen Curran 氏 (UCLA) 14:45-15:45
Free probability and planar algebras (ENGLISH)
Rasmus Bentmann 氏 (Univ. Copenhagen) 16:00-17:00
Kirchberg $X$-algebras with real rank zero and intermediate cancellation (ENGLISH)
Luis Santiago-Moreno 氏 (Univ. Oregon) 17:15-18:15
Classifying $C^*$-algebras up to W-stability (ENGLISH)

GCOEセミナー

14:45-15:45   数理科学研究科棟(駒場) 123号室
このセミナーはMiniworkshop on Operator Algebras IVの一環として行われます
Stephen Curran 氏 (UCLA)
Free probability and planar algebras (ENGLISH)
[ 講演参考URL ]
http://www.ms.u-tokyo.ac.jp/~yasuyuki/mini2013-4.htm

2013年03月08日(金)

FMSPレクチャーズ

10:30-12:00   数理科学研究科棟(駒場) 056号室
Benjamin Burton 氏 (The University of Queensland, Australia)
Knots, algorithms and linear programming: the quest to solve unknot recognition in polynomial time (ENGLISH)
[ 講演概要 ]
In this talk we explore new approaches to the old and difficult computational problem of unknot recognition. Although the best known algorithms for this problem run in exponential time, there is increasing evidence that a polynomial time solution might be possible. We outline several promising approaches, in which computational geometry, linear programming and greedy algorithms all play starring roles. We finish with a new algorithm that combines techniques from topology and combinatorial optimisation, which is the first to exhibit "real world" polynomial time behaviour: although it is still exponential time in theory, exhaustive experimentation shows that this algorithm can solve unknot recognition for "practical" inputs by running just a linear number of linear programs.

This is joint work with Melih Ozlen.

2013年03月07日(木)

統計数学セミナー

14:50-16:00   数理科学研究科棟(駒場) 006号室
参加をご希望される方は鎌谷 (阪大基礎工); kamatani at sigmath.es.osaka-u.ac.jpまでご連絡ください.
前園 宣彦 氏 (九州大学)
符号検定の連続化と有意確率の近似について (JAPANESE)
[ 講演概要 ]
本講演では符号検定の連続化とその分布の近似を議論する.カーネル型分布関数の推 定量を利用して検定統計量を構成し,そのPitmanの漸近相対効率は符号検定と同じで あることを示す.また新しい検定統計量はdistribution-freeではないが,漸近分布 は母集団分布に依存しないことを議論し,近似分布の改良であるエッジワース展開を 求める.カーネルの取り方により,エッジワース展開が分布に依存しないように構成 することが可能であることも示す.本研究は九州大学大学院数理学府・魯夢欣さんと の共同研究である.
[ 講演参考URL ]
http://www.sigmath.es.osaka-u.ac.jp/~kamatani/statseminar/2012/16.html

2013年03月06日(水)

講演会

16:00-17:30   数理科学研究科棟(駒場) 117号室
Frederic Le Roux 氏 (Institut de Mathematiques de Jussieu, Universite Pierre et Marie Curie)
The rotation set around a fixed point for surface homeomorphisms. (ENGLISH)
[ 講演概要 ]
We propose two definitions of a local rotation set. As applications, one
gets some criteria for the existence of periodic orbits, and a clear
explanation of Gambaudo-Le Calvez-Pecou's version of the Naishul theorem:
for surface diffeomorphisms, the rotation number of the derivative at a
fixed point which is not a sink nor a source is a topological invariant.
Tha local rotation set also provide an unexpected topological
characterization for the parabolic fixed points of holomorphic maps.

2013年03月05日(火)

統計数学セミナー

14:50-16:00   数理科学研究科棟(駒場) 006号室
参加をご希望される方は鎌谷 (阪大基礎工); kamatani at sigmath.es.osaka-u.ac.jpまでご連絡ください.
田中 冬彦 氏 (東京大学)
ベイズ予測に基いた波動関数の推定と純粋状態モデルの無情報事前分布 (JAPANESE)
[ 講演概要 ]
近年、量子状態トモグラフィにみられるように、量子物理実験において、統計的手法を用いた推定精度の向上が注目されている。本発表では、波動関数のパラメータ族が与えられた下で、少数の実験データから波動関数を推定する問題を考える。物理分野では、一般に、点推定に基いた推定しか議論されていないが、データが少ない場合にはパラメータの推定量の統計誤差が無視できない。本発表ではベイズ予測の考え方に基いた推定量を提案する。例として位置パラメータをもつガウス型の波動関数の推定を取り上げ、フィデリティ損失の下で、最尤推定(点推定)に基く推定より、ジェフリーズ事前分布を用いたベイズ予測に基く推定が一様に推定誤差を小さくすることを示す。後者は最良共変推定量にもなっている。 一方、このようなモデル(純粋状態モデル)における無情報事前分布の問題も、物理分野ではほとんど研究されてこなかった。本講演ではBernardoの考え方に注目し、パラメータ空間のコンパクト性を仮定した下で、純粋に量子論的な事前分布を提案する。導出の際に最小エントロピーが出てくるため、統計的モデリングなどへの応用も期待される。
[ 講演参考URL ]
http://www.sigmath.es.osaka-u.ac.jp/~kamatani/statseminar/2012/15.html

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 270号室
Oleg Emanouilov 氏 (Colorado State University)
Uniqueness for inverse boundary value problems by Dirichlet-to
-Neumann map on subboundaries (ENGLISH)
[ 講演概要 ]
We consider inverse boundary value problems for elliptic equations of second order and survey recent results on the uniqueness mainly by partial boundary data. In particular, in two dimensions, we show uniqueness results by means of Dirichlet data supported on an arbitrary subboundary $\\widetilde\\Gamma$ and Neumann data measured on $\\widetilde\\Gamma$. We describe the key idea for the proof: complex geometric optics solutions which are constructed by a Carleman estimate. Also we show the uniqueness by Dirichlet-to-Neumann map on subboundaries in three dimensions.

2013年03月04日(月)

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 270号室
M.I. Tribelsky 氏 (Landau Institute)
Resonant Light Scattering by Small Particles (ENGLISH)
[ 講演概要 ]
The problem of light scattering by a small spherical particle is studied within the framework of the exact solution of the Maxwell equations. It is shown that if imaginary part of the dielectric permittivity of the particle is small enough, the problem exhibits sharp giant resonances with very unusual properties. Specifically, the characteristic values of the electric and magnetic fields inside the particle and in its immediate vicinity are singular in the particle size. In non-dissipative case these quantities do not have definite limits when the radius of the particle tends to zero. The field of the Poynting vector in the immediate vicinity of the particle includes singular points, whose number, types and positions are very sensitive to the changes in the incident light frequency. As an example a bifurcation diagram, describing the behavior of the singular points in the vicinity of the dipole resonance for a particle with a certain fixed size is discussed.

2013年02月28日(木)

GCOEセミナー

16:00-17:00   数理科学研究科棟(駒場) 270号室
Mourad Choulli 氏 (Univ. Lorraine)
Stability of the determination of the surface impedance of an
obstacle from the scattering amplitude (ENGLISH)
[ 講演概要 ]
In this joint work with Mourad Bellassoued and Aymen Jbalia, we prove a stability estimate of logarithmic type for the inverse problem consisting in the determination of the surface impedance of an obstacle from the scattering amplitude. We present a simple and direct proof which is essentially based on an elliptic Carleman inequality.

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 270号室
Kazufumi Ito 氏 (North Carolina State Univ.)
$L_0$ optimization and Lagrange multiplier (ENGLISH)
[ 講演概要 ]
$L_p$ optimization with $p ¥in[0,1)$ is investigated. The difficulty of natural lack of weak lower-semicontinuity is addressed and the Lagrange multiplier theory is developed. Existence results and necessary optimality conditions are obtained, and the semismooth Newton method using the primal-dual active set is developed. The theory and algorithm are demonstrated for the case of optimal control problems. A maximum principle is derived and existence of controls, in some cases relaxed controls, is proved.

2013年02月27日(水)

GCOEセミナー

10:00-11:00   数理科学研究科棟(駒場) 270号室
Dietmar Hoemberg 氏 (Weierstrass Institute)
Sufficient optimality conditions for a semi-linear parabolic system related to multiphase steel production (ENGLISH)
[ 講演概要 ]
Multiphase steels combine good formability properties with high strength and have therefore become important construction materials, especially in automotive industry. The standard process route is hot rolling with subsequent controlled cooling to adjust the desired phase mixture. In the first part of the talk a phenomenological model for the austenite ferrite phase transition is developed in terms of a nucleation and growth process, where the growth rate depends on the carbon concentration in austenite. The approach allows for further extensions, e.g., to account for a speed up of nucleation due to deformation of austenite grains. The model is coupled with an energy balance to describe the phase transitions on a run-out table after hot rolling. Here, the most important control parameters are the amount of water flowing per time and the feed velocity of the strip. The spatial flux profile of the water nozzles has been identified from experiments.

Since the process window for the adjustment of the phase composition is very tight the computation of optimal process parameters is an important task also in practice. This is discussed in the second part of the talk using a classical optimal control approach, where a coefficient in the Robin boundary condition acts as the control. I will discuss necessary and sufficient optimality conditions, describe a SQP-approach for its numerical solution and conclude with some numerical results.

(joint work with K. Krumbiegel and N. Togobytska, WIAS)

2013年02月23日(土)

保型形式の整数論月例セミナー

13:30-16:00   数理科学研究科棟(駒場) 123号室
平野幹 氏 (愛媛大学) 13:30-14:30
Ramanujan巡回グラフとHardy-Littlewood予想 (JAPANESE)
[ 講演概要 ]
TBA
成田宏秋 氏 (熊本大学) 15:00-16:00
例外型実リー群$G_2$の一般化ホウィッタカー関数についてのある考察 (JAPANESE)
[ 講演概要 ]
TBA

2013年02月22日(金)

作用素環セミナー

16:30-18:00   数理科学研究科棟(駒場) 118号室
Stefaan Vaes 氏 (KU Leuven)
II$_1$ factors with a unique Cartan subalgebra (ENGLISH)

FMSPレクチャーズ

16:30-18:00   数理科学研究科棟(駒場) 118号室
Stefaan Vaes 氏 (KU Leuven)
II_1 factors with a unique Cartan subalgebra (ENGLISH)

GCOEセミナー

16:00-17:00   数理科学研究科棟(駒場) 270号室
Fatiha Alabau-Boussouira 氏 (Université de Lorraine)
Exact insensitizing controls for scalar wave equations and control of coupled systems (ENGLISH)
[ 講演概要 ]
The control of scalar PDE's such as the wave or heat equation is by now well-understood.
It consists in building a source term which can drive the solution from a given initial state to a final (reachable) desired state.
Exact insensitizing control are exact controls which should satisfy an additional requirement:
they should be robust to small unknown perturbations of the initial data. More precisely, they should, as exact controls, drive the solution to the desired state, but they also should insensitize a given measure of the solution to such perturbations. One can show that the existence of exact insensitizing controls for a scalar wave equation is equivalent to the exact controllability by a single control of a system of two wave equations coupled in cascade.
We shall present in this talk the challenging issues and give some recent results and perspectives for the exact insensitizing control of scalar wave equations. We shall also give some more general results on the controllability of coupled systems by a reduced number of controls.

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 270号室
Piermarco Cannarsa 氏 (Univ. Roma II)
Carleman estimates and Lipschitz stability for Grushin-type operators (ENGLISH)
[ 講演概要 ]
The Baouendi-Grushin operator is an important example of a degenerate elliptic operator that has strong connections with almost-riemannian structures. It is also the infinitesimal generator of a strongly continuous semigroup on Lebesgue spaces with very interesting properties from the point of view of control theory. Such properties will be discussed in this lecture, starting with approximate and null controllability.
We will then address the inverse source problem for these operators deriving a Lipschitz stability result.

2013年02月21日(木)

FMSPレクチャーズ

15:00-16:00   数理科学研究科棟(駒場) 056号室
Michael Mascagni 氏 (Florida State University
)
Monte Carlo Methods for Partial Differential Equations: Computing Permeability
(ENGLISH)
[ 講演概要 ]
We present a brief overview of Monte Carlo methods for the solution of elliptic and parabolic partial differential equations (PDEs). We begin with a review of the Feynman-Kac formula, and its use in the probabilistic representation of the solutions of elliptic and parabolic PDEs. We then consider some specific Monte Carlo methods used for obtaining the solution of simple elliptic partial differential equations (PDEs) as part of exterior boundary value problems that arise in electrostatics and flow through porous media. These Monte Carlo methods use Feynman-Kac to represent the solution of the elliptic PDE at a point as the expected value of functionals of Brownian motion trajectories started at the point of interest. We discuss the rapid solution of these equations, in complex exterior geometries, using both the "walk on spheres" and "Greens function first-passage" algorithms. We then concentrate on methods for quickly computing the isotropic permeability using the "unit
capacitance" and "penetration depth'' methods. The first of these methods, requires computing a linear functional of the solution to an exterior elliptic PDE. Both these methods for computing permeability are simple, and provide accurate solutions in a few seconds on laptop-scale computers. We then conclude with a brief look at other Monte Carlo methods and problems that arise on related application areas.

2013年02月19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
畠中 英里 氏 (東京農工大学)
On the ring of Fricke characters of free groups (JAPANESE)
[ 講演概要 ]
This is a joint work with Takao Satoh (Tokyo University of Science). We study a descending filtration of the ring of Fricke characters of a free group consisting of ideals on which the automorphism group of the free group naturally acts. Then by using it, we define a descending filtration of the automorphism group of a free group, and investigate a relation between it and the Andreadakis-Johnson filtration.

2013年02月18日(月)

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 270号室
Larisa A. Nazarova 氏 (Department
Institute of Mining Siberian Branch of Russian Academy of Sciences)
INVERSE PROBLEMS OF GEOMECHANICS AND ITS APPLICATION IN MINING AND GEOPHYSICS (ENGLISH)
[ 講演概要 ]
The communication devotes to the boundary, coefficient and mixed inverse problems in modeling solid mineral mining processes.
Direct and indirect methods for estimation of natural stress field components were compared.
Based on GPS data (South Siberia, 2000-2003) interpretation the possible indicator (sharp increase of horizontal strains increment in epicenter vicinity) of future strong seismic event was established.
The theoretical approach for evaluation of future earthquake focal parameters (hypocentre depth and fractal dimension of fault anomalous zone) was proposed. The approach is found on inverse problem solution by variation of daylight surface strains.
Using a viscoelastic model, a method is proposed to evaluating the equation-of-state parameters that describe deformation of structural units of the room-and-pillar implementation in bedded deposits composed of rocks developing rheological properties. The method is based on the inverse coefficient problem solution with the data on roof and floor convergence in stopes.
A method of day-to-day qualitative assessment of elastic and strength properties of backfill in flat bedded deposits has been developed on the basis of the solution of the coefficient inverse problem for a set of equations (quasi-static formulation) which describe deformation and failure of filling mass. Uniqueness of the solution only requires simultaneous minimization of two objective functions.

2013年02月16日(土)

東京無限可積分系セミナー

13:30-15:00   数理科学研究科棟(駒場) 117号室
Alexey Silantyev 氏 (Tokyo. Univ.)
Generalized Calogero-Moser type systems and Cherednik Algebras (ENGLISH)
[ 講演概要 ]
Calogero-Moser systems can be obtained using Dunkl operators, which
define the polynomial representation of the corresponding rational
Cherednik algebra. Parabolic ideals invariant under the action of the
Dunkl operators give submodules of Cherednik algebra. Considering the
corresponding quotient-modules one yields the generalized (or deformed)
Calogero-Moser systems. In the same way we construct the generalized
elliptic Calogero-Moser systems using the elliptic Dunkl operators
obtained by Buchstaber, Felder and Veselov. The Macdonald-Ruijsenaars
systems (difference (relativistic) Calogero-Moser type systems) can be
considered in terms of Double Affine Hecke Algebra (DAHA). We construct
appropriate submodules in the polynomial representation of DAHA, which
were obtained by Kasatani for some affine root systems. Considering the
corresponding quotient representation we derive the generalized
(deformed) Macdonald-Ruijsenaars systems for any affine root system,
which where obtained by Sergeev and Veselov for the A series. This is
joint work with Misha Feigin.

2013年02月08日(金)

講演会

10:30-11:30   数理科学研究科棟(駒場) 370号室
Zdzislaw Brzezniak 氏 (University of York)
Strong and weak solutions to stochastic Landau-Lifshitz equations (ENGLISH)
[ 講演概要 ]
I will speak about the existence of weak solutions (and the existence and uniqueness of strong solutions) to the stochastic Landau-Lifshitz equations for multi (and one)-dimensional spatial domains. I will also describe the corresponding Large Deviations principle and it's applications to a ferromagnetic wire.
The talk is based on a joint work with B. Goldys and T. Jegaraj.

博士論文発表会

09:45-11:00   数理科学研究科棟(駒場) 118号室
古場 一 氏 (東京大学大学院数理科学研究科)
Stability of Navier-Stokes-Boussinesq Type Systems(ナヴィエ・ストークス・ブジネスク型方程式の安定性) (JAPANESE)

博士論文発表会

11:00-12:15   数理科学研究科棟(駒場) 118号室
大島 芳樹 氏 (東京大学大学院数理科学研究科)
Discrete branching laws of Zuckerman\\'s derived functor modulesZuckerman(導来関手加群の離散的分岐則) (JAPANESE)

博士論文発表会

11:00-12:15   数理科学研究科棟(駒場) 118号室
大島 芳樹 氏 (東京大学大学院数理科学研究科)
Discrete branching laws of Zuckerman\\'s derived functor modulesZuckerman(導来関手加群の離散的分岐則) (JAPANESE)

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