過去の記録

過去の記録 ~11/11本日 11/12 | 今後の予定 11/13~

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
土岡俊介 氏 (東京大学大学院数理科学研究科)
Toward the graded Cartan invariants of the symmetric groups (JAPANESE)
[ 講演概要 ]
We propose a graded analog of Hill's conjecture which is equivalent to K\\"ulshammer-Olsson-Robinson's conjecture on the generalized Cartan invariants of the symmetric groups.
We give justifications for it and discuss implications between the variants.
Some materials are based on the joint work with Anton Evseev.

2014年04月14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) 126号室
山ノ井 克俊 氏 (東京工業大学)
幾何学的対数微分の補題の別証明 (JAPANESE)

2014年04月10日(木)

幾何コロキウム

10:00-11:30   数理科学研究科棟(駒場) 122号室
開始時間と開催場所などは変更されることがあるので, セミナーごとにご確認ください.
河井 公大朗 氏 (東大数理)
等質ケーリー錐部分多様体の変形について (JAPANESE)
[ 講演概要 ]
Cayley 部分多様体は、Spin(7) 多様体内の極小部分多様体で Harvey, Lawson により導入された calibrated submanifold の一種である。calibrated submanifold の変形は、最初 Mclean により研究された。彼はコンパクトな場合を調べ、現在では錐、漸近的に錐な場合など非コンパクトな場合への拡張が試みられている。Cayley 錐の変形のモジュライ空間は、一般には滑らかでないことが知られているが、本講演では、R^8の等質 Cayley 錐の場合に着目し、具体的に変形の様子を調べることを考える。

2014年04月09日(水)

作用素環セミナー

16:30-18:00   数理科学研究科棟(駒場) 122号室
Ryszard Nest 氏 (Univ. Copenhagen)
Index and determnant of n-tuples of commuting operators (ENGLISH)

2014年04月08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
正井 秀俊 氏 (東京大学大学院数理科学研究科)
On the number of commensurable fibrations on a hyperbolic 3-manifold. (JAPANESE)
[ 講演概要 ]
By work of Thurston, it is known that if a hyperbolic fibred
$3$-manifold $M$ has Betti number greater than 1, then
$M$ admits infinitely many distinct fibrations.
For any fibration $\\omega$ on a hyperbolic $3$-manifold $M$,
the number of fibrations on $M$ that are commensurable in the sense of
Calegari-Sun-Wang to $\\omega$ is known to be finite.
In this talk, we prove that the number can be arbitrarily large.

統計数学セミナー

13:00-14:10   数理科学研究科棟(駒場) 052号室
Alexandre Brouste 氏 (Universite du Maine, France)
Parametric estimation in fractional Ornstein-Uhlenbeck process (ENGLISH)
[ 講演概要 ]
Several statistical models that imply the fractional Ornstein-Uhlenbeck (fOU) process will be presented: direct observations of the process or partial observations in an additive independent noise, continuous observations or discrete observations. In this different settings, we exhibit large sample (or high-frequency) asymptotic properties of the estimators (maximum likelihood estimator, quadratic variation based estimator, moment estimator, …) for all parameters of interest of the fOU. We also illustrate our results with the R package yuima.
[ 講演参考URL ]
http://www.sigmath.es.osaka-u.ac.jp/~kamatani/statseminar/2014/00.html

2014年03月19日(水)

古典解析セミナー

16:00-17:00   数理科学研究科棟(駒場) 128号室
Anton Dzhamay 氏 (University of Northern Colorado)
Discrete Schlesinger Equations and Difference Painlevé Equations (ENGLISH)
[ 講演概要 ]
The theory of Schlesinger equations describing isomonodromic
dynamic on the space of matrix coefficients of a Fuchsian system
w.r.t.~continuous deformations is well-know. In this talk we consider
a discrete version of this theory. Discrete analogues of Schlesinger
deformations are Schlesinger transformations that shift the eigenvalues
of the coefficient matrices by integers. By discrete Schlesinger equations
we mean the evolution equations on the matrix coefficients describing
such transformations. We derive these equations, show how they can be
split into the evolution equations on the space of eigenvectors of the
coefficient matrices, and explain how to write the latter equations in
the discrete Hamiltonian form. We also consider some reductions of those
equations to the difference Painlevé equations, again in complete parallel
to the differential case.

This is a joint work with H. Sakai (the University of Tokyo) and
T.Takenawa (Tokyo Institute of Marine Science and Technology).

2014年03月14日(金)

GCOEセミナー

16:00-16:50   数理科学研究科棟(駒場) 118号室
Kazufumi Ito 氏 (North Carolina State Univ.)
A new finite difference scheme based on staggered grids for Navier Stokes equations (ENGLISH)
[ 講演概要 ]
We develop a new method that uses the staggered grid only for the pressure node, i.e., the pressure gird is the center of the square cell and the velocities are at the node. The advantage of the proposed method compared to the standard staggered grid methods is that it is very straight forward to treat the boundary conditions for the velocity field, the fluid structure interaction, and to deal with the multiphase flow using the immersed interface methods. We present our analysis and numerical tests.

GCOEセミナー

17:00-17:50   数理科学研究科棟(駒場) 118号室
Jun Zou 氏 (The Chinese University of Hong Kong)
Efficient Domain Decomposition Methods for a Class of Linear and Nonlinear Inverse Problems (ENGLISH)
[ 講演概要 ]
In this talk we shall present several new domain decomposition methods for solving some linear and nonlinear inverse problems. The motivations and derivations of the methods will be discussed, and numerical experiments will be demonstrated.

2014年03月13日(木)

講演会

10:15-11:45   数理科学研究科棟(駒場) 470号室
Michele Triestino 氏 (Ecole Normale Superieure de Lyon)
Almost sure triviality of the $C^1$-centralizer of random circle diffeomorphisms with periodic points (ENGLISH)
[ 講演概要 ]
By the end of the 80s, Malliavin and Shavgulidze introduced a measure on the space of C^1 circle diffeomorphisms which carries many interesting features. Perhaps the most interesting aspect is that it can be considered as an analog of the Haar measure for the group Diff^1_+(S^1).
The nature of this measure has been mostly investigated in connection to representation theory.
For people working in dynamical systems, the MS measure offers a way to quantify dynamical phenomena: for example, which is the probability that a random diffeomorphism is irrational? Even if this question have occupied my mind for a long time, it remains still unanswered, as many other interesting ones. However, it is possible to understand precisely what are the typical features of a diffeomorphism with periodic points.

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 122号室
Bernadette Miara 氏 (Univ. Paris-Est)
STABILITY IN THE OBSTACLE PROBLEM FOR A SHALLOW SHELL (ENGLISH)
[ 講演参考URL ]
http://fmsp.ms.u-tokyo.ac.jp/bm02.pdf

2014年03月12日(水)

講演会

10:15-11:45   数理科学研究科棟(駒場) 470号室
Michele Triestino 氏 (Ecole Normale Superieure de Lyon)
Invariant distributions for circle diffeomorphisms of
irrational rotation number and low regularity (ENGLISH)
[ 講演概要 ]
The main inspiration of this joint work with Andrés Navas is the beautiful result of Ávila and Kocsard: if f is a C^\\infty circle diffeomorphism of irrational rotation number, then the unique invariant probability measure is also the unique (up to rescaling) invariant distribution.
Using conceptual geometric arguments (Hahn-Banach...), we investigate the uniqueness of invariant distributions for C^1 circle diffeomorphisms of irrational rotation number, with particular attention to sharp regularity.
We prove that If the diffeomorphism is C^{1+bv}, then there is a unique invariant distribution of order 1. On the other side, examples by Douady and Yoccoz, and by Kodama and Matsumoto exhibit differentiable dynamical systems for which the uniqueness does not hold.

数理人口学・数理生物学セミナー

15:00-17:00   数理科学研究科棟(駒場) 126号室
Andre M. de Roos 氏 (University of Amsterdam)
When size does matter: Ontogenetic symmetry and asymmetry in energetics
(ENGLISH)
[ 講演概要 ]
Body size (≡ biomass) is the dominant determinant of population dynamical processes such as giving birth or dying in almost all species, with often drastically different behaviour occurring in different parts of the growth trajectory, while the latter is largely determined by food availability at the different life stages. This leads to the question under what conditions unstructured population models, formulated in terms of total population biomass, still do a fair job. To contribute to answering this question we first analyze the conditions under which a size-structured model collapses to a dynamically equivalent unstructured one in terms of total biomass. The only biologically meaningful case where this occurs is when body size does not affect any of the population dynamic processes, this is the case if and only if the mass-specific ingestion rate, the mass-specific biomass production and the mortality rate of the individuals are independent of size, a condition to which we refer as “ontogenetic symmetry”. Intriguingly, under ontogenetic symmetry the equilibrium biomass-body size spectrum is proportional to 1/size, a form that has been conjectured for marine size spectra and subsequently has been used as prior assumption in theoretical papers dealing with the latter. As a next step we consider an archetypical class of models in which reproduction takes over from growth upon reaching an adult body size, in order to determine how quickly discrepancies from ontogenetic symmetry lead to relevant novel population dynamical phenomena. The phenomena considered are biomass overcompensation, when additional imposed mortality leads, rather unexpectedly, to an increase in the equilibrium biomass of either the juveniles or the adults (a phenomenon with potentially big consequences for predators of the species), and the occurrence of two types of size-structure driven oscillations, juvenile-driven cycles with separated extended cohorts, and adult-driven cycles in which periodically a front of relatively steeply decreasing frequencies moves up the size distribution. A small discrepancy from symmetry can already lead to biomass overcompensation; size-structure driven cycles only occur for somewhat larger discrepancies.
[ 講演参考URL ]
http://staff.science.uva.nl/~aroos/

GCOEセミナー

15:00-17:00   数理科学研究科棟(駒場) 126号室
Andre M. de Roos 氏 (University of Amsterdam)
When size does matter: Ontogenetic symmetry and asymmetry in energetics (ENGLISH)
[ 講演概要 ]
Body size (≡ biomass) is the dominant determinant of population dynamical processes such as giving birth or dying in almost all species, with often drastically different behaviour occurring in different parts of the growth trajectory, while the latter is largely determined by food availability at the different life stages. This leads to the question under what conditions unstructured population models, formulated in terms of total population biomass, still do a fair job. To contribute to answering this question we first analyze the conditions under which a size-structured model collapses to a dynamically equivalent unstructured one in terms of total biomass. The only biologically meaningful case where this occurs is when body size does not affect any of the population dynamic processes, this is the case if and only if the mass-specific ingestion rate, the mass-specific biomass production and the mortality rate of the individuals are independent of size, a condition to which we refer as “ontogenetic symmetry”. Intriguingly, under ontogenetic symmetry the equilibrium biomass-body size spectrum is proportional to 1/size, a form that has been conjectured for marine size spectra and subsequently has been used as prior assumption in theoretical papers dealing with the latter. As a next step we consider an archetypical class of models in which reproduction takes over from growth upon reaching an adult body size, in order to determine how quickly discrepancies from ontogenetic symmetry lead to relevant novel population dynamical phenomena. The phenomena considered are biomass overcompensation, when additional imposed mortality leads, rather unexpectedly, to an increase in the equilibrium biomass of either the juveniles or the adults (a phenomenon with potentially big consequences for predators of the species), and the occurrence of two types of size-structure driven oscillations, juvenile-driven cycles with separated extended cohorts, and adult-driven cycles in which periodically a front of relatively steeply decreasing frequencies moves up the size distribution. A small discrepancy from symmetry can already lead to biomass overcompensation; size-structure driven cycles only occur for somewhat larger discrepancies.
[ 講演参考URL ]
http://staff.science.uva.nl/~aroos/

2014年03月11日(火)

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 118号室
Lucie Baudouin 氏 (LAAS-CNRS, equipe MAC)
Inverse problem for the waves : stability and convergence matters (ENGLISH)
[ 講演概要 ]
This talk aims to present some recent works in collaboration with Maya de Buhan, Sylvain Ervedoza and Axel Osses regarding an inverse problem for the wave equation. More specifically, we study the determination of the potential in a wave equation with given Dirichlet boundary data from a measurement of the flux of the solution on a part of the boundary. On the one hand, we will focus on the question of convergence of the space semi-discrete inverse problems toward their continuous counterpart. Several uniqueness and stability results are available in the literature about the continuous setting of the inverse problem of determination of a potential in the wave equation. In particular, we can mention a Lipschitz stability result under a classical geometric condition obtained by Imanuvilov and Yamamoto, and a logarithmic stability result obtained by Bellassoued when the observation measurement is made on an arbitrary part of the boundary. In both situations, we can design a numerical process for which convergence results are proved. The analysis we conduct is based on discrete Carleman estimates, either for the hyperbolic or for the elliptic operator, in which case we shall use a result of Boyer, Hubert and Le Rousseau. On the other hand, still considering the same inverse problem, we will present a new reconstruction algorithm of the potential. The design and convergence of the algorithm are based on the Carleman estimates for the waves previously used to prove the Lipschitz stability. We will finally give some simple illustrative numerical simulations for 1-d problems.

2014年03月10日(月)

GCOEセミナー

13:30-15:00   数理科学研究科棟(駒場) 123号室
Erwin Bolthausen 氏 (University of Zurich)
The two-dimensional random walk in an isotropic random environment (ENGLISH)

講演会

15:15-16:45   数理科学研究科棟(駒場) 123号室
Marielle Simon 氏 (ENS Lyon, UMPA)
Energy fluctuations in the disordered harmonic chain (ENGLISH)
[ 講演概要 ]
We study the energy diffusion in the disordered harmonic chain of oscillators: the usual Hamiltonian dynamics is provided with random masses and perturbed by a degenerate energy conserving noise. After rescaling space and time diffusively, we prove that energy fluctuations evolve following an infinite dimensional linear stochastic differential equation driven by the linearized heat equation. We also give variational expressions for the thermal diffusivity and an equivalent definition through the Green-Kubo formula. Since the model is non gradient, and the perturbation is very degenerate, the standard Varadhan's approach is reviewed under new perspectives.

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 118号室
Bernadette Miara 氏 (Univ. Paris-Est)
ELASTIC WAVES IN STRONGLY HETEROGENEOUS PLATES (ENGLISH)
[ 講演参考URL ]
http://fmsp.ms.u-tokyo.ac.jp/bm01.pdf

2014年03月06日(木)

GCOEセミナー

10:10-11:00   数理科学研究科棟(駒場) 002号室
このセミナーは 研究集会「異常拡散の数理とシミュレーション手法ならびに関連する課題」(主催・共催:数物フロンティア・リーディング大学院プログラム、卓越した大学院拠点形成支援補
J. Cheng 氏 (Fudan Univ.)
The Mathematical Model for the Contamination Problems and Related Inverse Problems (ENGLISH)
[ 講演概要 ]
In this talk, we discuss the motivation for the study of the abnormal diffusion models for the contamination problems. From the practical point of view, several inverse problems proposed and studied Theoretic results, for example, the uniqueness and stability are shown. The possibility of the application of these studies is mentioned.

GCOEセミナー

11:10-12:00   数理科学研究科棟(駒場) 002号室
このセミナーは 研究集会「異常拡散の数理とシミュレーション手法ならびに関連する課題」(主催・共催:数物フロンティア・リーディング大学院プログラム、卓越した大学院拠点形成支援補
W. Rundell 氏 (Texas A&M Univ.)
Inverse problems with fractional derivatives in the space variable (ENGLISH)
[ 講演概要 ]
This talk will look at some classical inverse problems where the highest order term in the spatial direction is replaced by a fractional derivative. There are again some surprising results over what is known in the usual case of integer order derivatives but also quite different from the case of fractional diffusion in the time variable. The talk will give some answers, but pose many more open problems.

GCOEセミナー

14:30-15:20   数理科学研究科棟(駒場) 002号室
このセミナーは 研究集会「異常拡散の数理とシミュレーション手法ならびに関連する課題」(主催・共催:数物フロンティア・リーディング大学院プログラム、卓越した大学院拠点形成支援補
Y. Luchko 氏 (Beuth Technical University of Applied Sciences)
Neutral-fractional diffusion-wave equation and some properties of its fundamental solution (ENGLISH)
[ 講演概要 ]
Recently, the so called neutral-fractional diffusion-wave equation was introduced and analysed in the case of one spatial variable. In contrast to the fractional diffusion of diffusion-wave equations, the neutral-fractional diffusion-wave equation contains fractional derivatives of the same order both in space and in time. The fundamental solution of the neutral-fractional diffusion-wave equation was shown to exhibit properties of both the solutions of the diffusion equation and those of the wave equation.
In the one-dimensional case, the fundamental solution of the neutral-fractional diffusion-wave equation can be interpreted as a spatial probability density function evolving in time. At the same time, it can be treated as a damped wave whose amplitude maximum and the gravity and mass centres propagate with the constant velocities that depend just on the equation order.
In this talk, the problems mentioned above are considered for the multi- dimensional neutral-fractional diffusion-wave equation. To illustrate analytical findings, some results of numerical calculations and plots are presented.

GCOEセミナー

16:20-17:10   数理科学研究科棟(駒場) 002号室
このセミナーは 研究集会「異常拡散の数理とシミュレーション手法ならびに関連する課題」(主催・共催:数物フロンティア・リーディング大学院プログラム、卓越した大学院拠点形成支援補
M. Cristofol 氏 (Aix-Marseille Univ.)
New kind of observations in an inverse parabolic problem (ENGLISH)
[ 講演概要 ]
In this talk, I analyze the inverse problem of determining the reaction term f(x,u) in reaction-diffusion equations of the form ¥partial_t u-D¥partial_{xx}u = f(x,u), where f is assumed to be periodic with respect to x in R. Starting from a family of exponentially decaying initial conditions u_{0,¥lambda}, I will show that the solutions u_¥lambda of this equation propagate with constant asymptotic spreading speeds w_¥lambda. The main result shows that the linearization of f around the steady state 0,¥partial_u f(x,0), is uniquely determined (up to a symmetry) among a subset of piecewise linear functions, by the observation of the asymptotic spreading speeds w_¥lambda.

2014年02月28日(金)

GCOEセミナー

13:00-14:00   数理科学研究科棟(駒場) 002号室
Patricia Gaitan 氏 (Aix-Marseille University)
Probing for inclusions for heat conductive bodies. Time independent and time dependent cases (ENGLISH)
[ 講演概要 ]
This work deals with an inverse boundary value problem arising from the equation of heat conduction. Mathematical theory and algorithm is described in dimensions 1{3 for probing the discontinuous part of the conductivity from local temperature and heat ow measurements at the boundary. The ap- proach is based on the use of complex spherical waves, and no knowledge is needed about the initial temperature distribution. In dimension two we show how conformal transformations can be used for probing deeper than is pos- sible with discs. Results from numerical experiments in the one-dimensional case are reported, suggesting that the method is capable of recovering loca- tions of discontinuities approximately from noisy data.
For moving inclusions, we consider an inverse boundary value problem for the heat equation on the interval (0; 1), where the heat conductivity (t; x) is piecewise constant and the point of discontinuity depends on time : (t; x) = k2 (0 < x < s(t)), (t; x) = 1 (s(t) < x < 1). Firstly we show that k and s(t) on the time interval [0; T] are determined from the partial Dirichlet- to-Neumann map : u(t; 1) ! @xu(t; 1); 0 < t < T, u(t; x) being the solu- tion to the heat equation such that u(t; 0) = 0, independently of the initial data u(0; x). Secondly we show that the partial Dirichlet-to-Neumann map u(t; 0) ! @xu(t; 1); 0 < t < T, u(t; x) being the solution to the heat equation such that u(t; 1) = 0, determines at most two couples (k; s(t)) on the time interval [0; T], independently of the initial data u(0; x).

GCOEセミナー

11:00-12:00   数理科学研究科棟(駒場) 002号室
Assia Benabdallah 氏 (Aix-Marseille University)
Minimal time for the null controllability of parabolic systems: the effect of the index of condensation of complex sequences (ENGLISH)

2014年02月27日(木)

GCOEセミナー

17:00-18:00   数理科学研究科棟(駒場) 370号室
Yves Dermenjian 氏 (Univ. of Marseille)
A Carleman estimate with discontinuous coefficients through an interface crossing the boundary, Part II: for a an anisotropic elliptic operator. (ENGLISH)

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