Seminar information archive

Seminar information archive ~02/06Today's seminar 02/07 | Future seminars 02/08~

Lie Groups and Representation Theory

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Takayuki Okuda (the University of Tokyo)
Proper actions of SL(2,R) on semisimple symmetric spaces (JAPANESE)
[ Abstract ]
Complex irreducible symmetric spaces which admit proper SL(2,R)-actions were classified by Katsuki Teduka.
In this talk, we generalize Teduka's method and classify semisimple symmetric spaces which admit proper SL(2,R)-actions.


Algebraic Geometry Seminar

16:40-18:10   Room #126 (Graduate School of Math. Sci. Bldg.)
松村 慎一 (東大数理)
[ Abstract ]
豊富な因子の部分多様体に沿った自己交点数は, 基本的かつ重要である.
また, 時間が許せば, 元々の問題意識であった制限型体積の複素解析的な側面に


16:00-17:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Cyrill Muratov (New Jersey Institute of Technology)
Droplet phases in non-local Ginzburg-Landau models with Coulomb repulsion in two dimensions
[ Abstract ]
In this talk I will present an analysis of the behavior of the minimal energy in non-local Ginzburg-Landau models with Coulomb repulsion in two space dimensions near the onset of multi-droplet patterns. As a first step, I will show that under suitable scaling the energy of minimizers becomes asymptotically equal to that of a sharp interface energy with screened Coulomb interaction. I will then show that the minimizers of the corresponding sharp interface energy consist of nearly identical circular droplets of small size separated by large distances. Finally, I will show that in a suitable limit these droplets become uniformly distributed throughout the domain. The analysis allows to obtain precise asymptotic behaviors of the bifurcation threshold, the minimal energy, the droplet radii, and the droplet density in the considered limit.

Seminar on Geometric Complex Analysis

10:30-12:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Filippo Bracci (Universita di Roma, ``Tor Vergata'')
Loewner's theory on complex manifolds (ENGLISH)
[ Abstract ]
Loewner's theory, introduced by Ch. Loewner in 1923 and developed later by Pommerenke, Kufarev, Schramm and others, has been proved to be a very powerful tool in studying extremal problems. In this talk we are going to describe a unified and general view of the deterministic Loewner theory both on the unit disc and on Kobayashi hyperbolic manifolds.
[ Reference URL ]

Mathematical Biology Seminar

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Horoshi HAENO (Memorial Sloan-Kettering Cancer Center)
骨髄増殖性疾患の起源細胞に関する数理的研究 (JAPANESE)


Monthly Seminar on Arithmetic of Automorphic Forms

13:30-16:00   Room #123 (Graduate School of Math. Sci. Bldg.)
MIYAZAKI Tadashi (Tokyo Univ. of agr. and indus.) 13:30-14:30
Principal series Whittaker functions on $Sp(2,C)$ (JAPANESE)
[ Abstract ]
Not given here.
HARASHITA Shushi (Yokohama National Univ.) 15:00-16:00
A paving of the Siegel 10-fold of positive characteristic (JAPANESE)
[ Abstract ]
Not given here.


Lie Groups and Representation Theory

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Uuganbayar Zunderiya (Nagoya University)
Generalized hypergeometric systems (ENGLISH)
[ Abstract ]
A new type of hypergeometric differential equations was introduced and studied by H. Sekiguchi. The investigated system of partial differential equation generalizes the Gauss-Aomoto-Gelfand system which in its turn stems from the classical set of differential relations for the solutions to a generic algebraic equation introduced by K.Mayr in 1937. Gauss-Aomoto-Gelfand systems can be expressed as the determinants of $2\\times 2$ matrices of derivations with respect to certain variables. H. Sekiguchi generalized this construction by looking at determinations of arbitrary $l\\times l$ matrices of derivations with respect to certain variables.

In this talk we study the dimension of global (and local) solutions to the generalized systems of Gauss-Aomoto-Gelfand hypergeometric systems. The main results in the talk are a combinatorial formula for the dimension of global (and local) solutions of the generalized Gauss-Aomoto-Gelfand system and a theorem on generic holonomicity of a certain class of such systems.

Applied Analysis

16:00-17:30   Room #002 (Graduate School of Math. Sci. Bldg.)
Alberto Tesei (University of Rome 1)
Long-time behaviour of solutions of a forward-backward parabolic equation
[ Abstract ]
We discuss some recent results concerning the asymptotic behaviour of entropy measure-valued solutions for a class of ill-posed forward-backward parabolic equations, which arise in the theory of phase transitions.

Classical Analysis

16:00-17:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Claude Mitschi (Univ. de Strasbourg)
The Galois group of projectively isomonodromic deformations (ENGLISH)
[ Abstract ]
Isomonodromic families of regular singular differential equations over $\\mathbb C(x)$ are characterized by the fact that their parametrized differential Galois group is conjugate to a (constant) linear algebraic group over $\\mathbb C$. We will describe properties of this differential group that reflect a special type of monodromy evolving deformation of Fuchsian differential equations.


Number Theory Seminar

17:30-18:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Gerard Laumon (CNRS, Universite Paris XI - Orsay)
The cohomological weighted fundamental lemma
[ Abstract ]
Using the Hitchin fibration, Ngo Bao Chau has proved the Langlands-Shelstad fundamental lemma. In a joint work with Pierre-Henri Chaudouard, we have extended Ngo's proof to obtain the weighted fundamental lemma which had been conjectured by Arthur. In the talk, I would like to present our main cohomological result.


Seminar on Mathematics for various disciplines

10:30-11:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Etsuro Yokoyama (Gakushuin University)
Analysis of growth rates of an ice crystal from supercooled heavy water under microgravity condition in KIBO of International Space Station
--basal plane growth rate and dendritic growth velocity


Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Christian Kassel (CNRS, Univ. de Strasbourg)
Torsors in non-commutative geometry (ENGLISH)
[ Abstract ]
G-torsors or principal homogeneous spaces are familiar objects in geometry. I'll present an extension of such objects to "non-commutative geometry". When the structural group G is finite, non-commutative G-torsors are governed by a group that has both an arithmetic component and a geometric one. The arithmetic part is given by a classical Galois cohomology group; the geometric input is encoded in a (not necessarily abelian) group that takes into account all normal abelian subgroups of G of central type. Various examples will be exhibited.

Tuesday Seminar of Analysis

16:30-18:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Jean-Marc Bouclet (Toulouse University, France)
Strichartz estimates and the Isozaki-Kitada parametrix
on asymptotically hyperbolic manifolds (ENGLISH)


Seminar on Geometric Complex Analysis

10:30-12:00   Room #128 (Graduate School of Math. Sci. Bldg.)
千葉 優作 (東大数理)
Degeneracy of holomorphic curves into the complements of hypersurfaces in a complex projective space
[ Reference URL ]


Lie Groups and Representation Theory

16:30-18:00   Room #126 (Graduate School of Math. Sci. Bldg.)
加藤周 (京都大学)
On the characters of tempered modules of affine Hecke
algebras of classical type
[ Abstract ]
We present an inductive algorithm to compute the characters
of tempered modules of an affine Hecke algebras of classical
types, based on a new class of representations which we call
"tempered delimits". They have some geometric origin in the
eDL correspondence.

Our new algorithm has some advantage to the Lusztig-Shoji
algorithm (which also describes the characters of tempered
modules via generalized Green functions) in the sense it
enables us to tell how the characters of tempered modules
changes as the parameters vary.

This is a joint work with Dan Ciubotaru at Utah.


Algebraic Geometry Seminar

16:40-18:10   Room #126 (Graduate School of Math. Sci. Bldg.)
Alexandru Dimca (Université Nice-Sophia Antipolis)
From Lang's Conjecture to finiteness properties of Torelli groups
[ Abstract ]
First we recall one of Lang's conjectures in diophantine geometry
on the interplay between subvarieties and translated subgroups in a
commutative algebraic group
(proved by M. Laurent in the case of affine tori in 1984).

Then we present the technique of resonance and characteristic varieties,
a powerful tool in the study of fundamental groups of algebraic varieties.

Finally, using the two ingredients above, we show that the Torelli
groups $T_g$
have some surprising finiteness properties for $g>3$.
In particular, we show that for any subgroup $N$ in $T_g$ containing
the Johnson kernel $K_g$, the complex vector space $N_{ab} \\otimes C$
is finite dimensional.

All the details are available in our joint preprint with S. Papadima


GCOE Seminars

10:00-15:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Masahiro Yamamoto (University of Tokyo) 10:00-10:50
産学連携による新たな数学の課題:非整数階拡散方程式への誘い (JAPANESE)
Shu Nakamura (University of Tokyo) 11:00-11:50
量子力学のスペクトル・散乱理論における数学的手法 (JAPANESE)
Kazufumi Ito (University of Tokyo, North Carolina State University) 13:20-14:10
Semismooth Newton法の理論、及び応用 (JAPANESE)
Georg Weiss (University of Tokyo) 14:10-15:00


Seminar on Probability and Statistics

13:00-14:10   Room #002 (Graduate School of Math. Sci. Bldg.)
Catherine Laredo (MIA, INRA)
Inference for partially observed Markov processes and applications
[ Abstract ]
We present some statistical methods for estimating the param- eters of a population dynamics model of annual plants. It is modelled using multitype branching processes with immigration. The data consist of counts in each type that are measured in several populations for a few consecu- tive years. Parametric inference is first carried out when count data of all types are observed. We prove statistical identifiability for all the parameters ruling the population dynamics model and derive consistent and asymptot- ically Gaussian estimators. However, it often occurs that, in practice, one or more types cannot be observed, leading to partially observed processes. Parametric inference is first studied in the case of Poisson distributions. We characterize the parameter subset where identifiability holds and de- rive consistent and asymptotically normal estimators for this parameter subset. Theses results are then extended to other distributions.

We apply these results to feral oilseed data. The model takes account of reproduction, immigration, and seed survival in a seed bank. The data consist of the number of plants in several developmental stages that were measured in a number of populations for few consecutive years. They are incomplete since seeds could not be counted.
[ Reference URL ]



17:00-18:00   Room #370 (Graduate School of Math. Sci. Bldg.)
Dr Bangti Jin (Center for Industrial Mathematics University of Bremen, Germany)
Heuristic Choice Rules for Convex Variational Regularization
[ Abstract ]
In this talk we shall consider heuristic rules for choosing regularization parameters for general convex variational regularization of linear inverse problems. Several rules of recent origin are described, and some theoretical issues, e.g. existence, convergence, and a posteriori error estimates, are discussed. Numerical examples will be presented to demonstrate their accuracy and practical utility.


16:00-17:00   Room #370 (Graduate School of Math. Sci. Bldg.)
M.M. Lavrentiev, Jr. (Sobolev Institute of Mathematics, Novosibirsk, Russia)
Modern computer architectures for tsunami simulation
[ Abstract ]
Simulation of tsunami wave propagation over the deep water is one of the most time consuming tasks of the tsunami warning system. The authors utilize Method of Splitting Tsunami (MOST) package, accepted by the National Ocean & Atmospheric Administration (NOAA), USA. The software generates calculation of wave propagation at deep water by splitting along coordinate axis. Nonlinear shallow water system is used as the governing equations. Some tasks of the algorithm could be executed in parallel mode, however, direct application of multi processor systems results only in two times performance gain. After a number of optimizations, the authors achieved 16 times performance gain. OpenMP technology was applied. When utilizing Sony PlayStation3 platform (IBM CELL BE architecture) 60 times code acceleration was accomplished. The best result was achieved with modern GPU (GForce 8800 and TESLA), 100 times performance gain.


GCOE Seminars

15:00-17:15   Room #370 (Graduate School of Math. Sci. Bldg.)
Mourad Bellassoued (Univ. of Bizerte) 15:00-16:00
Stability estimates for the anisotropic wave and Schrodinger equations from
the Dirichlet to Neumann map
[ Abstract ]
In this talk we want to obtain stability estimates for the inverse problem of determining the electric potential or the conformal factor in a wave or Schrodinger equations in an anisotropic media with Dirichlet data from measured Neumann boundary observations. This information is enclosed in the dynamical Dirichlet-to-Neumann map associated to the wave equation. We prove in dimension $n\\geq 2$ that the knowledge of the Dirichlet to Neumann map for the wave equation measured on the boundary uniquely determines the electric potential and we prove H\\"older-type stability in determining the potential. We prove similar results for the determination of a conformal factor close to 1.
Johannes Elschner (Weierstrass Institute Berlin, Germany) 16:15-17:15
On uniqueness in inverse elastic obstacle scattering
[ Abstract ]
The talk is on joint work with M. Yamamoto on the third and fourth exterior boundary value problems of linear isotropic elasticity. We present uniqueness results for the corresponding inverse scattering problems with polyhedral-type obstacles and a finite number of incident plane elastic waves.
Our approach is essentially based on a reflection principle for the Navier equation.



11:00-12:00   Room #366 (Graduate School of Math. Sci. Bldg.)
竹内 知哉 (North Carolina State University, USA)
A Regularization Parameter for Nonsmooth Tikhonov Regularization
[ Abstract ]
We develop a novel criterion for choosing regularization parameters for nonsmooth Tikhonov functionals. The proposed criterion is solely based on the value function, and thus applicable to a broad range of functionals. It is analytically compared with the local minimum criterion, and a posteriori error estimates are derived. An efficient numerical algorithm for computing the minimizer is developed, and its convergence properties are also studied. Numerical results for several common nonsmooth functionals are presented.



16:30-17:30   Room #128 (Graduate School of Math. Sci. Bldg.)
三角 淳 (東大数理)


Seminar on Probability and Statistics

15:00-16:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Cecilia Mancini (University of Florence)
[ Abstract ]
We consider two processes driven by Brownian motions plus drift and possibly infinite activity jumps.

Given discrete observations we separately estimate the covariation between the two Brownian parts and the sum of the co-jumps. This allows to gain insight into the dependence structure of the processes and has important applications in finance.

Our estimator is based on a threshold principle allowing to isolate the jumps over a threshold.

The estimator of the continuous covariation is asymptotically Gaussian and converges at speed square root of n when the jump components have finite variation. In presence infinite variation jumps the speed is heavily influenced both by the small jumps dependence structure and by their jump activity indexes.

This talk is based on Mancini and Gobbi (2009), and Mancini (2010).
[ Reference URL ]

Seminar on Probability and Statistics

14:00-15:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Alexandre Brouste (Université du Maine)
Statistical inference in the partial observation setting, in continuous time
[ Abstract ]
In various fields, the {\\it signal} process, whose law depends on an unknown parameter $ artheta \\in \\Theta \\subset \\R^p$, can not be observed directly but only through an {\\it observation} process. We will talk about the so called fractional partial observation setting, where the observation process $Y=\\left( Y_t, t \\geq 0 ight)$ is given by a stochastic differential equation: egin{equation} \\label{mod:modelgeneral} Y_t = Y_0 + \\int_0^t h(X_s, artheta) ds + \\sigma W^H_t\\,, \\quad t > 0 \\end{equation} where the function $ h: \\, \\R imes \\Theta \\longrightarrow \\R$ and the constant $\\sigma>0$ are known and the noise $\\left( W^H_t\\,, t\\geq 0 ight)$ is a fractional Brownian motion valued in $\\R$ independent of the signal process $X$ and the initial condition $Y_0$. In this setting, the estimation of the unknown parameter $ artheta \\in \\Theta$ given the observation of the continuous sample path $Y^T=\\left( Y_t , 0 \\leq t \\leq T ight)$, $T>0$, naturally arises.
[ Reference URL ]

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