Seminar information archive

Seminar information archive ~02/20Today's seminar 02/21 | Future seminars 02/22~

2014/09/08

FMSP Lectures

10:30-15:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Hung V. Tran (The University of Chicago)
Stochastic homogenization for first order Hamilton-Jacobi equations(I) (ENGLISH)
[ Reference URL ]
http://fmsp.ms.u-tokyo.ac.jp/Tran2014_0908-0912.pdf

2014/09/04

Lectures

12:10-13:00   Room #470 (Graduate School of Math. Sci. Bldg.)
Samuli Siltanen (University of Helsinki, Finland)
"X-ray imaging of moving objects" (ENGLISH)

2014/08/28

thesis presentations

10:00-11:15   Room #128 (Graduate School of Math. Sci. Bldg.)
李 曉龍 (東京大学大学院数理科学研究科)
On the C1 stabilization of homoclinic tangencies for diffeomorphisms in dimension three(3次元の微分同相写像に対するホモクリニック接触のC1安定化について) (JAPANESE)

2014/08/06

Mathematical Biology Seminar

14:50-16:20   Room #128 (Graduate School of Math. Sci. Bldg.)
Nicolas Bacaer (Insitut de Recherche pour le Developpement (IRD))
The stochastic SIS epidemic model in a periodic environment (ENGLISH)
[ Abstract ]
In the stochastic SIS epidemic model with a contact rate a,
a recovery rate bT is such that (log T)/N converges to c=b/a-1-log(b/a) as N grows to
infinity. We consider the more realistic case where the contact rate
a(t) is a periodic function whose average is bigger than b. Then (log
T)/N converges to a new limit C, which is linked to a time-periodic
Hamilton-Jacobi equation. When a(t) is a cosine function with small
amplitude or high (resp. low) frequency, approximate formulas for C
can be obtained analytically following the method used in [Assaf et
al. (2008) Population extinction in a time-modulated environment. Phys
Rev E 78, 041123]. These results are illustrated by numerical
simulations.

2014/07/29

Operator Algebra Seminars

16:30-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Cyril Houdayer (ENS Lyon)
Asymptotic structure of free Araki-Woods factors (ENGLISH)

2014/07/28

Numerical Analysis Seminar

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Tomoyuki Miyaji (RIMS, Kyoto University)
Computer assisted analysis of Craik’s and Pehlivan’s 3D dynamical systems (JAPANESE)
[ Reference URL ]
http://www.infsup.jp/utnas/

2014/07/25

Colloquium

16:30-17:30   Room #123 (Graduate School of Math. Sci. Bldg.)
Yasuhiro Takeuchi (Aoyama Gakuin University)
Mathematical modelling of Tumor Immune System Interaction (JAPANESE)
[ Abstract ]
We study the dynamical behavior of a tumor-immune system (T-IS) interaction model with two discrete delays,
namely the immune activation delay for effector cells (ECs) and activation delay for Helper T cells (HTCs).
By analyzing the characteristic equations, we establish the stability of two equilibria (tumor-free equilibrium and immune-control equilibrium) and the existence of Hopf bifurcations when two delays are used as the bifurcation parameter.
Our results exhibit that both delays do not affect the stability of tumor-free equilibrium.
However, they are able to destabilize the immune-control equilibrium and cause periodic solutions.
We numerically illustrate how these two delays can change the stability region of the immune-control equilibrium and display the different impacts to the control of tumors.
The numerical simulation results show that the immune activation delay for HTCs can induce heteroclinic cycles to connect the tumor-free equilibrium and immune-control equilibrium.
Furthermore, we observe that the immune activation delay for HTCs can even stabilize the unstable immune-control equilibrium.

thesis presentations

10:30-11:45   Room #128 (Graduate School of Math. Sci. Bldg.)
周 茂林 (東京大学大学院数理科学研究科)
On the study of front propagation in nonlinear free boundary problems(非線形自由境界問題における波面の伝播の研究) (JAPANESE)

2014/07/24

Applied Analysis

16:00-17:30   Room #128 (Graduate School of Math. Sci. Bldg.)
Nagasawa Takeyuki (Saitama University)
Decomposition of the Mobius energy (JAPANESE)

2014/07/23

Operator Algebra Seminars

16:30-18:00   Room #122 (Graduate School of Math. Sci. Bldg.)
George Elliott (Univ. Toronto)
The Cuntz semigroup---a critical component for classification? (ENGLISH)

Mathematical Biology Seminar

14:50-16:20   Room #128 (Graduate School of Math. Sci. Bldg.)
Naoki Masuda (University of Bristol, Department of Engineering Mathematics)
Resting-state brain networks, their energy landscapes, and sleep (JAPANESE)

2014/07/22

Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Jesse Wolfson (Northwestern University)
The Index Map and Reciprocity Laws for Contou-Carrere Symbols (ENGLISH)
[ Abstract ]
In the 1960s, Atiyah and Janich constructed the families index as a natural map from the space of Fredholm operators to the classifying space of topological K-theory, and showed it to be an equivalence. In joint work with Oliver Braunling and Michael Groechenig, we construct an analogous index map in algebraic K-theory. Building on recent work of Sho Saito, we show this provides an analogue of Atiyah and Janich's equivalence. More significantly, the index map allows us to relate the Contou-Carrere symbol, a local analytic invariant of schemes, to algebraic K-theory. Using this, we provide new proofs of reciprocity laws for Contou-Carrere symbols in dimension 1 (first established by Anderson--Pablos Romo) and 2 (established recently by Osipov--Zhu). We extend these reciprocity laws to all dimensions.

2014/07/19

Monthly Seminar on Arithmetic of Automorphic Forms

13:30-16:00   Room #123 (Graduate School of Math. Sci. Bldg.)
Yoshihiro Onishi (Miejyo University) 13:30-14:30
Hurwitz integrality of the power series expansion of the sigma function at the origin (JAPANESE)
Yoshihiro Onishi (Meijyo University) 15:00-16:00
種数 3 の trigonal curve から来る Kummer 多様体の定義方程式と Coble の超平面 (JAPANESE)

2014/07/17

Geometry Colloquium

10:00-11:30   Room #122 (Graduate School of Math. Sci. Bldg.)
Jingyi Chen (University of British Columbia)
The space of compact shrinking solutions to Lagrangian mean curvature flow in $C^2$ (ENGLISH)
[ Abstract ]
We will discuss compactness and rigidity of compact surfaces which are shrinking solutions to Lagrangian mean curvature flow. This is recent joint work with John Ma.

2014/07/16

Infinite Analysis Seminar Tokyo

10:30-12:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Andrei Negut (Columbia University, Department of Mathematics)
From the Hilbert scheme to m/n Pieri rules (ENGLISH)
[ Abstract ]
In this series of talks, we will discuss several occurrences of shuffle
algebras: in representation theory, in geometry of moduli spaces, and in
the combinatorics of symmetric functions. All the connections will be
explained in detail.

2014/07/15

Infinite Analysis Seminar Tokyo

10:30-12:00   Room #128 (Graduate School of Math. Sci. Bldg.)
Andrei Negut (Columbia University, Department of Mathematics)
From the shuffle algebra to the Hilbert scheme (ENGLISH)
[ Abstract ]
In this series of talks, we will discuss several occurrences of shuffle
algebras: in representation theory, in geometry of moduli spaces, and in
the combinatorics of symmetric functions. All the connections will be
explained in detail.

2014/07/14

Seminar on Geometric Complex Analysis

10:30-12:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Gopal Prasad (University of Michigan)
Higher dimensional analogues of fake projective planes (ENGLISH)
[ Abstract ]
A fake projective plane is a smooth projective complex algebraic surface which is not isomorphic to the complex projective plane but whose Betti numbers are that of the complex projective plane. The fake projective planes are algebraic surfaces of general type and have smallest possible Euler-Poincare characteristic among them. The first fake projective plane was constructed by D. Mumford using p-adic uniformization, and it was known that there can only be finitely many of them. A complete classification of the fake projective planes was obtained by Sai-Kee Yeung and myself. We showed that there are 28 classes of them, and constructed at least one explicit example in each class. Later, using long computer assisted computations, D. Cartwright and Tim Steger found that the 28 families altogether contain precisely 100 fake projective planes. Using our work, they also found a very interesting smooth projective complex algebraic surface whose Euler-Poincare characteristic is 3 but whose first Betti
number is 2. We have a natural notion of higher dimensional analogues of fake projective planes and to a large extent determined them. My talk will be devoted to an exposition of this work.

2014/07/13

Infinite Analysis Seminar Tokyo

14:00-15:00   Room #002 (Graduate School of Math. Sci. Bldg.)
Andrei Negut (Columbia University, Department of Mathematics)
From vertex operators to the shuffle algebra (ENGLISH)
[ Abstract ]
In this series of talks, we will discuss several occurrences of shuffle
algebras: in representation theory, in geometry of moduli spaces, and in
the combinatorics of symmetric functions. All the connections will be
explained in detail.

2014/07/12

Lie Groups and Representation Theory

13:20-17:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Mikhail Kapranov (Kavli IPMU) 13:20-14:20
Perverse sheaves on hyperplane arrangements (ENGLISH)
[ Abstract ]
Given an arrangement of hyperplanes in $R^n$, one has the complexified arrangement in $C^n$ and the corresponding category of perverse sheaves (smooth along the strata of the natural stratification).

The talk, based in a joint work with V. Schechtman, will present an explicit description of this category in terms of data associated to the face complex of the real arrangement. Such a description suggests a possibility of categorifying the concept of a oerverse sheaf in this and possibly in more general cases.
Masaki Kashiwara (RIMS) 14:40-15:40
Upper global nasis, cluster algebra and simplicity of tensor products of simple modules (ENGLISH)
[ Abstract ]
One of the motivation of cluster algebras introduced by
Fomin and Zelevinsky is
multiplicative properties of upper global basis.
In this talk, I explain their relations, related conjectures by Besrnard Leclerc and the recent progress by the speaker with Seok-Jin Kang, Myungho Kima and Sejin Oh.
Toshiyuki Kobayashi (the University of Tokyo) 16:00-17:00
Branching Problems of Representations of Real Reductive Groups (ENGLISH)
[ Abstract ]
Branching problems ask how irreducible representations π of groups G "decompose" when restricted to subgroups G'.
For real reductive groups, branching problems include various important special cases, however, it is notorious that "infinite multiplicities" and "continuous spectra" may well happen in general even if (G,G') are natural pairs such as symmetric pairs.

By using analysis on (real) spherical varieties, we give a necessary and sufficient condition on the pair of reductive groups for the multiplicities to be always finite (and also to be of uniformly bounded). Further, we discuss "discretely decomposable restrictions" which allows us to apply algebraic tools in branching problems. Some classification results will be also presented.

If time permits, I will discuss some applications of branching laws of Zuckerman's derived functor modules to analysis on locally symmetric spaces with indefinite metric.

Lie Groups and Representation Theory

09:30-11:45   Room #126 (Graduate School of Math. Sci. Bldg.)
Toshio Oshima (Josai University) 09:30-10:30
Hypergeometric systems and Kac-Moody root systems (ENGLISH)
Gordan Savin (the University of Utah) 10:45-11:45
Representations of covering groups with multiplicity free K-types (ENGLISH)
[ Abstract ]
Let g be a simple Lie algebra over complex numbers. McGovern has
described an ideal J in the enveloping algebra U such that U/J, considered as a g-module under the adjoint action, is a sum of all self-dual representations of g with multiplicity one. In a joint work with Loke, we prove that all (g,K)-modules annihilated by J have multiplicity free K-types, where K is defined by the Chevalley involution.

2014/07/11

Colloquium

16:30-17:30   Room #123 (Graduate School of Math. Sci. Bldg.)
Toshiyuki Kobayashi (Graduate School of Mathematical Sciences, University of Tokyo)
Global Geometry and Analysis on Locally Symmetric Spaces with
Indefinite-metric (JAPANESE)
[ Abstract ]
The local to global study of geometries was a major trend of 20th
century geometry,
with remarkable developments achieved particularly in Riemannian geometry.
In contrast, in areas such as pseudo-Riemannian geometry, familiar to us
as the space-time of relativity theory, and more generally in
pseudo-Riemannian geometry of general signature, surprising little is
known about global properties of the geometry even if we impose a
locally homogeneous structure.

I plan to explain two programs:

1. (global shape) Existence problem of compact locally homogeneous spaces,
and deformation theory.

2. (spectral analysis) Construction of the spectrum of the Laplacian,
and its stability under the deformation of the geometric structure.

by taking anti-de Sitter manifolds as a typical example.


FMSP Lectures

15:00-16:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Oleg Emanouilov (Colorado State Univ.)
Conditional stability estimate for the Calderon's problem in two dimensional case (ENGLISH)
[ Reference URL ]
http://fmsp.ms.u-tokyo.ac.jp/FMSPLectures_Emanouilov140711.pdf

2014/07/08

Tuesday Seminar on Topology

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Ingrid Irmer (JSPS, the University of Tokyo)
The Johnson homomorphism and a family of curve graphs (ENGLISH)
[ Abstract ]
Abstract: A family of curve graphs of an oriented surface $S_{g,1}$ will be defined on which there exists a natural orientation, coming from the orientation of subsurfaces. Distances in these graphs represent commutator lengths in $\\pi_{1}(S_{g,1})$. The displacement of vertices in the graphs under the action of the Torelli group is used to give a combinatorial description of the Johnson homomorphism."

Classical Analysis

16:00-17:30   Room #122 (Graduate School of Math. Sci. Bldg.)
Nakazono Nobutaka (University of Sydney)
ABS equations arising from q-P((A2+A1)^{(1)}) (JAPANESE)
[ Abstract ]
The study of periodic reductions from ABS equations to discrete Painlevé equations have been investigated by many groups. However, there still remain open questions:
(i) How do we identify the discrete Painlevé equation that would result from applying a periodic reduction to an ABS equation?
(ii) Discrete Painlevé equations obtained by periodic reductions often have insufficient number of parameters. How do we obtain the general case with all essential parameters?
To solve these problems, we investigated the periodic reductions from the viewpoint of Painlevé systems.

In this talk, we show how to construct a lattice where ABS equations arise from relationships between $\\tau$ functions of Painlevé systems and explain how this lattice relates to a hyper cube associated with an ABS equation on each face.
In particular, we consider the $q$-Painlevé equations, which have the affine Weyl group symmetry of type $(A_2+A_1)^{(1)}$.

2014/07/07

Algebraic Geometry Seminar

15:30-17:00   Room #122 (Graduate School of Math. Sci. Bldg.)
Sho Tanimoto (Rice University)
Balanced line bundles (JAPANESE)
[ Abstract ]
A conjecture of Batyrev and Manin relates arithmetic properties of
varieties with big anticanonical class to geometric invariants; in
particular, counting functions defined by metrized ample line bundles
and the corresponding asymptotics of rational points of bounded height
are interpreted in terms of cones of effective divisors and certain
thresholds with respect to these cones. This framework leads to the
notion of balanced line bundles, whose counting functions, conjecturally,
capture generic distributions of rational points. We investigate
balanced line bundles in the context of the Minimal Model Program, with
special regard to the classification of Fano threefolds and Mori fiber
spaces.
This is joint work with Brian Lehmann and Yuri Tschinkel.

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