GCOE Seminars

Seminar information archive ~03/28Next seminarFuture seminars 03/29~


Seminar information archive

2013/11/21

15:30-17:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Florin Ambro (IMAR)
Cyclic covers and toroidal embeddings (ENGLISH)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/documents/miniworkshop.pdf

2013/11/07

17:00-18:00   Room #370 (Graduate School of Math. Sci. Bldg.)
Bingyu Zhang (University of Cincinnati)
Maximum Regularity Principle for Conservative Evolutionary Partial Di erential Equations (ENGLISH)

2013/10/17

16:00-17:00   Room #470 (Graduate School of Math. Sci. Bldg.)
Fikret Goelgeleyen (Bulent Ecevit University)
Stability for Inverse problems for Ultrahyperbolic Equations (ENGLISH)
[ Abstract ]
In this work, we consider inverse problems of determining a coefficient or a source term in an ultrahyperbolic equation by some lateral boundary data.
We prove Hoelder estimates which are global and local and the key is Carleman estimates.

2013/10/17

17:00-18:00   Room #470 (Graduate School of Math. Sci. Bldg.)
kazufumi Ito (North Carolina State University)
Fluid-structure interaction model and Levelset method (ENGLISH)
[ Abstract ]
We derive a weak form and weak solution of the level set formulation of Cottet and Maitre for fluid-structure interaction problems with immersed surfaces. The method in particular exhibits appealing mass and energy conservation properties and a variational formulation of Peskin’s Immersed Boundary methods.

2013/10/09

16:00-17:00   Room #370 (Graduate School of Math. Sci. Bldg.)
Oleg Emanouilov (Colorado State Univ.)
Determination of the first order terms for elliptic partial differential equations using the partial Cauchy data (ENGLISH)
[ Abstract ]
In the bounded domain we consider the variant of the Calderon's problem for the second order partial differential equation with unknown first order terms. Under some geometric condition on domain we prove that the coefficients of this equation can be determined from the partial Cauchy data up to the gauge equivalence.

2013/03/11

14:45-15:45   Room #123 (Graduate School of Math. Sci. Bldg.)
Stephen Curran (UCLA)
Free probability and planar algebras (ENGLISH)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/mini2013-4.htm

2013/03/05

17:00-18:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Oleg Emanouilov (Colorado State University)
Uniqueness for inverse boundary value problems by Dirichlet-to
-Neumann map on subboundaries (ENGLISH)
[ Abstract ]
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.

2013/03/04

17:00-18:00   Room #270 (Graduate School of Math. Sci. Bldg.)
M.I. Tribelsky (Landau Institute)
Resonant Light Scattering by Small Particles (ENGLISH)
[ Abstract ]
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.

2013/02/28

16:00-17:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Mourad Choulli (Univ. Lorraine)
Stability of the determination of the surface impedance of an
obstacle from the scattering amplitude (ENGLISH)
[ Abstract ]
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.

2013/02/28

17:00-18:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Kazufumi Ito (North Carolina State Univ.)
$L_0$ optimization and Lagrange multiplier (ENGLISH)
[ Abstract ]
$L_p$ 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.

2013/02/27

10:00-11:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Dietmar Hoemberg (Weierstrass Institute)
Sufficient optimality conditions for a semi-linear parabolic system related to multiphase steel production (ENGLISH)
[ Abstract ]
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)

2013/02/22

16:00-17:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Fatiha Alabau-Boussouira (Université de Lorraine)
Exact insensitizing controls for scalar wave equations and control of coupled systems (ENGLISH)
[ Abstract ]
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.

2013/02/22

17:00-18:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Piermarco Cannarsa (Univ. Roma II)
Carleman estimates and Lipschitz stability for Grushin-type operators (ENGLISH)
[ Abstract ]
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.

2013/02/18

17:00-18:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Larisa A. Nazarova (Department
Institute of Mining Siberian Branch of Russian Academy of Sciences)
INVERSE PROBLEMS OF GEOMECHANICS AND ITS APPLICATION IN MINING AND GEOPHYSICS (ENGLISH)
[ Abstract ]
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.

2013/02/07

17:00-18:30   Room #370 (Graduate School of Math. Sci. Bldg.)
Asaf Iskandarov (Lenkaran State University)
Identification of quantum potentials in the Schrodinger equation (ENGLISH)
[ Abstract ]
In this lecture I will consider the identification problem of determining the unknown time-dependent coefficients of nonlinear Schrodinger equation.We applied the variational method and studied the correctness of direct and identification problems. We find a necessary condition of the solution and give a stable methed for solution.

2013/01/30

16:00-17:00   Room #118 (Graduate School of Math. Sci. Bldg.)
Marcel Bischoff (Univ. Göttingen)
Construction of models in low dimensional QFT using operator algebraic methods (ENGLISH)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/mini2013-3.htm

2013/01/28

16:00-17:00   Room #270 (Graduate School of Math. Sci. Bldg.)
Bernadette Miara (Universite Paris-Est)
The obstacle problem for a shallow membrane-Justification and stability (ENGLISH)
[ Abstract ]
This lecture is twofold.
In the first part we recall the difference between the three-dimensional unilateral contact problem (the so-called Signorini problem) and its two-dimensional limit (the obstacle problem) in the case of an elastic shell as it was considered in [1] and [2].
In the second part we consider a simplified set of equations which describe the equilibrium equations of a shallow membrane (as justified in [3]) in contact with a plane obstacle and we study the stability of the contact zone with respect to small changes of the applied force, which amounts to studying the variation of the boundary of this contact zone. This kind of stability was first established in the scalar case for the Laplacian operator [4] then for the biharmonic operator [5]. The interest of the vectorial case considered here is due to the coupling effects between the in-plane and the transverse components of the displacement field in the framework of linearized Marguerre-von K´arm´an shell model.
This is a joint work with Alain L´eger, CNRS, Laboratoire de M´ecanique et d’Acoustique, 13402, Marseille, France.

2013/01/24

14:00-15:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Leevan Ling (Hong Kong Baptist University)
Global radial basis functions method and some adaptive techniques (ENGLISH)
[ Abstract ]
It is now commonly agreed that the global radial basis functions method is an attractive approach for approximating smooth functions. This superiority does not come free; one must find ways to circumvent the associated problem of ill-conditioning and the high computational cost for solving dense matrix systems.
In this talk, we will overview different variants of adaptive methods for selecting proper trial subspaces so that the instability caused by inappropriately shaped parameters were minimized.

2013/01/24

15:00-16:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Christian Clason (Graz University)
Parameter identification problems with non-Gaussian noise (ENGLISH)
[ Abstract ]
For inverse problems subject to non-Gaussian (such as impulsive or uniform) noise, other data fitting terms than the standard L^2 norm are statistically appropriate and more robust. However, these formulations typically lead to non-differentiable problems which are challenging to solve numerically. This talk presents an approach that combines an iterative smoothing procedure with a semismooth Newton method, which can be applied to parameter identification problems for partial differential equations. The efficiency of this approach is illustrated for the inverse potential problem.

2013/01/23

16:30-18:00   Room #118 (Graduate School of Math. Sci. Bldg.)
David Evans (Cardiff University)
Exotic subfactors and conformal field theories (ENGLISH)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/tokyo-seminar.htm

2013/01/23

17:15-18:15   Room #370 (Graduate School of Math. Sci. Bldg.)
Volker Schulz (Trier University)
Shape and topology optimization in application (ENGLISH)
[ Abstract ]
Shape and topology optimization currently is of high interest for applications but also from a theoretical point of view. Recently, new developments in the shape calculus and in a related calculus for topology have enabled successful solutions of challenging optimization problems. This talk specifically reports on parameter free shape optimization in aerodynamics, thermoelastics and acoustics. Furthermore, novel results for the elastic topology optimization of the interior of wings are presented. We will try to give insight into the challenges in this field as well as the numerical solution approaches.

2013/01/16

14:40-15:40   Room #118 (Graduate School of Math. Sci. Bldg.)
Arnaud Brothier (KU Leuven)
Unique Cartan decomposition for II$_1$ factors arising from cross section equivalence relations (ENGLISH)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/mini2013-2.htm

2013/01/16

15:55-16:55   Room #118 (Graduate School of Math. Sci. Bldg.)
Michael Hartglass (UC Berkeley)
TBA (ENGLISH)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/mini2013-2.htm

2013/01/16

16:00-17:00   Room #370 (Graduate School of Math. Sci. Bldg.)
Oleg Emanouilov (Colorado State University)
3-D Calderon's Problem with partial Dirichlet-to Neumann map (ENGLISH)
[ Abstract ]
We present new results for the uniqueness of recovery of a potential in three dimensional Calderon's problem with partial Dirichlet-to-Neumann map.
The proof is based on complex geometric optics solutions and the Radon transform.

2013/01/11

10:00-11:00   Room #123 (Graduate School of Math. Sci. Bldg.)
Sven Raum (KU Leuven)
A duality between easy quantum groups and reflection groups (ENGLISH)
[ Reference URL ]
https://www.ms.u-tokyo.ac.jp/~yasuyuki/mini2013-1.htm

< Previous 12345 Next >