Upcoming Events

go to archive

Tuesday, 22.01.2019, 15:00 (WIAS-ESH)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Prof. A. Kebaier, Université Paris 13, France:
Asymptotic properties of maximum likelihood estimator for the drift parameters of jump-type square root processes
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Further Informations
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics

Host
WIAS Berlin
Tuesday, 22.01.2019, 15:15 (FU Berlin)
Oberseminar Nonlinear Dynamics
E. Pimentel, Pontifical Catholic University of Rio de Janeiro, Brazil:
Geometric methods in regularity theory for nonlinear PDEs
more ... Location
Freie Universität Berlin, Arnimallee 3, 14195 Berlin, Hinterhaus, Raum 130

Abstract
In this talk we examine the regularity theory of the solutions to a few examples of nonlinear PDEs. Arguing through a genuinely geometrical method, we produce regularity results in Sobolev and Hölder spaces, including some borderline cases. Our techniques relate a problem of interest to a further one - for which a richer theory is available - by means of a geometric structure, e..g., a path. Ideally, information is transported along such a path, giving access to finer properties of the original equation. In the first part of the talk, we cover examples including elliptic and parabolic fully nonlinear problems, the Isaacs equation and a double divergence model. Then we proceed to the setting of state-dependent degenerate problems and report recent (optimal) results. We close the talk with a discussion on open problems and further directions of work.

Host
Freie Universität Berlin
WIAS Berlin
Wednesday, 23.01.2019, 11:30 (WIAS-406)
Seminar Interacting Random Systems
P. Houdebert, Aix-Marseille Université, Frankreich:
Sharp phase transition for the Widom-Rowlinson model
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
The Widom-Rowlinson model is formally defined as two homogeneous Poisson point processes forbidding the points of different type to be too close. For this Gibbs model the question of uniqueness/ non-uniqueness depending on the two intensities is relevant. This model is famous because it was the first continuum Gibbs model for which phase transition was proven, in the symmetric case of equal intensities large enough. But nothing was known in the non-symmetric case, where it is conjectured that uniqueness would hold. In a recent work with D. Dereudre (Lille), we partially solved this conjecture, proving that for large enough activities the phase transition is only possible in the symmetric case of equal intensities. The proof uses percolation and stochastic domination arguments.

Further Informations
Seminar Interacting Random Systems

Host
WIAS Berlin
Wednesday, 23.01.2019, 13:00 (WIAS-ESH)
Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations / Mathematical Optimization
Prof. Dr. M. S. Aronna, Technische Universität:
On second order optimality conditions for control-affine problems: the finite and infinite dimensional case
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
In this talk I will present the main features of first and second order optimality conditions for optimal control problems of ordinary differential equations that are affine with respect to the control. Problems will be considered in the presence of control constraints. Both necessary and sufficient conditions for optimality will be presented. I will then show the extension of those results for a class of bilinear partial differential equations. Finally, if time allows it, I will briefly discuss the state-constrained case.

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Wednesday, 23.01.2019, 15:00 (WIAS-ESH)
Seminar Numerische Mathematik
Prof. V. A. Garanzha, Russian Academy of Sciences:
Moving adaptive meshes based on the hyperelastic stress deformation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
We suggest an algorithm for the time-dependent mesh deformation based on the minimization of hyperelastic quasi-isometric functional without introducing time derivatives. The source of deformation is a time-dependent metric tensor in Eulerian coordinates. Due to the nonlinearity of the Euler-Lagrange equations we can not assume that the norm of its residual is reduced to zero at each time step. Thus, time continuity of the moving mesh is not guaranteed since iterative minimization may result in considerable displacements even for infinitely small time steps. To solve this problem, we introduce a special variant of factorized representation of Lagrangian metric tensor and nonlinear interpolation procedure for factors of this metric tensor. Continuation problem with respect to interpolation parameters is similar to the hypoelastic deformation with a controlled stress relaxation. At each time step we start with a Lagrangian metric tensor which completely eliminates internal elastic stresses and makes current mesh an exact solution of the Euler-Lagrange equations. The continuation procedure gradually introduces internal stresses back while forcing the deformation to follow the prescribed Eulerian metric tensor. At each step of the continuation procedure the functional is approximately minimized using a few steps of the parallel preconditioned gradient search algorithm. We derive an auxiliary discrete evolution equation for target shape matrices (factors of Lagrangian metric tensor) which resembles stress relaxation equations in hypoelasticity. We present 2d and 3d examples of moving deforming meshes which serve to represent moving bodies for parallel immersed boundary flow solver.

Host
WIAS Berlin
Thursday, 24.01.2019, 16:00 (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
Dr. S. Schulz, Tyndall National Institute, Ireland:
Electronic, optical and transport properties of III--N alloys and heterostructures: Insights from and challenges for theoretical modelling
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
InGaN-based heterostructures have attracted considerable interest for a variety of different applications. For example, the key building blocks of modern light-emitting devices operating in the blue spectral region are c-plane InGaN/GaN quantum wells (QWs). It is remarkable that these devices are so successful, given the extremely high defect densities in InGaN/GaN systems. This defect insensitivity has been widely attributed to carrier localization effects introduced by alloy fluctuations, preventing carriers to reach non-radiative recombination centers. It is only recently that localization effects in InGaN QWs have been addressed in theoretical studies and, in comparison to other III-V materials and alloys, such such as InGaAs, several key properties are not well understood. This lack of understanding ranges from fundamental material properties up to devices related aspects. In this talk, electronic and optical properties of bulk alloys, such as AlInN or InGaN, as well as InGaN quantum wells will be discussed by means of atomistic models. These approaches range from first-principles density functional methods up to in-house developed empirical tight-binding models. Here, special attention is paid to nanoscale effects such as local fluctuations in intrinsic built-in fields. Theoretical results will be compared to available experimental data. Finally, theoretical and modeling challenges for instance in the area of transport calculations will be discussed and reviewed. Initial results of coupled tight-binding non-equilibrium Green?s function transport calculations will be presented.

Host
WIAS Berlin
Tuesday, 29.01.2019, 13:30 (WIAS-406)
Seminar Materialmodellierung
Prof. V. Romano, University of Catania, Italy:
Charge and phonon transport in graphene
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
The last years have witnessed a great interest for 2D-materials due to their promising applications. The most investigated one is graphene which is considered as a potential new material to exploit in nano-electronic and optoelectronic devices. Charge transport in graphene can be described with several degrees of physical complexity. At quantum level an accurate model is represented by the Wigner equation but in several cases its semiclassical limit, the Boltzmann equation, constitutes a fully acceptable model. However, the numerical difficulties encountered in the direct solution of both the Wigner and the semiclassical Boltzmann equation has prompted the development of hydrodynamical, energy transport and drift diffusion models, in view of the design of a future generation of electron devices where graphene replaces standard semiconductors like silicon and gallium arsenide. Moreover, thermal effects in low dimensional structures play a relevant role and, therefore, also phonon transport must be included. Interesting new mathematical issues related to the peculiar features of graphene arise. The main aspects will be discussed and recent results illustrated in the perspective of future developments, in particular the optimization of graphene field effect transistors.

Host
WIAS Berlin
Tuesday, 29.01.2019, 15:00 (WIAS-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
D. Dvinskikh, WIAS Berlin:
Distributed decentralized (stochastic) optimization for dual-friendly functions
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Host
WIAS Berlin
Wednesday, 30.01.2019, 10:00 (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Prof. J.-P. Florens, University of Toulouse:
Is completeness necessary? Penalized estimation in non identified linear models
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Wednesday, 13.02.2019, 11:30 (WIAS-406)
Seminar Interacting Random Systems
P. Neijjar, Institute of Science and Technology Austria (IST Austria), Österreich:
Product limit laws at shocks in (T)ASEP
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Further Informations
Seminar Interacting Random Systems

Host
WIAS Berlin
March 20 – 22, 2019 (IAP)
Workshop/Konferenz: Leibniz MMS Days 2019
more ... Location
Leibniz-Institute of Atmospheric Physics, Schlossstr. 6, 04318 Kühlungsborn, Germany

Host
WIAS Berlin