Upcoming Events

Due to infection prevention measures, participation in events at the institute is presently not possible for guests.

Many events are currently organized online. Information on how to access these events can be found by clicking “more” below the respective entry.


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Tuesday, 13.04.2021, 16:00 (Online Event)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Yangwen Sun, Humboldt-Universität zu Berlin:
Graph-spanning ratio test with application to change-point detection problem (online talk)
more ... Location
Online Event

Further Informations
Dieser Vortrag findet bei Zoom statt: https://zoom.us/j/492088715

Host
WIAS Berlin
Wednesday, 14.04.2021, 11:30 (Online Event)
Seminar Interacting Random Systems
Alexis Prevost, University of Cambridge, GB:
Cluster capacity functionals and isomorphism theorems for Gaussian free fields (online talk)
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Online Event

Abstract
Various isomorphisms theorem relate Gaussian free fields to random walk models, through their local times. Among them, the second Ray-Knight theorem can be extended in an isomorphism between the Gaussian free field and random interlacements on transient graphs. Following the work of Lupu and Sznitman, we will explain how the cable system method let us make this isomorphism more explicit, and how it relates to a certain cluster capacity functional for the Gaussian free field. Finally, we will present applications to percolation for the Gaussian free field on the cable system. Joint work with Alexander Drewitz (Cologne) and Pierre-François Rodriguez (London)

Further Informations
Seminar Interacting Random Systems (Online Event)

Host
WIAS Berlin
Wednesday, 14.04.2021, 15:15 (Online Event)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Flaviana Iurlano, Sorbonne Université Paris, Frankreich:
Shape optimization of light structures (online talk)
more ... Location
Online Event

Abstract
We prove rigorous results about the vanishing-mass limit of the classical problem to find a shape with minimal elastic compliance. Contrary to all previous results in the mathematical literature, which utilize a soft mass constraint by introducing a Lagrange multiplier, we here consider the hard mass constraint. Our results are the first to establish the convergence of approximately optimal shapes of (exact) size $varepsilonto 0$ to a limit generalized shape represented by a (possibly diffuse) probability measure. This limit generalized shape is a minimizer of the limit compliance, which involves a new integrand, namely the one conjectured by Bouchitté in 2001 and predicted heuristically before in works of Allaire & Kohn and Kohn & Strang from the 1980s and 1990s. This integrand gives the energy of the limit generalized shape understood as a fine oscillation of (optimal) lower-dimensional structures. Its appearance is surprising since the integrand in the original compliance is just a quadratic form and the non-convexity of the problem is not immediately obvious. In fact, it is the interaction of the mass constraint with the requirement of attaining the loading (in the form of a divergence-constraint) that gives rise to this new integrand. Our proofs rest on compensated compactness arguments applied to an explicit family of div-quasiconvex quadratic forms, computations involving the Hashin--Shtrikman bounds for the Kohn--Strang integrand, and the characterization of limit minimizers due to Bouchitté & Buttazzo.

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Thursday, 15.04.2021, 14:00 (Online Event)
Seminar Numerische Mathematik
Prof. Julia Novo, Universidad Autónoma de Madrid, Spanien:
Error analysis of proper orthogonal decomposition stabilized methods for incompressible flows
more ... Location
Online Event

Abstract
Proper orthogonal decomposition (POD) stabilized methods for the Navier-Stokes equations are presented. We consider two cases: the case in which the snapshots are based on a non inf-sup stable method and the case in which the snapshots are based on an inf-sup stable method. For both cases we construct approximations to the velocity and the pressure. For the first case, we analyze a method in which the snapshots are based on a stabilized scheme with equal order polynomials for the velocity and the pressure with local projection stabilization (LPS) for the gradient of the velocity and the pressure. For the POD method we add the same kind of LPS stabilization for the gradient of the velocity and the pressure as the direct method, together with grad-div stabilization. In the second case, the snapshots are based on an inf-sup stable Galerkin method with grad-div stabilization and for the POD model we also apply grad-div stabilization. In this case, since the snapshots are discretely divergence-free, the pressure can be removed from the formulation of the POD approximation to the velocity. To approximate the pressure, needed in many engineering applications, we use a supremizer pressure recovery method. Error bounds with constants independent of inverse powers of the viscosity parameter are proved for both methods. Numerical experiments show the accuracy and performance of the schemes.

Further Informations
For zoom login details please contact Alexander Linke linke@wias-berlin.de

Host
WIAS Berlin
Thursday, 15.04.2021, 14:00 (Online Event)
Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations / Mathematical Optimization
Steven-Marian Stengl, WIAS Berlin:
Combined regularization and discretization of equilibrium problems and primal-dual gap estimators
more ... Location
Online Event

Abstract
In this talk, we address the treatment of finite element discretizations of a class of equilibrium problems involving moving constraints. Therefore, a Moreau-Yosida based regularization technique, controlled by a parameter, is discussed. A generalized Gamma-convergence concept is utilized to obtain a priori results. The same technique is applied to the discretization and the combination of both. In addition, a primal-dual gap technique is used for the derivation of error estimators and a strategy for balancing between a refinement of the mesh and an update of the regularization parameter is established. The theoretical findings are illustrated for the obstacle problem as well as numerical experiments are performed for two quasi-variational inequalities with application to thermoforming and biomedicine, respectively.

Further Informations
Seminar Mathematical Optimization / Non-smooth Variational Problems and Operator Equations

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Tuesday, 20.04.2021, 15:00 (Online Event)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Dr. Caroline Geiersbach, WIAS Berlin:
Stochastic approximation with applications to PDE-constrained optimization under uncertainty (online talk)
more ... Location
Online Event

Further Informations
Dieser Vortrag findet bei Zoom statt: https://zoom.us/j/492088715

Host
WIAS Berlin
Wednesday, 21.04.2021, 15:15 (Online Event)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Nikolas Nüsken, Universität Potsdam:
The Stein geometry in machine learning: gradient flows, large deviations and convergence properties (online talk)
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Online Event

Abstract
Sampling or approximating high-dimensional probability distributions is a key challenge in computational statistics and machine learning. This talk will present connections to gradient flow PDEs and interacting particle systems, focusing on the recently introduced Stein variational gradient descent methodology. The construction induces a novel geometrical structure on the set of probability distributions related to a positive definite kernel function.We discuss the corresponding geodesic equations as well as large deviation functionals and leverage those to shed some light on the convergence properties of the algorithm. This is joint work with A. Duncan (Imperial College London), L. Szpruch (University of Edinburgh) and M. Renger (Weierstrass Institute Berlin).

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Tuesday, 27.04.2021, 10:00 (Online Event)
Seminar Numerische Mathematik
Prof. Sashikumaar Ganesan, Indian Institute of Science Bangalore; Prof. Volker John, WIAS Berlin:
Minisymposium on machine learning
more ... Location
Online Event

Further Informations
For zoom login details please contact Volker John john@wias-berlin.de

Host
WIAS Berlin
Wednesday, 28.04.2021, 15:15 (Online Event)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Katharina Hopf, WIAS Berlin:
Weak-strong uniqueness in energy-reaction-diffusion systems (online talk)
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Online Event

Abstract
We establish weak-strong uniqueness and stability properties of renormalised solutions to a class of energy-reaction-diffusion systems, which genuinely feature cross-diffusion effects. The systems considered are motivated by thermodynamically consistent models, and their formal entropy structure allows us to use as a key tool a suitably adjusted relative entropy method. Weak-strong uniqueness is obtained for general entropy-dissipating reactions without growth restrictions, and certain models with a non-integrable diffusive flux. The results also apply to a class of (isoenergetic) reaction-cross-diffusion systems.

Further Informations
Berliner Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)

Host
Humboldt-Universität zu Berlin
WIAS Berlin
April 29, 2021 (Online Event)
Workshop/Konferenz: FUHRI2021: Finite volUme metHods for Real-world applIcations
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Online Event

Host
WIAS Berlin
June 16 – 18, 2021 (Online Event)
Workshop/Konferenz: Nonlinear Dynamics in Semiconductor Lasers
more ... Location
Online Event

Host
WIAS Berlin