Veranstaltungen

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29. Mai – 2. Juni 2017 (WIAS-ESH)
Workshop/Konferenz: CRC 1114 Spring School: Methods for Particle Systems with Multiple Scales
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
SFB 1114: Scaling Cascades in Complex Systems
Dienstag, 30.05.2017, 13.30 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Prof. C. Gräser, Freie Universität Berlin:
Solving nonsmooth PDEs in Dune
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
The design of efficient numerical software for the solution of PDEs is a challenging task because different applications may have very different requirements. As a consequence a large set of libraries has been developed, each with its own focus but in general not compatible with each other.
The central idea of the Dune (distributed unified numerics environment) framework is to change the perspective and to design interfaces that allow to represent a large range of different implementations. This idea is applied on many scales leading to a broad spectrum of interfaces ranging from low level grid operations to high level simulation and code generation frameworks. Based on these principle Dune has evolved to a modular and flexible framework with constantly growing user base and a developer group spread over many institutions.
The talk consists of two parts: The first part will present the Dune framework while the second part briefly outlines how this is used to solve nonsmooth PDEs originating e.g. from applications in material science and biomechanics with state of the art multigrid methods.

Veranstalter
WIAS Berlin
Dienstag, 30.05.2017, 14.00 Uhr (WIAS-HVP)
Seminar Materialmodellierung
C. Visone, Università del Sannio - Benevento, Italien:
The applicative challenges of Smart Materials: From Sensing to Harvesting
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 4. Etage, Raum: 4.01

Abstrakt
The talk would provide a view on functional materials observed and employed at the macro-scale. Starting from the most known Multi-Functional materials, a common modeling approach, based on the definition of constitutive relationships, is discussed. Examples on the effectiveness of the constitutive equations in the analysis and design problems in engineering is illustrated, along with the basic challenges arising when these materials are of concern. Further, the statement of consistent constitutive relationships when rate-independent memory processes (hysteresis) are considered is also carried out, through the definition of models for multi-input/multi-output systems that formally satisfy the Duhem inequality. Practical examples and specific applications are also proposed.

Veranstalter
WIAS Berlin
Dienstag, 30.05.2017, 15.00 Uhr (WIAS-ESH)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
P. Fischer, Humboldt-Universität zu Berlin:
Overview of the paper "Estimating the cluster tree of a density by analyzing the minimal spanning tree of a sample" by Werner Stuetzle
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Dienstag, 30.05.2017, 15.15 Uhr (WIAS-ESH)
Oberseminar Nonlinear Dynamics
P. Lappicy, Free University Berlin:
Einstein constraints: A dynamical approach
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
The Einstein constraint equations describe the space of initial data for the evolution equations, dictating how space should curve within spacetime. Under certain assumptions, the constraints reduce to a scalar quasilinear parabolic equation on the sphere, and nonlinearity being the prescribed scalar curvature of space. We focus on self-similar solutions of Schwarzschild type, which describe the space of initial data of certain black holes, for example. The first main result gives a detailed study of the axially symmetric solutions, since the domain is now one dimensional and nodal properties can be used to describe certain asymptotics of the rescaled self-similar solutions. Such asymptotics describe the possible metrics arising at an event horizon of a black hole, depending on the metric inside the horizon. Those are described by Sturm attractors. In particular, we compute an example for a prescribed scalar curvature. The second main result states a symmetrization property of certain metrics in the event horizon, namely, how the symmetry of the spherical domain can influence the symmetry of solutions.

Veranstalter
Freie Universität Berlin
WIAS Berlin
Mittwoch, 31.05.2017, 10.00 Uhr (WIAS-HVP-4.13)
Forschungsseminar Mathematische Statistik
Prof. J. C. Escanciano, Indiana University Bloomington, USA:
Quantile-regression inference with adaptive control of size
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 4. Etage, Raum: 4.13

Abstrakt
Regression quantiles have asymptotic variances that depend on the conditional densities of the response variable given regressors. This paper develops a new estimate of the asymptotic variance of regression quantiles that leads any resulting Wald-type test or con dence region to behave as well in large samples as its infeasible counterpart in which the true conditional response densities are embedded. We give explicit guidance on implementing the new variance estimator to control adaptively the size of any resulting Wald-type test. Monte Carlo evidence indicates the potential of our approach to deliver con dence intervals for quantile regression parameters with excellent coverage accuracy over di erent quantile levels, data-generating processes and sample sizes. We also include an empirical application. Supplementary material is available online.

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Forschungsseminar ``Mathematische Statistik''

Veranstalter
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Donnerstag, 01.06.2017, 14.00 Uhr (WIAS-405-406)
Seminar Numerische Mathematik
Dr. S. Ganesan, Indian Institute of Science, Bangalore:
Stabilized three-field formulation of viscoelastic fluid flows
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstrakt
Viscoelastic flows can be found in a wide range of industrial and commercial applications such as enhanced oil recovery, pesticide deposition, medicinal/pharmaceutical sprays, drug delivery, injection molding, polymer melts, inkjet printing, additive manufacturing, cosmetics industry and food processing. Computations of viscoelastic fluid flows involve simultaneous solutions of the conformation stress tensor equation together with the momentum and mass balance equations. The constitutive equation is advection dominant at high Weissenberg numbers, which necessitates the use of stabilized numerical schemes to avoid local and global oscillations in the numerical solution. The common stabilization schemes used in the context of finite element computations of viscoelastic fluid flows in the literature are Streamline-upwind/Petrov--Galerkin (SUPG), discontinuous Galerkin (DG), discrete Elastic Viscous Stress Splitting (DEVSS) [1], Galerkin Least Square (GLS) [2] and Variational Multiscale method (VMS) [3].

In this talk, a three-field formulation based on the one-level Local Projection Stabilization (LPS) [4, 5] will be presented for computations of Oldroyd-B viscoelastic fluid flows with high Weissenberg numbers. One-level LPS is based on the enriched approximation space and the discontinuous projection space, where both spaces are defined on the same mesh. It allows us to use equal order interpolation spaces for the velocity and viscoelastic stress, whereas inf-sup stable finite elements are used for the velocity and pressure. Further, the coupled system of equations are solved in a monolithic approach. Since LPS stabilization terms are assembled only once, the proposed numerical scheme is computationally efficient in comparison with residual based methods. Numerical studies that show optimal order of convergence in the respective norms will be presented. Further, the numerical results of two benchmark problems: flow past a cylinder in a wide channel and lid-driven cavity flow will be given. Moreover, the effects of elasticity and inertia on the flow dynamics will be discussed.

References:
[1] R. Guenette, A. Fortin, A new mixed finite element method for computing viscoelastic flows, J. Non-Newtonian Fluid Mech., 60 (1995), 27--52.
[2] O. M. Coronado, D. Arora, M. Behr, M. Pasquali, Four-field Galerkin/least-squares formulation for viscoelastic fluids, J. Non-Newtonian Fluid Mech., 140 (2006), 132--144.
[3] E. Castillo, R. Codina, Variational multi-scale stabilized formulation for the stationary three-field incompressible viscoelastic flow problem, Comput. Methods Appl. Mech. Engrg., 279 (2014), 579--605.
[4] G. Matthies, P. Skrzypacz, L. Tobiska, A unified convergence analysis for local projection stabilisations applied to the oseen problem, M2AN Math. Model. Numer. Anal., 41 (2007), 713--742.
[5] S. Ganesan, G. Matthies, L. Tobiska, Local projection stabilization of equal order interpolation applied to the Stokes problem, Math. Comp., 77 (2008), 2039--2060.

Veranstalter
WIAS Berlin
Donnerstag, 01.06.2017, 16.00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
F. Bierbüsse, Humboldt-Universität zu Berlin:
Ultrashort dark solitons in the context of the short pulse equation
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Mittwoch, 07.06.2017, 15.15 Uhr (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Th. Frenzel, WIAS Berlin:
EDP-convergence for a wiggly energy model
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

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Berliner Oberseminar ``Nichtlineare Partielle Differentialgleichungen'' (Langenbach Seminar)

Veranstalter
WIAS Berlin
Humboldt-Universität zu Berlin
Mittwoch, 07.06.2017, 18.15 Uhr (WIAS-ESH)
Berliner Kolloquium Wahrscheinlichkeitstheorie/Berlin Young Probabilists' Seminar
Prof. Dr. S. Adams, University of Warwick, GB:
Large deviations and concentration of scaling limits for weakly pinned integrated random walks
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
We study scaling limits and corresponding large deviation principles of integrated random walks perturbed by an attractive force towards the origin. In particular we analyse the critical situation that the rate function admits more than one minimiser leading to concentration of measure problems. The integrated random walk models are in fact interface models with Laplacian interaction, and such linear chain models with Laplacian interaction appear naturally in the physical literature in the context of semi-flexible polymers. We discuss these connections as well as the ones with the related gradient models. These random fields are a class of model systems arising in the studies of random interfaces, critical phenomena, random geometry, field theory, and elasticity theory. If time permits we outline basic techniques and give an overview about future research projects in this area.

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Berliner Kolloquium Wahrscheinlichkeitstheorie

Veranstalter
Humboldt-Universität zu Berlin
Technische Universität Berlin
Universität Potsdam
WIAS Berlin
Mittwoch, 14.06.2017, 10.00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Prof. J.-M. Loubes, Université Toulouse Paul Sabatier, Frankreich:
Kantorovich distance based kernel for Gaussian processes : Estimation and forecast
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Monge-Kantorovich distances, otherwise known as Wasserstein distances, have received a growing attention in statistics and machine learning as a powerful discrepancy measure for probability distributions. Here, we focus on forecasting a Gaussian process indexed by probability distributions. For this, we provide a family of positive definite kernels built using transportation based distances. We provide a probabilistic understanding of these kernels and characterize the corresponding stochastic processes. We prove that the Gaussian processes indexed by distributions corresponding to these kernels can be efficiently forecast, opening new perspectives in Gaussian process modeling

Veranstalter
WIAS Berlin
Humboldt-Universität zu Berlin
Universität Potsdam
Donnerstag, 15.06.2017, 16.00 Uhr (WIAS-HVP-3.13)
Forschungsseminar Mathematische Modelle der Photonik
A. Zheguzi, Ferdinand-Braun-Institut Berlin:
Simulations of broad area high-power lasers with optical feedback
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13

Veranstalter
WIAS Berlin
Mittwoch, 21.06.2017, 15.30 Uhr (WIAS-HVP-4.13)
Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations / Mathematical Optimization
M. Bongini, Barcelona Graduate School of Economics:
Optimal Control Problems in Transport Dynamics
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 4. Etage, Raum: 4.13

Abstrakt
In this talk we shall discuss several results concerning the "indirect control of populations", i.e., how to influence a group of individuals by means of external agents with a directly controlled dynamics. By using the general theory of functionals defined on spaces of measures, we give sufficient conditions for the existence of optimal control strategies and then we present a Pontryagin Maximum Principle for such controls in the form of an Hamiltonian flow in the Wasserstein space of probability measure. Finally, we present an application of the above framework to the evacuation problem of a crowd from an unknown environment with the help of undercover stewards.

Veranstalter
WIAS Berlin
Donnerstag, 22.06.2017, 16.00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
Dr. C. Brée, WIAS:
Feedback-operator for a photonic crystal in the external cavity of a broad area laser diode
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Donnerstag, 29.06.2017, 16.00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
Dr. A. Pimenov, WIAS Berlin:
Efficient simulation and analysis of multi-mode laser dynamics using time-delay models
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin