Veranstaltungen

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24. – 26. Juni 2019 (WIAS-ESH)
Workshop/Konferenz: Workshop on Phase Transitions and Particle Systems
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Montag, 24.06.2019, 15:15 Uhr (WIAS-HVP-3.13)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. J. Gravesen, Technical University of Denmark, Dänemark:
Differential geometry and dimension reduction for nano structures
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13

Abstrakt
Many nano structures are essentially one or two dimensional and it is in this case often possible to reduce the equations from three to one or two dimensions. That gives huge computational savings but can also provide insight into how the geometry of structures influences the physical properties. In the case of the Schrödinger equation for a single particle this influence is expressed in the form of a simple curvature potential. For coupled equations such as the Luttinger--Kohn Hamiltonian the procedure is no longer straight forward. The boundary conditions pose some problems and an extra approximation is necessary. We will give an overview of the method and point to some of the possible pitfalls when a choice of frame is needed.

Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
Dienstag, 25.06.2019, 13:30 Uhr (WIAS-406)
Seminar Materialmodellierung
Prof. L. Heltai:
Unconventional frameworks for the simulation of coupled bulk-interface problems
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstrakt
Partial differential equations with interfaces, holes, cracks, or defects often require the numerical solution of coupled bulk-interface problems. In this talk, I will discuss and analyse some techniques that can be used to tackle this class of problems, using non-matching discretisations that combine finite element methods, regularization techniques, weighted Sobolev spaces, and reduce order models.

Veranstalter
WIAS Berlin
Dienstag, 25.06.2019, 15:00 Uhr (WIAS-405-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Dr. F. Telschow, University of California San Diego, USA:
Spatial confidence sets for raw effect size images
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Veranstalter
WIAS Berlin
Dienstag, 25.06.2019, 15:15 Uhr (WIAS-HVP-3.13)
Oberseminar Nonlinear Dynamics
S. Ruschel, TU Berlin:
Pulsing dynamics of a laser system with delayed feedback
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13

Abstrakt
We consider the Yamada model for an excitable or self-pulsating laser with saturable absorber in the presence of delayed optical self-feedback. We present some recent results regarding the stability and bifurcations of periodic light pulses that are sustained in the external cavity feedback loop, so called external cavity pulse trains.

Veranstalter
Freie Universität Berlin
WIAS Berlin
Mittwoch, 26.06.2019, 10:00 Uhr (WIAS-405-406)
Forschungsseminar Mathematische Statistik
Dr. A. Suvorikova, Universität Potsdam:
On CLT in Bures-Wasserstein space and beyond
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstrakt
In the first part of the talk we present some concentration and convergence properties of Bures-Wasserstein (BW) barycenters of hermitian finite-dimensional matrices, and explain how they can be used for investigation of geometry of DNA molecules modelled as a union of ridgid bodies. In the second part we show how the framework of classical resampling techniques can be extended to the case of the BW space, and introduce some geometrical intuition behind the construction of non-asymptotic confidence sets for BW barycenters.

Veranstalter
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Donnerstag, 27.06.2019, 16:00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
Dr. M. Kantner, WIAS Berlin:
Non-isothermal generalization of the Scharfetter--Gummel scheme for degenerate semiconductors
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Mittwoch, 03.07.2019, 10:00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Dr. C. Strauch, Universität Mannheim:
Concentration and nonparametric learning of diffusion processes
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
We start by discussing uniform concentration inequalities for continuous-time analogues of empirical processes and related stochastic integrals of ergodic diffusion processes. Our approach substantially relies on combining the device of martingale approximation and moment bounds which are obtained by the generic chaining method. As a concrete statistical application, we consider the question of estimating the drift function for a large class of ergodic diffusion processes. The unknown drift is supposed to belong to a nonparametric class of smooth functions of unknown order. We suggest a fully data-driven procedure which allows for rate-optimal drift estimation (with respect to sup-norm risk) and, at the same time, yields an asymptotically effiient estimator of the invariant density of the diffusion. In the last part of the talk, we sketch applications of our results to problems from stochastic control theory. One of the fundamental assumptions in stochastic control of continuous time processes is that the dynamics of the underlying (diffusion) process is known. This is, however, usually not fulfilled in practice. We study a toy model for harvesting and natural resource management, mathematically described as an impulse control problem. In variants of this model, we suggest ways to both learn the dynamics of the underlying process and control well at the same time. In particular, the combination of results from stochastic control and our previous analysis of the sup-norm risk allows to derive mathematical results for reinforcement learning.

Veranstalter
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Dienstag, 09.07.2019, 13:30 Uhr (WIAS-406)
Seminar Materialmodellierung
Prof. C. Gräser, Freie Universität Berlin, Institut für Mathematik:
Truncated nonsmooth Newton multigrid for nonsmooth minimization problems
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstrakt
Many problems originating from continuum mechanics and material sciencelead to large scale nonsmooth optimization problems after discretization in time and space. Examples are classical binary or multi-component phase field models for phase transition and separation, frictional contact problems, plasticity, and phase field-like approaches for brittle and ductile fracture. Since standard numerical methods like, e.g., multigrid are not directly applicable due to the nonsmoothness, generic nonsmooth optimization methods are frequently used for such problems which often comes at the price of reduced efficiency. In the talk we present the Truncated Nonsmooth Newton Multigrid (TNNMG) method which combines techniques from nonsmooth optimization with multigrid and domain decomposition ideas. Instead of a black box approach this is done in a structure aware fashion leading to iterative methods whose efficiency is comparable to state of the art methods for smooth problems while being robust with respect nonsmoothness. In the talk we will introduce the algorithm, discuss convergence, and present numerical examples for various applications illustrating the efficiency of the presented approach.

Veranstalter
WIAS Berlin
Freitag, 02.08.2019, 15:15 Uhr (WIAS-ESH)
MATHEON Special Guest Lecture
Prof. Y.-X. Yuan, Chinese Academy of Sciences, China:
Efficient optimization algorithms for large scale data analysis
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
In this talk, two classes of problems in large scale data analysis and their optimization algorithms will be discussed. The first class focuses on composite convex program problems, where I introduce algorithms including a regularized semi-smooth Newton method, a stochastic semi-smooth Newton method and a parallel subspace correction method. The second class is on optimization with orthogonality constraints, particularly on parallelizable approaches for linear eigenvalue problems and nonlinear eigenvalue problems, and quasi-Newton type methods. Numerical results of applications, e.g., electronic structure calculations, $l_1$-regularized logistic regression problems, Lasso problems and Hartree-Fock total energy minimization problems, will be highlighted.

Weitere Informationen
Special Guest Lecture

Veranstalter
WIAS Berlin
Samstag, 03.08.2019, 09:00 Uhr (TU-Berlin)
6th International Conference on Continuous Optimization
6th International Conference on Continuous Optimization
mehr ... Veranstaltungsort
Technische Universität, Straße des 17. Juni 135, 10623 Berlin, Main building (H)

Weitere Informationen
https://iccopt2019.berlin/

Veranstalter
WIAS Berlin
Technische Universität Berlin
Freie Universität Berlin
Humboldt-Universität zu Berlin
Mathematical Optimization Society
9. – 13. September 2019 (WIAS-ESH)
Workshop/Konferenz: PDE 2019: Partial Differential Equations in Fluids and Solids
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
This workshop fuses expertise on the analysis of PDEs in solids, fluid dynamics, complex fluids, and interaction of fluids with solid structure. Its goal is to create new synergies among these fields in order to advance analytical methods for current research related to systems with bulk-interface interaction, geometrically nonlinear materials, and fluid-structure interaction. This concerns, e. g., Lagrangian and Eulerian descriptions, free boundaries and moving domains, and variational approaches via energy/entropy methods.

Veranstalter
WIAS Berlin
18. – 20. September 2019 (WIAS-ESH)
Workshop/Konferenz: Optical Solitons and Frequency Comb Generation
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Mittwoch, 23.10.2019, 14:00 Uhr (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. A. Jüngel, Technische Universität Wien, Österreich:
Cross-diffusion systems: from spin semiconductors to biological populations with stochastic forcing
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Many real-world applications consist of multiple components, leading on the macroscopic scale to cross-diffusion systems which consist of strongly coupled parabolic equations. The applications may be very diverse and range from spin-polarized transport in semiconductors and ion transport in cell membranes to population dynamics. In this talk, some existence results for global-in-time weak solutions is proved, based on entropy methods. This technique was already used by Herbert Gajewski, and we detail some of his ideas to prove the large-time behavior and uniqueness of weak solutions, followed by some extensions like boundedness-by-entropy and martingale solutions to stochastic cross-diffusion systems.

Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin