Veranstaltungen

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Dienstag, 25.04.2017, 10.15 Uhr (WIAS-406)
Seminar Nichtlineare Optimierung und Inverse Probleme
Dr. J. Schwientek, Fraunhofer-Institut für Techno- und Wirtschaftsmathematik, Kaiserslautern:
Numerical methods for general(ized) semi-infinite optimization -- Applied to gemstone cutting
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstrakt
The talk is divided into two parts. In the first part I will give a short introduction to general(ized) semi-infinite programming (GSIP) and survey the numerical methods. At that we will look at one method in more detail, the transformation-based discretization method. It cleverly combines transforming a GSIP into a usual SIP problem and solving the latter one via discretization and exploiting the lower level convexity of the underlying GSIP problem.

The second part of my talk will focus on the most shimmering application of general semi-infinite optimization, the volume-maximal utilization of (colored) gemstones. There, the task is the following: Given an irregular raw gem which is provided with surface defects and interspersed with inclusions, produce a set of precious gems such that the profit is as high as possible. I will show how this task can be modeled and solved as a general semi-infinite optimization problem, and how we installed a new fully automatic industrial production process for producing the jewels.

Veranstalter
WIAS Berlin
Dienstag, 25.04.2017, 14.00 Uhr (WIAS-406)
Seminar Materialmodellierung
I. Thompson, University of Bath, GB:
Modelling device charge dynamics on the microscopic scale
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstrakt
We attempt to predict the properties of organic semiconductor (OSC) materials using a microscopic ab initio approach. Charge transport through organic semiconductors (OSCs) is qualitatively different from metallic semiconductors, charges hop between molecules discretely. Marcus theory describes the microscopic hopping mechanism, quantum chemistry methods can calculate the parameters and kinetic Monte Carlo methods can be used to model charge motion. We also need to describe realistic configurations of a set of given molecules. To combine all of these approaches into a single multi-scale model is the goal of the EXTMOS project. We present simulations of charge carrier motion in a system of discotic molecules with high levels of shape anisotropy; using explicitly calculated parameters we are able to capture and quantify the effect on charge transport anisotropy. We also consider the use of network models to describe collective behaviour.

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Seminar ``Materialmodellierung''

Veranstalter
WIAS Berlin
Dienstag, 25.04.2017, 14.15 Uhr (WIAS-ESH)
Seminar Nichtlineare Optimierung und Inverse Probleme
Prof. Dr. M. Yamamoto, University of Tokyo, Japan:
Inverse problems for an integro-hyperbolic equation for the viscoelasticity
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Dienstag, 25.04.2017, 15.00 Uhr (WIAS-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
N. Zhivotovskiy, IITP RAS, SkolTech:
Towards minimax optimal rates in classification and regression
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstrakt
In this talk, we consider two approaches that allow (in some cases) to obtain minimax rates of the prediction risk up to absolute constants. Classification problems will be considered under small noise conditions for an arbitrary distribution of objects, as well as cases of certain special distributions. In contrast to several standard results in the learning theory, our bounds are simultaneously optimal for entire families of classes.

Veranstalter
WIAS Berlin
Dienstag, 25.04.2017, 15.15 Uhr (WIAS-ESH)
Oberseminar Nonlinear Dynamics
J. Pimentel, Universidade Federal do ABC:
Permutation characterization for slowly non-dissipative equations
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
We study the longtime behavior of slowly non-dissipative scalar reaction-diffusion equations. By extending known results, we are able to obtain a complete decomposition of the non-compact global attractor and still manage to determine the heteroclinic connections based on the Sturm permutation method.

Veranstalter
Freie Universität Berlin
WIAS Berlin
Mittwoch, 26.04.2017, 10.00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Statistik
J. Weed, Massachusetts Institute of Technology, USA:
Optimal rates of estimation for the multi-reference alignment problem
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
How should one estimate a signal, given only access to noisy versions of the signal corrupted by unknown circular shifts? This simple problem has surprisingly broad applications, in fields from structural biology to aircraft radar imaging. We describe how this model can be viewed as a multivariate Gaussian mixture model whose centers belong to an orbit of a group of orthogonal transformations. This enables us to derive matching lower and upper bounds for the optimal rate of statistical estimation for the underlying signal.. These bounds show a striking dependence on the signal-to-noise ratio of the problem. Joint work with Afonso Bandeira and Philippe Rigollet.

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Forschungsseminar ``Mathematische Statistik''

Veranstalter
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
International Research Training Group 1792
Mittwoch, 26.04.2017, 15.15 Uhr (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. D. Peschka, WIAS Berlin:
Motion of thin droplets over surfaces - Numerical and modeling techniques for moving contact lines
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, 26.04.2017, 18.15 Uhr (WIAS-ESH)
Berliner Kolloquium Wahrscheinlichkeitstheorie/Berlin Young Probabilists' Seminar
Prof. Dr. A. Pilipenko, Ukrainian National Academy of Sciences, Ukraine:
On a selection problem for small noise perturbation of ODE in multidimensional case
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
The identification problem of the limit of an ODE with non-Lipschitz drift perturbed by a zero-noise is considered in a multidimensional framework. This problem is a classical subject of stochastic analysis, however the multidimensional case was poorly investigated. We consider two cases in particular:
(i) the drift coefficient has a jump discontinuity along an hyperplane and is Lipschitz continuous in the upper and lower half-spaces;
(ii) the drift is equivalent to a(phi) $r^alpha$ as $r$ tends to $0$, where (r,phi) are the polar coordinates, and alpha$<1$.

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Berliner Kolloquium Wahrscheinlichkeitstheorie

Veranstalter
Humboldt-Universität zu Berlin
Technische Universität Berlin
Universität Potsdam
WIAS Berlin
Donnerstag, 27.04.2017, 10.00 Uhr (WIAS-ESH)
Seminar Laserdynamik
S. W. Haugland, Technische Universität München:
What can we learn about chimera states from minimal cluster dynamics?
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Weitere Informationen
Seminar Laserdynamik

Veranstalter
WIAS Berlin