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Tuesday, 23.10.2018, 10:15 (WIAS-406)
Seminar Nichtlineare Optimierung und Inverse Probleme
Dr. D. Tiba, Romanian Academy, Bucharest:
Optimal control methods in shape optimization
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Host
WIAS Berlin
Tuesday, 23.10.2018, 15:00 (WIAS-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Dr. A. Naumov, National Research University Higher School of Economics, Russische Föderation:
Gaussian approximations for maxima of large number of quadratic forms of high-dimensional random vectors
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Further Informations
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics

Host
WIAS Berlin
Wednesday, 24.10.2018, 10:00 (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Dr. E. Stepanov, Russian Academy of Sciences, Russische Föderation:
Hybrid control in a model from molecular biology: Between continuous and discrete
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The central argument of the talk will be the rather modern concept in automated control: Hybrid controls through finite state machines in continuous dynamical models. It will be shown that hybrid systems present a highly complicated dynamics. Then a class of largely open problems arizing from molecular biology will be presented and studied, where the hybrid system comes out from a extra- ordinarily simple and completely classical models based on ODEs without any discrete object incorporated.

Further Informations
Forschungsseminar “Mathematische Statistik”

Host
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Wednesday, 24.10.2018, 14:00 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. P. Colli, Università di Pavia, Italien:
Shape memory alloys, phase-field models, Cahn--Hilliard systems
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The title collects some special keywords for research fields in the framework of phase transitions and free boundary problems describing an important research area receiving attention, interest, and a number of significant contributions from Jürgen Sprekels. This talk will offer the speaker the possibility of reviewing some models, problems, and results in the analysis and optimal control of the related systems of partial differential equations. And, more than that, it will be a pleasure for him to recall some thirty years enjoying math by his collaboration with J. Sprekels.

Host
WIAS Berlin
Wednesday, 24.10.2018, 15:00 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. D. Tiba, Romanian Academy, Bucharest:
Implicit parametrizations and applications in optimization and control
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The talk will discuss necessary conditions (with less Lagrange multipliers), perturbations and general algorithms in non-convex optimization problems. Optimal control problems with mixed constraints, governed by ordinary differential equations, will also be studied in this context. The treatment is based on a recent approach to implicit systems, constructing parametrizations of the corresponding manifold, via iterated Hamiltonian equations.

Host
WIAS Berlin
Thursday, 25.10.2018, 11:30 (WIAS-406)
Seminar Interacting Random Systems
A. Agazzi, Duke University, USA:
Large deviations and recurrence for chemical reaction networks
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
The microscopic dynamics of well-stirred networks of chemical reactions are modeled as jump Markov processes. At large volume, one may expect in this framework to have a straightforward application of large deviation theory. This is not at all true, for the jump rates are typically neither globally Lipschitz, nor bounded away from zero, with both blowup and absorption as quite possible scenarios. In joint work with Amir Dembo and Jean-Pierre Eckmann, we utilize Lyapunov stability theory to bypass this challenges and to characterize a large class of network topologies that satisfy the full Wentzell-Freidlin theory of asymptotic rates of exit from domains of attraction. The extension of such results to the estimation of transitions times between metastable states further requires the positive recurrence of such processes. This property depends critically on dynamics at of the jump Process when the concentration of some of the components are small. Precise statements on the connection between this property and the structure of the underlying network are an active area of research.

Further Informations
Seminar Interacting Random Systems

Host
WIAS Berlin
Wednesday, 07.11.2018, 11:30 (WIAS-406)
Seminar Interacting Random Systems
A. Tóbiás, Technische Universität Berlin:
Signal to interference ratio percolation for Cox point processes
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
We study signal-to-interference plus noise ratio (SINR) percolation for Cox point processes, i.e., Poisson point processes with a random intensity measure. SINR percolation was first studied by O. Dousse et al. in the case of a two-dimensional Poisson point process. It is a version of continuum percolation where the connection between two points depends on the locations of all points of the point process. Continuum percolation for Cox point processes was recently studied by C. Hirsch, B. Jahnel and E. Cali. We study the SINR graph model for a stationary Cox point process in two or higher dimensions. We show that under suitable moment or boundedness conditions on the path-loss function and the intensity measure, this graph has an infinite connected component if the spatial density of points is large enough and the interferences are sufficiently reduced (without vanishing). This holds in all dimensions larger than 1 if the intensity measure is asymptotically essentially connected, and in two dimensions also if the intensity measure is only stabilizing but the connection radius is large. A prominent example of the intensity measure is the two-dimensional Poisson--Voronoi tessellation. We show that its total edge length in a given square has some exponential moments. We conclude that its SINR graph has an infinite cluster if the path-loss function is bounded and has a power-law decay of exponent at least 3.

Further Informations
Forschungsgruppenseminar Interacting Random System

Host
WIAS Berlin
Thursday, 15.11.2018, 10:00 (WIAS-ESH)
Seminar Laserdynamik
Dr. G. Slekas, Vilnius Gediminas Technical University, Lithuania:
Solution of Boltzmann transport equation for photo-excited electrons in semiconductor with strong electric field
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Photoconductive terahertz antennas based on a low temperature grown gallium arsenide are one of the most popular and most promising terahertz wave generators developed so far. The operation of such antennas is based on relaxation of photo-excited electrons in high electric field. Electrons excited to the conductivity band of semiconductor are moving towards antennas contacts producing electric current, which induces terahertz pulse. Whereas the electron recombination time is less than picosecond, the dynamics of electrons is highly non-linear. Drift-diffusion model is the simplest non-trivial carrier transport model which is derived as the zeroth order moment of Boltzmann transport equation. For many decades it has been used as a basic tool for simulation of semiconductor devices. However, non-linear effects, such as electron velocity overshoot, are not described by drift-diffusion equations, so higher order transport models are used to include this effect into calculations. On the one hand, higher order models still require a lot of fine-tuning and a detailed understanding of the underlying physical phenomena. On the other hand, they are still not adapted to the case when initial distribution of electrons is far from thermal equilibrium, which is true in the latter case. Monte Carlo simulation is the golden tool for solution of Boltzmann equation. However this method is very computationally expensive, so it is not very reasonable for optimization problems.

Host
WIAS Berlin
Wednesday, 12.12.2018, 15:15 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. J. Rehberg, WIAS Berlin:
L bounds for the Neumann problem
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

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

Host
WIAS Berlin
Humboldt-Universität zu Berlin