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Thursday, 28.05.2015, 14.00 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Dr. P. A. Zegeling, Utrecht University:
Adaptive grids for detecting non-monotone waves and instabilities in a non-equilibrium PDE model from porous media
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Space-time evolution described by nonlinear PDE models involves patterns and qualitative changes induced by parameters. In this talk I will emphasize the importance of both the analysis and computation in relation to a bifurcation problem in a non-equilibrium Richard's equation from hydrology. The extension of this PDE model for the water saturation $S$ to take into account additional dynamic memory effects was suggested by Hassanizadeh and Gray in the 90's. This gives rise to an extra emphthird-order mixed space-time derivative term in the PDE of the form $tau   nabla cdot [T(S) nabla (S_t)]$. In one space dimension traveling wave analysis is able to predict the formation of steep non-monotone waves depending on $tau$. In 2D, the parameters $tau$ and the frequency $omega$ included in a small perturbation term, predict that the waves may become emphunstable, thereby initiating so-called gravity-driven fingering structures. This phenomenon can be analysed with a linear stability analysis and its effects are supported by the numerical experiments of the 2D time-dependent PDE model. For this purpose, we have used a sophisticated adaptive grid r-refinement technique based on a recently developed monitor function. The numerical experiments in one and two space dimension show the effectiveness of the adaptive grid solver.

Host
WIAS Berlin
Thursday, 28.05.2015, 16.00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
Prof. D. Turaev, Imperial College London, UK:
Chaotic dynamics in nonholonomic systems
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
Thursday, 28.05.2015, 16.15 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
Prof. D. Turaev, Imperial College London, UK:
Chaotic dynamics in nonholonomic systems
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Tuesday, 02.06.2015, 15.00 Uhr (WIAS-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Dr. P. Dvurechenski, WIAS Berlin:
Random gradient-free methods for web page ranking model learning
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
We consider a model of web-pages ranking which is based on a Markov Chain. Ranking vector is defined as a stationary distribution of this MC. Transition probabilities are defined by pages and links features (e.g. number of clicks, time spent on a page) and some unknown parameter vector. The goal is to find this parameter vector such that the model-based ranking vector is in a good consistence with relevance to the queries defined by experts. The problem is formulated as an optimization one which is solved by bilevel algorithm. The inner one calculates approximation for the ranking vector. The outer one is a random gradient-free method with inexact oracle.

Host
WIAS Berlin
Wednesday, 03.06.2015, 15.15 Uhr (WIAS-ESH)
BERLINER OBERSEMINAR Nichtlineare partielle Differentialgleichungen (Langenbach-Seminar)
Dr. S. Patrizi, WIAS Berlin:
Dislocations dynamics: From microscopic models to macroscopic crystal plasticity
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
hier

Host
WIAS Berlin
Humboldt-Universität zu Berlin
June 4 – 6, 2015 (Heilig-Geist-Kapelle)
Workshop/Konferenz: Structured Nonparametric Modeling
more ... Location
Humboldt-Universität zu Berlin, Wirtschaftswissenschaftliche Fakultät, Spandauer Str. 1, 10178 Berlin

Host
WIAS Berlin
SFB 649: Ökonomisches Risiko
International Research Training Group 1792
DFG Research Unit 1735
Wednesday, 10.06.2015, 10.00 Uhr (WIAS-HVP-4.13)
Forschungsseminar Mathematische Statistik
PhD A. Gasnikov, MIPT, Moscow, Russia:
On optimization aspects of finding Wasserstain(-Kantorovich) barycenter
more ... Location
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 4. Etage, Raum: 4.13

Abstract
In the talk we'll discuss recent works by Marco Cuturi (Kyoto Univ.) et al. devoted to the fast algorithm of computation of Wasserstain barycenter (Wb). In our approach we try to reduce a problem to another high dimensional convex optimization problem . The idea is to freeze the measures support by allowing the cardinalities of the support sets to be large enough. Then we have to solve a sadle-point convex-concave optimization problem (Cuturi et al. considered this problem to be nonsmooth convex optimization problem). We propose new different numerical approaches to solve this problem. 1. We generalize the approach by Cuturi and obtain a sharp bound on the rate of convergence. We have to solve a inner linear programming problem or entropy-linear problem. We have to propose optimal primal-dual methods for these problems and we need to choose optimal relation between the precision of solution for the inner problem and the precision of solution of the whole problem. Since we can't obtain the exact solution of the inner problem we have to properly choose the method for external problem which have the ability to work with inexact oracle. Here we used recent results by Dvurechensky-Gasnikov arXiv:1411.2876, Gasnikov-Dvurechensky-Nesterov arXiv:1411.4218 and Gasnikov-Nesterov et al. arXiv:1410.7719 2. We propose randomized (mirror descent) and non-randomized (mirror-prox) approaches for sadle-point problem which go back to the recent works of Nemirovski-Juditsky http://www2.isye.gatech.edu/ nemirovs/. 3. We propose randomized approaches based on the randomization of functional which has the form of a sum of large number of functions (see Agarwal-Bouttou arXiv:1410.0723v2 and references therein). This context is interesting in case when we have to find a Wb of huge number of empirical measures.

Further Informations
Forschungsseminar ``Mathematische Statistik''

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Universität Potsdam
Wednesday, 10.06.2015, 15.15 Uhr (WIAS-405-406)
BERLINER OBERSEMINAR Nichtlineare partielle Differentialgleichungen (Langenbach-Seminar)
Dr. B. Seguin, University of Dundee, UK:
Plant cell wall biomechanics: Model and multiscale analysis
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstract
hier

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

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Thursday, 11.06.2015, 14.00 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Prof. J. Novo, Universidad Autónoma de Madrid, Spain:
Local error estimates for the SUPG method applied to evolutionary convection-reaction-diffusion equations
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Local error estimates for the SUPG method applied to evolutionary convection-reaction-diffusion equations are considered. The steady case is reviewed and local error bounds are obtained for general order finite element methods. For the evolutionary problem, local bounds are obtained when the SUPG method is combined with the backward Euler scheme. The arguments used in the proof lead to estimates for the stabilization parameter that depend on the length on the time step. The numerical experiments show that local bounds seem to hold true both with a stabilization parameter depending only on the spatial mesh grid and with other time integrators.

Host
WIAS Berlin
Thursday, 11.06.2015, 16.15 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
Dr. M. Radziunas, WIAS Berlin:
Computation and analysis of longitudinal optical modes in multisection ring and edge emitting semiconductor lasers
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Tuesday, 16.06.2015, 10.15 Uhr (WIAS-406)
Seminar Nichtlineare Optimierung und Inverse Probleme
Dr. E. Klann, Technische Universität Berlin:
Geometric inverse problems with applications in tomography
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
In inverse problems one wants to find unknown parameters or structures by indirect measurements. Typical inverse problems occur in medical imaging, e.g., tomography. The task is to find the inner structure of an object, e.g., a human torso, from line integrals of some form of radiation that travelled through the object. In geometric inverse problems one wants to recover this inner structure also in terms of geometric information, i.e., the number of different interior objects (bone, liver, lung, etc.), their location and their shape. We present a Mumford-Shah type functional for the simultaneous reconstruction and segmentation of an object from tomography data. The minimization of the functional is realized using shape sensitivity analysis and carried out in the level-set framework. We show reconstructions and/or segmentations for several tomographic applications (SPECT/CT, limited angle tomography, region of interest CT).

Host
WIAS Berlin
Tuesday, 16.06.2015, 13.30 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Prof. S. K. Ganesan, Indian Institute of Science:
Finite element algorithms for massively parallel architectures
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Parallel algorithms with hybrid MPI and OpenMP implementations for a geometric multigrid solver in a nite element scheme will be presented in this talk. In particular, the mesh partitioning, the nite element mappers and communicators on a hierarchy of multigrid mesh will be discussed. Further, a multicolor strategy in the smoothing steps of the multigrid solver, parallel restrictions and prolongations using halo cells will be discussed.

Host
WIAS Berlin
Wednesday, 17.06.2015, 15.15 Uhr (WIAS-ESH)
BERLINER OBERSEMINAR Nichtlineare partielle Differentialgleichungen (Langenbach-Seminar)
Prof. Dr. V. Zagrebnov, Université d'Aix-Marseille, France:
Dynamical semigroups for unbounded repeated harmonic perturbation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
hier

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

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Thursday, 18.06.2015, 10.00 Uhr (WIAS-406)
Seminar Materialmodellierung
Dr. G. Li, Cambridge University, UK:
Microscopic effects on Brownian coagulation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Host
WIAS Berlin
Thursday, 18.06.2015, 16.15 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
Dr. W. Lewoczko-Adamczyk, Ferdinand-Braun-Institut Berlin:
Development and characteristics of narrow-linewidth semiconductor lasers with optical feedback
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Tuesday, 23.06.2015, 10.15 Uhr (WIAS-406)
Seminar Nichtlineare Optimierung und Inverse Probleme
Prof. Dr. H. Gottschalk, Bergische Universität Wuppertal:
Probabilistic failure mechanisms in fatigue life and optimal reliability via shape control
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
Mechanical components fail under cyclic loading due to fatigue of the materials. This process is highly stochastic as the time to the formation of mesoscopic cracks is subject to a statistical scatter of one order of magniture in lab experiments. In this talk, the probabilistic crack formation is modeled by spatio-temporal point processes with intensity depending locally on the mechanical load situation. This allows to compute failure probabilities at a given number of load cycles. A survey is given about experimental calibration and validation of these models, numerical implementation and their applications to gas turbine design. In mechanical design, reliability is one of the main design objectives. The mathematical quest thus is to find a shape for the component such that the failure probability is minimized. This optimization task can be understood as an optimal control problem with the elasticity PDE as the state equation and the boundary of the shape as control parameter. A proof for the existence of optimal shapes within certain regularity classes of the boundary is given using strong solutions and uniform Schauder estimates.

Host
WIAS Berlin
Wednesday, 24.06.2015, 15.15 Uhr (WIAS-ESH)
BERLINER OBERSEMINAR Nichtlineare partielle Differentialgleichungen (Langenbach-Seminar)
Dr. C. Rautenberg, Humboldt-Universität zu Berlin:
Analysis and approximation of evolutionary quasi-variational inequalities
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
hier

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

Host
WIAS Berlin
Humboldt-Universität zu Berlin
September 17 – 18, 2015 (WIAS-ESH)
Workshop/Konferenz: Workshop on Recent Developments in Inverse Problems
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
October 12 – 14, 2015 (WIAS-ESH)
Workshop/Konferenz: Waves, Solitons and Turbulence in Optical Systems (WASTOS15)
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
November 30 – December 4, 2015 (WIAS-ESH)
Workshop/Konferenz: PDE2015
Theory and Applications of Partial Differential Equations

more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
Universität Kassel
December 16 – 18, 2015 (WIAS-ESH)
Workshop/Konferenz: Stochastic Limit Analysis for Reacting Particle Systems
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
February 22 – 26, 2016 (WIAS-ESH)
Workshop/Konferenz: ERC Workshop "Modeling Materials and Fluids using Variational Methods''
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin