# Upcoming Events

- 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