Veranstaltungen

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Dienstag, 18.06.2019, 13:30 Uhr (WIAS-406)
Seminar Materialmodellierung
Prof. A. Acharya, Carnegie Mellon University, USA:
Line defect dynamics and solid mechanics
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstrakt
Continuum mechanics has been a successful model for studying macroscopic deformations and the forces causing them. The usual framework allows the study of continuous deformations giving way to surfaces of discontinuity, but does not provide an adequate framework for considering the dynamics of the terminating lines of surfaces of discontinuity, were such to occur. It turns out that such terminating lines of surfaces of discontinuity serve as a model of common line defects that arise in a host of materials; dislocations and grain/phase boundary junctions in crystalline and soft matter. I will describe a framework for considering line defect dynamics within continuum mechanics. I will show how the kinematics of line defect dynamics provides a unifying theme for describing the defects mentioned above, resulting in an augmentation of the classical balance laws of continuum mechanics with a microscopic conservation law for topological charge carried by these defect lines. The theory will be illustrated with examples related to dislocation dynamics with inertia, the computation of fields of interfacial defects like the star disclination and grain boundary disconnections.

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Seminar Materialmodellierung

Veranstalter
WIAS Berlin
Dienstag, 18.06.2019, 15:00 Uhr (WIAS-405-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Priv.-Doz. Dr. P. Mathë, WIAS Berlin:
The modulus of continuity in Bayesian inverse problems
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstrakt
We shall discuss how the convergence rates of direct and inverse problems are related through the modulus of continuity.

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Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics

Veranstalter
WIAS Berlin
Mittwoch, 19.06.2019, 10:00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Dr. H. Hron, Palacký University, Olomouc, Czech Republic:
Weighting of densities in Bayes spaces with application to simplicial functional principal component analysis
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Probability density functions (PDFs) can be understood as functional data carrying relative information. As such, standard methods of functional data analysis (FDA) are not appropriate for their statistical processing. They are typically designed in the L2 space (with Lebesgue reference measure), thus cannot be directly applied to densities, as the metrics of L2 does not honor their geometric properties. This has recently motivated the construction of the so-called Bayes Hilbert spaces, which result from the generalization of the Aitchison geometry for compositional data to the in nite dimensional setting. More precisely, if we focus on PDFs restricted to a bounded support (that is mostly used in practical applications), they can be represented with respect to the Lebesgue reference measure using the Bayes space of positive real functions with square-integrable logarithm. The reference measure can be easily changed through the well-known chain rule and interpreted as a weighting technique in Bayes spaces. Moreover, it impacts on the geometry of the Bayes spaces and results in so-called weighted Bayes spaces. The aim of this contribution is to show the e ects of changing the reference measure from the Lebesgue measure to a general probability measure focusing on its practical implications for the Simplicial Functional Principal Component Analysis (SFPCA). A centered log-ratio transformation is proposed to map a weighted Bayes spaces into an unweighted L2 space (i.e. with Lebesgue reference measure), thus it enables to apply standard statistical methods such as SFPCA on PDFs.

Veranstalter
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Mittwoch, 19.06.2019, 15:15 Uhr (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. J. Ginster, Technische Universität Berlin:
Plasticity as the Γ-limit of models for straight, parallel dislocations
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Crystal plasticity is the effect of a crystal undergoing a permanent change of shape in response to applied forces. At the atomic scale, dislocations - local defects of the crystalline lattice concentrated on lines - are considered to play a main role in this effect. In this talk, we will derive a macroscopic strain-gradient plasticity theory from two different semi-discrete models for straight, parallel edge dislocations. Firstly, we complement the existing literature by considering a rotationally invariant energy with mixed growth. The main advantage of this formulation is that it does not need the ad-hoc definition of a core-radius. In addition to the Γ-convergence result we present a rigidity result for fields with non-vanishing curl in this setting. Secondly, we will address the fact that most results in the literature are derived under the assumption that the present dislocations are separated on a mesoscopic scale. We will show how to overcome this assumption by an adaption of the ball construction technique which was developed in the context of the Ginzburg--Landau model for superconductivity.

Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
24. – 26. Juni 2019 (WIAS-ESH)
Workshop/Konferenz: Workshop on Phase Transitions and Particle Systems
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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
Donnerstag, 27.06.2019, 16:00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
J.-P. Koester, Ferdinand-Braun-Institut, Berlin:
Traveling wave model based simulation of tunable multi-wavelength diode laser and MOPA systems
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

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.

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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