Upcoming Events

Due to infection prevention measures, participation in events at the institute is presently not possible for guests.

Many events are currently organized online. Information on how to access these events can be found by clicking “more” below the respective entry.


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Wednesday, 25.11.2020, 10:00 (Online Event)
Forschungsseminar Mathematische Statistik
Dr. Alexander Kreiß, KU Leuven:
Unbiased Markov chain Monte Carlo methods with couplings
more ... Location
Online Event

Abstract
We will consider multivariate stochastic processes indexed either by vertices or pairs of vertices of a dynamic network. Under a dynamic network we understand a network with a fixed vertex set and an edge set which changes randomly over time. We will assume that the spatial dependence-structure of the processes conditional on the network behaves in the following way: Close vertices (or pairs of vertices) are dependent, while we assume that the dependence decreases conditionally on that the distance in the network increases. We make this intuition mathematically precise by considering three concepts based on correlation, beta-mixing with time-varying beta-coefficients and conditional independence. These concepts allow proving weak-dependence results, e.g. an exponential inequality. These results will be useful for studying asymptotic regimes in which the network grows (i.e. the number of vertices tends to infinity) and we can expect that a growing network results in a larger distance between most vertices. Since the network is dynamic we allow that vertices move around the network and come close to different vertices. In order to demonstrate the use of these concepts in an application we study the asymptotics (for growing networks) of a goodness of fit test in a dynamic interaction network model based on a Cox-type model for counting processes. This model is then applied to bike-sharing data.

Further Informations
Der Vortrag findet bei Zoom statt: https://zoom.us/j/159082384

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Wednesday, 25.11.2020, 11:30 (Online Event)
Seminar Interacting Random Systems
Willem van Zuijlen:
Total mass asymptotics of the parabolic Anderson model
more ... Location
Online Event

Abstract
We consider the parabolic Anderson model with a white noise potential in two dimensions. This model is also called the stochastic heat equation with a multiplicative noise. We study the large time asymptotics of the total mass of the solution. Due to the irregularity of the white noise, in two dimensions the equation is a priori not well-posed. Using paracontrolled calculus or regularity structures one can make sense of the equation by a renormalisation, which can be thought of as “subtracting infinity of the potential”. To obtain the asymptotics of the total mass we use the spectral decomposition, an alternative Feynman-Kac type representation and heat-kernel estimates which come from joint works with Khalil Chouk, Wolfgang König and Nicolas Perkowski.

Further Informations
Seminar Interacting Random Systems

Host
WIAS Berlin
Wednesday, 25.11.2020, 15:15 (Online Event)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Annika Bach, Technische Universität München:
Geometrically frustrated spin systems: The antiferromagnetic XY model on the triangular lattice (online talk)
more ... Location
Online Event

Abstract
Antiferromagnetic spin systems are magnetic lattice systems in which the exchange interaction between two spins (i.e., vectors in S1) favors anti-alignment. Such systems are said to be geometrically frustrated if, due to the geometry of the lattice, there is no orientation of spins that simultaneously minimizes all pairwise interactions. This is the case for the antiferromagnetic XY model on the two-dimensional triangular lattice. As a consequence, the system has two families of ground states which can be distinguished one from the other by what is called their chirality. In this talk we present a recent result obtained in collaboration with M. Cicales, L. Kreutz, and G. Orlando, where we characterise the discrete-to-continuum Gamma-limit of the XY-model energy in a regime which detects chirality transitions on one-dimensional interfaces between the two admissible chirality phases.

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Thursday, 26.11.2020, 15:00 (Online Event)
TES-Seminar on Energy-based Mathematical Methods and Thermodynamics
Prof. Dr. Miroslav Grmela, Polytechnique Montréal:
Multiscale thermodynamics (online talk)
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Online Event

Abstract
Multiscale thermodynamics is a theory of relations among levels of investigation of complex systems. It includes the classical equilibrium thermodynamics as a special case but it is applicable to both static and time evolving processes in externally and internally driven macroscopic systems that are far from equilibrium and are investigated on microscopic, mesoscopic, and macroscopic levels. In this talk we formulate the multiscale thermodynamics, explain its origin, and illustrate it in mesoscopic dynamics that combines levels, see [1] for more details. [1] M. Grmela: Multiscale Thermodynamics. arxiv-preprint 2020.

Further Informations
Please register on this link: https://mathplus.de/topic-development-lab/tes-winter-2020-21/tes-seminar-on-energy-based-mathematical-methods-and-thermodynamics/

Host
Technische Universität Berlin
WIAS Berlin
Thursday, 26.11.2020, 16:00 (Online Event)
Forschungsseminar Mathematische Modelle der Photonik
Regina Finsterhölzl, TU Berlin:
Applying feedback control on quantum many-body systems within the matrix-product-state framework
more ... Location
Online Event

Host
WIAS Berlin
Tuesday, 01.12.2020, 15:00 (Online Event)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Roman Kravchenko, Humboldt-Universität zu Berlin:
Distributed optimization with quantization for computing Wasserstein barycenters
more ... Location
Online Event

Further Informations
Dieser Vortrag findet bei Zoom statt: https://zoom.us/j/492088715

Host
WIAS Berlin
December 2 – 3, 2020 (Online Event)
Workshop/Konferenz: ECMI Webinar “Math for Industry 4.0 - Models, Methods and Big Data”
more ... Location
Online Event

Host
WIAS Berlin
Wednesday, 02.12.2020, 10:00 (Online Event)
Forschungsseminar Mathematische Statistik
Dr. Yegor Klochkov, University of Cambridge, UK:
Robust K-means clustering under two moments
more ... Location
Online Event

Abstract
We consider the robust algorithms for the k-means clustering problem where a quantizer is constructed based on N independent observations. Our main results are median of means based non-asymptotic excess distortion bounds that hold under the two bounded moments assumption in a general separable Hilbert space. In particular, our results extend the renowned asymptotic result of Pollard(1981) who showed that the existence of two moments is sufficient for strong consistency of an empirically optimal quantizer in R^d. In a special case of clustering in R^d, under two bounded moments, we prove matching (up to constant factors) non-asymptotic upper and lower bounds on the excess distortion, which depend on the probability mass of the lightest cluster of an optimal quantizer. Our bounds have the sub-Gaussian form, and the proofs are based on the versions of uniform bounds for robust mean estimators. This is joint work with Alexei Kroshnin and Nikita Zhivotovskiy.

Further Informations
Der Vortrag findet bei Zoom statt: https://zoom.us/j/159082384

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Tuesday, 08.12.2020, 15:00 (Online Event)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Dr. Pavel Dvurechensky, WIAS Berlin:
Accelerated alternating minimization methods
more ... Location
Online Event

Abstract
We combine alternating minimization (AM) and Nesterov-type momentum acceleration and propose a generic accelerated alternating minimization method with a $1/k^2$ convergence rate in terms of the objective for convex problems and $1/k$ in terms of the squared gradient norm for non-convex problems, where $k$ is the iteration counter. Our method does not require any knowledge of neither convexity of the problem nor function parameters such as smoothness constant, i.e. it is adaptive to convexity and smoothness. Further, we develop its primal-dual modification for convex problems with linear constraints. We consider two applications of our methods to highlight their properties. The first one is the non-convex collaborative filtering problem, and the second one is optimal transport, where our primal-dual method takes a form of accelerated Sinkhorn's algorithm or accelerated Iterative Bregman Projections algorithm. In both applications, we show numerically that our methods outperform the baselines. In the second application, we also obtain state-of-the-art complexity results for optimal transport problems.

Further Informations
Dieser Vortrag findet bei Zoom statt: https://zoom.us/j/492088715

Host
WIAS Berlin
Wednesday, 09.12.2020, 11:30 (Online Event)
Seminar Interacting Random Systems
Robert Patterson:
tba
more ... Location
Online Event

Further Informations
Seminar Interacting Random Systems

Host
WIAS Berlin
Wednesday, 09.12.2020, 15:15 (Online Event)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Grigor Nika, WIAS Berlin:
Effective bulk-surface thermistor models for OLEDs (online talk)
more ... Location
Online Event

Abstract
We consider a thin-film OLED device placed on a flat surface, part of a bulk substrate material. The device is assumed to have N>2 layers and total thickness h>0. An effective electrothermal model is derived by considering the limit of vanishing thickness as it approaches zero under physically motivated scalings. The effective equations consist of two equations for the lateral current flow in the top and bottom electrodes and an iterative set of algebraic equations for the vertical flow in the organic layers posed on the flat surface where the OLED is placed and coupled to the heat equation in the bulk substrate material.

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

Host
WIAS Berlin
Thursday, 10.12.2020, 15:00 (Online Event)
TES-Seminar on Energy-based Mathematical Methods and Thermodynamics
Dr. Martin Kružík, Czech Academy of Sciences:
Equilibrium for multiphase solids with Eulerian interfaces (online talk)
more ... Location
Online Event

Abstract
We describe a general phase-field model for hyperelastic multiphase materials. The model features an elastic energy functional that depends on the phase-field variable and a surface energy term that depends in turn on the elastic deformation, as it measures interfaces in the deformed configuration. We prove the existence of energy minimizing equilibrium states and Gamma-convergence of diffuse-interface approximations to the sharp-interface limit. This is a joint work with D. Grandi, E. Mainini and U. Stefanelli.

Further Informations
Please register on this link: https://mathplus.de/topic-development-lab/tes-winter-2020-21/tes-seminar-on-energy-based-mathematical-methods-and-thermodynamics/

Host
Technische Universität Berlin
WIAS Berlin
Wednesday, 13.01.2021, 11:30 (Online Event)
Seminar Interacting Random Systems
Sabine Jansen, Universität München, null:
tba (online talk)
more ... Location
Online Event

Further Informations
Seminar Interacting Random Systems

Host
WIAS Berlin