Upcoming Events

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January 28 – 30, 2020 (WIAS-ESH)
Workshop/Konferenz: Workshop on PDE Constrained Optimization under Uncertainty and Mean Field Games
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
Wednesday, 29.01.2020, 10:00 (WIAS-405-406)
Forschungsseminar Mathematische Statistik
Nadja Klein, Humboldt-Universität zu Berlin:
Bayesian regression copulas
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Host
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Monday, 03.02.2020, 14:00 (WIAS-ESH)
INSTITUTSKOLLOQUIUM
Prof. Dr.-Ing. Georg Duda, Charité Berlin, Julius Wolff Institute for Biomechanics and Musculoskeletal Regeneration:
From Mechanical Forces to Tissue Straining - How to Employ Biophysical Cues to Guide Regeneration
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Conceptually, our research aims at understanding endogenous cascades of tissue formation, cytokine signaling and cellular self-organization especially in bone. Mechanical straining and adaptation due to mechanical cues plays a central role in all these tissues. The aim of our work is to understand the mechano-biological cues of regeneration and adaptation and how they can be employed to enable healing even in tissues with impaired regenerative capacity such as muscle, cartilage or tendon. All approaches are motivated by clinical challenges, are based on in vivo patient measurements, employ basic research principles and aim at being translated into daily clinical routine. Examples of translation include innovative concepts for joint replacement procedures, angle stable fixation of implants or cell therapies for immune-modulation to empower tissue regeneration.

Host
WIAS Berlin
Wednesday, 05.02.2020, 10:00 (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Prof. Tim Sullivan, Freie Universität Berlin:
A rigorous theory of conditional mean embeddings
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Conditional mean embeddings (CME) have proven themselves to be a powerful tool in many machine learning applications. They allow the efficient conditioning of probability distributions within the corresponding reproducing kernel Hilbert spaces (RKHSs) by providing a linear-algebraic relation for the kernel mean embeddings of the respective probability distributions. Both centered and uncentered covariance operators have been used to define CMEs in the existing literature. In this talk, we develop a mathematically rigorous theory for both variants, discuss the merits and problems of either, and significantly weaken the conditions for applicability of CMEs. In the course of this, we demonstrate a beautiful connection to Gaussian conditioning in Hilbert spaces.

Host
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Wednesday, 05.02.2020, 11:30 (WIAS-406)
Seminar Interacting Random Systems
Richard Pymar, Birkbeck University of London:
Mixing times of exclusion processes on regular graphs
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
Place k black particles and n-k white particles on the vertices of an n vertex graph, with one per vertex. Suppose each edge rings at rate 1 independently, and when an edge rings particles at the end-points switch positions. Oliveira conjectured that this "k-particle exclusion process" has mixing time of order at most that of k independent particles. Together with Jonathan Hermon we prove a bound for regular graphs which is in general within a log log n factor from this conjecture when k>n^c and which, in certain cases, verifies the conjecture. As a result we obtain new mixing time bounds for the exclusion process on expanders and the hypercube.

Further Informations
Seminar Interacting Random Systems

Host
WIAS Berlin
Wednesday, 05.02.2020, 15:15 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Riccardo Cristoferi, Heriot-Watt University:
Epitaxial crystal growth with adatoms
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Surface diffusion is one of the most important mechanisms driving crystal growth. When bulk diffusion is much faster than the surface one, the evolution of the profile of the crystal is described by the so called Einstein--Nernst relation. According to this law, the normal velocity of the profile is related to the chemical potential. This evolution equation has a variational flavor, in that it can be obtained as a gradient flow of a suitable free energy. Albeit usually neglected, adatoms (atoms freely diffusing on the surface of the crystal) seem to play a fundamental role in the description of the behaviour of a solid-vapor interfaces. For this reason, some years ago Fried and Gurtin introduced a system of evolution equations to describe such a situation, where adatoms are treated as a separate variable of the problem. Also such system of evolution equations can be seen as the gradient flow of an energy. In this talk a first step in the programme of studying the above mentioned evolution equations from a variational point of view is presented. In particular, the focus is on the static problem in the small mass regime, where the elastic energy is negligible. Ground states, effective energy, and phase filed approximation suitable for numerical purposes are discussed. This latter is embedded in a general framework that allows to treat similar problems for a large class of functionals. The talk is based on works in collaboration with Marco Caroccia (Roma Tor Vergata), and Laurent Dietrich (Lycée Fabert).

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Thursday, 06.02.2020, 14:00 (WIAS-ESH)
Seminar Numerische Mathematik
Dr. Holger Stephan, WIAS Berlin:
A general concept of majorization and a corresponding Robin Hood method
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The Robin Hood method is a numerical method for constructing a double-stochastic matrix that maps a given vector to another vector that is also given. This is possible if the preimage majorizes the image. The majorization of vectors is a special order sometimes called the Lorentz order. A double-stochastic matrix is a special case of a Markov (or stochastic) matrix. In the case of a general Markov matrix, it is not yet clear when such a construction is possible, what kind of condition similar to the majorization must be fulfilled by the given vectors, nor is a numerical method for determining the matrix known (regardless some heuristic iterative versions of the Robin-Hood method).
In the talk, we give a complete solution to all these problems, including a general direct Robin Hood method. It turns out that the construction of a Markov matrix from two given pairs of two vectors is possible if and only if the pairs satisfy a certain order condition. If one interprets the vectors as states of a physical system, then this order is exactly the order known as the natural time order or the second law of thermodynamics.

Host
WIAS Berlin
Wednesday, 12.02.2020, 15:15 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. Fredi Tröltzsch, Technische Universität Berlin:
Optimal and feedback control of some reaction-diffusion equations
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The optimal control of some systems of nonlinear reaction-diffusion equations is considered including the Nagumo and FitzHugh--Nagumo equations. These equations are known to develop traveling wave fronts, spiral waves or scroll rings as solutions. Well-posedness of the system, differentiability of the control-to-state mapping, and optimality conditions of first order are briefly sketched. In particular, the case of sparse optimal control is addressed. Moreover, the optimization of time-delays in local and nonlocal Pyragas type feedback control up to the control by measures is discussed. Various numerical examples illustrate the great diversity of geometrical patterns and their control.

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Thursday, 13.02.2020, 14:00 (WIAS-ESH)
Seminar Numerische Mathematik
Dr. Gabriel R. Barrenechea, University of Strathclyde, Scotland:
Low-order divergence-free finite element methods
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
In this talk I will review results on a divergence-free reconstruction of the lowest order pair for the Navier-Stokes equation. More precisely, from a stabilised P1xP0 scheme, a divergence-free velocity field is built as the result of a lift of the pressure jumps, and it is then plugged in the convective term of the momentum equation. This process provides a method that can be proven stable without the need to suppose the mesh refined enough. We first apply this idea to the transient Navier-Stokes equations, where estimates independent of the viscosity are derived. Then, the applicability of this idea is extended to a steady-state generalised Boussinesq system.

Host
WIAS Berlin
Thursday, 27.02.2020, 14:00 (WIAS-ESH)
Seminar Numerische Mathematik
Dr. Anton Stephan, Institut für Physik der Atmosphäre:
Modeling Navier--Stokes equations for high Reynolds number flows and complex geometries in aerodynamic applications
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The flight of an aircraft through a turbulent environment presents a difficult numerical problem. Though it can be easily described by the Navier-Stokes equations, it is impossible to perform a direct numerical simulation resolving all physically relevant scales. For several decades, numerous different models have been developed which perform very well for very specific problems. However, since the aircraft flight includes complex geometries as well as large spatial dimensions these models fail to capture all important features of the problem.
The vision of establishing a simulation system for virtual flight in a realistic environment is addressed by the coupling of two separate flow solvers in a bi-directional manner. This enables for example the simulation of a flight through gusts, trailing vortices and clear air turbulence, including the effects on the aircraft and the roll-up of trailing vortices and their further development until final decay. A compressible Reynolds-Averaged Navier-Stokes (RANS) solver resolves the near-field around an aircraft model. An incompressible Large-Eddy Simulation (LES) solver is used to model the atmosphere around the aircraft with its wake footprint in the LES domain. This hybrid simulation setup is used to investigate complex physical problems occurring in different flight scenarios.

Host
WIAS Berlin
March 12 – 13, 2020 (WIAS-ESH)
Workshop/Konferenz: International Workshop: Uncertainty and Fluctuations in Thermodynamics
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
Wednesday, 10.06.2020, 15:15 (WIAS-HVP-3.13)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. Pierluigi Colli, Università di Pavia, Italien:
Optimal control of a tumor growth model with chemotaxis and singular potentials
more ... Location
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13

Host
Humboldt-Universität zu Berlin
WIAS Berlin
June 17 – 19, 2020 (WIAS-ESH)
Workshop/Konferenz: Junior Female Researchers in Probability
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The goal of the workshop is to offer junior female researchers in stochastics a platform to talk about their own research work and to get acquainted with important research topics presented by well-established female researchers. To cover various topics in probability and its applications, two keynote talks by outstanding female probabilists and four invited talks are planned. Moreover, a number of contributed talks will be chosen by the organizing committee among the submitted abstracts.

Host
Technische Universität Berlin
Humboldt-Universität zu Berlin
WIAS Berlin
November 2 – 4, 2020 (WIAS-ESH)
Workshop/Konferenz: Workshop on Stochastic Geometry and Communications
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin