Upcoming Events

go to archive

Friday, 19.01.2018, 14:00 (WIAS-ESH)
Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations / Mathematical Optimization
Prof. Dr. S. Bartels, Albert-Ludwigs-Universität Freiburg:
Finite element methods for nonsmooth problems and application to a problem in optimal insulation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Nonsmooth problems arise in the mathematical modeling of contact and obstacle problems, the description of plastic material behavior, and mathematical image processing. The unknown functions are typically characterized as minimizers of nondifferentiable functionals. Numerical schemes approximately solve these problems either via duality methods or classically by making use of appropriate regularizations. In the talk we discuss the discretization and iterative solution of a model problem defined on functions of bounded variation. The numerical analysis of finite element discretizations leads to reduced convergence rates which can be improved using adaptive mesh refinement. Suitable iterative solution procedures are ADMM schemes, for which we propose an automatic step size adjustment strategy, and gradient flows, for which we demonstrate the unconditional stability of a semi-implicit time discretization. The methods are applicable in the numerical determination of optimal insulating films for heat conducting bodies. Below a critical value of available insulation mass an unexpected break of symmetry occurs.

Further Informations
Joint Research Seminar on Mathematical Optimization / Non-smooth Variational Problems and Operator Equations

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Tuesday, 23.01.2018, 14:00 (WIAS-406)
Seminar Materialmodellierung
Prof. J. Giesselmann, RWTH Aachen:
Modelling error estimates and model adaptation in compressible flows
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
tba

Host
WIAS Berlin
Tuesday, 23.01.2018, 15:00 (WIAS-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Dr. P. Pigato, WIAS Berlin:
The exploding skew of implied volatility
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
We show how a simple local volatility model, with volatility function discontinuous at-the-money, is capable of reproducing the explosion of the implied volatility skew, observed on empirical data. We use such local volatility as a leverage function, in a stochastic-local volatility model, obtaining good fits of the whole implied volatility surface on empirical observations.

Host
WIAS Berlin
Wednesday, 24.01.2018, 10:00 (WIAS-ESH)
Forschungsseminar Mathematische Statistik
A. Maurer, München:
Concentration for functions of bounded interaction
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Some multivariate functions have the property that their variation in any argument does not change too much when another argument is modi ed. The talk will give some examples and concentrates on the random variable W obtained by applying such a function to a vector of independent variables. Functions with weakly interacting arguments share some important properties with sums: the expectation of W can be estimated by a version of Bernstein's inequality and its variance can be tightly estimated in terms of an iid sample, which has only one datum more than the function has arguments. There is also a version of the central limit theorem.

Host
Universität Potsdam
Humboldt-Universität zu Berlin
WIAS Berlin
Wednesday, 24.01.2018, 15:15 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. H. Neidhardt, WIAS Berlin:
On the spectral shift function: Recent results
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

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

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Tuesday, 30.01.2018, 15:00 (WIAS-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Prof. A. Gasnikov, Moscow Institute of Physics and Technology, Russia:
Recent developments of accelerated gradient descent, part III
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Host
WIAS Berlin
Wednesday, 31.01.2018, 10:00 (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Prof. E. Gassiat, Universite Paris-Sud:
Estimation of the proportion of explained variation in high dimensions
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The estimation of the heritability of a phenotypic trait based on genetic data may be set as the estimation of the proportion of explained variation in high dimensional linear models. I will be interested in understanding the impact of: not knowing the sparsity of the regression parameter, not knowing the variance matrix of the covariates on minimax estimation of heritability. In the situation where the variance of the design is known, I will present an estimation procedure that adapts to unknown sparsity. When the variance of the design is unknown and no prior estimator of it is available, I will show that consistent estimation of heritability is impossible. (Joint work with N. Verzelen, and PHD thesis of A. Bonnet).

Host
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Thursday, 01.02.2018, 14:00 (WIAS-ESH)
Seminar Quantitative Biomedizin
Dr. E. Sinibaldi, Italian Institute of Technology:
Selected modeling approaches for biomedical applications and biorobotics tools
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The effective deployment of theranostic agents (including drugs), smart?materials?based systems and interfaces to target regions (prospectively) in the human body where to perform the sought actions also requires theoretical models and physical tools. Modeling the delivery and the (remote) actuation/stimulation of the aforementioned agents/systems/interfaces, in particular, permits to compensate for experimental conditions hard to characterize and to better interpret the experimental results, thus paving the way for quantitative therapy design and control. This is complemented by model-based design of related experimental devices, flexible tools able to safely navigate anatomical pathways, and miniaturized effectors. In this talk I will firstly present the solution to an inverse problem, namely to determine the velocity profile in a vessel cross-section starting from the flow-rate, which is relevant to pulsatile biological flows (blood and cerebro-spinal fluid flows), with application, e.g., to magnetic particle targeting. Then I will address numerical models for intrathecal drug-delivery (drug infusion in the cerebro-spinal fluid, also accounting for transport to the spinal cord) and simplified analytical models for intra-tissue drug-delivery (particle transport into porous/poroelastic media, with application to intratumoral thermotherapy). Finally, I will overview model-based approaches for: piezoelectric nanoparticle-mediated cell stimulation; real-scale physical models of the blood-brain barrier; flexible biorobotics probes; miniature (bioinspired) actuators and effectors.

Host
WIAS Berlin
Friday, 02.02.2018, 14:30 (WIAS-ESH)
Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations / Mathematical Optimization
Th. Ruf, Gerolsbach:
On a variational approach to the nonlinear wave equation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
In a 2012 paper, E. Serra and P. Tilli proved a conjecture by E. de Giorgi stating that global weak solutions of wave equations such as w” - Delta w + wlwl^(p-2) = 0 on R^+ times  R^d can be obtained as limits of minimizers of suitable variational functionals. We generalize this proof to equations of the form w” - Delta w + f_w (t; x; w) = 0 with p-growth conditions on f, also replacing R^d by an arbitrary open set O subset R^d and suitable boundary conditions.

Further Informations
Joint Research Seminar on Mathematical Optimization / Non-smooth Variational Problems and Operator Equations

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Thursday, 15.02.2018, 16:00 (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
J.-P. Koester, Ferdinand-Braun-Institut Berlin:
Simulation of pulsed laser diodes driven far above threshold with WIAS--BALaser and comparison with experiment
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin