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Wednesday, 22.05.2019, 10:00 (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Prof. G. Heller, Macquarie University, Sydney:
Part I: Parameter orthogonality and the GAMLSS family of distributions
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Parameter orthogonality is a desirable property of statistical distributions having more than one parameter. When parameters are orthogonal then their maximum likelihood estimates are asymptotically independent. Within the exponential family, the mean and dispersion parameter are orthogonal; however in general this is not the case. This work is motivated by a trial in Parkinson's disease patients in which one of the outcomes is the number of falls. Inspection of the data reveals that the Poisson-inverse Gaussian (PiG) distribution is appropriate, and that the experimental treatment reduces not only the mean, but also the variability, substantially. Conventional analysis assumes a treatment effect on the mean, either adjusted or unadjusted for covariates, and a constant dispersion parameter. We find that we reach quite different conclusions on the treatment effect on the mean, depending on whether or not a model is specified for the dispersion parameter.

Host
Universität Potsdam
Humboldt-Universität zu Berlin
WIAS Berlin
Wednesday, 22.05.2019, 11:15 (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Prof. G. Heller, Macquarie University, Sydney:
Part II: Ordinal regression models for continuous scales
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Visual Analogue Scales (VAS) are used for measuring quantities which are intangible and difficult to measure on conventional scales, such as pain, anxiety and quality of life. These are generally used for self-rating. Subjects are given a linear scale of 100 mm and asked to put a mark where they perceive themselves. The scale has verbal anchor descriptors at each extreme, such as (in the pain context) ?no pain? and ?worst pain imaginable?. The VAS reading is taken as the measurement from the left endpoint to the subject's mark, and is usually normalized to lie in the interval [0,1]. Statistical analysis of the VAS is controversial. While it is a bounded, continuous variable, several authors have argued that it is ordinal, rather than ratio in nature, and should be treated as such. The issue is that, for example, a 1-cm difference in VAS scores at the lower end of the scale does not necessarily represent the same difference in the intangible outcome as a 1-cm difference at the upper end; and a doubling of VAS score may not translate to a doubling of e.g. the pain or anxiety. This problem is overcome by treating VAS measurements as ordinal rather than ratio data. We therefore refer to scales of this type as continuous ordinal. We have developed a regression framework for continuous ordinal responses. We express the likelihood in terms of a function connecting the scale with an underlying continuous latent variable and approximate this function non-parametrically. Then a general semi-parametric regression framework for continuous scales is developed. The model is shown to be a conditional transformation model, and is generalizable to a much wider range of uses than the context in which it was developed. We illustrate our method on a quality of life data set.

Host
Universität Potsdam
Humboldt-Universität zu Berlin
WIAS Berlin
Wednesday, 22.05.2019, 15:15 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. P. Colli, Università di Pavia, Italien:
Well-posedness, regularity and asymptotic analyses for a fractional phase field system
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
Humboldt-Universität zu Berlin
WIAS Berlin
May 23 – 25, 2019 (WIAS-ESH)
Workshop/Konferenz: 11th Annual ERC Berlin-Oxford Young Researchers Meeting on Applied Stochastic Analysis
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
Technische Universität Berlin
University of Oxford
Thursday, 23.05.2019, 16:00 (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
Dr. M. Chernysheva, Leibniz Institute of Photonic Technology, Jena:
Highlights of pulse generation and dynamics in mode-locked all-fibre and SOA-based fibre lasers
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
Tuesday, 28.05.2019, 10:15 (WIAS-406)
Seminar Nichtlineare Optimierung und Inverse Probleme
Dr. B. Sprungk, Georg-August-Universität Göttingen:
Noise-level robust sampling methods for Bayesian inverse problems
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Host
WIAS Berlin
Wednesday, 29.05.2019, 10:00 (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Prof. D. Belomestny, Universität Duisburg-Essen:
Density deconvolution under general assuptions on measurement error distribution
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The subject of my talk is the density deconvolution problem under general assumptions on the measurement error distribution. Typically deconvolution estimators are constructed using Fourier transform techniques, and the main assumption is that the measurement error characteristic function does not vanish on the real line. This assumption is rather strong and does not hold in many cases of interest. Here we develop a new technique to deal with this problem which allows us to recover the standard convergence rates without additional assumptions on the measurement error distribution. Joint work with A. Goldenshluger (University of Haifa).

Host
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
Wednesday, 29.05.2019, 15:00 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. P. Tolksdorf, Université Paris-Est - Créteil Val-de-Marne, Frankreich:
On the Lp-theory for second-order elliptic operators in divergence-form with complex coefficients (Part 1)
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Given a complex, elliptic coefficient function we investigate for which values of p the corresponding second-order divergence form operator, complemented with Dirichlet, Neumann or mixed boundary conditions, generates a strongly continuous semigroup on Lp(Ω). Additional properties like analyticity of the semigroup, H-calculus and maximal regularity are also discussed. Finally we prove a perturbation result for real coefficients that gives the whole range of p's for small imaginary parts of the coefficients. Our results are based on the recent notion of p-ellipticity, reverse Hölder inequalities and Gaussian estimates for the real coefficients.

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

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Monday, 03.06.2019, 11:00 (WIAS-ESH)
Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations / Mathematical Optimization
S. Metzner, PTB / TU Berlin:
Approximate large-scale Bayesian inference with application to magnetic resonance fingerprinting
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
A class of nonlinear, large-scale regression problems is considered where the parameters model the spatial distribution of some property. Specific assumptions about the regression function are made and a homoscedastic Gaussian sampling distribution is assumed. The class of problems includes the task of Magnetic Resonance Fingerprinting (MRF), a new approach for quantitative Magnetic Resonance Imaging that allows for the estimation of absolute values of tissue related parameters like proton density and spin relaxation times. The properties of a Bayesian inference for the considered class of regression problems is investigated when different types of priors are employed, including Gaussian Markov random field priors expressing spatial smoothness. The properties of the resulting posteriors are explored and conditions for propriety of the posterior and existence of its moments established. An approximate calculation scheme is proposed and its practicability demonstrated up to dimensions of 105. Finally, the approach is applied to MRF. In using simulated data with known ground truth, it is shown that by using the prior knowledge of smoothness in the spatial distribution of the sought parameters, the results are significantly better than those achieved through maximum likelihood estimation.

Host
WIAS Berlin
Monday, 03.06.2019, 11:30 (WIAS-ESH)
Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations / Mathematical Optimization
Dr. G. Dong, Humboldt-Universität zu Berlin:
Quantitative magnetic resonance imaging: From fingerprinting to integrated physics-based models
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
In this talk, we introduce a novel method for quantitative MRI. The proposed approach simultaneously recovers the tissue parameters as the recently developed method magnetic resonance fingerprinting (MRF). However, in comparison with MRF and many of its variants, our new model is dictionary free. Thus, its accuracy is independent of the discretization size of the dictionary. The efficiency of our new method is proved theoretically and also verified by numerical examples.

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

Host
WIAS Berlin
Tuesday, 04.06.2019, 13:30 (WIAS-406)
Seminar Materialmodellierung
Dr. G. Antunes Monteiro, Tschechische Akademie der Wissenschaften, Prag, Tschechische Republik:
On the convergence of viscous approximation for rate-independent processes with regulated inputs
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
The vanishing viscosity method is a popular tool for describing rate-independent evolution. It consists in the analysis of the limiting behavior of a regularized problem obtained by introducing a viscous dissipation mechanism which stabilizes the process. In this talk, we discuss some issues related to viscous approximations to rate-independent processes when different choices of the viscosity operator are considered. We show that the viscous limit exists, and the associated input-output operator is continuous in the space of regulated functions. Notably, we observe that the vanishing viscosity limit may exhibit some unexpected behavior when the input has some jump discontinuities.

Host
WIAS Berlin
Wednesday, 05.06.2019, 15:00 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. P. Tolksdorf, Université Paris-Est - Créteil Val-de-Marne, Frankreich:
On the Lp-theory for second-order elliptic operators in divergence-form with complex coefficients (Part 2)
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Given a complex, elliptic coefficient function we investigate for which values of p the corresponding second-order divergence form operator, complemented with Dirichlet, Neumann or mixed boundary conditions, generates a strongly continuous semigroup on Lp(Ω). Additional properties like analyticity of the semigroup, H-calculus and maximal regularity are also discussed. Finally we prove a perturbation result for real coefficients that gives the whole range of p's for small imaginary parts of the coefficients. Our results are based on the recent notion of p-ellipticity, reverse Hölder inequalities and Gaussian estimates for the real coefficients.

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

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Wednesday, 12.06.2019, 15:15 (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
F. Della Porta, Max-Planck-Institut für Mathematik Leipzig:
The nonlocal Cahn--Hilliard--Hele--Shaw system with regular and singular potential
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The Cahn--Hilliard--Hele--Shaw system (also called the Cahn--Hilliard--Darcy system) can be used to describe the evolution of binary immiscible fluids in a Hele--Shaw cell or in porous media, and has been recently used as a buildingblock for some tumor-growth models. In my talk, I will introduce a physically motivated nonlocal variant of the Cahn--Hilliard--Hele--Shaw system, and present some related analytical results. These include the well-posedness of the system, the existence of a global attractor, and the convergence of solutions to equilibria as time goes to infinity (in the two-dimensional case). We discuss both the case with regular and singular potential.

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Thursday, 27.06.2019, 16:00 (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
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
Friday, 02.08.2019, 15:15 (WIAS-ESH)
MATHEON Special Guest Lecture
Prof. Y.-X. Yuan, Chinese Academy of Sciences, China:
Efficient optimization algorithms for large scale data analysis
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
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.

Further Informations
Special Guest Lecture

Host
WIAS Berlin
Saturday, 03.08.2019, 09:00 (TU-Berlin)
6th International Conference on Continuous Optimization
6th International Conference on Continuous Optimization
more ... Location
Technische Universität, Straße des 17. Juni 135, 10623 Berlin, Main building (H)

Further Informations
https://iccopt2019.berlin/

Host
WIAS Berlin
Technische Universität Berlin
Freie Universität Berlin
Humboldt-Universität zu Berlin
Mathematical Optimization Society
September 9 – 13, 2019 (WIAS-ESH)
Workshop/Konferenz: PDE 2019: Partial Differential Equations in Fluids and Solids
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
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.

Host
WIAS Berlin
September 18 – 20, 2019 (WIAS-ESH)
Workshop/Konferenz: Optical Solitons and Frequency Comb Generation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin