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Thursday, 11.02.2016, 10.00 Uhr (WIAS-406)
Analysis-Stochastik-Seminar
Dr H. Stephan, WIAS Berlin:
An overview on classical physical methods (Lagrange, Hamilton, Hamilton-Jacobi)
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Host
WIAS Berlin
Thursday, 11.02.2016, 14.00 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
C. Bartsch, WIAS Berlin:
An assessment of solvers for saddle point problems emerging from the incompressible Navier-Stokes equations
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
In this talk we present an assessment of the performance of different solvers for linear saddle point problems. In fluid dynamics large linear saddle point problems emerge from the linearization and discretization of the Navier?Stokes equations. Preconditioned Krylov subspace methods such as FGMRES are a popular choice to solve these large linear systems. We employ FGMRES with two different types of preconditioners: A geometric multigrid preconditioner with different implementations of Vanka type smoothers is compared with the least squares commutator preconditioner (LSC) of Elman et al.
The LSC preconditioner has been modified recently as to include boundary conditions, and comparisons of the LSC approach with geometric multigrid preconditioners are not available so far. We incorporate the original and the boundary corrected LSC preconditioner into our studies. For comparison of these preconditioned iterative methods we also consider the direct solvers UMFPACK and PARDISO.
The solvers are appplied to several variants of the commmon benchmark example of a flow around a cylinder in two dimensions, for the steady state and the time-dependent Navier--Stokes equations.

Host
WIAS Berlin
Thursday, 11.02.2016, 16.00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
A. Zeghuzi, Ferdinand-Braun-Institut:
Ableitung eines verbesserten elektro-thermischen Modells für das WIAS-BALaser-Programm
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
Humboldt-Universität zu Berlin
WIAS Berlin
February 18, 2016 (WIAS-ESH)
Workshop/Konferenz: XVII. Berliner Mathematica-Tag
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
Additive Software GmbH
WIAS Berlin
February 22 – 26, 2016 (WIAS-ESH)
Workshop/Konferenz: ERC Workshop "Modeling Materials and Fluids using Variational Methods''
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
Tuesday, 23.02.2016, 13.30 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Dr. C. Bertoglio, Universidad de Chile, Chile:
Noninvasive pressure drop estimation in blood flows
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Pressure gradients across stenotic blood vessels is an important clinical index for diagnosis of the pathological severity of the disease. While the clinical gold standard for its measurement is the invasive catheterization, Phase-Contrast MR-imaging has emerged as a promising tool for enabling a non-invasive quantification of the pressure drop from the measured velocity field. However, current methods for recovering the pressure drop lack of robustness with respect to data perturbations. In this work we present a family of approaches that integrate velocity measures over a control volume in order to recover the stenosis pressure drop. We test the precision and robustness of different variants of the method on several numerical examples using perturbed synthetic data.

Host
WIAS Berlin
Thursday, 25.02.2016, 10.15 Uhr (WIAS-406)
Seminar Nichtlineare Optimierung und Inverse Probleme
Dr. J. Heiland, MPI Magdeburg:
A generalized POD space-time Galerkin scheme for parameter dependent dynamical systems and optimal control
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Host
WIAS Berlin
Friday, 26.02.2016, 10.15 Uhr (WIAS-406)
Seminar Nichtlineare Optimierung und Inverse Probleme
Prof. A. Araújo, University of Coimbra, Portugal:
Modelling light scattering in the human retina
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
The human retina is a complex structure in the eye that is responsible for the sense of vision. It is part of the central nervous system, composed by several layers, among which the outer nuclear layer that comprises the cells bodies of light sensitive photoreceptor cells (rods and cones). There are a number of eye-related pathologies that can be identified by the detailed analysis of the retinal layers. These pathologies can be diagnosed more conclusively with the help of the increasingly popular noninvasive optical imaging technique optical coherence tomography (OCT). In this talk we report a methodology to assess cell level alterations on the human retina responsible for functional changes observable in the OCT data in healthy ageing and in disease conditions, in the absence of structural alterations.

In particular, we will discuss the mathematical model that describes the electromagnetic wave's propagation through the eye's structures in order to create a virtual OCT scan. We use a leap-frog type discontinuous Galerkin method for the discretization of the time-dependent Maxwell's equations and we will focus on deriving stability and convergent estimates of fully discrete schemes. We consider anisotropic permittivity tensors, which arise naturally in our application of interest. An important aspect in computational electromagnetic problems is the implementation of the boundary conditions.

This work is being developed in the Institute for Biomedical Imaging and Life Sciences (IBILI) of the Faculty of Medicine of the University of Coimbra and in the Laboratory for Computational Mathematics of the Centre for Mathematics of the University of Coimbra, in the framework of a research project in the field of Biomedical Engineering. This project gathered a group of experts in mathematics, physics, engineers and medical doctors and was supported by FCT, the Portuguese funding agency for science, research and technology.

Joint work with
Silvia Barbeiro[1], Rui Bernardes[3], Francisco Caramelo[2], Antonio Correia[3], Maria Isabel Marques[2], Miguel Morgado[2,4], Luis Pinto[1], Miriam Santos[3] and Pedro Serranho[2,5]

[1] CMUC, Department of Mathematics, University of Coimbra, Portugal
[2] IBILI, Faculty of Medicine, University of Coimbra, Portugal
[3] AIBILI-Association for Innovation and Biomedical Research on Light and Image, Coimbra, Portugal
[4] Department of Physics, University of Coimbra, Portugal
[5] Mathematics Section, Department of Science and Technology, Universidade Aberta, Lisbon, Portugal

Host
WIAS Berlin