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Tuesday, 21.02.2017, 15.00 Uhr (WIAS-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
A. Locatelli, Universität Potsdam:
Adaptation to noise parameters in non-parametric active learning
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
In this talk, I will present the non-parametric Active Learning classification setting already studied in Minsker (2012a) and show non-trivial strategies that can adapt to the smoothness of the regression function as well as the noise parameter and that require strictly weaker Assumptions than in previous work. We will first study the deterministic setting (i.e. one has access to the true value of the regression function) to build intuition, and then move on to the stochastic setting (noisy binary classification).

Host
WIAS Berlin
Thursday, 23.02.2017, 09.30 Uhr (WIAS-406)
FG Stochastische Systeme mit Wechselwirkung
Dr. T. Hulshof, University of Technology, Niederlande:
Higher order corrections for anisotropic bootstrap percolation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
Bootstrap percolation is a very simple model for growth from a random initial configuration on finite lattices. The model has many applications, for instance to model the spread of infections and to model magnets at low temperatures, to name two, but it is also interesting from a purely mathematical perspective. The model parameter has a critical value, at which the behaviour changes sharply. One interesting feature of bootstrap percolaton is a phenomenon called the ?bootstrap paradox? which relates to a big discrepancy between numerical and theoretical estimates of the critical value of bootstrap percolation models. I will discuss work in progress in which we give the most accurate theoretical estimate for the critical value of any bootstrap model to date, compare it with new numerical estimates, and show how it (tentatively) resolves the paradox. This talk is based on joint work with Hugo Duminil-Copin and Aernout van Enter, and on work with Robert Fitzner.

Host
WIAS Berlin
Wednesday, 01.03.2017, 15.15 Uhr (WIAS-406)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. P. Colli, University of Pavia, Italien:
About a non-smooth regularization of a forward-backward parabolic equation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstract
A variation of the Cahn-Hilliard equation, describing diffusion of species by a suitable regularization of a "forward-backward" parabolic equation is discussed. In the concerned system, the general viscous regularization is expressed by a maximal monotone graph acting on the time derivative of the concentration and presenting a strong coerciveness property. The phase variable stands for the concentration of a chemical species and it evolves under the influence of a non-convex free energy density. For the chemical potential a non-homogeneous Dirichlet boundary condition is assumed. Existence and continuous dependence results are shown. The talk reports on a joint work with E. Bonetti and G. Tomassetti.

Further Informations
Berliner Oberseminar ``Nichtlineare Partielle Differentialgleichungen'' (Langenbach Seminar)

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Thursday, 02.03.2017, 14.00 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Dr. L. O. Müller, Norwegian University of Science and Technology:
A local time stepping solver for one-dimensional blood flow
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
We present a finite volume solver for one-dimensional blood flow simulations in networks of elastic and viscoelastic vessels, featuring high-order space-time accuracy and local time stepping (LTS). The solver is built on:
(i) a high-order finite-volume type numerical scheme,
(ii) a high-order treatment of the numerical solution at internal vertexes of the network (junctions);
(iii) an accurate LTS strategy.
Several applications of the method will be presented. First, we apply the LTS scheme to the Anatomically Detailed Arterial Network model (ADAN), comprising 2142 arterial vessels. Second, we show results of a computational study where the ADAN model is coupled to automatically generated microvascular networks in order to elucidate aspects on the pathopysiology of small vessel disease for cerebral arteries.

Host
WIAS Berlin
Friday, 03.03.2017, 10.00 Uhr (WIAS-ESH)
Seminar Partielle Differentialgleichungen
S. Melchionna, University of Vienna, Österreich:
A variational approach to symmetry, monotonicity and comparison for doubly-nonlinear equations
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
We advance a variational method to prove qualitative properties such as symmetries, monotonicity, upper and lower bounds, sign properties, and comparison principles for a large class of doubly-nonlinear evolutionary problems including gradient flows, some nonlocal problems, and systems of nonlinear parabolic equations. Our method is based on the so-called Weighted-Energy-Dissipation (WED) variational approach. This consists in defining a global parameter-dependent functional over entire trajectories and proving that its minimizers converge to solutions to the target problem as the parameter goes to zero. Qualitative properties and comparison principles can be easily proved for minimizers of the WED functional and, by passing to the limit, for the limiting problem. Several applications of the abstract results to systems of nonlinear PDEs and to fractional/nonlocal problems are presented.

Further Informations
Seminar Partielle Differentialgleichungen

Host
WIAS Berlin
Tuesday, 14.03.2017, 10.15 Uhr (WIAS-406)
Seminar Nichtlineare Optimierung und Inverse Probleme
Dr. J. Linn, Fraunhofer-Institut für Techno- und Wirtschaftsmathematik, Kaiserslautern:
Simulation of flexible cables in car assembly
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Host
WIAS Berlin
Monday, 20.03.2017, 14.00 Uhr (WIAS-ESH)
Seminar Quantitative Biomedizin
Th. Niendorf, Charité Max Delbrück Center for Molecular Medicine:
Explorations into ultrahigh field magnetic resonance
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The development of ultrahigh field magnetic resonance (UHF-MR) is moving forward at an amazing speed that is breaking through technical barriers almost as fast as they appear. UHF-MR has a staggering number of potential uses in neuroscience, neurology, radiology, cardiology, internal medicine, physiology, oncology, nephrology, ophthalmology and other related clinical fields. With almost 40,000 MR examinations already performed at 7.0 Tesla, the reasons for moving UHF-MR into clinical applications are more compelling than ever.

Host
WIAS Berlin
Wednesday, 29.03.2017, 13.15 Uhr (WIAS-ESH)
Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations / Mathematical Optimization
Ch. Clason, Universität Duisburg-Essen:
Convex relaxation of hybrid discrete-continuous control problems
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
Wednesday, 29.03.2017, 15.15 Uhr (WIAS-ESH)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. M. Demuth, Technische Universität Clausthal:
On eigenvalues of non-selfadjoint operators: A comparison of two approaches
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
Thursday, 30.03.2017, 14.00 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Prof. J.H.M. ten Thije Boonkkamp, Eindhoven University of Technology, Netherlands:
Complete flux schemes fOR conservation laws of advection-diffusion-reaction typ
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Complete flux schemes are recently developed numerical flux approximation schemes for conservation laws of advection-diffusion-reaction type; see e.g. [1, 2]. The basic complete flux scheme is derived from a local one-dimensional boundary value problem for the entire equation, including the source term. Consequently, the integral representation of the flux contains a homogeneous and an inhomogeneous part, corresponding to the advection-diffusion operator and the source term, respectively. Suitable quadrature rules give the numerical flux. For time-dependent problems, the time derivative is considered a source term and is included in the inhomogeneous flux, resulting in an implicit semi-discretisation. The implicit system proves to have much smaller dissipation and dispersion errors than the standard semidiscrete system, especially for dominant advection. Just as for scalar equations, for coupled systems of conservation laws, the complete flux approximation is derived from a local system boundary value problem, this way incorporating the coupling between the constituent equations in the discretization. Also in the system case, the numerical flux (vector) is the superpostion of a homogeneous and an inhomogeneous component, corresponding to the advection-diffusion operator and the source term vector, respectively. The scheme is applied to multispecies diffusion and satisfies the mass constraint exactly.
References:
[1] J.H.M. ten Thije Boonkkamp and M.J.H. Anthonissen, ``The finite volume-complete flux scheme for advection-diffusion-reaction equations'', J. Sci. Comput., 46, 47--70, (2011).
[2] J.H.M. ten Thije Boonkkamp, J. van Dijk, L. Liu and K.S.C. Peerenboom, ``Extension of the complete flux scheme to systems of comservation laws'', J. Sci. Comput., 53, 552?568, (2012).

Host
WIAS Berlin
Thursday, 06.04.2017, 14.00 Uhr (WIAS-ESH)
Seminar Numerische Mathematik
Prof. D. Silvester, University of Manchester, GB:
Accurate time-integration strategies for modelling incompressible flow bifurcations
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Eigenvalue analysis is a well-established tool for stability analysis of dynamical systems. However, there are situations where eigenvalues miss some important features of physical models. For example, in models of incompressible fluid dynamics, there are examples where linear stability analysis predicts stability but transient simulations exhibit significant growth of infinitesimal perturbations. In this study, we show that an approach similar to pseudo-spectral analysis can be performed inexpensively using stochastic collocation methods and the results can be used to provide quantitive information about the nature and probability of instability.

Host
WIAS Berlin