Veranstaltungen

Dienstag, 19.11.2024, 13:30 Uhr (WIAS-406)

Seminar Materialmodellierung
Angeliki Koutsimpela, Universität Augsburg:
Mean-field limits for interacting particle systems
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Veranstalter
WIAS Berlin

Mittwoch, 13.11.2024, 15:15 Uhr (WIAS-405-406)

Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Lukas Abel, Humboldt-Universität zu Berlin:
A scaling law for a model of epitaxial growth with dislocations
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstrakt
Epitaxy is a special form of crystal growth and of great importance in modern technology. We consider a crystalline film on a (rigid) substrate. The misfit between the crystal structures of the film and the substrate can lead to dislocations and can have an influence on the morphology of the film. Dislocations are topological defects of the crystallographic lattice. In this talk we will study a variational model from the literature. It is based on linearized elasticity and additionally takes into account the surface energy of the film's free surface as well as the dislocation nucleation energy. In particular we will discuss a new scaling law for the infimum of the energy. This includes a new construction for the upper bound and a new variant of a ball-construction combined with thorough local estimates for the lower bound. The results indicate that in certain parameter regimes, the formation of dislocations is expected. Reference: Preprint arXiv no. 2403.13646, https://arxiv.org/abs/2403.13646

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Oberseminar “Nichtlineare Partielle Differentialgleichungen” (Langenbach Seminar)

Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin

Donnerstag, 07.11.2024, 15:00 Uhr (WIAS-405-406)

Seminar Materialmodellierung
Dr. Tomáš Bodnár, Czech Technical University in Prague, Tschechische Republik:
On the use of viscoelastic fluids flows models in hemolysis prediction
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstrakt
The mathematical modeling and numerical simulations of blood flows is a very challenging problem due to complex rheological properties of blood. The blood can be considered as a suspension of red blood cells in blood plasma, resulting in a shear-thinning and viscoelastic behavior of the whole blood. It is well known that high levels of stress in blood flows, typically found in ventricular assist devices for example, can lead to blood damage - the hemolysis. Under high stress the red blood cells can be damaged or ruptured, which can lead to serious medical consequences. This is why a considerable effort has been dedicated by numerous researchers to prediction of the blood damage, based on the detailed knowledge of the flow field. There exists a number of models for hemolysis, but non of them is generally accepted as a definitive, convenient and reliable tool for prediction of hemolysis. The aim of the presented talk is to point out the importance of inclusion of non-Newtonian rheology of blood in the hemolysis predictions. The similarity between some of the promising stretch based tensorial models of hemolysis and the non-linear viscoelastic rheology models offers the possibility to estimate the hemolysis directly from the local stretch tensor. This possibility will be presented and discussed in detail.

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Seminar Materialmodellierung

Veranstalter
WIAS Berlin

Mittwoch, 30.10.2024, 15:15 Uhr (WIAS-405-406)

Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. Tomáš Roubíček, Czech Academy of Sciences, Tschechische Republik:
Time discretization in visco-elastodynamics at large displacements and strains in the Eulerian frame
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstrakt
The fully-implicit time discretization (i.e. the backward Euler formula) is applied to compressible nonlinear dynamical models of viscoelastic media in the Eulerian description, i.e. in the actual deforming configuration. The Kelvin--Voigt rheology or also, in the deviatoric part, the Jeffreys (also called anti-Zener) rheology describing a (possibly nonlinear) creep or a rate-dependent plasticity are considered. Both a linearized convective model at large displacements with a convex stored energy and the fully nonlinear large strain variant with a (possibly generalized) polyconvex stored energy are considered. The time-discrete suitably regularized schemes (suggesting an implementable numerical strategy) are devised for both these heavily nonlinear cases. The numerical stability and, considering the multipolar 2nd-grade viscosity, also convergence towards weak solutions are proved, exploiting the convexity of the kinetic energy when written in terms of linear momentum instead of velocity. In the fully nonlinear case, the examples of neo-Hookean and Mooney--Rivlin materials are presented. A comparison with models of viscoelastic barotropic fluids is also made and thermodynamical extension is outlined, too.

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Oberseminar “Nichtlineare Partielle Differentialgleichungen” (Langenbach Seminar)

Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin

Donnerstag, 24.10.2024, 14:00 Uhr (WIAS-405-406)

Seminar Numerische Mathematik
Prof. Dr. Winnifried Wollner, Universität Hamburg:
Gradient-robustness in the context of optimal control
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Veranstalter
WIAS Berlin

Mittwoch, 23.10.2024, 10:00 Uhr (WIAS-HVP-3.13)

Forschungsseminar Mathematische Statistik
Prof. Dr. Weining Wang, University of Groningen, Niederlande:
Conditional nonparametric variable screening by neural factor regression
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13

Abstrakt
High-dimensional covariates often admit linear factor structure. To effectively screen correlated covariates in high-dimension, we propose a conditional variable screening test based on non-parametric regression using neural networks due to their representation power. We ask the question whether individual covariates have additional contributions given the latent factors or more generally a set of variables. Our test statistics are based on the estimated partial derivative of the regression function of the candidate variable for screening and a observable proxy for the latent factors. Hence, our test reveals how much predictors contribute additionally to the non-parametric regression after accounting for the latent factors. Our derivative estimator is the convolution of a deep neural network regression estimator and a smoothing kernel. We demonstrate that when the neural network size diverges with the sample size, unlike estimating the regression function itself, it is necessary to smooth the partial derivative of the neural network estimator to recover the desired convergence rate for the derivative. Moreover, our screening test achieves asymptotic normality under the null after finely centering our test statistics that makes the biases negligible, as well as consistency for local alternatives under mild conditions. We demonstrate the performance of our test in a simulation study and two real world applications.

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Forschungsseminar Mathematische Statistik

Veranstalter
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin

Mittwoch, 16.10.2024, 15:15 Uhr (WIAS-405-406)

Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Janusz Ginster, WIAS Berlin:
Formation of microstructure for singularly perturbed problems related to helimagnets and shape-memory alloys
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Weitere Informationen
Berliner Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)

Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin

Mittwoch, 16.10.2024, 10:00 Uhr (WIAS-HVP-3.13)

Forschungsseminar Mathematische Statistik
Prof. Dr. Botond Szabo, Bocconi University, Italien:
Privacy constrained semiparametric inference
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13

Abstrakt
For semi-parametric problems differential private estimators are typically constructed in a case-by-case basis. In this work we develop a privacy constrained semi-parametric plug-in approach, which can be used in general, over a collection of semi-parametric problems. We derive minimax lower and matching upper bounds for this approach and provide an adaptive procedure in case of irregular (atomic) functionals. Joint work with Lukas Steinberger (Vienna) and Thibault Randrianarisoa (Toronto, Vector Institute).

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Forschungsseminar Mathematische Statistik

Veranstalter
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin

14. Oktober 2024 (HU Berlin HVP)

Workshop/Konferenz: WIAS Alumni Day 2024
mehr ... Veranstaltungsort
Humboldt-Universität zu Berlin, Hausvogteiplatz 5-7, R. 0007

Abstrakt
The Weierstrass Institute invites to the first WIAS Alumni Day. This event is intended to promote the exchange between current and former WIAS employees and to evolve our alumni program. We are particularly looking forward to contributions from former WIAS members Johannes Neumann and Florian Schmid, who will talk about their career paths and experiences. In addition, we intend to use an open discussion format such as World Café to structure the communication of the participants (which depends on the final composition of the group of participants and will be planned in more detail after the registration deadline). Finally, we are inviting you to a get-together in the rooms of our recently renovated and redesigned library.

Veranstalter
WIAS Berlin

14. – 15. Oktober 2024 (WIAS-405-406)

Workshop/Konferenz: Exploring Calcium Channel Dynamics: From Molecular Insights to Macroscopic Ion Flow
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstrakt
This workshop aims to explore the mechanisms of ion channels from various perspectives, including molecular dynamics, continuum models, and experimental approaches. It will address how these perspectives align or diverge, tackle the challenge of bridging scales from atomic to cellular levels, and discuss how theory and experiment inform and validate each other while highlighting current frontiers and future directions in the field.

Veranstalter
Zuse Institute Berlin
WIAS Berlin