Veranstaltungen

Dienstag, 22.09.2026, 14:00 Uhr (WIAS-ESH)

Seminar Numerische Mathematik
Dr. Yiannis Hadjimichael, WIAS Berlin:
Semiconductor nanowires bent by a one-sided stressor shell: Modelling, simulation and experimental results
mehr ... Veranstaltungsort
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Strain engineering in semiconductor nanowires enables precise control of electronic properties through deformation, piezoelectric, and flexoelectric effects. Bending nanowires without fracturing produces large strain gradients that change the band-gap gradient via a deformation-potential interaction. Under extreme strain gradients, the system can generate not only quasi-electric fields but also actual electric fields arising from spatial variations in both piezoelectric and flexoelectric polarization. Thus, unlike quasi-electric fields, electrons and holes drift in opposite directions, which spatially separates charge carriers. In this talk, we present a finite-strain electromechanical model for strongly bent core/shell nanowires with different cross-sectional geometries. The model incorporates lattice-mismatch-induced strain and piezoelectricity under a one-sided stressor-shell heterostructure, as motivated by TEM experiments, and accounts for adatom diffusion and strain-energy minimization. We solve the coupled partial differential equations using the finite element method to obtain three-dimensional strain fields for zincblende and wurtzite GaAs nanowires. The results demonstrate the impact of physically accurate geometries and reveal significant consequences for torsion, chirality, and piezoelectricity. Furthermore, we discuss the model?s potential to disentangle piezoelectric and flexoelectric effects in GaAs polytypes. Ultimately, this approach could clarify how strain gradients and electric fields from piezoelectric and flexoelectric polarization collectively govern carrier dynamics.

Veranstalter
WIAS Berlin

Donnerstag, 01.10.2026, 10:30 Uhr (WIAS-Library)

Software and Data Seminar
Dr. Laura Prieto Saavedra, WIAS Berlin:
Compute servers: Same tasks, new workflow
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411

Abstrakt
Are you still getting used to the new way of using the servers at the institute? Join us for a practical and informal introduction to HTCondor, where we will see how to launch your simulations in the new way, starting from the basics. Through simple examples, we will run Julia, Python and MATLAB simulations, compare the old and new approaches, and see how easily you can launch multiple simulations without having to manage them one by one. No prior HTcondor experience needed. Access to the servers is required. Bring your examples or share them in advance, so you can leave with a working workflow for your day-to-day research.

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Seminar Software and Data

Veranstalter
WIAS Berlin

Donnerstag, 08.10.2026, 10:30 Uhr (WIAS-Library)

Software and Data Seminar
Julia Community, at WIAS:
Julia Sessions: Packages, environments and other topics
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411

Abstrakt
The Julia sessions take place monthly. This is an open and informal meeting for everyone interested in Julia, whether you are just curious about the language, learning or using Julia in your work, or even if you are already an experienced Julia user. The aim is to learn from each other, discuss Julia-related questions and topics, and share experiences, ideas, tips and challenges from using Julia in research and everyday work. In this session, we will briefly go through installing Julia for beginners and discuss the main differences between Julia and other programming languages. Then we will discuss packages and environments, as well as setting up (collaborative) projects. Other questions and topics are also welcome. Everyone interested in Julia is welcome - no prior experience required.

Veranstalter
WIAS Berlin

Mittwoch, 14.10.2026, 11:30 Uhr (WIAS-406)

Seminar Interacting Random Systems
Azadeh Parvaneh, Universität Bielefeld:
Large Deviation Principle for Friendship Biases in Galton-Watson Trees
mehr ... Veranstaltungsort
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstrakt
The friendship bias of a vertex is defined as the difference between the average degree of its neighbours and its own degree; for isolated vertices, this bias is considered to be zero. According to the sign of the friendship bias, vertices can naturally be classified as "negative", "neutral", or "positive". The friendship paradox says that the average friendship bias is non-negative for all finite undirected graphs, whether simple graphs or multigraphs. However, the combined number of neutral and positive vertices can be significantly smaller than the number of negative vertices. For instance, in a complete graph on a large number of vertices with a single edge removed, only the two endpoints of the removed edge are positive, while all other vertices are negative. The fractions of different vertex types can also vary across graphs and reflect aspects of the geometry of a graph. The typical behaviour of these fractions has been studied for sparse random graphs that are locally tree-like, as well as for finite and infinite Galton-Watson trees. In this talk, we analyse the atypical behaviour of the fractions of vertex types along a random downward path in an infinite Galton-Watson tree by deriving a large deviation principle as the branching depth grows. The rate function is characterised through a variational problem involving relative entropy under a linear constraint. We discuss its properties in the case of binary branching. [Based on joint work with Frank den Hollander.]

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Seminar Interacting Random Systems

Veranstalter
WIAS Berlin

Donnerstag, 15.10.2026, 14:00 Uhr (WIAS-ESH)

Seminar Numerische Mathematik
Dr. Jose Rodrigo Rojo Garcia, WIAS Berlin:
Bayesian optimal experimental design with Wasserstein information criteria
mehr ... Veranstaltungsort
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Bayesian optimal experimental design (BOED) is a widely used method for reducing uncertainty in Bayesian inversion. A classical design criterion is the Expected Information Gain, which measures discrepancy between prior and posterior probability measures via Kullback-Leibler divergence. Nevertheless, some limitations arise in this classical approach, for instance, the comparison of probability measures with different supports. In order to mitigate these issues, a new proposal based on the p-Wasserstein distance is proposed as a utility function. The present work establishes results of well-posedness, consistency, interpretation, a closed formula for linear Gaussian case, prior and likelihood stability, empirical measure convergence rate, numerical demonstrations, and some numerical algorithms".

Veranstalter
WIAS Berlin

Donnerstag, 22.10.2026, 10:30 Uhr (WIAS-Library)

Software and Data Seminar
Dr. Laura Prieto Saavedra, WIAS Berlin:
Numerical solution of a Poisson equation using FEniCsx and deal.II
mehr ... Veranstaltungsort
Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411

Abstrakt
When developing and studying new numerical methods, it is often useful to have a simple and reliable computational setup for testing ideas, verifying results and comparing discretizations. In this seminar, we will introduce two implementations to solve a Poisson equation numerically using two well-established open-source FEM libraries for solving PDEs: FEniCSx and deal.II. We will go through the math, the basic problem setup, and the essential components of each code, and demonstrate how they can be easily adapted to more difficult problems (e.g., other boundary conditions, other discretizations, etc.). The goal is to provide a simple, reusable starting point that can be modified for different research purposes. No prior FEniCSx or deal.II experience is needed. Basic programming experience is helpful, but not required.

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Seminar Software and Data

Veranstalter
WIAS Berlin

Mittwoch, 28.10.2026, 11:30 Uhr (WIAS-406)

Seminar Interacting Random Systems
Lars Schröder, University of Twente:
tba
mehr ... Veranstaltungsort
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstrakt
tba

Veranstalter
Humboldt-Universität zu Berlin
Technische Universität Berlin
WIAS Berlin
International Research Training Group 2544

3. – 6. November 2026 (WIAS-ESH)

Workshop/Konferenz: Stochastic processes with reinforcement
mehr ... Veranstaltungsort
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin

Mittwoch, 18.11.2026, 11:30 Uhr (WIAS-406)

Seminar Interacting Random Systems
Ulrik Thinggaard Hansen, University of Innsbruck:
tba
mehr ... Veranstaltungsort
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Abstrakt
tba

Veranstalter
Humboldt-Universität zu Berlin
Technische Universität Berlin
WIAS Berlin
International Research Training Group 2544

Mittwoch, 18.11.2026, 14:15 Uhr (WIAS-ESH)

Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Gianna Götzmann, Universität Augsburg:
Perturbed minimizing movements of time-dependent functionals on metric spaces
mehr ... Veranstaltungsort
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Minimizing movement schemes are a fundamental tool for approximating evolution equations that have a gradient-flow structure with respect to an energy. Motivated by homogenization problems involving, for instance, geometries that evolve in time, we consider Gamma-converging perturbations of time-dependent driving energies. We study the convergence of the corresponding minimizing movement scheme and provide sufficient conditions under which limits of the scheme are (time-dependent) curves of maximal slope for the limit energy. We further exhibit examples showing that, in general, such a stability property may fail, with the limit motion depending on the relation between the time-discretization parameter τ and the perturbation parameter ϵ. This is joint work with Jan-Frederik Pietschmann and Antonio Tribuzio.

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

Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin