Upcoming Events
- June 23 – 26, 2025 (Harnack-Haus)
- Workshop/Konferenz: 4th Annual Conference of SPP 2265 Random Geometric Systems 2025
more ... Location
Harnack-Haus -- Tagungsstätte der Max-Planck-Gesellschaft
Host
WIAS Berlin
- Tuesday, 24.06.2025, 14:00 (WIAS-HVP-3.13)
- Seminar Numerische Mathematik
Moaad Khamlich, SISSA, Trieste:
Efficient numerical strategies for regularized semi-discrete optimal transport
more ... Location
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13
Abstract
Semi-discrete optimal transport (SOT), which concerns mapping a continuous probability measure to a discrete one, is a fundamental problem with wide-ranging applications in fields like mesh generation, data quantization, and generative modeling. Entropic regularization is a widely-used technique to make this problem more tractable, enabling efficient solutions via convex duality. However, solving the regularized SOT (RSOT) dual problem poses a significant computational bottleneck. Specifically, the evaluation of the dual objective function and its gradient requires, in principle, dense interactions between every point on the continuous source domain and all N points of the discrete target measure. This leads to a computational complexity that scales poorly, rendering large-scale problems intractable. This talk will present a cohesive numerical framework designed to overcome these challenges by integrating several synergistic acceleration strategies. At the core of our approach, we accelerate the dual objective evaluation by combining distance-based truncation of the Gibbs kernel with fast spatial queries using R-trees, effectively exploiting the kernel's exponential decay to reduce complexity. To further enhance performance and accelerate overall convergence, we employ a multilevel, coarse-to-fine strategy inspired by multigrid methods. By creating hierarchical representations of both the continuous source mesh and the discrete target measure, we solve the problem on a coarse scale and use the result as a high-quality initial guess for finer levels. This is complemented by a regularization scheduling scheme, which improves numerical stability and robustness by starting with a larger, easier-to-solve problem and progressively decreasing the regularization parameter. When combined, these methods significantly reduce the computational burden associated with RSOT. We will demonstrate through numerical experiments that this framework not only makes large-scale problems computationally feasible but also achieves speedups of several orders of magnitude compared to standard solvers, paving the way for its practical application in computationally demanding scenarios.
Host
WIAS Berlin
- Tuesday, 24.06.2025, 15:00 (WIAS-405-406)
- Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Sorelle Murielle Toukam, WIAS Berlin:
Expected signature of diffusion processes
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Further Informations
Dieser Vortrag findet auch via Zoom statt: https://zoom.us/j/492088715
Host
WIAS Berlin
- Wednesday, 25.06.2025, 14:15 (WIAS-405-406)
- Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. Tomáš Roubíček, Czech Academy of Sciences, Tschechische Republik:
Brief notes about Earth's atmosphere energy budget, entropy, climate, and CO2 emissions
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Abstract
The goal of this talk is to present some of the less commonly discussed findings and connections in the atmospheric-emissions-climate field from a non-expert perspective. First, the basic physics of the Earth's atmosphere relevant to the climate, energy balance, and Erwin Schrödinger's idea of the role of negative entropy for the existence of life in open thermodynamic systems will be briefly surveyed. Then the presentation will focus on CO2 in the Earth's atmosphere, including e.g. Svante Arrhenius' historical idea of the greenhouse effect due to CO2. In particular, the development of CO2 concentration and temperature in geological time horizons will be mentioned, as well as recent Antarctic research and their reflection in climate-environmental activism (Al Gore etc). Finally, selected facts about the modern development of anthropogenic CO2 emissions in a socio-economic context will be presented, together how the atmospheric CO2 concentration can be predicted in a very simplified (and approximative) way in the near future in dependence on implementation of the Paris climatic agreement.
Further Informations
Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Host
Humboldt-Universität zu Berlin
WIAS Berlin
- Thursday, 26.06.2025, 14:00 (WIAS-405-406)
- Seminar Materialmodellierung
Dr. Nadire Nayir, Paul-Drude-Institut für Festkörperelektronik:
From equations to materials: The logic of modeling thin film growth
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Abstract
The synthesis of technologically vital thin films presents complex, multiscale challenges that lie at the intersection of physics, chemistry, and increasingly, mathematics. As materials science progresses toward predictive design and precise control of growth processes, mathematical modeling has become indispensable for understanding how microscopic rules shape macroscopic behavior. With a particular emphasis on simulation techniques rooted in quantum mechanics and Newtonian mechanics, in this talk, I will explain how atomic interactions are described mathematically -- starting from basic concepts like interatomic forces and potential energy surfaces, and moving toward how these are used in time-evolution schemes to simulate atomic motion. These elements form the foundation of computational models that help us understand key processes in thin film growth, such as how nuclei form, how domains align and grow, and how defects emerge and evolve on a substrate. To connect further these atomic-scale models with experimentally observable behavior, we will then turn to multiscale modeling, which provides a systematic way to combine different levels of description. I will show how we link atomistic simulations with continuum methods -- including phase-field models which describe morphological evolution and domain coarsening, and computational fluid dynamics, which captures macroscopic transport phenomena in the growth environment (as in chemical vapor deposition or hybrid molecular beam epitaxy). At this stage, I will walk through how they are coupled together to form an integrated, multiscale modeling framework. By grounding simulation techniques in their mathematical origins, this talk aims to provide a deeper understanding of how theoretical models mirror real-world materials behavior. Ultimately, I hope to show how mathematics not only powers atomistic simulations but also serves as a conceptual bridge between fundamental physics and the technological development of advanced materials.
Further Informations
Seminar Materialmodellierung
Host
WIAS Berlin
- Tuesday, 01.07.2025, 15:00 (WIAS-405-406)
- Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
Dr. Helena Kremp, WIAS Berlin:
Overcoming the order barrier for approximations of nonlinear SPDEs with additive space-time white noise
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Further Informations
Dieser Vortrag findet auch via Zoom statt: https://zoom.us/j/492088715
Host
WIAS Berlin
- Wednesday, 02.07.2025, 11:00 (WIAS-Library)
- Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations / Mathematical Optimization
Eleonora Ficola, Universität Hamburg:
Existence and duality theory for linear-growth variational problems with measures
more ... Location
Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411
Abstract
We consider functionals F with linear growth in the gradient variable coupled with a non-linear integral term respect to a (possibly signed) Radon measure on bounded domains in Rn. After achieving a generalized parametric lower-semicontinuity result, we then provide necessary and sufficient conditions for existence of BV-minimizers of F, discussing typical examples as well as limit cases. In parallel, we determine the corresponding dual maximization problem set in the class of divergence-measure vector fields and we reformulate the optimality relations in terms of a refined version of Anzellotti's pairing between measures and functions. By introducing a suitable notion of solutions to the Euler-Lagrange equation associated to F, we then demonstrate that our BV theory is complete and it provides natural extension to the Sobolev model. The seminar is based on joint work with Thomas Schmidt (Universität Hamburg).
Further Informations
Joint Research Seminar on Nonsmooth Variational Problems and Operator Equations
Host
WIAS Berlin
- Wednesday, 02.07.2025, 11:30 (WIAS-405-406)
- Seminar Interacting Random Systems
Jonas Köppl, WIAS Berlin:
Two edges suffice: the planar lattice two-neighbor graph percolates
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Abstract
The $k$-neighbor graph is a directed percolation model on the hypercubic lattice $Z^d$ in which each vertex independently picks exactly $k$ of its $2d$ nearest neighbors at random, and we open directed edges towards those. We prove that the $2$-neighbor graph percolates on $Z^2$, i.e., that the origin is connected to infinity with positive probability. The proof rests on duality, an exploration algorithm, a comparison to i.i.d. bond percolation under constraints as well as enhancement arguments. As a byproduct, we show that i.i.d. bond percolation with forbidden local patterns has a strictly larger percolation threshold than $1/2$. Additionally, our main result provides further evidence that, in low dimensions, less variability is beneficial for percolation.
Host
WIAS Berlin
- July 3 – 5, 2025 (WIAS-ESH)
- Workshop/Konferenz: 21st Annual Berlin-Oxford Young Researchers Meeting on Applied Stochastic Analysis
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Host
Technische Universität Berlin
University of Oxford
WIAS Berlin
- Wednesday, 09.07.2025, 11:30 (WIAS-405-406)
- Seminar Interacting Random Systems
Johannes Bäumler, UCLA:
tba
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Abstract
tba
Host
WIAS Berlin
- Wednesday, 09.07.2025, 14:15 (WIAS-ESH)
- Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. Amru Hussein, Universität Kassel:
The three limits of the hydrostatic approximation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Abstract
The primitive equations are a large scale model for ocean and atmosphere. Formally, they are derived from the 3D-Navier--Stokes equations by the assumption of a hydrostatic balance. This can be formalized by a rescaling procedure on an $varepsilon$-thin domain where one considers anisotropic viscosities with vertical viscosity $varepsilon^gamma$ and $varepsilon$-independent horizontal viscosity. Now, the choice of the order $gamma$ leads to different limit equations:
For $gamma=2$, one obtains the primitive equations with full viscosity term $-Delta$;
For $gamma>2$, one obtains the primitive equations with only horizontal viscosity term $- Delta_H$;
For $gamma <2$, one obtains the 2D Navier-Stokes equations.
Thus, there are three possible limits of the hydrostatic approximation depending on the assumption on the vertical viscosity. Here, we show how maximal regularity methods and quadratic inequalities - reminiscent of the Fujita-Kato methods - can be an efficient approach to prove norm-convergences in all three cases. This is a joint work with Ken Furukawa, Yoshikazu Giga, Matthias Hieber, Takahito Kashiwabara, and Marc Wrona, see https://arxiv.org/abs/2312.03418 for a preprint.
Further Informations
Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Host
Humboldt-Universität zu Berlin
WIAS Berlin
- September 29 – October 1, 2025 (WIAS-ESH)
- Workshop/Konferenz: Mathematical Analysis of Fluid Flows by Variational Methods
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Host
Freie Universität Berlin
Universität Leipzig
WIAS Berlin
- October 15 – 17, 2025 (WIAS-ESH)
- Workshop/Konferenz: Recent Developments in Spatial Interacting Random Systems
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Host
WIAS Berlin
- November 3 – 7, 2025 (WIAS-Library)
- Workshop/Konferenz:
more ... Location
Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411
Abstract
The ARISE project (Analysis of Robust Numerical Solvers for Innovative Semiconductors in View of Energy Transition) brings together the RAPSODI team at Inria Lille and the NUMSEMIC team at WIAS Berlin. It focuses on developing advanced mathematical and numerical models for drift-diffusion models for charge transport with mobile ions, with applications for novel semiconductor devices such as perovskite solar cells and memristors, as well as ionic solutions or corrosion phenomena.
Host
WIAS Berlin
