Veranstaltungen
- Mittwoch, 15.10.2025, 10:00 Uhr (WIAS-HVP-3.13)
- Forschungsseminar Mathematische Statistik
Prof. Dr. Carlos Soto, University of Massachusetts Amherst, USA:
Differential privacy over manifolds and shape space
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Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13
Abstrakt
In this work we consider the problem of releasing a differentially private statistical summary that resides on a Riemannian manifold. We present extensions of the Laplace and K-norm mechanisms that utilizes intrinsic distances and volumes on the manifold. We also consider in detail the specific case where the summary is the Fréchet mean of data residing on a manifold. We demonstrate that our mechanism is rate optimal and depends only on the dimension of the manifold, not on the dimension of any ambient space, while also showing how ignoring the manifold structure can decrease the utility of the sanitized summary. Lastly, we illustrate our framework in three examples of particular interest in statistics: the space of symmetric positive definite matrices, which is used for covariance matrices, the sphere, which can be used as a space for modeling discrete distributions, and Kendall's 2D planar shape space.
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Dieser Vortrag findet hybrid statt. Die Teilnahme per Zoom ist über den (neuen!) Link: https://zoom.us/j/159082384
Veranstalter
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin
- 15. – 17. Oktober 2025 (WIAS-ESH)
- Workshop/Konferenz: Recent Developments in Spatial Interacting Random Systems
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Veranstalter
WIAS Berlin
- Mittwoch, 15.10.2025, 14:15 Uhr (WIAS-Library)
- Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Annalaura Rebucci, MPI für Mathematik in den Naturwissenschaften:
On the De Giorgi--Nash--Moser regularity theory for kinetic hypoelliptic operators
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Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411
Abstrakt
We present new results that extend the De Giorgi--Nash--Moser theory to a class of hypoelliptic equations naturally arising in kinetic theory. These operators are mathematically characterized by two parts: a diffusion part governed by the (fractional) Laplace operator in some set of variables and a first order operator that contains the directions of missing ellipticity. A key ingredient to prove our results is a Poincaré inequality, which we derive from the construction of suitable trajectories. The trajectories we rely on are quite flexible and allow us to consider equations with an arbitrary number of Hörmander commutators and whose diffusive part is either local (second-order) or nonlocal (fractional order). We later combine the Poincaré inequality with a L2 - L∞ estimate, a Log-transformation and a classical covering argument (Ink--Spots Theorem) to deduce Harnack inequalities and Höllder regularity along the line of De Giorgi method. This talk is based on a series of papers in collaboration with F. Anceschi, H. Dietert, J. Guerand, A. Loher and C. Mouhot.
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Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
- Donnerstag, 16.10.2025, 14:00 Uhr (WIAS-406)
- Seminar Numerische Mathematik
Laura Prieto Saavedra, WIAS Berlin:
An efficient stabilized Navier-Stokes solver to simulate turbulent flows in process-intensified devices
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Abstrakt
Process intensification aims to design innovative equipment that enhances mass and heat transfer without negatively affecting the environment and process costs. Process-intensified devices, such as, static mixers and spinning disc reactors, have common characteristics that can be summarized as follows: complex (curved) geometries, concurrent physical phenomena (turbulence, energy and mass transfer, chemical reactions) and (rotating) transient incompressible flows at an intermediate Reynolds number (Re?[103,105]). The hydrodynamics within these devices are complex, and experimental methods are no longer sufficient to fully characterize the flow behavior. The numerical modeling of the flow, also known as Computational Fluid Dynamics (CFD), helps overcome these limitations. However, the simulation of turbulent flows remains a challenge even with modern high-performance computing architectures. In this talk, we present a stabilized solver for the incompressible Navier-Stokes equations implemented in a matrix-free fashion with a sum-factorization approach. We solve the fully-coupled discretized problem in a monolithic way using a geometric multigrid preconditioner for the solution of the linear system. The solver is implemented in Lethe, an open-source CFD software, which uses the deal.II finite element library and a continuous Galerkin discretization. We validate and verify the solver using a variety of steady-state and transient benchmarks for turbulent flow. The results show better scalability and lower memory requirements than the results obtained using a matrix-based approach, rendering efficient high-order parallel simulations for complex practical problems.
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Numerical mathematics seminars
Veranstalter
WIAS Berlin
- Dienstag, 21.10.2025, 13:30 Uhr (WIAS-406)
- Seminar Numerische Mathematik
Hongpeng Li, WIAS Berlin:
Coupling of conforming and mixed finite element methods for a model of wave propagation in thermo-poroelasticity in the frequency domain
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Abstrakt
The thermo-poroelasticity model characterizes the coupling between mechanical deformation, fluid flow, and heat transfer in porous media. As an extension of Biot's classical poroelasticity theory, which models fluid-solid interaction under the isothermal condition, it incorporates the impact of temperature changes on solid displacement, as well as the compressibility and thermal expansion of both solid and fluid phases. We investigate a full-dynamic, linear thermo-poroelasticity model, containing inertial and relaxation terms with second-order time derivatives. The mathematical and numerical analysis of this model is performed in the frequency rather than time domain. We analyze the variational formulation within the framework of Fredholm's alternative and T-coercivity. The well-posedness is rigorously proved under reasonable parameter assumptions. We propose a stabilized coupling of conforming and mixed finite element methods, which are free of volume locking, pressure and temperature oscillations. By incorporating projections in certain sesquilinear forms, the well-posedness of the finite element solutions can be obtained through the same reasoning as in the continuous case. The optimal error estimates are derived for all variables. Numerical experiments validate the accuracy and robustness of our formulation.
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Numerical Mathematics
Veranstalter
WIAS Berlin
- Mittwoch, 22.10.2025, 11:30 Uhr (WIAS-405-406)
- Seminar Interacting Random Systems
Helia Shafigh, WIAS Berlin:
Responsive dormancy of a spatial population among a moving trap
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Abstrakt
In this talk, we study a spatial model for dormancy in a random environment via a two-type branching random walk in continuous-time, where individuals switch between dormant and active states depending on the current state of a fluctuating environment (responsive switching). The branching mechanism is governed by the same random environment, which is here taken to be a simple symmetric random walk. We will interpret the presence of this random walk as a trap which attempts to kill the individuals whenever it meets them. The responsive switching between the active and dormant state is defined so that active individuals become dormant only when a trap is present at their location and remain active otherwise. Conversely, dormant individuals can only wake up once the environment becomes trap-free again. We quantify the influence of dormancy on population survival by analyzing the long-time asymptotics of the expected population size. The starting point for our mathematical considerations and proofs is the Parabolic Anderson Model via the Feynman-Kac formula. In particular, we investigate the quantitative role of dormancy by extending the Parabolic Anderson Model to a two-type random walk framework.Joint work with Leo Tyrpak.
Veranstalter
WIAS Berlin - Mittwoch, 22.10.2025, 14:15 Uhr (WIAS-Library)
- Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Annamaria Massimini, Ecole Nationale des Ponts et Chaussées, FR:
Finite volumes for a generalized Poisson--Nernst--Planck system with cross-diffusion
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Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411
Abstrakt
Modeling concentrated ion mixtures in solvents like water is a complex research area with key applications in biology (e.g., ion transport through protein channels) and electrochemistry (e.g., batteries). In this talk, I will present a finite volume scheme for modeling the diffusion of ions in constrained geometries using a degenerate Poisson--Nernst--Planck system with size exclusion yielding cross-diffusion. The proposed method utilizes a two-point flux approximation and is part of the exponentially fitted scheme framework. The scheme is shown to be thermodynamically consistent, as it ensures the decay of some discrete version of the free energy. Classical numerical analysis results - existence of discrete solution, convergence of the scheme as the grid size and the time step go to 0 - follow. The long-time behavior of the scheme is also investigated, both from a theoretical and numerical point of view. Numerical simulations confirm our findings, but also point out some possibly very slow convergence towards equilibrium of the system under consideration. This is a joint work with Clément Cànces and Maxime Herda.
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Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
- Mittwoch, 29.10.2025, 11:30 Uhr (WIAS-405-406)
- Seminar Interacting Random Systems
Hanna Stange, Universität Münster:
Non-local transport distance for point processes
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Abstrakt
We introduce a non-local transport distance on the space of point processes and analyse the induced geometry. We show -- among other things -- that the Ornstein--Uhlenbeck semigroup is the gradient flow of the specific relative entropy, functional inequalities like a Talagrand inequality, and exponential convergence of the Ornstein--Uhlenbeck flow to the Poisson point process. Towards the end, we discuss ongoing work on the extension of the framework adapted to Papangelou point processes. Based on joint work with Martin Huesmann and Matthias Erbar.
Veranstalter
WIAS Berlin
- 4. – 6. November 2025 (WIAS-ESH)
- Workshop/Konferenz: Mathematics for Smart Energy
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Veranstalter
WIAS Berlin
- Mittwoch, 19.11.2025, 14:15 Uhr (WIAS-ESH)
- Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Lutz Recke, Humboldt-Universität zu Berlin:
An H-convergence-based implicit function theorem and homogenization of nonlinear non-smooth elliptic systems
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
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Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
- Donnerstag, 20.11.2025, 14:00 Uhr (WIAS-406)
- Seminar Materialmodellierung
Dr. Andrea Giudici, University of Oxford, GB:
From particle stresses to electrolyte flow: How mechanics affects the performance of lithium-ion batteries
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Abstrakt
Lithium-ion batteries are typically described by electrochemical models, yet mechanical effects play a decisive role in their operation and degradation. During cycling, swelling of active particles generates stresses and deformations that propagate across scales. These mechanical effects couple back into electrochemistry in two distinct ways.First, stresses around active particles modify lithium transport by altering the local chemical potential, leading to shifts in voltage curves that cannot be captured by standard Doyle?Fuller?Newman-type models. Using asymptotic homogenisation, we extend reduced-order models to incorporate this multiscale coupling systematically.Second, electrode swelling changes porosity and drives electrolyte flows. These flows interact with concentration gradients, causing an irreversible redistribution of electrolyte salt?typically bulk accumulation and edge depletion?conditions that promote lithium plating and performance loss. We model the flow-concentration coupling and derive a closed-form expression for the resulting electrolyte-movement-induced salt inhomogeneity (EMSI) in terms of swelling, porosity, permeability, and nonlinear mechanics, providing a mechanistic explanation of this degradation pathway.
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Material Modeling Seminar
Veranstalter
WIAS Berlin
- 12. – 13. Januar 2026 (WIAS-ESH)
- Workshop/Konferenz: Recent Trends in Coupled Network Systems
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Veranstalter
WIAS Berlin
- 2. – 4. März 2026 (IHP)
- Workshop/Konferenz: Leibniz MMS Days 2026
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Leibniz Institute for High Performance Microelectronics Frankfurt/Oder
Veranstalter
Leibniz Institute for High Performance Microelectronics Frankfurt/Oder
WIAS Berlin
- 1. – 5. Juni 2026 (WIAS-ESH)
- Workshop/Konferenz: ESGI 194 - The Berlin Study Group with Industry
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Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Veranstalter
WIAS Berlin