Veranstaltungen
- Dienstag, 21.04.2026, 14:15 Uhr (WIAS-ESH)
- Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Ass.-Prof. Malte Kampschulte, Charles University, Tschechische Republik:
Variational methods for problems with inertia and their limits
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Abstrakt
For static and quasi-static problems, (iterated) minimization has long been one of the most important tools to prove existence of solutions. The main advantage of these variational approaches is that they able to deal with complicated nonlinearities and nonconvexities in a rather natural fashion, directly relying on the description of a problem in terms of its physical energy. In contrast, for dynamic problems, i.e. those involving inertia, such variational approaches so far have been much less used in practical existence proofs. The aim of this talk is to present our recent and not so recent attempts at bridging this gap, using a "time-delayed" approach which uses energetical descriptions and minimization as both a modelling approach, as well as a way of showing existence of solutions. This will be illustrated in with a number of problems from recent publications, involving solids, fluids and their interaction. Furthermore we will see how the same ideas can be used to study limit systems of parameter-dependent families of such problems in a similarly general fashion. This is based on joint works with, among others, B.Benešová, D.Breit, A.Češík, G.Gravina, M.Kružík and S.Schwarzacher.
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Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
- Donnerstag, 23.04.2026, 10:00 Uhr (WIAS-ESH)
- Forschungsseminar Mathematische Modelle der Photonik
Lasse Ermoneit, WIAS Berlin:
Epitaxial profile optimization in Si/SiGe heterostructures: Engineering valley splitting for spin qubits
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
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Forschungsseminar Mathematische Modelle der Photonik
Veranstalter
WIAS Berlin
- Dienstag, 28.04.2026, 13:30 Uhr (WIAS-406)
- Seminar Numerische Mathematik
Dr. Yupei Xie:
Weak discrete maximum principles and maximum norm stability of finite element methods
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Veranstalter
WIAS Berlin
- Mittwoch, 29.04.2026, 11:30 Uhr (WIAS-406)
- Seminar Interacting Random Systems
Elena Magnanini, WIAS Berlin:
Non-Standard Fluctuations of the edge density in the edge-triangle Model
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Abstrakt
Exponential Random Graph Models extend the classical (dense) Erdős?Rényi random graph by incorporating higher-order structural features through a Hamiltonian formalism inspired by statistical mechanics. Among these, the edge-triangle model is a basic but non trivial example, where the competition between edge and triangle terms leads to a rich phase structure. In this talk we will give an overview of known limit theorems and concentration results for subgraph densities, with particular emphasis on an open problem: a non-standard CLT for the edge density. The conjecture will be supported by a mean-field analysis, which allows for explicit computations and suggests a different fluctuation scaling, while also providing some insight into related open questions. This talk is based on joint works with A. Bianchi, F. Collet, and G. Passuello.
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Seminar Interactin Random Systems
Veranstalter
WIAS Berlin
- Mittwoch, 29.04.2026, 14:15 Uhr (WIAS-ESH)
- Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Stefanie Schindler, WIAS Berlin:
Time-asymptotic self-similarity of the damped Euler equations in parabolic scaling variables
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Abstrakt
In this talk, we study the long-time behavior of solutions to the compressible Euler equations with frictional damping on the whole space, assuming nonzero direction-dependent values for the density at spatial infinity. By introducing parabolic scaling variables, we reformulate the system and derive a relative entropy inequality. This framework allows us to show that the density converges to a self-similar solution of the porous medium equation, while the limiting momentum is governed by Darcy's law. We also obtain convergence rates that explicitly depend on the flatness of the limiting profile. The main part of the analysis focuses on weak solutions in the one-dimensional case, and we further extend the results to energy-variational solutions in the multidimensional setting. This research is joint work with Thomas Eiter (WIAS).
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Berliner Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Veranstalter
Humboldt-Universität zu Berlin
WIAS Berlin
- Donnerstag, 30.04.2026, 14:00 Uhr (WIAS-405-406)
- Seminar Materialmodellierung
Dr. Dennis Trautwein, Universität Regensburg:
Energy-stable and convergent numerical methods for viscoelastic fluid models
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Raum: 405/406
Abstrakt
Viscoelastic fluid models couple the incompressible Navier-Stokes equations with nonlinear evolution equations for the elastic stress tensor (such as Oldroyd-B or Giesekus). Despite their importance, developing numerical schemes that remain energy-stable and convergent under large elastic deformations remains a significant challenge. In this presentation, we review prominent numerical strategies from the literature and address their properties like energy-stability and rigorous convergence. We analyze key techniques such as the log-conformation representation, discrete chain-rule approximations, and structure-preserving methods utilizing local/global auxiliary variables. While the rigorous convergence of such methods is generally unknown, we present a novel (subsequence) convegence result in 2D for the Giesekus model, notably without artificial regularization in the limit system. Finally, we demonstrate the robustness of these methods through numerical tests at high Weissenberg numbers, where conventional schemes typically lose positivity of the conformation tensor.
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Seminar Materialmodellierung
Veranstalter
WIAS Berlin
- Dienstag, 05.05.2026, 14:00 Uhr (WIAS-ESH)
- Berlin Oberseminar: Optimization, Control and Inverse Problems
Prof. Karl Kunisch, Universität Graz, Austria:
A machine learning based approximation of semi-concave functions with applications to optimal control
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Abstrakt
Semiconcave functions are of vital importance for many variational problems, including optimal feedback control, game theory, and optimal transport. To investigate this class of functions we leverage the fact that semiconcave functions can be represented as the infimum of a countable family of C^2 functions. This infimum is expressed in a form that allows approximation by finitely many functions, which, combined with smoothing operations, remains semiconcave. Moreover, the gradients of the elements in the expansion of the approximating functions form a probability distribution, a property of particular interest for the value function in optimal control. We conclude by proposing a benchmark problem for a nonlinear optimal control problem, depending on a parameter which allows to vary the value function between being C^1 regular and semiconcave. This is joint work with D. Vasquez-Varas, Univ. Santiago, Chile
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Berlin Oberseminar: Optimization, Control and Inverse Problems
Veranstalter
WIAS Berlin
- Mittwoch, 13.05.2026, 11:30 Uhr (WIAS-406)
- Seminar Interacting Random Systems
Quan Shi, AMSS Chinese Academy of Sciences:
Two phase transitions for catalytic branching Markov chains
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Abstrakt
Consider a continuous-time branching Markov chain $(Z_t,tge 0)$ on a locally finite graph $G$ rooted at $mathbfo$. Each particle moves according to an irreducible Markov process $xi$ and branches at a rate that depends on their location: the branching rate is $lambda_rtge 0$ at the root and $lambdage 0$ elsewhere. The offspring distribution is supercritical with mean $m>1$, has no extinction and finite second moment. We characterize the recurrence/transience phase transition for this catalytic branching Markov chain. Furthermore, under suitable assumptions we prove a second phase transition concerning the asymptotic behaviour of the relative empirical density, $(Z_t(G))^-1 Z_t$, where $Z_t$ is the empirical measure of the particles and $Z_t(G)$ is the total population size. If $(m-1)(lambda_0-lambda)> gamma_esc$, where $gamma_esc$ is the escape probability that $xi$ never returns to the root, then $(Z_t(G))^-1 Z_t$ converges almost surely to a deterministic probability measure. If $(m-1)(lambda_0-lambda)in (0, gamma_esc]$, then $(Z_t(G))^-1 Z_t$ converges almost surely to zero. When the graph is the integer lattice $G=mathbbZ^d$ and $xi$ is the simple random walk, our results confirm several conjectures of Mailler and Schapira [Ann. Appl. Probab. 2026], which studied this model via a different approach. Based on a joint work in progress with Xinxin Chen (Bejing Normal Unversity), Nina Gantert (Technical University of Munich) and Haojie Hou (Beijing Institute of Technology).
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Seminar Interacting Random Systems (Hybrid Event)
Veranstalter
WIAS Berlin
- Mittwoch, 20.05.2026, 11:30 Uhr (WIAS-406)
- Seminar Interacting Random Systems
Julian Kern, FU Berlin:
tba
mehr ... Veranstaltungsort
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Abstrakt
tba
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Seminar Interacting Random Systems (Hybrid Event)
Veranstalter
WIAS Berlin
- Mittwoch, 27.05.2026, 11:30 Uhr (WIAS-406)
- Seminar Interacting Random Systems
David Dereudre, University of Lille:
tba
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Abstrakt
tba
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Seminar Interactin Random Systems
Veranstalter
WIAS Berlin
- 1. – 5. Juni 2026 (WIAS-ESH)
- Workshop/Konferenz: ESGI 194 - The Berlin Study Group with Industry
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Veranstalter
WIAS Berlin
- Donnerstag, 11.06.2026, 14:00 Uhr (WIAS-ESH)
- Seminar Materialmodellierung
Prof. Dr. Dieter Bothe, Technische Universität Darmstadt:
Sharp interface modelling fundamentals for two-phase fluid systems
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Abstrakt
The sharp interface framework enables a thermodynamically consistent description of two-phase fluid systems, representing interfaces as moving hypersurfaces separating bulk phases. Starting from classical balance laws for mass and momentum, the local kinematics of two-phase flows with phase change and interfacial slip is addressed. Since the associated kinematic differential equation may exhibit non-uniqueness, the notion of co-moving sets must first be consolidated in order to establish a two-phase Reynolds transport theorem. On this basis, balance laws and jump conditions for multicomponent two-phase fluid systems are formulated, consistently coupling bulk and interfacial dynamics. Building on the Gibbsian concept of interfaces as autonomous lower-dimensional thermodynamic subsystems, extensions with interfacial mass are introduced, enabling full thermodynamic coupling with the adjacent bulk phases and thereby promoting the interface to an interphase. Finally, extensions to multi-velocity and multi-temperature formulations are outlined.
Veranstalter
WIAS Berlin
- 6. – 8. Juli 2026 (WIAS-ESH)
- Workshop/Konferenz: Spreading Dynamics in Random Environment
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Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Veranstalter
WIAS Berlin
