Upcoming Events
- Tuesday, 05.05.2026, 14:00 (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
more ... Location
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Abstract
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
Further Informations
Berlin Oberseminar: Optimization, Control and Inverse Problems
Host
WIAS Berlin
- Wednesday, 13.05.2026, 11:30 (WIAS-406)
- Seminar Interacting Random Systems
Quan Shi, AMSS Chinese Academy of Sciences:
Two phase transitions for catalytic branching Markov chains
more ... Location
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Abstract
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).
Further Informations
Seminar Interacting Random Systems (Hybrid Event)
Host
WIAS Berlin
- Wednesday, 20.05.2026, 11:30 (WIAS-406)
- Seminar Interacting Random Systems
Julian Kern, FU Berlin:
tba
more ... Location
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Abstract
tba
Further Informations
Seminar Interacting Random Systems (Hybrid Event)
Host
WIAS Berlin
- Thursday, 21.05.2026, 10:30 (WIAS-Library)
- Software and Data Seminar
Laura Prieto Saavedra, WIAS Berlin:
Introduction to ParaView
more ... Location
Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411
Further Informations
Seminar Software and Data
Host
WIAS Berlin
- Wednesday, 27.05.2026, 11:30 (WIAS-406)
- Seminar Interacting Random Systems
David Dereudre, University of Lille:
Rigidity of Riesz gases
more ... Location
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)
Abstract
In this talk, we will survey the rigidity of Riesz gases, which are equilibrium states (or Gibbs measures) in $mathbbR^d$ of continuum particle systems subjected to the Riesz potential. Here, rigidity refers to hyperuniformity, number rigidity, or symmetry breaking (such as crystallization or cyclic factor property). Several results will be presented, along with a number of conjectures.
Further Informations
Seminar Interactin Random Systems
Host
WIAS Berlin
- Wednesday, 27.05.2026, 14:15 (WIAS-ESH)
- Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. Tomáš Roubíček, Czech Academy of Sciences, Tschechische Republik:
The Stefan problem with a phase transition between visco-elastic fluids and finitely-strained solids
more ... Location
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Abstract
The compressible fluid-solid interaction (FSI) with a thermomechanical phase transition is formulated at large strains in the Eulerian frame. The Jeffreys (also called anti-Zener) rheology in the deviatoric part with an additional viscosity is used. The main philosophy for the mechanical solid-liquid transition is that the viscous (or viscoplastic) response depends on temperature and may completely degenerate towards a viscoelastic fluid during thawing, which then allows for free flow of the fluid and its freezing in a new configuration and possibly again subsequent melting towards the fluid unlimitedly repeating such cycles. The classical Stefan problem related with the latent heat of the 1st-order (i.e. here thawing-freezing) phase transition is augmented by involving kinetic overheating and undercooling. The (sketched) analysis by a time discretization with a suitable truncation is applied to a higher-gradient modification of the original problem, i.e. involving the concept of multipolar nonsimple material. Some enhancements of the basic model as phase-field fracture in the solid phase or a diffusant dependency (like a salinity variation within the sea water/ice transition or a nickel content variation within the Earth inner/outer core transition) will be outlined, too.
Further Informations
Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Host
Humboldt-Universität zu Berlin
WIAS Berlin
- Thursday, 28.05.2026, 10:30 (WIAS-Library)
- Software and Data Seminar
Nikolas Tapia:
Introduction to Lean
more ... Location
Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411
Further Informations
Software and Data Seminar
Host
WIAS Berlin
- June 1 – 5, 2026 (WIAS-ESH)
- Workshop/Konferenz: ESGI 194 - The Berlin Study Group with Industry
more ... Location
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Host
WIAS Berlin
- Thursday, 11.06.2026, 14:00 (WIAS-ESH)
- Seminar Materialmodellierung
Prof. Dr. Dieter Bothe, Technische Universität Darmstadt:
Sharp interface modelling fundamentals for two-phase fluid systems
more ... Location
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Abstract
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.
Host
WIAS Berlin
- July 6 – 8, 2026 (WIAS-ESH)
- Workshop/Konferenz: Spreading Dynamics in Random Environment
more ... Location
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Host
WIAS Berlin
- November 3 – 6, 2026 (WIAS-ESH)
- Workshop/Konferenz: Stochastic processes with reinforcement
more ... Location
Weierstraß-Institut, Anton-Wilhelm-Amo-Str. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal
Host
WIAS Berlin