Upcoming Events

Wednesday, 30.04.2025, 10:00 (WIAS-HVP-3.13)

Forschungsseminar Mathematische Statistik
Ratmir Miftachov, Humboldt Universität zu Berlin:
Early stopping for regression trees
more ... Location
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13

Abstract
We develop early stopping rules for growing regression tree estimators. The fully data-driven stopping rule is based on monitoring the global residual norm. The best-first search and the breadth-first search algorithms together with linear interpolation give rise to generalized projection or regularization flows. A general theory of early stopping is established. Oracle inequalities for the early-stopped regression tree are derived without any smoothness assumption on the regression function, assuming the original CART splitting rule, yet with a much broader scope. The remainder terms are of smaller order than the best achievable rates for Lipschitz functions in dimension . In real and synthetic data the early stopping regression tree estimators attain the statistical performance of cost-complexity pruning while significantly reducing computational costs.

Host
Humboldt-Universität zu Berlin

Wednesday, 30.04.2025, 14:15 (WIAS-Library)

Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Rossella Giorgio, Technische Universität Wien, Österreich:
Nonlocal analysis of energies in micromagnetics
more ... Location
Weierstraß-Institut, Hausvogteiplatz 5-7, 10117 Berlin, R411

Abstract
In this talk we provide conditions in order to formally justify a nonlocal analysis of energies in Micromagnetics. Specifically, we first consider a nonlocalto-local approximation of exchange energy functionals, extending the wellknown Bourgain--Brezis--Mironescu formula to encompass the scenario where antisymmetric contributions are encoded. The key points are a pointwise convergence result and a Gamma-convergence argument. After the nonlocal approximation, we investigate the existence and qualitative properties of minimizers, focusing on the competition between a nonlocal symmetric exchange interaction, which penalizes spatial variations in magnetization, and a magnetostatic self-energy term that accounts for long-range dipolar interactions. For spherical domains, we generalize Brown's fundamental results by identifying critical radii such that uniform magnetizations are preferable for the small-body regime, while non-uniform magnetization configurations become dominant in the large-body regime. This is joint work with E. Davoli, G. Di Fratta and L. Lombardini.

Further Informations
Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)

Host
Humboldt-Universität zu Berlin
WIAS Berlin

Wednesday, 07.05.2025, 14:15 (WIAS-405-406)

Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. Edriss Titi, University of Cambridge, UK and Texas A&M University, USA:
On a generalization of the Bardos--Tartar conjecture to nonlinear dissipative PDEs
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstract
In this talk I will show that every solution of a KdV-Burgers--Sivashinsky type equation blows up in the energy space, backward in time, provided the solution does not belong to the global attractor. This is a phenomenon contrast to the backward behavior of the 2D Navier--Stokes equations, subject to periodic boundary condition, studied by Constantin, Foias, Kukavica and Majda, but analogous to the backward behavior of the Kuramoto--Sivashinsky equation discovered by Kukavica and Malcok. I will also discuss the backward behavior of solutions to the damped driven nonlinear Schrödinger equation, the complex Ginzburg--Landau equation, and the hyperviscous Navier--Stokes equations. In addition, I will provide some physical interpretation of various backward behaviors of several perturbations of the KdV equation by studying explicit cnoidal wave solutions. Furthermore, I will discuss the connection between the backward behavior and the energy spectra of the solutions. The study of backward behavior of dissipative evolution equations is motivated by a conjecture of Bardos and Tartar which states that the solution operator of the two-dimensional Navier--Stokes equations maps the phase space into a dense subset in this space.

Further Informations
Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)

Host
Humboldt-Universität zu Berlin
WIAS Berlin

Wednesday, 14.05.2025, 10:00 (WIAS-HVP-3.13)

Forschungsseminar Mathematische Statistik
Prof. Dr. Vladimir Spokoiny, WIAS Berlin:
Estimation and classification for DNN: Bless of dimension
more ... Location
Weierstraß-Institut, Hausvogteiplatz 11A, 10117 Berlin, 3. Etage, Raum: 3.13

Further Informations
Dieser Vortrag findet hybrid statt. Die Teilnahme per Zoom ist über den (neuen!) Link: https://hu-berlin.zoom-x.de/j/62476510180?pwd=1bws9DORlDM2Iub3ANrb7zzDNANvsJ.1

Host
Humboldt-Universität zu Berlin
Universität Potsdam
WIAS Berlin

Wednesday, 14.05.2025, 14:00 (WIAS-405-406)

Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Prof. Dr. Pierluigi Colli, Università di Pavia, Italien:
Solvability and optimal control in spatially structured epidemic models
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstract
Compartmental models are widely used in the mathematical modeling of infectious diseases, where the population is divided into distinct groups or compartments based on disease status. In this talk, we present results - obtained in collaboration with various co-authors - related to compartmental epidemic models that evolve within spatially heterogeneous environments. These models lead to nonlinear systems of reaction-diffusion partial differential equations, subject to homogeneous Neumann boundary conditions and appropriate initial conditions. Particular attention is given to a class of models incorporating a modified chemotaxis-type term, reflecting movement influenced by spatial infection gradients. We will discuss existence and uniqueness of solutions, and outline some optimal control problems.

Further Informations
Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)

Host
Humboldt-Universität zu Berlin
WIAS Berlin

Wednesday, 14.05.2025, 15:30 (WIAS-405-406)

Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Ass. Prof. Andrea Signori, Politecnico di Milano, Italien:
Mathematical models of active phase separation and droplet dynamics
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstract
Active phase separation gives rise to striking phenomena, such as the suppression of coarsening and the spontaneous growth and division of droplets, that sharply contrast with the behavior seen in classical systems. Whereas classical phase separation favors the growth of larger domains at the expense of smaller ones, chemically active mixtures can sustain a stable population of droplets with finite size. These dynamics have been proposed as a model for protocells, shedding light on the emergence of self-organized prebiotic structures and the transition from non-living to living matter. In this talk, I will present a mathematical framework for modeling the dynamics of active droplets, using both the phase-field formulation (via the Cahn--Hilliard equation) and the sharp-interface limit (described by the Mullins--Sekerka free-boundary problem). I will explore the connection between these two approaches and discuss the well-posedness and stability of the resulting models, focusing on planar and radial configurations. Finally, I will present numerical simulations that support the asymptotic analysis and highlight complex behaviors such as droplet division and shell formation.

Further Informations
Oberseminar “Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)

Host
Humboldt-Universität zu Berlin
WIAS Berlin

Monday, 19.05.2025, 11:30 (WIAS-405-406)

Seminar Interacting Random Systems
Peter Gracar, University of Leeds:
tba
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Further Informations
Seminar Interacting Random Systems

Host
WIAS Berlin

Wednesday, 21.05.2025, 11:30 (WIAS-405-406)

Seminar Interacting Random Systems
Adrian Röllin, National University of Singapore:
Centered Subgraph Counts in Dense Random Graphs
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstract
Complex networks appear in many fields, from social media to biology, and understanding their structure often boils down to studying how frequently small subgraphs (such as triangles or squares) appear. In this talk, I will introduce the idea of centered subgraph counts: a way of measuring subgraph occurrences that corrects for the dependence that we observe among regular subgraph counts. By focusing on these centered counts, we can describe and quantify the natural 'fluctuations' in dense random networks via tools first developed by Janson and Nowicki in the study of generalised U-statistics in the 90s. I will explain how these theoretical results lead to practical methods for assessing how well a given network fits a chosen statistical model--often referred to as a goodness-of-fit analysis.

Further Informations
Seminar Interactin Random Systems

Host
WIAS Berlin

Wednesday, 21.05.2025, 14:15 (WIAS-ESH)

Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
PD Dr. Olaf Klein, WIAS Berlin:
Uncertainty quantification for a model for a magnetostrictive material involving a hysteresis operator
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Host
WIAS Berlin
Humboldt-Universität zu Berlin
Freie Universität Berlin

Tuesday, 27.05.2025, 15:00 (WIAS-ESH)

Forschungsseminar Mathematische Modelle der Photonik
Prof. Dmitry Turaev, Imperial College London, GB:
TBA
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Further Informations
Forschungsseminar Mathematische Modelle der Photonik

Host
WIAS Berlin

Wednesday, 04.06.2025, 11:30 (WIAS-405-406)

Seminar Interacting Random Systems
Elena Pulvirenti, Delft University of Technology:
tba
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Further Informations
Seminar Interacting Random Systems

Host
WIAS Berlin

Thursday, 05.06.2025, 14:00 (WIAS-405-406)

Seminar Numerische Mathematik
Adrian Hill, TU Berlin:
SparseConnectivityTracer.jl
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Host
WIAS Berlin

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

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