Upcoming Events

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Monday, 20.06.2022, 16:00 (WIAS-ESH)
Seminar Numerische Mathematik
Prof. Maxim A. Olshanskii, University of Houston, USA:
Numerical analysis of surface fluids
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
In this talk we focus on numerical analysis for systems of PDEs governing the motion of material viscous surfaces, the topic motivated by continuum-based modeling of lateral organization in plasma membranes. We shall consider several systems of fluid and phase-field equations defined on evolving surfaces and discuss some recent results about well-posedness of such problems. We further introduce a computational approach and numerical analysis for the resulting systems of PDEs. The methods are combined to deliver a computationally tractable and thermodynamically consistent model describing the dynamics of a two-phase viscous layer. The talk closes with an illustration of the model capacity to predict lateral ordering in multicomponent vesicles of different lipid compositions.

Host
WIAS Berlin
Wednesday, 22.06.2022, 10:00 (WIAS-ESH)
Forschungsseminar Mathematische Statistik
PhD Stanislav Minsker, University of Southern California, USA:
U-statistics of growing order and sub-Gaussian mean estimators (hybrid talk)
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
Since their introduction by Halmos and Hoeffding in mid-twentieth century, U-statistics became the source of interesting questions in probability theory and found many applications in mathematical statistics. Most of the existing body of research is devoted to the properties of U-statistics of fixed order. In this talk, we will present examples where U-statistics of order that grows with the sample size naturally appear. We will introduce a version of Bernstein's inequality for such U-statistics that exhibits optimal dependence on the variance parameter, discuss the main technical tools required to prove it, as well as its application to the estimation of a univariate mean. In the second part of the talk, we will discuss the Bahadur-Kiefer representation of the geometric median in high dimensions and its implications for robust estimation of the multivariate mean. Finally, we will establish connection between these topics and some open questions in the theory of U-processes.

Further Informations
Der Vortrag findet bei Zoom statt: https://zoom.us/j/159082384

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Wednesday, 22.06.2022, 12:30 (WIAS-405-406)
Seminar Interacting Random Systems
Lukas Lüchtrath, Universität zu Köln:
The various phases of long-range inhomogeneous percolation
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Raum: 405/406

Abstract
We consider a large class of inhomogeneous spatial random graphs where the vertex set is given by a Poisson process in Euclidean space and each vertex carries additionally an i.i.d. weight. Edges are drawn in such a way that short edges and edges to large-weight vertices are preferred. This allows in particular the study of models that combine long-range interactions and heavy-tailed degree distributions. The occurrence of long edges together with the hierarchy of the vertices coming from the weights typically leads to very well connected graphs. We identify a sharp phase transition where the existence of a subcritical percolation phase becomes impossible. This transition depends on both the power law of the degree distribution and on the geometric model parameter, showing the significant effect of clustering on the graph?s topology. We consider afterwards the specifics of dimension one in parameter regimes where a subcritical phase exists. Due to the geometric restrictions of the line, it is fairly hard to generate infinite clusters in this case and many established models admit no supercritical phase. We identify sharply how the combination of weights and long-range effects can lead to infinite clusters in situations where both effects alone are not strong enough for an infinite cluster to exist. Natural examples that are contained in our framework are for instance the random connection model, the Poisson Boolean model, scale-free percolation, the age-dependent random connection model and their soft versions. Joint work with Peter Gracar, Christian Mönch and Peter Mörters.

Further Informations
Seminar Interacting Random Systems (Hybrid Event)

Host
WIAS Berlin
Thursday, 23.06.2022, 14:00 (WIAS-ESH)
Seminar Materialmodellierung
Dr. Giovanni Ligorio, Humboldt-Universität zu Berlin:
Neuromorphic device development: From modification of surfaces to modification of functions (hybrid talk)
more ... Location
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstract
The versatility offered by organic molecules and polymers holds great functional and economic potential for optoelectronic devices. The chemical modification of electrodes with organic materials is a common approach in our group for tuning the electronic landscape between interlayers in devices, thus facilitating charge carrier injection/extraction and improving device performance. A common tool to modify the electrode interfaces is to use covalently bound molecules carrying a permanent electric dipole group. Beside employing molecules with constant dipole, we also investigated the possibility to use switchable photochromic molecules which undergo structural modification when illuminated with light. This allows a dynamic and reversable control of the electronic properties. The gained control over the device performance enables additional functionalities in devices, such as neuromorphic applications. Neuromorphic engineering takes inspiration from the functionalities and structure of the brain to solve complex tasks and enable learning. Yet, hardware realization that simulates the synaptic activities realized with electrical devices is still not as advanced as the common implementation in computer software. In my talk I will present different approaches to emulate synapses and to fabricate both (i) optical and (ii) electronic synaptic devices. The first (i) were achieved by employing the above-mentioned photochromic molecules. This allowed control of the optical properties of gold films by reversibly modulating the surface plasmon resonance. The second (ii) were achieved by fabricating two-terminal devices based on mixed ionic-electronic conducting polymers that serve as active layer for ions and charge carrier conduction. The precise understanding and modeling of device functions will allow to fully exploit the potential of these synthetic synapses. For this purpose, a mathematical description of their behaviour might allow to move from single devices to networks and enable in materia computing.

Further Informations
Hybrid Event - please take into consideration that the number of on-site participants is limited to 24.

Host
WIAS Berlin
Friday, 24.06.2022, 13:00 (Online Event)
E-Coffee-Lecture
Henrik Pletat/Andrej Fink, WIAS IT Dep.:
Services of the WIAS IT-Department
more ... Location
Online Event

Host
WIAS Berlin