Upcoming Events

Due to infection prevention measures, participation in events at the institute is presently not possible for guests.

Many events are currently organized online. Information on how to access these events can be found by clicking “more” below the respective entry.


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Tuesday, 26.01.2021, 15:15 (Online Event)
Oberseminar Nonlinear Dynamics
Tibor Krisztin, University of Szeged, Hungary:
Periodic and connecting orbits for the Mackey--Glass equation
more ... Location
Online Event

Abstract
We consider the Mackey-Glass equation x' (t)=-ax(t)+b (x^k(t-1))/(1+x^n (t-1)) with positive parameters a,b,k,n. First, for the discontinuous limiting (n??) case, an orbitally asymptotically stable periodic orbit is constructed for some fixed parameter values a,b,k. Then it is shown that for large values of n and with the same parameters a,b,k, the Mackey-Glass equation also has an orbitally asymptotically stable periodic orbit near to the periodic orbit of the discontinuous equation. The shape of the obtained stable periodic solutions can be complicated. The existence of connecting orbits will be discussed as well.

Further Informations
Diesen Vortrag können Sie mit Zoom verfolgen unter: https://zoom.us/j/82815629022.

Host
Freie Universität Berlin
WIAS Berlin
Wednesday, 27.01.2021, 15:15 (Online Event)
Berliner Oberseminar „Nichtlineare partielle Differentialgleichungen” (Langenbach-Seminar)
Dr. Sebastian Throm, Westfälische Wilhelms-Universität Münster:
Universal long-time asymptotics for coagulation equations (online talk)
more ... Location
Online Event

Abstract
In this talk, we will consider the long-time behaviour of coagulating systems. Clustering phenomenon can be observed in many processes in nature and industry and also on a broad range of scales. Our focus will be on Smoluchowski's coagulation equation and the question of universal scaling for large times - a problem which is known as scaling hypothesis. In particular, we will present a recent result proving this conjecture for perturbations of a constant rate kernel.

Further Informations
Oberseminar “Nichtlineare Partielle Differentialgleichungen” (Langenbach Seminar)

Host
Humboldt-Universität zu Berlin
WIAS Berlin
Thursday, 28.01.2021, 15:00 (Online Event)
TES-Seminar on Energy-based Mathematical Methods and Thermodynamics
Ass. Prof. Markus Hütter, Eindhoven University of Technology, Niederlande:
Finite-size effects in complex fluids: Phenomenology of fluctuations, stochastics, and statistical mechanics (online talk)
more ... Location
Online Event

Abstract
In general, in every system with dissipation there are also fluctuations; the fluctuation-dissipation theorem is a key result of nonequilibrium statistical mechanics, which is encoded e.g. in the GENERIC framework [1,2,3]. Correspondingly, also complex fluids, which contain the relaxation of the microstructure (e.g. polymer chains), must show behavior with fluctuations. Fluctuations are relevant particularly for the behavior on small scales, where they are not averaged out, e.g. in micro-/nano-fluidics and microrheology. To date, models for complex fluids do not include fluctuations systematically. In our recent work, we have extended conformation-tensor based models for complex fluids by including thermal fluctuations in a thermodynamically consistent way [4]. Furthermore, this work has been complemented by establishing a link between the fluctuating conformation-tensor models and the underlying description of polymer chains as bead-spring dumbbells [5]. To achieve this link, we follow two routes: (1) stochastic calculus, followed by averaging (direct approach); (2) nonequilibrium statistical mechanics, which includes the derivation of the coarse-grained relaxation tensor, the fluctuations, and the thermodynamic potential (particularly entropy). Denoting the number of polymer chains by N, it is shown that a finite (rather than infinite) value for N gives rise to a correction to the conventional entropy for the conformation tensor and leads to the fluctuations that vanish only in the thermodynamic limit (N to infinity). Finally, some subtleties are pointed out related to the appearance of the so-called spurious drift in the stochastic differential equation for the conformation tensor. References: [1] M. Grmela, H.C. Öttinger, Phys. Rev. E 56(6) (1997) 6620?6632 (http://dx.doi.org/10.1103/PhysRevE.56.6620) [2] H.C. Öttinger, M. Grmela, Phys. Rev. E 56(6) (1997) 6633?6655 (http://dx.doi.org/10.1103/PhysRevE.56.6633) [3] H.C. Öttinger, Beyond Equilibrium Thermodynamics, Wiley, Hoboken, 2005. [4] M. Hütter, M.A. Hulsen, P.D. Anderson, J. Non-Newtonian Fluid Mech. 256 (2018) 42?56 (https://doi.org/10.1016/j.jnnfm.2018.02.012) [5] M. Hütter, P.D. Olmsted, D.J. Read, Eur. Phys. J. E 43 (2020) 71 (http://dx.doi.org/10.1140/epje/i2020-11999-x)

Further Informations
TES-Seminar on Energy-based Mathematical Methods and Thermodynamics

Host
Technische Universität Berlin
WIAS Berlin
Tuesday, 02.02.2021, 13:30 (Online Event)
Seminar Numerische Mathematik
Volker Kempf, Bundeswehr-Universität München:
Anisotropic and pressure-robust finite element discretizations for the Stokes equations
more ... Location
Online Event

Abstract
The incompressible Stokes equations show a fundamental invariance property, meaning that the velocity solution is not affected by a change of the right hand side data in form of a gradient field. Due to relaxation of the divergence constraint most common finite element discretizations, like the Taylor-Hood or Mini-element, are however not pressure-robust, i.e. they do not reproduce this property on the discrete level. The mentioned classical methods are also in general not inf-sup stable on anisotropic meshes with potentially unbounded aspect ratio, which are used e.g. when treating singularities caused by re-entrant edges.

Further Informations
For zoom login details please contact Alexander Linke linke@wias-berlin.de

Host
WIAS Berlin
Wednesday, 03.02.2021, 11:30 (Online Event)
Seminar Interacting Random Systems
Elena Pulvirenti, Delft University of Technology, Niederlande:
The Widom-Rowlinson model: metastability, mesoscopic and microscopic fluctuations for the critical droplet (online talk)
more ... Location
Online Event

Abstract
We introduce the equilibrium Widom-Rowlinson model on a two-dimensional finite torus in which the energy of a particle configuration is attractive and determined by the union of small discs centered at the positions of the particles. We then discuss the metastable behaviour of a dynamic version of the WR model. This means that the particle configuration is viewed as a continuous time Markov process where particles are randomly created and annihilated as if the outside of the torus were an infinite reservoir with a given chemical potential. In particular, we start with the empty torus and are interested in the first time when the torus is fully covered by discs in the regime at low temperature and when the chemical potential is supercritical. In order to achieve the transition from empty to full, the system needs to create a sufficiently large droplet, called critical droplet, which triggers the crossover. We compute the distribution of the crossover time and identify the size and the shape of the critical droplet. The analysis relies on a mesoscopic and microscopic description of the surface of the critical droplet. It turns out that the critical droplet is close to a disc of a certain deterministic radius, with a boundary that is random and consists of a large number of small discs that stick out by a small distance. We will show how the analysis of surface fluctuations in the WR model allows us to derive the leading order term of the condensation time and also the correction order term. This is a joint work with Frank den Hollander (Leiden), Sabine Jansen (Munich) and Roman Kotecky (Prague & Warwick).

Further Informations
Seminar Interacting Random Systems

Host
WIAS Berlin
Thursday, 04.02.2021, 16:00 (Online Event)
Forschungsseminar Mathematische Modelle der Photonik
Dr. Shalva Amiranashvili, WIAS Berlin:
Parallel splitting methods
more ... Location
Online Event

Host
WIAS Berlin
Thursday, 25.02.2021, 16:00 (Online Event)
Forschungsseminar Mathematische Modelle der Photonik
Siavash Qodratipur, HU Berlin:
Surface plasmon polaritons in nano-structures
more ... Location
Online Event

Host
WIAS Berlin