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Seminars - Summer term 2020

Seminar “Special problems in colloidal physics”

Location: HHU Düsseldorf, Online Seminar
Program:
DateSpeakerTopicTime
Mon 20.04.2020   R. Wittmann  Symmetries in classical density functional theory and statistical mechanics  14:30 s.t.
Fri 08.05.2020   L. Fischer  Magnetically induced elastic deformations of magnetic gels and elastomers containing particles of mixed size  14:30 s.t.
Fri 15.05.2020   P. Monderkamp  Liquid crystals in complex confinement  14:30 s.t.
Fri 05.06.2020   A. Zampetaki  A particle model for chemotactic bacteria and penguin huddling  14:30 s.t.
Mon 15.06.2020   A. Ider  Optimal navigation for microswimmers  14:30 s.t.
Wed 17.06.2020   J. Kolker  PNiPAm microgels under interfacial confinement  14:30 s.t.
Fri 19.06.2020   J. Grauer  Particle navigation in an unknown environment  14:30 s.t.
Fri 26.06.2020   A. Sprenger  Self-propelled particles in anisotropic environments  14:30 s.t.
Fri 17.07.2020   S. Mandal  Active agents in complex environments  14:30 s.t.
Prof. Dr. H. Löwen

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Seminar “Special problems in computer simulation of soft matter”

Location: HHU Düsseldorf, Online Seminar
Program:
DateSpeakerTopicTime
Fri 08.05.2020   L. Fischer  Magnetically induced elastic deformations of magnetic gels and elastomers containing particles of mixed size  14:30 s.t.
Fri 15.05.2020   P. Monderkamp  Liquid crystals in complex confinement  14:30 s.t.
Mon 25.05.2020   N. Küchler  Kinetic pathways for the transformation of a glass-forming fluid to a crystal  14:30 s.t.
Fri 05.06.2020   A. Zampetaki  A particle model for chemotactic bacteria and penguin huddling  14:30 s.t.
Wed 17.06.2020   J. Kolker  PNiPAm microgels under interfacial confinement  14:30 s.t.
Fri 19.06.2020   J. Grauer  Particle navigation in an unknown environment  14:30 s.t.
Mon 22.06.2020   B. Sanvee  Numerical Simulations of Lorentzgases  14:30 s.t.
Wed 24.06.2020   M. Golkia  Inhomogeneous flow patterns in super-cooled liquids and glasses under shear  14:30 s.t.
Fri 17.07.2020   S. Mandal  Active agents in complex environments  14:30 s.t.
Prof. Dr. J. Horbach

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Seminar “Soft Matter”

Location: HHU Düsseldorf, Online Seminar
Program:
DateSpeakerAffiliationTime
Thu 18.06.2020   Ben Goddard  University of Edinburgh, Scotland, United Kingdom  14:30 s.t.
Ben Goddard: „Mathematical Foundations of DDFT”
University of Edinburgh, Scotland, United Kingdom - Seminar@HHUD: 18.6.2020 14:30 s.t., Seminarroom Online

I will present mathematical results for a class of DDFTs, posed in the overdamped (high friction) regime, including hydrodynamic interactions, with no-flux boundary conditions. The system of interest consists of a continuity equation, coupled to a self-consistency equation for the flux. After explaining the derivation of the system from the inertial dynamics, I will present conditions that ensure the existence of unique solutions to the non-local, non-linear PDE system. I will also show that the solution is strictly positive for all positive time, and give a prori estimates for the rate of convergence to equilibrium, both in norm and relative entropy. Whilst the results are necessarily of a technical nature, I will try to present the intuition behind the results, rather than the mathematical details.

Joint work with Serafim Kalliadasis, Rory Mills-Williams, and Greg Pavliotis.

Mathematical Foundations of DDFT
Important notice - different location - Seminarroom Online
Wed 27.05.2020   Fabian Jan Schwarzendahl  University of California, Merced, United States of America  14:30 s.t.
Density heterogeneities and percolation of microswimmers
Thu 27.02.2020   Frank Smallenburg  Laboratoire de Physique des Solides, Orsay, France  14:30 s.t.
Manipulating the local structure and dynamics of supercooled liquids
Fri 17.01.2020   Laura Natali  Sapienza University of Rome, Italy  11:00 s.t.
Active transport of Biopolymers
Fri 10.01.2020   Simone Ciarella  TU Eindhoven, The Netherlands  14:30 s.t.
Microgel simualtion
Fri 10.01.2020   Liesbeth Janssen  TU Eindhoven, The Netherlands  14:00 s.t.
Microgel theory
Tue 07.01.2020   Davide Breoni  Institut für Theoretische Physik, Universität Innsbruck, Österreich  14:30 s.t.
Torus spectroscopy of the chiral Heisenberg quantum phase transition with quantum Monte Carlo simulations
Tue 03.12.2019   Maciej Lisicki  University of Warsaw, Poland  14:30 s.t.
Maciej Lisicki: „Pumping and swimming: two faces of phoretic flows”
University of Warsaw, Poland - Seminar@HHUD: 3.12.19 14:30 s.t., Seminarroom 25.32 O2.51

Janus particles with the ability to move phoretically in self-generated chemical concentration gradients are model systems for active matter. On the other hand, chemically active surfaces can lead to microscale flow generation, bacoming an effective pumping mechanism in inertia-less small-scale flows. In this talk, I will review briefly both phenomena relating to the same concept of phoretic flow generation. Asymmetry needed for the flow to be initiated can be induced by geometry or by chemical patterning. I will show examples of both ways and some applications in biomimetic systems of fully three-dimensional phoretic swimmers.

Pumping and swimming: two faces of phoretic flows
Wed 27.11.2019   Abhinav Sharma  Leibniz-Institut für Polymerforschung, Dresden  15:30 s.t.
Lorentz forces in active systems induce inhomogeneity and bulk fluxes
Mon 25.11.2019   Gerhard Jung & Thomas Franosch  Institut für Theoretische Physik, Universität Innsbruck, Austria  11:30 s.t.
Gerhard Jung & Thomas Franosch: „Static and dynamic properties of hard spheres in confinement”
Institut für Theoretische Physik, Universität Innsbruck, Austria - Seminar@HHUD: 25.11.19 11:30 s.t., Seminarroom 25.32 O2.51

Hard spheres confined by two parallel flat walls exhibit a rich phenomenology. This includes a non-monotonic dependence of the structure factor with wall distance [1], the emergence of exotic crystalline structures due to the competition of two length scales, viz. the particle size and the wall distance [2] and a multiple reentrant glass transition [1]. In this talk, I will elaborate on two selected phenomena, namely the confinement-induced separation and crystallization of polydisperse hard spheres and the dynamic properties of confined glass-forming liquids.

Fractional crystallization has been observed in bulk systems with polydisperse hard spheres at very high volume fraction [3]. Here, I will discuss how a similar effect emerges due to the aforementioned competition of length scales in confined geometry. This leads to the formation of crystals with much smaller polydispersity as the particles in the fluid phase. A possible application is the controlled separation of a hard sphere mixture in wedge geometry.

In the second part, I will present a detailed analysis of the dynamic properties of confined hard-sphere glasses predicted by mode-coupling theory. This includes the investigation of the coherent and incoherent scattering functions, an analysis of the α and β relaxation processes and a comparison to results from event-driven molecular dynamics simulations.

References

  1. Mandal, S. et al.; Nat. Comm. 2014, 5, 4435
  2. Schmidt, M.; Löwen, H.; Phys. Rev. E 1997, 55, 7228
  3. Fasolo, M.; Sollich, P.; Phys. Rev. E 2004, 70, 041410
Static and dynamic properties of hard spheres in confinement
Prof. Dr. Egelhaaf, Prof. Dr. Horbach, Prof. Dr. Löwen

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Colloquia

Location: HHU Düsseldorf, Lecture Hall 5J (Building 25.31 Level 00)
Program:
DateSpeakerAffiliationTime
Thu 23.01.2020   Prof. Dr. Jörg Rottler  University of British Columbia, Vancouver, Canada  16:30 s.t.
Prof. Dr. Jörg Rottler: „The nonequilibrium physics of driven amorphous soft matter: plasticity and collective effects”
University of British Columbia, Vancouver, Canada - Seminar@HHUD: 23.1.2020 16:30 s.t., Lecture hall 25.31 O0.5J

This talk will describe the yielding transition in disordered solids, a nonequilibrium phase transition between arrested and flowing states of matter. We use computer simulations at the particle scale to characterize the elementary shear transformations responsible for plastic flow, determine how they interact elastically and illustrate the resulting scale dependent shear strain correlations in (active and passive) amorphous packings. We then show how the statistics of the intermittent stick-slip motion that is typically observed macroscopically in these materials at slow mechanical driving can be related to the microscopic distribution of residual stresses that we measure in the simulations. Despite strong correlations, the statistical properties of steady state flow can then be captured by a mean field description that takes into account the broadly distributed mechanical excitations.

The nonequilibrium physics of driven amorphous soft matter: plasticity and collective effects
Fri 17.01.2020   Prof. Dr.-Ing. Rupert Klein  Freie Universität Berlin  16:45 s.t.
Prof. Dr.-Ing. Rupert Klein: „Mathematical Colloquium: How Mathematics helps structuring climate discussions”
Freie Universität Berlin - Seminar@HHUD: 17.1.2020 16:45 s.t., Lecture hall 25.22 O0.5H

Mathematics in climate research is often thought to be mainly a provider of techniques for solving the continuum mechanical equations for the flows of the atmosphere and oceans, for the motion and evolution of Earth´s ice masses, and the like. Three examples will elucidate that there is a much wider range of opportunities.

Climate modellers often employ reduced forms of "the continuum mechanical equations" to efficiently address their research questions of interest. The first example discusses how mathematical analysis can provide systematic guidelines for the regime of applicability of such reduced model equations.

Meteorologists define "climate", in a narrow sense, as "the statistical description in terms of the mean and variability of relevant quantities over a period of time" (World Meteorological Society; see the website for a broader sense definition). Now, climate researchers are most interested in changes of the climate over time, and yet there is no unique, well-defined notion of "time dependent statistics". In fact, there are restrictive conditions which data from time series need to satisfy for classical statistical methods to be applicable. The second example describes recent developments of analysis techniques for time series with non-trivial temporal trends.

Modern climate research has joined forces with economy and the social sciences to generate a scientific basis for informed political decisions in the face of global climate change. One major type of problems hampering progress of the related interdisciplinary research consists of often subtle language barriers. The third example describes how mathematical formalization of the notion of "vulnerability" has helped structuring related interdisciplinary research efforts.

Mathematical Colloquium: How Mathematics helps structuring climate discussions
Thu 09.01.2020   Prof. Dr. Johann Rafelski  University of Arizona, Tucson, USA  16:30 s.t.
Prof. Dr. Johann Rafelski: „Special Relativity and Strong Fields”
University of Arizona, Tucson, USA - Seminar@HHUD: 9.1.2020 16:30 s.t., Lecture hall 25.31 O0.5J

Special Relativity (SR), the foundation of modern physics, experiences a renaissance as a discipline and is rapidly evolving: We are probing the acceleration/strong electromagnetic field frontier in relativistic heavy ion experiments, and thinking ahead to the very high intensity laser-particle interaction. We are facing a challenge: Teaching of SR to future researchers in these field. SR remains poorly represented in many introductory text books. No-expert lecturers do not correctly understand SR and related elementary physics phenomena. The unfinished formulation of SR when forces are not gravity will be explained. Strong EM fields will be introduced.

Special Relativity and Strong Fields
Thu 12.12.2019   Prof. Dr. Ralf Metzler  Universität Potsdam, Institut für Physik und Astronomie  16:30 s.t.
Prof. Dr. Ralf Metzler: „Brownian motion and beyond”
Universität Potsdam, Institut für Physik und Astronomie - Seminar@HHUD: 12.12.19 16:30 s.t., Lecture hall 25.31 O0.5J

Roughly 190 years ago Robert Brown reported the "rapid oscillatory motion" of microscopic particles, the first systematic study of what we now call Brownian motion. At the beginning of the 20th century Albert Einstein, Marian Smoluchowski and Pierre Langevin formulated the mathematical laws of diffusion. Jean Perrin‘s experiments 110 years ago then prompted a very active field of ever refined diffusion experiments.

Despite the long-standing history of Brownian motion, after an historic introduction I will report several new developments in the field of diffusion and stochastic processes. This new research has been fuelled mainly by novel insights into complex microscopic systems such as living biological cells, made possible by Nobel-Prize winning techniques in laser physics, superresolution microscopy, or through supercomputing studies. Topics covered include Brownian yet non-Gaussian diffusion, the geometry-control of chemical reactions and anomalous diffusion with a power-law time dependence of the mean squared displacement. For the latter, questions of ergodicity and ageing will be discussed.

Brownian motion and beyond
Thu 05.12.2019   Dr. Bastian Aurand  Institut für Laser- und Plasmaphysik, Heinrich-Heine-Universität Düsseldorf  16:30 s.t.
Dr. Bastian Aurand: „Novel target schemes for laser-driven proton acceleration”
Institut für Laser- und Plasmaphysik, Heinrich-Heine-Universität Düsseldorf - Seminar@HHUD: 5.12.19 16:30 s.t., Lecture hall 25.31 O0.5J

The acceleration of charged particles by super-intense laser-matter interactions has gained a high interest within the last decades. The unique features of the so-called plasma-accelerators, like their compact design, ultra-short particle bursts or high particle-flux compared to conventional accelerators can be a milestone, for example as a diagnostic tool in physics or to simplify applications like hadron therapy. Besides the fundamental research on the different processes used to accelerate particles, more and more effort is taken in the last years to pave the way towards applications using the unique features of those beams.

In this talk, I will present different approaches to improve laser-driven proton acceleration, e.g. towards a higher repetition-rate, better energy stability, less debris production or the shaping of the spatial beam profile. I will start with a brief introduction into the field by comparing conventional particle accelerators to plasma-accelerators and highlight today’s state of the art. Discussing the best-studied mechanism, the so-called Target-Normal-Sheath-Acceleration (TNSA) is the base to introduce modifications, like a double laser focus or the effect of improved target geometry. While both schemes are a variation of TNSA, I will identify the general drawbacks of this method and show two alternative approaches using isolated, mass-limited targets. In the first experiment, a controlled droplet formation from a liquid stream is used, resulting in targets which are larger than the laser focus, leading to a hybrid mechanism. Finally, a hydrogen cluster source will be presented, delivering targets which are Coulomb-exploded by the laser. This mechanism is inherently more stable against fluctuations during the laser-matter interaction and allows at the same time a fine-tuning of the particle energy within a wide range.

A comparison of the approaches will summarize the talk along with identifying future tasks and work-packages towards the goal of applicable laser-driven particle accelerators.

Novel target schemes for laser-driven proton acceleration
Mon 07.10.2019   Prof. Dr. Matthias Karg  Heinrich-Heine-Universität Düsseldorf  17:00 s.t.
Current research at the institute for colloids and nanooptics
Tue 01.10.2019   Prof. Dr. Hari Srikanth  University of South Florida, USA  16:30 s.t.
Prof. Dr. Hari Srikanth: „Tuning magnetic anisotropy in nanostructures for biomedical applications”
University of South Florida, USA - Seminar@HHUD: 1.10.2019 16:30 s.t., Lecture hall 6A

Magnetic nanoparticles have been building blocks in applications ranging from high density recording to spintronics and nanomedicine. Magnetic anisotropies in nanoparticles arising from surfaces, shapes and interfaces in hybrid structures are important in determining the functional response in various applications.

In this talk I will first introduce the basic aspects of anisotropy, how to tune it in nanostructures and ways to measure it. I will discuss resonant RF transverse susceptibility, that we have used extensively, as a powerful method to probe the effective anisotropy in magnetic materials. Tuning anisotropy has a direct impact on the performance of functional magnetic nanoparticles in biomedical applications such as contrast enhancement in MRI and magnetic hyperthermia cancer therapy. There is a need to improve the specific absorption rate (SAR) or heating efficiency of nanoparticles for hyperthermia and I will focus on the role of tuning surface and interfacial anisotropy with a goal to enhance SAR.

Strategies going beyond simple spherical structures such as exchange coupled core-shell nanoparticles, nanowire, nanotube geometries can be exploited to increase saturation magnetization, effective anisotropy and heating efficiency in magnetic hyperthermia. This lecture will combine insights into fundamental physics of magnetic nanostructures along with recent research advances in their application in nanomedicine.

Tuning magnetic anisotropy in nanostructures for biomedical applications
WE Physik, Heinrich-Heine-Universität Düsseldorf

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Seminar about Bachelor, Master and other Theses from the Institut for Theoretical Physics II

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Link: Physics Colloquium
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