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Seminars - Summer term 2017

Seminar “Special problems in colloidal physics”

Location: HHU Düsseldorf, Seminarroom 25.32.O2.51
Program:
DateSpeakerTopicTime
Wed 03.05.2017   G. Pessot  Self-induced polar order for pushers and pullers  14:30 s.t.
Mon 08.05.2017   C. Hoell  Dynamical density functional theory for circle swimmers  14:30 s.t.
Wed 10.05.2017   C. Sitta  Tetratic phases of rectangles using DFT  14:30 s.t.
Wed 31.05.2017   C. Scholz  There's something hidden in the basement - active matter driven by vibrations!  14:30 s.t.
Thu 01.06.2017   E. Allahyarov  A review of new developments in responsive nanocomposites  14:30 s.t.
Mon 12.06.2017   S. Babel  DDFT of charged particles in an electric field  14:30 s.t.
Wed 14.06.2017   S. Jahanshahi  The Brazil nut and reverse Brazil nut effects  14:30 s.t.
Mon 26.06.2017   U. Zimmermann  Dynamical Density Functional Theory in 2D Microchannels  14:30 s.t.
Wed 28.06.2017   M. Puljiz  Effective elastic moduli of structurally anisotropic composite materials  14:30 s.t.
Fri 30.06.2017   F. Smallenburg
 A. Gabriëlse
 Melting of crystals of charged colloidal particles
 Crystallization of nanoparticles with square-shoulder interactions
 14:30 s.t.
Prof. Dr. H. Löwen

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Seminar “Special problems in computer simulation of soft matter”

Location: HHU Düsseldorf, Seminarroom 25.32.O2.51
Program:
DateSpeakerTopicTime
Wed 03.05.2017   G. Pessot  Self-induced polar order for pushers and pullers  14:30 s.t.
Mon 29.05.2017   S. Ganguly  Interfacial free energies at solid-solid interfaces  14:30 s.t.
Wed 31.05.2017   C. Scholz  There's something hidden in the basement - active matter driven by vibrations!  14:30 s.t.
Thu 01.06.2017   E. Allahyarov  A review of new developments in responsive nanocomposites  14:30 s.t.
Mon 12.06.2017   S. Babel  DDFT of charged particles in an electric field  14:30 s.t.
Wed 14.06.2017   S. Jahanshahi  The Brazil nut and reverse Brazil nut effects  14:30 s.t.
Fri 16.06.2017   N. Siboni  Diffusion in magnetic Lorentz gas  14:30 s.t.
Thu 29.06.2017   M. Golkia  Residual stresses in glasses  14:30 s.t.
Fri 30.06.2017   F. Smallenburg
 A. Gabriëlse
 Melting of crystals of charged colloidal particles
 Crystallization of nanoparticles with square-shoulder interactions
 14:30 s.t.
Thu 27.07.2017   M. Eshraghi  Calculation of interfacial free energy via Thermodynamic Integration (TI)  14:30 s.t.
Prof. Dr. J. Horbach

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Seminar “Soft Matter”

Location: HHU Düsseldorf, Seminarroom 25.32.O2.51
Program:
DateSpeakerAffiliationTime
Wed 26.07.2017   Vladimir S. Filinov  Russian Academy of Sciences, Moscow, Russia  14:30 s.t.
t.b.a.
Wed 17.05.2017   Rolf Schilling  Johannes-Gutenberg-Universität Mainz  14:30 s.t.
Extremely Confined Fluids: Thermodynamics and Dynamics
Thu 04.05.2017   Christina Kurzthaler  Universität Innsbruck, Austria  14:30 s.t.
Christina Kurzthaler: „From self-propelled particles to semiflexible polymers”
Universität Innsbruck, Austria - Seminar@HHUD: 4.5.17 14:30 s.t., Seminarroom 25.32 O2.51

Self-propelled particles are intrinsically out of equilibrium and exhibit peculiar dynamical behavior. These active agents are subject to strong stochastic fluctuations, that compete with their persistent swimming motion. So far most studies consider the lowest order moments of the displacements only, while more general spatiotemporal information is encoded in the directly measurable intermediate scattering function, i.e. the Fourier transform of the probability density. In this talk, I will discuss analytic solutions of the intermediate scattering function of an active Brownian particle and a Brownian circle swimmer, and show, that our theoretical predictions agree very well with experimental observations of Janus particles. The mathematical analog to the self-propelled particle constitutes the semiflexible polymer. I will also provide an exact solution for the partition sum of a semiflexible polymer under compression and analyze its buckling behavior in terms of the force-extension relation.

From self-propelled particles to semiflexible polymers
Fri 21.04.2017   Céline Ruscher  Institut Charles Sadron, Strasbourg, France  14:30 s.t.
Voronoi glasses: a new model for probing glass transition
Thu 09.02.2017   Wei Li  Universität Bochum  14:30 s.t.
Wei Li: „Cooperative Control of Multi-Agents On Non-Euclidean Manifolds”
Universität Bochum - Seminar@HHUD: 9.2.17 14:30 s.t., Seminarroom 25.32 O2.51

References

  • Wei Li (), "Collective motion of swarming agents evolving on a sphere manifold: A fundamental framework and characterization," Scientific Reports, vol. 5, Article ID: 13603, 2015. DOI:10.1038/srep13603
  • Wei Li, Mark W. Spong, "Unified cooperative control of multiple agents on a sphere for different spherical patterns," IEEE Transactions on Automatic Control, vol. 59, no. 5, pp. 1283-1289, May 2014
Cooperative Control of Multi-Agents On Non-Euclidean Manifolds
Mon 06.02.2017   Ben Guy  School of Physics and Astronomy, The University of Edinburgh, Edinburgh, United Kingdom  10:30 s.t.
Ben Guy: „The rheology of suspensions of intermediate-sized particles”
School of Physics and Astronomy, The University of Edinburgh, Edinburgh, United Kingdom - Seminar@HHUD: 6.2.2017 10:30 s.t., Seminarroom 25.32 O2.51

The flow of concentrated particulate suspensions plays a central role in many industrial sectors, ranging from the drilling of oil to the manufacture of confectionery. In spite of its ubiquity, concentrated suspension flow is poorly understood, even for model systems with well-controlled particle interactions. In the last two decades, considerable progress has been made in understanding the flow of granular suspensions (diameter d>50 micron), for which contact forces and inter-particle friction play a controlling role, and of colloidal suspensions (d<1 micron), for which entropic interactions dominate. A physical understanding of the intermediate size regime (1 micron<d<50 micron) remains elusive, however, even though many industrial dispersions inhabit precisely this regime. By performing experiments on well-characterised model systems, we have established a generic framework for the rheology of suspensions of intermediate-sized particles. In each system, one can identify two viscosity "branches" diverging at different concentrations, corresponding to the jamming volume fractions for lubricated and frictional particle-particle contacts [1]. If finite-range repulsion is present, the system undergoes a stress-dependent transition between the branches that manifests as shear thickening [2], supporting a recent theory of thickening by Wyart and Cates [3]. We discuss methods for controlling the two divergences, e.g., by introducing surface modifiers or size polydispersity, paving the way for a predictive description of concentrated suspension rheology.

References

  1. B. M. Guy, M. Hermes and W. C. K. Poon, Phys. Rev. Lett. 115, 088304 (2015)
  2. N. Y. C. Lin et. al., Phys. Rev. Lett. 115, 228304 (2015)
  3. M. Wyart and M. E. Cates, Phys. Rev. Lett. 112, 098302 (2014)
The rheology of suspensions of intermediate-sized particles
Thu 15.12.2016   Abdallah Daddi-Moussa-Ider  Universität Bayreuth  15:30 s.t.
Diffusion nearby elastic cell membranes
Thu 15.12.2016   Alan Denton  North Dakota State University, USA  11:30 s.t.
Soft Colloidal Particles in Crowded Environments
Fri 02.12.2016   Edan Lerner  University of Amsterdam, The Netherlands  14:30 s.t.
Edan Lerner: „Nonlinear plastic modes”
University of Amsterdam, The Netherlands - Seminar@HHUD: 2.12.16 14:30 s.t., Seminarroom 25.32 O2.51

Understanding the yielding transition observed upon deforming a glass beyond its elastic limit requires the proper identification of the micro-mechanical objects, akin to dislocations in crystals, that carry plastic flow. In my talk I will introduce a theoretical framework within which a robust, micro-mechanical definition of precursors to plastic instabilities in glassy solids naturally emerges. I will demonstrate how these precursors, coined nonlinear plastic modes, can be calculated without resorting to conventional harmonic eigenmode analyses, but instead by properly accounting for nonlinearities of the potential energy landscape. I will explain how nonlinear plastic modes are coupled to external deformations, and will argue that the a-priori detection of the soft-spots field in model glasses can be effectively carried out by a nonlinear plastic modes analysis.

Nonlinear plastic modes
Thu 24.11.2016   René Wittmann  University of Fribourg, Switzerland  14:30 s.t.
René Wittmann: „Effective interactions of active particles: interfacial phase behavior and mechanical properties”
University of Fribourg, Switzerland - Seminar@HHUD: 24.11.16 14:30 s.t., Seminarroom 25.32 O2.51

We employ classical density functional theory to study the self-organization in active systems.

We use a first-principles approach to map the self-propulsion onto an effective pair interaction potential, which has been shown [1] to account for the motility-induced phase separation (MIPS) observed for active Brownian particles.

n this talk we introduce an effective external potential and investigate inhomogeneous situations. Solely as a result of their activity, we predict [2] that active (Brownian) particles undergo a variety of interfacial phase transitions, e.g., wetting and capillary condensation in purely repulsive systems or drying and capillary evaporation of attractive colloids.

Finally, we explain why the effective thermodynamic pressure and interfacial tension do not represent the proper results one would measure mechanically and demonstrate how these can be recovered within a more general framework.

References

  1. T.F.F. Farage, P. Krinninger and J.M. Brader, Phys. Rev. E 91, 042310 (2015)
  2. R. Wittmann and J.M. Brader, EPL 114, 68004 (2016)
Effective interactions of active particles: interfacial phase behavior and mechanical properties
Mon 21.11.2016   Joachim Dzubiella  Helmholtz-Zentrum Berlin und Humboldt-Universität Berlin  14:30 s.t.
Joachim Dzubiella: „Rational design of stimuli-responsive nanoreactors”
Helmholtz-Zentrum Berlin und Humboldt-Universität Berlin - Seminar@HHUD: 21.11.16 14:30 s.t., Seminarroom 25.32 O2.51

The catalysis by metal nanoparticles is one of the fastest growing fields in nanoscience. However, the optimal control of catalytic activity and selectivity in nanoparticle catalysis remains a grand scientific challenge. Here, we describe our ongoing efforts how to theoretically derive design rules for the optimization of nanoparticle catalysis (in the fluid phase) by means of thermosensitive yolk-shell and core-shell carrier systems. In the latter, nanoparticles are stabilized in solution by an encapsulating, thermosensitive hydrogel shell. The latter contains and shelters the reaction. The physicochemical properties of this polymeric 'nanogate' react to stimuli in the environment and thus permit the reactant fluxes and with that the catalytic reaction to be switched and tuned, e.g., by the temperature, salt concentration, or solvent composition. Hence, the novel hybrid character of these emerging 'nanoreactors' opens up unprecedented ways for the control of nanocatalysis due to new designable degrees of freedom, if theoretical understanding and rational design principles are available.

Rational design of stimuli-responsive nanoreactors
Wed 02.11.2016   Christian Scholz  Friedrich-Alexander-Universität Erlangen-Nürnberg  14:30 s.t.
Christian Scholz: „Dancing to the Vibes - Demixing of active granular rotors”
Friedrich-Alexander-Universität Erlangen-Nürnberg - Seminar@HHUD: 2.11.16 14:30 s.t., Seminarroom 25.32 O2.51

The majority of animal life performs active motion, i.e. organisms store energy within internal degrees of freedom and later release it in terms of directed motion. While in biological organisms this topic itself has been studied extensively, from swimming bacteria to flocks of animals, interest grew also in physical systems of inanimate objects that perform active motion. Most noticeable artificial microswimmers, but also active granular walkers.

We create a system of 3D-printed active rotors, driven by vertical vibrations. Weobserve a phase separated stationary state, where rotors demix into domains of likewise rotation. The temporal evolution of the patterns from the mixed initial state can be quantified from the size of the clusters in analogy to spinodal decomposition. The particle motion can be mapped onto a Langevin equation, which via molecular dynamics simulations allows a direct comparison between experiment and simulation.

Dancing to the Vibes - Demixing of active granular rotors
Tue 11.10.2016   Vishwas V. Vasisht  Georgetown University, USA  11:00 s.t.
Evolution of dense amorphous systems under shear and vibration
Prof. Dr. Egelhaaf, Prof. Dr. Horbach, Prof. Dr. Löwen

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poroSys-Talks

File: poroSys Talkslist

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Colloquia

Location: HHU Düsseldorf, Lecture Hall 5J (Building 25.31 Level 00)
Program:
DateSpeakerAffiliationTime
Thu 26.01.2017   Prof. Karsten Flensberg  Niels Bohr Institute, University of Copenhagen, Denmark  16:30 s.t.
Towards Majorana-based topological qubits?
Thu 19.01.2017   Prof. Michael Eikerling  Simon Fraser University, Vancouver, Canada  16:30 s.t.
The Physics of Electrochemical Energy Conversion
Thu 08.12.2016   PD Dr. Antonio Di Piazza  Max-Planck-Institut für Kernphysik, Heidelberg  16:30 s.t.
Tests of classical and quantum electrodynamics in intense laser beams
Thu 24.11.2016   Prof. Dr. Susana Huelga  Universität Ulm  16:30 s.t.
Vibrations, Quanta and Biology
Thu 27.10.2016   Prof. Joseph Indekeu  Theoretical Physics, KU Leuven, Belgium  16:30 s.t.
Short-range wetting in two dimensions: is it always second-order?
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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