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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  13:30 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.
Wed 28.06.2017   M. Puljiz  Two magnetically interacting rigid inclusions in a soft gel  13:30 s.t.
Wed 28.06.2017   U. Zimmermann  Dynamical Density Functional Theory in 2D Microchannels  14:30 s.t.
Fri 30.06.2017   A. Gabriëlse  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  13:30 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   M. Golkia  Residual stresses in glasses  14:30 s.t.
Fri 30.06.2017   A. Gabriëlse  Crystallization of nanoparticles with square-shoulder interactions  14:30 s.t.
Wed 02.08.2017   M. Eshraghi  Yukawa fluids and solids near hard walls: Evidence for a pre-freezing transition  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
Mon 31.07.2017   Pinaki Chaudhuri  The Institute of Mathematical Sciences, Chennai, India  14:30 s.t.
Long-range dynamic correlations during aging of gels
Fri 28.07.2017   Suvendu Mandal  Universität Innsbruck, Austria  14:30 s.t.
Suvendu Mandal: „The dynamics of driven and active Brownian particles”
Universität Innsbruck, Austria - Seminar@HHUD: 28.7.17 14:30 s.t., Seminarroom 25.32 O2.51

While the linear response is well-characterized in terms of the fluctuation-dissipation theorem, few exact results are available for strong driving. Here we study the time-dependent velocity of a colloidal particle immersed in a dilute suspension of hard spheres in response to a step force switched on at time zero using Brownian dynamics simulations. Our main quantity of interest is the time-dependent mobility and its approach to the stationary state mobility. A stationary state solution for the mobility exact in first order of the packing fraction has been established earlier in terms of a power-series expansion with respect to the force on the tracer particle [1]. We extend this result to the case of arbitrarily strong driving including the complete time-dependence of the response upon switching on the force. We show that in the stationary state, our analytic solution recovers the anticipated limit for strong driving [1] and captures the response in first order of the packing fraction for any strength of the force.

We also investigate active colloidal hard-sphere glasses using Brownian dynamics simulations. While the properties of passive colloidal glasses are fairly understood over the years, not much is known for active colloidal glasses. In this talk we discuss the decoupling between active speed and rotational diffusion in colloidal glasses. These findings agree with theoretical predictions obtained by the mode-coupling theory of the glass transition.

References

  1. T. M. Squires and J. F. Brady, Physics of Fluids 17, 0731
The dynamics of driven and active Brownian particles
Wed 26.07.2017   Vladimir S. Filinov  Russian Academy of Sciences, Moscow, Russia  14:30 s.t.
Vladimir S. Filinov: „Peculiarities of momentum distribution functions of strongly correlated charged fermions”
Russian Academy of Sciences, Moscow, Russia - Seminar@HHUD: 26.7.17 14:30 s.t., Seminarroom 25.32 O2.51

The main difficulty for path integral Monte Carlo studies of Fermi systems results from the requirement of antisymmetrization of the density matrix [1] and is known in literature as the ′sign problem′ [2-6] . To overcome this issue the new numerical version of the Wigner approach to quantum mechanics for treatment thermodynamic properties of degenerate systems of fermions has been developed. The new path integral representation of quantum Wigner function in the phase space has been obtained for canonical ensemble. Explicit analytical expression of the Wigner function accounting for Fermi statistical effects by effective pair pseudopotential has been presented. Derived pseudopotential depends on coordinates, momenta and degeneracy parameter of fermions and takes into account coordinate – momentum principle uncertainly.

The new quantum Monte-Carlo method for calculations of average values of arbitrary quantum operators has been proposed.

To test the developed approach calculations of the momentum distribution function of the degenerate ideal system of Fermi particles has been carried out in a good agreement with analytical Fermi distributions.

On other hand the first results on influence of interparticle interaction on momentum distribution functions show appearance of quantum "tails" in the Fermi distributions.

References

  1. Feynman R P and Hibbs A R (1965) Quantum Mechanics and Path Integrals (New York: McGraw-Hill)
  2. Filinov V S (2014) High Temperature, 52, 615
  3. Filinov V (2001) J. Phys. A: Math. Gen. 34, 1665
  4. McMahon J M, Morales M A, Pierleoni C, Ceperley D (2012) Rev. Mod. Phys. 84 1607
  5. Ceperley D (1991) J.Stat. Phys. 63 1237; (1992) Phys. Rev. Let. 69 331
  6. Militzer B and Pollock R (2000) Phys. Rev. E 61, 3470
  7. Galitskii V M and Yakimets V V (1967) Zh. Eksp. Teor. Fiz. 51 957; 1967 Sov. Phys. JETP 24 637
  8. Eletskii A V, Starostin A N and Taran M D (2005) Physics - Uspekhi 48 281
Peculiarities of momentum distribution functions of strongly correlated charged fermions
Tue 25.07.2017   Surajit Sengupta  TIFR, Hyderabad, India  15:30 s.t.
Do thermodynamically stable rigid crystals exist?
Mon 10.07.2017   Smarajit Karmakar  TIFR, Hyderabad, India  15:30 s.t.
Growth of Amorphous Order and its role in the Dynamics of Supercooled Liquids
Tue 27.06.2017   William van Megen  RMIT Melbourne, Australia  14:30 s.t.
William van Megen: „Collective modes in hard sphere systems; cage effect”
RMIT Melbourne, Australia - Seminar@HHUD: 27.6.17 14:30 s.t., Seminarroom 25.32 O2.51

It’s axiomatic that the slowing of diffusion, increasing sluggishness of flow and delay of the structural relaxation a fluid when its density is increased are due to the increasing congestion among the particles comprising the fluid. It is also generally accepted that these manifestations of dynamic slowing are due to the ”cage effect“ the microscopic picture in which particles are trapped, at least momentarily, by their respective neighbours. An attempt to examine the role of caging more closely considers the spread of the displacement distributions of Brownian particles. These distributions are necessarily biased by the presence of neighbouring particles. Accommodation of this bias by those neighbours conserves the displacement distribution locally and presents a collective mechanism for exploring configuration space that turns out to be more efficient than the intrinsic Brownian motion. Blocking of the bias effects caging of some particles, however locally in space and time. This incurs, through the impost of global conservation of probability (the average number of caged particles), a delayed, non-local collective process. Both collective mechanisms incur delay or stretching of time correlation functions, in particular the particle number and flux densities. This presentation identifies and distinguishes these mechanisms in existing data from dynamic light scattering experiments and computer simulations on systems of particles with hard sphere interactions.

Collective modes in hard sphere systems; cage effect
Fri 02.06.2017   Gerd Schröder-Turk  Murdoch University, Perth, Australia  14:30 s.t.
Mixtures of Pears and Oranges: From inverse micelles to labyrinth-like bicontinuous phases
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
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 20.07.2017   Prof. Dr. Tanja Schilling  Universität Freiburg  16:30 s.t.
Prof. Dr. Tanja Schilling: „Playful Physics”
Universität Freiburg - Seminar@HHUD: 20.07.2017 16:30 s.t., Lecture hall 25.31 O0.5J

Chemotactic motion is the motion of living organisms in response to chemical signals as e.g. motion of bacteria towards sources of food. We discuss chemotaxis in a porous medium using as a model a biased (6quot;hungry") random walk on a percolating cluster. Incidentally, the model closely resembles the 1980s arcade game Pac-Man. We observe that, on the percolating cluster, the hungry random walker's mean-squared displacement shows anomalous dynamics that follow a power law with a dynamical exponent different from both that of a self avoiding random walk as well as that of an unbiased random walk. The change in dynamics with the propensity to move towards food is well described by a dynamical exponent that depends continuously on this propensity.

In the second part we apply a similar, physics-based approach to a more complex game, the game of chess. The complexity of a game is usually estimated in terms of the size of its state space (i.e. the number of possible configurations) and the size of its game tree (i.e. the number of distinct possible games). For chess these have been estimated to be on the order of its game tree (i.e. the number of distinct possible games). For chess these have been estimated to be on the order of 1042 resp 10120 . A chess player's experience however, shows that many possible configurations never occur in real play. The connectivity of state-space seems to matter significantly for the complexity. Using transition path sampling we show that the state space of chess consists of ca. 1020 pockets that are only weakly connected. The pockets are distinguished mainly by their pawn structure. Real games take place only in a few of these pockets. That chess is still highly complex can be attributed to the fact that 1022 - although considerably smaller than the entire set of states - is still a very large number.

Playful Physics
Thu 29.06.2017   Prof. Dr. Holger Stark  Institut für Theoretische Physik, Technische Universität Berlin  16:30 s.t.
Microswimmers: From design principles to their emergent collective behavior
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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