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Seminare - Sommer Semester 2018

Seminar über "spezielle Probleme in der Theorie der Kolloide"

Ort: HHU Düsseldorf, Seminarraum 25.32.O2.51
Programm:
DatumSprecher/inThemaZeit
Mo 09.04.2018   C. Hoell  Dynamical density functional theory of microswimmers: straight and circle swimming  14:30 s.t.
Mi 11.04.2018   S. Jahanshahi  From microwimmers to microflyers II  14:30 s.t.
Mi 09.05.2018   A. Ider  Hydrodynamics of microswimmers in a nematic liquid crystal  14:30 s.t.
Mo 11.06.2018   B. Liebchen  Active Molecules  14:30 s.t.
Mi 13.06.2018   S. Mandal  Velocity autocorrelation function of Brownian particles  14:30 s.t.
Do 21.06.2018   S. Goh  Density functional theory for 2D ferrogels  14:30 s.t.
Mo 16.07.2018   M. Eshraghi  Hard-Core Yukawa crystal-liquid interfacial free energy via thermodynamic integration  14:30 s.t.
Di 17.07.2018   S. Babel  Feedback-driven colloidal suspension  14:30 s.t.
gez.: Prof. Dr. H. Löwen

oben

Seminar über "Spezielle Probleme der Computersimulation weicher Materie"

Ort: HHU Düsseldorf, Seminarraum 25.32.O2.51
Programm:
DatumSprecher/inThemaZeit
Mi 11.04.2018   S. Jahanshahi  From microwimmers to microflyers II  14:30 s.t.
Mo 11.06.2018   B. Liebchen  Active Molecules  14:30 s.t.
Mi 13.06.2018   S. Mandal  Velocity autocorrelation function of Brownian particles  14:30 s.t.
Fr 15.06.2018   M. Golkia  Mechanical properties of deformed glasses  14:30 s.t.
Do 21.06.2018   S. Goh  Density functional theory for 2D ferrogels  14:30 s.t.
Mo 16.07.2018   M. Eshraghi  Hard-Core Yukawa crystal-liquid interfacial free energy via thermodynamic integration  14:30 s.t.
gez.: Prof. Dr. J. Horbach

oben

Seminar “Soft Matter”

Ort: HHU Düsseldorf, Seminarraum 25.32.O2.51
Programm:
DatumSprecher/inInstitutZeit
Mi 08.08.2018   Dennis Schubert  Universität Hannover  14:30 s.t.
t.b.a.
Fr 15.06.2018   Sebastian Gonzalez  University of Chile, Santiago de Chile, Chile  15:30 s.t.
Making flagella with active colloids
Do 14.06.2018   Aljaz Godec  Mathematical Biophysics Group, Max Planck Institute for Biophysical Chemistry, Göttingen  14:30 s.t.
Aljaz Godec: „Dynamics at low-copy numbers: from few-encounter kinetics to single-molecule local times”
Mathematical Biophysics Group, Max Planck Institute for Biophysical Chemistry, Göttingen - Seminar@HHUD: 14.6.2018 14:30 s.t., Seminarroom 25.32 O2.51

A new paradigm emerges when considering molecular reaction kinetics in the few-encounter limit occurring, e.g. in transcription regulation or in diseases triggered by protein misfolding, where already the first reactive event is ‘catastrophic’. Similarly, “time−average statistical mechanics” is required for a correct theoretical description of single-molecule dynamics, which explicitly takes into account trajectory-to-trajectory fluctuations over finite observation times.

In the first part of the talk we will present rigorous results on first passage time statics in rugged energy landscapes and highlight their importance for understanding few-encounter kinetics. The second part of the talk will focus on local-time statistics for single-molecule dynamics, first in a canonical setting and afterwards applied to the analysis of tagged particle dynamics in single-file diffusion. We will conclude with a short perspective and open questions.

Dynamics at low-copy numbers: from few-encounter kinetics to single-molecule local times
Fr 18.05.2018   Surajit Sengupta  TIFR Hyderabad, India  14:30 s.t.
Surajit Sengupta: „Do non-affine atomic displacements in apo-proteins reveal eventual binding pathways?”
TIFR Hyderabad, India - Seminar@HHUD: 18.5.18 14:30 s.t., Seminarroom 25.32 O2.51

Designing drugs which target specific proteins involved in diseases consumes a lot of time and effort in the pharmaceutical industry. In recent times, in silico design of drugs using all-atom molecular modelling has started to provide crucial inputs. Even so, discovery of binding pathways of small molecules both at the primary binding site, as well as sites for allosteric control, is time consuming and often fortuitous. We provide here a framework within which critical conformational changes likely to occur during binding are quantified from statistical analysis of configurations of proteins in their apo, or inactive form, greatly simplifying identification of target residues. We illustrate this idea by analysing ligand binding pathways for two proteins T4-Lysozyme and Src kinase, which are active respectively in the immune system and cancer.

Do non-affine atomic displacements in apo-proteins reveal eventual binding pathways?
Do 19.04.2018   Masoud Hoore  Institute of Complex Systems and Institute for Advance Simulation, Forschungszentrum Jülich  14:30 s.t.
Masoud Hoore: „Modeling primary hemostasis”
Institute of Complex Systems and Institute for Advance Simulation, Forschungszentrum Jülich - Seminar@HHUD: 19.4.18 14:30 s.t., Seminarroom 25.32 O2.51

von Willebrand factors (VWFs) are the largest plasma proteins, playing a crucial role in blood clotting by adhering to platelets and forming aggregates. These aggregates form critically at high shear rates and dissolve reversibly at low shear rates. The emergence of a critical shear rate, beyond which aggregates form and below which they dissolve, has an interesting impact on aggregation in blood flow. As red blood cells (RBCs) migrate to the center of the vessel in blood flow, a RBC free layer (RBC-FL) is left close to the walls into which the platelets and VWFs are pushed back from the bulk flow. This margination process provides maximal VWF-platelet aggregation probability within the RBC-FL. Using mesoscale hydrodynamic simulations of aggregate dynamics in blood flow, it is shown that the aggregates form and grow in RBC-FL wherein shear rate is high for VWF stretching. By growing, the aggregates penetrate to the bulk flow and get under an order of magnitude lower shear rates. Consequently, they dissolve and get back into the RBC-FL. This mechanical limitation for aggregates prohibits undesired thrombosis and vessel blockage by aggregates, while letting the VWFs and platelets to aggregate close to the walls where they are actually needed.

Modeling primary hemostasis
Do 05.04.2018   Werner Krauth  Laboratoire de Physique Statistique, École normale supérieure, Paris, France  14:30 s.t.
Phase transitions in two dimensions: From the classic hard-disk model to active systems
Fr 23.03.2018   Manis Chaudhuri  t.b.a.  14:30 s.t.
Exploring crystal-glass transition on the single particle level with core-shell microgels
Do 22.03.2018   Roberto Cerbino  Universitá degli Studi di Milano, Italy  14:30 s.t.
Roberto Cerbino: „Unjamming by flocking in epithelial cell monolayers”
Universitá degli Studi di Milano, Italy - Seminar@HHUD: 22.3.2018 14:30 s.t., Seminarroom 25.32 O2.51

It is now increasingly recognised that cell collectives undergo a transition to a glassy or jammed state that is akin to the one observed in molecular and colloidal matter. In mature epithelial tissues, such transition may ensure the proper development of elasticity but, whenever a tissue must adapt to changes or perturbations of its physiological state, unjamming might be advantageous. By combining experiments and simulations, we studied the dramatic reawakening of cell motility that occurs at constant cell density when a jammed mammary epithelial cell monolayer is perturbed by overexpression of one single protein. Directed cell migration emerges when cell-cell interactions promote coherence of local cell polarization, which is reminiscent of flocking in birds and other animal species. We discuss the relevance of these flocking states for tumour dissemination.

Unjamming by flocking in epithelial cell monolayers
Do 15.02.2018   Katherine Rumble  The University of Edinburgh, United Kingdom  14:30 s.t.
Katherine Rumble: „Particles Stabilising Unconventional Emulsions”
The University of Edinburgh, United Kingdom - Seminar@HHUD: 15.2.18 14:30 s.t., Seminarroom 25.32 O2.51

In this seminar I will discuss two topics: the centrifugal compression of the bijel and the formation of bridged emulsions stabilised rod-shaped particles.

Bijels (bicontinuous interfacially jammed emulsion gels) are interesting emulsions with two continuous liquid phases separated by a particle-stabilised interface. It has the potential to be useful in applications where a large surface area to volume is beneficial, for example in catalyst supports, energy storage devices or microreactors. Before any application can be realised it is important to study the mechanical properties of the bijel. Using the method of centrifugal compression, these properties were investigated and it was found that the structure was relatively easily deformed. The expulsion of liquids appears to have a key role in the compression of the bijel.

Bridged emulsions are particle-stabilised emulsions where the particles can stabilise two droplet interfaces simultaneously leading to clusters of droplets. It was found that when using rod-shaped particles as stabilisers bridged emulsions were formed regardless of the aspect ratio, the shear rate of emulsification or the particle content. However, a normal emulsion was formed at pH 2 and therefore the bridging is attributed to the charge of the particles because the particles are negatively charged at any pH above 2. Long rods were also found to form strong bridges that were not broken under gentle shear whereas the bridges formed by short rods were broken under gentle shear.

Particles Stabilising Unconventional Emulsions
Mi 31.01.2018   Tanmoy Sarkar  IIT Bombay, India  11:30 s.t.
Tanmoy Sarkar: „Grain size distribution in sheared polycrystals”
IIT Bombay, India - Seminar@HHUD: 31.1.18 11:30 s.t., Seminarroom 25.32 O2.51

Plastic deformation in solids induced by external stresses is of both fundamental and practical interest. Using both phase field crystal modeling and molecular dynamics simulations, we study the shear response of monocomponent polycrystalline solids. We subject mesocale polycrystalline samples to constant strain rates in a planar Couette flow geometry for studying its plastic flow, in particular its grain deformation dynamics. As opposed to equilibrium solids where grain dynamics is mainly driven by thermal diffusion, external stress/strain induce a much higher level of grain deformation activity in the form of grain rotation, coalescence, and breakage, mediated by dislocations. Despite this, the grain size distribution of this driven system shows only a weak power-law correction to its equilibrium log-normal behavior. We interpret the grain reorganization dynamics using a stochastic model.

References

  1. Sarkar, T. et al. Phys. Rev. Materials 1, 070601(R) (2017)
Grain size distribution in sheared polycrystals
Mo 29.01.2018   Peter Virnau  Universität Mainz  14:30 s.t.
Peter Virnau: „Critical Behavior of Active Brownian Particles / Knots in Polymer Melts and Chromosomes”
Universität Mainz - Seminar@HHUD: 29.1.2018 14:30 s.t., Seminarroom 25.32 O2.51

In this talk I will report on three very recent (and somewhat distinct) projects. In the first project, we study active Brownian particles as a paradigm for genuine non-equilibrium phase transitions. Access to the critical point in computer simulations is obstructed by the fact that the density is conserved. We propose a modification of sampling finite-size fluctuations and successfully test this method for the 2D Ising model. Using this model allows us to determine accurately the critical point of two dimensional active Brownian particles at Pecr=40, Φcr=0.597. Based on this estimate, we study the corresponding critical exponents β, γ/ν and ν. Our results are incompatible with the 2D-Ising exponents, thus raising the question whether there exists a corresponding non-equilibrium universality class.

In the second project, we investigate the occurrence of knots in polymer melts. In polymer physics it is typically assumed that chains in melts can be described by effective random walks without excluded volume interactions. We show that this paradigm is problematic as the latter severely overrate the occurrence of knots. Interestingly, we find that the structure of a chain in a melt is very similar to the structure of a single chain undergoing a collapse transition at the Theta-point, which in turn are not well-represented by random walks either. Finally, I will report on very recent developments on the structure of DNA in the cell nucleus. A few months ago, three-dimensional structures of individual chromosomes and genomes in nuclei of single haploid mouse embryonic stem (ES) cells have been determined for the first time based on Hi-C chromosome conformation contact data.  In this project, we further analyze these structures and provide first evidence that G1 phase chromosomes are knotted, consistent with the fact that plots of contact probability vs sequence separation show a power law dependence that is intermediate between that of a fractal globule and an equilibrium structure.

Critical Behavior of Active Brownian Particles / Knots in Polymer Melts and Chromosomes
Mi 10.01.2018   Vladimir Khodygo  Aberystywth University, United Kingdom  14:30 s.t.
Vladimir Khodygo: „Heterogeneous populations of active rods confined within two dimensional channels”
Aberystywth University, United Kingdom - Seminar@HHUD: 10.1.18 14:30 s.t., Seminarroom 25.32 O2.51

Active swarms, consisting of of individual agents which consume energy to move, are known to produce a diverse range of collective behavior. Many examples of active swarms are biological in nature (e.g. fish shoals and bird flocks) and have been modeled extensively by numerical simulations. Numerical simulations of swarms assume that the swarm is homogeneous: that is that every agent has exactly the same dynamical properties. However, real biological swarms are often heterogeneous, such as in the case of a microbial population in the gut or in the soil (where many different species of bacteria may be present simultaneously). Here we conduct molecular dynamics simulations of active rods confined within a two-dimensional rectangular channel. Such simulations serve as a simple model for the dynamics of a swarm of motile rod-like bacteria in the absence of hydrodynamic effects. We explore the case of mixed swarms in which self-propelled rods have a range of motilities and steric interactions. Our results show that the confining boundaries play a strong role in driving the segregation of such mixed populations.

Heterogeneous populations of active rods confined within two dimensional channels
Mo 18.12.2017   Nick Koumakis  School of Physics and Astronomy, University of Edinburgh, United Kingdom  14:30 s.t.
Nick Koumakis: „Studies of model bacteria as "living active colloids"”
School of Physics and Astronomy, University of Edinburgh, United Kingdom - Seminar@HHUD: 18.12.2017 14:30 s.t., Seminarroom 25.32 O2.51

Active matter, containing self-propelling constituents, has recently sparked the interest of the soft matter scientific community. Active components may be biological or even chemically driven particles. The ability of active matter to provide energy through motion at a microscopic level, produces interesting phenomena, such as effective interactions, swarming, internally generated flows and activity induced phase transitions. Here, we use Escherichia coli bacteria as "living active colloids" to touch on a few exciting examples of active matter systems. We will initially discuss the interactions between swimmers and passive particles in an application that uses activity to transport particles to target locations. We will then move on to an example of self-assembly of light-driven bacteria which become active only when illuminated. Finally we will discuss how swimming bacteria produce of trails in a complex fluid near criticality.

Studies of model bacteria as "living active colloids"
Fr 15.12.2017   Marco Heinen  Universidad de Guanajuato, León, Mexico  14:30 s.t.
Marco Heinen: „Structure and Diffusion of a Fractal Hard Sphere Fluid”
Universidad de Guanajuato, León, Mexico - Seminar@HHUD: 15.12.17 14:30 s.t., Seminarroom 25.32 O2.51

Porous media can host complex fluids in a non-integer (fractal) dimensional configuration space. An example of high application relevance is reservoir rock containing oil, water, natural gas, or multiphase mixtures thereof. The fractal structure of porous media, and the diffusion of single particles through the pores of such media are well-studied problems. However, dense fluid phases of strongly interacting particles in fractal confinement have not yet received the same attention and remain mostly unexplored until today. In recent work [1] we have introduced statistical mechanical methods to compute the equilibrium correlations among dense, disordered phases of mesoscopic particles in 1:68(2)-dimensional fractal confinement by Monte Carlo simulations. Our simulation results are in good agreement with the predictions of the Percus-Yevick integral equation, analytically continued from integer to non-integer dimension and solved numerically by a spectral method. The anomalous diffusive dynamics of fractal hard spheres in thermodynamic equilibrium is probed by fractal Dynamic Monte Carlo simulations, and reveals a number of peculiarities that are not observed for point particles in fractal dimension, nor for hard spheres in integer dimension: Extended hard spheres in fractal dimension exhibit anomalous diffusion with two different (short-time and long-time) exponents of the mean squared displacement as a function of time, even in case of non-interacting particles that form an ideal gas. For dense fluids of interacting, non-overlapping fractal hard spheres, we observe a superposition of anomalous diffusion, due to the fractal configuration space, and subdiffusion due to the particle interactions at intermediate time scales.

References

  1. M. Heinen, S.K. Schnyder, J.F. Brady & H. Löwen, PRL 115, 052301 (2015)
Structure and Diffusion of a Fractal Hard Sphere Fluid
Mo 11.12.2017   Lorenz Baumgarten  TU Dortmund  14:30 s.t.
Buckling elastischer Kapseln bei thermischen Fluktuationen
gez.: Prof. Dr. Egelhaaf, Prof. Dr. Horbach, Prof. Dr. Löwen

oben

Kolloquien

Ort: HHU Düsseldorf, Hörsaal 5J (Gebäude 25.31 Ebene 00)
Programm:
DatumSprecher/inInstitutZeit
Do 19.07.2018   Prof. Dr. Neil Telling  Keele University, Biomedical NanoPhysics, United Kingdom  16:30 s.t.
Prof. Dr. Neil Telling: „Towards an understanding of heating effects and magnetisation response of magnetic nanoparticles associated with living cells”
Keele University, Biomedical NanoPhysics, United Kingdom - Seminar@HHUD: 19.07.2018 16:30 s.t., Lecture hall 25.31 O0.5J

In this talk I will review the physical mechanisms behind the magnetic nanoparticle based heating effects that show great promise for localised hyperthermia treatment in cancer. In particular I will discuss how developing a full understanding of the interactions of nanoparticles with their local environment is essential to achieve effective heating within real biological systems, and the current limitations that constrain progress in this area. Within this context I will describe the results of recent work aimed at enhancing nanoparticle heating effects, through consideration of intrinsic particle properties such as magnetic anisotropy, as well as by examining the behaviour of nanoparticles once associated with cancer cells. I will also discuss how magnetic nanoparticle surfaces can evolve when in contact with biological media and how such processes affect their interaction with cells.

Towards an understanding of heating effects and magnetisation response of magnetic nanoparticles associated with living cells
Do 12.07.2018   Prof. Dr. Cornelia Denz  Universität Münster, Nichtlineare Photonik  16:30 s.t.
Prof. Dr. Cornelia Denz: „Light´s grip - how tailored light fields assemble and analyze nano particles, droplets or cells”
Universität Münster, Nichtlineare Photonik - Seminar@HHUD: 12.7.18 16:30 s.t., Lecture hall 25.31 O0.5J

Light can hold, move and measure micro- and nano particle without touching. Optical tweezers exploit focused laser light to measure forces at the nanoscale and quantify elasticity. Complex tailored light field allow extending this application range, transferring holographic optical tweezers into an extraordinary metrology tool for biophysics and biophotonics.

This way, three dimensional configurations of micro- and nano particles can be generated in parallel and dynamically modified, creating spatially selective sensors. Also, fluid droplets can be manipulated by tailored light cages. Particles can also be introduced into cells to study cellular mechanics in a spatially resolved way, paving the way to decipher origins of cell migration and morphogenesis or analyse infections and inflammation.

In this presentation, we will introduce the principles of holographic optical tweezers and sub-sequently demonstrate how to use complex light fields for applications in soft matter, biophotonics and medical cell diagnosis.

Light´s grip - how tailored light fields assemble and analyze nano particles, droplets or cells
Do 14.06.2018   Prof. Dr. Gerhard Wilde  Institut für Materialphysik, Universität Münster  16:30 s.t.
Prof. Dr. Gerhard Wilde: „Deformation of metallic glasses - an experimental perspective”
Institut für Materialphysik, Universität Münster - Seminar@HHUD: 14.6.18 16:30 s.t., Lecture hall 25.31 O0.5J

Plastic deformation of metallic glasses is mostly localized in plate-like mesoscopic defects, so-called shear bands. Although their occurrence is well known and often limits the mechanical performance of the vitreous material, their actual physical properties remain fairly unknown. Here, experimental data on the rate of atomic diffusion within shear bands of deformed specimens have been obtained using the radiotracer method. Additionally, novel TEM-based methods served to experimentally determine the local specific volume as well as the local degree of medium-range order and the local chemical composition quantitatively, inside and outside of shear bands. Moreover, local strain fields at shear bands have also been analyzed and the impact of shear deformation and relaxation on the low-temperature heat capacity anomaly known as the “Boson peak” has been addressed, revealing complex dependencies on time, temperature and strain. Relaxation experiments showed an unexpected temporal evolution of the shear bands, including so-called cross-over behavior and first “in-situ” diffusion analyses reveal extremely large tracer penetration depths. These experimental results are discussed with respect to the underlying mechanism during the early stages of shear band activation and their temporal evolution as well as concerning the properties characterizing these “defects” in deformed metallic glasses.

Deformation of metallic glasses - an experimental perspective
Do 17.05.2018   Dr. Thomas Franosch  Universität Innsbruck, Österreich  16:30 s.t.
Non-equilibrium dynamics of active agents and driven particles in microrheology
Do 12.04.2018   Prof. Dr. Paul van der Schoot  Universiteit Eindhoven, Netherlands  16:30 s.t.
Geometric percolation in dispersions of rod-like colloids - impact of particle tortuosity and spontaneous symmetry breaking
Mo 29.01.2018   Prof. Nicolas Vogel  Friedrich-Alexander-Universität Erlangen-Nürnberg  17:00 s.t.
Prof. Nicolas Vogel: „Colloid clusters from confined self-assembly”
Friedrich-Alexander-Universität Erlangen-Nürnberg - Seminar@HHUD: 29.1.18 17:00 s.t., Lecture hall 26.11 6A

Colloids assemble into crystals upon increase of volume fraction. Complex structures can be achieved by varying composition, interaction, or shape of the constituent colloidal particles. Another method to modify the crystallization process is to utilize interfacial effects from confinement. Recently it has been shown that entropy favors icosahedral symmetry for colloids assembling in spherical confinement. Here we use droplet-based microfluidics to create homogeneous emulsion droplets as sources for defined spherical confinement. This allows systematic investigation of the assembly behavior of clusters containing between 100 and 10000 near- monodisperse colloidal spheres. We observe a discrete series of magic colloid clusters with icosahedral symmetry, borrowing the concept from atomic magic clusters. A two-step simulation scheme is proposed to reproduce accurately the structures observed in experiments. To understand and explain the formation of the magic colloid clusters, we propose a geometric model of Mackay and anti-Mackay shells and extract extremal principles. Our results underline possibilities to create complex structures from simple building blocks. The colloid clusters may find use as templates, photonic materials and building blocks for hierarchical assemblies.

References

  • De Nijs, Bart, et al. "Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement." Nature materials 14.1 (2015): 56-60.
  • Vogel, Nicolas, et al. "Color from hierarchy: Diverse optical properties of micron-sized spherical colloidal assemblies." Proceedings of the National Academy of Sciences 112.35 (2015): 10845-10850.
  • Damasceno, Pablo F., Michael Engel, and Sharon C. Glotzer. "Predictive self-assembly of polyhedra into complex structures." Science 337.6093 (2012): 453-457.
Colloid clusters from confined self-assembly
Do 11.01.2018   Prof. Dr. Jörg Baschnagel  Université de Strasbourg  16:30 s.t.
Shear modulus and shear stress relaxation in glass-forming and polymer systems
Für die Dozenten der Physik

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Seminar über Examensarbeiten aus dem Institut für Theoretische Physik, Lehrstuhl II

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Link: Physikalisches Kolloquium
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