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Seminars - Winter term 2018 / 2019

Seminar “Special problems in colloidal physics”

Location: HHU Düsseldorf, Seminarroom 25.32.O2.51
Program:
DateSpeakerTopicTime
Wed 21.11.2018   S. Jahanshahi  From microswimmers to microflyers III  14:30 s.t.
Wed 28.11.2018   S. Mandal  Inertial effects on the collective behavior of active particles  14:30 s.t.
Fri 07.12.2018   S. Babel  Feedback-driven colloids  14:30 s.t.
Wed 19.12.2018   M. Puljiz  Dynamics of discrete particles in continuous environments  14:30 s.t.
Mon 21.01.2019   S. Goh  DFT for 2D ferrogels: magnetostrictions and elastic moduli  14:30 s.t.
Tue 22.01.2019   M. Eshraghi  Crystal-fluid interface in hard-core Yukawa systems  14:30 s.t.
Thu 24.01.2019   C. Hoell  Dynamical density functional theory for rod-like microswimmers  14:30 s.t.
Fri 25.01.2019   A. Sprenger  Memory effects in active chemotactic particles  14:30 s.t.
Mon 28.01.2019   A. Ider  Active penetration of a magnetically self-assembled model membrane  14:30 s.t.
Tue 29.01.2019   C. Scholz  A very brief introduction to neural networks  14:30 s.t.
Wed 30.01.2019   L. Fischer  Elastic deformation by magnetic 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 28.11.2018   S. Mandal  Inertial effects on the collective behavior of active particles  14:30 s.t.
Mon 03.12.2018   S. Ganguly  Grain boundaries: rigid and rough  14:30 s.t.
Tue 22.01.2019   M. Eshraghi  Crystal-fluid interface in hard-core Yukawa systems  14:30 s.t.
Mon 28.01.2019   A. Ider  Active penetration of a magnetically self-assembled model membrane  14:30 s.t.
Tue 29.01.2019   C. Scholz  A very brief introduction to neural networks  14:30 s.t.
Wed 30.01.2019   L. Fischer  Elastic deformation by magnetic interactions  14:30 s.t.
Thu 31.01.2019   M. Golkia  Percolation analysis in supercool liquids  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 05.12.2018   David Fairhurst  School of Science and Technology, Nottingham Trent University, Nottingham, United Kingdom  10:15 s.t.
David Fairhurst: „The Jellycopter: stable levitation using a magnetic stirrer”
School of Science and Technology, Nottingham Trent University, Nottingham, United Kingdom - Seminar@HHUD: 5.12.18 10:15 s.t., Seminarroom

In laboratories around the world, scientists use magnetic stirrers to mix solutions and dissolve powders. It is well known that at high drive rates the stir bar jumps around erratically with poor mixing, leading to its nick-name 'flea'. Investigating this behaviour, we discovered a state in which the flea levitates stably above the base of the vessel, supported by magnetic repulsion between flea and drive magnet. The vertical motion is oscillatory and the angular motion a superposition of rotation and oscillation. By solving the coupled vertical and angular equations of motion, we characterised the flea's behaviour in terms of two dimensionless quantities: (i) the normalized drive speed and (ii) the ratio of magnetic to viscous forces. However, Earnshaw's theorem states that levitation via any arrangement of static magnets is only possible with additional stabilising forces. In our system, we find that these forces arise from the flea's oscillations which pump fluid radially outwards, and are only present for a narrow range of Reynold's numbers. At slower, creeping flow speeds, only viscous forces are present, whereas at higher speeds, the flow reverses direction and the flea is no longer stable. We also use both the levitating and non-levitating states to measure rheological properties of the system.

The Jellycopter: stable levitation using a magnetic stirrer
Thu 15.11.2018   J. Kolker  TU Dortmund  14:30 s.t.
Lattice models for activ particles
Mon 01.10.2018   Alexandra Zampetaki  Universität Hamburg  14:30 s.t.
Alexandra Zampetaki: „Tunable interactions and structures through different 1D substrates”
Universität Hamburg - Seminar@HHUD: 1.10.18 14:30 s.t., Seminarroom 25.32 O2.51

This talk is divided into two parts. In the first part I will present some highlights of our research on systems of helically confined charges. The confinement of identical charged particles on a helical substrate induces an effective oscillatory two-body potential with geometrically tunable features. Such an unconventional potential affects significantly the equilibrium and dynamics of the constrained particles, allowing among others for a deformation of the vibrational band structure and an intriguing bending response, both controlled by the geometry.

In the second part of my talk I will discuss our very recent results regarding the dynamics of polar active matter in the presence of a moving periodic substrate. It turns out that by suitably tuning the parameters of such a substrate we can control the dynamics of polar active particles, achieving a macroscopic directed transport in the opposite direction to that of the substrate‘s motion.

Tunable interactions and structures through different 1D substrates
Mon 17.09.2018   René Wittmann  University of Fribourg, Switzerland  14:30 s.t.
Single-particle distributions in density functional theory
Mon 03.09.2018   Shang Yik Reigh  Max-Planck-Institute for Intelligent Systems, Stuttgart, Germany  14:30 s.t.
Shang Yik Reigh: „Chemically powered micro- and nano-motors by diffusiophoresis”
Max-Planck-Institute for Intelligent Systems, Stuttgart, Germany - Seminar@HHUD: 3.9.18 14:30 s.t., Seminarroom 25.32 O2.51

Molecular motors such as kinesins and dyneins in cell walk along microtubules or actin filaments and transport cargos such as lipid or proteins. The motors accomplish their goals by converting chemical energy to mechanical work. Mimicking the biological motors, man have made artificial motors in a laboratory. The synthetic motors may self-propel in solution with various propulsion sources such as chemicals, heat, electric fields, etc, communicate with each other, and work together to accomplish a common goal. To achieve self-propulsion and efficient swimming, the motors should overcome strong thermal fluctuations from solvent, which induce Brownian motions, and also the regime of low-Reynolds-number fluid attributed to their tiny sizes, where fluid viscosity is dominant over inertia. Here, I would like to address basic principles and underlying physics in motors motions by diffusiophoresis, where chemical and hydrodynamic interactions are coupled, by using continuum theory and microscopic particlebased simulations. I will start with the Janus motor, a spherical particle with a half coated by the catalytic and the other half by the non-catalytic part, and extend the theory to the dimer motors and the dynamics of two separated particles. The theory, simulations, and experiments are compared and the results promise to provide a proper understanding of the nature of self-propelling motors, flow fields, hydrodynamic interactions, and hopefully emergent collective behaviors of many motors.

References

  1. P. H. Colberg, S. Y. Reigh, B. Robertson, and R. Kapral, Acc. Chem. Res. 47 3504 (2014)
  2. S. Y. Reigh and R. Kapral, Soft Matter 11 3149 (2015)
  3. S. Y. Reigh, M.-J. Huang, J. Schofield and R. Kapral, Phil. Trans. R. Soc. A 374 20160140 (2016)
  4. S. Y. Reigh, P. Chuphal, S. Thakur, and R. Kapral, Soft Matter 14 6043 (2018)
Chemically powered micro- and nano-motors by diffusiophoresis
Thu 09.08.2018   Pinaki Chaudhuri  The Institute of Mathematical Sciences, Chennai, India  14:30 s.t.
Thermal and allied transport in glass forming materials
Wed 08.08.2018   Dennis Schubert  Universität Hannover  14:30 s.t.
Integrable Structures in the Hofstadter model
Fri 27.07.2018   Francisca Guzmán Lastra  Universidad Mayor, Santiago de Chile, Chile  11:00 s.t.
Surfing on bacterial carpets
Fri 15.06.2018   Sebastian Gonzalez  University of Chile, Santiago de Chile, Chile  15:30 s.t.
Making flagella with active colloids
Thu 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
Fri 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?
Thu 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
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 20.12.2018   Prof. Dr. Stefan U. Egelhaaf  Heinrich-Heine-Universität Düsseldorf  16:30 s.t.
Prof. Dr. Stefan U. Egelhaaf: „Manipulating particles with light – The Nobel Prize in Physics 2018”
Heinrich-Heine-Universität Düsseldorf - Seminar@HHUD: 20.12.2018 16:30 s.t., Lecture hall 25.31 O0.5J

Arthur Ashkin was awarded (a share of) the Nobel Prize in Physics 2018 'for the optical tweezers and their application to biological systems'. I will explain why optical means, so-called optical tweezers, can be used to manipulate small objects, in the range from nanometers to micrometers. This is particularly appealing because the objects can be manipulated without directly interfering with the sample. Optical tweezers are nowadays applied to a broad range of objects, including colloids, biomolecules and living cells. The diversity of systems and questions which can be addressed using optical tweezers will be illustrated with examples. This includes experiments performed in our lab, which are based on optical tweezers but also take this concept a step further.

Manipulating particles with light – The Nobel Prize in Physics 2018
Thu 22.11.2018   Dr. Götz Lehmann  Heinrich-Heine-Universität Düsseldorf  16:30 s.t.
Dr. Götz Lehmann: „Eigenschaften und Anwendungen akustischer Metamaterialien”
Heinrich-Heine-Universität Düsseldorf - Seminar@HHUD: 22.11.2018 16:30 s.t., Lecture hall 25.31 O0.5J

Akustische Metamaterialien bestehen aus „Meta-Atomen”, elementaren Bausteinen, die größer sind als Atome, jedoch kleiner als die Wellenlänge von Schallwellen. Es sind die Struktur dieser Bausteine und ihre geometrische Anordnung, die über die Ausbreitung von Schallwellen in Metamaterialien entscheiden. Auf diese Weise lassen sich akustische Eigenschaften realisieren, die mit gewöhnlichen Materialien unmöglich sind.

Die akustischen Eigenschaften eines Materials sind in der Regel bestimmt durch die Massendichte und den Kompressionsmodul. Es erscheint uns völlig selbstverständlich, dass diese Parameter keine negativen Werte annehmen können. In Metamaterialien besitzt nun einer der Parameter, oder sogar beide, einen Wert kleiner Null. In meinem Vortrag werde ich vorstellen, wie sich effektiv negative Werte für diese beiden Parameter realisieren lassen und welche Konsequenzen dies für die Ausbreitung von Schall hat.

Im zweiten Teil des Vortrages werde ich über mögliche Anwendungen von akustischen Metamaterialien sprechen. Neben extrem dünnen Schallisolierungen lassen sich akustische Superlinsen und Tarnkappen konstruieren. Superlinsen erlauben das Fokussieren von Schallwellen jenseits der Beugungslimits, was gerade im Bereich der Ultraschalldiagnostik Interesse weckt. Mit Hilfe von akustischen Tarnkappen lässt sich die Gegenwart von Objekten vor dem Schallfeld verstecken.

Eigenschaften und Anwendungen akustischer Metamaterialien
Thu 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
Thu 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
Thu 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
Thu 17.05.2018   Dr. Thomas Franosch  Universität Innsbruck, Österreich  16:30 s.t.
Non-equilibrium dynamics of active agents and driven particles in microrheology
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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