Faculty of Physics University of Warsaw > Events > Seminars > Soft Matter and Complex Systems Seminar

Soft Matter and Complex Systems Seminar

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room 1.40, Pasteura 5 at 09:30

Przemysław Czechowski (FUW)

Simulating Granular Materials with Video Games Physics Engines

Physics Engines developed for the gaming and film industry are gaining popularity in recent years among researchers as flexible and efficient tools for simulating multibody dynamics. In this talk, we will present how an open-source Bullet Physics engine was used to create a simplified model of the regolith of the martian moon Phobos. Elements of the Bullet Physics pipeline will be discussed, with a focus on broad phase collision detection algorithms (Axis Sweep and Dynamic Bounding Volumes Tree). We will share experiences from adapting Bullet Physics to create a high-precision simulation of a cone penetration test for a sample consisting of 6000 uniform spherical grains. The efficiency and stability of the model will be analyzed with a focus on sensitivity to internal model parameters and collision detection algorithm used. Resource estimation for upscaling the model to a larger number of bodies will be presented. Bullet Physics will be evaluated in general as a tool for various research applications.

The seminar will be conducted on Zoom
https://us02web.zoom.us/j/82784273907

room 1.40, Pasteura 5 at 09:30

Gesse Roure (University of Colorado Boulder)

Modeling of Particle Capture By Expanding Droplets

The present work investigates the binary interaction between a solid particle and a semipermeable spherical drop that expands due to osmosis in an external, pure-extensional flow field. Computational results from numerical integration of trajectories determine a transient collision efficiency, which describes the influence of hydrodynamic interactions and osmotic flow on particle capture. The results show that drop expansion, which decays slowly with time, greatly increases particle capture rates. Moreover, as the engulfment parameter increases, there is a transition from flow-dominated capture to expansion-dominated capture. For the case of a non-expanding droplet, we provide a numerical solution for the transient pair distribution function, which enables us to explain the transient particle capture rate in terms of the microstructure of the suspension. Furthermore, we derive an analytical expression for the initial collision efficiency at zero times, which agrees with our numerical data. The numerical results for non-expanding droplets at long times show increasing collision efficiency as the permeability increases and when the size ratio is near unity, in agreement with previous steady-state calculations. The effects of inner salt diffusion on drop expansion are also discussed.

The seminar will be conducted on Zoom
https://us02web.zoom.us/j/82784273907

room 1.40, Pasteura 5 at 09:30

Jędrzej Wardyn, Stanisław Żukowski, Mateusz Poniatowski (IFT UW)

Student talks: time crystals, jellyfish growth, and diffusion of elastic molecules

Jędrzej Wardyn
A short overview on time crystals
I will provide an introduction of the idea of time-crystals and rather short, but recent history of its existence and stability. By examining its experimental realisations, I will try to describe its relations to other physical systems and phenomena.

Stanisław Żukowski
Quick review of the jellyfishes growth
Instead of blood vessels as in mammals, jellyfishes have a gastrovascular system consisting of canals in which sea water flows transporting nutrients and oxygen to the surrounding tissue. In this short talk I would like to present some ideas on how we can understand the evolution of this canal network in terms of well known pattern formation processes like cracking or viscous fingering.

Mateusz Poniatowski
Diffusion coefficients of elastic molecules
The talk will be about a novel method of calculating a diffusioncoefficients of molecules in a coarse-grained representation.

The seminar will be conducted on Zoom
https://zoom.us/j/92987083349?pwd=YTZLSFVWUnJzdE4xS1drR3dqMVFDdz09

join us at 09:30

Anna Maciołek (MPI for Intelligent Systems, Stuttgart and ICHF PAN.)

Optically heated Janus colloids in a binary liquid mixture: motility and transient coarsening

Colloidal particles covered by materials that absorb light receive an increasing attention in various fields of research and in many important applications, for example, bio-medical applications. Such particles become hot under illumination by laser. This gives rise to a variety of curious phenomena, which may be of practical use. For instance, an optically heated colloid suspended in a binary liquid mixture may self-propel or, if trapped by a laser beam, it becomes a microscopic engine.

Using a fluid particle dynamics approach we investigate a propulsion mechanism for a gold-capped Janus particle as a function of the wettability contrast between capped and uncapped sides of a Janus particle and of a heating power for symmetric and nonsymmetric binary solvent. We also have immobilized this particle in a narrow channel and study nonequilibrium dynamics of a binary solvent around it using experiment and theory. Our results demonstrate that a remarkably complex time evolution of the concentration field around the colloid is governed by combined effects of temperature gradient and wettability, and crucially depends on whether the colloid is free to move or trapped. Moreover, we discover an important role of transient dynamics for self-propulsion.

The seminar will be conducted on Zoom
https://us02web.zoom.us/j/82784273907

room 1.40, Pasteura 5 at 09:30

Michał Tomza (IFT UW)

Ultracold ion-atom collisions in the quantum regime

Hybrid systems of laser-cooled trapped ions and ultracold atomscombined in a single experimental setup have recently emerged as a new platform for fundamental research in quantum physics [1]. Reaching the ultracold s-wave quantum regime has been one of the most important challenges in this field for a long time. Unfortunately, the lowest attainable temperatures in experiments using the Paul ion trap are limited by the possible rf-field-induced heating related to the micromotion [2]. Recently, buffer gas cooling of a single ion in a Paul trap to the quantum regime of ion-atom collisions was realized and a deviation from classical Langevin theory was observed by studying the spin-exchange dynamics, indicating quantum effects in the ion-atom collisions [3]. In my seminar, I will present how in collaboration with experimental groups from Amsterdam [3] and Stuttgart [4] we have overcome this limitation and how electronic structure theory and nuclear dynamics simulations guided and explained experimental efforts.

[1] Tomza et al, Rev. Mod. Phys. 91, 035001 (2019)
[2] Cetina et al., Phys. Rev. Lett. 109, 253201 (2012)
[3] Feldker et al, Nat. Phys. Nature Phys. 16, 413 (2020)
[4] Schmid et al, Phys. Rev. Lett. 120, 153401 (2018)

The seminar will be conducted on Zoom
https://zoom.us/j/92987083349?pwd=YTZLSFVWUnJzdE4xS1drR3dqMVFDdz09

room 1.40, Pasteura 5 at 09:30

Marta Wacławczyk (IGF UW)

Conformal invariance in turbulence

For more than two decades there have been speculations on the existence of the conformal group (CG) in the statistics of certain class of hydrodynamic models, which includes two-dimensional turbulence and the quasi-geostrophic approximation.The CG can be understood as a "local scaling" and plays a remarkable role in physics, as most of the non-trivial exact solutions of dynamical and statistical models follow from the underlying CG transformation.The talk will concern analytical study of the evolution equation for one-point probability density function of scalar variables in the class of hydrodynamic models. It will be argued that characteristic lines of these equations are CG invariant under certain conditions.

The seminar will be conducted on Zoom
https://zoom.us/j/92987083349?pwd=YTZLSFVWUnJzdE4xS1drR3dqMVFDdz09

room 1.40, Pasteura 5 at 09:30

Jakub Spiechowicz (University of Silesia)

Anomalous kinetics out of thermodynamic equilibrium

Fascinated by the complexity and smallness of the living cell in this talk I will discuss recent developments in anomalous kinetics out of thermodynamic equilibrium. Molecular motors, i.e. tiny proteins (e.g. kinesin) which power the intracellular transport, provide an ideal model system for such a purpose. I will describe their dynamics in the framework of driven Brownian motors, namely, classical Brownian particles far away from thermodynamic equilibrium moving in a nonlinear spatially periodic potential landscape. Both anomalous diffusion as well as anomalous directed transport in the form of negative mobility will be covered. I will demonstrate also very exceptional coexistence of the anomalous diffusion and negative mobility effects in a nonlinear nonequilibrium Brownian motion.

The seminar will be conducted on Zoom
https://zoom.us/j/92987083349?pwd=YTZLSFVWUnJzdE4xS1drR3dqMVFDdz09

join us at 09:30

Alexander Chamolly (ENS Paris)

Making a point — how to understand microswimmers with singularities

Solving a complex physical problem numerically is like cooking a stew. You throw a lot of ingredients together and the result might be delicious, but it’s often hard to say what part made the difference. By challenging ourselves to think before we compute and reduce a problem to its essential ingredients, we may achieve much greater insight into why a physical system behaves a certain way. In this talk I will look at swimming bacteria and use minimal fluid dynamical models to explain what drives the bundling of their flagellar filaments, why there exists an optimal length for those, and why the shape of the cell matters for its propulsion. If there is time, I will use the same ideas to also explain how a rolling colloid can trap and transport cargo along an interface.

The seminar will be conducted on Zoom
https://zoom.us/j/92987083349?pwd=YTZLSFVWUnJzdE4xS1drR3dqMVFDdz09

join us at 09:30

Paweł Żuk (IChF PAN, Lancaster University)

Charging of Overlapping Double Layers in a Cylindrical Nanopore

The charging of electrical double layers inside a cylindrical pore has applications to supercapacitors, batteries, desalination and biosensors. The charging dynamics in the limit of thin double layers, i.e., when the double layer thickness is much smaller than the pore radius, is commonly described using an effective RC transmission line circuit. Here, we perform direct numerical simulations (DNS) of the Poisson-Nernst-Planck equations to study the double layer charging for the scenario of overlapping double layers, i.e., when the double layer thickness is comparable to the pore radius. We develop an analytical model thataccurately predicts the results of DNS. Also, we construct a modified effective circuit for the overlappingdouble layer limit, and find that the modified circuit is identical to the RC transmission line but with different values and physical interpretation of the capacitive and resistive elements. In particular, the effective surface potential is reduced, the capacitor represents a volumetric current source, and the charging timescale is weakly dependent on the ratio of the pore radius and the double layer thickness.

The seminar will be conducted on Zoom
https://zoom.us/j/92987083349?pwd=YTZLSFVWUnJzdE4xS1drR3dqMVFDdz09

room 1.40, Pasteura 5 at 09:30

Marek Napiórkowski (IFT UW)

Non-universal Casimir Forces at approach to Bose-Einstein Condensation

We will discuss the Casimir forces for an ideal Bose gas enclosed between two infinite parallel walls separated by the distance D. The walls are characterized by the Dirichlet boundary conditions. The leading term describing the large-distance decay of Casimir forces between the walls corresponds to repulsive forces decaying as 1/D^2 with a non-universal amplitude.

The seminar will be conducted on Zoom
https://zoom.us/j/92987083349?pwd=YTZLSFVWUnJzdE4xS1drR3dqMVFDdz09

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