Soft Matter and Complex Systems Seminar
2006/2007 | 2007/2008 | 2008/2009 | 2009/2010 | 2010/2011 | 2011/2012 | 2012/2013 | 2013/2014 | 2014/2015 | 2015/2016 | 2016/2017 | 2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025
2017-01-27 (Friday)
room 1.40, Pasteura 5 at 09:30 
Rafał Ołdziejewski (CFT PAN)Quantum droplets in ultracold dipolar gases
In recent experiments, an ultracold gas of dysprosium atoms (164Dy) was driven into a regime where dipole-dipole interactions are expected to lead to instability and collapse. Unexpectedly, instead of collapsing, the gas formed spatially ordered structure of stable droplets with high density. We will argue that description of the droplet state requires going beyond the mean field theory and show how to incorporate realistic interatomic interactions in the model.
2017-01-13 (Friday)
room 1.40, Pasteura 5 at 09:30
Michał Pecelerowicz (IFT UW)Deterministic and stochastic models of Laplacian growth
Laplacian growth is one of the fundamental mechanisms of pattern formation, driving such natural processes like viscous fingering or two-dimensional combustion in a Hele-Shaw geometry. The characteristic features of these processes include a strong competition between spontaneously formed dendrite-like structures, and tip-splitting effects when dendrites bifurcate into secondary branches. Many of these processes can be described in terms of a simple deterministic model in which growth takes place only at the tips of the fingers and the dynamics is expressed in terms of the Loewner equation [1].
In other systems, the dynamics is to a large extent noise-driven. Examples include diffusion-limited aggregation, dielectric breakdown or fracturing processes. The description of such processes can be provided by means of a simple model, in which growth is represented as a random sequence of elementary conformal maps [2], which is convenient for numerical treatment.
During the seminar I will discuss both the deterministic and the stochastic model and I will present the resulting structures and characteristic effects.
[1] L. Carleson and N. Makarov, J. Anal. Math. 87, 103 (2002).
[2] M.B. Hastings, L.S. Levitov, Physica D 116 (1998) 244-252
In other systems, the dynamics is to a large extent noise-driven. Examples include diffusion-limited aggregation, dielectric breakdown or fracturing processes. The description of such processes can be provided by means of a simple model, in which growth is represented as a random sequence of elementary conformal maps [2], which is convenient for numerical treatment.
During the seminar I will discuss both the deterministic and the stochastic model and I will present the resulting structures and characteristic effects.
[1] L. Carleson and N. Makarov, J. Anal. Math. 87, 103 (2002).
[2] M.B. Hastings, L.S. Levitov, Physica D 116 (1998) 244-252
2016-12-16 (Friday)
room 1.40, Pasteura 5 at 09:30
Michał Bogdan (University of Cambridge)Minimal hydrodynamical models of collective tissue motion
Many processes of prime physiological importance rely on collective and coordinated motion of large groups of cells or entire tissue fragments. Examples include the first phase of cancer invasion and wound healing. Genetic and biochemical cues influencing how that collective motion unfolds have been studied comprehensively. However, the role of mechanical factors is not understood that well. I will present preliminary results of a minimal hydrodynamical model developed in our group, constructed to explain observed patterns of motion in cancer invasion and wound healing.
2016-12-09 (Friday)
room 1.02, Pasteura 5 at 09:30
Paweł Żuk (IPPT PAN)On the mechanical basis of living cell chemistry
Inside the living cell all the molecules constantly undergo the translational and rotational Brownian motion. Most of them exhibit very specific behavior as chemical reagents keeping the cell alive. We would like to present our results on the connecting the mechanical movement of the molecules with the chemical information that is carried by them and the state of the cell as a whole system. Our novel approach allows to analyze large amounts of the instances of the chemical evolution of the system based on the mesoscopic simulations for real times in parallell.
2016-12-02 (Friday)
room 1.40, Pasteura 5 at 09:30
Piotr Warchoł (Jagiellonian University, Kraków)The Tracy-Widom distribution - an introduction
The statistical behaviour of the largest eigenvalue of a random hermitian matrix with independent entries is governed by the so-called Tracy-Widom distribution. It turns out that the latter appears in quite a few problems in physics, notably in the context of the KPZ equation. Moreover, the Tracy-Widom distribution has been recently realised experimentally in growing interfaces of turbulent liquid crystal. In my talk I will try to give a pedagogical introduction to this topic, mostly in the context of Random Matrix Theory.
2016-11-25 (Friday)
room 1.40, Pasteura 5 at 09:30
Maciej Jasiński (CeNT UW)The Mpemba Effect, do we really need an explanation?
We have used Molecular Dynamics simulations, to study process of water freezing with three different water models: TIP4P, OPC and TIP5P. In our simulations, systems containing water – air interface, were quenched from a range of temperatures to study effect of an initial conformation of water molecules onto an ice nucleation time and structure of formed ice.
We have observed ice nucleation in all investigated water models; interestingly that effect wasn’t reported previously for the TIP5P and OPC models. While it was suggested previously, that homogenous freezing of water starts in the subsurface, in our simulations the nucleation was observed both in the subsurface and the bulk water.
In agreement with the previous experiments, we observed in our simulations that initially warmer water sometimes freezes faster than the cold one. Interestingly, in our studies, similarly as in the available experimental works, we couldn't define a set of parameters that will ensure occurrence of that phenomenon. This may suggest that, observations of the Mpemba Effect are results of the stochastic nature of ice nucleation process, rather than manifestation of unknown water property.
We have observed ice nucleation in all investigated water models; interestingly that effect wasn’t reported previously for the TIP5P and OPC models. While it was suggested previously, that homogenous freezing of water starts in the subsurface, in our simulations the nucleation was observed both in the subsurface and the bulk water.
In agreement with the previous experiments, we observed in our simulations that initially warmer water sometimes freezes faster than the cold one. Interestingly, in our studies, similarly as in the available experimental works, we couldn't define a set of parameters that will ensure occurrence of that phenomenon. This may suggest that, observations of the Mpemba Effect are results of the stochastic nature of ice nucleation process, rather than manifestation of unknown water property.
2016-11-04 (Friday)
room 2.08, Pasteura 5 at 09:30
Anthony Ladd (Unversity of Florida)Numerical simulations of fracture dissolution
Fractures take up only about 1% of the subsurface pore space, but in soluble rocks they make the most important contribution to groundwater transport; for example in the development of karst formations. The increase in permeability due to dissolution of the fracture surfaces gives rise to a number of questions that are important for waste storage systems, sequestration, oil and gas recovery, and dam stability.
In this talk I will review numerical simulations of fracture dissolution using 1D, 2D, and 3D models for the fracture geometry. Historically, lower dimensional models have added considerable insight to our understanding of the dynamics of a dissolving fracture. I will outline the important contributions from these models and their limitations in comparison with recent fully three-dimensional simulations. While it has been known for some time that one-dimensional models omit crucial aspects of the dissolution dynamics, recently we have shown that two dimensional models do not correctly describe the flow in tube-like conduits which develop as the fracture dissolves.
Three-dimensional simulations have shown that the elliptical conduits characteristic of karst formations evolve very early in the dissolution, even prior to breakthrough. They can be nucleated from local enhancements of aperture, from spatially random aperture distributions, or even from variations in the central plane of an otherwise smooth fracture. The shape of the conduit depends on flow rate: at small flow rates they are circular, but expand horizontally into elliptical shapes as the flow rate increases.
In this talk I will review numerical simulations of fracture dissolution using 1D, 2D, and 3D models for the fracture geometry. Historically, lower dimensional models have added considerable insight to our understanding of the dynamics of a dissolving fracture. I will outline the important contributions from these models and their limitations in comparison with recent fully three-dimensional simulations. While it has been known for some time that one-dimensional models omit crucial aspects of the dissolution dynamics, recently we have shown that two dimensional models do not correctly describe the flow in tube-like conduits which develop as the fracture dissolves.
Three-dimensional simulations have shown that the elliptical conduits characteristic of karst formations evolve very early in the dissolution, even prior to breakthrough. They can be nucleated from local enhancements of aperture, from spatially random aperture distributions, or even from variations in the central plane of an otherwise smooth fracture. The shape of the conduit depends on flow rate: at small flow rates they are circular, but expand horizontally into elliptical shapes as the flow rate increases.
2016-10-28 (Friday)
room 1.40, Pasteura 5 at 09:30
Grzegorz Łach (Institute of Theoretical Physics, UW)Exact 2D critical temperatures from the solutions of 1D models
I will present a recent observation on how the exact critical temperatures of Ising and Potts models on triangular, square, hexagonal and kagome lattices can be extracted from the (elementary) solutions of their one-dimentional equivalents.
2016-10-21 (Friday)
room 1.40, Pasteura 5 at 09:30
Gustavo Abade (University of Warsaw, Institute of Geophysics)Active microrheology in a colloidal glass of hard spheres
The talk will address the dynamics of a probe particle driven by a constant forcethrough a colloidal glass of hard spheres. This nonequilibrium andanisotropic problem is investigated using a new implementation of themode-coupling approximation with multiple relaxation channels andLangevin dynamics simulations. An important feature of the system isthe critical force, above which the probe delocalizes. Frictioncoefficients of delocalized probes decrease with force, indicatingforce-thinning behavior. Probe van Hove functions predicted by thetheory show exponential tails reminiscent of an intermittent dynamicsof the probe. This scenario is microscopically supported bysimulations.