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
2015-01-23 (Friday)
room 2.08, Pasteura 5 at 09:30 
prof. Bogdan Cichocki (IFT UW)Brownian motion of a particle with an arbitrary shape
Brownian motion of a particle with an arbitrary shape is investigated theoretically. Analytical expressions for the time-dependent cross-correlations of the Brownian translational displacement and particle orientation change are derived.
2015-01-16 (Friday)
room 2.08, Pasteura 5 at 09:30
dr Kamil Kwiatkowski (IFT UW)Physical aspects of thermal decomposition of biomass particle
We focus on processes of thermal conversion of porous material intogases. Two important types of such processes are pyrolysis andgasification of biomass. Mass and energy transfer, chemical reactionsand their kinetic mechanisms for thin and thick particles will bebriefly discussed.
An experiment on pyrolysis and gasification of a thick wood particlewill be presented together with the corresponding numerical simulations.The results of numerical simulations of pyrolysis matched the results ofthe experiment qualitatively (e.g. presence of the front of pyrolysis)and quantitatively (e.g. good estimation of pyrolysis time). Thephenomena often associated with pyrolysis such as cracking, shrinkage orswelling proved to be rather unimportant from the numerical modellingperspective. The numerically estimated time of char gasification wassignificantly longer than the measured one until fragmentation of thechar particle into small elements was taken into account. The effect offragmentation appeared to be of crucial importance for gasificationmodelling
An experiment on pyrolysis and gasification of a thick wood particlewill be presented together with the corresponding numerical simulations.The results of numerical simulations of pyrolysis matched the results ofthe experiment qualitatively (e.g. presence of the front of pyrolysis)and quantitatively (e.g. good estimation of pyrolysis time). Thephenomena often associated with pyrolysis such as cracking, shrinkage orswelling proved to be rather unimportant from the numerical modellingperspective. The numerically estimated time of char gasification wassignificantly longer than the measured one until fragmentation of thechar particle into small elements was taken into account. The effect offragmentation appeared to be of crucial importance for gasificationmodelling
2015-01-09 (Friday)
room 2.08, Pasteura 5 at 09:30
prof. Maria Ekiel-Jeżewska (IPPT PAN)From asking questions about proteins towards solving conceptual problems of microhydrodynamics
I will discuss an example of research which originated from specific questions of chemists, who wanted to determine conformation of proteins from measurements of their self-diffusion and intrinsic viscosity. It turned out that to answer these questions, fundamental problems in microhydrodynamics need to be solved.
[1] Adamczyk Z., Cichocki B., Ekiel-Jezewska M.L., Slowicka A.M., Wajnryb E., Wasilewska M., Fibrinogen conformations and charge in electrolyte solutions derived from DLS and dynamic viscosity measurements,J. Colloid Interface Sci., 385, 244, 2012.
[2] Cichocki B., Ekiel-Jezewska M.L., Wajnryb E., Communication: Translational Brownian motion for particles of arbitrary shape, J. Chem. Phys., 136, 071102, 2012.
[1] Adamczyk Z., Cichocki B., Ekiel-Jezewska M.L., Slowicka A.M., Wajnryb E., Wasilewska M., Fibrinogen conformations and charge in electrolyte solutions derived from DLS and dynamic viscosity measurements,J. Colloid Interface Sci., 385, 244, 2012.
[2] Cichocki B., Ekiel-Jezewska M.L., Wajnryb E., Communication: Translational Brownian motion for particles of arbitrary shape, J. Chem. Phys., 136, 071102, 2012.
2014-12-19 (Friday)
room 2.08, Pasteura 5 at 09:30
Paweł Żuk (IFT UW)Unusual behavior of capacitor with AC voltage
I will present preliminary results of an analysis of micro capacitorfilled with electrolyte responding to the AC voltage. The analysis interms of micrometer scale fluid flow and charge dynamics revealsinteresting phenomena like charge separation, charge inflow into thecapacitor and nontrivial pressure field dynamics. It is an attempt toexplain surprising experimental results. Most calculations are done inOpenFOAM environment for solving PDE using finite volume method.
2014-12-12 (Friday)
room 2.08, Pasteura 5 at 09:30
Karine Petrus (IFT UW)Influence of layering on the formation and growth of dissolution pipes in karst systems
In karst systems, hydraulic conduits called dissolution pipes (a.k.a. wormholes) are formed as a result of the dissolution of limestone rocks by the water surcharged with CO2. The dissolution pipes are the end result of a positive feedback between spatial variations in porosity in the initial matrix and the local dissolution rate. A small enhancement in porosity at some point in the reaction front increases the fluid flow in that region, which convects reactant further downstream. By this means any local variation in porosity is amplified as the reaction front passes through and propagates downstream with the front, eventually developing into dissolution pipes. As dissolution proceeds the growing pipes interact, competing for the available flow, and eventually the growth of the shorter ones ceases.
Here, we investigate numerically the effect of rock stratification on the dissolution pipe growth, using a simple model system with a number of horizontal bedding planes, which are less porous than the rest of the matrix. Stratification is shown to affect the resulting piping patterns in a variety of ways. First of all, it enhances the competition between the pipes, impeding the growth of the shorter ones and enhancing the flow in the longer ones, which therefore grow longer.Next, it affects the shapes of individual dissolution pipes, with characteristic widening of the profiles in between the layers and narrowing within the layers.
These results are in qualitative agreement with the piping morphologies observed in nature. Importantly, measuring the ratio between the pipe diameters in different layers can provide one with information on the conditions prevailing during the formation of the pattern as well as on the physical characteristics of the layers in a given natural system.Finally, we relate our results to the Laplacian path models, in which the growth takes place only at the tips of the long-and-thin fingers. This description, although simplified, turns out to capture many features of the dynamics of the dissolution pipe system and allows for the effective prediction of the resulting patterns.
Here, we investigate numerically the effect of rock stratification on the dissolution pipe growth, using a simple model system with a number of horizontal bedding planes, which are less porous than the rest of the matrix. Stratification is shown to affect the resulting piping patterns in a variety of ways. First of all, it enhances the competition between the pipes, impeding the growth of the shorter ones and enhancing the flow in the longer ones, which therefore grow longer.Next, it affects the shapes of individual dissolution pipes, with characteristic widening of the profiles in between the layers and narrowing within the layers.
These results are in qualitative agreement with the piping morphologies observed in nature. Importantly, measuring the ratio between the pipe diameters in different layers can provide one with information on the conditions prevailing during the formation of the pattern as well as on the physical characteristics of the layers in a given natural system.Finally, we relate our results to the Laplacian path models, in which the growth takes place only at the tips of the long-and-thin fingers. This description, although simplified, turns out to capture many features of the dynamics of the dissolution pipe system and allows for the effective prediction of the resulting patterns.
2014-12-05 (Friday)
room 2.08, Pasteura 5 at 09:30
Karol Makuch (IFT UW)Rotational self-diffusion in suspensions of repulsive particles
The seminar is dedicated to the problem of rotational self-diffusion coefficient in suspensions of spherical particles.The particles interact with repulsive Yukawa-hard-core potential.The rotational self-diffusion coefficient for different volume fractions is calculated within the Beenakker-Mazur method. The results of our calculations within the Beenakker-Mazur method are assessed by comparison with numerical simulations which we also perform.
2014-11-28 (Friday)
room 2.08, Pasteura 5 at 09:30
Piotr Fronczak (Politechnika Warszawska)Gravity model of trade and fractal character of the world trade network
2014-11-14 (Friday)
room 2.08, Pasteura 5 at 09:30
Ryszard Kutner (ZFB IFD WF UW)Socio- and econophysical version of two-dimensional three-state Potts model of cunning traders (spins)
Mateusz Denys, Tomasz Gubiec, and Ryszard Kutner
ZFB IFD WF UW
Abstract
Presentation of our refined socio-econophysic version of two-dimensional and three-state Potts model is a principal aim of this talk [1]. This model can be considered as a refined one as it takes into account the perfidious or cunning traders who transmit their opinions (or advices) to his nearest neighbors and simultaneously they are doing something quite opposite. For instance, the transmition of the advice `buy assets' can simultaneously accompany their selling. This model was used by us to the description of empirical data concerning the statistics of interoccurrence times between excessive losses, i. e., excessing some threshold of resistance from losses (in the commonly used Value-at-Risk analysis this threshold is simply called the `level of losses'). The analysis of losses and their risk is a central subject not only of the finance but also of the socio-economical sciences. Our results have a universal character in the sense that all of them are well described (to good approximation) by the Tsallis q-exponentials. Our model is the first microscopic one which gave so good agreement with empirical data and enabled the formulation by us the precise scientific project for the nearest future.
[1] M. Denys, T. Gubiec, and R. Kutner: `Universality of Tsallis q-exponential of interoccurrence times within the microscopic model of cunning agents', arXiv:1411.1689v1 [q-fin.ST], 5 Nov 2014; `Contributed talk' presented by PhD-student Mateusz Denys on the `Social Modeling and Simulations + Econophysics Colloquium 2014', Nichii Gakkan Kobe Port Island Center, Kobe, Japan 4-6 Nov. 2014.
ZFB IFD WF UW
Abstract
Presentation of our refined socio-econophysic version of two-dimensional and three-state Potts model is a principal aim of this talk [1]. This model can be considered as a refined one as it takes into account the perfidious or cunning traders who transmit their opinions (or advices) to his nearest neighbors and simultaneously they are doing something quite opposite. For instance, the transmition of the advice `buy assets' can simultaneously accompany their selling. This model was used by us to the description of empirical data concerning the statistics of interoccurrence times between excessive losses, i. e., excessing some threshold of resistance from losses (in the commonly used Value-at-Risk analysis this threshold is simply called the `level of losses'). The analysis of losses and their risk is a central subject not only of the finance but also of the socio-economical sciences. Our results have a universal character in the sense that all of them are well described (to good approximation) by the Tsallis q-exponentials. Our model is the first microscopic one which gave so good agreement with empirical data and enabled the formulation by us the precise scientific project for the nearest future.
[1] M. Denys, T. Gubiec, and R. Kutner: `Universality of Tsallis q-exponential of interoccurrence times within the microscopic model of cunning agents', arXiv:1411.1689v1 [q-fin.ST], 5 Nov 2014; `Contributed talk' presented by PhD-student Mateusz Denys on the `Social Modeling and Simulations + Econophysics Colloquium 2014', Nichii Gakkan Kobe Port Island Center, Kobe, Japan 4-6 Nov. 2014.
2014-11-07 (Friday)
room 2.08, Pasteura 5 at 09:30
Damian Zdulski (IFT UW)Influence of interactions on a phase diagram of topological insulators
During the course of seminar I am going to present influence of Falicov-Kimball type interactions on the phase diagram and topological properties of the Kane-Mele model. The calculations were performed within the Hartree-Fock and Hubbard I approximations.
2014-10-24 (Friday)
room 2.08, Pasteura 5 at 09:30
Karol Wędołowski (IFT UW)Dynamics of a liquid film interacting with a nano-probe
Imaging of deformable surfaces with the help of the Atomic Force Microscope (AFM) is performed mainly in the non-contact mode, in which the tip of the AFM oscillates above the surface of the sample. If the tip approaches the sample too much the jump-to-contact phenomenon can occur,which creates a capillary bridge between the sample and the tip. This can disturb the measurements significantly and needs to be avoided. Equilibrium predictions of the surface deformation give an estimate on the minimum distance at which the tip can approach the liquid surface. However, it appears that the dynamic effects are of great importance in this problem and need to be taken into account.
I will introduce a systematic theoretical model of the liquid film dynamics, which reveals the relevant time scales and predicts deformation of liquid films interacting with a nano-sized objects. The model simplifies to the lubrication approximation in the case of very thin films, which was recently analyzed in the literature. I will show how different parameters of the tip oscillations influence the surface deformation and that the restriction to the lubrication approximation can lead to noticeable errors even for relatively thin films.
I will introduce a systematic theoretical model of the liquid film dynamics, which reveals the relevant time scales and predicts deformation of liquid films interacting with a nano-sized objects. The model simplifies to the lubrication approximation in the case of very thin films, which was recently analyzed in the literature. I will show how different parameters of the tip oscillations influence the surface deformation and that the restriction to the lubrication approximation can lead to noticeable errors even for relatively thin films.