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Wydział Fizyki UW > Badania > Seminaria i konwersatoria > Soft Matter and Complex Systems Seminar
2016-03-11 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30  Calendar icon
Jacek Wojtkiewicz (KMMF UW)

Catastrophe theory vs. phase transitions: some historical (and not only) remarks (part II)

I will review some approaches to describe second-order phase transitions (PhT) with the use of theory of singularities of maps (ST) (customarily although not quite correctly called 'catastrophe theory'). Most representative names here are Landau and Thom. The common opinion is that description of phase transitions by singularity theory is wrong as it gives mean-field critical exponents. I will argue that the programme: PhT vs ST has both right and wrong aspects. Moreover, I will conjecture that singularities of maps are still closely related to description of phase transitions and critical region - not immediately, but through Laplace integrals (or rather certain extensions of this notion).
2016-03-04 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30  Calendar icon
Jacek Wojtkiewicz (KMMF UW)

Catastrophe theory vs. phase transitions: some historical (and not only) remarks

I will review some approaches to describe second-order phase transitions (PhT) with the use of theory of singularities of maps (ST) (customarily although not quite correctly called 'catastrophe theory'). Most representative names here are Landau and Thom. The common opinion is that description of phase transitions by singularity theory is wrong as it gives mean-field critical exponents. I will argue that the programme: PhT vs ST has both right and wrong aspects. Moreover, I will conjecture that singularities of maps are still closely related to description of phase transitions and critical region - not immediately, but through Laplace integrals (or rather certain extensions of this notion).
2016-02-26 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30  Calendar icon

There will be agenda fixing meeting

2016-01-22 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30  Calendar icon
Maria Ekiel-Jeżewska (IPPT PAN)

Migration of vesicles and flexible fibers in Poiseuille flow

Dynamics of flexible fibers and vesicles in unbounded planar Poiseuilleflow in the low-Reynolds-number regime are shown to exhibit similar basicfeatures, when their equilibrium (moderate) aspect ratio is the same andvesicle viscosity contrast is relatively high. The lateral migration andaccumulation of these two types of flexible objects are analyzednumerically.
2016-01-15 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30  Calendar icon
Jacek Wojtkiewicz (KMMF UW)

The Mermin-Wagner theorem in zero temperature (part II)

The well-known Mermin-Wagner theorem tells that in the lattice spin systems possessing continuous symmetry, for lattice dimensions 1 and 2, there is no long-range order at positive temperatures. The aim of the talk is to review an extension (after A. Auerbach et al.) of this theorem to the zero-temperature case: the ground state is not ordered if there is an energy gap over the ground state.
2016-01-08 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30  Calendar icon
Jacek Wojtkiewicz (KMMF UW)

The Mermin-Wagner theorem in zero temperature

The well-known Mermin-Wagner theorem tells that in the lattice spin systems possessing continuous symmetry, for lattice dimensions 1 and 2, there is no long-range order at positive temperatures. The aim of the talk is to review an extension (after A. Auerbach et al.) of this theorem to the zero-temperature case: the ground state is not ordered if there is an energy gap over the ground state.
2015-12-18 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30  Calendar icon
Paweł Kondratiuk (IFT UW)

(In)stability of a dissolution-precipitation front

One of the mechanisms of pattern formation in hydrogeochemical systems is the reactive-infiltration instability, which occurs whenever a porous rock undergoes dissolution due to exposure to a constant inflow of reactants brought by the infiltrating fluid. As a result of positive feedbacks between the flow, reactant transport and matrix evolution, planar dissolution fronts are inherently unstable and spontaneously break up, leading to the formation of highly porous flow paths, dubbed "wormholes". The phenomenon has been studied by a number of authors and is already quite well understood.

In natural systems, however, dissolution of the minerals in the primary rock is often accompanied by reprecipitation of the dissolution products, which form secondary minerals. Contrary to simple dissolution, the porosity profiles in this case are in general non-monotonic. Performing linear stability analysis of the model stationary reaction front, we show that the dissolution-precipitation fronts can also be unstable, even if the secondary rock is even less porous (and less permeable) than the primary one. We also present the fully nonlinear evolution of the system, studied by numerical simulations.
2015-12-04 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30  Calendar icon
Paweł Żuk (IFT UW)

Viscosity of complex molecules in Rotne-Prager-Yamakawa approximation on the example of a dumbbell

Viscosity of suspension is a macroscopically measurable quantity originating in the microscopic structure of the colloid. Based on the viscosity measurements it is possible to infer about the microscopic details of the colloid like equilibrium shape of the particles suspended in the fluid. I will present a method to calculate viscosity of the solution of complex molecules modeled with spheres in Rotne-Prager-Yamakawa approximation and demonstrate it on the example of a dilute solution of dumbbells (rigid and non-rigid).
2015-11-27 (Piątek)
Zapraszamy do sali 1.40, ul. Pasteura 5 o godzinie 09:30  Calendar icon
Ryszard Kutner (IFD UW)

From financial markets to Earthquakes: Universal superstatistics – superscaling

We use a continuous-time random walk (CTRW) to model (i) market fluctuation data from times when traders experience excessive losses or excessive profits and (ii) the analogous Earthquakes fluctuation data. We analytically derive superstatistics that accurately model empirical market activity data (supplied by Bogachev, Ludescher, Tsallis, and Bunde) and Earthquakes data of Corral that exhibit transition thresholds. We measure the inter-event times between excessive losses, excessive profits, and Earthquake amplitudes by using the mean inter-event time as a control variable to derive a universal description of empirical data collapse. Our superstatistic value is a weighted sum of two components, (i) a power-law corrected by the lower incomplete gamma function, which asymptotically tends toward robustness but initially gives an exponential, and (ii) a power-law damped by the upper gamma function, which tends toward the power-law only during short inter-event times. We find that the scaling shape exponents that drive both components subordinate themselves and a “superscaling” configuration emerges. We use superstatistics to describe the hierarchical activity when component (i) reproduces the negative feedback and component (ii) reproduces the the stylized fact of volatility clustering. Moreover, our results indicate that there is a functional (but not literal) balance between excessive profits and excessive losses that can be described using the same body of superstatistics, but different calibration values and driving parameters.
2015-11-20 (Piątek)
Zapraszamy do sali 2.08, ul. Pasteura 5 o godzinie 09:30  Calendar icon
Filip Dutka (IFT UW)

Microfluidic step-emulsifier stabilizing volume of droplets against flow rate variation

The talk will be in the spirit of applied microfluidics, however there are still few questions of theoretical background to be answered. We report a new method for generation of tightly monodisperse nanoliter droplets by introduction of solely the dispersed phase into the system, without the need for precise control of its rate of flow. The system allows to generate libraries of nanoliter droplets from microliter samples of liquid delivered to the system with e.g. an automatic pipette. Dependence of the droplet viscosity on the volume of the droplets is still a puzzler.
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