AMRC Seminar Series

The AMRC hosts a series of seminars on subjects in statistical physics and fluid dynamics.

Malte Henkel (Universite de Lorraine, Nancy, France)

Physical ageing in systems without detailed balance
Friday September 13, 2013, 15:00 h, DH Seminar room

Ageing phenomena and scaling behaviour have been considered in many systems with detailed balance such as simple magnetic systems. Therefore it is an interesting question to extend these studies to systems without detailed balance, a paradigmatic example of which are reaction-diffusion systems. In these systems particles undergo diffusion on a lattice and in addition there occurs particle creation and annihilation. In recent numerical investigations in a specific system of this type dynamical scaling behaviour was found and in turned out, that an equality between two critical exponents, known from systems with detailed balance, does not hold true any more.

Olesya Mryglod (ICMP, Lviv, Ukraine)

Temporal characteristics of human dynamics in a virtual world
Wednesday July 24, 2013, 15:00 h, DH Seminar room

Modern computational social science incorporates new approaches for studying society [1]. Using the so-called digital footprints (recorded data about human actions: e-mail activity, mobile calls, purchases with credit cards etc.), it is possible to quantitatively analyse the individual and collective behavior patterns in order to get some new knowledge about the general `rules' which govern the society. Playing online games offer an example of well-documented collective human activities [2].

Here, we analyse the temporal characteristics of players behaviour in the free massive multiplayer online browser game. Having the data for more than 20,000 players, we build and analyse the distributions of interevent times between their consecutive actions on the amalgamated collective and individual levels. Some features of these distributions reflect the well-known real-life phenomena, such as circadian and weekly cycles or bursts of activity which follows the important events in the world. The peculiarities of different kinds of actions cause the differences between the corresponding interevent time distributions. The distinctions between dynamics of highly active players and those with just small number of actions are shown as well.

[1] Lazer D. et al., Computational Social Science, SCIENCE, 2009, vol. 323, 721-723.

[2] Szell M., Thurner S., Measuring social dynamics in a massive multiplayer online game, Social Networks, 2012, vol. 32, 313-329.

Mariana Krasnytska (ICMP, Lviv, Ukraine)

Critical behaviour of the Potts model on complex networks
Wednesday July 17, 2013, 15:00 h, DH Seminar room

The Potts model is one of the most popular spin models of statistical physics. Prevailing majority of the work done so far corresponds to the lattice version of the model. However, many natural or man-made systems are much better described by the topology of a network or a random graph. We consider the q- state Potts model on a complex network for which the node-degree distribution manifests a power-law decay governed by the exponent λ. We work within the mean-filed approximation, since for systems on random uncorrelated scale-free networks (where the very notion of a space dimension is ill-defined) this method is known often to give asymptotically exact results. Depending on particular values of q and λ one observes either the first-order or the second-order phase transition or the system is ordered at any temperature. In a case study, we consider the limit q → 1 (percolation) and find a correspondence between the magnetic exponents and those describing percolation on a scale-free network. Interestingly, logarithmic corrections to scaling appear at λ = 4 in this case.

Panagiotis Theodorakis (Imperial College, London, UK)

Understanding the super-spreading mechanism of surfactant-laden flows via a combined molecular and continuum approach
Wednesday July 10, 2013, 15:00 h, DH Seminar room

The spreading of fluids over solid substrates has recently attracted much interest due to its numerous applications in a plethora of industrial and biomedical applications, e.g., coating flows, detergency, enhanced-oil-recovery, treatment of respiratory distress syndrome, just to name a few. In many applications, the addition of surfactant molecules is required in order to facilitate the spreading of a liquid over a substrate. To this end, specific surfactants can enable the so-called “super-spreading”, where complete wetting of the liquid over the hydrophobic substrate rapidly takes place. In this context, theoretical studies provide a macroscopic description of the spreading mechanism in the presence of surfactants, but they disregard effects due to the molecular architecture or the specific interactions between the building blocks of the system. On the other hand, computer simulations, which may account for such effects, are restricted to small systems, and, for this reason, are unable to provide a continuum description of the spreading mechanism. In this study, we adopt a multi-scale approach where a suitable set of parameters obtained from the particle-based simulations is transferred to the continuum theory. In particular, we present a thorough analysis for cases of both insoluble and soluble surfactants with concentrations that can, in the latter case, exceed the critical micelle, or aggregate, concentration. Effects of the surfactant on the moving contact line of the liquid and sorption kinetics above and below the critical micelle concentration are taken into account.

Johannes Zierenberg (Leipzig University, Germany)

Condensation of Lattice Gas and Aggregation of Polymers
Wednesday July 3, 2013, 15:00 h, DH Seminar room