Long-range Spreading Research Articles

Detecting Robust Patterns in the Spread of Epidemics: A Case Study of Influenza in the United States and France

In this paper, the authors develop a method of detecting correlations between epidemic patterns in different regions that are due to human movement and introduce a null model in which the travel-induced correlations are cancelled. They apply this method to the well-documented cases of seasonal influenza outbreaks in the United States and France. In the United States (using data for 1972-2002), the authors observed strong short-range correlations between several states and their immediate neighbors, as well as robust long-range spreading patterns resulting from large domestic air-traffic flows. The stability of these results over time allowed the authors to draw conclusions about the possible impact of travel restrictions on epidemic spread. The authors also applied this method to the case of France (1984-2004) and found that on the regional scale, there was no transportation mode that clearly dominated disease spread. The simplicity and robustness of this method suggest that it could be a useful tool for detecting transmission channels in the spread of epidemics.

Modelling development of epidemics with dynamic small-world networks

We discuss the dynamics of a minimal model for spreading of infectious diseases, such as various types of influenza. The spreading takes place on a dynamic small-world network and can be viewed as comprising short- and long-range spreading processes. We derive approximate equations for the epidemic threshold as well as the spreading dynamics, and show that there is a good agreement with numerical discrete time-step simulations. We then analyse the dependence of the epidemic saturation time on the initial conditions, and outline a possible method of utilizing the model in predicting the development of epidemics based on early figures of infected. Finally, we compare time series calculated with our model to real-world data.

The role of the Gestalt principle of similarity in the watercolor illusion

The watercolor illusion presents two main effects: a long-range assimilative color spreading (coloration effect), and properties imparting a strong figure status (figural effect) to a region delimited by a dark (e.g. purple) contour flanked by a lighter chromatic contour (e.g. orange). In four experiments, the strength of the watercolor illusion to determine figure-ground organization is directly compared (combined or pitted against) with the Gestalt principle of similarity both of color and line width. The results demonstrated that (i) the watercolor illusion and, particularly, its figural effect won over the classical Gestalt factors of similarity; (ii) the watercolor illusion cannot be due to the coloration effect as suggested by the similarity principle; (iii) coloration and figural effects may be independent in the watercolor illusion, and (iv) the watercolor illusion can be considered as a principle of figure-ground segregation on its own. Two parallel and independent processes as proposed within the FACADE model (Grossberg, 1994, 1997) are suggested to account for the two effects of coloration and figural enhancement in the watercolor illusion.

The field theory approach to percolation processes

We review the field theory approach to percolation processes. Specifically, we focus on the so-called simple and general epidemic processes that display continuous non-equilibrium active to absorbing state phase transitions whose asymptotic features are governed, respectively, by the directed (DP) and dynamic isotropic percolation (dIP) universality classes. We discuss the construction of a field theory representation for these Markovian stochastic processes based on fundamental phenomenological considerations, as well as from a specific microscopic reaction-diffusion model realization. Subsequently we explain how dynamic renormalization group (RG) methods can be applied to obtain the universal properties near the critical point in an expansion about the upper critical dimensions d c = 4 (DP) and 6 (dIP). We provide a detailed overview of results for critical exponents, scaling functions, crossover phenomena, finite-size scaling, and also briefly comment on the influence of long-range spreading, the presence of a boundary, multispecies generalizations, coupling of the order parameter to other conserved modes, and quenched disorder.

Reconstruction of fluid Langmuir monolayers under shear forces

Scanning probe microscopy observations of monolayers of a classical boundary lubricant, stearic acid (STA), reveal long-range dynamics of wear and reconstruction of monomolecular films under the shear forces caused by the sliding tip. In the range of sliding velocities studied, the friction forces behave non-monotonically with a maximum value around 0.2 μm/s. The STA monolayer in a fluid state displays a flow of material from the worn area and its redistribution to form local heterogeneous multilayers. The range of influence of the material removal on the monolayer structure around the worn area is up to 80 μm, or more than an order of magnitude larger than the actual worn area. Surface diffusion of mobile organic material is responsible for the observed long-range spreading of local shear stresses produced in the area of wear. It demonstrates the non-local nature of the stress-induced reconstruction in the fluid monolayers, in contrast with solid monolayers, which show very localized wearing processes.