Slow crack propagation through a disordered medium: Critical transition and dissipation

We show that the intermittent and self-similar fluctuations displayed by a slow crack during the propagation in a heterogeneous medium can be quantitatively described by an extension of a classical statistical model for fracture. The model yields the correct dynamical and morphological scaling, and allows to demonstrate that the scale invariance originates from the presence of a non-equilibrium, reversible, critical transition which in the presence of dissipation gives rise to self organized critical behaviour.Comment: 16 pages, 4 figures, to be published on EPL (http://epljournal.edpsciences.org/

Loss separation for dynamic hysteresis in magnetic thin films

We develop a theory for dynamic hysteresis in ferromagnetic thin films, on the basis of the phenomenological principle of loss separation. We observe that, remarkably, the theory of loss separation, originally derived for bulk metallic materials, is applicable to disordered magnetic systems under fairly general conditions regardless of the particular damping mechanism. We confirm our theory both by numerical simulations of a driven random--field Ising model, and by re--examining several experimental data reported in the literature on dynamic hysteresis in thin films. All the experiments examined and the simulations find a natural interpretation in terms of loss separation. The power losses dependence on the driving field rate predicted by our theory fits satisfactorily all the data in the entire frequency range, thus reconciling the apparent lack of universality observed in different materials.Comment: 4 pages, 6 figure

Dynamical correlations in the escape strategy of Influenza A virus

The evolutionary dynamics of human Influenza A virus presents a challenging theoretical problem. An extremely high mutation rate allows the virus to escape, at each epidemic season, the host immune protection elicited by previous infections. At the same time, at each given epidemic season a single quasi-species, that is a set of closely related strains, is observed. A non-trivial relation between the genetic (i.e., at the sequence level) and the antigenic (i.e., related to the host immune response) distances can shed light into this puzzle. In this paper we introduce a model in which, in accordance with experimental observations, a simple interaction rule based on spatial correlations among point mutations dynamically defines an immunity space in the space of sequences. We investigate the static and dynamic structure of this space and we discuss how it affects the dynamics of the virus-host interaction. Interestingly we observe a staggered time structure in the virus evolution as in the real Influenza evolutionary dynamics.Comment: 14 pages, 5 figures; main paper for the supplementary info in arXiv:1303.595

Dynamic hysteresis in Finemet thin films

We performed a series of dynamic hysteresis measurements on three series of Finemet films with composition Fe$_{73.5}$Cu$_1$Nb$_3$Si$_13.5$B$_9$, using both the longitudinal magneto-optical Kerr effect (MOKE) and the inductive fluxometric method. The MOKE dynamic hysteresis loops show a more marked variability with the frequency than the inductive ones, while both measurements show a similar dependence on the square root of frequency. We analyze these results in the frame of a simple domain wall depinning model, which accounts for the general behavior of the data.Comment: 3 pages, 3 figure

Towards a strong coupling theory for the KPZ equation

After a brief introduction we review the nonperturbative weak noise approach to the KPZ equation in one dimension. We argue that the strong coupling aspects of the KPZ equation are related to the existence of localized propagating domain walls or solitons representing the growth modes; the statistical weight of the excitations is governed by a dynamical action representing the generalization of the Boltzmann factor to kinetics. This picture is not limited to one dimension. We thus attempt a generalization to higher dimensions where the strong coupling aspects presumably are associated with a cellular network of domain walls. Based on this picture we present arguments for the Wolf-Kertez expression z= (2d+1)/(d+1) for the dynamical exponent.Comment: 10 pages, 4 figures, "Horizons in Complex Systems", Messina, December 2001 (H. E. Stanley, 60th birthday