Dislocation avalanche correlations

Recently, mechanical tests on ice as well as dislocation dynamics simulations have revealed that plastic flow displays a scale-free intermittent dynamics characterized by dislocation avalanches with a power law distribution of amplitudes. To further explore the complexity of dislocation dynamics during plastic flow, we present a statistical analysis of dislocation avalanche correlations and avalanche triggering. It is shown that the rate of avalanche triggering immediately after any avalanche is larger than the background activity due to uncorrelated events. This self-induced triggering increases in intensity, and remains over the background rate for longer times, as the amplitude of the mainshock increases. This analysis suggests that stress redistributions and the associated collective dislocation rearrangements may be responsible for aftershock triggering in the complex process of plastic deformation.Comment: 8 pages, 3 figures, presented at ICSMA-13, August 2003, Budapes

Dynamical correlations near dislocation jamming

Dislocation assemblies exhibit a jamming or yielding transition at a critical external shear stress value $\sigma=\sigma_c$. Nevertheless the nature of this transition has not been ascertained. Here we study the heterogeneous and collective nature of dislocation dynamics within a crystal plasticity model close to $\sigma_c$, by considering the first-passage properties of the dislocation dynamics. As the transition is approached in the moving phase, the first passage time distribution exhibits scaling, and a related peak {\it dynamical} susceptibility $\chi_4^*$ diverges as $\chi_4^* \sim (\sigma-\sigma_c)^{-\alpha}$, with $\alpha \approx 1.1$. We relate this scaling to an avalanche description of the dynamics. While the static structural correlations are found to be independent of the external stress, we identify a diverging dynamical correlation length $\xi_y$ in the direction perpendicular to the dislocation glide motion.Comment: 4 pages, 5 figure

Deblocking of interacting particle assemblies: from pinning to jamming

A wide variety of interacting particle assemblies driven by an external force are characterized by a transition between a blocked and a moving phase. The origin of this deblocking transition can be traced back to the presence of either external quenched disorder, or of internal constraints. The first case belongs to the realm of the depinning transition, which, for example, is relevant for flux-lines in type II superconductors and other elastic systems moving in a random medium. The second case is usually included within the so-called jamming scenario observed, for instance, in many glassy materials as well as in plastically deforming crystals. Here we review some aspects of the rich phenomenology observed in interacting particle models. In particular, we discuss front depinning, observed when particles are injected inside a random medium from the boundary, elastic and plastic depinning in particle assemblies driven by external forces, and the rheology of systems close to the jamming transition. We emphasize similarities and differences in these phenomena.Comment: 20 pages, 8 figures, submitted for a special issue of the Brazilian Journal of Physics entitled: Statistical Mechanics of Irreversible Stochastic Models - I

Dislocation jamming and Andrade creep

We simulate the glide motion of an assembly of interacting dislocations under the action of an external shear stress and show that the associated plastic creep relaxation follows Andrade's law. Our results indicate that Andrade creep in plastically deforming crystals involves the correlated motion of dislocation structures near a dynamic transition separating a flowing from a jammed phase. Simulations in presence of dislocation multiplication and noise confirm the robustness of this finding and highlight the importance of metastable structure formation for the relaxation process.Comment: 4 pages, 4 EPS figure

Debt Intolerance

This paper introduces the concept of "debt intolerance," which manifests itself in the extreme duress many emerging market economies experience at levels of indebtedness that would seem manageable by advanced country standards. The paper argues that "safe" external debt-to-GNP thresholds for debt-intolerant countries depend on the country's default and inflation history and may be as low as 15 percent in some cases. Debt intolerance is linked to the phenomenon of serial default that has plagued many countries over the past two centuries. Understanding and measuring debt intolerance is fundamental to assessing the problems of debt sustainability, debt restructuring, capital market integration, and the scope for international lending to ameliorate crises. The paper makes a first pass at quantifying debt intolerance, including delineating debtors' "clubs" and regions of vulnerability, based on a history of credit events for a large number of countries going back to the 1820s.macroeconomics, Debt Intolerance

Addicted to Dollars

Dollarization, in a broad sense, is increasingly a defining characteristic of many emerging market economies. How important is this trend quantitatively and how important is it for the conduct of monetary policy and the choice of exchange rate regimes? Though these questions have become a hot topic in both the theory and policy literature, most efforts are remarkably uninformed by evidence, in no small part because meaningful data has been lacking, except for a very narrow range of assets. This paper attempts to move the discussion forward and shed light on the critical questions by proposing a measure of dollarization that is broad both conceptually and in terms of country coverage. We use this measure to identify trends in the evolution of dollarization in the developing world in the last two decades, and to ascertain the consequences that dollarization has had on the effectiveness of monetary and exchange rate policy. We find that, contrary to the general presumption in the literature, a high degree of dollarization does not seem to be an obstacle to monetary control or to disinflation. A level of dollarization does, however, appear to increase exchange rate pass-through, reinforcing the claim that fear of floating' is a greater problem for highly dollarized economies. We also review the developing countries' record in combating their addiction to dollars. Concretely, we try to explain why some countries have been able to avoid certain forms of the addiction, and examine the evidence on successful de-dollarization.

Numerical study of broadband spectra caused by internal shocks in magnetized relativistic jets of blazars

The internal-shocks scenario in relativistic jets has been used to explain the variability of blazars' outflow emission. Recent simulations have shown that the magnetic field alters the dynamics of these shocks producing a whole zoo of spectral energy density patterns. However, the role played by magnetization in such high-energy emission is still not entirely understood. With the aid of \emph{Fermi}'s second LAT AGN catalog, a comparison with observations in the $\gamma$-ray band was performed, in order to identify the effects of the magnetic field.Comment: Proceedings of the meeting The Innermost Regions of Relativistic Jets and Their Magnetic Fields, June 10-14, 2013, Granada (Spain), 4 pages, 3 figure