On the dependence of the avalanche angle on the granular layer thickness

A layer of sand of thickness h flows down a rough surface if the inclination is larger than some threshold value theta which decreases with h. A tentative microscopic model for the dependence of theta with h is proposed for rigid frictional grains, based on the following hypothesis: (i) a horizontal layer of sand has some coordination z larger than a critical value z_c where mechanical stability is lost (ii) as the tilt angle is increased, the configurations visited present a growing proportion $_s of sliding contacts. Instability with respect to flow occurs when z-z_s=z_c. This criterion leads to a prediction for theta(h) in good agreement with empirical observations.Comment: 6 pages, 2 figure

Dissipative collapse of the adiabatic piston

An adiabatic piston, separating two granular gases prepared in the same macroscopic state, is found to eventually collapse to one of the sides. This new instability is explained by a simple macroscopic theory which is furthermore in qualitative agreement with hard disk molecular dynamics.Comment: 7 pages, 5 figure

Nontrivial temporal scaling in a Galilean stick-slip dynamics

We examine the stick-slip fluctuating response of a rough massive non-rotating cylinder moving on a rough inclined groove which is submitted to weak external perturbations and which is maintained well below the angle of repose. The experiments presented here, which are reminiscent of the Galileo's works with rolling objects on inclines, have brought in the last years important new insights into the friction between surfaces in relative motion and are of relevance for earthquakes, differing from classical block-spring models by the mechanism of energy input in the system. Robust nontrivial temporal scaling laws appearing in the dynamics of this system are reported, and it is shown that the time-support where dissipation occurs approaches a statistical fractal set with a fixed value of dimension. The distribution of periods of inactivity in the intermittent motion of the cylinder is also studied and found to be closely related to the lacunarity of a random version of the classic triadic Cantor set on the line.Comment: 7 pages including 6 figure

Identificação de 'outliers' em levantamentos amostrais.

O objetivo deste trabalho é apresentar uma sequência de procedimentos que levam à identificação de ?outliers? em um levantamento amostral cuja variável-resposta tem distribuição normal

Atualização da rede de drenagens e inserção de sua nomenclatura no Estado do Mato Grosso do Sul.

O Projeto GeoMS visa à identificação, à caracterização e ao mapeamento das áreas desmatadas, à cobertura vegetal e ao uso da terra, para auxiliar a implantação de projetos estratégicos, promover a preservação e a conservação ambiental, além de um desenvolvimento sustentável do Estado do Mato Grosso do Sul (PROJETO GEOMS, 2011). O projeto é dividido basicamente em três áreas: o desenvolvimento do Sistema Interativo de Suporte ao Licenciamento Ambiental (Sisla) (SISLA, 2011); o levantamento e mapeamento de áreas degradadas e cobertura vegetal e uso da terra; e o ajuste da drenagem e delimitação das bacias hidrográficas. Um dos objetivos dessa terceira parte é a atualização das drenagens do Estado do Mato Grosso do Sul

Magnetic states of linear defects in graphene monolayers: effects of strain and interaction

The combined effects of defect-defect interaction and of uniaxial or biaxial strains of up to 10\% on the development of magnetic states on the defect-core-localized quasi-one-dimensional electronic states generated by the so-called 558 linear extended defect in graphene monolayers are investigated by means of {\it ab initio} calculations. Results are analyzed on the basis of the heuristics of the Stoner criterion. We find that conditions for the emergence of magnetic states on the 558 defect can be tuned by uniaxial tensile parallel strains (along the defect direction) at both limits of isolated and interacting 558 defects. Parallel strains are shown to lead to two cooperative effects that favor the emergence of itinerant magnetism: enhancement of the DOS of the resonant defect states in the region of the Fermi level and tuning of the Fermi level to the maximum of the related DOS peak. A perpendicular strain is likewise shown to enhance the DOS of the defect states, but it also effects a detunig of the Fermi level that shifts away from the maximum of the DOS of the defect states, which inhibts the emergence of magnetic states. As a result, under biaxial strains the stabilization of a magnetic state depends on the relative magnitudes of the two components of strain.Comment: 9 pages 8 figure

Gene expression during regeneration of zebrafish (danio rerio) fins: relative expression levels of mineralization – related gla proteins

Most animals have the ability to regenerate epidermal injuries yet only a few can regenerate largely severed appendages that comprise several different tissues. Nowadays zebrafish is one of the most used metazoan models in regeneration studies in particular for investigation of molecular events during fin regeneration process. Fin regeneration starts through the formation of a blastema, a set of heterogeneous mesenchyma-like cells located between stump tissues and the wounded epidermis. This event, denominated epimorphic regeneration, comprises strict growth control and cell reprogramming leading to faithful restoration of the lost parts

Chaotic behavior in a Z_2 x Z_2 field theory

We investigate the presence of chaos in a system of two real scalar fields with discrete Z_2 x Z_2 symmetry. The potential that identify the system is defined with a real parameter r and presents distinct features for r>0 and for r<0. For static field configurations, the system supports two topological sectors for r>0, and only one for r<0. Under the assumption of spatially homogeneous fields, the system exhibts chaotic behavior almost everywhere in parameter space. In particular a more complex dynamics appears for r>0; in this case chaos can decrease for increasing energy, a fact that is absent for r<0.Comment: Revtex, 13 pages, no figures. Version with figures in Int. J. Mod. Phys. A14 (1999) 496

Fluctuation-Induced Casimir Forces in Granular Fluids

We have numerically investigated the behavior of driven non-cohesive granular media and found that two fixed large intruder particles, immersed in a sea of small particles, experience, in addition to a short range depletion force, a long range repulsive force. The observed long range interaction is fluctuation-induced and we propose a mechanism similar to the Casimir effect that generates it: the hydrodynamic fluctuations are geometrically confined between the intruders, producing an unbalanced renormalized pressure. An estimation based on computing the possible Fourier modes explains the repulsive force and is in qualitative agreement with the simulations.Comment: 4 pages, 3 figures. Accepted in Phys. Rev. Letter