Dynamical aspects of Kinouchi-Copelli model: emergence of avalanches at criticality

We analyze the behavior of bursts of neural activity in the Kinouchi-Copelli model, originally conceived to explain information processing issues in sensory systems. We show that, at a critical condition, power-law behavior emerges for the size and duration of the bursts (avalanches), with exponents experimentally observed in real biological systems.Comment: Paper accepted for Brazilian Conference on Dynamics, Control and Applications (oral presentation and poster). 4 pages, 5 figure

Particle Creation by a Moving Boundary with Robin Boundary Condition

We consider a massless scalar field in 1+1 dimensions satisfying a Robin boundary condition (BC) at a non-relativistic moving boundary. We derive a Bogoliubov transformation between input and output bosonic field operators, which allows us to calculate the spectral distribution of created particles. The cases of Dirichlet and Neumann BC may be obtained from our result as limiting cases. These two limits yield the same spectrum, which turns out to be an upper bound for the spectra derived for Robin BC. We show that the particle emission effect can be considerably reduced (with respect to the Dirichlet/Neumann case) by selecting a particular value for the oscillation frequency of the boundary position

Parabolic dunes in north-eastern Brazil

In this work we present measurements of vegetation cover over parabolic dunes with different degree of activation along the north-eastern Brazilian coast. We are able to extend the local values of the vegetation cover density to the whole dune by correlating measurements with the gray-scale levels of a high resolution satellite image of the dune field. The empirical vegetation distribution is finally used to validate the results of a recent continuous model of dune motion coupling sand erosion and vegetation growth.Comment: 18 pages, 14 figures, aubmitted to Geomorpholog

¿Conflictos en la integración regional? Consideraciones acerca de la superposición de los acuerdos internacionales de inversión, los acuerdos comerciales regionales y la OMC

La creciente interdependencia económica internacional resultó en el desarrollo de diversas organizaciones y acuerdos regionales como los acuerdos comerciales regionales, los acuerdos internacionales de inversión y la Organización Mundial de Comercio (omc). En el panorama actual, diversos países son miembros de estos acuerdos y organizaciones concomitantemente. El gran incremento de los resultados de soluciones de diferencias debido al éxito del Entendimiento sobre Solución de Diferencias (esd) de la omc y el crecimiento paralelo del uso de las provisiones de los aii sobre solución de diferencias entre Estados e inversores llevaron a afirmaciones sobre el distanciamiento del derecho internacional de las inversiones y el derecho internacional comercial, lo que podría generar problemas con relación a la coherencia y estabilidad del derecho económico

Quantum radiation in a plane cavity with moving mirrors

We consider the electromagnetic vacuum field inside a perfect plane cavity with moving mirrors, in the nonrelativistic approximation. We show that low frequency photons are generated in pairs that satisfy simple properties associated to the plane geometry. We calculate the photon generation rates for each polarization as functions of the mechanical frequency by two independent methods: on one hand from the analysis of the boundary conditions for moving mirrors and with the aid of Green functions; and on the other hand by an effective Hamiltonian approach. The angular and frequency spectra are discrete, and emission rates for each allowed angular direction are obtained. We discuss the dependence of the generation rates on the cavity length and show that the effect is enhanced for short cavity lengths. We also compute the dissipative force on the moving mirrors and show that it is related to the total radiated energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review

Inertial forces in the Casimir effect with two moving plates

We combine linear response theory and dimensional regularization in order to derive the dynamical Casimir force in the low frequency regime. We consider two parallel plates moving along the normal direction in $D-$dimensional space. We assume the free-space values for the mass of each plate to be known, and obtain finite, separation-dependent mass corrections resulting from the combined effect of the two plates. The global mass correction is proportional to the static Casimir energy, in agreement with Einstein's law of equivalence between mass and energy for stressed rigid bodies.Comment: 9 pages, 1 figure; title and abstract changed; to appear in Physical Review

Isolated Bulbar Conjunctival Kaposi's Sarcoma as a Primary Presentation of AIDS: A Case Report

Kaposi's sarcoma (KS) is a malignant vascular tumor, caused by the human herpesvirus 8. It is one of the commonest tumors in human immunodeficiency virus (HIV) patients and not uncommonly the first manifestation of acquired immunodeficiency syndrome (AIDS). Case. We present a case of an isolated bulbar conjunctival KS on a 43-year-old HIV positive male, with no other lesions. Excision and cryotherapy were performed, and the patient remains free of lesions to date. Conclusion. Isolated bulbar conjunctival KP is an unusual site for its initial presentation and must be kept in mind in HIV positive patients