Effective transport barriers in nontwist systems

In fluids and plasmas with zonal flow reversed shear, a peculiar kind of transport barrier appears in the shearless region, one that is associated with a proper route of transition to chaos. These barriers have been identified in symplectic nontwist maps that model such zonal flows. We use the so-called standard nontwist map, a paradigmatic example of nontwist systems, to analyze the parameter dependence of the transport through a broken shearless barrier. On varying a proper control parameter, we identify the onset of structures with high stickiness that give rise to an effective barrier near the broken shearless curve. Moreover, we show how these stickiness structures, and the concomitant transport reduction in the shearless region, are determined by a homoclinic tangle of the remaining dominant twin island chains. We use the finite-time rotation number, a recently proposed diagnostic, to identify transport barriers that separate different regions of stickiness. The identified barriers are comparable to those obtained by using finite-time Lyapunov exponents.FAPESPCNPqCAPESMCT/CNEN (Rede Nacional de Fusao)Fundacao AraucariaUS Department of Energy DE-FG05-80ET-53088Physic

Vanishing Viscosity Limits and Boundary Layers for Circularly Symmetric 2D Flows

We continue the work of Lopes Filho, Mazzucato and Nussenzveig Lopes [LMN], on the vanishing viscosity limit of circularly symmetric viscous flow in a disk with rotating boundary, shown there to converge to the inviscid limit in $L^2$-norm as long as the prescribed angular velocity $\alpha(t)$ of the boundary has bounded total variation. Here we establish convergence in stronger $L^2$ and $L^p$-Sobolev spaces, allow for more singular angular velocities $\alpha$, and address the issue of analyzing the behavior of the boundary layer. This includes an analysis of concentration of vorticity in the vanishing viscosity limit. We also consider such flows on an annulus, whose two boundary components rotate independently. [LMN] Lopes Filho, M. C., Mazzucato, A. L. and Nussenzveig Lopes, H. J., Vanishing viscosity limit for incompressible flow inside a rotating circle, preprint 2006

Potencial de radão em setores da Zona de Ossa Morena

O radão é considerado a maior fonte de exposição a radiação ionizante dentro de habitações, motivo pelo qual é essencial conhecer a sua distribuição espacial. Este trabalho tem como objetivo o estudo do potencial de radão de rochas aflorantes na Zona de Ossa Morena (ZOM). Para tal, foram colhidas 132 amostras nos principais setores da ZOM. Os resultados obtidos demonstram a enorme variabilidade das propriedades radiológicas e físicas nas litologias analisadas. As atividades de 226Ra e de radão são, em média, inferiores nas rochas calco-silicatadas e rochas ígneas básicas e ultrabásicas e superiores nas rochas graníticas e sienitos. Os metassedimentos, rochas de alto grau metamórfico, granodioritos, dioritos e tonalitos apresentam atividades de 226Ra e de radão intermédias e similares entre si. A porosidade, que determina a capacidade de migração de radão no meio, é superior nos metassedimentos e inferior nas rochas ígneas, independentemente do seu caráter

A Dain Inequality with charge

We prove an upper bound for angular-momentum and charge in terms of the mass for electro-vacuum asymptotically flat axisymmetric initial data sets with simply connected orbit space