Nonlinear elastic polymers in random flow

Polymer stretching in random smooth flows is investigated within the framework of the FENE dumbbell model. The advecting flow is Gaussian and short-correlated in time. The stationary probability density function of polymer extension is derived exactly. The characteristic time needed for the system to attain the stationary regime is computed as a function of the Weissenberg number and the maximum length of polymers. The transient relaxation to the stationary regime is predicted to be exceptionally slow in the proximity of the coil-stretch transition.Comment: 10 pages, to be published in J. Fluid Mec

Renormalized transport of inertial particles in surface flows

Surface transport of inertial particles is investigated by means of the perturbative approach, introduced by Maxey (J. Fluid Mech. 174, 441 (1987)), which is valid in the case the deflections induced on the particle trajectories by the fluid flow can be considered small. We consider a class of compressible random velocity fields, in which the effect of recirculations is modelled by an oscillatory component in the Eulerian time correlation profile. The main issue we address here is whether fluid velocity fluctuations, in particular the effect of recirculation, may produce nontrivial corrections to the streaming particle velocity. Our result is that a small (large) degree of recirculation is associated with a decrease (increase) of streaming with respect to a quiescent fluid. The presence of this effect is confirmed numerically, away from the perturbative limit. Our approach also allows us to calculate the explicit expression for the eddy diffusivity, and to compare the efficiency of diffusive and ballistic transport.Comment: 18 pages, 13 figures, submitted to JF

Level, Slope, Curvature of Sovereign Yield Curve and Fiscal Behaviour

We study fiscal behaviour and the sovereign yield curve in the U.S. and Germany in the period 1981:I-2009:IV. The latent factors, level, slope and curvature, obtained with the Kalman filter, are used in a VAR with macro and fiscal variables, controlling for financial stress conditions. In the U.S., fiscal shocks have generated (i) an immediate response of the short-end of the yield curve, associated with the monetary policy reaction, lasting between 6 and 8 quarters, and (ii) an immediate response of the longend of the yield curve, lasting 3 years, with an implied elasticity of about 80% for the government debt ratio shock and about 48% for the budget balance shock. In Germany, fiscal shocks entail no significant reactions of the latent factors and no response of the monetary policy interest rate. In particular, while (i) budget balance shocks created no response from the yield curve shape, (ii) surprise increases in the debt ratio caused some increase in the short-end and the long-end of the yield curve in the following 2nd and 3rd quarters.yield curve, fiscal policy, financial markets.

Large-Eddy Simulation closures of passive scalar turbulence: a systematic approach

The issue of the parameterization of small scale (``subgrid'') turbulence is addressed in the context of passive scalar transport. We focus on the Kraichnan advection model which lends itself to the analytical investigation of the closure problem. We derive systematically the dynamical equations which rule the evolution of the coarse-grained scalar field. At the lowest-order approximation in $l/r$, $l$ being the characteristic scale of the filter defining the coarse-grained scalar field and $r$ the inertial range separation, we recover the classical eddy-diffusivity parameterization of small scales. At the next-leading order a dynamical closure is obtained. The latter outperforms the classical model and is therefore a natural candidate for subgrid modelling of scalar transport in generic turbulent flows.Comment: 10 LaTex pages, 1 PS figure. Changes: comments added below previous (3.10); Previous (3.16) has been corrected; Minor changes in the conclusion

Level, slope, curvature of sovereign yield curve and fiscal behaviour

We study fiscal behaviour and the sovereign yield curve in the U.S. and Germany in the period 1981:I-2009:IV. The latent factors, level, slope and curvature, obtained with the Kalman filter, are used in a VAR with macro and fiscal variables, controlling for financial stress conditions. In the U.S., fiscal shocks have generated (i) an immediate response of the short-end of the yield curve, associated with the monetary policy reaction, lasting between 6 and 8 quarters, and (ii) an immediate response of the longend of the yield curve, lasting 3 years, with an implied elasticity of about 80% for the government debt ratio shock and about 48% for the budget balance shock. In Germany, fiscal shocks entail no significant reactions of the latent factors and no response of the monetary policy interest rate. In particular, while (i) budget balance shocks created no response from the yield curve shape, (ii) surprise increases in the debt ratio caused some increase in the short-end and the long-end of the yield curve in the following 2nd and 3rd quarters.FC

Point-source dispersion of quasi-neutrally-buoyant inertial particles

We analyze the evolution of the distribution, both in the phase space and in the physical space, of inertial particles released by a spatially-localized (punctual) source and advected by an incompressible flow. The difference in mass density between fluid and particles is assumed as small, and represents the basic parameter for a regular perturbative expansion. By means of analytical techniques such as Hermitianization, we derive a chain of equations of the advection--diffusion--reaction type, easily solvable at least numerically. Our procedure provides results also for finite particle inertia, away from the over-damped limit of quasi-tracer dynamics.Comment: Submitted to EPJ

Programa para a estimativa do custo e produção de energia eléctrica para uma residência

Este trabalho apresenta um programa de computador que permite determinar o custo e a produção de energia proporcionada por abastecimento pela empresa fornecedora de energia eléctrica e por instalações fotovoltaicas, eólicas e híbridas (fotovoltaicas e eólicas), em função da localização da instalação em território lusitano. Este programa leva em consideração a economia efectuada e o prazo de amortização do investimento. O programa foi realizado com a utilização das seguintes linguagens de programação: HTML, JavaScript e PHP. Pretende-se disponibilizar o uso deste programa através da Internet, para que a sua utilização possa ser alargada ao máximo número de pessoas possível.Fundação para a Ciência e a Tecnologia (FCT), financiadora com fundos FEDER e OE do Projecto POCTI/ESE/48242/2002

Population structure in high shore littorinids: contrast between riprap and rocky shores

World Congress of Malacology, Ponta Delgada, July 22-28, 2013.The number of anthropogenic structures deployed in coastal areas has increased markedly in recent times and many studies have now shown that these structures seldom mimic the natural habitais they replace. To date, however, most such studies have focused on the numbers and relative abundance of species and little is known about how these structures affect the patterns of species aggregation and size structure, despite the fact that variations in these parameters may have important ecological consequences at population and community levels. Here we compare the relative abundance, patterns of aggregation and size structure of two high shore gastropod littorinids (Tectarius striatus and Melarhaphe neritoides) on riprap and adjacent rocky shores. While the relative abundance of T. striatus was similar on riprap and natural rocky shores, M. neritoides was significantly more abundant on rocky shores. At small spatial scales (cm’s) both littorinids specics showed more aggregated distributions on riprap. At larger scales (cm’s), both littorinids were also more aggregated on riprap although this was only significant for T. striatus. Habitat type influenced the size structure whith both species attaining a significantly larger size on riprap. Here we add to the wider literature by showing that anthropogenic structures can affect intertidal assemblages in ways other than richness or the relative abundance of organisms alone. The here documented variation in patterns of aggregation and size structure between habitats likely influence the population dynamics of these species and may have wider community level consequences

Fobia Escolar ou Síndrome de Vómitos Cíclicos? - Um caso clínico de vómitos inexplicáveis

O síndrome de vómitos cíclicos é uma perturbação funcional crónica de etiologia desconhecida, caracterizada por episódios paroxísticos e recorrentes de vómitos intensos, que duram horas a dias, com remissão completa dos sintomas entre os episódios. Factores de stress infecciosos, psicológicos e físicos podem precipitar os episódios. Afecta aproximadamente 2% da população pediátrica. Neste trabalho é descrito um caso clínico onde esta entidade foi considerada no diagnóstico diferencial.info:eu-repo/semantics/publishedVersio

Renewable energy in Portugal: legislation, incentives and suggestions

This paper presents the evolution of renewable energy generation in Portugal in the last decade, and explains the legislation and incentives in existence. The paper also presents suggestions that could incentive small and medium consumers to install renewable energy power plants (namely of wind power and photovoltaic types) in their facilities. These power plants would have to accomplish present legislation regarding “reactive energy” production during peak power consumption period, and besides, would have to assure power quality levels. On the other hand, reversible energy meters should be used, so that it would be registered the consumption of energy from the energy company, or the delivery of energy to the energy company. The equipments which could implement these characteristics are briefly described.Fundação para a Ciência e a Tecnologia, (FCT), POCTI/ESE/41170/2001