Scalar field black holes

With a suitable decomposition of its energy-momentum tensor into pressureless matter and a vacuum type term, we investigate the spherical gravitational collapse of a minimally coupled, self-interacting scalar field, showing that it collapses to a singularity. The formed blackhole has a mass $M \sim 1/m$ (in Planck units), where $m$ is the mass of the scalar field. If the latter has the axion mass, $m \sim 10^{-5}$ eV, the former has a mass $M \sim 10^{-5} M_{\odot}$.Comment: 8 pages, no figure

Non-adiabatic Chaplygin gas

The split of a generalised Chaplygin gas with an equation of state p = -A/\rho^{\alpha} into an interacting mixture of pressureless matter and a dark-energy component with equation of state p_{\Lambda} = - \rho_{\Lambda} implies the existence of non-adiabatic pressure perturbations. We demonstrate that the square of the effective (non-adiabatic) sound speed c_s of the medium is proportional to the ratio of the perturbations of the dark energy to those of the dark matter. Since, as demonstrated explicitly for the particular case \alpha = -1/2, dark-energy perturbations are negligible compared with dark-matter perturbations on scales that are relevant for structure formation, we find |c_s^2| << 1. Consequently, there are no oscillations or instabilities which have plagued previous adiabatic Chaplygin-gas models.Comment: Version to appear in Physics Letters

Equality of opportunity and educational achievement in Portugal

Portugal has one of the highest levels of income inequality in Europe, and low wages and unemployment are concentrated among low skill individuals. Education is an important determinant of inequality. However, there are large differences in the educational attainment of different individuals in the population, and the sources of these differences emerge early in the life-cycle when families play a central role in individual development. We estimate that most of the variance of school achievement at age 15 is explained by family characteristics. Observed school inputs explain very little of adolescent performance. Children from highly educated parents benefit of rich cultural environments in the home and become highly educated adults. Education policy needs to be innovative: (1) it needs to explicitly recognize the fundamental long run role of families on child development; (2) it needs to acknowledge the failure of traditional input based policies

Variations of the Energy of Free Particles in the pp-Wave Spacetimes

We consider the action of exact plane gravitational waves, or pp-waves, on free particles. The analysis is carried out by investigating the variations of the geodesic trajectories of the particles, before and after the passage of the wave. The initial velocities of the particles are non-vanishing. We evaluate numerically the Kinetic energy per unit mass of the free particles, and obtain interesting, quasi-periodic behaviour of the variations of the Kinetic energy with respect to the width $\lambda$ of the gaussian that represents the wave. The variation of the energy of the free particle is expected to be exactly minus the variation of the energy of the gravitational field, and therefore provides an estimation of the local variation of the gravitational energy. The investigation is carried out in the context of short bursts of gravitational waves, and of waves described by normalised gaussians, that yield impulsive waves in a certain limit.Comment: 20 pages, 18 figures, further arguments supporting the localizability of the gravitational energy are presented, published in Univers

Redução dos impactos ambientais da pecuária de corte no Acre.

A pecuária de corte é a atividade responsável por aproximadamente 75% dos 1.420.300 hectares de áreas desmatadas no Acre (9,3%). A partir da década de 70, a Embrapa Acre iniciou ações de pesquisa e desenvolvimento em propriedades do Estado, com o objetivo de desenvolver tecnologias que permitissem viabilizar sistemas de produção animal sustentáveis que contribuíssem para atender à demanda interna de carne, gerar excedentes exportáveis e, ao mesmo tempo, reduzir os impactos ambientais desta atividade.bitstream/item/135533/1/3673.pd

Sistemas sustentáveis de pecuária leiteira para a agricultura familiar no Acre.

A pecuária leiteira é uma atividade de crescente importância na agricultura familiar no Acre, tanto em áreas de colonização como em reservas extrativistas e áreas indígenas. Entretanto, esta atividade resulta em grandes impactos ambientais negativos., decorrentes dos desmatamentos, perda de biodiversidade e degradação dos solos. Além disso, a pecuária leiteira, desenvolvida por pequenos produtores, apresenta baixa rentabilidade decorrente dos baixos índices zootécnicos. Há duas décadas, a Embrapa Acre desenvolve tecnologias para responder ao desafio de viabilizar sistemas de produção sustentáveis para a pecuária leiteira, economicamente rentáveis e de reduzido impacto ambiental para a agricultura familiar no Acre.bitstream/item/135543/1/3674.pd