Self-bound models of compact stars and recent mass-radius measurements

The exact composition of a specific class of compact stars, historically referred to as "neutron stars", is still quite unknown. Possibilities ranging from hadronic to quark degrees of freedom, including self-bound versions of the latter have been proposed. We specifically address the suitability of strange star models (including pairing interactions) in this work, in the light of new measurements available for four compact stars. The analysis shows that these data might be explained by such an exotic equation of state, actually selecting a small window in parameter space, but still new precise measurements and also further theoretical developments are needed to settle the subject.Comment: To appear in PR

Exact and Quasi-exact Models of Strange Stars

We construct and compare a variety of simple models for strange stars, namely, hypothetical self-bound objects made of a cold stable version of the quark-gluon plasma. Exact, quasi-exact and numerical models are examined to find the most economical description for these objects. A simple and successful parametrization of them is given in terms of the central density, and many differences among the models are explicitly shown and discussed.Comment: 20 pp. 15 figures, to appear in IJMP

Phase lags of quasi-periodic oscillations across source states in the low-mass X-ray binary 4U 1636-53

While there are many dynamical mechanisms and models that try to explain the origin and phenomenology of the quasi-periodic oscillations (QPOs) seen in the X-ray light curves of low-mass X-ray binaries, few of them address how the radiative processes occurring in these extreme environments give rise to the rich set of variability features actually observed in these light curves. A step towards this end comes from the study of the energy and frequency dependence of the phase lags of these QPOs. Here we used a methodology that allowed us to study, for the first time, the dependence of the phase lags of all QPOs in the range of 1 Hz to 1300 Hz detected in the low-mass X-ray binary 4U 1636-53 upon energy and frequency as the source changes its states as it moves through the colour-colour diagram. Our results suggest that within the context of models of up-scattering Comptonization, the phase lags dependencies upon frequency and energy can be used to extract size scales and physical conditions of the medium that produces the lags

Mapeamento de índice de estresse hídrico da cultura do feijoeiro (Phaseolus vulgaris L.) em pivô central por meio de termometria a infravermelho.

O principal objetivo deste trabalho foi o mapeamento de índice de estresse hídrico da cultura (IEHC) do feijoeiro (Phaseolus vulgaris L.) em pivô central por meio de termometria a infravermelho. Um transdutor de temperatura a infravermelho (TTIR) registrou os valores de temperaturas do dos seI da cultura (Te) e do ar (Ta), déficit de pressão de vapor do ar (DPV) e radiação solar. Uma equação relacionando a diferença Te-Ta atual (dT) com os limites inferior e superior de Te-Ta (dTj e dTs) foi usada nos cálculos dos valores de IEHC. Equações relacionando a diferença Te-Ta com o DPV constituíram estes limites. Um sistema de posicionamento global diferencial possibilitou o georreferenciamento dos locais de medições de altimetria da área, da diferença Te - Ta e de produtividade de grãos da cultura e a integração dos dados a um sistema de informação geográfica (SIG). O TTIR mostrou-se eficaz no mapeamento de IEHC e possibilitou a caracterização e análise da variabilidade do estresse hídrico da cultura e produtividade de grãos. Valores de IEHC de 0,0 a 0,2 foram encontrados em 65,3 % da área irrigada. Apenas 7 % da área irrigada forneceu rendimentos de grãos da ordem de 2000 a 3000 Kg/ha. As áreas da parte mais elevada do pivô apresentaram as menores produtividade e os maiores valores de IEHC, devido principalmente a baixa uniformidade de distribuição de água do sistema de irrigação