Non-adiabatic collapse of a quasi-spherical radiating star

A model is proposed of a collapsing quasi-spherical radiating star with matter content as shear-free isotropic fluid undergoing radial heat-flow with outgoing radiation. To describe the radiation of the system, we have considered both plane symmetric and spherical Vaidya solutions. Physical conditions and thermodynamical relations are studied using local conservation of momentum and surface red-shift. We have found that for existence of radiation on the boundary, pressure on the boundary is not necessary.Comment: 8 Latex pages, No figures, Revtex styl

Microstresses and microstructure in thick cobalt-based laser deposited coatings

Microstresses in a thick laser clad Co-based coating on steel substrate were investigated with 3D X-ray microscopy using an intense synchrotron microfocused beam. The microstructure was examined with tight microscopy and field emission scanning electron microscopy equipped with X-ray energy dispersive spectroscopy and Electron Back Scattering Diffraction (orientation imaging microscopy). Microhardness and scratch resistance variations inside the coating are related to the local microstructure influenced by additional heating and by melt convection during the laser track overlapping. The residual microstrains were accessed with a high spatial resolution defined by the size of the synchrotron microbeam. Type 11 residual strains and stresses on the level of individual grains and dendrites were analyzed in terms of tensor invariants, hydrostatic and von Mises shear stress, along the depth of a slightly diluted clad track. The upper part of the coating shows a constant spread of hydrostatic stresses between -500 and 500 MPa; towards the bottom of the track the spread of these stresses increases almost linearly with depth. A correlation between the microstructural features and the spread of the hydrostatic microstresses was found. It is concluded that microstresses in individual neighboring grains are inhomogeneously dispersed. (c) 2007 Elsevier B.V. All rights reserved

The Mass Function of Field Galaxies at 0.4 < z < 1.2 Derived From the MUNICS K-Selected Sample

We derive the number density evolution of massive field galaxies in the redshift range 0.4 < z < 1.2 using the K-band selected field galaxy sample from the Munich Near-IR Cluster Survey (MUNICS). We rely on spectroscopically calibrated photometric redshifts to determine distances and absolute magnitudes in the rest-frame K-band. To assign mass-to-light ratios, we use two different approaches. First, we use an approach which maximizes the stellar mass for any K-band luminosity at any redshift. We take the mass-to-light ratio of a Simple Stellar Population (SSP) which is as old as the universe at the galaxy's redshift as a likely upper limit. Second, we assign each galaxy a mass-to-light ratio by fitting the galaxy's colours against a grid of composite stellar population models and taking their M/L. We compute the number density of galaxies more massive than 2 x 10^10 h^-2 Msun, 5 x 10^10 h^-2 Msun, and 1 x 10^11 h^-2 Msun, finding that the integrated stellar mass function is roughly constant for the lowest mass limit and that it decreases with redshift by a factor of ~ 3 and by a factor of ~ 6 for the two higher mass limits, respectively. This finding is in qualitative agreement with models of hierarchical galaxy formation, which predict that the number density of ~ M* objects is fairly constant while it decreases faster for more massive systems over the redshift range our data probe.Comment: 6 pages, 2 figures, to appear in the proceedings of the ESO/USM Workshop "The Mass of Galaxies at Low and High Redshift", Venice (Italy), October 24-26, 200

The Munich Near-Infrared Cluster Survey (MUNICS) - Number density evolution of massive field galaxies to z ~ 1.2 as derived from the K-band selected survey

We derive the number density evolution of massive field galaxies in the redshift range 0.4 < z < 1.2 using the K-band selected field galaxy sample from the Munich Near-IR Cluster Survey (MUNICS). We rely on spectroscopically calibrated photometric redshifts to determine distances and absolute magnitudes in the rest-frame K-band. To assign mass-to-light ratios, we use an approach which maximizes the stellar mass for any K-band luminosity at any redshift. We take the mass-to-light ratio, M/L_K, of a Simple Stellar Population (SSP) which is as old as the universe at the galaxy's redshift as a likely upper limit. This is the most extreme case of pure luminosity evolution and in a more realistic model M/L_K will probably decrease faster with redshift due to increased star formation. We compute the number density of galaxies more massive than 2 10^10 h^-2 solar masses, 5 10^10 h^-2 solar masses, and 1 10^11 h^-2 solar masses, finding that the integrated stellar mass function is roughly constant for the lowest mass limit and that it decreases with redshift by a factor of roughly 3 and by a factor of roughly 6 for the two higher mass limits, respectively. This finding is in qualitative agreement with models of hierarchical galaxy formation, which predict that the number density of ~ M* objects is fairly constant while it decreases faster for more massive systems over the redshift range our data probe.Comment: 4 pages, 5 figures, accepted for publication in ApJ Letter

The dynamics of apparent horizons in Robinson-Trautman spacetimes

We present an alternative scheme of finding apparent horizons based on spectral methods applied to Robinson-Trautman spacetimes. We have considered distinct initial data such as representing the spheroids of matter and the head-on collision of two non-rotating black holes. The evolution of the apparent horizon is presented. We have obtained in some cases a mass gap between the final Bondi and apparent horizon masses, whose implications were briefly commented in the light of the thermodynamics of black holes.Comment: 9 pages, 7 figure

Efeito da idade da vaca sobre o peso ao nascimento e peso à desmama de bezerros criados extensivamente na sub-região do Paiaguás, Pantanal Sul-Mato-Grossense.

O estudo foi realizado com intuito de avaliar o efeito da idade da vaca ao parto sobre os pesos de bezerros ao nascimento e a desmama corrigidos para os 205 dias de idade, de um rebanho comercial de bovinos de corte anelorados, pertencentes a uma propriedade particular que realiza a atividade de cria extensiva em pasto nativo e está localizada na sub-região do Paiaguás, Pantanal Sul-Mato-Grossense. Utilizou-se informações de peso ao nascimento e peso à desmama corrigidos para os 205 dias de idade de 183 animais, assim como informações da idade da vaca ao parto. Foram realizadas análises de regressão para avaliar o efeito da idade da vaca ao parto sobre as características em estudo. A idade da vaca ao parto influenciou significativamente sobre as características de peso ao nascimento e peso à desmama corrigido para os 205 dias de idade. Tanto para peso ao nascer quanto para peso à desmama aos 205 dias, as idades iniciais e finais das vacas apresentaram resultados abaixo da média estimada. Deste modo, há necessidade de considerar o efeito da idade da vaca ao parto sobre as características produtivas, para que os animais, candidatos à seleção, tenham seus valores genéticos preditos com maior confiabilidade, garantindo assim maximização do ganho genético, por meio da seleção dos melhores reprodutores