Limits of the energy-momentum tensor in general relativity

A limiting diagram for the Segre classification of the energy-momentum tensor is obtained and discussed in connection with a Penrose specialization diagram for the Segre types. A generalization of the coordinate-free approach to limits of Paiva et al. to include non-vacuum space-times is made. Geroch's work on limits of space-times is also extended. The same argument also justifies part of the procedure for classification of a given spacetime using Cartan scalars.Comment: LaTeX, 21 page

Photoassociative ionization of Na inside a storage ring

Motivated by recent interest in low dimensional arrays of atoms, we experimentally investigated the way cold collisional processes are affected by the geometry of the considered atomic sample. More specifically, we studied the case of photoassociative ionization (PAI) both in a storage ring where collision is more unidirectional in character and in a trap with clear undefinition of collision axis. First, creating a ring shaped trap (atomotron) we investigated two-color PAI dependence with intensity and polarization of a probing laser. The intensity dependence of the PAI rate was also measured in a magneto-optical trap presenting equivalent temperature and density conditions. Indeed, the results show that in the ring trap, the value of the PAI rate constant is much lower and does not show evidences of saturation, unlike in the case of the 3D-MOT. Cold atomic collisions in storage ring may represent new possibilities for study.Comment: 5 pages, 5 figures; Accepted by Optics Communicatio

Conical refraction in generalized biaxial media: A geometric algebra approach

It is well-know that conical refraction occurs for electric anisotropic biaxial crystals when the wave vector has the direction of the medium optic axes. In this paper, we show that conical refraction occurs in an analogous away for a more general type of biaxial media that have simultaneously electric and magnetic anisotropies. Furthermore, the new coordinate-free approach based on geometric algebra, developed by the authors in previous papers to address anisotropy, is shown to shed new light on this classic topic of optics that is conical refraction.info:eu-repo/semantics/acceptedVersio

Charge-density waves in one-dimensional Hubbard superlattices

We study the formation of charge density waves (CDW's) in one-dimensional Hubbard superlattices, modeled by a repeated pattern of repulsive (U>0) and free (U=0) sites. By means of Lanczos diagonalizations for the ground state, we calculate the charge structure factor. Our results show that while the superlattice structure affects the modulation of the charge density waves, the periodicity can still be predicted through an effective density. We also show that, for a fixed repulsive layer thickness, the periodicity of the CDW is an oscillatory function of the free layer thickness.Comment: 4 pages, 4 figure

Descrição de sistemas de criação tradicionais de ovinos da Nhecolândia, Pantanal, MS.

Este trabalho tem como objetivo principal resgatar o conhecimento empírico sobre o sistema de criação tradicional de ovinos no Pantanal, caracterizando-o e descrevendo-o a partir de oito fazendas da sub-região da Nhecolândia, Pantanal, MS. Devido a crescente demanda do mercado por carne ovina, os produtores do Pantanal podem diversificar a produção animal. A região apresenta potencial para a produção de ovelhas pantaneiras para cruzamentos no planalto, produção de cordeiros (orgânicos), produção de subsistência da fazenda, entre outros. Para tanto, há a necessidade de desenvolver práticas sustentáveis de manejo da ovinocultura no Pantanalbitstream/item/80589/1/CT94.pd

A layering model for superconductivity in the borocarbides

We propose a superlattice model to describe superconductivity in layered materials, such as the borocarbide families with the chemical formul\ae\ $RT_2$B$_2$C and $RT$BC, with $R$ being (essentially) a rare earth, and $T$ a transition metal. We assume a single band in which electrons feel a local attractive interaction (negative Hubbard-$U$) on sites representing the $T$B layers, while U=0 on sites representing the $R$C layers; the multi-band structure is taken into account minimally through a band offset $\epsilon$. The one-dimensional model is studied numerically through the calculation of the charge gap, the Drude weight, and of the pairing correlation function. A comparison with the available information on the nature of the electronic ground state (metallic or superconducting) indicates that the model provides a systematic parametrization of the whole borocarbide family.Comment: 4 figure

Efeitos de variantes do gene da aromatase sobre caracteristicas de crescimento, reprotutivas e de habilidade materna em ovinos de uma população multirracial.

Resumo: Foi verificado o efeito das variantes do gene da aromatase sobre características produtivas e reprodutivas de ovinos de uma população multirracial. Para isto, fêmeas de diferentes grupos genéticos foram genotipadas e a influência do genótipo do animal sobre seu desempenho ou sobre o desempenho de suas crias foi analisada pelo método dos quadrados mínimos. Fêmeas BB apresentaram menor idade ao primeiro parto para o grupo genético ½ Dorper e menor intervalo de partos para a raça Santa Inês. Nestes mesmos grupos genéticos, as fêmeas AB apresentaram maiores pesos totais de crias desmamadas por matriz e por parto. Existem evidências que fêmeas BB apresentam melhores desempenhos reprodutivos, contrariamente às fêmeas AB que apresentam melhores habilidades maternas. Entretanto, maiores investigações são necessárias para comprovar estas evidências; [Allelic Frequency from Aromatase Gene in Meat Sheep]. Abstract: The effect of variants for aromatase gene on productive and reproductive traits in sheep from a multiracial population was verified. Females of different genetic groups were genotyped and the influence of the genotype of the animal on your performance or on the performance of yours lambs was analyzed by the least square method. BB females presented lower age at first lambing for ½ Dorper and lower lambing interval for Santa Inês breed. In these same genetic groups, AB females presented larger total weight of weaned lambs per female and per lambing. There are evidences that BB females presented better reproductive performance, contrarily to AB females that presented better maternal ability. However, more investigations are necessary to prove these evidences