Einstein Equations
Mostrando 13-24 de 38 artigos, teses e dissertações.
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13. Sediment yield in watersheds under different geo-environmental contexts: measured and modelling / ProduÃÃo de Sedimentos em Bacias HidrogrÃficas Sob Diferentes Contextos Geoambientais: Medida e Modelagem.
Sediment yield assessment is necessary in watersheds when it is desired to improve the quality of analysis, contributing for a consistent evaluation of water availability and, therefore, high-quality water resources management. The general objective was to evaluate the sediment yield in watersheds under different geo-environmental contexts. Three small basin
Publicado em: 2008
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14. Energy-momentum distribution of the Weyl-Lewis-Papapetrou and the Levi-Civita metrics
This paper is devoted to compute the energy-momentum densities for two exact solutions of the Einstein field equations by using the prescriptions of Einstein, Landau-Lifshitz, Papapetrou and Möller. The spacetimes under consideration are the Weyl-Lewis-Papapetrou and the Levi-Civita metrics. The Weyl metric becomes the special case of the Weyl-Lewis-Papapet
Brazilian Journal of Physics. Publicado em: 2007-12
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15. Rotating and counterrotating relativistic thin disks as sources of stationary electrovacuum spacetimes
A detailed study is presented of the counterrotating model (CRM) for electrovacuum stationary axially symmetric relativistic thin disks of infinite extension without radial stress, in the case when the eigenvalues of the energy-momentum tensor of the disk are real quantities, so that there is not heat flow. We find a general constraint over the counterrotati
Brazilian Journal of Physics. Publicado em: 2007-09
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16. Tratamento das equações de Eintein-Yang-Mills para soluções numericas com simetria esferica auto-gravitante e simetria axial no espaço-tempo de Minkowski / Set up of Einstein-Yang-Mills equation for numerical solutions of self-gravitating spherical symmetric fields and axial simmetric fields on Minkowski space-time
Nesse trabalho delineamos a teoria clássica para o campo de Einstein-Yang-Mills e elaboramos um conjunto particular de equações para obtermos soluções numéricas. Estudamos dois casos com simetria espaço-temporal: Simetria esférica com campo auto-gravitante e simetria axial no espaço-tempo de Minkowski. Utilizamos métodos numéricos das linhas para
Publicado em: 2007
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17. Estabilidade de curvas tipo-tempo fechadas em variedades lorentzianas / Stability of closed timelike curves in Lorentzian manifolds
Several solutions of Einstein?s field equations admit closed timelike curves (CTCs). We study the linear stability of this kind of curve. We analyze the CTCs in Gödel universe and we find that these curves are stable. The same occurs with the CTCs of a particular case of Gödel-type metric with flat background and with CTCs of a model that contains a single
Publicado em: 2007
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18. Criação da matéria em cosmologias com velocidade da luz variável e eletrônico não-linear
In this work we obtain the cosmological solutions and investigate the thermodynamics of matter creation in two diferent contexts. In the first we propose a cosmological model with a time varying speed of light c. We consider two diferent time dependence of c for a at Friedmann-Robertson- Walker (FRW) universe. We write the energy conservation law arising fro
Publicado em: 2006
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19. Models of disks and other self-gravitating structures in general relativity / Modelos de discos e outras estruturas auto-gravitantes em relatividade geral
Exact solutions of Einstein field equations that represent space-times with disklike matter distributions are constructed using the inverse method (image method). These solutions include static thin perfect uid disks with and without halos, static thin charged perfect uid disks and models of thin charged dust disks. New solutions in various coordinate system
Publicado em: 2006
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20. The embedding of spacetime into cauchy developments
Using the Campbell-Magaard theorem we show that any analytic spacetime can be locally embedded into the Cauchy development of legitimate initial data for the five dimensional vacuum Einstein equations. The embedding presents the domain of dependence property and the Cauchy stability with respect to those initial data.
Brazilian Journal of Physics. Publicado em: 2005-12
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21. Validity of semiclassical gravity in the stochastic gravity approach
In semiclassical gravity the back-reaction of the classical gravitational field interacting with quantum matter fields is described by the semiclassical Einstein equations. A criterion for the validity of semiclassical gravity based on the stability of the solutions of the semiclassical Einstein equations with respect to quantum metric perturbations is discu
Brazilian Journal of Physics. Publicado em: 2005-06
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22. Holographic gravity and the surface term in the Einstein-Hilbert action
Certain peculiar features of Einstein-Hilbert (EH) action provide clues towards a holographic approach to gravity which is independent of the detailed microstructure of spacetime. These features of the EH action include: (a) the existence of second derivatives of dynamical variables; (b) a non trivial relation between the surface term and the bulk term; (c)
Brazilian Journal of Physics. Publicado em: 2005-06
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23. Oscilações de buracos negros / Black hole oscillations
In the past few years, black hole oscillations became a very interesting research area mainly due to the possibility of proving the existence of such celestial bodies through the gravitational radiation emitted by them. In this work, the study of the propagation of different kinds of incident waves on a black hole is presented under the mathematical point of
Publicado em: 2005
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24. Circular cosmic string loop in Brans-Dicke theory
The gravitational field of a stationary circular cosmic string loop, externally supported against collapse, is investigated in the context of Brans-Dicke theory in the weak field approximation of the field equations. The solution is quasi-conformally related to the corresponding solution in Einstein's General Relativity(GR) and goes over to the corresponding
Braz. J. Phys.. Publicado em: 2001-09