9 research outputs found
Non-minimally coupled tachyon field with Noether symmetry under the Palatini approach
A model for a homogeneous, isotropic, flat Universe composed by dark energy
and matter is investigated. Dark energy is considered to behave as a tachyon
field, which is non-minimally coupled to gravity. The connection is treated as
metric independent when varying the action, providing an extra term to the
Lagrangian density. The self-interaction potential and coupling are naturally
found by imposing a Noether symmetry to the system. We analyze the evolution of
the density parameters and we compare the results obtained for the deceleration
parameter, luminosity distance and Hubble parameter with those found in
literature from observational data.Comment: 6 pages, 4 figures to be published in the AIP Conference Proceeding
Espalhamento de luz em uma mistura binaria de gases monoatomicos e poliatomicos
Orientador:Gilberto Medeiros KremerDissertacao(mestrado)-Universidade Federal do Parana, Setor de Ciencias ExatasResumo: A distribuição espectral da luz espalhada por flutuações tĂ©rmicas microscĂłpicas prĂłximas do equilĂbrio e calculada para uma mistura binaria de gases monoatĂ´micos e poliatĂ´micos a partir de um modelo hidrodinâmico estendido. Neste modelo, as equações hidrodinâmicas linearizadas da teoria termodinâmica irreversĂvel sĂŁo suplementadas com uma equação de relaxação para a pressĂŁo dinâmica do gás poliatĂ´mico. As molĂ©culas do gás monoatĂ´mico sĂŁo consideradas como esferas perfeitamente rĂgidas, elásticas e lisas, enquanto que as molĂ©culas do gás poliatĂ´mico como esferas perfeitamente rĂgidas, elásticas e rugosas. Os resultados mostram que a equação de relaxação exerce grande influencia nas misturas em que a massa da partĂcula monoatĂ´mica e menor que a massa da molĂ©cula poliatĂ´mica, quando a concentração do gás poliatĂ´mico e muito maior que a do gás monoatĂ´mico. Como uma aplicação sĂŁo analisados os espectros da luz espalhada para misturas de He - CH4, Xe - CH4 e Ne - CD4.Abstract: The spectral distribution of light scattered by microscopic thermal fluctuations about equilibrium is calculated for a binary mixture of monoatomic and poliatomic gases. The linearized hydrodynamic equations of irreversible thermodynamic theory of mixtures are supplemented with a relaxation equation for the dynamic pressure of the polyatomic gas. The molecules of the monoatomic gas are characterized by perfectly smooth, elastic and rigid spheres, while the molecules of the polyatomic gas by perfectly rough, elastic and rigid spheres. The results show that the relaxation equation has great influence for mixtures in which the mass of the monoatomic particle is lighter than the mass of the polyatomic molecule providing that the concentration of the polyatomic gas is greater than the monoatomic one. As an application the spectra of light scattered from mixtures of He - CH4, Xe - CH4 and Ne - CD4 are analysed
Reaction rates and transport in neutron stars
Understanding signals from neutron stars requires knowledge about the
transport inside the star. We review the transport properties and the
underlying reaction rates of dense hadronic and quark matter in the crust and
the core of neutron stars and point out open problems and future directions.Comment: 74 pages; commissioned for the book "Physics and Astrophysics of
Neutron Stars", NewCompStar COST Action MP1304; version 3: minor changes,
references updated, overview graphic added in the introduction, improvements
in Sec IV.A.
Post-Newtonian Jeans Equation for Stationary and Spherically Symmetrical Self-Gravitating Systems
The post-Newtonian Jeans equation for stationary self-gravitating systems is derived from the post-Newtonian Boltzmann equation in spherical coordinates. The Jeans equation is coupled with the three Poisson equations from the post-Newtonian theory. The Poisson equations are functions of the energy-momentum tensor components which are determined from the post-Newtonian Maxwell–Jüttner distribution function. As an application, the effect of a central massive black hole on the velocity dispersion profile of the host galaxy is investigated and the influence of the post-Newtonian corrections are determined