Schwinger's Principle and Gauge Fixing in the Free Electromagnetic Field

A manifestly covariant treatment of the free quantum eletromagnetic field, in a linear covariant gauge, is implemented employing the Schwinger's Variational Principle and the B-field formalism. It is also discussed the abelian Proca's model as an example of a system without constraints.Comment: 8 pages. Format PTPtex. No figur

Bulk Viscous Cosmological Models in Barber's Second Self Creation Theory

Barber's second self creation theory with bulk viscous fluid source for an LRS Bianchi type-I metric is considered by using deceleration parameter to be constant where the metric potentials are taken as function of $x$ and $t$. The coefficient of bulk viscosity is assumed to be a power function of the mass density. Some physical and geometrical features of the models are discussedComment: latex, 10 pages, submitted in Int. J. Mod. Phys.

Hamilton-Jacobi formalism for Linearized Gravity

In this work we study the theory of linearized gravity via the Hamilton-Jacobi formalism. We make a brief review of this theory and its Lagrangian description, as well as a review of the Hamilton-Jacobi approach for singular systems. Then we apply this formalism to analyze the constraint structure of the linearized gravity in instant and front-form dynamics.Comment: To be published in Classical and Quantum Gravit

An analysis of cosmological perturbations in hydrodynamical and field representations

Density fluctuations of fluids with negative pressure exhibit decreasing time behaviour in the long wavelength limit, but are strongly unstable in the small wavelength limit when a hydrodynamical approach is used. On the other hand, the corresponding gravitational waves are well behaved. We verify that the instabilities present in density fluctuations are due essentially to the hydrodynamical representation; if we turn to a field representation that lead to the same background behaviour, the instabilities are no more present. In the long wavelength limit, both approachs give the same results. We show also that this inequivalence between background and perturbative level is a feature of negative pressure fluid. When the fluid has positive pressure, the hydrodynamical representation leads to the same behaviour as the field representation both at the background and perturbative levels.Comment: Latex file, 18 page

Bopp-Podolsky black holes and the no-hair theorem

Bopp-Podolsky electrodynamics is generalized to curved space-times. The equations of motion are written for the case of static spherically symmetric black holes and their exterior solutions are analyzed using Bekenstein's method. It is shown the solutions split-up into two parts, namely a non-homogeneous (asymptotically massless) regime and a homogeneous (asymptotically massive) sector which is null outside the event horizon. In addition, in the simplest approach to Bopp-Podolsky black holes, the non-homogeneous solutions are found to be Maxwell's solutions leading to a Reissner-Nordstr\"om black hole. It is also demonstrated that the only exterior solution consistent with the weak and null energy conditions is the Maxwell's one. Thus, in light of energy conditions, it is concluded that only Maxwell modes propagate outside the horizon and, therefore, the no-hair theorem is satisfied in the case of Bopp-Podolsky fields in spherically symmetric space-times.Comment: 9 pages, updated to match published versio

Produção de mudas frutíferas no Nordeste.

Objetivando conhecer a situacao da producao de mudas no contexto da fruticultura nordestina, a Embrapa Agroindustria Tropical, realizou um levantamento nos estados de Sergipe, Alagoas,Pernambuco, Paraiba, Rio Grande do Norte, Ceara, Piaui e Maranhao.bitstream/CNPAT-2010/5359/1/Ct-027.pd

Considerações gerais sobre organogênese.

bitstream/CNPA/18322/1/DOC150.pd

Neck position therapy efficiency in positional obstructive sleep apnea treatment and sleep quality

info:eu-repo/semantics/publishedVersio