Constraints on non-minimally coupled curved space electrodynamics from astrophysical observations

We study interactions of electro-magnetic fields with the curvature tensor of the form $\lambda R_{\mu \nu \alpha \beta}F^{\mu \nu}F^{\alpha \beta}$. Such coupling terms though are invariant under general coordinate transformation and CPT, however violate the Einstein equivalence principle. These couplings do not cause any energy dependent dispersion of photons but they exhibit birefringence. We put constraints on the coupling constant $\lambda$ using results from solar system radar ranging experiments and millisecond-pulsar observations. We find that the most stringent constraint comes from pulsar observations and is given by $\lambda < 10^{11} cm^2$ obtained from the timing of binary pulsar PSR B1534+12.Comment: 9 pages latex, accepted in CQ

Uso de carvão como filtro para manipueira visando produção de fertilizante de liberação lenta.

Os subprodutos resultantes do processamento da mandioca têm sido grandes responsáveis por sérios problemas de contaminação do meio ambiente, poluindo solos e cursos de água doce. A manipueira é o resíduo líquido gerado pela prensagem das raízes nas indústrias de processamento de mandioca. A biomassa carbonizada (biochar) utilizada como filtro para resíduo líquido, a manipueira, possibilita a redução da carga poluente desse resíduo.PDF. 074_11

Effective Hamiltonian for non-minimally coupled scalar fields

Performing a relativistic approximation as the generalization to a curved spacetime of the flat space Klein-Gordon equation, an effective Hamiltonian which includes non-minimial coupling between gravity and scalar field and also quartic self-interaction of scalar field term is obtained.Comment: 4 page

A perturbative solution for gravitational waves in quadratic gravity

We find a gravitational wave solution to the linearized version of quadratic gravity by adding successive perturbations to the Einstein's linearized field equations. We show that only the Ricci squared quadratic invariant contributes to give a different solution of those found in Einstein's general relativity. The perturbative solution is written as a power series in the $\beta$ parameter, the coefficient of the Ricci squared term in the quadratic gravitational action. We also show that, for monochromatic waves of a given angular frequency $\omega$, the perturbative solution can be summed out to give an exact solution to linearized version of quadratic gravity, for $0<\omega<c/\mid\beta\mid^{1/2}$. This result may lead to implications to the predictions for gravitational wave backgrounds of cosmological origin.Comment: 9 pages, to appear in CQ

Some interesting features of new massive gravity

A proof that new massive gravity - the massive 3D gravity model proposed by Bergshoeff, Hohm and Townsend (BHT) - is the only unitary system at the tree level that can be constructed by augmenting planar gravity through the curvature-squared terms, is presented. Two interesting gravitational properties of the BHT model, namely, time dilation and time delay, which have no counterpart in the usual Einstein 3D gravity, are analyzed as well.Comment: Submitted to Classical and Quantum Gravit

Contenido de metales pesados en abonos orgánicos, sustratos y plantas cultivadas en organopónicos: Heavy metals content in organic manures, substrates and plants cultivated in organoponics.

La utilización de abonos orgánicos (AO) de diversos orígenes, como los compost obtenidos a partir de residuales sólidos urbanos (RSU), en organopónicos de la agricultura urbana, es una alternativa para la producción de alimentos conbajos insumos. Para el uso de estos productos, se requiere una evaluación sistemática de sus contenidos en metales pesados (MP), porque pueden acumularse en los suelos y sustratos, alterar el equilibrio biológico de los mismos y afectar al rendimiento de los cultivos y la salud animal, inclusive la del hombre. Se evaluó la metodología analítica de mayor exactitud y porcentaje de recobrado en la determinación de Cadmio (Cd), Plomo (Pb) y Níquel (Ni) y se empleó para el estudio del contenido de estos MP en AO y sustratos así como su efecto en las hortalizas que se producen en organopónicos de La Habana y Guantánamo. Se encontró que los compost obtenidos a partir de los RSU provenientes de la basura doméstica extraída de los vertederos sin previa clasificación y los substratos preparados a partir de estos, presentan contenidos de MP, especialmente Cd y Pb, por encima de los límites máximos permisibles (LMP), por lo que no deben ser empleados para l

Causal Anomalies in Kaluza-Klein Gravity Theories

Causal anomalies in two Kaluza-Klein gravity theories are examined, particularly as to whether these theories permit solutions in which the causality principle is violated. It is found that similarly to general relativity the field equations of the space-time-mass Kaluza-Klein (STM-KK) gravity theory do not exclude violation of causality of G\"odel type, whereas the induced matter Kaluza-Klein (IM-KK) gravity rules out noncausal G\"odel-type models. The induced matter version of general relativity is shown to be an efficient therapy for causal anomalies that occurs in a wide class of noncausal geometries. Perfect fluid and dust G\"odel-type solutions of the STM-KK field equations are studied. It is shown that every G\"odel-type perfect fluid solution is isometric to the unique dust solution of the STM-KK field equations. The question as to whether 5-D G\"odel-type non-causal geometries induce any physically acceptable 4-D energy-momentum tensor is also addressed.Comment: 16 page. LaTex file. To appear in Int. J. Mod. Phys. A (1998

Godel brane

We consider the brane-world generalisation of the Godel universe and analyse its dynamical interaction with the bulk. The exact homogeneity of the standard Godel spacetime no longer holds, unless the bulk is also static. We show how the anisotropy of the Godel-type brane is dictated by that of the bulk and find that the converse is also true. This determines the precise evolution of the nonlocal anisotropic stresses, without any phenomenological assumptions, and leads to a self-consistent closed set of equations for the evolution of the Godel brane. We also examine the causality of the Godel brane and show that the presence of the bulk cannot prevent the appearance of closed timelike curves.Comment: Revised version, to match paper published in Phys. Rev.

Aptidão agrícola das terras do município de Buenos Aires, Pernambuco.

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New solutions in 3D gravity

We study gravitational theory in 1+2 spacetime dimensions which is determined by the Lagrangian constructed as a sum of the Einstein-Hilbert term plus the two (translational and rotational) gravitational Chern-Simons terms. When the corresponding coupling constants vanish, we are left with the purely Einstein theory of gravity. We obtain new exact solutions for the gravitational field equations with the nontrivial material sources. Special attention is paid to plane-fronted gravitational waves (in case of the Maxwell field source) and to the circularly symmetric as well as the anisotropic cosmological solutions which arise for the ideal fluid matter source.Comment: Revtex, 21 pages, no figure