Interacting Ricci-like holographic dark energy

In a flat Friedmann–Lemaitre–Robertson–Walker background, a scheme of dark matter–dark energy interaction is studied considering a holographic Ricci-like model for the dark energy. Without giving a priori some specific model for the interaction function, we show that this function can experience a change of sign during the cosmic evolution. The parameters involved in the holographic model are adjusted with Supernova data and we obtained results compatible with the observable universe.     

Modelling mechanical behaviour of limestone under reservoir conditions

High porosity and low permeability limestone has presented pore collapse. As fluid is withdrawn from these reservoirs, the effective stresses acting on the rock increase. If the strength of the rock is overcome, pore collapse may occur, leading to irreversible compaction of porous media with permeability and porosity reduction. It impacts on fluid withdrawal. Most of reservoirs have been discovered in weak formations, which are susceptible to this phenomenon. This work presents a study on the mechanical behaviour of a porous limestone from a reservoir located in Campos Basin, offshore Brazil. An experimental program was undergone in order to define its elastic plastic behaviour. The tests reproduced the loading path conditions expected in a reservoir under production. Parameters of the cap model were fitted to these tests and numerical simulations were run. The numerical simulations presented a good agreement with the experimental tests. Copyright © 2006 John Wiley & Sons, Ltd.     

Orbital Elements of 2004 Perseid Meteoroids Perturbed by Jupiter

Jupiter and Saturn produce important gravitational impulses on meteoroids released by comet 109P/Swift-Tuttle. The meteoroids from this comet once released follow retrograde orbits that during their periodic approaches to these planets (within 1.6 and 0.9 A.U., respectively) are impulsed gaining orbital energy. This perturbation effect is translated into a net inward shift in the node of the perturbed meteoroids. Such geometry with Jupiter occurred in 2004 over a meteoroid trail ejected by this comet during the 1862 A.D. return of the comet to perihelion. In order to study the predicted outburst produced by one-revolution meteoroids, the Spanish Photographic Meteor Network (SPMN) performed an extensive campaign. As a part of this observational effort here are presented 10 accurate meteoroid orbits. We discuss their origin by comparing them with the theoretical orbital elements of the dust trails intercepting the Earth during the 2004 Perseid return.     

Anisotropic Bianchi Type-II Cosmological Models in Self-Creation Cosmology

Totally anisotropic Bianchi type-II cosmological solutions are presented in Barber's second self-creation theory of gravitation both in vacuum and in the presence of stiff-matter. The corresponding cosmological models have no finite singularity. The stiff-matter model gives essentially an empty universe for large time. Some physical and kinematical properties of the models are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of oblateness on triangular solutions at critical mass

At critical mass the triangular equilibria in the planar restricted three-body problem, when the more massive primary is an oblate spheroid with its equatorial plane coincident with the plane of motion, are in general unstable due to the presence of secular terms in the solutions of linearized equations of motion in the vicinity of these points. Existence of retrograde elliptic periodic orbits is established through suitable velocity components. The eccentricity of these orbits increases with the oblateness.     

The LRS Bianchi type-I perfect fluids space-times

An algorithm is derived for constructing spatially-homogeneous perfect fluid solutions of Einstein's field equations which are of Bianchi type-I and are locally rotationally-symmetric. Starting from Bayin and Krisch solution a new exact solution is obtained. Some physical and kinematic properties of the cosmological model are discussed.     

A class of new Bianchi I perfect fluid space-times

A procedure to generate new exact solutions to Einstein equations for perfect fluids is applied to LRS Bianchi type I line-element. Starting from some known solutions a class of new perfect fluid solutions of Bianchi type I are presented. The physical and kinematical properties of spatially homogeneous and anisotropic cosmological models are studied.