Some FRW viscous models with variable G, c and cosmological constant

We consider several viscous model with metric type FRW, with k=0 and with generic equation of state. We take into account too, the conservation principle for the energy-momentum tensor. We find trivially, a set of solutions through dimensional analysis.Comment: 7 pages. submitted to General Relativity and Gravitatio

Cosmological Models with Some Variable Constant

Various models are under consideration with metric type flat FRW whose energy-momentum tensor is described by a perfect fluid whose generic equation state and taking into account the conservation principle, but considering some of the constants as variable. A set of solutions through dimensional analysis is trivially found. The numeric calculations carried out show that the results obtained are not discordant with those presently observed for cosmological parameters. However, the model seems irreconcilable with electromagnetic and quantum quantities. This makes us think that we are working with faulty hypothesis from the startComment: 7 pages. LaTeX2e. Submitted to Astro. Space .Scie

Cosmological models with variable constants

The behavior of the constants, G,c,h,a,e,m and Lambda, considering them as variable, in the framework of a flat cosmological model with FRW symmetries described by a bulk viscous fluid and considering mechanisms of adiabatic matter creation are investigated. Within two models; one with radiation predominance and another of matter predominance, this behavior are studied.Comment: 15 pages. submitted to IJT

Bulk Viscous Cosmological Model with G and Lambda Variables Through Dimensional Analysis

A model with flat FRW symmetries and G and Lambda variable,is considered in such a way that the momentum-energy tensor that describes the model is characterized by a bulk viscosity parameter. In this paper it is showed how to apply the dimensional method in order to solve the outlined equations in a trivial way.Comment: 7 pages. LaTeX2e. Submitted to General Relativity and Gravitatio

Enlargement of Planck`s System of Absolute Units

In this paper, we want to make to see the convenience of the amplification of the Planck`s system of absolute units through the introduction of two new constant, the dynamical constant and the permitividad of the vacuum upon rejecting that the electron charge has mechanical dimensions and adopting it as Planck`s charge. We apply these results to clarify the homogeneity and isotropy in the very early universe.Comment: 7 pages. Submitted to Il Nuovo Cimento

Full Causal Bulk Viscous Cosmological Models with Variable G and Lambda

We study the evolution of a flat Friedmann-Robertson- Walker Universe, filled with a bulk viscous cosmological fluid, in the presence of variable gravitational and cosmological constants. The dimensional analysis of the model suggest a proportionality between the bulk viscous pressure of the dissipative fluid and the energy density. With the use of this assumption and with the choice of the standard equations of state for the bulk viscosity coefficient, temperature and relaxation time, the general solution of the field equations can be obtained, with all physical parameters having a power-law time dependence. The symmetry analysis of this model, performed by using Lie group techniques, confirms the unicity of the solution for this functional form of the bulk viscous pressure.Comment: 9 pages. ReVTeX

Approximate Analytical Solution for the Dynamic Model of Large Amplitude Non-Linear Oscillations Arising in Structural Engineering

In this work we obtain an approximate solution of the strongly nonlinear second order differential equation $\frac{d^{2}u}{dt^{2}}+\omega ^{2}u+\alpha u^{2}\frac{d^{2}u}{dt^{2}}+\alpha u\left( \frac{du}{dt}\right)^{2}+\beta \omega ^{2}u^{3}=0$, describing the large amplitude free vibrations of a uniform cantilever beam, by using a method based on the Laplace transform, and the convolution theorem. By reformulating the initial differential equation as an integral equation, with the use of an iterative procedure, an approximate solution of the nonlinear vibration equation can be obtained in any order of approximation. The iterative approximate solutions are compared with the exact numerical solution of the vibration equation.Comment: 8 pages, 1 figure, accepted for publication in Journal of Applied Mathematics and Engineerin

Aplications of Dimensional Analysis to Cosmology

In this paper we apply dimensional analysis (D.A.) to two cosmological models: Einstein-de Sitter and one Friedmann-Robertson-Walker (FRW) with radiation predominance. We believe that this method leads to the simplest form of solution the differential equations that arise in both models and would be useful as a base for the solution of more complex models. The aim of the paper is therefore rather pedagogical since it tries to show different dimensional techniques.Comment: 9 pages. We have amended some grammatical mistakes and we have added a small section where we explain the employed dimensional metho

Some FRW models with variable G and cosmological constant

We consider several model with metric type FRW, with k=0 and with generic equation of state. We take into account too, the conservation principle for the energy-momentum tensor. We find trivially, a set of solutions through dimensional analysis. We emphasite that the solution for G depend on the equation of state and for the cosmological constant no.Comment: 7 pages. submitted to General Relativity and Gravitatio

Normalized angular momentum deficit: A tool for comparing the violence of the dynamical histories of planetary systems

Population studies of the orbital characteristics of exoplanets in multi-planet systems have highlighted the existence of an anticorrelation between the average orbital eccentricity of planets and the number of planets of their host system, that is, its multiplicity. This effect was proposed to reflect the varying levels of violence in the dynamical evolution of planetary systems. Previous work suggested that the relative violence of the dynamical evolution of planetary systems with similar orbital architectures can be compared through the computation of their angular momentum deficit (AMD). We investigated the possibility of using a more general metric to perform analogous comparisons between planetary systems with different orbital architectures. We considered a modified version of the AMD, the normalized angular momentum deficit (NAMD), and used it to study a sample of 99 multi-planet systems containing both the currently best-characterized extrasolar systems and the solar system, that is, planetary systems with both compact and wide orbital architectures. We verified that the NAMD allows us to compare the violence of the dynamical histories of multi-planet systems with different orbital architectures. We identified an anticorrelation between the NAMD and the multiplicity of the planetary systems, of which the previously observed eccentricity-multiplicity anticorrelation is a reflection. Our results seem to indicate that phases of dynamical instabilities and chaotic evolution are not uncommon among planetary systems. They also suggest that the efficiency of the planetary formation process in producing high-multiplicity systems is likely to be higher than that suggested by their currently known population.Comment: 6 pages, 1 table, 3 figures. Accepted for publication on Astronomy & Astrophysic