Time Variation Of Constants Research Articles

A Cosmological View for the Time - Variation of the Fundamental Constants of Nature

Time variation of constants of nature is still a question of debate among astronomers, physicists, geologists, and palaeontologists. But are the fundamental physical constants really varying in space or time and how changing these parameters may occur?. Paul Dirac was interested in this question in the large number hypothesis (LNH). He arrived by coincidence at the revolutionary hypothesis that the gravitational constant G should be varied inversely with the cosmic time t. LNH sparked off many ideas and arguments about the possibility of time or space variations of the fundamental constants of nature. In this work, we review details and arguments regarding the time and space variation of dimensional and dimensionless constants based on a detailed comparison for the recorded literature over about one and a half-century.

The time-dependent boundary element method formulation applied to dynamic analysis of Euler-Bernoulli beams: the linear θ method

In this paper, the dynamic analysis of Euler-Bernoulli beams is performed with the time-dependent Boundary Element Method formulation (TD-BEM). In the standard formulation, the variables related to the essential boundary conditions (displacement and rotation) are assumed to vary linearly in time, i.e., within each time interval, whereas the variables related to the natural boundary conditions (shear force and bending moment) are assumed to have a constant time variation. Different hypothesis concerning the time behavior of these quantities lead to unstable and inaccurate results. In the linear θ method, on the other hand, all the variables are assumed to have a linear time variation and reliable results are achieved. These results can be seen in the examples presented in this article, which contain the four usual types of beams under continuously distributed and concentrated loadings.

Transient heat conduction by the boundary element method: D-BEM approaches

SUMMARY This work is concerned with the development of different domain-BEM (D-BEM) approaches to the solution of two-dimensional diffusion problems. In the first approach, the process of time marching is accomplished with a combination of the finite difference and the Houbolt methods. The second approach starts by weighting, with respect to time, the basic D-BEM equation, under the assumption of linear and constant time variation for the temperature and for the heat flux, respectively. A constant time weighting function is adopted. The time integration reduces the order of the time derivative that appears in the domain integral; as a consequence, the initial conditions are directly taken into account. Four examples are presented to verify the applicability of the proposed approaches, and the D-BEM results are compared with the corresponding analytical solutions.Copyright © 2011 John Wiley & Sons, Ltd.

Transient dynamic elastoplastic analysis by the time-domain BEM formulation

This paper presents a time-domain BEM formulation applied to the solution of transient dynamic elastoplastic problems. The initial stress approach is adopted to solve the elastoplastic problem. Linear time variation is assumed for the displacements and initial stress components whereas traction components are assumed to have a constant time variation. Boundary discretization employs linear elements and the part of the domain where plastic deformation is expected to occur is discretized by employing linear triangular cells. Time integrals are computed analytically, boundary integrals are computed numerically and the domain integrals are computed by following a semi-analytical procedure. A numerical example is presented and the results are compared with another BEM formulation.

Space derivatives in the time domain BEM analysis for the scalar wave equation

In this paper, the expression for the space derivatives of Volterra's integral representation, which governs scalar wave propagation problems, is obtained by employing the concept of finite part of an integral. In order to illustrate how to apply this concept to the case under consideration, linear and constant time variation are assumed for the potential and its normal derivative, respectively. The final kernels expressions, obtained when analytical time integration is carried out, are presented and particularized according to the position of the wave front. A numerical example is presented, allowing for the verification of the accuracy of the proposed procedure.