849 research outputs found
Approximate Noether gauge symmetries of Bardeen model
We investigate the approximate Noether gauge symmetries of the geodesic
Lagrangian for the Bardeen spacetime model. This is accommodated by a set of
new approximate Noether gauge symmetry relations for the perturbed geodesic
Lagrangian in the spacetime. A detailed analysis to the spacetime of Bardeen
model up to third-order approximate Noether gauge symmetries is presented.Comment: 7 pages, 1 table, submitted to the EPJ
New Exact Spherically Symmetric Solutions in gravity by Noether's symmetry approach
The exact solutions of spherically symmetric space-times are explored by
using Noether symmetries in gravity with the scalar
curvature, a scalar field and the kinetic term of . Some of
these solutions can represent new black holes solutions in this extended theory
of gravity. The classical Noether approach is particularly applied to acquire
the Noether symmetry in gravity. Under the classical Noether
theorem, it is shown that the Noether symmetry in gravity yields
the solvable first integral of motion. With the conservation relation obtained
from the Noether symmetry, the exact solutions for the field equations can be
found. The most important result in this paper is that, without assuming
, we have found new spherically symmetric solutions in
different theories such as: power-law gravity, non-minimally
coupling models between the scalar field and the Ricci scalar , non-minimally couplings between the scalar field
and a kinetic term , and also in extended
Brans-Dicke gravity . It is also demonstrated that the
approach with Noether symmetries can be regarded as a selection rule to
determine the potential for , included in some class of the
theories of gravity.Comment: Accepted for publication in JCAP. The title and the abstract have
been changed and new exact solutions have been added with more cases. The
existence of horizons of our solutions has been discussed to
Classification of Static Plane Symmetric Spacetimes according to their Matter Collineations
In this paper we classify static plane symmetric spacetimes according to
their matter collineations. These have been studied for both cases when the
energy-momentum tensor is non-degenerate and also when it is degenerate. It
turns out that the non-degenerate case yields either {\it four}, {\it five},
{\it six}, {\it seven} or {\it ten} independent matter collineations in which
{\it four} are isometries and the rest are proper. There exists three
interesting cases where the energy-momentum tensor is degenerate but the group
of matter collineations is finite-dimensional. The matter collineations in
these cases are either {\it four}, {\it six} or {\it tenComment: 15 pages, LaTex, no figure
Physics-based prognostic modelling of filter clogging phenomena
In industry, contaminant filtration is a common process to achieve a desired level of purification, since contaminants in liquids such as fuel may lead to performance drop and rapid wear propagation. Generally, clogging of filter phenomena is the primary failure mode leading to the replacement or cleansing of filter. Cascading failures and weak performance of the system are the unfortunate outcomes due to a clogged filter. Even though filtration and clogging phenomena and their effects of several observable parameters have been studied for quite some time in the literature, progression of clogging and its use for prognostics purposes have not been addressed yet. In this work, a physics based clogging progression model is presented. The proposed model that bases on a well-known pressure drop equation is able to model three phases of the clogging phenomena, last of which has not been modelled in the literature yet. In addition, the presented model is integrated with particle filters to predict the future clogging levels and to estimate the remaining useful life of fuel filters. The presented model has been implemented on the data collected from an experimental rig in the lab environment. In the rig, pressure drop across the filter, flow rate, and filter mesh images are recorded throughout the accelerated degradation experiments. The presented physics based model has been applied to the data obtained from the rig. The remaining useful lives of the filters used in the experimental rig have been reported in the paper. The results show that the presented methodology provides significantly accurate and precise prognostic results
Classification of Spherically Symmetric Static Spacetimes according to their Matter Collineations
The spherically symmetric static spacetimes are classified according to their
matter collineations. These are studied when the energy-momentum tensor is
degenerate and also when it is non-degenerate. We have found a case where the
energy-momentum tensor is degenerate but the group of matter collineations is
finite. For the non-degenerate case, we obtain either {\it four}, {\it five},
{\it six} or {\it ten} independent matter collineations in which four are
isometries and the rest are proper. We conclude that the matter collineations
coincide with the Ricci collineations but the constraint equations are
different which on solving can provide physically interesting cosmological
solutions.Comment: 15 pages, no figure, Late
- …