1,721,150 research outputs found
sj-xlsx-1-exn-10.1177_26331055221109174 – Supplemental material for Sleep Quality of Covid-19 Recovered Patients in India
No full textSupplemental material, sj-xlsx-1-exn-10.1177_26331055221109174 for Sleep Quality of Covid-19 Recovered Patients in India by Raina Chhajer and Sunil Dutt Shukla in Neuroscience Insights</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Realistic charged stellar models
Full text linkThesis (Ph. D.) University of KwaZulu-Natal, Westville, 2007.In this thesis we seek exact solutions to the isotropic Einstien-Maxwell system that model the interior of relativistic stars. The field equations are transformed to a simpler form using the transformation of Durgapal and Bannerji (1983); the integration of the system is reduced to solving the condition of pressure isotropy. This condition is a recurrence relation with variable rational coe±cients which can be solved in general. New classes of solutions of linearly independent functions are obtained in terms of special functions and elementary functions for different spatial geometries. Our results contain models found previously including the superdense Tikekar (1990) neutron star model, the uncharged isotropic Maharaj and Leach (1996) solutions, the Finch and Skea (1989) model and the Durgapal and Bannerji (1983) superdense neutron star. Our general class of solutions also contain charged relativistic spheres found previously, including the model of Hansraj and Maharaj (2006) and the model of Thirukkanesh and Maharaj (2006). In addition, two exact analytical solutions describing the interior of a charged strange quark star are obtained by applying the MIT bag equation of state. We regain the Mak and Harko (2004) solution for a charged quark star as a special case
New realistic solutions for charged matter with an equation of state.
Full text linkM. Sc. University of KwaZulu-Natal, Westville 2010.The purpose of this thesis is to provide new exact solutions to the Einstein-Maxwell
system which are physically reasonable. We assume that the spacetime is static and
spherically symmetric with a charged anisotropic matter distribution. The equation of
state is linear. We show that the class of models found by Thirukkanesh and Maharaj
(2008) has a singularity in the charge density at the centre of the sphere. Two new
exact classes of solutions to the Einstein-Maxwell are found in terms of elementary
functions. This contains models in which there is no singularity in charge density.
From our general models, we can regain the Thirukkanesh and Maharaj (2008) models
and other models as special cases. The physical analysis show that the solutions are
relevant for the description of realistic compact relativistic stars. We demonstrate
that the mass corresponds to a compact relativistic body with anisotropy in presence
of charge. We show that the electromagnetic field appreciably affects the value of
the mass. A detailed physical analysis of the matter variables and electromagnetic
quantities is performed. The models generated are consistent with the quark stars
containing strange matter
New analytical stellar models in general relativity.
Full text linkThesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2009.We present new exact solutions to the Einstein and Einstein-Maxwell field equations that model the interior of neutral, charged and radiating stars. Several new classes of solutions in static spherically symmetric interior spacetimes are found in the presence of charge. These correspond to isotropic matter with a specified electric field intensity. Our solutions are found by choosing different rational forms for one of the gravitational potentials and a particular form for the electric field. The models generated contain results found previously including Finch and Skea (1989) neutron stars, Durgapal and Bannerji (1983) dense stars, Tikekar (1990) superdense stars in the limit of vanishing charge. Then we study the general situation of a compact relativistic object with anisotropic pressures in the presence of the electromagnetic field. We assume the equation of state is linear so that the model may be applied to strange stars with quark matter and dark energy stars. Several new classes of exact solutions are found, and we show that the densities and masses are consistent with real stars. We regain as special cases the Lobo (2006) dark energy stars, the Sharma and Maharaj (2007) strange stars and the realistic isothermal universes of Saslaw et al (1996). In addition, we consider relativistic radiating stars undergoing gravitational collapse when the fluid particles are in geodesic motion. We transform the governing equation into Bernoulli, Riccati and confluent hypergeometric equations. These admit an infinite family of solutions in terms of simple elementary functions and special functions. Particular models contain the Minkowski spacetime and the Friedmann dust spacetime as limiting cases. Finally, we model the radiating star with shear, acceleration and expansion in the presence of anisotropic pressures. We obtain several classes of new solutions in terms of arbitrary functions in temporal and radial coordinates by rewriting the junction condition in the form of a Riccati equation. A brief physical analysis indicates that these models are physically reasonable
Spherically symmetric cosmological solutions.
Full text linkThesis (Ph.D.)-University of Natal, Durban, 1996.This thesis examines the role of shear in inhomogeneous spherically symmetric spacetimes
in the field of general relativity. The Einstein field equations are derived for
a perfect fluid source in comoving coordinates. By assuming a barotropic equation
of state, two classes of nonaccelerating solutions are obtained for the Einstein field
equations. The first class has equation of state p = ⅓µ and the second class, with
equation of state p = µ, generalises the models of Van den Bergh and Wils (1985).
For a particular choice of a metric potential a new class of solutions is found which
is expressible in terms of elliptic functions of the first and third kind in general. A
class of nonexpanding cosmological models is briefly studied. The method of Lie
symmetries of differential equations generates a self-similar variable which reduces
the field and conservation equations to a system of ordinary differential equations.
The behaviour of the gravitational field in this case is governed by a Riccati equation
which is solved in general. Another class of solutions is obtained by making an ad
hoc choice for one of the gravitational potentials. It is demonstrated that for a stiff
fluid a particular case of the generalised Emden-Fowler equation arises
Conformal symmetries : solutions in two classes of cosmological models.
Full text linkThesis (M.Sc.)-University of Natal, Durban, 1991.In this thesis we study the conformal symmetries in two locally rotationally symmetric
spacetimes and the homothetic symmetries of a Bianchi I spacetime. The
conformal Killing equation in a class AIa spacetime (MacCallum 1980), with a G4
of motions, is integrated to obtain the general solution subject to integrability conditions.
These conditions are comprehensively analysed to determine the restrictions
on the metric functions. The Killing vectors are contained in the general conformal
solution. The homothetic vector is obtained and the explicit functional dependence
of the metric functions determined. The class AIa spacetime does not admit a nontrivial
special conformal factor. We also integrate the conformal Killing equation
in the anisotropic locally rotationally symmetric spacetime of class A3 (MacCallum
1980), with a G4 of motions, to obtain the general conformal Killing vector and the
conformal factor subject to integrability conditions. The Killing vectors are obtained
as a special case from the general conformal solution. The homothetic vector is found
for a nonzero constant conformal factor. The explicit functional form of the metric
functions is determined for the existence of this homothetic vector. The spatially
homogeneous and anisotropic A3 spacetime also does not admit a nontrivial special
conformal vector. In the Bianchi I spacetime, with a G3 of motions, the conformal
Killing equation is integrated for a constant conformal factor to generate the homothetic
symmetries. The integrability conditions are solved to determine the functional
dependence of the three time-dependent metric functions
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