12,191 research outputs found
The Inaudible Bereaved: A Critical Analysis of the Voice of a Bereaved Syrian Refugee in the UK: A Case Study.
This paper presents a case study from a larger research project on the experience of bereavement in Syrian refugees in the UK. In the larger study, five participants were interviewed for their individual bereavement narratives. The qualitative methodology employed was Langdridge’s Critical Narrative Analysis, which follows six distinct iterative stages. This paper describes the individual narrative of one of the five participants in the study and follows it through these stages. This includes contextualising the narrative within the broader overall themes from the research, and looking at the narrative through a postcolonial lens. The aim is to provide a rich sense of the participant's experience as described through his voice, as well as offering an alternative perspective developed using critical theory. It is hoped this research might contribute to mental and social care provision in the UK, especially bereavement services and organisations, for this population
Scalar radiation from Chameleon-shielded regions
I study the profile of the Chameleon field around a radially pulsating mass.
Focusing on the case in which the background (static) Chameleon profile
exhibits a thin-shell, I add small perturbations to the source in the form of
time-dependent radial pulsations. It is found that the Chameleon field inherits
a time-dependence, there is a resultant scalar radiation from the region of the
source and the metric outside the spherically symmetric mass is not static.
This has several interesting and potentially testable consequences.Comment: 4 pages, 4 figures, slightly edited version matching the journal
versio
Electronic Structure of Hyperkagome Na4Ir3O8
We investigate the electronic structure of the frustrated magnet Na4Ir3O8
using density functional theory. Due to strong spin-orbit coupling, the
hyperkagome lattice is characterized by a half-filled complex of states, making
it a cubic iridium analogue of the high temperature superconducting cuprates.
The implications of our results for this unique material are discussed.Comment: expanded discussion with extra figures - 6 pages, 10 figure
Spin Hamiltonian of Hyperkagome Na4Ir3O8
We derive the spin Hamiltonian for the quantum spin liquid Na4Ir3O8, and then
estimate the direct and superexchange contributions between near neighbor
iridium ions using a tight binding parametrization of the electronic structure.
We find a magnitude of the exchange interaction comparable to experiment for a
reasonable value of the on-site Coulomb repulsion. For one of the two tight
binding parametrizations we have studied, the direct exchange term, which is
isotropic, dominates the total exchange. This provides support for those
theories proposed to describe this novel quantum spin liquid that assume an
isotropic Heisenberg model.Comment: 9 pages, 4 figure
Model of hard spheroplatelets near a hard wall
A system of hard spheroplatelets near an impenetrable wall is studied in the
low-density Onsager approximation. Spheroplatelets have optimal shape between
rods and plates, and the direct transition from the isotropic to biaxial
nematic phase is present. A simple local approximation for the one-particle
distribution function is used. Analytical results for the surface tension and
the entropy contributions are derived. The density and the order-parameter
profiles near the wall are calculated. The preferred orientation of the short
molecule axes is perpendicular to the wall. Biaxiality close to the wall can
appear only if the phase is biaxial in the bulk.Comment: 11 pages, 9 figures, revised version published in PR
Estimating spinning binary parameters and testing alternative theories of gravity with LISA
We investigate the effect of spin-orbit and spin-spin couplings on the
estimation of parameters for inspiralling compact binaries of massive black
holes, and for neutron stars inspiralling into intermediate-mass black holes,
using hypothetical data from the proposed Laser Interferometer Space Antenna
(LISA). We work both in Einstein's theory and in alternative theories of
gravity of the scalar-tensor and massive-graviton types. We restrict the
analysis to non-precessing spinning binaries, i.e. to cases where the spins are
aligned normal to the orbital plane. We find that the accuracy with which
intrinsic binary parameters such as chirp mass and reduced mass can be
estimated within general relativity is degraded by between one and two orders
of magnitude. We find that the bound on the coupling parameter omega_BD of
scalar-tensor gravity is significantly reduced by the presence of spin
couplings, while the reduction in the graviton-mass bound is milder. Using fast
Monte-Carlo simulations of 10^4 binaries, we show that inclusion of spin terms
in massive black-hole binaries has little effect on the angular resolution or
on distance determination accuracy. For stellar mass inspirals into
intermediate-mass black holes, the angular resolution and the distance are
determined only poorly, in all cases considered. We also show that, if LISA's
low-frequency noise sensitivity can be extrapolated from 10^-4 Hz to as low as
10^-5 Hz, the accuracy of determining both extrinsic parameters (distance, sky
location) and intrinsic parameters (chirp mass, reduced mass) of massive
binaries may be greatly improved.Comment: 29 pages, 9 figures. Matches version accepted in Physical Review D.
More stringent checks in the inversion of the Fisher matri
Black Hole-Neutron Star Mergers: Disk Mass Predictions
Determining the final result of black hole-neutron star mergers, and in
particular the amount of matter remaining outside the black hole at late times
and its properties, has been one of the main motivations behind the numerical
simulation of these systems. Black hole-neutron star binaries are amongst the
most likely progenitors of short gamma-ray bursts --- as long as massive
(probably a few percents of a solar mass), hot accretion disks are formed
around the black hole. Whether this actually happens strongly depends on the
physical characteristics of the system, and in particular on the mass ratio,
the spin of the black hole, and the radius of the neutron star. We present here
a simple two-parameter model, fitted to existing numerical results, for the
determination of the mass remaining outside the black hole a few milliseconds
after a black hole-neutron star merger (i.e. the combined mass of the accretion
disk, the tidal tail, and the potential ejecta). This model predicts the
remnant mass within a few percents of the mass of the neutron star, at least
for remnant masses up to 20% of the neutron star mass. Results across the range
of parameters deemed to be the most likely astrophysically are presented here.
We find that, for 10 solar mass black holes, massive disks are only possible
for large neutron stars (R>12km), or quasi-extremal black hole spins (a/M>0.9).
We also use our model to discuss how the equation of state of the neutron star
affects the final remnant, and the strong influence that this can have on the
rate of short gamma-ray bursts produced by black hole-neutron star mergers.Comment: 11 pages, 7 figure
Lower Bounds on Mutual Information
We correct claims about lower bounds on mutual information (MI) between
real-valued random variables made in A. Kraskov {\it et al.}, Phys. Rev. E {\bf
69}, 066138 (2004). We show that non-trivial lower bounds on MI in terms of
linear correlations depend on the marginal (single variable) distributions.
This is so in spite of the invariance of MI under reparametrizations, because
linear correlations are not invariant under them. The simplest bounds are
obtained for Gaussians, but the most interesting ones for practical purposes
are obtained for uniform marginal distributions. The latter can be enforced in
general by using the ranks of the individual variables instead of their actual
values, in which case one obtains bounds on MI in terms of Spearman correlation
coefficients. We show with gene expression data that these bounds are in
general non-trivial, and the degree of their (non-)saturation yields valuable
insight.Comment: 4 page
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