15,264 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
Inducing topological order in a honeycomb lattice
We explore the possibility of inducing a topological insulator phase in a
honeycomb lattice lacking spin-orbit interaction using a metallic (or Fermi
gas) environment. The lattice and the metallic environment interact through a
density-density interaction without particle tunneling, and integrating out the
metallic environment produces a honeycomb sheet with in-plane oscillating
long-ranged interactions. We find the ground state of the interacting system in
a variational mean-field method and show that the Fermi wave vector, kF, of the
metal determines which phase occurs in the honeycomb lattice sheet. This is
analogous to the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism in which the
metal's kF determines the interaction profile as a function of the distance.
Tuning kF and the interaction strength may lead to a variety of ordered phases,
including a topological insulator and anomalous quantum-hall states with
complex next-nearest-neighbor hopping, as in the Haldane and the Kane-Mele
model. We estimate the required range of parameters needed for the topological
state and find that the Fermi vector of the metallic gate should be of the
order of 3Pi/8a (with a being the graphene lattice constant). The net coupling
between the layers, which includes screening in the metal, should be of the
order of the honeycomb lattice bandwidth. This configuration should be most
easily realized in a cold-atoms setting with two interacting Fermionic species.Comment: 7 pages; 2 figures; Version 2 - added references; added an appendix
about screenin
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
Vortex Fractionalization in a Josephson Ladder
We show numerically that, in a Josephson ladder with periodic boundary
conditions and subject to a suitable transverse magnetic field, a vortex
excitation can spontaneously break up into two or more fractional excitations.
If the ladder has N plaquettes, and N is divisible by an integer q, then in an
applied transverse field of 1/q flux quanta per plaquette the ground state is a
regular pattern of one fluxon every q plaquettes. When one additional fluxon is
added to the ladder, it breaks up into q fractional fluxons, each carrying 1/q
units of vorticity. The fractional fluxons are basically walls between
different domains of the ground state of the underlying 1/q lattice. The
fractional fluxons are all depinned at the same applied current and move as a
unit. For certain applied fields and ladder lengths, we show that there are
isolated fractional fluxons. It is shown that the fractional fluxons would
produce a time-averaged voltage related in a characteristic way to the ac
voltage frequency.Comment: 13 Figures. 10 page
A Fast Chi-squared Technique For Period Search of Irregularly Sampled Data
A new, computationally- and statistically-efficient algorithm, the Fast
algorithm, can find a periodic signal with harmonic content in
irregularly-sampled data with non-uniform errors. The algorithm calculates the
minimized as a function of frequency at the desired number of
harmonics, using Fast Fourier Transforms to provide performance.
The code for a reference implementation is provided.Comment: Source code for the reference implementation is available at
http://public.lanl.gov/palmer/fastchi.html . Accepted by ApJ. 24 pages, 4
figure
Evaporation of a Kerr black hole by emission of scalar and higher spin particles
We study the evolution of an evaporating rotating black hole, described by
the Kerr metric, which is emitting either solely massless scalar particles or a
mixture of massless scalar and nonzero spin particles. Allowing the hole to
radiate scalar particles increases the mass loss rate and decreases the angular
momentum loss rate relative to a black hole which is radiating nonzero spin
particles. The presence of scalar radiation can cause the evaporating hole to
asymptotically approach a state which is described by a nonzero value of . This is contrary to the conventional view of black hole
evaporation, wherein all black holes spin down more rapidly than they lose
mass. A hole emitting solely scalar radiation will approach a final asymptotic
state described by . A black hole that is emitting scalar
particles and a canonical set of nonzero spin particles (3 species of
neutrinos, a single photon species, and a single graviton species) will
asymptotically approach a nonzero value of only if there are at least 32
massless scalar fields. We also calculate the lifetime of a primordial black
hole that formed with a value of the rotation parameter , the minimum
initial mass of a primordial black hole that is seen today with a rotation
parameter , and the entropy of a black hole that is emitting scalar or
higher spin particles.Comment: 22 pages, 13 figures, RevTeX format; added clearer descriptions for
variables, added journal referenc
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
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