177 research outputs found
Discrete quantum gravity in the framework of Regge calculus formalism
An approach to the discrete quantum gravity based on the Regge calculus is
discussed which was developed in a number of our papers. Regge calculus is
general relativity for the subclass of general Riemannian manifolds called
piecewise flat ones. Regge calculus deals with the discrete set of variables,
triangulation lengths, and contains continuous general relativity as a
particular limiting case when the lengths tend to zero. In our approach the
quantum length expectations are nonzero and of the order of Plank scale
. This means the discrete spacetime structure on these scales.Comment: LaTeX, 16 pages, to appear in JET
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Radiotherapy students' perceptions of support provided by clinical supervisors
Aim: The aim of this study was to explore the experiences of radiotherapy students on clinical placement, specifically focussing on the provision of well-being support from clinical supervisors.
Materials and methods: Twenty-five students from the University of the West of England and City University of London completed an online evaluation survey relating to their experiences of placement, involving Likert scales and open-ended questions.
Results: The quantitative results were generally positive; however, the qualitative findings were mixed. Three themes emerged: (1) provision of information and advice; (2) an open, inclusive and supportive working environment; and (3) a lack of communication, understanding, and consistency.
Findings: Students' experiences on placement differed greatly and appeared to relate to their specific interactions with different members of staff. It is suggested that additional training around providing well-being support to students may be of benefit to clinical supervisors
Regge calculus in the canonical form
(3+1) (continuous time) Regge calculus is reduced to Hamiltonian form. The
constraints are classified, classical and quantum consequences are discussed.
As basic variables connection matrices and antisymmetric area tensors are used
supplemented with appropriate bilinear constraints. In these variables the
action can be made quasipolinomial with as the only deviation from
polinomiality. In comparison with analogous formalism in the continuum theory
classification of constraints changes: some of them disappear, the part of I
class constraints including Hamiltonian one become II class (and vice versa,
some new constraints arise and some II class constraints become I class). As a
result, the number of the degrees of freedom coincides with the number of links
in 3-dimensional leaf of foliation. Moreover, in empty space classical dynamics
is trivial: the scale of timelike links become zero and spacelike links are
constant.Comment: 24 pages,Plain LaTeX,BINP 93-4
Regge Calculus as a Fourth Order Method in Numerical Relativity
The convergence properties of numerical Regge calculus as an approximation to
continuum vacuum General Relativity is studied, both analytically and
numerically. The Regge equations are evaluated on continuum spacetimes by
assigning squared geodesic distances in the continuum manifold to the squared
edge lengths in the simplicial manifold. It is found analytically that,
individually, the Regge equations converge to zero as the second power of the
lattice spacing, but that an average over local Regge equations converges to
zero as (at the very least) the third power of the lattice spacing. Numerical
studies using analytic solutions to the Einstein equations show that these
averages actually converge to zero as the fourth power of the lattice spacing.Comment: 14 pages, LaTeX, 8 figures mailed in separate file or email author
directl
A fully (3+1)-D Regge calculus model of the Kasner cosmology
We describe the first discrete-time 4-dimensional numerical application of
Regge calculus. The spacetime is represented as a complex of 4-dimensional
simplices, and the geometry interior to each 4-simplex is flat Minkowski
spacetime. This simplicial spacetime is constructed so as to be foliated with a
one parameter family of spacelike hypersurfaces built of tetrahedra. We
implement a novel two-surface initial-data prescription for Regge calculus, and
provide the first fully 4-dimensional application of an implicit decoupled
evolution scheme (the ``Sorkin evolution scheme''). We benchmark this code on
the Kasner cosmology --- a cosmology which embodies generic features of the
collapse of many cosmological models. We (1) reproduce the continuum solution
with a fractional error in the 3-volume of 10^{-5} after 10000 evolution steps,
(2) demonstrate stable evolution, (3) preserve the standard deviation of
spatial homogeneity to less than 10^{-10} and (4) explicitly display the
existence of diffeomorphism freedom in Regge calculus. We also present the
second-order convergence properties of the solution to the continuum.Comment: 22 pages, 5 eps figures, LaTeX. Updated and expanded versio
Police officers and post traumatic stress disorder: discussing the deficit in research, identification and prevention in England and Wales
This article will review available literature regarding Post Traumatic Stress Disorder (PTSD) within policing in England and Wales, with a particular focus on its early identification and prevention.
An overview of PTSD will be given as well as an exploration of why police officers are potentially more susceptible to this mental health condition compared to other members of society. Key factors in the early identification and prevention of PTSD will be outlined, with a focus on crisis intervention techniques which have been subject to considerable academic study.
There is limited research available from England and Wales that looks specifically at PTSD in policing, this research deficit will be highlighted and key areas of research which need to be explored further will be given so that this problem can be both identified and prevented in officers
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Brief Report: Schema Consistent Misinformation Effects in Eyewitnesses with Autism Spectrum Disorder
A number of studies have demonstrated schema-related misinformation effects in typical individuals, but no research to date has examined this with witnesses with autism spectrum disorder (ASD), despite their impaired ability to generate core elements that define everyday events. After witnessing slides depicting a bank robbery, 16 adults with ASD and 16 matched comparison individuals were exposed to post-event misinformation that was either schema typical or atypical. Consistent with previous work, the comparison group went onto report more schema typical misinformation than atypical misinformation. However, so too did the ASD group, suggesting that individuals with ASD do have understanding of the causal links between events, persons and actions, an important finding from both theoretical and applied perspectives
Evaluating the Current Status of American Shad Stocks in Three Virginia Rivers
Directed commercial fisheries for American shad Alosa sapidissima in the primary Virginia tributaries of the Chesapeake Bay have been under moratorium since 1994. Monitoring of adult American shad within these rivers has been ongoing since 1998 through a cooperative program involving commercial fishers. The monitoring program is designed to mimic traditional commercial fishing practices so that stock status can be inferred by comparing contemporary catch-per-unit-effort levels with those derived from historic logbooks. In this paper, we present analyses of the available monitoring and historic catch rate data along with updated stock status information for American shad in the James, York, and Rappahannock rivers. Two analytical methods were used to derive annual indices of relative abundance; both methods yielded very similar patterns for each river system. Comparisons of contemporary and historic indices of relative abundance suggest that American shad in the James and York rivers continue to persist at low levels of abundance. Measures of stock abundance in the Rappahannock River have been higher than the logbook reference value for much of the monitoring period. However, current moratoria and restoration strategies, which include hatchery releases of fry, the removal of obstructions blocking spawning and nursery habitat, and reductions in bycatch from other fisheries, should continue into the foreseeable future
Discrete approaches to quantum gravity in four dimensions
The construction of a consistent theory of quantum gravity is a problem in
theoretical physics that has so far defied all attempts at resolution. One
ansatz to try to obtain a non-trivial quantum theory proceeds via a
discretization of space-time and the Einstein action. I review here three major
areas of research: gauge-theoretic approaches, both in a path-integral and a
Hamiltonian formulation, quantum Regge calculus, and the method of dynamical
triangulations, confining attention to work that is strictly four-dimensional,
strictly discrete, and strictly quantum in nature.Comment: 33 pages, invited contribution to Living Reviews in Relativity; the
author welcomes any comments and suggestion
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