The Construction of Sorkin Triangulations

Some time ago, Sorkin (1975) reported investigations of the time evolution and initial value problems in Regge calculus, for one triangulation each of the manifolds $R*S^3$ and $R^4$. Here we display the simple, local characteristic of those triangulations which underlies the structure found by Sorkin, and emphasise its general applicability, and therefore the general validity of Sorkin's conclusions. We also make some elementary observations on the resulting structure of the time evolution and initial value problems in Regge calculus, and add some comments and speculations.Comment: 5 pages (plus one figure not included, available from author on request), Plain Tex, no local preprint number (Only change: omitted "\magnification" command now replaced

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

Negative workplace behaviour: temporal associations with cardiovascular outcomes and psychological health problems in Australian police

Negative workplace behaviour, such as workplace bullying, is emerging as an important work-related psychosocial hazard with the potential to contribute to employee ill health. We examined the risk of two major health issues (poor mental and cardiovascular health) associated with current and past exposure to negative behaviour in the workplace. Data from 251 police officers, who completed an anonymous mail survey at two time-points spaced 12 months apart, support the potential role of exposure to negative workplace behaviour in the development of physical disease and psychological illness. Specifically, we saw significant effects associated with past exposure to such behaviour on indicators of poor cardiovascular health, and a significant effect of current exposure on the indicator of mental health problems. Our findings reinforce the need to continue to study links between employee health and both negative workplace behaviour and more severe cases of bullying, particularly the mechanisms involved to strengthen theory in this area, and to protect against employee ill health (specifically cardiovascular outcomes and psychological problems) by preventing negative behaviour at work. Copyright (C) 2010 John Wiley & Sons, Ltd

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 $10^{-33}cm$. This means the discrete spacetime structure on these scales.Comment: LaTeX, 16 pages, to appear in JET

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 $\arcsin$ 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

Charged-particle magnetic-quadrupole spectrometer for neutron induced reactions

A spectrometer has been developed for measuring the charged particle production cross sections and spectra in neutron-induced reactions. The spectrometer consists of a magnetic quadrupole doublet which focuses the charged particles onto a silicon surface barrier detector telescope which is 2 meters or more from the irradiated sample. Collimators, shielding, and the large source-to- detector distance reduce the background enough to use the spectrometer with a 14- MeV neutron source producing 4 . 10$sup 12$ n/s. The spectrometer has been used in investigations of proton, deuteron, and alpha particle production by 14-MeV neutrons incident on various materials. Protons with energies as low as 1.1 MeV have been measured. The good resolution of the detectors has also made possible an improved measurement of the neutron- neutron scattering length from the 0$sup 0$ proton spectrum from deuteron breakup by 14-MeV neutrons. (auth

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