Beyond the Small-Angle Approximation For MBR Anisotropy from Seeds

In this paper we give a general expression for the energy shift of massless particles travelling through the gravitational field of an arbitrary matter distribution as calculated in the weak field limit in an asymptotically flat space-time. It is {\it not} assumed that matter is non-relativistic. We demonstrate the surprising result that if the matter is illuminated by a uniform brightness background that the brightness pattern observed at a given point in space-time (modulo a term dependent on the oberver's velocity) depends only on the matter distribution on the observer's past light-cone. These results apply directly to the cosmological MBR anisotropy pattern generated in the immediate vicinity of of an object like a cosmic string or global texture. We apply these results to cosmic strings, finding a correction to previously published results for in the small-angle approximation. We also derive the full-sky anisotropy pattern of a collapsing texture knot.Comment: 23 pages, FERMILAB-Pub-94/047-

Exploring suicidal behaviours by probation clients—a qualitative near-lethal study

Background Existing research emphasizes that offenders serving community based sentences are at an increased risk of suicide compared with the general population, however, there is little understanding about the causes of this risk. The aim of the current research was to understand how to support probation clients and prevent suicide, by exploring the experiences of probation clients who carried out near-lethal suicide attempts whilst under probation supervision. Methods In-depth interviews were carried out with seven probation clients who made near-lethal suicide attempts whilst serving a probation sentence. Data were analysed using Interpretative Phenomenological Analysis. Results Participants recounted negative experiences which they perceived to be linked to their suicidal feelings and behaviours, such as experiencing bereavements, perceived loss of control over their mental state or situation, and difficulties relating to stages of their probation sentence. Participants expressed severe difficulties with trusting authorities, making disclosure of suicidal feelings problematic. However, participants emphasized the role that purposeful and meaningful activity can play in suicide prevention. Conclusions Suicide prevention strategies must be tailored to the needs of probation clients across the UK. Mandatory training for probation staff is recommended to help reduce suicides, and support from external agencies should be sought where possible

A Semi-Analytical Analysis of Texture Collapse

This study presents a simplified approach to studying the dynamics of global texture collapse. We derive equations of motion for a spherically symmetric field configuration using a two parameter ansatz. Then we analyse the effective potential for the resulting theory to understand possible trajectories of the field configuration in the parameter space of the ansatz. Numerical results are given for critical winding and collapse time in spatially flat non-expanding, and flat expanding universes. In addition, the open non-expanding and open-expanding cases are studied.Comment: 12 pages, figures available from author, BROWN-HET-895, uses phyzz

Factors deterring and prompting the decision to attempt suicide on the railway networks: findings from 353 online surveys and 34 semi-structured interviews

Background There is a suicide on the British railways every 36 hours. However, the reasons why people choose to die by train are not well understood. Aims To explore factors influencing and discouraging the decision to attempt suicide on the railway networks. Method We conducted an online survey and qualitative interviews with individuals who had contemplated or attempted suicide by train. Results A total of 353 survey responders had considered and 23 had attempted suicide at rail locations (including railways and metro/underground); a third of these cases were impulsive. The most frequently reported motivations for contemplating or attempting suicide were perceptions of quick and certain lethality (54 and 37%, respectively) and easy access to rail settings (33 and 38%, respectively). The main factor discouraging people from rail suicide was its wider impact, especially on train drivers (19%). In qualitative interviews (N = 34) the desire to avoid intervention from others was also a common motivating factor for attempting suicide on the railway networks. Conclusions People attempt suicide by train because railway settings are easy to access and because of an inaccurate perception of certain and quick lethality. Tackling exaggerated perceptions of lethality may help reduce suicides by train

Numerical Methods in Cosmological Global Texture Simulations

Numerical simulations of the evolution of a global topological defect field have two characteristic length scales --- one macrophysical, of order the field correlation length, and the other microphysical, of order the field width. The situation currently of most interest to particle cosmologists involves the behaviour of a GUT-scale defect field at the epoch of decoupling, where the ratio of these scales is typically of order $10^{50}$. Such a ratio is unrealisable in numerical work, and we consider the approximations which may be employed to deal with this. Focusing on the case of global texture we outline the implementation of the associated algorithms, and in particular note the subtleties involved in handling texture unwinding events. Comparing the results in each approach then establishes that, subject to certain constraints on the minimum grid resolution, the methods described are both robust and consistent with one another.Comment: LaTeX, IMPERIAL/TP/93-94/2

On Random Bubble Lattices

We study random bubble lattices which can be produced by processes such as first order phase transitions, and derive characteristics that are important for understanding the percolation of distinct varieties of bubbles. The results are relevant to the formation of topological defects as they show that infinite domain walls and strings will be produced during appropriate first order transitions, and that the most suitable regular lattice to study defect formation in three dimensions is a face centered cubic lattice. Another application of our work is to the distribution of voids in the large-scale structure of the universe. We argue that the present universe is more akin to a system undergoing a first-order phase transition than to one that is crystallizing, as is implicit in the Voronoi foam description. Based on the picture of a bubbly universe, we predict a mean coordination number for the voids of 13.4. The mean coordination number may also be used as a tool to distinguish between different scenarios for structure formation.Comment: several modifications including new abstract, comparison with froth models, asymptotics of coordination number distribution, further discussion of biased defects, and relevance to large-scale structur

Power Spectrum Estimators For Large CMB Datasets

Forthcoming high-resolution observations of the Cosmic Microwave Background (CMB) radiation will generate datasets many orders of magnitude larger than have been obtained to date. The size and complexity of such datasets presents a very serious challenge to analysing them with existing or anticipated computers. Here we present an investigation of the currently favored algorithm for obtaining the power spectrum from a sky-temperature map --- the quadratic estimator. We show that, whilst improving on direct evaluation of the likelihood function, current implementations still inherently scale as the equivalent of the cube of the number of pixels or worse, and demonstrate the critical importance of choosing the right implementation for a particular dataset.Comment: 8 pages LATEX, no figures, corrected misaligned columns in table

Behaviours preceding suicides at railway and underground locations: a multimethodological qualitative approach

Background: Suicides by train have devastating consequences for families, the rail industry, staff dealing with the aftermath of such incidents, and potential witnesses. To reduce suicides and suicide attempts by rail it is important to learn how safe interventions can be made. However, very little is known about how to identify someone who may be about to make a suicide attempt at a railway location (including underground/subways). The current research employed a novel way of understanding what behaviours might immediately precede a suicide or suicide attempt at these locations. Design and Methods: A qualitative thematic approach was used for three parallel studies. Data were gathered from several sources including: interviews with individuals who survived a suicide attempt at a railway or underground location (N=9); CCTV footage of individuals who died by suicide at a rail or underground location (N=16); and qualitative survey data providing views from rail staff (N=79). Results: Our research suggests there are several behaviours that people may carry out before a suicide or suicide attempt at a rail location including: station hopping and platform switching; limiting contact with others; positioning themselves at the end of the track where the train/tube approaches; allowing trains to pass by; and carrying out repetitive behaviours. Interpretation: There are several behaviours that may be identifiable in the moments leading up to a suicide or suicide attempt on the railways, which may present opportunities for intervention. These findings have implications for several stakeholders including rail providers, transport police and other organisations focused on suicide prevention

Analytical modeling of large-angle CMBR anisotropies from textures

We propose an analytic method for predicting the large angle CMBR temperature fluctuations induced by model textures. The model makes use of only a small number of phenomenological parameters which ought to be measured from simple simulations. We derive semi-analytically the $C^l$-spectrum for $2\leq l\leq 30$ together with its associated non-Gaussian cosmic variance error bars. A slightly tilted spectrum with an extra suppression at low $l$ is found, and we investigate the dependence of the tilt on the parameters of the model. We also produce a prediction for the two point correlation function. We find a high level of cosmic confusion between texture scenarios and standard inflationary theories in any of these quantities. However, we discover that a distinctive non-Gaussian signal ought to be expected at low $l$, reflecting the prominent effect of the last texture in these multipoles

On The Absence Of Open Strings In A Lattice-Free Simulation Of Cosmic String Formation

Lattice-based string formation algorithms can, at least in principle, be reduced to the study of the statistics of the corresponding aperiodic random walk. Since in three or more dimensions such walks are transient this approach necessarily generates a population of open strings. To investigate whether open strings are an artefact of the lattice we develop an alternative lattice-free simulation of string formation. Replacing the lattice with a graph generated by a minimal dynamical model of a first order phase transition we obtain results consistent with the hypothesis that the energy density in string is due to a scale-invariant Brownian distribution of closed loops alone.Comment: 9 pages ReVTeX, 1 Postscript figure, minor changes for publicatio