Application of a Bayesian Method to Absorption Spectral-Line Finding in Simulated ASKAP Data

The large spectral bandwidth and wide field of view of the Australian SKA Pathfinder radio telescope will open up a completely new parameter space for large extragalactic HI surveys. Here we focus on identifying and parametrising HI absorption lines which occur in the line of sight towards strong radio continuum sources. We have developed a method for simultaneously finding and fitting HI absorption lines in radio data by using multi-nested sampling, a Bayesian Monte Carlo algorithm. The method is tested on a simulated ASKAP data cube, and is shown to be reliable at detecting absorption lines in low signal-to-noise data without the need to smooth or alter the data. Estimation of the local Bayesian evidence statistic provides a quantitative criterion for assigning significance to a detection and selecting between competing analytical line-profile models.Comment: 8 pages, 5 figures and 1 table; accepted for publication in PAS

Low pay and pensions: planning for old age in a real world of insecurity, financial constraint and competing demands.

This thesis is a study of current pension policy and its likelihood of providing a decent retirement income that guarantees a quality of life for the low paid, namely a retirement above subsistence level and one that offers them dignity and personal autonomy. The low paid often experience financial difficulties during their working lives and owing to competing financial demands not only do they struggle to make ends meet but find it difficult to put aside savings for their futures. This research was a social investigation and examined current government thinking and its approach to redress these problems. It used a multi-methodological approach underpinned by four components: a literature review; a comprehensive analysis of research reports that focused on individuals' saving habits; semi structured interviews with the low paid to explain their real life experiences; and an analysis of contemporary proposals. The literature review highlighted that since the 1950s there has been a shift from socialisation of risk, where risk is shared by the state employer and employee, to an individualisation of risk in pension policy and 'New' Labour has continued along this route. Moreover, low pay remains a prominent issue today just as much as it did at the beginning of the 20th century. It is this combination of continued low paid and increased risk on the employee that has exacerbated the plight for many in low pay employment. The current solution supported by government relies on using means testing to protect the poorest whilst expecting others to be 'responsible' citizens and provide for their retirement under the rhetoric of 'rights' and 'responsibility'. Yet as this research established many in the latter category are considered low paid by the Low Pay Unit. It is this problem of definition that has led policy makers to fail to understand that the low paid are in fact unable to make money purchase pension schemes viable. This has now been recognised by other organisations, political parties and academics. Now even the pro-market right have acknowledged the failure of the private sector to bridge the gap vacated by the state under twenty years of neo-liberal policy and argue that means testing, once favoured by the Conservative Party, acts as a disincentive to save towards a second-tier private pension. Key findings in this thesis include: first that the low paid do in fact have a positive attitude towards saving but it is their lack of ability and real opportunity that prevents them from saving towards a decent second-tier pension. Thus there is a contradiction in policy that seeks to improve attitude and awareness of the low paid to improve their situation. Second, that the government presides over a low paid economy and this is a political choice that favours pro-business labour market policies. Third, current government attitude continues to ignore the warnings from both pro-state left and pro-market right sources that a continuation of a pension policy relying on means testing in fact acts as a poverty trap. And finally, the plight of the low paid remains bleak and will worsen in the future if neo-liberal policy continues without increased state intervention

Is space really expanding? A counterexample

In all Friedman models, the cosmological redshift is widely interpreted as a consequence of the general-relativistic phenomenon of EXPANSION OF SPACE. Other commonly believed consequences of this phenomenon are superluminal recession velocities of distant galaxies and the distance to the particle horizon greater than c*t (where t is the age of the Universe), in apparent conflict with special relativity. Here, we study a particular Friedman model: empty universe. This model exhibits both cosmological redshift, superluminal velocities and infinite distance to the horizon. However, we show that the cosmological redshift is there simply a relativistic Doppler shift. Moreover, apparently superluminal velocities and `acausal' distance to the horizon are in fact a direct consequence of special-relativistic phenomenon of time dilation, as well as of the adopted definition of distance in cosmology. There is no conflict with special relativity, whatsoever. In particular, INERTIAL recession velocities are subluminal. Since in the real Universe, sufficiently distant galaxies recede with relativistic velocities, these special-relativistic effects must be at least partly responsible for the cosmological redshift and the aforementioned `superluminalities', commonly attributed to the expansion of space. Let us finish with a question resembling a Buddhism-Zen `koan': in an empty universe, what is expanding?Comment: 12 pages, no figures; added Appendix with a calculation of the cosmological redshift in `private space

On the Existence of Radiation Gauges in Petrov type II spacetimes

The radiation gauges used by Chrzanowski (his IRG/ORG) for metric reconstruction in the Kerr spacetime seem to be over-specified. Their specification consists of five conditions: four, which we treat here as valid gauge conditions, plus an additional condition on the trace of the metric perturbation. In this work, we utilize a newly developed form of the perturbed Einstein equations to establish a condition -- on a particular tetrad component of the stress-energy tensor -- under which the full IRG/ORG can be imposed. Using gauge freedom, we are able to impose the full IRG for Petrov type II and type D backgrounds, using a different tetrad for each case. As a specific example, we work through the process of imposing the IRG in a Schwarzschild background, using a more traditional approach. Implications for metric reconstruction using the Teukolsky curvature perturbations in type D spacetimes are briefly discussed.Comment: 21 pages, uses iop style files. v2: proved a stronger result for type II backgrounds, added a subsection on remaining gauge freedom in the full IRG and improved calrity and readability throughout due to insightful referee comments; published as Class. Quantum Grav. 24 (2007) 2367-238