Inhomogeneity and Nonlinear Preheating

We investigated the possibility that nonlinear gravitational effects influence the preheating era after inflation, using numerical solutions of the inhomogeneous Einstein field equations. We compared our results to perturbative calculations and to solutions of the nonlinear field equations in a rigid (unperturbed) spacetime, in order to isolate gravitational phenomena. We confirm the broad picture of preheating obtained from the nonlinear field equations in a rigid background, but find gravitational effects have a measurable impact on the dynamics. The longest modes in the simulation grow much more rapidly in the relativistic calculation than with a rigid background. We used the Weyl tensor to quantify the departure from homogeneity in the universe. We saw no evidence for the sort of gravitational collapse that leads to the formation of primordial black holes.Comment: Talk given at Marcel Grossmann Meeting IX. 3 pages, 1 figur

Proper local scoring rules on discrete sample spaces

A scoring rule is a loss function measuring the quality of a quoted probability distribution $Q$ for a random variable $X$, in the light of the realized outcome $x$ of $X$; it is proper if the expected score, under any distribution $P$ for $X$, is minimized by quoting $Q=P$. Using the fact that any differentiable proper scoring rule on a finite sample space ${\mathcal{X}}$ is the gradient of a concave homogeneous function, we consider when such a rule can be local in the sense of depending only on the probabilities quoted for points in a nominated neighborhood of $x$. Under mild conditions, we characterize such a proper local scoring rule in terms of a collection of homogeneous functions on the cliques of an undirected graph on the space ${\mathcal{X}}$. A useful property of such rules is that the quoted distribution $Q$ need only be known up to a scale factor. Examples of the use of such scoring rules include Besag's pseudo-likelihood and Hyv\"{a}rinen's method of ratio matching.Comment: Published in at http://dx.doi.org/10.1214/12-AOS972 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Addressing the intersection between alcohol consumption and antiretroviral treatment : needs assessment and design of interventions for primary healthcare workers, the Western Cape, South Africa

Background: At the points where an infectious disease and risk factors for poor health intersect, while health problems may be compounded, there is also an opportunity to provide health services. Where human immunodeficiency virus (HIV) infection and alcohol consumption intersect include infection with HIV, onward transmission of HIV, impact on HIV and acquired immunodeficiency syndrome (AIDS) disease progression, and premature death. The levels of knowledge and attitudes relating to the health and treatment outcomes of HIV and AIDS and the concurrent consumption of alcohol need to be determined. This study aimed to ascertain the knowledge, attitudes and practices of primary healthcare workers concerning the concurrent consumption of alcohol of clinic attendees who are prescribed antiretroviral drugs. An assessment of the exchange of information on the subject between clinic attendees and primary healthcare providers forms an important aspect of the research. A further objective of this study is an assessment of the level of alcohol consumption of people living with HIV and AIDS attending public health facilities in the Western Cape Province in South Africa, to which end, the study reviewed health workers' perceptions of the problem's extent. A final objective is to contribute to the development of evidence-based guidelines for AIDS patients who consume alcohol when on ARVs. The overall study purpose is to optimise antiretroviral health outcomes for all people living with HIV and AIDS, but with specific reference to the clinic attendees studied in this research. Methods: Overall the research study utilised mixed methods. Three group-specific questionnaires were administered between September 2013 and May 2014. The resulting qualitative data presented here supplements the results of the quantitative data questionnaires for HIV and AIDS clinic attendees, which have been analysed and written up separately. This arm of the research study comprised two, separate, semi-structured sets of interviews: one face-to-face with healthcare workers at the same primary healthcare clinics from which the clinic attendees were sampled, and the other with administrators from the local government health service via email. The qualitative analysis from the primary healthcare worker interviews has been analysed using thematic content analysis. Results: The key capacity gaps for nurses include the definition of different patterns and volumes of alcohol consumption, resultant health outcomes and how to answer patient questions on alcohol consumption while on antiretroviral treatment. Not only did the counsellors lack knowledge regarding alcohol abuse and its treatment, but they were also they were unclear on their role and rights in relation to their patients. Doctors highlighted the need for additional training for clinicians in diagnosing alcohol use disorders and information on the pharmacological interventions to treat alcoholism. Conclusion: Pertinent knowledge regarding patient alcohol consumption while taking ARVs needs to be disseminated to primary healthcare workers

QUANTIFICATION OF MARINE MEGAFAUNAL DISTRIBUTION PATTERNS USING A REMOTELY OPERATED VEHICLE

This thesis documents the development and application of the Automated Benthic Image Scaling System (ABISS), a novel structured lighting array for calculating image scale, accounting for perspective, to allow quantitative non-destructive megafaunal sampling using observations from a Remotely Operated Vehicle (ROV). Megafauna are important components of marine soft sediment assemblages that influence the composition of the associated assemblage and the flux of energy across the sediment-water interface, by altering the physical and chemical characteristics of the sediment during bioturbation. However, megafaunal species are not sampled adequately using traditional techniques. Megafaunal abundance estimates derived from ROV observations were validated against those derived from direct diver observations and results suggested that data were in close agreement. To quantify spatial variation of the megafaunal assemblage, spatially referenced images were collected with a maximum sample separation of 400 m within a broader area of homogeneous sediment in Plymouth Sound (United Kingdom) during May 2000 and March 2001. Results demonstrated that the spatial distribution of the megafaunal assemblage was neither uniform nor stable temporally. A hierarchy of spatial structure was detected, whereby, patches with minimum radius between 123-163 m were nested within patches up to 400 m radius. To assess the megafaunal contribution to endobenthic biomass, the population size structure and biomass of the dominant megafaunal bivalve Lutraria lutraria was estimated from measurements of the siphon tips. Results indicated that the population size structure was stable between years despite significant differences in abundance. In addition, L lutraria contributed approximately 90% of the endobenthic biomass, indicating that traditional assessment of benthic biomass by consideration of macrofaunal samples alone will underestimate severely the biomass and respiration of the entire endobentic assemblage. Novel techniques of quantifying the spatial distribution of megafaunal assemblages presented in this thesis offer ways forward to address how variation of megafaunal spatial structure affects macrofaunal assemblage structure, and to discuss the application of remote imaging to map and predict quantitatively the conservation value of subtidal soft sediments.Plymouth Marine Laborator

Adaptive Smoothing for Trajectory Reconstruction

Trajectory reconstruction is the process of inferring the path of a moving object between successive observations. In this paper, we propose a smoothing spline -- which we name the V-spline -- that incorporates position and velocity information and a penalty term that controls acceleration. We introduce a particular adaptive V-spline designed to control the impact of irregularly sampled observations and noisy velocity measurements. A cross-validation scheme for estimating the V-spline parameters is given and we detail the performance of the V-spline on four particularly challenging test datasets. Finally, an application of the V-spline to vehicle trajectory reconstruction in two dimensions is given, in which the penalty term is allowed to further depend on known operational characteristics of the vehicle.Comment: 25 pages, submitte

Inhomogeneity and the Post-Inflationary Universe

We discuss the interaction between perturbations in the inflaton and the background during the preheating phase in simple inflationary models. By numerically solving the Einstein field equations we are able to assess the impact of non-linear gravitational effects on preheating, and to assess the accuracy of perturbative discussions of the preheating epoch.Comment: COSMO-98 Proceeding

Brane Gas Inflation

We consider the brane gas picture of the early universe. At later stages, when there are no winding modes and the background is free to expand, we show that a moving 3-brane, which we identify with our universe, can inflate even though it is radiation-dominated. The crucial ingredients for successful inflation are the coupling to the dilaton and the equation of state of the bulk. If we suppose the brane initially forms in a collision of higher-dimensional branes, then the spectrum of primordial density fluctuations naturally has a thermal origin.Comment: 4 pages, 1 figur