Gauge Five Brane Dynamics And Small Instanton Transitions In Heterotic Models

We present the first examples of cosmological solutions to four-dimensional heterotic models which include an evolving bundle modulus. The particular bundle modulus we consider corresponds to the width of a gauge five brane. As such our solutions can be used to describe the evolution in one of these models after a small instanton transition. We find that certain properties are generic to these solutions, regardless of initial conditions. This enables us to make some definite statements about the dynamics subsequent to a small instanton transition despite the fact that we cannot microscopically describe the process itself. We also show that an effective description of the small instanton transition by a continuous matching of fields and their first derivatives is precluded by the form of the respective low-energy theories before and after the transition.Comment: 16 pages, 3 figure

A general theory for preferential sampling in environmental networks

This paper presents a general model framework for detecting the preferential sampling of environmental monitors recording an environmental process across space and/or time. This is achieved by considering the joint distribution of an environmental process with a site--selection process that considers where and when sites are placed to measure the process. The environmental process may be spatial, temporal or spatio--temporal in nature. By sharing random effects between the two processes, the joint model is able to establish whether site placement was stochastically dependent of the environmental process under study. The embedding into a spatio--temporal framework also allows for the modelling of the dynamic site---selection process itself. Real--world factors affecting both the size and location of the network can be easily modelled and quantified. Depending upon the choice of population of locations to consider for selection across space and time under the site--selection process, different insights about the precise nature of preferential sampling can be obtained. The general framework developed in the paper is designed to be easily and quickly fit using the R-INLA package. We apply this framework to a case study involving particulate air pollution over the UK where a major reduction in the size of a monitoring network through time occurred. It is demonstrated that a significant response--biased reduction in the air quality monitoring network occurred. We also show that the network was consistently unrepresentative of the levels of particulate matter seen across much of GB throughout the operating life of the network. Finally we show that this may have led to a severe over-reporting of the population--average exposure levels experienced across GB. This could have great impacts on estimates of the health effects of black smoke levels.Comment: 33 pages of main text, 48 including the supplementary materia

A Numerical Model of Crossed Andreev Reflection and Charge Imbalance

We present a numerical model of local and nonlocal transport properties in a lateral spin valve structure consisting of two magnetic electrodes in contact with a third perpendicular superconducting electrode. By considering the transport paths for a single electron incident at the local F/S interface - in terms of probabilities of crossed or local Andreev reflection, elastic cotunneling or quasiparticle transport - we show that this leads to nonlocal charge imbalance. We compare this model with experimental data from an aluminum-permalloy (Al/Py) lateral spin valve geometry device and demonstrate the effectiveness of this simple approach in replicating experimental behavior.Comment: 9 pages, 14 figure

Modeling Non-Stationary Processes Through Dimension Expansion

In this paper, we propose a novel approach to modeling nonstationary spatial fields. The proposed method works by expanding the geographic plane over which these processes evolve into higher dimensional spaces, transforming and clarifying complex patterns in the physical plane. By combining aspects of multi-dimensional scaling, group lasso, and latent variables models, a dimensionally sparse projection is found in which the originally nonstationary field exhibits stationarity. Following a comparison with existing methods in a simulated environment, dimension expansion is studied on a classic test-bed data set historically used to study nonstationary models. Following this, we explore the use of dimension expansion in modeling air pollution in the United Kingdom, a process known to be strongly influenced by rural/urban effects, amongst others, which gives rise to a nonstationary field

HIV/AIDS, growth and poverty in KwaZulu-Natal and South Africa: Integrating firm-level surveys with demographic and economywide modeling

"This paper estimates the economic impact of HIV/AIDS on KwaZulu-Natal (KZN) and the rest of South Africa (RSA). We extend previous studies by employing an integrated analytical framework that combines the following: firm-level surveys of workers' HIV prevalence by sector and occupation; a demographic model that produces both population and workforce projections; and a regionalized economywide model linked to a survey-based micro-simulation module. This framework permits a full macro-microeconomic assessment. The results indicate that HIV/AIDS greatly reduces annual economic growth, mainly by lowering the long-term rate of technical change. However, the impacts on income poverty are small, and inequality is reduced by HIV/AIDS. This is because high unemployment among low-income households minimizes the economic costs of increased mortality. In contrast, slower economic growth hurts higher-income households despite the lower prevalence of HIV among these households. We conclude that the increase in economic growth achieved through addressing HIV/AIDS is sufficient to offset the population pressure this move will place on income poverty. Moreover, incentives to mitigate HIV/AIDS lie not only with poorer infected households, but also with uninfected higher-income households. Our findings reveal that HIV/AIDS will place a substantial burden on future economic development in KZN and RSA, confirming the need for policies to curb the economic costs of this pandemic." from authors' abstractHIV/AIDS, Growth, Poverty, Development strategies, KwaZulu-Natal,