Computational and theoretical aspects of a grain-boundary model at finite deformations

A model to describe the role of grain boundaries in the overall response of a polycrystalline material at small length scales subject to finite deformations is presented. Three alternative thermodynamically consistent plastic flow relations on the grain boundary are derived and compared using a series of numerical experiments. The numerical model is obtained by approximating the governing relations using the finite element method. In addition, the infinitesimal and finite deformation theories are compared, and the limitations of the former made clear

Some properties of the dissipative model of strain-gradient plasticity

A theoretical and computational investigation is carried out of a dissipative model of rate-independent strain-gradient plasticity and its regularization. It is shown that the flow relation, when expressed in terms of the Cauchy stress, is necessarily global. The most convenient approach to formulating the flow relation is through the use of a dissipation function. It is shown, however, that the task of obtaining the dual version, in the form of a normality relation, is a complex one. A numerical investigation casts further light on the response using the dissipative theory in situations of non-proportional loading. The elastic gap, a feature reported in recent investigations, is observed in situations in which passivation has been imposed. It is shown computationally that the gap may be regarded as an efficient path between a load-deformation response corresponding to micro-free boundary conditions, and that corresponding to micro-hard boundary conditions, in which plastic strains are set equal to zero.Comment: 26 pages, 10 figure

Examining the influence of socio-economic status, area level deprivation and exposure to air pollution on asthma in childhood in England

The co-location of air pollution and socio-economic deprivation is increasingly well documented and studies have found that the socio-spatial distribution of health-related environmental characteristics, specifically air pollution, can be an important driver of geographical inequalities in health. The most deprived members of society face the highest exposures and the greatest risks due to a concept termed the triple jeopardy. Children face an increased susceptibility to air pollution exposure, and exposure can result in a range of health issues, such as asthma. Linking longitudinal data from the Millennium Cohort Study (MCS), air pollution data available from EMEP4UK, and area level deprivation data from the Index of Multiple Deprivation, this thesis aims to explore the relationship between air pollution exposure, and both individual and area level socio-economic status to understand how these exposures interact to impact respiratory health in children. Following data linkage, cross-sectional analysis, time series analysis and multilevel modelling are employed to examine the data. Multilevel modelling is used to appropriately attribute variations in spatial health outcomes to differences between places, differences between people within places and differences over time. The use of multilevel modelling is an innovative step in understanding the relationship between socio-economic factors, air pollution and health outcomes. Multilevel modelling found that 85% of the variation in asthma prevalence in children lies within MSOAs, whilst 14% of the variation was found to be over time. In comparison, 47% of the variation in wheezing was found to be due to differences over time. Two- and three-way interaction terms were included in the analysis to explore the impact of individual level socio-economic status, area level deprivation and air pollution exposure on asthma and wheezing prevalence in children, however no association was found. Moving forward, focussing interventions on improving both individual and area level socio-economic status, and implementing policies to lower pollution in the most deprived areas could help alleviate the health burden faced by the most deprived in society when exposed to air pollution

A study of the utilization of the skills of licensed practical nurses.

Thesis (M.S.)--Boston Universit

Gender Bias in Selection for Honors Mathematics at Kempsville Middle School

The following objectives were established to guide the conduct of this research study: 1. To identify the percentage of females enrolled in the general population of the seventh and eighth grades at Kempsville Middle School; 2. To identify the percentage of females enrolled in the seventh and eighth grade honors mathematics courses at Kempsville Middle School; 3. To determine if a significant difference exists between the percentages determine in objectives one and two above; 4. To interview the personnel involved with the honors mathematics selection process and to review it for gender impartiality

Parsec-scale magnetic fields in Arp 220

We present the first very-long-baseline interferometry (VLBI) detections of Zeeman splitting in another galaxy. We used Arecibo Observatory, the Green Bank Telescope, and the Very Long Baseline Array to perform dual-polarization observations of OH maser lines in the merging galaxy Arp 220. We measured magnetic fields of $\sim$1-5 mG associated with three roughly parsec-sized clouds in the nuclear regions of Arp 220. Our measured magnetic fields have comparable strengths and the same direction as features at the same velocity identified in previous Zeeman observations with Arecibo alone. The agreement between single dish and VLBI results provides critical validation of previous Zeeman splitting observations of OH megamasers that used a single large dish. The measured magnetic field strengths indicate that magnetic energy densities are comparable to gravitational energy in OH maser clouds. We also compare our total intensity results to previously published VLBI observations of OH megamasers in Arp 220. We find evidence for changes in both structure and amplitude of the OH maser lines that are most easily explained by variability intrinsic to the masing region, rather than variability produced by interstellar scintillation. Our results demonstrate the potential for using high-sensitivity VLBI to study magnetic fields on small spatial scales in extragalactic systems.Comment: 9 pages, accepted to MNRA

Dosage compensation in birds

AbstractThe Z and W sex chromosomes of birds have evolved independently from the mammalian X and Y chromosomes [1]. Unlike mammals, female birds are heterogametic (ZW), while males are homogametic (ZZ). Therefore male birds, like female mammals, carry a double dose of sex-linked genes relative to the other sex. Other animals with nonhomologous sex chromosomes possess “dosage compensation” systems to equalize the expression of sex-linked genes. Dosage compensation occurs in animals as diverse as mammals, insects, and nematodes, although the mechanisms involved differ profoundly [2]. In birds, however, it is widely accepted that dosage compensation does not occur [3–5], and the differential expression of Z-linked genes has been suggested to underlie the avian sex-determination mechanism [6]. Here we show equivalent expression of at least six of nine Z chromosome genes in male and female chick embryos by using real-time quantitative PCR [7]. Only the Z-linked ScII gene, whose ortholog in Caenorhabditis elegans plays a crucial role in dosage compensation [8], escapes compensation by this assay. Our results imply that the majority of Z-linked genes in the chicken are dosage compensated

A 0535+26: Back in business

In May/June 2005, after 10 years of inactivity, the Be/X-ray binary system A 0535+26 underwent a major X-ray outburst. In this paper data are presented from 10 years of optical, IR and X-ray monitoring showing the behaviour of the system during the quiescent epoch and the lead up to the new outburst. The results show the system going through a period when the Be star in the system had a minimal circumstellar disk and then a dramatic disk recovery leading, presumably, to the latest flare up of X-ray emission. The data are interpreted in terms of the state of the disk and its interaction with the neutron star companion.Comment: Accepted for publication in MNRA

Restoration of Lake Hakanoa: Results of model simulations

This report was requested by Waikato District Council. It covers the lake water quality of, and possible restoration scenarios for, Lake Hakanoa a riverine lake situated in Huntly. The lake is used as a recreational resource by the community. In the past it has been reported to have had very poor water quality and is known to be eutrophic. It is currently in an algal-dominated, devegetated state and has low water clarity. The shallowness of this lake makes it potentially susceptible to resuspension of sediments through wind action. A community group, Friends of Hakanoa, has been responsible for the formation of a path around the perimeter of the lake, retiring about 3.6% of the catchment from pastoral farming and creating a riparian margin. Results from more recent reports and this report indicate a trend of improving water quality which may be related to recent restoration actions such as re-establishment of a riparian margin