The effect of host heterogeneity and parasite intragenomic interactions on parasite population structure

Understanding the processes that shape the genetic structure of parasite populations and the functional consequences of different parasite genotypes is critical for our ability to predict how an infection can spread through a host population and for the design of effective vaccines to combat infection and disease. Here, we examine how the genetic structure of parasite populations responds to host genetic heterogeneity. We consider the well-characterized molecular specificity of major histocompatibility complex binding of antigenic peptides to derive deterministic and stochastic models. We use these models to ask, firstly, what conditions favour the evolution of generalist parasite genotypes versus specialist parasite genotypes? Secondly, can parasite genotypes coexist in a population? We find that intragenomic interactions between parasite loci encoding antigenic peptides are pivotal in determining the outcome of evolution. Where parasite loci interact synergistically (i.e. the recognition of additional antigenic peptides has a disproportionately large effect on parasite fitness), generalist parasite genotypes are favoured. Where parasite loci act multiplicatively (have independent effects on fitness) or antagonistically (have diminishing effects on parasite fitness), specialist parasite genotypes are favoured. A key finding is that polymorphism is not stable and that, with respect to functionally important antigenic peptides, parasite populations are dominated by a single genotype

Enacting professional identity:an exploration of teacher educators’ entanglement with educational technologies in FE

This study focuses on the technology practices of teacher educators in further education (FE) colleges as a site for the negotiation of professional identity. As the culture of performativity and accountability has grown across the English education system, FE has become progressively standardised, centrally mandated and regulated. This has led to debates about teacher professional autonomy and the underlying values of an education system ostensibly oriented towards neoliberalist consumer markets. Policymakers present both the professionalisation of the FE workforce and the effective use of technology as crucial to achieving educational objectives. However, amid substantial interventions into FE teacher education and practice, decisions about educational technology use are seemingly entrusted to teaching professionals. Drawing on the analytical resources of sociocultural and sociomaterial theory, this qualitative case study of three teacher education teams explores how teacher educators negotiate professional identity within the figured worlds of FE. Although underrepresented in research, the literature indicates that this group has an important role in achieving government objectives for improved learner outcomes. This study’s findings suggest that teacher educators identify with the key discourses of their context and professional role to different degrees, and seek to reconcile competing versions of professionalism. Teacher educator work is replete with technology and the appearance of professional choice in many technology practices is illusory. This is found to affect perceptions of technology as integral to teacher educator expertise and the extent to which technology is used in the politically desired ways. Adding to the growing body of research on teacher educator professionalism and higher education (HE) in FE contexts, this thesis foregrounds the influence of the FE culture and conditions of employment on the (re)formation of teacher educator professional identity and demonstrates the potential of technology practices as an access point for further identity research

Tooth wear in the deciduous dentition : a cross cultural and longitudinal study

Thesis (M.D.S.) -- University of Adelaide, Dept. of Dentistry, 199

Stable Speckle Patterns for Nano-scale Strain Mapping up to 700 °C

The digital image correlation (DIC) of speckle patterns obtained by vapour-assisted gold remodelling at 200 – 350 °C has already been used to map plastic strains with submicron resolution. However, it has not so far proved possible to use such patterns for testing at high temperatures. Here we demonstrate how a gold speckle pattern can be made that is stable at 700 °C, to study deformation in a commercial TiAl alloy (Ti-45Al-2Nb- 2Mn(at%)-0.8 vol% TiB$_2$). The pattern is made up of a uniformly sized random array of Au islands as small as 15 nm in diameter, depending on reconstruction parameters, with a sufficiently small spacing to be suitable for nano-scale, nDIC, strain mapping at a subset size of 60 × 60 nm$^2$ . It can be used at temperatures up to 700 °C for many hours, for high cycle fatigue testing for instance. There is good particle attachment to the substrate. It can withstand ultra-sound cleaning, is thermally stable and has a high atomic number contrast for topography-free backscatter electron imaging.EPSRC / Rolls-Royce Strategic Partnership (EP/M005607/1

Dislocations as channels for the fabrication of sub-surface porous GaN by electrochemical etching

Porosification of nitride semiconductors provides a new paradigm for advanced engineering of the properties of optoelectronic materials. Electrochemical etching creates porosity in doped layers whilst leaving undoped layers undamaged, allowing the realisation of complex three-dimensional porous nanostructures, potentially offering a wide range of functionalities, such as in distributed Bragg reflectors. Porous/non-porous multilayers can be formed by etching whole, as-grown wafers uniformly in one simple process, without any additional processing steps. The etch penetrates from the top down, through the undoped layers, leaving them almost untouched. Here, atomic-resolution electron microscopy is used to show that the etchant accesses the doped layers via nanometre-scale channels that form at dislocation cores and transport the etchant and etch products to and from the doped layer respectively. Results on AlGaN and non-polar GaN multilayers indicate the same mechanism is operating, suggesting this approach may be applicable in a range of materials

Evaluation of methods for one-dimensional spatial analysis of two-dimensional patterns in mouse chimaeras

The relative extent of cell mixing in tissues of mouse chimaeras or mosaics can be studied by comparing the distributions of the two cell populations in the tissues. However, the mean patch size is misleading because it is affected by both the extent of cell mixing and the relative contributions of the two cell populations. Previous work suggested that effects attributable to differences in tissue composition among chimaeras can be factored out either by correcting the mean patch size or by using the median patch size for the minority cell population and restricting the analysis to grossly unbalanced chimaeras. In the present study, computer simulations of two-dimensional mosaic arrays of black and white squares (representing cells) were used to simulate chimaeric tissues. Random arrays simulated tissues with extensive cell mixing, arrays of cell clumps (representing coherent clones) simulated less mixed tissues, and striped arrays simulated tissues with elongated but fragmented descendent clones. The computer simulations predicted that (i) the median patch length (minority cell population) and the corrected mean patch length would both distinguish between random and clumped patterns and (ii) differences in the variation of the composition of two perpendicular series of one-dimensional transects would distinguished between stripes and randomly orientated patches. Both predictions were confirmed by analysis of histological sections of the retinal pigment epithelium from fetal and adult mouse chimaeras. This study demonstrates that two types of non-random two-dimensional variegated patterns (clumps and stripes) can be identified in chimaeras without two-dimensional reconstruction of serial sections

Structure and composition of non-polar (11-20) InGaN nanorings grown by modified droplet epitaxy

Droplets grown by modified droplet epitaxy on non-polar (11-20) surfaces of InGaN epilayers on GaN have been seen to be associated with underlying ring-like structures. This work discusses droplet etching as a possible mechanism for ring formation, and droplet creeping as a possible explanation for the droplets sitting askew of the ring centre. Transmission electron microscopy (TEM) analysis shows the droplets to move along the c-axis, and indicates that they have a very high In content.The authors gratefully acknowledge funding from the Engineering and Physical Sciences Research Council (Grant number EP/M011 682/1).This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1002/pssb.20155263