Structural defects in II-VI epitaxial Layers

This study has principally been concerned with the structural assessment of a range of II-VI epitaxial layers using the combined techniques of cross-sectional transmission electron microscopy and microdiffraction. Iodine reactive ion sputtering has been used for the final stage of sample preparation, and this has been shown to produce electron transparent foils with a greatly reduced artefactual defect content, as compared with samples prepared by argon ion milling.- The two conflicting conventions for the polarity determination of CdTe, as proposed by Warekois (1962) and Fewster (1983), have led to considerable confusion in the recent international literature. This issue has been resolved using the microdiffraction technique to identify the best {111} CdTe polar face for the epitaxial growth of (Hg,Cd)Te. This proved to be the {ĪĪĪ}Te: surface, and this result is in agreement with the Fewster convention for CdTe crystal polarity. The study of wide band-gap II- VI compounds has been mainly concerned with heterostructures of ZnSe/ZnS grown by MOVPE on (001) oriented GaAs. Observations along orthogonal directions demonstrated the strong anisotropy in the defect distribution of these epitaxial layers. Microtwins were found exclusively in the [IĪ0] epi- layer projection lying on advancing {111}A planes. A model has been proposed, based on the differential motion of a and β dislocations in the sphalerite structure, to explain the defect anisotropy. It is considered that the large difference in the ionic radii of Zn(^2+) and S(^2-), and material doping are primarily responsible for this phenomenon. The study of narrow band-gap II-VI compounds has been mainly concerned with the structural assessment of hybrid substrates for the epitaxial growth of (Hg,Cd)Te. Lamella twins lying parallel to the interfacial plane characterised {111} CdTe epitaxial layers grown by MOVPE on {100} and {in}B GaAs, and on {ĪĪĪ}B CdTe substrates, while the {100} CdTe/{100}GaAs system exhibited a network of misfit dislocations. MOVPE grown layers of (Hg,Cd)Te on both {ĪĪĪ}B CdTe and CdTe/{ĪĪĪ}B GaAs hybrid substrates have also been investigated. This study is complemented by an assessment of the anisotropic defect distribution in MBE grown (Cd,Zn)Te/CdTe strained layer superlattices, which have potential application as high quality lattice matched substrates for (Hg,Cd)Te. Finally a provisional study of the intermediate band-gap ZnTe and ZnTe/CdTe multilayer system is presented

Characterisation of dispersions within annealed HVOLF thermally sprayed AlSnCu coatings

High velocity oxy-liquid fuel (HVOLF) AlSnCu coatings are characterised following annealing for up to 5 hours at 300°C. A combination of statistical analysis of BSE images and TEM observations demonstrate the decrease in the number of sub-micron and nanoscale Sn particles with annealing, commensurate with a decrease in the coating microhardness. TEM evidence further suggests the coarsening of nanoscale Sn through a mechanism of a liquid phase migration within the Al matrix. EELS and EFTEM additionally allow the identification of the precipitation of theta'

The role of informal protected areas in maintaining biodiversity in the Western Ghats of India

Although it is widely believed that an important function of protected areas is to conserve species that are unable to survive elsewhere, there are very few empirical studies in which a comparison is made between biodiversity of protected areas and that of the cultivated landscape surrounding them. We examined the diversity of trees, birds, and macrofungi at 58 sites in three land-use types in a tree-covered landscape in Kodagu district in the Western Ghats of India. Ten forest reserve sites in the formal protected area, and 25 sacred groves and 23 coffee plantations in the neighboring cultivated landscape were sampled. A total of 215 tree, 86 bird, and 163 macrofungus species were recorded. The forest reserve had a large number of trees that were restricted in their distribution, and the sacred groves had a large number of macrofungi. We observed that deciduous trees and non-forest-dwelling birds increased, and evergreen trees and forest-dwelling birds decreased with increasing intensity of land management. We found that trees having non-timber uses and macrofungi useful to the local people, as well as those with medicinal properties, were abundant in sacred groves. We found no significant differences in the distribution of endemic and threatened birds across the three land-use types. Although endemic trees were more abundant in the forest reserve than in sacred groves, threatened trees were more abundant in sacred groves than in the forest reserve. We attribute the high diversity in sacred groves to the native tree cover in shade coffee plantations. We conclude that informal protected areas are as important as formal ones for biodiversity conservation in Kodagu. We recommend that a conservation strategy that recognizes informal protection traditions is essential for successful biodiversity conservation in regions where formal reserves are surrounded by a matrix of cultivated land

An exploratory investigation into the potential of mobile virtual reality for the treatment of paruresis – a social anxiety disorder

This paper describes the initial exploratory phase of developing a VR intervention designed to alleviate the problems people with Paruresis experience when they need to utilise public toilet facilities. The first phase of the study produced a virtual environment, based upon a public toilet, which would run on the widely available Gear VR or Oculus Go HMD. The purpose of this prototype was to facilitate an informed discussion with a focus group of Paruresis patients, to obtain preliminary conclusions on whether they were interested in such an intervention and whether it offered potential to help alleviate the condition. In partnership with the UK Paruresis Trust the software was reviewed by both potential users and domain specialists. Results showed that the majority of participants reported a stress response to the stimulus of the virtual public toilet, indicating that it could be effective as a platform for graduated exposure therapy. Focus group feedback, and input from domain experts, was utilised as part of a participatory design methodology to guide the priorities for a second phase of development. The exploratory study concluded that this approach offers great potential as a future treatment for people with Paruresis

Robustness from flexibility in the fungal circadian clock

Background Robustness is a central property of living systems, enabling function to be maintained against environmental perturbations. A key challenge is to identify the structures in biological circuits that confer system-level properties such as robustness. Circadian clocks allow organisms to adapt to the predictable changes of the 24-hour day/night cycle by generating endogenous rhythms that can be entrained to the external cycle. In all organisms, the clock circuits typically comprise multiple interlocked feedback loops controlling the rhythmic expression of key genes. Previously, we showed that such architectures increase the flexibility of the clock's rhythmic behaviour. We now test the relationship between flexibility and robustness, using a mathematical model of the circuit controlling conidiation in the fungus Neurospora crassa. Results The circuit modelled in this work consists of a central negative feedback loop, in which the frequency (frq) gene inhibits its transcriptional activator white collar-1 (wc-1), interlocked with a positive feedback loop in which FRQ protein upregulates WC-1 production. Importantly, our model reproduces the observed entrainment of this circuit under light/dark cycles with varying photoperiod and cycle duration. Our simulations show that whilst the level of frq mRNA is driven directly by the light input, the falling phase of FRQ protein, a molecular correlate of conidiation, maintains a constant phase that is uncoupled from the times of dawn and dusk. The model predicts the behaviour of mutants that uncouple WC-1 production from FRQ's positive feedback, and shows that the positive loop enhances the buffering of conidiation phase against seasonal photoperiod changes. This property is quantified using Kitano's measure for the overall robustness of a regulated system output. Further analysis demonstrates that this functional robustness is a consequence of the greater evolutionary flexibility conferred on the circuit by the interlocking loop structure. Conclusions Our model shows that the behaviour of the fungal clock in light-dark cycles can be accounted for by a transcription-translation feedback model of the central FRQ-WC oscillator. More generally, we provide an example of a biological circuit in which greater flexibility yields improved robustness, while also introducing novel sensitivity analysis techniques applicable to a broader range of cellular oscillators

The application of tripod polishing and focused ion beam milling to the TEM specimen preparation of HVOF thermally sprayed coatings

The microstructure of high velocity oxy fuel thermally sprayed coatings is highly anisotropic and inhomogeneous. Tripod polishing has enabled the preparation of samples with up to 0.5mm diameter electron transparent areas, where a statistically significant number of features could be examined. Conversely, FIB has been used to prepare TEM samples for site-specific analysis of sub-micron regions of interest, e.g. for the interface characterisation between metallic coatings and the substrate, or the study of secondary precipitation on pre-existing phases in cermet coatings

Antimicrobial resistance of Escherichia coli isolates from broiler chickens and humans

BACKGROUND: Antimicrobial usage is considered the most important factor promoting the emergence, selection and dissemination of antimicrobial-resistant microorganisms in both veterinary and human medicine. The aim of this study was to investigate the prevalence and genetic basis of tetracycline resistance in faecal Escherichia coli isolates from healthy broiler chickens and compare these data with isolates obtained from hospitalized patients in Jamaica. RESULTS: Eighty-two E. coli strains isolated from faecal samples of broiler chickens and urine and wound specimens of hospitalized patients were analyzed by agar disc diffusion to determine their susceptibility patterns to 11 antimicrobial agents. Tetracycline resistance determinants were investigated by plasmid profiling, transformations, and amplification of plasmid-borne resistance genes. Tetracycline resistance occurred at a frequency of 82.4% in avian isolates compared to 43.8% in human isolates. In addition, among avian isolates there was a trend towards higher resistance frequencies to kanamycin and nalidixic acid (p < 0.05), while a greater percentage of human isolates were resistant to chloramphenicol and gentamicin (p < 0.05). Multiple drug resistance was found in isolates from both sources and was usually associated with tetracycline resistance. Tetracycline-resistant isolates from both avian and human sources contained one or several plasmids, which were transmissible by transformation of chemically-competent E. coli. Tetracycline resistance was mediated by efflux genes tetB and/or tetD. CONCLUSION: The present study highlights the prevalence of multiple drug resistant E. coli among healthy broiler chickens in Jamaica, possibly associated with expression of tetracycline resistance. While there did not appear to be a common source for multiple drug resistance in the strains from avian or human origin, the genes encoding resistance are similar. These results suggest that genes are disseminated in the environment and warrant further investigation of the possibility for avian sources acting as reservoirs for tetracycline resistance