A COMPARISON OF DEFECT ENERGIES IN MGO USING MOTT-LITTLETON AND QUANTUM-MECHANICAL PROCEDURES

The authors compare the predictions of Mott-Littleton calculations, based on empirical interatomic potentials, with predictions based on self-consistent solutions of the Schrodinger equation for embedded clusters. Simple vacancy and substitutional defects in MgO are modelled using both the classical Mott-Littleton and quantum mechanical methods. Particular attention is paid to the size of the quantum mechanical cluster, the different ways that polarisation is taken into account and the choice of basis set. Results are presented for closed-shell systems only, namely V"Mg and Vo vacancies and for Li'Mg, Na'Mg, AlMg, Fo and Clo substitutional impurities. They find a respectable level of agreement between the quite distinct approaches. This both validates the classical calculations and indicates useful generalisations combining the two approache

GEOMETRY AND CHARGE-DISTRIBUTION OF H-CENTERS IN THE FLUORITE STRUCTURE

The analysis of experimental optical and spin-resonance data for the H centre gives a consistent picture of the local geometry and one-electron wavefunctions. One of the two ions in the F2- molecular ion remains very close to the perfect lattice site the other is at a distance close to that found in other F2- centres. This analysis is confirmed by atomistic calculations using the HADES code. The results are used to give a preliminary analysis of the self-trapped exciton data

Concluding remarks: Reaction mechanisms in catalysis: perspectives and prospects

We consider the current status of our understanding of reaction mechanisms in catalysis in the light of the papers presented in this Discussion. We identify some of the challenges in both theoretical and experimental studies, which we illustrate by considering three key reactions

Microscopic origin of the optical processes in blue sapphire

Al2O3 changes from transparent to a range of intense colours depending on the chemical impurities present. In blue sapphire, Fe and Ti are incorporated; however, the chemical process that gives rise to the colour has long been debated. Atomistic modelling identifies charge transfer from Ti(III) to Fe(III) as being responsible for the characteristic blue appearance

THE VIEWS OF MERWELENE VANDER MER WE AND HER TEAM ABOUT THE FASHION PHOTOGRAPHY WORKING ENVIRONMENT

ThesisFashion is seen as a glamorous world full of beautiful people and exorbitant amounts of money. I t was decided to get a closer look at this world as seen through the eyes of those who participate. This study consists of two components. A practical component comprising studio and on location photographs and a theoretical component dealing with fashion worlUng environment. As South Africa is becoming a non-sexist society and women are part of the main business stream, it was decided to focus on the highly successful photographic icon of fashion photography, Merwelene van der Merwe. The main aim of the study was to research the interaction between the fashion photographer and the main participants in a fashion photograph, in order to get each individual's interpretation of what makes a successful fashion photograph and fashion photographer. This was achieved through a preliminary intervic'W with Merwelene van der Merwe to see if the aim of the study was feasible. As the f,rst interview was most successful, the decision was made to place more emphasis on Merwelene van der Merwe. Follow-up interviews and a week's stay with Merwelene resulted. Articles, two television interviews and all other available material was researched to get a more comprehensive picture. As Merwelene has a unique way of speaJUng, the author decided to give her interviews verbatim so that the reader can feel the "electricity" generated by Merwelene. The intervi~ws were done in Afrikaans, Merwelene's home language. In this dissertation, all questions are given in English and Afrikaans. All questions are preceded by a Q and all answers by an A. To get a more comprehensive picture, the following people who form part of Merwelene's team were interviewed: (1) Her assistants Doret, (2)her model Simone,(3) her hair and make-up artist Marilyn, (4) an art director of an advertising agency Sandy and (5) a client Mariette. The dissert.ation is devided into four chapters, the first chapter, Merwelene van der Merwe discusses her background and outlook on life. In chapter two, Merwelene discusses fashion photography as a success ful busin ess. Chapter three covers the team she works with and their yiews. The final chapter concentrates on Merwelene's work as a fas hion photographer. Here two divergent photographs are discussed

Induced polygenic variability using combination treatment of gamma rays and ethyl methane sulphonate in blackgram (Vigna mungo (L.) Hepper)

Induced mutation in plant improvement has been proven to be one of the alternative ways to generate new sources of genetic variation in blackgram. In this study, dry seeds of VBN 4 blackgram were treated with combination treatment of both gamma rays (400, 500 and 600 Gy) and ethyl methane sulphonate (EMS) (50, 60 and 70 mM) to study the polygenic characters in M2 generation. The mean values for plant height, number of primary branches, number of clusters per plant, number of pods per plant, number of seeds per pod and single plant yield decreased below the control in most of the treatments. The mean single plant yield was more than for the control at 400 Gy+60 mM and 600 Gy+50 mM. Moderate and high phenotypic coefficients of variation (PCV) and genotypic coefficients of variation (GCV) were recorded in yield component characters such as plant height, number of primary branches, number of clusters per plant and number of pods per plant. A high amount of heritability and GA as per cent of mean was noted for plant height, number of clusters per plant, number of primary branches per plant, number of pods per plant, pod length, number of seeds, 100 seed weight and single plant yield. This denoted that these characters are governed largely by additive gene effect, which may be favorably exploited for improvement through simple selection in M2 generation.Key words: Gamma rays, ethyl methane sulphonate (EMS), blackgram, polygenic variability, M2 generation

A tribute to the scientific career of Neville Greaves: the Daresbury years

We present a personal account of both the developments in technique and instrumentation led by Neville Greaves and the scientific applications which they enabled. We focus on the pioneering period at the Synchrotron Radiation Source, Daresbury in the 1980s and 90s. We discuss and illustrate the lasting impact of these key developments on chemistry, materials and catalytic scienc

Efficient and accurate approach to modeling the microstructure and defect properties of LaCoO3

Complex perovskite oxides are promising materials for cathode layers in solid oxide fuel cells. Such materials have intricate electronic, magnetic, and crystalline structures that prove challenging to model accurately. We analyze a wide range of standard density functional theory approaches to modeling a highly promising system, the perovskite LaCoO3, focusing on optimizing the Hubbard U parameter to treat the self-interaction of the B-site cation's d states, in order to determine the most appropriate method to study defect formation and the effect of spin on local structure. By calculating structural and electronic properties for different magnetic states we determine that U=4 eV for Co in LaCoO3 agrees best with available experiments. We demonstrate that the generalized gradient approximation (PBEsol+U) is most appropriate for studying structure versus spin state, while the local density approximation (LDA+U) is most appropriate for determining accurate energetics for defect properties