Magister Scientiae - MSc / Extracts from the root bark, stem bark, and leaves of R. natalensis were screened for antibacterial activity against standard bacterial strains; Staphylococcus aureas, Escherichia coli and Pseudomonas aureginosa, and fungi; Candida albicans, Trichophyton mentagrophytes or Microsporum gyseum. Chromatographic techniques were utilized to isolate pure compounds. This study validates and documents, in a systematic way, the antimicrobial properties of the R. natalensis used for many years by many people of the world. It also provides valuable information for further phytochemical isolation and characterization studies of active compounds, necessary for the development of new drugs. The extractions were carried out using broad spectrum of solvents (hexane, dichloromethane, ethyl acetate, and methanol). Fractionation was done using standard chromatographic techniques. A total of seven (7) compounds were isolated from R. natalensis. Three of the isolates were characterized and their structures were unambiguously established by detailed spectroscopic analysis that involved high resolution mass spectrometry, 1D and 2D-NMR spectral data experiments 1H, 13C, DEPT, COSY, HMBC, and NOESY. These compounds are: 3-(1-(2,4-dihydroxyphenyl)-3,3-bis(4- hydroxyphenyl)-1-oxopropan-2-yl)-7-methoxy- 4H-chromone-4-one (39), Rhuschromone, a novel compound isolated for the first time, 2’,4’-dihydroxychalcone-(4-O-5’’’)-4’’,2’’’,4’’’- trihydroxychalcone (40) and 3-((Z)-heptadec-13-enyl) benzene- 1,2-diol (41), an urushiol. Compound 39 recorded the highest activity zone of inhibition (21mm) against S. aureas, which was found to be 50% as active the chloramphenicol standard used. The traditional use of the extracts in infections and inflammatory conditions is rationalized based on the content of theisolated compounds, and it has been proposed that the total crude extract, with its contents of so many bioactive compounds, could be formulated for use in many infections, microbial or fungal. Furthermore, not all of the species studied to date have been fully characterized for potential bioactivities. Thus, there remains a significant research gap spanning the range from lead chemical discovery through process development and optimization in order to better understand the full bioactive potential of many of these plants. / South Africa

No description available.

Metal-polymer nanocomposite materials were found to have highly tunable opti- cal properties. Density functional theory-based calculations were employed to study trends in Ag/polyvinylidene fluoride nanocomposite optical properties. The frequency- dependent imaginary part of the dielectric constant was calculated from dipolar inter- band transitions. The metallic inclusion introduced both occupied and unoccupied states into the large polymer band gap. Thus, higher inclusion volume fractions generally led to stronger composite optical response. Spectra from monodisperse sys- tems correlated well with nanoparticle quantum confinement models. A polydisperse system exhibited optical properties that correlated best with interparticle distances along the field direction. Nanodisk and nanorod-shaped inclusions had tunable re- sponse from field polarization, aspect ratio, crystallographic projections, and nanorod end-cap morphology. / Graduate / 0495

M.Sc. (Physics) / Silicon thin films can be manufactured with the aid of various deposition techniques, each with its own unique properties. In this study the optical properties of silicon manufactured with physical vapour deposition from an electron beam source were studied as a function of layer thickness, deposition rate and substrate temperature. The index of refraction (n and k) as well as optical gap eg. were determined with the aid of characterization models derived specific for optical techniques. These models are covered extensively in the thesis. It was found that the layers were homogeneous and stable, but that the deposition rate and substrate temperature did have a large influence on the properties of the layers. The results show that structural changes, first from the collumnar structure to an amorphous structure and with a further increase in substrate temperature, also a transition from the amorphous to a microcrystalline structure do occure at temperatures considerably lower than what was previously anticipated. With variations in deposition rate it was found that the disorder in the coating will increase with an increase in rate resulting in a reverse transition from the microcrystalline structure to the amorphous structure. Optical gaps in the range 1. 12eV to approximately 1. 38eV were found to be possible with the correct choice of deposition parameters...

M.Sc. / An experimental study on the magnetic properties of the (Cr86Ru14)1–x(V,Mn)x alloy system is reported in this thesis. The work focusses mainly on two aspects of the magnetic behaviour of this alloy system; firstly that of the base alloy Cr86Ru14 having a Ru concentration on the magnetic phase diagram of the Cr-Ru system that is close to a putative quantum critical point (QCP) (xc ≈ 17 at.% Ru), and secondly, of the effects of tuning this base alloy towards (V-addition) or away (Mn-addition) from the QCP. For the Cr86Ru14 base alloy, measurements of the electrical resistivity and elastic constants as functions of temperature and pressure are reported. These are supplemented by thermal expansion and neutron diffraction measurements as a function of temperature through the Néel transition temperature, TN.

Le tassement des sols est l'un des principaux processus de dégradation des sols en Europe. Il est principalement dû à la mécanisation des activités agricoles et forestières qui se traduit par des passages d’engins de plus en plus lourds, très souvent en conditions climatiques défavorables. La directive cadre pour la protection des sols en préparation envisage de demander aux Etats membres de l’Union Européenne de recenser les zones les plus sensibles au tassement en vue d’appliquer des mesures de prévention ou de réhabilitation. Le but de notre étude est de développer une méthode d’estimation des risques de tassement des sols et de l’appliquer à l’échelle de la France métropolitaine. La sensibilité des sols au tassement dépend du type de sol et augmente avec la teneur en eau. L’intensité du tassement dépend de la charge appliquée à la surface du sol. L’estimation des risques de tassement repose sur la fréquence d’occurrence d’une teneur en eau critique qui engendre une intensité de tassement pénalisant le fonctionnement des sols et des cultures. Elle fait appel à deux modèles : le modèle de culture STICS pour le calcul de l’évolution journalière de la teneur en eau des sols, le modèle de déformation COMPSOIL pour le calcul des teneurs en eau critiques en fonction des engins utilisés. Ces deux modèles sont appliqués sur la Base de Données Géographique des Sols de France au 1/1 000 000ème. Une amélioration du paramétrage du module hydrique de STICS adapté à cette base de données est proposée. Les risques de tassement des sols sont estimés pour trois périodes d’intervention au cours d’une culture de blé d’hiver ou de maïs : le semis, la fertilisation azotée et la récolte, en fonction de scénarios climatiques actuels et futurs. Plusieurs critères de définition d’un sol tassé et d’un risque de tassement ont été utilisés. La cartographie des risques de tassement (1) s’avère très sensible au choix de ces critères, (2) résulte de la combinaison des trois facteurs : type de sol, climat et système de culture, sans facteur prédominant. La méthodologie proposée, basée sur l’utilisation de modèles de fonctionnement hydromécanique, est bien adaptée à l’estimation des risques de tassement des horizons de surface des sols cultivés. Une caractérisation plus précise des propriétés mécaniques des sols français est à envisager pour réduire les incertitudes sur la cartographie des risques. / Soil compaction is one of the major processes of soil degradation in Europe. Compaction is mainly due to the mechanization ofagricultural and forest activities which involve use of increasingly heavy machines, even when the weather conditions may beunfavourable. The European Union Directive for soil protection in preparation will require for the Member States to zone soilcompaction risk for determining priority areas for soil prevention or soil improvement. In this context, the aim of this study is tobuild a methodology to soil compaction risk at national scale. The susceptibility of soil to compaction increases with the soil watercontent. The soil compaction risks are deduced from frequency of appearance of critical water content which implies systematiccompaction. Soil water content is estimated with the crop model STICS for 30 years on the whole French soils. Before simulations,we must (1) estimate critical water content as a function of soil and applied stress; (2) parameterize the hydraulic module of STICSso that it is adapted to the whole French soils; (3) parameterize the mechanical functioning of French soils. The results are mappedwith the Soil geographical data base of France at 1/1 000 000. The compaction risks are thus estimated for three periods of farmingoperation during winter wheat and maize cultivation: soil conditioning/sowing, nitrogenous fertilising and harvest for present andfuture climates. These three operations are characterized by the applied stress and the climatic conditions. Several criteria definingcompacted soil and compaction risk were used. Maps of soil compaction risk appeared sensitive to these criteria and also showed that compaction risk is resulting from the interaction of three factors: soil types, climate and farming systems without any dominating.The proposed methodology based on use of hydraulic and mechanical models is well adapted to the estimation of compaction risk for cultivated topsoil. But, mechanical properties for French soils must be characterised more precisely in future to limit uncertainties in the mapping of soil compaction risk.

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Rock physical properties are usually associated with important geologic features within mineral deposits and can be used to define the location, depth and size of the deposit, type of ore, or physical property contrast between the host and country rock. Geophysical surveys are sensitive to physical properties and therefore are widely used in mining exploration, especially in concealed terrains. The surveys can be performed at multiple scales, resulting in corresponding physical property datasets at different scales. Survey scale can vary from core or hand sample, involving few cubic centimeters, to regional-scale surveys providing information about physical property contrasts between distinct regional geological features. The understanding of the relationship between the physical property distributions with the sample volume (e.g. district, deposit, and drill-hole scale) is required where point scale physical property measurements are going to be consistent with measurements at larger volumetric scales during the integration of data for geophysical modeling The approach used to address the problem of understanding the scaling relations of physical properties, was achieved by considering them as second order stationary regionalized variables and then applying the random function formalism, provided by geostatistics theory. Geostatistics provide the required framework to characterize, quantify, model and link the spatial variability of the random variable at the different volumetric scales. The aim of this study is to apply geostatistics to effectively integrate data collected at several scales and bring knowledge to the understanding of the scaling relations of magnetic susceptibility. For this purpose, measurements of magnetic susceptibility available from Flin Flon copper-zinc district in Canada will be used. The data available at point scale were collected with hand portable magnetic susceptibility meter. The larger volumetric scale dataset were acquired using frequency domain electromagnetic instruments capable of measuring larger sample volumes, and then used to obtain magnetic susceptibility models using geophysical inversion algorithms. Once different scale models of magnetic susceptibility were available, quantification of the scaling relation using geostatistics, specifically variogram models and dispersion variance were determined. The understanding provided by the scaling analysis of the Flin-Flon magnetic data is applied to data from the Rio Blanco copper district in central Chile. Magnetic susceptibility measurements collected with a hand magnetic susceptibility meter on drill-core is integrated in larger scale volumes used for geophysical inversion modeling of regional scale airborne magnetic field measurements to recover magnetic susceptibility models. The methodology resulting from this application of geostatistics is used to address the problem of integrating multiple scales of physical property data in an effective way. The resulting physical property models capture the small-scale magnetic susceptibility variability observed and can guide larger-scale variability within geophysical inversion models. Establishing reliable statistical correlations between physical properties and rock units controlling ore within deposits are crucial steps leading predictive mine exploration tools. Any numerical modeling approach to establish these correlations should consider in some way the scaling nature of both physical property and ore content. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The mechanical properties of ion implanted ceramics are primarily a function of the radiation damage produced by the implantation process. For crystalline ceramics this damage is chiefly nuclear displacements, though for glasses electronic effects have also been observed. In this study a number of single crystal and polycrystalline ceramics and a soda-lime-silica glass have been implanted with a range of ions in the energy range 90keV to 400keV and the changes in mechanical properties produced have been followed using hardness, indentation fracture and scratch testing. The damage structures which remain after implantation will control both the indentation hardness and surface fracture properties of cetamics. Changing the temperature of the substrate during implantation (in the range. 150K to 760K) has been found to alter this damage state and hence produce changes in the measured mechanical properties. In this temperature range, the effects of damage annealing at low doses were found to be minor for sapphire although for MgO damage annealing was found to result in a eduction of the radiation-induced hardening above 473K. The surface softening and stress relief accompanying amorphisation at higher doses was found to be strongly temperature dependent. Thus, the recrystallisation of amorphous material is important in determining the final mechanical properties of the implanted specimens. The tribological properties of the implanted ceramics were investigated using single pass scratch tests. Friction coefficients were found to increase with dose up to the onset of amorphisation, even when visible scratch tracks were produced. This increse is due to changes in adhesion between the slider and the flat induced by ion implantation. The reasons for these changes are as of yet unclear, though a possible explanation could be the removal of surface adsorbates which has been observed for MgO. Similar mechanical and tribological property changes observed for the polycrystalline ceramics as for the single crystal systems, but some extra effects were observed.

No description available.