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Reflectarrays that emulate paraboloidal main-reflectors, and hyperboloidal or ellipsoidal sub-reflectors, have undergone a great deal of development over the past two decades. More recently, research on the topic has concentrated on overcoming some remaining disadvantages, re-examining certain design issues, and extending reflectarray functionality. This thesis concerns itself with fixed-beam offset-fed single-layer main-reflectarrays and sub-reflectarrays comprised of square or rectangular variable size conducting elements. Both full-wave analyses and experiment are used in all the deliberations. In order to examine reflectarray operating mechanisms the thesis first describes a component-by-component technique whereby the role of the various reflectarray parts can be assessed by determining their individual and aggregate contributions to the reflectarray near- and far-fields. This technique is used to diagnose the fact that feed-image-lobes that appear at off-centre frequencies are caused not only by the groundplane as first thought, but by an imbalance in the complex currents on the patches and groundplane at such frequencies. The use of sub-wavelength elements is shown to suppress such unwanted lobes. The thesis then uses receive- and transmit-modes analysis to show that beam squint at off-centre frequencies, often not accounted for when stating the gain bandwidth of a reflectarray, is due to the shifting of the true focal points away from the geometrical one at these frequencies. It is demonstrated that a two-feed reflectarray arrangement is capable of eliminating beam squint, and that the use of smaller focal length to aperture size (F/D) ratios removes the grating lobes that can appear in such two-feed reflectarrays due to clustering of the aperture amplitude distribution. Finally, the thesis studies the effect of the reality that the angle of incidence of the feed fields on the various reflectarray elements is not the same for all elements, even though this is most often assumed when using element reflection phase versus element size databases in performing reflectarray designs. Careful full-wave analysis reveals that it is not only the dependence of element reflection phase on incidence angle that is important, but that the individual element pattern beamwidths change and distort as this angle increases. This is important not only from the point of view of the coupling of the feed fields to the elements, but also as far as the angular sector within which the reradiated fields are important. Thus sub-reflectarrays, whose radiation patterns are considerably wider than main-reflectors, are more susceptable to incidence angle effects. It is shown that the use of sub-wavelength elements in a reflectarray largely ensures its immunity to such effects.

The chronotropic and inotropic responses to isoprenaline and salbutamol were determined in the chloralose anaesthetized dog. The myocardium was denervated, sympathetically and parasympathetically to prevent direct neural influence on the heart rate and myocardial contractility. The heart rate was determined from the E.C.G. Myocardial contractility was indicated by the change in the maximum rate of rise of left ventricular pressure (dP/dt max) at a constant electrically paced heart rate. The structure-activity relationships for salbutamol and isoprenaline were determined from dose-response curves and by plotting the change in contractility (ΔdP/dt max) against the change in heart rate (ΔHR). The data obtained from this series of experiments indicated that the only difference between the effects of the agonists on the inotropic and chronotropic responses of the myocardium was the lower affinity of salbutamol for the adrenergic receptor as indicated by the 100 times greater concentration required to produce the same response level. Previously reported in vitro studies with the guinea pig atrium and dog papillary muscle had indicated that a smaller inotropic response to salbutamol should have been expected. To test this discrepancy between the present in vivo experimentation, and the previous in vitro work, studies were designed to test the guinea pig atrium and the dog papillary muscle in vitro. The effects of the agonists were studied on the isolated guinea pig atrium in a manner that paralleled the in vivo dog study. With the organ bath at 25°C, the chronotropic response, measured by the change in free contraction rate (ΔR), and the inotropic response, determined from the change in peak tension developed (ΔT) during electrical stimulation at 2 Hz, to a single randomly ordered dose of salbutamol or isoprenaline were determined. Salbutamol acted as a partial agonist, that is, had a lower efficacy than isoprenaline. However, the relative effect of each drug on the inotropic and chronotropic responses was almost identical. In the isolated dog papillary muscle, salbutamol displayed a much lower efficacy, producing only 20% of the maximum isoprenaline increase in peak tension developed to the cummulative addition of agonist. The affinity of salbutamol for the adrenergic receptor in this preparation was much lower than that observed in vivo when compared with isoprenaline, 5,000:1 and 100:1 respectively. The structure-activity relationships for salbutamol and isoprenaline showed that the relative effects of these agonists on the in vivo denervated dog myocardial inotropic and chronotropic responses were similar. This observation indicates that the adrenergic receptors of the dog myocardium mediating the inotropic and chronotropic responses are structurally similar at a site complementary to the phenyl ring of the agonist molecule. However,, a definite conclusion regarding the adrenergic receptors responsible for the inotropic response cannot be made because of the unexplained difference in inotropic response observed with ventricular muscle in vivo and in vitro. Examination of the structure-activity relationships for salbutamol and isoprenaline in the in vitro guinea pig atrium indicates that, in this preparation also, the adrenergic receptors involved in the two measured responses are probably structurally similar. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

After unilateral lesions of the mesotelencephalic dopamine (DA) system, the administration of DA receptor agonists results in circling. This response is believed to reflect an asymmetry in mesotelencephalic DA activity. Moreover, drug-induced circling is thought to be directed away from the projection of higher dopaminergic activity. Recently, it has been reported that circling can be established and maintained using operant procedures in surgically intact and drug naive rats. The phenomenon of conditioned circling has been associated with an asymmetrical change in DA metabolism within the striatum and nucleus accumbens. The present series of experiments was designed to characterize further the involvement of mesotelencephalic DA in conditioned circling. Rats trained to circle for water according to a continuous schedule of reinforcement did not exhibit increased DA metabolism within either the striatum or the nucleus accumbens (Experiment I). However, a bilateral augmentation was observed when rates of responding were increased by implementing an intermittent schedule of reinforcement (Experiment II). Concurrent increases in the biosynthesis of DA, as estimated by accumulation of DOPA following the administration of a DOPA decarboxylase inhibitor, were not observed (Experiment III). Experiments IVa and IVb examined the extent to which inherent directional biases, which play a role in determining the magnitude and direction of drug-induced circling, influenced the acquisition and performance of the conditioned circling response. No effects were evident. Moreover, a symmetrical, bilateral enhancement in DA metabolism was observed in the striatum, irrespective of directional preferences. While conditioned circling can be established and maintained by reinforcing the response with food, food itself influenced DA metabolism and therefore precluded the detection of changes in DA metabolism specific to the circling response. Specifically, striatal and accumbens DA metabolism was augmented to a similar extent in animals given matched amounts of non-contingently presented food (Experiment V). Concentrations of DA, DOPAC and homovanillic acid (HVA) were found to be differentially distributed throughout the striatum (Experiment Via), suggesting a possible chemical basis for the heterogeneity of striatal DAergic functions. Changes in striatal DA metabolism associated with conditioned circling were observed only within localized regions of the anterior striatum (Experiment VIb). All changes noted were, however, bilateral in nature. Finally, unilateral lesions of the mesotelencephalic DA projection, following the establishment of the conditioned circling response, disrupted responding, irrespective of the relative locus of the lesion (i.e. ipsilateral or contralateral to the direction of turning) (Experiment VII). However, the extent of the behavioral deficit was more severe following contralaterally placed lesions. It is concluded that circling, established and maintained by positive reinforcement, is subserved by a bilateral augmentation in DA metabolism within the nucleus accumbens and discrete regions of the striatum. However, lesion studies indicate an asymmetrical involvement of the ipsilateral and contralateral projections in this response. / Medicine, Faculty of / Graduate

Abstract Academic support in IT Governance focuses static viewpoints on IT Governance. IT Governance in a global context has to cater for intensive competition, cultural diversity, and various fluctuating economic conditions. A static model of IT Governance and organisation cannot adequately address these issues. A major goal of this Dissertation is to develop a Framework for component-based IT Governance using dynamic Linkage Mechanisms to allow the determination of an optimum (resource-) flow. Linkage Mechanisms are dynamic arrangements and IT Governance Service Value Channels between IT Governance Components in the IT Governance Domain and allow communication between them. The (resource-) flow is based on transactions. These dynamic networks of relationships allow for greater flexibility and agility in acquiring, combining and deploying required IT Resources and IT assets. In this new research approach methods of the Object-oriented Modelling and Operations Research are applied to IT Governance disciplines. The result of this Dissertation is a generic, model-based, reusable and expandable 'building block' for the component-based design of an IT Governance Domain. This building block is composed of process oriented models, structured processes, strategies for optimisation and application use cases. It is shown how the architecture for the performance of a concrete IT Governance Domain is instrumented and in this way a component-based IT Governance is performed. Possible addressees of the results of this Dissertation are following: - ITG architects and (software-) developers who would like to implement the components, services or a platform for component-based ITG; - ITG managers or Chief Information Officers (CIO) who would like to construct a better understanding for requirements and relationships in the context ITG; - Auditors who would like to control and audit the conformity of an ITG Domain against a generic requirements catalogue; - Authors of Standards and Best Practice-Frameworks in the ITG area as-well-as scientists who are working with related research questions in the context ITG.

The polycrystalline nickel-base superalloys RR1000 and Udimet 720Li (U720Li) were developed for turbine disc applications. These alloys contain a higher volume fraction of the ordered γ' phase (close to 50%) when compared to previous generation alloys (~ 25%) in order to ensure that they retain high strength at operating temperatures exceeding 700°C. The increased percentage of precipitates in the material leads to higher levels of constraint between matrix and the precipitates, and this will have consequences for the deformation mechanisms of the aggregate. It is therefore important to understand how the increased volume fraction of precipitates affects the deformation behaviour of the material. This is not only crucial for the design of the optimum microstructure, but also for lifing models, which predict the lifetime of a component. It is the aim of the present work to improve the understanding of the deformation behaviour of these alloys by focussing on the influence of the γ' precipitate size. These alloys usually comprise a complex trimodal γ' size distribution, which complicates studies on the dependence of the deformation behaviour on the precipitate size. Hence, simplified model microstructures were generated here with a unimodal γ' size distribution. The model microstructures were subjected to in-situ loading experiments with neutron diffraction at temperatures of 20°C, 500°C and 750°C. Neutron diffraction measurements during loading revealed the elastic lattice strain response of both the γ and the γ' phases, which can indicate changes in their respective deformation behaviour. These measurements showed a load transfer from γ to γ' for some test conditions, which indicated that γ was able to deform with noticeably less deformation in the γ' phase. With a larger γ' precipitate size and/or higher test temperature, the tendency for load transfer increased. A post-mortem analysis of the deformed microstructures using advanced electron microscopy techniques (EBSD, ECCI, TEM) showed that shearing of the γ' precipitates dominated the deformed microstructures at 20°C and 500°C and was also observed after deformation at 750°C. Deformation was less localised in the microstructures with large γ' precipitates, which might be correlated with the increased trend for load transfer. The onset of multiple slip or the activation of Orowan looping as an additional deformation mechanism are suggested as possible explanations for these observations.

Many basal forebrain and mesopontine tegmental cholinergic projection systems tend to overlap in their origins. This raises the possibility that these projection systems are collateralized to innervate divergent areas. In experiment one, the degree to which basal forebrain and mesopontine tegmental neurons that innervate the reticular thalamic nucleus have axons that collateralize to innervate the cortex as well was examined with a retrograde fluorescence labeling method combined with immunohistochemistry. A significant portion of the labeled neurons in the region of the nucleus basalis magnocellularis and pedunculopontine tegmental nucleus projecting to the reticular thalamic nucleus were observed to be also labeled (double-labeled) following intracortical tracer injections. Many of these double-labeled neurons displayed choline acetyltransferase choline acetyltransferase immunoreactivity. It was also shown that numerous basal forebrain neurons that innervated the reticular thalamic nucleus contained the calcium-binding protein, parvalbumin. These neurons tended to be located more rostrally than the ChAT immunoreactive neurons; primarily in the region of the ventral pallidum. There was some indication that parvalbumin-containing neurons in the basal forebrain that innervate the reticular thalamic nucleus also have axons that branch to innervate the cortex. Finally, none of the basal forebrain neurons innervating the reticular thalamic nucleus was found to contain somatostatin. In experiment two, the degree to which basal forebrain neurons have axons that collateralize to innervate the interpeduncular nucleus and hippocampus was examined with retrograde fluorescence labeling methods. Labeled neurons projecting to both of these limbic structures were observed only occasionally. Comparison of the distribution of single labeled neurons innervating each of these structures revealed that within the region of origin, in the horizontal limb of the diagonal band, neurons innervating the interpeduncular nucleus tended to be located dorsally to those innervating the hippocampus. The results of these experiments are discussed in relation to their anatomical and functional implications toward a greater understanding of the basal forebrain and mesopontine cholinergic and non-cholinergic projection systems. / Medicine, Faculty of / Graduate

Both chronic psychosocial stress and chronic administration of corticosterone have been shown to alter serotonergic type 2A (5-HT2A) receptor activity. A non-invasive behavioural index of 5-HT2A receptor activity is the frequency of "wet dog shakes" (WDS) or serotonergic stereotypy. In addition to WDS, 5-HT2A receptors mediate effects on sexual behaviour in the rat, in particular, inhibition in the male and stimulation in the female. In the present series of experiments, the potential involvement of stress and corticosterone in the regulation of WDS and sexual behaviour in the male and female rat was investigated. In Experiments 1-4, chronic exposure to several different forms of psychosocial stress was found to facilitate female and inhibit male rat sexual behaviour while concurrently increasing the display of WDS in both sexes. In Experiment 5, nefazodone, an antidepressant with 5-HT2A antagonistic properties, blocked the effects of stress on WDS but not sexual behaviour in female rats. In Experiments 6-7, the corticosterone synthesis inhibitor, metyrapone, blocked the effects of stress on sexual proceptivity and WDS in female rats. Metyrapone blocked the effects of stress on WDS but not sexual behaviour in male rats. In Experiments 8-9, high doses of corticosterone administered chronically facilitated female and inhibited male rat sexual behaviour while concurrently increasing WDS in both sexes. In Experiments 10-11, the 5-HT2A antagonist ketanserin was found to completely attenuate the effects of corticosterone on sexual behaviour and WDS in both male and female rats. In Experiments 12-13, the acute administration of corticosterone was found to exert no effect on either sexual behaviour or WDS in male or female rats. The present results indicate that both chronic corticosterone treatment and exposure to chronic stress inhibit male and facilitate female sexual behaviour while concurrently increasing WDS behaviour. The stress-induced facilitation of WDS appears to be related to elevated corticosterone levels and is suggestive of increased 5-HT2A activity. Both corticosterone and stress exerted effects on sexual behaviour in the direction that would be predicted by increased 5-HT2A activity. While the effects of corticosterone on sexual behaviour appear to be mediated by 5-HT2A activity, the effects of stress on sexual behaviour do not appear to be related to either elevations in corticosterone levels or alterations in 5-HT2A activity. / Arts, Faculty of / Psychology, Department of / Graduate

Temmincks pangolins are the world’s most trafficked mammal. This animal is unique to Southern Africa, and just as rare are the conservationists who are working against all odds to save this species from extinction. While the incidence of poaching within South Africa is increasing, as is the value of a pangolin, the conservation workspace is rapidly becoming increasingly dangerous. In light of the above, one cannot help but be concerned for the well-being of the pangolin conservationists. Despite engaging in meaningful work, the conservationists are exposing themselves to prolonged stress that is likely to impact their well-being. The purpose of this study is to explore the well-being of Temmincks pangolin conservationists in terms of state and trait depression as well as burnout. Furthermore, the study aims to understand whether coping mechanisms or resilience mitigate the effect of the potential depression and burnout. Therefore, a sequential explanatory mixed-method design was adopted for this study. The quantitative data was gathered using the Maslach Burnout Inventory General Survey (MBI-GS), the State Trait Personality Inventory Form Y (STPI-Y) depression subscale, the Coping Orientations to Problems Experienced (COPE) questionnaire and the Predictive 6 Factor Resilience Scale (PR6). The qualitative data was collected utilising a semi-structured interview. Results indicated that the participants were currently experiencing both state and trait depression. Additionally, a third of the sample is at risk of developing burnout. In spite of this, the participants displayed the presence of goal focus, tenacity and collaborative spirit. These elements of resilience were shown to assist the conservationists to persist through adversity. The participants also showed the use of effective coping mechanisms, namely; accepting, planning and critically engaging with perceived stressors. These coping mechanisms were shown to enhance the presence of the resilience indicators. Thus, despite depression and burnout impacting negatively on their well-being, the participants are utilising coping mechanisms and resilience which enhances their well-being. Recommendations included a developmental workshop focusing on fostering effective coping mechanisms to build stronger resilience and ward off potential burnout and possibly ameliorate current depression experiences. / Dissertation (MA (Psychology))--University of Pretoria, 2020. / Psychology / MA (Psychology) / Unrestricted