Our current knowledge of the Solar System, with a particular emphasis on the systems of interplanetary objects, is reviewed, and the theory of meteors and the reflection of radio waves from meteoric ionization is then discussed. A description of the meteor radar is given and a method of calibrating the antenna beam is developed. The main project comprises two parts: (a) A general survey of the radar echorate for 20 major and minor meteor streams and the sporadic meteor background, conducted from Grahamstown over the period 1986 April to 1988 January, is described. Definite shower activity was observed for all of the major and some of the minor showers. (b) Based on a scheme proposed by previous workers (Morton & Jones), a method of recovering meteor radiant distributions from the distribution of echo directions is developed. We devise a technique of compensating for possible distortions of the resulting radiant maps, which may arise due to the arisotropic antenna beam. This involves a system of echo-weighting. Radiant maps which showed considerably less distortion than those of the above workers were obtained without the weighting procedure. It is concluded that, although the method in its present form introduces spurious features into the maps, the principle is sound and should eventually be refined to produce the desired compensation

No description available.

No / The right hemisphere has often been viewed as having a dominant role in the processing of emotional information. Other evidence indicates that both hemispheres process emotional information but their involvement is valence specific, with the right hemisphere dealing with negative emotions and the left hemisphere preferentially processing positive emotions. This has been found under both restricted (Reuter-Lorenz & Davidson, 1981) and free viewing conditions (Jansari, Tranel, & Adolphs, 2000). It remains unclear whether the valence-specific laterality effect is also sex specific or is influenced by the handedness of participants. To explore this issue we repeated Jansari et al.'s free-viewing laterality task with 78 participants. We found a valence-specific laterality effect in women but not men, with women discriminating negative emotional expressions more accurately when the face was presented on the left-hand side and discriminating positive emotions more accurately when those faces were presented on the right-hand side. These results indicate that under free viewing conditions women are more lateralised for the processing of facial emotion than are men. Handedness did not affect the lateralised processing of facial emotion. Finally, participants demonstrated a response bias on control trials, where facial emotion did not differ between the faces. Participants selected the left-hand side more frequently when they believed the expression was negative and the right-hand side more frequently when they believed the expression was positive. This response bias can cause a spurious valence-specific laterality effect which might have contributed to the conflicting findings within the literature.

This study proposed an experimental test of theoretical models related to emotion and space representation in the brain. Previous research has established that emotion is represented, processed, expressed, and regulated largely by the right hemisphere. Furthermore, there is evidence from experimental paradigms and clinical case reports to suggest that the same hemisphere plays a dominant role in the processing of external space. A conceptual difficulty of clinical and neural network overlap arises when right hemisphere disorders of emotion are compared with those of spatial representation. The current experiment tested some of these hypotheses about emotion regulation and spatial representation in the right hemisphere using nonclinical subjects under a cortical stress paradigm designed to mimic the conditions of cortical duress. An additional goal was an extension of a previous study that examined emotional influence on spatial orientation. Results did not support our initial hypotheses. Subsequent analyses did provide some evidentiary support for some theories related to emotion and brain function. Additionally, patterns of subject performance were observed that support traditionally held theories of differential hemispheric function with regard to emotion and spatial behavior. These findings are discussed within the context of theories of emotion, spatial function, and disorders secondary to right hemisphere damage. / Doctor of Philosophy / This is a study examining the role of emotion and stress on the allocation of attention in the individual’s external environment. Further examined was the role that brain systems involved in attention, emotion, and spatial representation and the correlation with brain damage and syndromes that result in disruption to these systems. Conceptual difficulties regarding overlapping brain areas that contribute to different functions serve as the foundation for understanding both how these systems work and the behavioral manifestations of their dysfunction. Finally, further elucidating the role of these neural systems in contributing to self-awareness, emotion regulation, and the representation of external space was the ultimate objective of this study.

Please read the Summary in the section 00front of this document / Thesis (PhD)--University of Pretoria, 2005. / Genetics / Unrestricted

The temporary slowdown in large-scale surface warming during the early 2000s has been attributed to both external and internal sources of climate variability. Using semiempirical estimates of the internal low-frequency variability component in Northern Hemisphere, Atlantic, and Pacific surface temperatures in concert with statistical hindcast experiments, we investigate whether the slowdown and its recent recovery were predictable. We conclude that the internal variability of the North Pacific, which played a critical role in the slowdown, does not appear to have been predictable using statistical forecast methods. An additional minor contribution from the North Atlantic, by contrast, appears to exhibit some predictability. While our analyses focus on combining semiempirical estimates of internal climatic variability with statistical hindcast experiments, possible implications for initialized model predictions are also discussed.

No description available.

Despite the long time since the introduction and spread of pine plantations in southern hemisphere countries there has been no study of the suitability of this exotic and novel type of vegetation on the native avifauna. This thesis aims to add understanding of this habitat replacement and its effects on the forest bird community. This research included a series of studies to assess the quality of mature pine plantations for the forest avifauna in comparison to what is in native forests. The first two studies determine the effects on the forest bird community of the fragmentation and replacement of native forest in a gradient of substitution. The results showed a direct relationship between level of substitution and loss of functional diversity, and that fragmentation predicts the bird assemblage in pine stands. The next two studies used data from an intensive ringing season to assess differences in the condition of populations inhabiting each habitat. Birds, in general, were found in better condition in native fragments than in pine plantations. Moreover, a despotic distribution was determined for a migrant species and a gradient in habitat quality was found in relation to proximity to native forest. The next two studies used information from a nest-box survey set in a gradient of sites with substitution of native forest. The results showed that the type of forest cover and their proportion in the landscape may affect the breeding performance of some species. Finally, in the last study I evaluated the foraging niche of bird species in each habitat. Compared with native forest, niche breath reduced while the niche overlap increased in pine plantations for most species. The results suggest that pine plantations are poor quality habitat for the bird community and that the substitution of native forests increases selective pressure.

Stroke is the leading cause of serious, long-term disability and nearly half of older stroke survivors experience moderate to severe disability. A common impairment following stroke is impaired discourse production. Functional outcome studies have proposed that the recovery of discourse abilities is critical to achieving a good quality of life. Communication impairments often persist into the chronic stages of recovery and can cause individuals to withdraw from social situations. Discourse production deficits may not be apparent in basic communication interactions, but become more obvious during complex conversations following non-aphasic brain injury (NABI) or right hemisphere stroke (RHD). The purpose of this three-part dissertation was to examine discourse production deficits following NABI and the current practices of speech-language pathologists in the assessment and treatment of discourse deficits. The first study examined the macrolinguistic processes of discourse, which included local coherence, global coherence and cohesion, following NABI. Ten individuals with NABI and 10 heathy controls, closely matched for age, gender, and education, provided a narrative recount of an event. Discourse samples were analyzed for local coherence, global coherence, and cohesion. Results indicated that individuals with NABI demonstrated impaired global coherence compared to healthy controls with relatively intact local coherence and cohesion. Although global coherence deficits were identified in the discourse of individuals with NABI, empirical evidence suggests that speech-language pathologists do not routinely assess or treat discourse production deficits. The second study explored the current practices of speech-language pathologists in the assessment and treatment of individuals with NABI with a specific focus on discourse production deficits using a phenomenological approach. Nine speech-language pathologists participated in semi-structured 1:1 interviews. Results indicated that speech-language pathologists do not routinely assess and treat discourse production deficits due to competing internal values and external or environmental demands. However, speech-language pathologists reported that discourse deficits are present following NABI and are characterized by impaired topic maintenance or global coherence. Participants reported that they were routinely assessing and treating the underlying cognitive process of attention in hopes that it would generalize to improved topic maintenance or global coherence. However, little is known about the relationship between selective attention and global coherence. The third study examined the maintenance of global coherence across discourse tasks and explored the relationship between selective attention and global coherence. Eleven participants with non-aphasic brain injury secondary to right hemisphere stroke participated in the study. Participants provided discourse samples in response to five discourse tasks in a single-task and dual-task condition. Additionally, participants completed the Stroop test to examine selective attention abilities. Results indicated that mean global coherence scores differed across discourse tasks, and that mean global coherence scores for stories was significantly higher than for simple recount and single picture description tasks. To examine the relationship between selective attention and global coherence, mean global coherence scores in the single-task and dual-task condition were compared. Mean global coherence scores were lower in the dual-task condition for all five discourse tasks. Mean global coherence scores for the complex recount task were significantly lower in the dual-task condition. This suggests that the maintenance of global coherence is influenced by attention abilities. There was no significant correlation between performance on the Stroop task and the maintenance of global coherence for any of the five discourse tasks.

Regions that have experienced recent successive cold winters such as the Northeast of North America and Siberia have endured critical social and economic impacts from anomalous low temperatures in recent years, despite warming global temperatures. It is well known that the Tropospheric Polar Vortex (TPV), or jet stream, is a primary influence on many mid-latitude winter weather patterns. However, the strong circumpolar westerlies that maximize at around 60° latitude just above the tropopause, known as the Stratospheric Polar Vortex (SPV), can affect tropospheric circulation and thus winter weather in the Northern Hemisphere. Strong upward propagating waves can affect the geographic extent and strength of the SPV resulting in a weakened polar vortex state, which can in turn bring persistent weather events to the mid-latitudes. Here, an index of SPV spatiotemporal variability is presented using observation based analysis of zonal wind and geopotential height to show changes in SPV behavior at a seasonal scale from 1950-2018. Utilizing the CMIP5 suite of global climate models, historical and projected simulations of the SPV's climatological extent and strength are analyzed from 1915 to the end of this century, taking into account models with enhanced stratospheric representation. Simulated results are largely consistent with trends in the observational data, which suggest continued increases in average SPV size throughout this century. If future SPV disturbances increase in frequency, there could be negative impacts in ecosystem and agricultural health, infrastructure damage, and to human safety. A more advanced understanding of SPV trends and anomalous events could improve forecasts of cold air outbreaks (CAOs) and severe or persistent winter weather.