MSc (Botany) / Department of Botany

The main objective of this study was the application and comparison of different assays in assessing toxicity of cyanobacterial samples, and also characterizing toxicity of the field samples. Therefore, toxicity of purified microcystin-LR (MC-LR) and cyanobacterial samples collected from the Hartbeespoort (HBP) Dam (winter and summer seasons of 2005/2006) and Kruger National Park (KNP) were investigated and compared using the ELISA, mouse bioassay, catfish primary hepatocytes (in vitro assay) and protein phosphatase inhibition (PPi) assays. During sampling in the summer season at the HBP Dam, the dam surface was covered with a thick-green layer of cyanobacterial scum and a foul smell coming from the water surface was always present. Only blue-green streaks of cyanobacteria covered the dam surface during the winter season. All HBP Dam samples (winter and summer samples) and KNP samples (Nhlanhanzwani Dam, Mpanama Dam and Sunset Dam) were dominated by Microcystis aeruginosa with the exception of Makhohlola Dam samples which were found to have no cyanobacteria. The World Health Organization (WHO) has proposed a guideline value for human use of 1.0 µg/L (0.001 mg/L) for MC-LR, the most common microcystin (MC) variant, in drinking water (WHO 1998), whereas 2 000 Microcystis cells/mL have been recommended as the limit of cyanobacteria in drinking water for animals (DWAF 1996). Cyanotoxin concentrations exceeding the prescribed guideline value were detected in all HBP Dam samples (ELISA results ranging between 3.67 to 86.08 mg/L; PPi results ranging between 2.99 to 54.90 mg/L) and KNP samples (ELISA results ranging between 0.1 to 49.41 mg/L; PPi results ranging between 0.006 to 10.95 mg/L) using both the ELISA and PPi assays. In the current study, a dose of about 175 µg/kg of purified MC-LR was demonstrated to be lethal in male CD-1 SPF mice. The HBP Dam summer samples and Nhlanganzwani Dam samples were the only cyanobacterial samples that resulted in death (acute toxicity) of mice. In order to be able to investigate further the in vivo effects of cyanotoxins, transmission electron microscopy (TEM) was used to complement results obtained from the in vivo assay. Ultrastructural changes of varying degree were observed in livers of mice exposed to both the HBP Dam winter and summer samples. Early stages of hepatocyte to hepatocyte disassociation, slight vesiculation of endoplasmic reticulum (ER) and swollen mitochondria were the most significant ultrastructural changes produced in mouse hepatocyte tissues by the HBP Dam winter samples. The most significant ultrastructural changes produced in mouse hepatocyte tissues by the HBP Dam summer samples were massive hepatic haemorrhage indicated by the appearance of erythrocytes between hepatocytes and the extensive vesiculation of ER. This is the first time that the African sharptooth catfish primary hepatocyte model has been used to assess the hepatotoxicity of purified MC-LR and cyanotoxin-containing water samples. In this study, the toxicity of cyanobacterial samples and purified MC-LR to cause hepatotoxicity in mice was confirmed in vitro using the catfish primary cell line. A comparison among the cyanobacterial samples using EC50 showed the following hepatotoxicity trend in the catfish primary cell line: HBP Dam summer samples > Nhlanganzwani Dam samples > HBP Dam winter samples > Mpanama Dam samples > Sunset Dam samples > Makhohlola Dam samples. The HBP Dam samples were the most hepatotoxic and Makhohlola Dam samples were the least hepatotoxic. The EC50 for purified MC-LR using the catfish primary hepatocytes was about 91 nM. A statistical comparison of the assays used in this study (i.e. ELISA, PPi, mouse test and cytotoxicity [catfish primary hepatocyte] assays) was performed based on the Kappa coefficient (K). An almost perfect agreement (K > 0.80) was observed between the mouse test and cytotoxicity assay; mouse test and ELISA; cytotoxicity assay and ELISA; and ELISA and PPi assay. In conclusion, field samples collected during the summer season were found to have very high levels of toxins and a higher degree of toxicity when compared to the winter samples. The cytotoxicity assay using African sharptooth catfish (Clarias gariepinus) primary hepatocytes has been shown for the first time to produce results similar to those observed when using the mouse bioassay in assessing cyanobacterial toxicity. Therefore, this primary cell line may be used as a potential alternative to the mouse assay in toxicity testing of cyanotoxins. Three KNP dams (Nhlanganzwani Dam, Mpanama Dam and Sunset Dam) investigated in this study were found to contain Microcystis aeruginosa. All four KNP dams (Nhlanganzwani Dam, Mpanama Dam, Makhohlola Dam and Sunset Dam) had cyanotoxin levels above the prescribed guideline value, which is of concern and warrants further investigations to the effects on wildlife in the park. Future studies will include use of High Performance Liquid Chromatography (HPLC) to investigate the toxin profile of the field samples in order to fully describe the different classes/or types of toxins present in the samples. More validation studies that could give a more comprehensive understanding about the sensitivity of the catfish primary cell line for microcystins will also be undertaken. / Dissertation (MSc (Paraclinical Studies))--University of Pretoria, 2007. / Paraclinical Sciences / unrestricted

This thesis explored different approaches of clustering residential data. The goal was to develop a model with applications in load forecasting contexts, specifically in situations where only a limited amount of residential data is available. Four different types of approaches were explored, one of which utilised not only data pertaining to the load profile but also data related to the residency. Effects of seasonal and weekly variations were studied to identify how the load profiles were affected by these parameters. In the end the developed clusters were evaluated using silhouette scores as well as using load forecasting models developed outside of the thesis.

No description available.

This study, drawing on the Progress in International Reading Literacy (PIRLS) Literacy 2016 learner achievement data, aimed to examine the relationship between teacher profiles in terms of teachers’ age, years of experience and formal qualification, teachers’ participation in formal and informal professional development activities and South African Grade 4 learners’ reading literacy achievement when controlling for the socio-economic status of the learners. To accommodate all the variables used in the study, a new conceptual framework was developed. This study was initiated as a result of the PIRLS Literacy 2016 results which revealed that South African Grade 4 learners achieved the lowest reading literacy scores out of the 6 participating countries. This study is a secondary analysis utilising standard multiple regression analysis of the PIRLS Literacy 2016 achievement data and the contextual data from the teacher and school questionnaires. The study’s results revealed that there is no statistically significant relationship between South African teachers’ participation in either formal or informal professional development and learners’ reading literacy achievement. Based on the literature however, the emphasis was placed on the educational significance of teachers’ participation in effective professional development activities. / Dissertation (MEd)--University of Pretoria 2020. / Science, Mathematics and Technology Education / MEd / Unrestricted

We present a. survey of high dispersion UV and optical spectra of Herbig Ae/Be (HAeBe) and related stars. We find accreting, circumstellar gas over the velocity range +100 to +400 km s-1, and absorption profiles similar to those seen toward β Pic, in 36% of the 33 HAeBe stars with IUE data as well as in 3 non-emission B stars. We also find evidence of accretion in 7 HAeBe stars with optical data only. Line profile variability appears ubiquitous. As a group, the stars with accreting gas signatures have higher ν sin i than the stars with outflowing material, and tend to exhibit large amplitude (≥ 1m) optical light variations. All of the program stars with polarimetric variations that are anti-correlated with the optical light, previously interpreted as the signature of a dust disk viewed close to equator-on, also show spectral signatures of accreting gas. These data imply that accretion activity in HAeBe stars is preferentially observed when the line of sight transits the circumstellar dust disk. Our data imply that the spectroscopic signatures of accreting circumstellar material seen in β Pic are not unique to that object, but instead are consistent with interpretation of β Pic as a comparatively young A star with its associated circumstellar disk.

Recombination line profile shapes are derived for ionized spherical stellar winds at radio wavelengths. It is assumed that the wind is optically thick owing to free-free opacity. Emission lines of arbitrary optical depth are obtained assuming that the free-free photosphere forms in the outer, constant expansion portion of the wind. Previous works have derived analytic results for isothermal winds when the line and continuum source functions are equal. Here, semi-analytic results are derived for unequal source functions to reveal that line shapes can be asymmetric about line center. A parameter study is presented and applications discussed.

Six geomorphic study reaches were established in 2002 along a forested mountain stream (gradients range from 0.02 to 0.05) on Cal Poly's Swanton Pacific Ranch in Santa Cruz County, California. These study reaches are a component of paired and nested watershed studies in the approximately 500 hectare Little Creek watershed. The overall goal of this study was to monitor water quality and channel conditions before, during, and after a selective harvest of redwood. A selective harvest occurred in the North Fork of Little Creek in Summer 2008. In August 2009, approximately 90% of the Little Creek Watershed was burned in the Lockheed Fire. Channel change was evaluated by measuring ground profiles using traditional survey methods. Cross section and longitudinal profiles are surveyed annually every summer in the six study reaches. Change is assessed through evaluation of cross sections and longitudinal profiles, analysis of bed elevation and cross-sectional area change data, and analysis of residual pool characteristics and longitudinal profile variability. Changes in the channel during this time have been relatively small and are typically associated with movement or introduction of coarse woody debris to the stream channel. However, during the study period no large stream flow events occurred (return interval at the closest USGS gauging station does not exceed 5 years). Historically, large debris flow events have occurred in this watershed, with well documented events in 1955 and 1998. The survey data is an important tool for understanding change detection in channel characteristics before and after harvesting, and following fire disturbance.

Introduction : l'adolescence est une phase de remaniements intenses, et ce de manière inter ou intrapersonnelle, de l'image qu'on a de soi et de son corps, au fantasme de l'adulte que l'on espère devenir. L'adolescente cherche sa place, dans sa famille en tant que « plus une enfant mais pas encore une adulte », dans ses relations avec ses pairs, et avec l'Autre. Mais l'anorexie bloque ces processus de changement, en enfermant la jeune fille dans un corps qui n'est plus tout à fait enfant, mais surtout pas femme. La problématique de l'affect est centrale dans ces troubles. Quand certaines sont dans un trop-plein d'émotions non-régulables, d'autres sont dans le refus du ressenti. Mais est-ce propre à l'anorexie, l'état dépressif ou une résultante de cette période de crise qu'est l'adolescence ? Le concept récent d'intelligence et de compétence émotionnelle aborde et modélise toutes les capacités et les difficultés émotionnelles qu'une personne peut avoir, et permet de percevoir de manière plus globale les différentes facettes de la structure affective d'un individu. Objectifs : nous voulons isoler les difficultés émotionnelles chez ces patientes en les comparant à des adolescentes sans troubles du comportement alimentaire mais présentant une dépression, et à des adolescentes contrôles, afin d'établir quels types de profils émotionnels existent dans l'anorexie mentale à l'adolescence. Méthodologie : 40 patientes présentant une anorexie restrictive ou purgative sont rencontrées lors de leurs suivis en hospitalisation ou en consultations au sein de l'Institut Mutualiste Montsouris, ainsi que 18 adolescentes dépressives, et 39 adolescentes contrôles. Afin d'évaluer leurs compétences émotionnelles, les sujets ont répondu à une batterie de questionnaires ainsi qu'une expérience de Reconnaissance Emotionnelle Faciale. Les données ont été analysées par des outils statistiques de comparaison et de Classification Ascendante Hiérarchique. Résultats : on retrouve des problématiques de manque de confiance en soi et de failles narcissiques à l'adolescence, communes à tous les groupes, néanmoins les patientes présentant une anorexie ont davantage de difficulté ayant trait à l'identification des émotions, leur régulation - en trop ou pas assez- et trois profils émotionnels ressortent de nos analyses. Un premier présentant une forte labilité affective, chez qui l'Affect est subi sans possibilité de modulation et de régulation adaptée, un second dans l'hyper-contrôle affectif, et un troisième intermédiaire, dans lequel se juxtaposent des traits alexithymiques et une appétence reconnue mais crainte pour une vie affective. Conclusion : l'évaluation des compétences émotionnelles d'un patient, avant de décider de la nature de la prise en charge à proposer, nous semble importante à systématiser. De plus, dans les recherches portant sur l'anorexie mentale, la constitution des groupes devrait se faire en fonction du profil émotionnel présenté plutôt que par l'opposition anorexie restrictive vs. anorexie purgative. / Introduction: Adolescence is a period of intense reorganization, in and out, intrapersonally and interpersonally, of our self-image and of our body, and to the fantasy of the adult that we hope to become. The teenage girl looks for her place: in her family, as " more than a child but no yet an adult ", in her relations with his(her) peers, and with the 'special Other'. But Anorexia Nervosa blocks these processes of change by locking the girl into a body which is not completely one of a healthy child, but especially not one of a woman and a potential mother. The problematic of the Affect is central to these disorders. While some are experiencing one too many feelings that they cannot regulate, others are in denial or refusal of an affective experience. But is it specific to Anorexia Nervosa, the depressive state in which some of the patients are in, or is it a result of this period of crisis that is adolescence? Furthermore, the recent concept of emotional intelligence and ability model approaches all the capacities and the emotional difficulties which can be met in an individual, and allows one to perceive and collect in a more global way the various facets of the emotional structure of an individual. Objectives: We aim to isolate the emotional difficulties in place in these patients by comparing them with both teenagers without eating disorders but presenting with depression, as well as with healthy teenagers, to establish which types of emotional profiles exist in anorexia nervosa in adolescence. Methodology: 40 patients presenting a restrictive anorexia or binge and purge type are met during their hospitalization or in consultations within the Mutualist Institute Montsouris, as well as 18 depressive teenagers, and 39 teenagers without any psychiatric disorder. To assess their emotional abilities, subjects were asked to undergo a series of questionnaires as well as an experience of Facial Emotional Recognition. The data was analysed by statistical tools of comparison and Ascendant Hierarchical Clustering. Results: We found problems of lack of self-confidence and narcissistic wounds in adolescents, common to all the groups, nevertheless the patients presenting with anorexia nervosa had more difficulties with the identification of emotions, their regulation - over or under regulated, and three emotional profiles stood out from our analyses. The first one presented a strong emotional lability, for which the Affect is endured without any possibility of modulation or adapted regulation, the second presented an emotional hyper-control, and the third, which is more intermediate, presented juxtaposed alexithymia traits and a recognized and ambivalent desire for an emotional life. Conclusion: Assessing a patient's emotional competencies before deciding on a therapeutic course should become a standard procedure. And researchers should divide anorexic populations in their protocols depending on their emotional profile rather than their anorexic sub-type (restrictive or binge/purge).

Magnesium deficiency in rats is known to precipitate audiogenic seizures. An unknown mineral factor in a diet mixture was found to substantially reduce the seizure occurence in magnesium deficient vii animals. This was corrected when the same mineral mixture was remade. Subsequently the faulty mineral mixture was discarded. This research .. as aimed at determining the mineral factor responsible for the observed changes in seizure occurence, and also aimed at investigating the relationships of serum calcium, magnesium and phosphorus concentrations to seizure susceptibility. Treatments to change the serum concentrations of these minerals included dietary manipulation, subcutaneous injection of calcitonin, of 1 ,25-dihydroxycholecalciferol, of calcium and of phosphorus. Animals fed magnesium deficient, low phosphorus diet and magnesium deficient animals fasted over-night were found to have significantly lower audiogenic seizure susceptibility than all other magnesium deficient animals regardless of treatment. Reduced audiogenic seizure susceptibility was not produced by any of the injections. The reduction in seizure with the magnesium deficient, low phosphorus diet indicates that phosphorus is an important factor in the mechanism of audiogenic seizuring in magnesium deficient rats.