Degree of Master of Science by research only: A dissertation submitted to the faculty of science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. Department of Physics Faculty of Science University of the Witwatersrand January 4, 2016 / Quasi-simultaneous observations of a flaring blazar source at multiple frequencies, offer an unprecedented view of the region surrounding a supermassive black hole during a large energy outburst. Blazars are active galaxies that host a super massive black hole releasing large amounts of energy through narrow jets of highly relativistic plasma located along the polar axes. Within these jets, electrons and protons move at relativistic speeds creating interactions that generate radio waves and gamma-rays that travel down the jet towards the observer. Based on the angle of inclination of the source towards the observer ( < 20◦), we can study relativistically boosted emission to peer into regions where high-energy particles (gamma-rays) are thought to be generated. Using high cadence monitoring campaigns, both the slow and fast variations in the source flux can be traced in detail revealing spatial and temporal information about the source state and activity. In this dissertation I studied the physics behind the variable behavior of the bright blazar PKS 1424-418, also known as J1427-4206. PKS 1424-418 is a Southern Hemisphere blazar that recently underwent a number of flaring events detected by FERMI-LAT. The study was specifically concerned with the behavior of PKS 1424-418 during the outburst/flaring events that occurred between 19 October 2012 and 9 October 2013. PKS 1424-418’s daily gamma-ray flux reached an average of 1.4 ± 0.2 x 10−6 ph cm−2 s−1 for E > 100 MeV, triggering radio follow up observations with the Hartebeesthoek Radio Astronomy Observatory 26 m radio telescope at 2.3-GHz, 4.8-GHz, 8.4-GHz and 12.2-GHz frequencies. The objective was to examine the nature of the relationship between the high-energy gamma rays detected by FERMI-LAT and the low-energy radio waves detected by the Hart26m radio telescope. In the study we investigated the relationship between the two energy regimes using Discrete cross-correlation functions to estimate the time-lags between two corresponding frequencies. We also studied the spectral index variation to establish the source behavior over the observing period at multiple epochs. A Lomb-Scargle periodicity search was also performed to investigate whether some periodic modulation was present in the gamma-ray data as it varied quite dramatically on shorter time-scales. Observations in gamma-rays and radio frequencies were done using the All-Sky mode and drift scan technique respectively at the different frequencies. Results indicated the existence of a strong correlation between the gamma-ray and radio data, with the gamma rays leading the radio. With each gamma-ray flaring event the radio spectra indicated some spectral hardening and the possibility of an 86 day gamma-ray period in the shorter term flares was also established in the study. This study however only shows the large scale relationship between time-series over the entire observing period. On smaller scales, each gamma-ray and radio flare is unique and as such requires individual analysis for each respective component. to successfully achieve this, more data is needed to confirm the individual radio flaring periods. Observations at VLBI scales are extremely useful in this kind of work and instrumental in studying the source structure behavior during flaring and will form part of the future work planned for studying blazar source variability.

A thesis submitted to the School of Physics, Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, June 2015. / Galaxy clusters are the largest virialised and most recently formed cosmic structures. Their study is therefore a powerful mechanism to probe the large scale properties of the universe. A full understanding of the non-thermal properties of galaxy clusters has not yet been achieved. In particular, the origin of radio halos in galaxy clusters is still a topic of debate today. Several models have been proposed to explain the origin of radio halos but all of these models present some problems either in reproducing observations or in predicting the values of their parameters. Recent observations of radio halos in clusters have shown that in some clusters the morphology of the radio emission appears to be more correlated with the distribution of galaxies than it is with the thermal gas. It has also been observed that while most clusters exhibit a correlation between the radio and X-ray luminosities, there are clear exceptions to this rule. Motivated by these observations, we propose a new theory to explain the origin of radio halos in clusters: that the radio emission observed in clusters is produced by electrons injected by different galaxies and di using in the intra cluster medium. In developing our theory, we study the diffusion of relativistic electrons in galaxies by obtaining a very general solution of the diffusion equation which describes the transport of cosmic rays. This solution allows us to study the spatial, spectral and temporal properties of relativistic electrons and their radio emission for a wide range of cosmic objects. We test this model by applying it to the radio galaxy M51 and reproduce its spatial and spectral properties. We also study the evolution of M51-like galaxies. The model is then applied to study radio halos in clusters of galaxies. We investigate how the properties of these radio halos change when the number and types of sources in a cluster are varied. We compare the results of this model with the observed radio map and density flux spectrum for several galaxy clusters, specifically the low-luminosity cluster CL1446+26 and other clusters with a range of luminosities. Our model provides a very promising explanation of the properties of radio halos in galaxies and clusters of galaxies. The observed properties like the morphology of radio maps in galaxy clusters, the ux spectrum and the correlation between radio and X-ray luminosities, can be reproduced by our model. This is done by considering the combination and evolution of galactic sources having radio properties similar to those of M51. Our model is simple and nevertheless very promising and therefore refining it can lead to a better understanding of the origin of radio halos.

A research report submitted to the Faculty of Science, in partial fulfilment of the requirements for the degree of Master of Science, University of the Witwatersrand, Johannesburg, 2015. / Pedagogical Content Knowledge (PCK) is a knowledge base for teaching that has been shown to be topic-specific. PCK in a particular science topic enables a teacher to pedagogically transform Content Knowledge (CK) to teach that topic. This ability to transform CK for teaching purposes is a version of PCK recognised as Topic-Specific Pedagogical Content Knowledge (TSPCK). TSPCK, like PCK, is not transferable, thus we cannot assume that good pedagogical transformations observed in one topic can be consequently observed in another. In addition it has been shown that the PCK knowledge base for teaching is tacit in nature. This means that most teachers with such a knowledge base are not aware of it explicitly, or how they develop it. The purpose of the study was to explore the mechanism which pre-service teachers used to apply learnt reasoning to transform CK in a new topic.

Extensive brackishwater aquaculture, which is a dominant land-based aquaculture system in Indonesia, has experienced variable success in most farming locations in the country due to poor understanding of spatial assessment of environmental factors and rudimentary site selection criteria. Despite tremendous potential, the application of GIS and remote sensing in spatial assessment has tended to focus on Boolean (Crisp) logic that is often unable to effectively handle the complexity and spatial variability of key environmental factors for the development of aquaculture. This study explored the possibility of integrating fuzzy logic techniques into GIS and remote sensing technology to generate more robust mapping protocols in aquaculture, compensating for the disadvantages of the Crisp method. Two models were developed in two different provinces in Indonesia to spatially assess soil and hydrological constraints on extensive brackishwater aquaculture. The soil assessment focussed on acid sulfate soils (ASS) and sandy-textured sediments in Aceh, and the hydrological study focused on investigating important wave parameters that influence the suitability of coastal areas for siting extensive pond units in South Sulawesi. The study showed that fuzzy-based classification methods, integrated into the image analysis, was highly effective in identifying existing and potential pond areas for extensive brackishwater aquaculture compared to the best result of the commonly used Crisp method. By addition of one or more key environmental variables of ASS into the fuzzy-classified existing and potential ponds areas, a very robust predictive tool to identify potential ponds areas affected by ASS in Kembang Tanjung, Aceh was developed. A more detailed assessment of ASS developed in this study also successfully highlighted the severity of sandy-soils and identified them as another key soil variable that has and will severely impact on pond productivity. The second model developed by the study enables fuzzy logic to be integrated into GIS to predict the possible areas impacted by moderate to high energy wave conditions and possible ways of minimising their direct and indirect impacts. The models developed in this study were shown to work well in both study sites and can be applied elsewhere. The mapping outputs are easy to interpret even by stakeholders with no prior training in map reading. Overall, the models have the potential to reduce planning errors and to improve decision making in aquaculture provided that quality data sources are used.

University of Macau / Faculty of Science and Technology / Department of Computer and Information Science

In 1993, the Asia-Pacific Economic Cooperation forum (APEC) held the first APEC Economic Leaders Meeting (AELM). Raising APEC interaction to the top track, the level of leaders, proved to be an effective and powerful dynamic; the AELM continues to meet annually and to shape APEC policy. The focus on the AELM as the source of vision and direction reinforces the pivotal importance of this political assemblage, reassures the populace that leaders do prevail and all is well: essential ingredients, according to Clifford Geertz, of political theater. The role of journalists, the contemporary scribes or critics, is to inform the audience of this political drama. The objective of this research is to demonstrate that real political value exists in the 'Staging of APEC' in terms of effective economic and political integration of benefit to broad regional interests. The findings draw on the results of a content analysis of news reports covering the first six years of the AELM (1993-1998). Formally, the AELM is an opportunity for regional political leaders to engage in regional policy formation outlined by the pillars of APEC (trade liberalization, facilitation and cooperation) guided by the principals of open regionalism and concerted unilateralism. Activity on the formal, or main stage, also flows to the small stage where leaders merge in a neutral venue. On this stage, leaders are free to examine distinctly non-economic, yet intersecting interests including domestic agendas, human rights and pluri-lateral security concerns. Together, these dual stages, neither one complete without the other, form the political theatre of APEC and provide the value added for the leaders and ultimately for the Asia – Pacific region.

Extensive brackishwater aquaculture, which is a dominant land-based aquaculture system in Indonesia, has experienced variable success in most farming locations in the country due to poor understanding of spatial assessment of environmental factors and rudimentary site selection criteria. Despite tremendous potential, the application of GIS and remote sensing in spatial assessment has tended to focus on Boolean (Crisp) logic that is often unable to effectively handle the complexity and spatial variability of key environmental factors for the development of aquaculture. This study explored the possibility of integrating fuzzy logic techniques into GIS and remote sensing technology to generate more robust mapping protocols in aquaculture, compensating for the disadvantages of the Crisp method. Two models were developed in two different provinces in Indonesia to spatially assess soil and hydrological constraints on extensive brackishwater aquaculture. The soil assessment focussed on acid sulfate soils (ASS) and sandy-textured sediments in Aceh, and the hydrological study focused on investigating important wave parameters that influence the suitability of coastal areas for siting extensive pond units in South Sulawesi. The study showed that fuzzy-based classification methods, integrated into the image analysis, was highly effective in identifying existing and potential pond areas for extensive brackishwater aquaculture compared to the best result of the commonly used Crisp method. By addition of one or more key environmental variables of ASS into the fuzzy-classified existing and potential ponds areas, a very robust predictive tool to identify potential ponds areas affected by ASS in Kembang Tanjung, Aceh was developed. A more detailed assessment of ASS developed in this study also successfully highlighted the severity of sandy-soils and identified them as another key soil variable that has and will severely impact on pond productivity. The second model developed by the study enables fuzzy logic to be integrated into GIS to predict the possible areas impacted by moderate to high energy wave conditions and possible ways of minimising their direct and indirect impacts. The models developed in this study were shown to work well in both study sites and can be applied elsewhere. The mapping outputs are easy to interpret even by stakeholders with no prior training in map reading. Overall, the models have the potential to reduce planning errors and to improve decision making in aquaculture provided that quality data sources are used.

Thesis (Ph. D.)--Columbia University, 1934. / Vita. Published also without thesis note. Bibliography: p. 367-386.

Thesis (Ph. D.)--New York University, 1930. / Published also without thesis note. Cover title: The technique of international conferences. Bibliography: p. 106-116.

edited by N. J. Grant and B. C. Giessen. Section I. / Includes bibliographical references and index.