Globular clusters are extreme stellar populations. They have the highest stellar density, and host both the oldest and most metal-poor stellar populations in the Galaxy. Their densities make them excellent testbeds for stellar dynamics, while the properties of their stars allows us to test our understanding of old and metal-poor stellar evolution. This thesis is comprised of three projects studying the two nearest globular clusters, NGC 6397 and Messier 4. By examining high-quality HST photometry of NGC 6397, we have constrained the binary fraction in both the central regions, and beyond the half-light radius. We find a binary fraction of ~0.05 in the core and ~0.015 in the outskirts. In the context of recent N-body simulations by Hurley et al., we interpret the observed binary fraction in the outer field as the primordial binary fraction. This value is lower than typically assumed, and has implications for cluster dynamics and N-body modeling. We report the discovery that young white dwarfs are dynamically hotter than their progenitors. Using the same photometry as mentioned above, and archival HST photometry of Messier 4, we have found that young white dwarfs have an extended radial distribution, and therefore a higher velocity dispersion, compared with older white dwarfs and their progenitors. This implies the existence of a ``natal kick''. Implications for cluster dynamics and stellar evolution are discussed. Finally, we present the spectra of 23 white dwarfs in Messier 4 obtained with the Keck/LRIS and Gemini/GMOS spectrographs. We find that all white dwarfs are of type DA. Assuming the same DA/DB ratio as is observed in the field, the chance of finding no DBs in our sample due to statistical fluctuations is 0.006. This suggests DB formation is suppressed in the cluster environment. Furthermore, we constrain the mass of these white dwarfs by fitting models to the spectral lines. Our best estimate of the masses of the white dwarfs currently forming in Messier 4 is 0.51+/-0.02 M_sun.This extends the empirical constraint on the initial-final mass relation over the entire range of initial masses that could have formed white dwarfs in a Hubble time. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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Classification schemes are embedded into everyday life and people often expect that each category is fixed and stands alone from one another (Bowker & Star, 2000). In terms of gender, this is evident when people focus on gender as either male or female. With the increasing presence of people who are openly transgendered in the workplace (Taranowski, 2008), people’s expectations about gender as something ‘that just is’ are questioned. There is an emerging research literature focusing on people who transition in their work environments, but comparatively little on their coworkers. This research focuses on the experiences of the coworkers’ to examine how they interpret the meaning of gender after their colleague transitioned from being a “man” to being a “woman”. By analyzing and interpreting people’s behaviours in the context of a workplace where an individual reconstructs what it means to embody a specific gender identity, the feelings and behaviours that arise when expectations about gender are contradicted can be examined.

In this work, the phase behavior of binary systems comprising nitrogen and a noble element (nitrogen + argon and nitrogen + krypton) was studied at high density in the condensed state. Following the work of Lotz et al.[2001], the main goal of this work was to further investigate the pressure-concentration phase diagram as well as to look for the possible formation of van der Waals compounds at elevated pressures and room temperature and study their physical properties, using both vibrational spectroscopy and X-ray diffraction. The observed phases, formed by single atoms and/or simple molecules in the binary systems were solved and modeled for their corresponding crystalline structures. From experimental results, lattice parameters for all crystalline structures and phase transitions, if detected, have been observed to shift with respect to that of the pure substances. The analyses and characterization of these binary systems are discussed in detail.

A vertical-style data structure and operations on data in that structure are explored and tested in the domain of sliding window average algorithms for geographical information systems (GIS) data. The approach allows working with data of arbitrary precision, which is centrally important for very large GIS data sets. The novel data structure can be constructed from existing multi-channel image data, and data in the structure can be converted back to image data. While in the new structure, operations such as addition, division, and bit-level shifting can be performed in a parallelized manner. It is shown that the computation of averages for sliding windows on this data structure can be performed faster than using traditional computation techniques, and the approach scales to larger sliding window sizes.

My dissertation is an investigation into the basic Physics of phase separation fronts. Such phase-separation fronts occur in many practical applications, like the formation of immersion precipitation membranes, Temperature induced phase-separation of polymeric blends, or the formation of steel. Despite the fact that these phenomena are ubiquitous no generally acceptable theory of phase-separation front exists. I believe the reason lies in the complexity of many of these material systems where a large number of physical effects (like phase-separation, crystallization, hydrodynamics, etc) cooperate to generate these structures. As a Physicist, I was driven to develop an understanding of these systems, and we choose to start our investigation with the simplest system that would incorporate a phase-separation front. So we initially limited our study to systems with a purely diffusive dynamics. The phase-separation front is induced by a control-parameter front that is a simple step function advancing with a prescribed velocity. We investigated these systems numerically using a lattice Boltzmann method and also investigated them analytically as much as possible. Starting from a one-dimensional front moving with a constant velocity we then extended the complexity of the systems by increasing the number of dimensions, examining a variable front velocity, and finally by including hydrodynamics.

There has been a growing interest in addiction research on what role identity has to play in terms of recovery from drug addiction. One field of study that has gained traction in this area is the social identity approach, which argues that those in recovery tend to go from an ‘addict identity’ towards a ‘recovery identity’ when enrolled in treatment. This has been criticized by critical addiction studies, who argue that this notion is fueling an already established set of binary oppositions such as normality/abnormality, health/sickness etc., said to permeate addiction discourse. They argue that identity works to restrain the lives of those in recovery, and that these binary oppositions are problematic and both stigmatizes and pathologizes former drug users to mere products of recovery. The present thesis therefore interrogates these notions further by exploring the experiences of individuals enrolled in twelve step recovery, to see how identity formation and binary assumptions are experienced by former addicts themselves. The thesis employs a qualitative approach, and data were collected through 10 semi-structured interviews with active members of Narcotics Anonymous during March and April 2021. By applying actor network theory (ANT), the analysis of the study suggests that former addicts tend to present various identity-claims besides those only tied to recovery practices. Also, enrolling in twelve step recovery and identifying as a recovering addict seemed to enrich, rather than restrain their lives. Although binary assumptions and a struggle for normality seemed a burden in active substance abuse, it is suggested to be a necessary feature of recovery in terms of providing a framework for life. Thus, the analysis suggests that recovery might be a more fluid process than these respective fields tend to assume, and that binary assumptions are perhaps a necessity in terms of staying abstinent. / Det finns ett växande intresse inom beroendeforskning gällande identitetens roll i tillfrisknande från drogmissbruk. Ett forskningsfält som belyser detta är det gällande social identitet, som hävdar att de i tillfrisknande tenderar att gå från en ’beroendeidentitet’ till en ’tillfrisknandeidentitet’ i behandling. Samtidigt kritiseras detta av teoretiker från kritiska beroendestudier, som argumenterar för att denna föreställning ger stöd åt en redan etablerad uppfattning om binära motsättningar gällande normalitet/abnormitet, hälsa/sjukdom osv., som fått fäste inom beroendediskursen. De hävdar att identitet verkar genom att begränsa livet för individer i behandling, och att dessa binära motsättningar är problematiska då de bidrar till att stigmatisera och patologisera missbrukare till att bli produkter av sin behandling. Syftet med detta arbete är därför att undersöka dessa föreställningar genom att granska erfarenheter av individer som är aktiva inom tolvstegsbehandling, för att se hur identitetsformering och binära föreställningar upplevs av före detta missbrukare själva. Detta arbete använder sig av en kvalitativ ansats, och insamlandet av data skedde genom 10 semi-strukturerade intervjuer med aktiva medlemmar i Anonyma Narkomaner i Mars och April 2021. På arbetets resultat applicerades actor network theory (ANT), och analysen indikerar att före detta missbrukare tenderar att identifiera sig med diverse andra praktiker än de endast kopplade till behandling. Analysen visar även att identifikation med tolvstegsbehandling tenderade att öppna upp och berika livet för de i tillfrisknande, snarare än att begränsa det. Även om binära uppfattningar och en kamp för normalitet tenderade att vara en börda för individer i aktivt missbruk, så verkar det vara en nödvändig egenskap av tillfrisknandet genom att förse dessa med ett ramverk för hur de kan leva sina liv. Sammanfattningsvis visar studien att identitet i tillfrisknande verkar vara en mer rörlig och icke-fixerad process än vad dessa fält hävdar, och att binära uppfattningar är en nödvändighet för att bibehålla en fortsatt nykterhet.

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This dissertation presents an analysis of the angle modulated particle swarm optimisation (AMPSO) algorithm. AMPSO is a technique that enables one to solve binary optimisation problems with particle swarm optimisation (PSO), without any modifications to the PSO algorithm. While AMPSO has been successfully applied to a range of optimisation problems, there is little to no understanding of how and why the algorithm might fail. The work presented here includes in-depth theoretical and emprical analyses of the AMPSO algorithm in an attempt to understand it better. Where problems are identified, they are supported by theoretical and/or empirical evidence. Furthermore, suggestions are made as to how the identified issues could be overcome. In particular, the generating function is identified as the main cause for concern. The generating function in AMPSO is responsible for generating binary solutions. However, it is shown that the increasing frequency of the generating function hinders the algorithm’s ability to effectively exploit the search space. The problem is addressed by introducing methods to construct different generating functions, and to quantify the quality of arbitrary generating functions. In addition to this, a number of other problems are identified and addressed in various ways. The work concludes with an empirical analysis that aims to identify which of the various suggestions made throughout this dissertatioin hold substantial promise for further research. / Dissertation (MSc)--University of Pretoria, 2017. / Computer Science / MSc / Unrestricted

MSCAGR / Department of Agricultural Economics and Agribusiness / The study was conducted in the Mutale Local Municipality, Vhembe District of South Africa on a proportionally randomly selected sample of 153 smallholder farmers after clustering them into agricultural zones and commodity groupings (vegetables under irrigation, dryland maize and citrus fruit farming). Data were collected through a structured qualitative and quantitative questionnaire that was administered face-to-face to respondents and captured into the SPSS Version 24 computer program. The same program was used to analyse data through cross tabulations and logistic regression modelling. In particular, the study focussed on the impact of socio-economic characteristics, challenges that farmers face and views of extension officers on transforming subsistence farmers towards commercialization. The most critical findings of the study were dominance of women, lower youth participation, poor training and educational achievements, non-membership to agricultural organizations, low income levels and dependence on social grants and lack of credit as factors that could impact on farmers’ transformation process. Farmers’ challenges that could impact on transformation were identified as lack of production inputs, water, access to market and supportive infrastructure such as mechanization. However, the views of extension officers regarding transformation centred mostly around insufficient land holdings, climate change and financial support. In contrast to farmers, extension officers viewed market access as a minor challenge. The study recommended for development of strategies that could increase youth participation in farming such as start-up credit, reduction of dependence on social grants by adopting strategies that could increase productivity and thus income, exposure to funding opportunities through training and increased involvement of institutions of higher learning into smallholder farming activities.