Faculty of Engineering and the Built Environment; School of Electrical and Information Engineering; MSC Dissertation / In the recent past the Eskom network operated out-of-step at three occasions. Eskom questions whether the out-of-step relays responded as they should have. This is based on the fact that not all the out-of-step relays operated during these events. This dissertation shows that shunts can make the impedance locus behave nonclassically to the extent that the present practices Eskom uses for out-of-step relaying become inappropriate for application at certain busbars of the network. This is illustrated by showing that when the characteristic of the relay at Hydra, situated on the Mpumalanga side of Hydra, is set using the classical approach, the mentioned relay will not detect swings that have their electrical centre south of Hydra. A modified two generator model is used to show the effect shunts have. The phrase “improved two generator model” refers to this model. The improved two generator model is derived to represent the section of the Eskom network that links Mpumalanga to the Western Cape.

The thesis addresses the influence of compressible effects on the stability of deflagration waves. Due to the quasi-isobaric nature of slow flames, compressible effects in laminar flames are usually neglected. Nevertheless, turbulent deflagrations may propagate at substantially higher speeds, suggesting that compressible effects may play a role in their dynamics. In the present thesis, the stability of diffusion-dominated high-speed deflagrations is addressed. The deflagration is studied in the thickened regime, hence addressing the long wavelength limit of these deflagrations. The deflagrations are modelled by the compressible reactive Navier-Stokes equations with a single-step Arrhenius reaction model. The 2D stability of the steady traveling-wave solution is studied by direct simulation. It is found that, as the flame compressibility becomes significant, not only does the growth rates of the cellular profile of the deflagration waves increase, but the traditional correlation of the burning velocity and the flame surface area become far less strong. Significant compression regions form in front of the nonlinear flames. These compression regions have been found to increase the growth rates by increasing the temperature of the unburned gas in front of the flames, as well as convecting the flame forward. The results show that the flame propagation velocity in references to the unburned gas was significantly faster than the burning velocity. The vorticity was given consideration, as the compressibility of flame increase one can expect the baroclinic source to be of greater significance. The vorticity was show to, in effect, increase as compressibility increases while unexpectedly having a stabilizing direction of rotation on the cellular structure of the flames.

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Passwords are the dominant form of authentication on the web today. However,many users choose weak passwords and reuse the same password on multiple sites, thus increasing their vulnerability to having their credentials leaked or stolen. Two-factor authentication strengthens existing password authentication schemes against impersonation attacks and makes it more difficult for attackers to reuse stolen credentials on other websites. Despite the added security benefits of two-factor authentication, there are still many open questions about its usability. Many two-factor authentication systems in widespread usage today have not yet been subjected to adequate usability testing. Previous comparative studies have demonstrated significant differences in usability between various single-factor authentication systems.The main contributions of this work are as follows. First, we developed a novel user behavior model that describes four phases of interaction between a user and an authentication system. This model is designed to inform the design of future usability studies and will enable researchers and those implementing authentication systems to have a more nuanced understanding of authentication system usability. Second, we conducted a comparative usability study of some of the most common two-factor authentication systems. In contrast to previous authentication usability studies, we had participants use the system for a period of two weeks and collected both timing data and SUS metrics on the systems under test. From these studies, we make several conclusions about the state of usability and acceptance of two-factor authentication, finding that many users want more security for their sensitive online accounts and are open to using multiple forms of two-factor authentication. We also suggest that security researchers draw upon risk communication theory to better help users make informed security decisions.

This research project is intended to assist with the identification of relapse factors for alcoholics who have relapsed after their twelve‑step program. It is beneficial to understand relapse factors for alcoholics in order to provide effective treatment plans, services, and goals that will assist in attaining sobriety from alcohol. The research study used a qualitative approach; the data was collected through interviews from participants at the Cedar House agency in Bloomington, CA. The data was collected and then analyzed for possible themes of relapse factors. Themes that developed from interviews conducted with alcoholics that had relapsed after their twelve‑step programs were: commitment to therapy, unemployment, availability of healthy support, shame and guilt in seeking support, loneliness, and lack of support from family/peers and community. There are limitations to this study which, include a small sample size and interviews were held at only one agency that incorporated the twelve‑step process. Future studies should be implemented to confirm the results of this study.

The introduction of a Thomistic framework to contemporary models of addiction provides new insight that may prove useful in efforts toward therapy and understanding. Aquinas's conception of the human soul and its proper functioning contrasts with the suggested disordered functioning of the addict's soul in such a way that this may prove useful for addicts attempting to interpret their physical, psychological, and moral feelings or intuitions. This framework can then be related to the common contemporary addiction therapy found in Alcoholics Anonymous and other Twelve Step programs in order to provide a greater understanding of what psychological and moral processes may be at work within the addict with the hope that greater understanding will lead to more effective therapy.

This thesis is an investigation into ways of seeing 12 Step fellowships. The latter provide a popular but controversial means of recovery from various addictive behaviours. The conceptual basis of 12 Step fellowships is the idea that addictions are an illness or disease, and this idea has become the focus of the negative critiques of 12 Step fellowships. Concepts of illness and disease are closely related to concepts of personhood. What 12 Step discourses construct as 'illness' can also be understood as a condition characterised by failure of human capacities for agency, choice, and responsibility. How we understand 12 Step discourses of addiction, illness, and recovery will depend greatly upon the concepts of personhood, illness, and knowledge that inform our view. In order to investigate the concepts that make diverging views of 12 Step fellowships possible, this study develops post-Enlightenment concepts of personhood, illness and knowledge. I use these concepts as a lens with which to examine the negative critiques, and to provide a more positive reading of 12 Step fellowships and illness concepts. In doing so, this thesis aims to show, first, that a positive view that can articulate the value of 12 Step fellowships to 12 Step members is possible, and second, that 12 Step fellowship discourses are philosophically interesting and challenge modern western notions of the self and its capacities. The thesis has six chapters. Chapter One presents an overview of the study, and introduces the basic concepts and practices of 12 Step fellowships. Chapter Two presents an epistemology called perspectivism which provides my research methodology as well as a means of analysing the epistemological assumptions at work in the negative critiques of 12 Step discourses. In order to understand how the capacities of the self may fail, and how such failures might be remedied, Chapter Three presents a post-Enlightenment theorisation of personhood as constituted, embodied, and socially embedded subjectivity. This theorisation enables us to examine how embodied selves may be constituted with diminished capacities for agency, responsibility, and choice, and permits the construction of an account of addiction that explains why addictive disorders are a significant social problem in contemporary western societies. Finally, this theorisation enables us to investigate the concepts of personhood that inform the negative critiques. Chapter Four investigates how concepts of illness inform the negative critiques, and shows that it is possible to understand terms such as 'illness' and 'disease' in a non-medical sense. Arguably, such understandings are better able to illuminate the connection between the notion of illness and recovery practices in 12 Step discourses of addiction. Chapter Five uses the conceptual framework provided by Chapters Two, Three, and Four to present a positive view of 12 Step fellowships and discourses. The three key features of this view are, first, that 12 Step fellowship discourses describe addictions as an illness of the self; second, they provide a phenomenology of the sick self; and third, 12 Step recovery discourses and practices are consistent with the notion that the constituted self is limited, and can be reconstituted or changed through practice of the 12 Step recovery program. Together, these three key features show us that 12 Step fellowships provide a valuable social resource for people with limited capacities for self-regulation to help themselves and each other. Chapter Six considers the implications of this more positive view of 12 Step fellowships in terms of the primary and secondary aims of this thesis.

The study of measurement invariance in polytomous items that targets individual score levels is known as differential step functioning (DSF; Penfield, 2007, 2008). DSF methods provide specific information describing the manifestation of the invariance effect within particular score levels and therefore serve a diagnostic role in identifying the individual score levels involved in the item's invariance effect. The analysis of DSF requires the creation of a set of dichotomizations of the item response variable. There are two primary approaches for creating the set of dichotomizations to conduct a DSF analysis. The first approach, known as the adjacent categories approach, is consistent with the dichotomization scheme underlying the generalized partial credit model (GPCM; Muraki, 1992) and considers each pair of adjacent score levels while treating the other score levels as missing. The second approach, known as the cumulative approach, is consistent with the dichotomization scheme underlying the graded response model (GRM; Samejima, 1997) and includes data from every score level in each dichotomization. To date, there is limited research on how the cumulative and adjacent categories approaches compare within the context of DSF, particularly as applied to a real data set. The understanding of how the interpretation and practical outcomes may vary given these two approaches is also limited. The current study addressed these two issues. This study evaluated the results of a DSF analysis using both the adjacent categories and cumulative dichotomization schemes in order to determine if the two approaches yield similar results and interpretations of DSF. These approaches were applied to data from a polytomously scored alternate assessment administered to children with significant cognitive disabilities. The results of the DSF analyses revealed that the two approaches generally led to consistent results, particularly in the case where DSF effects were negligible. For steps where significant DSF was present, the two approaches generally guide analysts to the same location of the item. However, several aspects of the results rose questions about the use of the adjacent categories dichotomization scheme. First, there seemed to be a lack of independence of the adjacent categories method since large DSF effects at one step are often paired with large DSF effects in the opposite direction found in the previous step. Additionally, when a substantial DSF effect existed, it was more likely to be significant using the cumulative approach over the adjacent categories approach. This is likely due to the smaller standard errors that lead to greater stability of the cumulative approach. In sum, the results indicate that the cumulative approach is preferable over the adjacent categories approach when conducting a DSF analysis.

Transport Molecules play a crucial role for cell viability. Amongst others, linear motors transport cargos along rope-like structures from one location of the cell to another in a stochastic fashion. Thereby each step of the motor, either forwards or backwards, bridges a fixed distance. While moving along the rope the motor can also detach and is lost. We give here a mathematical formalization of such dynamics as a random process which is an extension of Random Walks, to which we add an absorbing state to model the detachment of the motor from the rope. We derive particular properties of such processes that have not been available before. Our results include description of the maximal distance reached from the starting point and the position from which detachment takes place. Finally, we apply our theoretical results to a concrete established model of the transport molecule Kinesin V.

<p>Disturbances in power systems are common and they result in electromechanical oscillations called power swing. The power swings could be severe and it may lead to loss of synchronism among the interconnected generators. This is referred to as out-of-step condition. The voltage and current swings during an out-of-step condition damage power system equipments and also cause unwanted operations of various protective devices. The protection systems require an effective algorithm for fast and accurate detection of out-of-step condition. </p> <p>This research is focused on the development of a simple and effective out-of-step relay capable of detecting out-of-step condition in a complex power system. To achieve this, the research has gone through four distinct stages: development of an algorithm, simulation, hardware implementation and its testing. </p> <p>An out-of-step algorithm is proposed based on equal area criterion in time domain. The equal area criterion in time domain is obtained by modifying the traditional equal area criterion in power angle domain. A single machine infinite bus system, a two machine infinite bus system and a three machine infinite bus system and a 17-bus multiple machines system are used as case studies and are modeled using simulation tool(PSCAD). </p> <p>To test the effectiveness of the proposed algorithm, various out-of-step conditions are simulated by applying disturbances at various locations in the above chosen power system configurations. For hardware implementation and testing of the algorithm, a digital signal processing board (ADSP-BF533 from Analog Devices ) is used. To test the performance of the developed digital relay in a closed loop, real time power system signals are necessary and therefore for this purpose, a Real Time Digital Simulator (RTDS) available in the power research laboratory is used. The RTDS simulator mimics the actual power systems in real time. The signals required by the relays can be tapped from the RTDS and the signals coming from relay can be fed back into the RTDS, which makes the closed loop testing of the digital relay possible. This research has yielded a simple out-of-step algorithm and unlike the other out-of-step detection techniques proposed in the literature does not need offline system studies to arrive at a solution.The developed digital out-of-step relay is capable of making decisions based only on the information available from its point of installation, thus it avoids the communication devices which is advantageous for the out-of-step protection of a complex power system. Finally, the simulation results show that the proposed algorithm can be applied to any power configurations and is faster compared to the conventional concentric rectangle schemes used in the literature.</p>