Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (MScEng)--University of Stellenbosch, 2001, / ENGLISH ABSTRACT: A frequency domain Power Line Carrier (PLC) simulation program, with the ability to simulate signal attenuation including the coupling equipment, was developed. This simulation program was put to the test against the independent program of Professor L.M. Wedepohl and against practical field measurements. The predictions of the two programs were in precise agreement for a wide range of input parameters. Results from the field tests and predictions also showed close agreement. Further investigations, applying the simulation program, explained how ground conductors and soil resistivity influences PLC signal propagation. An experiment, which was developed to monitor PLC signal attenuation, was installed on the PLC system between Koeberg power station and Acacia substation, both near Cape Town. Data logged continuously over 28 days, indicated measurable and deterministic PLC signal attenuation variations with typical time constants of a few hours. Simulations of the PLC system indicated that the signal amplitude variations were influenced by changes in the height above the ground plane of the phase conductor. This significant finding creates the possibility to obtain real time knowledge of the sag of an Over Head Transmission Line (OHTL) by exploiting an operational PLC system. The knowledge about real time sag can be used in economical dynamic ampacity control systems. The practical and financial benefits to the electricity supply and distribution industry can be significant. / AFRIKAANSE OPSOMMING: 'n Frekwensie gebied "Power Line Carrier" (PLC) simulasie program wat die sein verswakking en die koppeling verliese kan naboots, is ontwikkel. Die program is getoets teen die onafhanklike program van Professor L.M. Wedepohl asook praktiese metings in die veld. Die vooruitskatings van beide programme is presies die selfde vir 'n wye reeks van parameters. Metings en nabootsings het ook noue ooreenstemming getoon. Verdere ondersoek, m. b. v. die program, is gedoen ten einde te verduidelik hoe grond-geleiers en grond weerstand die PLC sein se voortplanting beïnvloed. 'n Eksperiment om die PLC sein se verswakking mee te monitor is ontwerp. Die eksperiment was geïnstalleer in die PLC stelsel tussen Koeberg kernkragstasie en Acacia substasie, naby Kaapstad. Die eksperiment was vir 28 dae geaktiveer en die data wat die eksperiment opgelewer het toon meetbare PLC sein verswakking met tyd konstantes van 'n paar uur. Verdere nabootsings het gewys dat die veranderende verswakking in die PLC seinsterkte toegeskryf kan word aan die wisseling in hoogte van die fase geleiers bo die grondvlak. Hierdie bevinding is van besondere belang aangesien dit die moontlikheid oopmaak om die gemiddelde sak van kraglyne in reële tyd en onder bedryfs toestande te kan meet. Die informasie van die reële sak van kraglyne kan gebruik word in effektiewe stroomdrae-vermoë beheer stelsels. Die praktiese en finansiële voordele wat krag voorsieners en verspreiders hieruit kan put kan aansienlik wees.

Thesis (MEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Unshielded distribution lines has a poor performance during lightning activity. Lightning initiates flashovers between the phases and earth and causes line breakers to trip several times during a lightning storm. In addition equipment like fuses, surge arresters and transformers are damaged by lightning and cause in some cases long power interruptions to customers. The application of line surge arresters on distribution lines is a solution that is implemented worldwide to limit the lightning related problems. This thesis investigated using line surge arresters in conjunction with bushing-mount fuses to decrease nuisance fusing and transformer damage during lightning activity. Two new pieces of equipment (dropout surge arresters and transformer bushingmount fuses) were developed and strategically placed on 4 different distribution lines. Equipment failures decreased by 90 % while financially the project had an excellent return on investment. / AFRIKAANSE OPSOMMING: Distribusie lyne sonder skermdrade presteer swak gedurende weerlig aktiwiteit. Weerlig veroorsaak oorvonking tussen fases en aard geleiers wat lei tot breker klinke. Transformators, sekerings, stuwingsafleiers en ander toerusting word ook deur weerlig beskadig en veroorsaak in sommige gevalle lang toevoer onderbrekings. Installering van lyn stuwingsafleiers op distribusielyne is 'n metode wat wêreldwyd gebruik word om oorvonking en weerligskade te beperk. Hierdie tesis ondersoek die installering van lyn stuwingsafleiers en deurvoerder gemonteerde sekerings om transformator skade en onnodige blaas van sekerings te beperk tydens weerlig aktiwiteit. Nuwe toerusting (uitval stuwingsafleiers en transformator deurvoerder gemonteerde sekerings) was ontwikkel en strategies op 4 verskillende distribusie lyne geïnstalleer. 'n Negentig persent vermindering in toerusting beskadiging is behaal terwyl die projek finansiël 'n goeie opbrengs op belegging meegebring het.

Made available in DSpace on 2014-06-12T15:56:44Z (GMT). No. of bitstreams: 2 arquivo2985_1.pdf: 5101466 bytes, checksum: 86a375e15b77076e9eb9adffbe664c52 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2010 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Uma linha de produtos de software (LPS) é definida como um conjunto de sistemas de software que compartilham características em comum, mas que são suficientemente distintos entre si, desenvolvidos a partir de um conjunto de artefatos reusáveis. Modelos de features e configuração são usados para possibilitar a geração automática de produtos a partir destes artefatos. Um modelo de features representa o conjunto de possíveis configurações de produto de uma LPS, enquanto o modelo de configuração estabelece o mapeamento entre features e implementação. Por exemplo, associando expressões de features, na forma de proposições lógicas, a artefatos. Os benefícios de produtividade que a abordagem de LPS fornece tornam possível que uma LPS seja capaz de gerar milhares de produtos. Neste contexto, erros cometidos ao especificar o modelo de configuração podem resultar em produtos inválidos - o problema da composição segura. Este problema pode ser difícil de ser detectado manualmente, já que os modelos de features e configuração podem tornar-se muito complexos. Gerar todos os produtos de uma LPS pode não ser prático, dado que existem LPS em que é possível gerar milhares de produtos. No entanto, mesmo modelos de configuração que não permitem a geração de produtos inválidos podem ter problemas na sua estrutura interna, como complexidade e duplicação, especialmente no contexto de LPS grandes, onde sua manutenção pode se tornar difícil. Precisamos nos certificar de que não introduzimos erros ao corrigir estes problemas. Neste trabalho, é proposta uma abordagem automática de verificação de composição segura para LPS baseadas em modelos de configuração. Esta abordagem é baseada na tradução de instâncias específicas de modelos de features e configuração em lógica proposicional, usando uma teoria codificada com Alloy. O suporte ferramental fornecido pelo Alloy Analyzer auxilia a verificação. Também é proposto um catálogo de refatoramentos simples para modelos de configuração, como uma maneira de evitar erros ao corrigir problemas na estrutura interna de tais modelos. Este catálogo é formalizado usando uma teoria geral para modelos de configuração especificada com o Prototype Verification System (PVS). Nós avaliamos a abordagem de verificação usando sete versões de uma LPS, com modelos de features que possibilitam a geração de até 272 produtos. Os resultados demonstram a vantagem de usar esta abordagem ao invés de gerar todos os produtos da LPS, já que o tempo médio para compilar um único produto da LPS é maior que o tempo para analisá-la na maior das versões analisadas. Também avaliamos o catálogo de refatoramento provando consistência (soundness) dos refatoramentos propostos no provador de teoremas de PVS

Made available in DSpace on 2014-06-12T16:01:17Z (GMT). No. of bitstreams: 2 arquivo7562_1.pdf: 3512712 bytes, checksum: d7dd3b157b1e7c89309ff683efdc8a2f (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2011 / Atualmente a decisão de trabalhar, ou não, com Linhas de Produtos de Software (LPS) se tornou um requisito obrigatório para o planejamento estratégico das empresas que trabalham com domínio específico. LPS possibilita que as organizações alcancem reduções significativas nos custos de desenvolvimento e manutenção, melhorias quantitativas na produtividade, qualidade e satisfação do cliente. Por outro lado, os pontos negativos em adotar LPS são demanda extra de investimentos para criar os artefatos reusáveis, fazer mudana¸s organizacionais, etc. Além disso, teste é mais complicado e crítico em linhas de produtos do que em sistemas simples. Porém, continua sendo a forma mais efetiva para garantia de qualidade em LPS. Por isso, aprender a escolher as ferramentas certas para teste em LPS é um benefício que contribui pra redução de alguns desses problemas enfrentados pelas empresas. Apesar do crescente número de ferramentas disponíveis, teste em LPS ainda necessita de ferramentas que apoiem o nível de teste de sistema, gerenciando a variabilidade dos artefatos de teste. Neste contexto, este trabalho apresenta uma ferramenta de teste de linhas de produtos de software para construir testes de sistema a partir dos casos de uso que endereçam desafios para teste em LPS identificados na revisão literária. A ferramenta foi desenvolvida com o intuito de reduzir o esforço necessário para realizar as atividades de teste no ambiente de LPS. Além disso, esta dissertação apresenta um estudo exploratório sistemático que tem como objetivo investigar o estado da arte em relação a ferramentas de teste, sintetizando as evidências disponíveis e identificar lacunas entre as ferramentas, disponíveis na literatura. Este trabalho também apresenta um estudo experimental controlado para avaliar a eficácia da ferramenta proposta

Interfacer les photographies et les bases de données géographiques est une démarche utile pour les architectes, les historiens, les géographes mais aussi pour le grand public. Affecter une position géographique à une photographie permet en effet de décrire son contenu potentiel en s'appuyant sur les informations contenues dans une base de données géographique. L'objectif de la thèse est de proposer une méthode permettant de localiser automatiquement une photographie urbaine en la comparant avec des images de synthèse en 3D générées de manière systématique à partir d'un modèle virtuel des bâtiments. Le principe est que la photographie partage avec les images des caractéristiques géométriques qui permettent de les rapprocher et donc de déduire la localisation de la photographie à partir de la position connue de l'image. La méthode utilisée pour retrouver les images de synthèse correspondantes est un appariement entre les lignes présentes dans la photographie et les lignes détectées dans les images de synthèse par la transformation de Hough. Cet appariement est suivi par une analyse statistique permettant de proposer une localisation probable avec une valeur d'approximation associée.Malgré les obstacles présents dans les photographies, cette approche utilisant uniquement les lignes est une solution simple et potentiellement efficace pour le positionnement de photographies. Plusieurs scénarios d'usage sont proposés : la géolocalisation d'une image, la validation du positionnement d'une image localisée et l'utilisation de photographies pour repérer des changements dans le paysage urbain. / Interfacing photographs with geographic databases is a useful approach not only for architects, historians, geographers but also for a general audience. By assigning a geographical position to a picture it becomes possible to describe its potential content based on the information contained in the geographic database.The aim of the thesis is to propose a method to locate automatically an urban photograph by comparing this photograph with 3D images generated systematically from a virtual model of the buildings. The principle is to put in relation a photograph with the synthetic images that are sharing analog geometric characteristics and therefore to deduce the location of the photograph from the known position of the image. In order to nd synthetic images related to a photograph the method used is a matching between detected lines in the photograph and the images based on Hough transform. This matching is followed by a statistical analysis to propose a probable location with an estimation of accuracy. Despite the obstacles present in the photographs, this approach usingonly lines is simple and potentially effective for positioning photographs in urban space. Several scenarios of use are proposed : first location of an image, validation of the position of an image broadly located and use of photographs to identify change in the urban landscape.

The game of rugby has been played for over a century and yet its intricacies are still not fully understood. The key ingredient coaches are seeking is what can be added to a team’s make-up that will result in an increase in that teams level of playing success. The objective of this study is the exploration of the biomechanical aspects of movement in a rugby context specifically looking at the stages before, during and after contact. The hypothesis is that the optimal use of running lines in rugby union will lead to more successful breaches in the opposition’s defensive lines thus an increase in linebreaks will occur. In order to make a comparison based on scientific research principles, nine matches played during the 2001 season was compared with nine matches played during the 2002 season. For each match played in the 2001 and 2002 seasons the total number of linebreaks achieved in a match was calculated. In addition the total number of linebreaks achieved in the 2002 season was further subdivided into the specific categories of intervention in order to determine which intervention had the biggest impact on the total number of linebreaks achieved. By means of video footage of the matches played notational analysis was performed and information was gathered in order to gain data for further evaluation. The actions regarding the execution of the linebreaks were evaluated manually in respect of the intervention that was imposed during the coaching of the team during the 2002 season. Without exception a comparison between similar teams played during both seasons indicated that the total number of linebreaks achieved during the 2002 season was much higher than when the team competed against similar opposition during the 2001 season. The aggregate numbers indicated a significant increase in linebreaks from the 2001 to 2002 season. This conclusion was achieved by means of a simple T-test. Firstly an applied F-test test was done to determine whether the two samples had equal variances or not. Under the null hypothesis we assume that the variances of the two samples are equal, while the alternative states that the two samples have different variances. A value for the test statistic that is greater than the critical value will lead to a rejection of the null hypothesis. The test statistic was calculated and evaluated against the F (8,8) = 2.59 critical value on a 5% level of significance. The value of 15.921 is greater than the critical value of 2.95 and therefore the null hypothesis cannot be accepted, concluding that the two samples do not have equal variances. We then proceeded to test whether the 2002 average linebreaks are significantly higher than the average linebreaks achieved in the 2001 season. Under the null hypothesis the two sample averages are equal. Under the alternative, the 2002 average is higher than the 2001 average. In contrast to normal T-tests this specific test was a one-sided upper or right hand test due to the fact that we are testing whether the one average is greater and not equal to the other. Therefore, we would only reject the null hypothesis of equal sample averages if the test statistic were greater than the appropriate critical value. The calculated test statistic is 4.4827 and was evaluated against the t 0.05,9 = 1.833 critical value. Once again we cannot accept the null hypothesis. Therefore we can conclude that the average of the total linebreaks made during the 2002 season is statistically greater than the average of the total linebreaks made during the 2001 season. The results of this study therefore indicate that the new techniques incorporated into the coaching of the team in 2002 did positively influence the number of linebreaks when compared to the 2001 season. / Dissertation (MA (Human Movement Science))--University of Pretoria, 2005. / Biokinetics, Sport and Leisure Sciences / unrestricted

The goal of this study is to gain a better understanding of the factors that play a role in dominant collisions in rugby as well as the relative significance of dominant collisions as an indicator of success. By means of video footage of matches played during the 2003-2005 Super 12 competitions, notational analysis was performed and information was gathered in order to gain the relative data. The hypothesis stands that if a team is aware of the factors that lead to a dominant collision, are able to execute them in a match situation, that team should be more successful. The following key performance measurements were evaluated in order to indicate how each factor affected the level of success of a team. They are as follows: average total number of collisions for a try to be scored, average total number of forced missed tackles for a try to be scored, ratio of dominant collisions versus passes executed when a try is scored and average positive velocity change of dominant collisions resulting in a try being scored. In order to prove the hypotheses a k-sample case will be used. The samples are related, thus the data used is interval and ratio. Therefore, the test used will be the repeated measures ANOVA test, a special form of n-way analysis of variance. The statistical evaluation is the critical test value where the d.f values are as following: Key Measurement (3,8), Year Rating (2,8), Year Rating by Key Measurement (3,8). When comparing these with a statistical table for critical values of the F distribution for Ą = 0.05, the critical values are as following: (3,8): 4.07, (2,8): 4.46, and (3,8): 4.07. Thus, the statistical results are grounds for accepting all three null hypotheses and concluding that there is a statistical significance of at least 95% with an alpha of 0.05 between the means in all three instances. This shows that the data captured for the twelve teams for all tries scored by these teams over a period of three years and for the four key measurements, have a statistical significance of 95% for the readings respectively. After evaluation of the data and making use of regression analysis and multiple regressions in order to establish the correlation between log position and the four key measurements there can be no doubt that the teams that finished higher on the log did indeed perform better according to the identified key performance measurements. / Thesis (DPhil (Human Movement Science))--University of Pretoria, 2006. / Biokinetics, Sport and Leisure Sciences / unrestricted

M.Sc. / The transmission system of Eskom occupies approximately 28 000 km of servitude that crosses a number of biomes in South Africa. The management of these servitudes, with respect to the impacts that the system has on the surrounding environment, as well as the effect of biotic, social and natural phenomena on the electrical system, needs to be carefully managed. This study investigates these bi-directional influences to determine which are pertinent to the management to the transmission line servitudes. This study also derives a number of strategic actions and accountabilities for all participating departments in the Transmission Division of Eskom, who are involved in the management of one or more phases of the life cycle of the servitude.

Linhas de produção são sistemas fabris para produção em larga escala, com grande importância no sistema industrial atual. Como se trata de um sistema já consolidado, é natural que existam métricas de desempenho e estratégias para otimização de eficiência para as diversas configurações de linhas de produção existentes. Este trabalho se concentra em linhas seriais não-ritmadas e estocásticas. Em particular, o interesse é no efeito de se desbalancear adequadamente uma linha de produção para melhorar sua produtividade, o que é denominado na literatura de fenômeno Tigela (Bowl phenomenon). Uma revisão da literatura mostrou que esse fenômeno já foi estudado em diferentes cenários: linhas com e sem buffers, diversos perfis de carga ao longo da linha e diferentes distribuições probabilísticas regendo os tempos de execução das tarefas. Contudo, nenhum dos estudos considerou a indivisibilidade das tarefas, isto é, o fato de que cada tarefa deve ser executada em uma única estação. Essa é a principal lacuna explorada neste estudo. Para isso, são utilizadas instâncias recentemente propostas do Problema Simples de Balanceamento de Linhas de Produção (SALBP, na sigla em inglês) e instâncias do Problema de Designação de Trabalhadores e Balanceamento de Linhas de Produção (ALWABP), que são solucionadas a partir de modelos de programação inteira mista que induzem soluções de acordo com o efeito Tigela. Essas soluções são utilizadas em um modelo de simulação estocástico, também apresentado neste trabalho. Em linhas gerais, os resultados mostram que as soluções do SALBP e ALWABP obtidas podem se beneficiar do efeito Tigela. Além disso, a variedade das instâncias utilizadas nos experimentos argumentam em favor de uma maior capacidade de generalização dos resultados para casos práticos se comparados aos casos simplificados previamente discutidos na literatura. / Assembly lines are large-scale production systems with great value in modern industrial systems. Perfomance measures and strategies have been proposed in order to evaluate and improve the efficiency of numerous assembly line configurations. This dissertation focuses on serial unpaced (stochastic) assembly lines. In particular, the interest of this study is in the effect of deliberately unbalacing the line in a specific manner in order to enhance its performance, a strategy that exploits the so-called Bowl phenomenon. The literature has studied this phenomenon in different scenarios: buffered and unbuffered lines, different workload profiles along the line and different probabilistic task time distributions. However, none of the identified studies considers task indivisibility, an intrisic characteristic of real-world assembly line balancing problems, namely, each task has to be executed in a single station. This is the main gap explored in this study. Thereunto, we use recently proposed instances for the Simple Assembly Line Balancing Problem (SALBP) and some Assembly Line Worker Assignment and Balancing Problem (ALWABP) instances, which are solved using mixed integer programming models capable of inducing bowl workload profiles. These solutions are used as input in a stochastic simulation model, also presented in this study. Overall, the results show that SALBP and ALWABP solutions may benefit from the Bowl phenomenon. Furthermore, the variety of the instances considered in the experiments allows for a better generalization of the results to real-world scenarios if compared to the simplified cases previously shown in the literature.