It is relatively straightforward to establish equilibrium inmagnetically confined plasmas, but the plasma is frequentlysucceptible to a variety of instabilities that are driven bythe free energy in the magnetic field or in the pressuregradient. These unstable modes exhibit effects that affect theparticle, momentum and heat confinement properties of theconfiguration. Studies of the dynamics of several of the mostimportant modes are the subject of this thesis. The studies arecarried out on plasmas in the reversed field pinch (RFP)configuration. One phenomenon commonly observed in RFPs is mode walllocking. The localized nature of these phase- and wall lockedstructures results in localized power loads on the wall whichare detrimental for confinement. A detailed study of the walllocked mode phenomenon is performed based on magneticmeasurements from three RFP devices. The two possiblemechanisms for wall locking are investigated. Locking as aresult of tearing modes interacting with a static field errorand locking due to the presence of a non-ideal boundary. Thecharacteristics of the wall locked mode are qualitativelysimilar in a device with a conducting shell system (TPE-RX)compared to a device with a resistive shell (Extrap T2). Atheoretical model is used for evaluating the threshold valuesfor wall locking due to eddy currents in the vacuum vessel inthese devices. A good correlation with experiment is observedfor the conducting shell device. The possibility of succesfully sustaining discharges in aresistive shell RFP is introduced in the recently rebuiltdevice Extrap T2R. Fast spontaneous mode rotation is observed,resulting in low magnetic fluctuations, low loop voltage andimproved confinement. Wall locking is rarely observed. The lowtearingmode amplitudes allow for the theoretically predictedinternal nonresonant on-axis resistive wall modes to beobserved. These modes have not previously been distinguisheddue to the formation of wall locked modes. The internal andexternal nonresonant resistive wall modes grow on the timescale of the shell penetration time. These growth rates dependon the RFP equilibrium. The internal nonresonant resistive wallmodes dominate in Extrap T2R, especially for shallow reverseddischarges. The external nonresonant modes grow solely in deepreversal discharges. <b>Keywords</b>Nuclear fusion, reversed field pinch, resistiveinstabilities, wall locked modes, tearing modes, resistiveshell modes, field errors, EXTRAP-T2, EXTRAP-T2R, TPE-RX

<p>It is relatively straightforward to establish equilibrium inmagnetically confined plasmas, but the plasma is frequentlysucceptible to a variety of instabilities that are driven bythe free energy in the magnetic field or in the pressuregradient. These unstable modes exhibit effects that affect theparticle, momentum and heat confinement properties of theconfiguration. Studies of the dynamics of several of the mostimportant modes are the subject of this thesis. The studies arecarried out on plasmas in the reversed field pinch (RFP)configuration.</p><p>One phenomenon commonly observed in RFPs is mode walllocking. The localized nature of these phase- and wall lockedstructures results in localized power loads on the wall whichare detrimental for confinement. A detailed study of the walllocked mode phenomenon is performed based on magneticmeasurements from three RFP devices. The two possiblemechanisms for wall locking are investigated. Locking as aresult of tearing modes interacting with a static field errorand locking due to the presence of a non-ideal boundary. Thecharacteristics of the wall locked mode are qualitativelysimilar in a device with a conducting shell system (TPE-RX)compared to a device with a resistive shell (Extrap T2). Atheoretical model is used for evaluating the threshold valuesfor wall locking due to eddy currents in the vacuum vessel inthese devices. A good correlation with experiment is observedfor the conducting shell device.</p><p>The possibility of succesfully sustaining discharges in aresistive shell RFP is introduced in the recently rebuiltdevice Extrap T2R. Fast spontaneous mode rotation is observed,resulting in low magnetic fluctuations, low loop voltage andimproved confinement. Wall locking is rarely observed. The lowtearingmode amplitudes allow for the theoretically predictedinternal nonresonant on-axis resistive wall modes to beobserved. These modes have not previously been distinguisheddue to the formation of wall locked modes. The internal andexternal nonresonant resistive wall modes grow on the timescale of the shell penetration time. These growth rates dependon the RFP equilibrium. The internal nonresonant resistive wallmodes dominate in Extrap T2R, especially for shallow reverseddischarges. The external nonresonant modes grow solely in deepreversal discharges.</p><p><b>Keywords</b>Nuclear fusion, reversed field pinch, resistiveinstabilities, wall locked modes, tearing modes, resistiveshell modes, field errors, EXTRAP-T2, EXTRAP-T2R, TPE-RX</p>

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Most South African subtitles are produced and broadcast in English despite the fact that English is the first language of only 8.2% of the entire population (Statistics South Africa, 2004). Therefore, current English subtitles are predominantly received as second language text. This poses questions as to how people perceive these subtitles, and if and how their reading of English second language (L2) subtitles differs from their reading of L1 (non-English) subtitles. In recent years, eye tracking has proven to be a valuable method in observing and measuring the eye movements of people watching and reading subtitles. In order to explain the use of eye tracking and in order to answer the question at hand, this study comprises a literature review and an empirical study. The literature review gives an in-depth account of previous studies that used eye tracking to study reading and elaborates on the parameters used to account for various findings. The two empirical components of this study examined the accessibility and effectiveness of English L2 subtitles by presenting native speakers of Afrikaans and Sesotho with subtitles displayed (a) in their native language, Afrikaans or Sesotho, and (b) in L2 English, while monitoring their eye movements with an SMI iViewX™ Hi-Speed eye tracker and comparing the data with that of English L1 speakers reading English subtitles. Participants were also given static text to read (accompanied by a corresponding comprehension test) in order to see if there was a relation between participants’ first and second language reading of static text and that of subtitling. Additionally, participants were given a questionnaire on their reading behaviour, reading preferences, access to subtitled television programming and reading of subtitles in order to find explanations for occurrences in the data. The initial hypothesis was that there would be a difference in L1 and L2 subtitle reading and attention allocation as measured by key eye-tracking parameters. Using ANOVAs, statistically significant differences were indeed found, but the differences were much more significant for the Sesotho L1 than the Afrikaans L1 speakers. After excluding possible confounding factors that were analysed in attempt to refute this hypothesis, the conclusion was that participants inherently read L1 and L2 subtitles differently. The hypothesis is therefore supported. However, the difference in L1 and L2 subtitle reading was not the only significant finding – the Sesotho L1 speakers’ reading data revealed a greater underlying issue, namely literacy. The problem of low literacy levels can be attributed to the participants’ socioeconomic background and history, and needs to be addressed urgently. Recommendations for future research include that the current study be broadened in terms of scope, sampling size, representativeness and experimental material; that the focus be shifted to the rest of the languages spoken in South Africa for which the users do not have a shared sense of bilingualism and for which the L1 skills and levels of L1 literacy vary; and to further explore the relation between the reading of static text and subtitle reading in order to ensure adequate subtitle reading in terms of proportional attention allocation. However, the issue of low literacy levels will have to be addressed urgently; only then will the South African viewing public be able to gain full access to any form of broadcast communicative material or media, and only then will they be able to benefit from subtitling and all that it offers. / North-West University (South Africa). Vaal Triangle Campus.

Most South African subtitles are produced and broadcast in English despite the fact that English is the first language of only 8.2% of the entire population (Statistics South Africa, 2004). Therefore, current English subtitles are predominantly received as second language text. This poses questions as to how people perceive these subtitles, and if and how their reading of English second language (L2) subtitles differs from their reading of L1 (non-English) subtitles. In recent years, eye tracking has proven to be a valuable method in observing and measuring the eye movements of people watching and reading subtitles. In order to explain the use of eye tracking and in order to answer the question at hand, this study comprises a literature review and an empirical study. The literature review gives an in-depth account of previous studies that used eye tracking to study reading and elaborates on the parameters used to account for various findings. The two empirical components of this study examined the accessibility and effectiveness of English L2 subtitles by presenting native speakers of Afrikaans and Sesotho with subtitles displayed (a) in their native language, Afrikaans or Sesotho, and (b) in L2 English, while monitoring their eye movements with an SMI iViewX™ Hi-Speed eye tracker and comparing the data with that of English L1 speakers reading English subtitles. Participants were also given static text to read (accompanied by a corresponding comprehension test) in order to see if there was a relation between participants’ first and second language reading of static text and that of subtitling. Additionally, participants were given a questionnaire on their reading behaviour, reading preferences, access to subtitled television programming and reading of subtitles in order to find explanations for occurrences in the data. The initial hypothesis was that there would be a difference in L1 and L2 subtitle reading and attention allocation as measured by key eye-tracking parameters. Using ANOVAs, statistically significant differences were indeed found, but the differences were much more significant for the Sesotho L1 than the Afrikaans L1 speakers. After excluding possible confounding factors that were analysed in attempt to refute this hypothesis, the conclusion was that participants inherently read L1 and L2 subtitles differently. The hypothesis is therefore supported. However, the difference in L1 and L2 subtitle reading was not the only significant finding – the Sesotho L1 speakers’ reading data revealed a greater underlying issue, namely literacy. The problem of low literacy levels can be attributed to the participants’ socioeconomic background and history, and needs to be addressed urgently. Recommendations for future research include that the current study be broadened in terms of scope, sampling size, representativeness and experimental material; that the focus be shifted to the rest of the languages spoken in South Africa for which the users do not have a shared sense of bilingualism and for which the L1 skills and levels of L1 literacy vary; and to further explore the relation between the reading of static text and subtitle reading in order to ensure adequate subtitle reading in terms of proportional attention allocation. However, the issue of low literacy levels will have to be addressed urgently; only then will the South African viewing public be able to gain full access to any form of broadcast communicative material or media, and only then will they be able to benefit from subtitling and all that it offers. / North-West University (South Africa). Vaal Triangle Campus.

To fully exploit the capability of NV centers in diamond as magnetic sensors and quantum bits, the optimum production recipe as well as the method to enhance its optical performance has been studied in this work. The NV centers in bulk diamond were prepared by ion implantation and electron irradiation, and the optimum dose and temperature are found by comparing its optical and magnetic performance both experimentally and theoretically. In addition, the enhancement of optical performance and size characterization of NV centers in nanodiamonds will be discussed in this work.

The eye lens grows continuously throughout life and changes its shape as the eye changes focus from a distant to a near object (the process of accommodation). These changes are complex because they may affect not only the shape of the lens, but also its refractive index distribution. To date there has been no satisfactory technique for directly and non-invasively measuring these changes. In this study the refractive index distribution through the isolated lens was measured non-invasively using a novel MRI technique. The dependence of the refractive index value of lens tissue on its transverse relaxation rate (R2) was determined empirically from measurements on lens homogenate samples. Using a multi-spin-echo imaging sequence, data were acquired for constructing R2 maps of a central slice through the isolated lens. These R2 maps were transformed to refractive index maps using the empirically determined dependence of refractive index on R2. Using a standard algorithm for ray tracing through gradient index media, the propagation of light rays through the index map were simulated. The optical properties of the lens, such as focal length, were then measured. The technique was validated by also directly measuring the focal length of each lens using laser ray tracing. The subtle changes in refractive index distribution that are responsible for the dramatic change in the optical properties of the isolated lens with age, were observed for the first time. The decrease in surface power of the isolated lens with age accounted only partially for the decrease in total lens power with age, the remainder resulting from a reduction in the gradient of refractive index (GRIN) power. It is likely that this reduction in GFUN power is the mechanism by which the eye maintains emmetropia (good distant vision) with age despite the increasing curvature of its surfaces. The reduction in the GRIN power of the lens was found to be mainly due to a flattening of the refractive index profile in the central region of the lens, accompanied by steepening of the profile near the edge of the lens. In agreement with a previous MRI study of the isolated human eye lens, this study found a decrease in the refractive index of the nucleus with age. However the age related change in this study was not as large and not found to be statistically significant. The results demonstrate that existing simple models for the optics of the eye lens are inadequate to accurately describe its properties. Several more sophisticated models were considered in an attempt to describe better the age-dependent changes that occur in both the power of the lens and its longitudinal aberration. Mathematical modelling was also used to simulate the accommodative process and investigate possible changes in the index distribution of the lens that may occur with accommodation. A preliminary in vivo study was performed aimed at observing the change in the refractive index distribution of the eye lens with age and accommodation. These results demonstrated the feasibility of the technique for in vivo applications and showed that within experimental error there is little change in the central refractive index of the lens with age. However the resolution achievable with standard clinical imaging sequences and signal detection hardware was not optimal for in vivo refractive index mapping of changes in the human eye lens with accommodation. Finally therefore, methods for refining the technique for in vivo applications are discussed which may make it possible to directly and simultaneously measure both the shape and refractive index distribution of the lens with age and accommodation.

Diffusion tensor imaging (DTI) is a specialist MRI modality that can identify microstructural changes or abnormalities in the brain. It can also be used to show fibre tract pathways. Both of these features were used in this thesis. Firstly, standard imaging analysis techniques were used to study the effects of mild, repetitive closed head injury on a group of professional boxers. Such data is extremely rare, so the findings of regions of brain abnormalities in the boxers are important, adding to the body of knowledge about more severe traumatic brain injury. The author developed a novel multivariate analysis technique which was used on the same data. This new technique proved to be more sensitive than the standard univariate methods commonly used. An important part of diagnosing and monitoring brain damage involves the use of biomarkers. A novel investigation of whether diffusion parameters obtained from DTI data could serve as bio-markers of cognitive impairment in Parkinson's disease was conducted. This also involved developing a multivariate approach, which displayed increased sensitivity compared with any of the component parameters used singly, and suggested these diffusion measures could be robust bio-markers of cognitive impairment. Fibre tract connectivity between regions of the brain is also a potentially valuable measure for diagnosis and monitoring brain integrity. The feasibility of this was investigated in a multi-modal MRI study. Functional MRI (fMRI) identifies regions of activation associated with a particular task. DTI can then find the pathway of the fibre bundles connecting these regions. The feasibility of using regional connectivity to interrogate brain integrity was investigated using a single healthy volunteer. Fibre pathways between regions activated and deactivated by a working memory paradigm were determined. Though the results are only preliminary, they suggest that this line of research should be continued.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-08-27T00:29:23Z No. of bitstreams: 1 MoizesDaSilvaMelo_DISSERT.pdf: 1403747 bytes, checksum: d910e8743f2cf3fa46d99902729b8c73 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-09-02T20:06:24Z (GMT) No. of bitstreams: 1 MoizesDaSilvaMelo_DISSERT.pdf: 1403747 bytes, checksum: d910e8743f2cf3fa46d99902729b8c73 (MD5) / Made available in DSpace on 2016-09-02T20:06:24Z (GMT). No. of bitstreams: 1 MoizesDaSilvaMelo_DISSERT.pdf: 1403747 bytes, checksum: d910e8743f2cf3fa46d99902729b8c73 (MD5) Previous issue date: 2016-02-18 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / A alta variabilidade de um processo est? diretamente relacionada com a m? qualidade do mesmo, portanto, reduzi-la ? a maneira de melhorar o processo. Os m?todos estat?sticos est?o inclu?dos ao planejamento de melhoria de processos, dentre os quais os gr?ficos de controle s?o o mais eficientes e utilizados. Esta disserta??o prop?e dois novos gr?ficos de controle para monitorar um vetor de m?dias de um processo bivariado. O primeiro, chamado de new npxy, emprega um gr?fico por atributos. O procedimento consiste em inspecionar e classificar, atrav?s dos limites discriminantes, cada unidade da amostra como aprovada ou reprovada. Os limites discriminantes s?o ajustados de tal forma que tem-se uma fra??o especificada de unidades reprovadas quando o processo est? sob controle. Em seguida o n?mero de unidades reprovadas ? plotado no gr?fico, e caso seja maior que o limite de controle, o processo ? parado para ajuste. O segundo gr?fico utiliza os gr?ficos new npxy e T2. Este procedimento consiste em dividir uma amostra de tamanho $n$ em duas partes (n1 e n2), determinadas por um processo de otimiza??o. As unidades da primeira sub-amostra s?o avaliadas por atributos e plotadas em um gr?fico de controle new npxy. Caso seja detectada a presen?a de alguma causa especial, inspeciona-se a sub-amostra de tamanho n2 por vari?veis por meio do gr?fico T2. O procedimento ? interrompido para o ajuste se a presen?a de alguma causa especial for detectada em ambos gr?ficos de controle. A possibilidade de n?o inspecionar todos os itens da amostra pode promover uma redu??o tanto no custo quanto no tempo de inspe??o. A an?lise de desempenho foi realizada comparando o n?mero m?dio de amostras at? o alarme verdadeiro (NMA1). Verificou-se que os gr?ficos propostos apresentam desempenho satisfat?rio e s?o concorrentes com o gr?fico T2. Os resultados foram obtidos com o aux?lio do software estat?stico R.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In the current competitive market, a great part of companies has as the main goal the search for continuous improvement of their products and services. Therefore, the application of statistical methods has great relevance in the quality evaluation, helping in the understanding and monitoring of the processes. In such context, the present study concerns to the use of multivariate control charts in the evaluation of the productive processes in the presence of cross-correlation, which the objective is to verify the continuous casting process stability in the production of still billets by means of Hotelling's T2 multivariate control charts applied in the estimated residual mathematical linear models. Initially, the existence of data autocorrelation was verified, it is necessary the ARIMA modeling, because when it happens, it is necessary to determine the residues and apply multivariate control charts to the residues and not on the original variables. The existence of correlation showed to be meaningful among the variables, being one of the assumptions for the statistical application T2. When the T2 chart instability is verified, it was necessary to identify the variable or the set of variables of steel temperatures in the distributor and in the distributor weight, which are responsible for the instability. Later, the estimated residues were decomposed into principal components, and with the help of the correlation of the original variables and the principal components, the variables which most contributed to the formation of each component were identified. Therefore, it was possible to detect the variables which caused the system instability, once for the steel temperature in the distributor were the T4 and T5, followed by T6, T3, T7 and T2 and for the weight of the distributor, PD4, PD5, PD3, PD6 and PD2, respectively. This way, the estimated residues from the mathematical models, the use of multivariate chart control Hotelling's T2 and the decomposition into principal components which were able to represent the productive process. This methodology allowed the understanding of the behavior of the variables and helped the monitoring of this process, as well as, in the determination of the possible variables which caused the instability in the continuous casting process. / No atual mercado competitivo, grande parte das empresas tem como principal objetivo a busca da melhoria contínua dos seus produtos e serviços. Assim, a aplicação de métodos estatísticos apresenta grande relevância na avaliação da qualidade, auxiliando na compreensão e monitoramento de processos. Nesse contexto, o presente estudo aborda a utilização de gráficos de controle multivariados na avaliação do processo produtivo na presença de correlação cruzada, cujo objetivo é verificar a estabilidade do processo de lingotamento contínuo na fabricação de tarugos de aço por meio do gráfico de controle multivariado T2 de Hotelling aplicado nos resíduos estimados de modelos matemáticos lineares. Inicialmente, foi verificada a existência de autocorrelação nos dados, sendo necessária a utilização da modelagem ARIMA, pois quando isso ocorre, deve-se proceder à determinação dos resíduos e aplicar os gráficos de controle multivariados aos resíduos e não nas variáveis originais. A existência de correlação cruzada mostrou-se significativa entre as variáveis, sendo um dos pressupostos para a aplicação da estatística T2. Verificada a instabilidade no gráfico T2, buscaram-se identificar a variável ou conjunto de variáveis das temperaturas do aço no distribuidor e peso do distribuidor, responsáveis pela instabilidade. Posteriormente, os resíduos estimados foram decompostos em componentes principais, e com o auxílio da correlação entre as variáveis originais e as componentes principais, identificou-se as variáveis que mais contribuíram para a formação de cada componente. Assim, foi possível detectar as variáveis causadoras da instabilidade do sistema, sendo que para às temperaturas do aço no distribuidor foram às temperaturas T4 e T5, seguidas de T6, T3, T7 e T2 e para o peso do distribuidor, PD4, PD5, PD3, PD6 e PD2, respectivamente. Deste modo, os resíduos estimados oriundos dos modelos matemáticos, a aplicação dos gráficos de controle multivariados T2 de Hotelling e a decomposição em componentes principais foram capazes de representar o processo produtivo. Esta metodologia possibilitou a compreensão do comportamento das variáveis e auxiliou no monitoramento do processo, bem como, na determinação das possíveis variáveis causadoras da instabilidade no processo de lingotamento contínuo.