Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The ability of satellites to actively control their attitude has changed the way we live. Navigation systems, satellite television, and weather forecasting, for example, all rely on satellites which are able to determine and control their attitude accurately. This project was aimed at designing and analysing an attitude determination and control system (ADCS) for a 20 kg Earth observation satellite by means of simulation. A realistic simulation toolset, which includes the space environment, sensor, and actuator models, was created using MATLAB and Simulink. An ADCS hardware suite was selected for the satellite based on a given set of pointing and stability requirements, as well as current trends in the small satellite industry. The hardware suite consists of among others a star tracker and three reaction wheels. A variety of estimators and controllers were investigated, after which an application specific ADCS state machine was defined. The state machine included a Safe Mode for de-tumbling, a Nominal Mode for normal operation, a Forward Motion Compensation (FMC) Imaging Mode for Earth observation, and a Target Tracking Mode for ground station tracking. Simulation results indicated that de-tumbling, coarse and fine sun tracking, FMC factor 4 imaging, and target tracking were successfully implemented. Lastly, the satellite’s pointing error and stability were determined to be less than 70 arcseconds and 7 arcseconds per second respectively, both values well within the given requirements. / AFRIKAANSE OPSOMMING: Satelliete se vermoë om hul oriëntasie aktief te beheer, het die manier waarop ons lewe, verander. Navigasiestelsels, satelliettelevisie en weervoorspelling, byvoorbeeld, maak staat op satelliete wat hul oriëntasie akkuraat kan bepaal en beheer. Die mikpunt van hierdie projek was die ontwerp en analise van ’n oriëntasiebepaling- en -beheerstelsel (ADCS) vir ’n 20 kg aardwaarnemingsatelliet deur middel van simulasie. ’n Realistiese simulasieopstelling, wat modelle van die ruimteomgewing, sensore en aktueerders insluit, was ontwikkel deur gebruik te maak van MATLAB en Simulink. ’n ADCS hardewarestel was gekies vir die satelliet op grond van ’n stel rig- en stabiliteitsvereistes, sowel as die huidige tendense in die klein-satellietbedryf. Die hardewarestel bestaan onder andere uit ’n stervolger en drie reaksiewiele. Nadat verskeie afskatters en beheerders ondersoek was, was ’n toepassingspesifieke ADCS toestandmasjien gedefinieer. Die toestandmasjien het ’n Veilige Modus vir onttuimelling, ’n Nominale Modus vir normale operasie, ’n Vorentoe-bewegingskompensering (FMC) Beeldskandeermodus vir aardwaarneming en ’n Teikenvolgmodus vir grondstasie volging ingesluit. Simulasieresultate het aangedui dat onttuimeling, growwe- en fyn sonvolging, FMC faktor 4 beeldskandering en teikenvolging suksesvol geïmplementeer was. Laastens was die satelliet se rigfout en stabiliteit bepaal as minder as 70 boogsekondes en 7 boogsekondes per sekonde onderskeidelik, albei waardes gemaklik binne die vereistes.

Coal spirals are widely used in coal preparation plants around the world to clean fine coal, typically in the 1 x 0.15 mm size range. Despite their popularity and the trend toward increased automation in modern coal preparation plants, adjustments to the critical process variable for coal spirals, i.e., product splitter position, continue to be done manually. Since spiral feed in a plant tends to fluctuate on a regular basis, timely manual adjustment of splitter position in tens or hundreds of spirals operating in a plant is nearly impossible. As a result, the clean coal yield from a spiral and also the overall plant suffers on a regular basis. The main goal of this study was to develop a suitable sensor and control system to adjust the product splitter position of a full-scale spiral. Some of the basic properties of coal slurry were thoroughly investigated for their on-line measurability and for their correlations with the density of the constituent solid particles. After experimenting with electrical capacitance- and conductivity- (i.e., reciprocal of resistivity) based sensing techniques, a conductivity-based tube sensor was developed for measuring density of solid particles in the spiral trough. Two sensors were used to establish a density gradient in the critical region across the spiral trough at the discharge end. Based on this continuously monitored density gradient, a PIC24 microcontroller was programmed to send a signal to a DC gear motor that would move the splitter arm in the appropriate direction when sufficient variation in conductivity was detected. Currently, a cycle time of 5 minutes is used for the spiral control system; however, in a commercial application, the cycle time could be lengthened to 30 or 60 minutes. The automation system has been validated by examining the performance of a full-scale spiral while deliberately changing factors like feed solid content, feed washability characteristics, and feed slurry ionic concentration. With a full-scale compound spiral programmed to achieve a specific gravity of separation at 1.65 by an automatic adjustment of the splitter position, the actual D50 values achieved for two separate tests were 1.64 and 1.73. The close proximity of target and actual D50 values is indicative of the effectiveness of the developed system. The next step in near-term commercialization of this proprietary spiral control system will be a longer term (several months) in-plant demonstration. The main goal of this study was to develop a suitable sensor and control system to adjust the product splitter position of a full-scale spiral. One of the basic properties of coal slurry was thoroughly investigated for its on-line measurability and for its correlation with the constituent solid density of the slurry. After experimenting with electrical capacitance- and conductivity- (i.e., reciprocal of resistivity) based sensing techniques, a conductive-based tube sensor was selected for measuring solids density of particles in the spiral trough. Two sensors were used to establish a density gradient in the critical region across the spiral trough at the discharge end. Based on this continuously monitored density gradient, a PIC24 microcontroller was programmed to send a signal to a DC gear motor that would move the splitter arm when sufficient variation in conductivity was detected. Currently, a cycle time of 5 minutes is used for the spiral control system; however, in a commercial application, the cycle time could be lengthened to 30 or 60 minutes. The automation system has been validated by examining the performance of a full-scale spiral while deliberately changing factors like feed solid content, feed washability characteristics, and feed slurry ionic concentration. With compound spirals programmed to achieve a specific gravity of separation at 1.65, actual D50 values achieved for two separate tests were 1.64 and 1.73. The close proximity of target and actual D50 values is indicative of the effectiveness of the developed system. The next step in near-term commercialization of this proprietary spiral control system will be a longer term (several months) in-plant demonstration.

El presente trabajo de investigación se realiza con la finalidad de evaluar la incidencia del control interno en el proceso de las cuentas por pagar en un contexto de proteger el activo disponible de la empresa Herramientas y accesorios SAC.La propuesta de llevar a cabo un adecuado sistema de control interno en las operaciones de cuentas por pagar contribuye eficazmente en cada una de las operaciones del efectivo y su acertada toma de decisiones. The present research work is carried out with the purpose of evaluating the incidence of internal control in the process of accounts payable in a context of protecting the available assets of the company Tools and accessories SAC.The proposal to carry out an adequate internal control system in the accounts payable operations contributes effectively in each one of the operations of the cash and its successful decision making.

abstract: This dissertation treats a number of related problems in control and data analysis of complex networks. First, in existing linear controllability frameworks, the ability to steer a network from any initiate state toward any desired state is measured by the minimum number of driver nodes. However, the associated optimal control energy can become unbearably large, preventing actual control from being realized. Here I develop a physical controllability framework and propose strategies to turn physically uncontrollable networks into physically controllable ones. I also discover that although full control can be guaranteed by the prevailing structural controllability theory, it is necessary to balance the number of driver nodes and control energy to achieve actual control, and my work provides a framework to address this issue. Second, in spite of recent progresses in linear controllability, controlling nonlinear dynamical networks remains an outstanding problem. Here I develop an experimentally feasible control framework for nonlinear dynamical networks that exhibit multistability. The control objective is to apply parameter perturbation to drive the system from one attractor to another. I introduce the concept of attractor network and formulate a quantifiable framework: a network is more controllable if the attractor network is more strongly connected. I test the control framework using examples from various models and demonstrate the beneficial role of noise in facilitating control. Third, I analyze large data sets from a diverse online social networking (OSN) systems and find that the growth dynamics of meme popularity exhibit characteristically different behaviors: linear, “S”-shape and exponential growths. Inspired by cell population growth model in microbial ecology, I construct a base growth model for meme popularity in OSNs. Then I incorporate human interest dynamics into the base model and propose a hybrid model which contains a small number of free parameters. The model successfully predicts the various distinct meme growth dynamics. At last, I propose a nonlinear dynamics model to characterize the controlling of WNT signaling pathway in the differentiation of neural progenitor cells. The model is able to predict experiment results and shed light on the understanding of WNT regulation mechanisms. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

Made available in DSpace on 2014-10-09T12:26:23Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:18Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Detta examensarbete är en del av en förstudie av en hydrauliskt bromsad vagn avsedd att bogseras för uthållighetstestning av militära fordon. Denna del behandlar konstruktionen av styrsystemet till bromsvagnen. I rapporten beskrivs programmering av ett styrsystem med hänsyn till ett parallellt utvecklat hydrauliksystem, identifiering av tänkbara leverantörer av komponenter, och sammanställandet av en analys över feleffekter. Resultatet blev ett styrsystem programmerat i CODESYS komplett med ett operatörsgränssnitt, ett blockschema över systemet, och en feleffektsanalys. Slutsatsen blev att en prototyp skulle kunna byggas utifrån detta arbete men man bör överväga en modifikation av systemet och också beakta vissa risker. / This degree project is part of a prestudy of a hydraulic brake wagon designed to be towed for endurance testing of military vehicles. This report presents the design of the control system for the brake wagon. It describes the programming of a control system for a hydraulic system developed in parallel, the search of potential component suppliers, and the compilation of a failure analysis. The result was a control system programmed in CODESYS, with an operator interface, a block diagram of the system and a Failure Mode Effect Analysis. The conclusion is that a prototype could be built based on this work but a modification of the system and certain risks should be considered. / Projekt Bromsvagn

Este estudo investiga, sob a ótica da teoria da contingência, os efeitos dos fatores contingenciais sobre o perfil do sistema de controle gerencial (SCG) das empresas brasileiras tendo como objetivo compreender as características do SCG, em função dos fatores contingenciais. São examinados os efeitos diretos e interativos dos fatores contingenciais internos estratégia, estrutura, tecnologia da informação e estágio do ciclo de vida organizacional e do ambiente no perfil do SCG. Avalia-se também o efeito do SCG no desempenho organizacional. Esta pesquisa defende a tese de que os fatores contingenciais internos e externos influenciam o perfil do SCG que possui associação com o desempenho, sendo possível estabelecer arranjos (fit) entre fatores contingenciais, características do SCG e desempenho organizacional. As hipóteses relativas aos efeitos dos fatores contingenciais no SCG preveem que o ambiente, fator contingencial externo, possui associação com os fatores contingenciais internos i) estratégia, ii) estrutura, iii) estágio do CVO e iv) tecnologia da informação; que o ambiente e os fatores contingenciais internos possuem associação com o perfil do SCG e que o SCG possui associação com o desempenho. A amostra envolveu 120 empresas brasileiras de grande porte e os dados para obtenção de informações sobre as mesmas foram coletados através de uma survey (levantamento). Para o tratamento dos dados, foram utilizadas as técnicas estatísticas de análise fatorial, análise de clusters e modelagem de equações estruturais. Os resultados indicaram que quando analisadas em um único grupo de empresas, não foi possível identificar associação entre os fatores contingenciais e o SCG e deste com o desempenho organizacional, rejeitando-se as hipóteses estabelecidas. Entretanto, ao separar as empresas em dois grupos distintos, i) indústria e ii) comércio e serviços, a hipótese de associação entre o fator contingencial ambiente e o SCG foi aceita. Também foram aceitas as hipóteses de: i) associação do ambiente com os fatores contingenciais internos da organização, ii) de associação dos fatores contingenciais internos com o SCG e, finalmente, iii) do SCG com o desempenho organizacional. A validação das hipóteses da pesquisa indica que a escolha e a utilização dos artefatos do SCG sofrem influência dos fatores contingenciais vivenciados pela empresa. Os resultados da pesquisa estão sujeitos a algumas limitações: i) as respostas refletem a percepção dos profissionais de controladoria das empresas, ii) a amostra não é probabilística e, portanto, todas as inferências não podem ser generalizadas para a população. Entretanto, considerando o atual estágio da pesquisa em contabilidade gerencial no Brasil, a pesquisa fornece uma visão importante de um grupo de empresas classificadas entre as maiores do País. Esta análise pode ser o ponto de partida para futuras pesquisas que utilizem a teoria da contingência. / This study investigates, from the perspective of contingency theory, the effects of contingency factors on the profile of the management control system (SCG) of Brazilian companies. The study examines the direct and interactive effects of internal contingency factors - strategy, structure, information technology and stage of organizational life cycle - and the environment in the profile of the SCG. It also evaluates the effect of SCG on organizational performance. This research supports the view that the contingent factors internal and external influence the profile of the SCG that has membership to the performance, it is possible to make arrangements (fit) between contingency factors, characteristics of the SCG and organizational performance. The assumptions of the effects of contingency factors in the SCG predict that the environment, external contingency factor, has association with membership to the internal contingency factors i) strategy, ii) structure, iii) stage of the CVO and iv) information technology, the environment and the internal contingency factors are associated with the profile of the SCG and the SCG has association with the performance. The sample involved 120 Brazilian companies large and the data to obtain information about them was collected through a survey (survey). For the treatment of data, we used the statistical techniques of factor analysis, cluster analysis and structural equation modeling. The results showed that when analyzed in a single group of companies, we could not identify an association between contingency factors and the SCG and this organizational performance, rejecting the hypotheses. However, the separate companies in two distinct groups: i) industry and ii) trade and services, the hypothesis of association between the environment and contingency factor SCG was accepted. We also accept the following hypotheses: i) linking the environment with the contingency factors internal to the organization, ii) the association of contingency factors internal to the SCG and, finally, iii) the SCG with organizational performance. The validation of the hypotheses of research indicates that the choice and use of artifacts from the SCG are influenced by the contingent factors experienced by the company. The survey results are subject to some limitations: i) the responses reflect the perceptions of professionals controlling companies, ii) the sample is not probabilistic and, therefore, all inferences can not be generalized to the population. However, considering the current state of research in management accounting in Brazil, the study provides important insight into a group of companies ranked among the highest in Brazil. This analysis can be the starting point for future studies using the contingency theory.

Made available in DSpace on 2014-10-09T12:26:23Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:18Z (GMT). No. of bitstreams: 0 / A demanda por energia no mundo moderno é crescente, em particular nos países em desenvolvimento. Dentre as fontes de energia atualmente disponíveis a opção nuclear tem merecido destaque pelas suas qualidades de não afetar o meio ambiente por meio de emissões de gases de efeito estufa e nem demandar grandes áreas. Porém, a sociedade tem requerido melhoria da segurança dos novos reatores e as empresas de energia necessitam maior disponibilidade das centrais. O projeto do IRIS, um reator nuclear integral a água pressurizada, vem atender a esses requisitos. Um sistema de identificação e classificação de transientes ajudaria a melhorar a segurança e a aumentar a disponibilidade do IRIS, melhorando sua competitividade. Como contribuição para o desenvolvimento de um sistema como esse foi desenvolvido e estudado o Sistema de Identificação e Classificação de Transientes SICT com capacidade de monitorar a operação da central e disponibilizar informações sobre seu estado operacional. O SICT foi desenvolvido usando a técnica de redes neuronais, mais especificamente os Mapas Auto-Organizáveis (Self-Organizing Maps - SOM). Para o treinamento do SICT foram usados resultados de simulação do IRIS com o código RELAP5. Para comprovar a metodologia de usar resultados de simulações, cujos valores têm características diferentes daqueles medidos, foi feito uma aplicação do SICT para uma instalação experimental, o Circuito Térmico NO 1 CT1. A partir de experimentos termo-hidráulicos no CT1 e de simulações deste com o RELAP5, pôde-se verificar a validade dessa metodologia. Tem-se disponível para estudos futuros uma nodalização do CT1 validada, uma nodalização do IRIS testada para vários transientes, normais e anormais, e um banco de dados de resultados de simulação do IRIS. Está também disponível, em um CD em anexo a esta tese, os arquivos fontes do aplicativo desenvolvido, SICT, e de alguns programas auxiliares, os dados dos experimentos realizados no CT1 e dados de entrada e resultados de simulações do CT1 com o RELAP5. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Les systèmes multi-agents sont des systèmes dynamiques composés par plusieurs éléments qui interagissent entre eux. Ces éléments sont appelés agents. Un agent est un système dynamique caractérisé par deux propriétés. La première est que les agents sont autonomes— c’est-à-dire qu’ils ne sont pas dirigés par l’environnement extérieur et ils peuvent évoluer selon un comportement auto-organisé. La seconde est que les agents sont capables de communiquer entre eux pour accomplir des tâches complexes, telles que la coopération, la coordination et la résolution de conflits. L’un des problèmes courants concernant les systèmes multi-agents est la synchronisation. Les agents sont synchronisés lorsque leur évolution dans le temps converge vers une trajectoire commune. Plusieurs applications du monde réel peuvent être conceptualisés comme des problèmes de synchronisation des systèmes multi-agents : par exemple, l’alignement en vitesse ( flocking en anglais), et le contrôle de la formation du mouvement de groupes cohérents. La synchronisation des systèmes multi-agents peut être obtenue grâce à différentes techniques de contrôle. Dans cette thèse nous proposons des méthodes de contrôle centralisées et distribuées pour la synchronisation des systèmes multi-agents. Nous développons des conditions nécessaires et suffisantes pour la synchronisation des systèmes multi-agents, composés par des agents identiques et linéaires qui ne changent pas dans le temps, en utilisant une approche Lyapunov. Ces conditions sont utilisées pour la conception de lois de contrôles distribuées. ensuite, nous étendons les résultats aux systèmes multi-agents soumis à des perturbations externes, assurant un niveau de performance désiré grâce à une technique de contrôle de type 퐻 ∞ . enfin, nous étendons l’analyse aux systèmes multi-agents avec contraintes sur les actionneurs, en utilisant des techniques de contrôle anti-windup. Nous évaluons l’efficacité et les performances des stratégies de contrôle proposées dans plusieurs simulations, dont deux d’entre elles sont inspirées par des applications issues du monde réel. La première est le contrôle du vol en formation d’avions, et la seconde est l’analyse de la transmission de contenus vidéo comme un problème de synchronisation. Nous comparons aussi les résultats obtenus avec des techniques de contrôle alternatives. / Multi-agent systems are dynamical systems composed of multiple interacting elements known as agents . Each agent is a dynamical system with two characteristics. First, it is capable of autonomous action—that is, it is able to evolve according to a self-organised behavior, which is not influenced by the external environment. Second, it is able to exchange information with other agents in order to accomplish complex tasks, such as coordination, cooperation, and conflict resolution. One commonly studied problem in multi-agent systems is synchronization. The agents are synchronized when their time evolutions converge to a common trajectory. Many real-world applications, such as flocking and formation control, can be cast as synchronization problems. Agent synchronization can be achieved using different approaches. In this thesis, we propose distributed and centralized control paradigms for the synchronization of multi-agent systems. We develop necessary and sufficient conditions for the synchronization of multi-agent systems, composed by identical linear time-invariant agents, us- ing a Lyapunov-based approach. Then we use these conditions to design distributed synchronization controllers. Then, we extend this result to multi-agent systems subject to external disturbances enforcing disturbance rejection with 퐻 ∞ control techniques. Furthermore, we extend the analysis to multi-agent systems with actuator constraints using LMI-based anti-windup techniques. We test the proposed control design strategies in simulated examples among which two are inspired by real-world applications. In the first, we study airplane formation control as a synchronization problem. In the second, we analyze the delivery of video streams as a synchronization problem and we compare the results to existing controllers.

In this thesis I focus on the audit of financial statements from the perspective of the auditor. The first part contains the definition of basic theoretical concepts in this area and a description of audit procedures. This knowledge is used in the practical part for audit verification of operations with fixed assets in a particular entity. According to the findings I draw conclusions and proposals for solutions of deficiencies.