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In this thesis, a feasibility study will be conducted in order to determine if the usage of acontrol moment gyroscope is a possibility for a micro satellite as its attitude control. Thegoal is to conclude if gyroscopes are suitable replacements for the current reaction wheelswhich are acting as the attitude control for the satellite. In the first part of the thesis thegeneral function of the control moment gyroscope and three different types of arrangementsare displayed with all their respective advantages and disadvantages. Then one ofthem will be designed to fit within the restrictions of 1U. The full design of the pyramidconfiguration was chosen due to its compact size and spherical angular momentum envelope.The full design contains all the components such as motors, flywheels, mounts,frame, screws etc. which provide a cost estimate which is a huge input in determiningthe feasibility of this thesis. In the future the manufacture of the pyramid configurablecontrol moment gyroscopes shall be tested in the future with a more advanced steeringlaw in order to determine the full potential of the attitude control system.

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Esta dissertação apresenta a modelagem matemática de um giroscópio de controle de momento (CMG) e aplica técnicas de controle digital para o controle de atitude dessa planta. CMGs são atuadores importantes para o controle de atitude de corpos no espaço, tais como satélites e veículos espaciais. Desenvolve-se a modelagem da planta por meio da mecânica Lagrangiana e estudam-se técnicas específicas de controle PID (proporcional-integral-derivativo) e LQR (linear-quadratic regulator ) digitais para aplicação em sistemas com a planta nas configurações desacoplada e acopladas de fase mínima e não-mínima. Realizam-se ensaios via simulação, com o modelo não-linear da planta, bem como via experimentos práticos, com o sistema real, para validar os controladores projetados. Com isso, obtêm-se resultados positivos com ambas as técnicas estudadas, com exceção ao caso acoplado de fase não-mínima, para o qual uma das técnicas não foi capaz de controlar a atitude da planta. / This dissertation presents the mathematical modeling of a control moment gyroscope (CMG) and applies digital control techniques for its attitude control. CMGs are important actuators for bodies attitude control in the space, such as satellites and space vehicles. The system modeling is developed with the Lagrangian mechanics and a digital proportionalintegral- derivative (PID) and a digital linear-quadratic regulator (LQR) control techniques are studied and applied to a decoupled system and coupled systems with minimum and non-minimum phases. Simulation tests with the non-linear plant model and experimental tests with the real plant are done in order to validate the control techniques. Then, positive results are reached with both studied techniques, excepting in the coupled system with non-minimum phase, in which one technique was not able to control it.

Esta dissertação apresenta a modelagem matemática de um giroscópio de controle de momento (CMG) e aplica técnicas de controle digital para o controle de atitude dessa planta. CMGs são atuadores importantes para o controle de atitude de corpos no espaço, tais como satélites e veículos espaciais. Desenvolve-se a modelagem da planta por meio da mecânica Lagrangiana e estudam-se técnicas específicas de controle PID (proporcional-integral-derivativo) e LQR (linear-quadratic regulator ) digitais para aplicação em sistemas com a planta nas configurações desacoplada e acopladas de fase mínima e não-mínima. Realizam-se ensaios via simulação, com o modelo não-linear da planta, bem como via experimentos práticos, com o sistema real, para validar os controladores projetados. Com isso, obtêm-se resultados positivos com ambas as técnicas estudadas, com exceção ao caso acoplado de fase não-mínima, para o qual uma das técnicas não foi capaz de controlar a atitude da planta. / This dissertation presents the mathematical modeling of a control moment gyroscope (CMG) and applies digital control techniques for its attitude control. CMGs are important actuators for bodies attitude control in the space, such as satellites and space vehicles. The system modeling is developed with the Lagrangian mechanics and a digital proportionalintegral- derivative (PID) and a digital linear-quadratic regulator (LQR) control techniques are studied and applied to a decoupled system and coupled systems with minimum and non-minimum phases. Simulation tests with the non-linear plant model and experimental tests with the real plant are done in order to validate the control techniques. Then, positive results are reached with both studied techniques, excepting in the coupled system with non-minimum phase, in which one technique was not able to control it.

Student Number : 0413249D - MSc research report - Faculty of Science / Cassava is one of the most important staple crops in the world and is consumed by over 700 million people around the globe and is a profitable product commercially due to the high starch content of its tubers. One of the future aims is to produce cassava that is high yielding, resistant to cassava mosaic geminiviruses (CMGs) and high in starch content. To be able to achieve commercially attractive cassava varieties, research need to be carried out to investigate the virus resistance status of different cassava cultivars, which can later be used in the future breeding programme. In South Africa, cassava is used for commercial starch manufacturing purposes, as a cash crop and a food source by small-scale farmers. Cassava Mosaic Disease (CMD) is having a negative impact on yield of the crop globally and therefore dropping profitability of cassava on a commercial scale. The aims of this research were to propagate thirteen cassava cultivars and then to test them for virus susceptibility or resistance. Eleven cassava cultivars received from the International Institute of Tropical Agriculture (IITA) were tested for resistance or susceptibility against South African cassava mosaic virus (SACMV). Two local, commercial cultivars T200 and T400, were tested for East African cassava mosaic virus (EACMV) and African cassava mosaic virus (ACMV) resistance. Cassava cultivars were successfully propagated in vitro and thereafter transferred into soil and acclimatized to adapt to environmental conditions. When the plantlets were three weeks old, the plantlets were infected with cassava mosaic viruses. Plants were infected with SACMV via Agrobacterium-mediated transfer and infectious EACMV and ACMV monomers were used to biolistically bombard the plantlets. Resistance/susceptibility results of seven of the thirteen cultivars were obtained with SACMV, these cultivars being T200 (susceptible), T400 (susceptible), TME3 (highly resistant), I30572 (susceptible), I420251 (highly susceptible), I60506 (susceptible) and TMS60444 (susceptible). Due to destruction by fungal gnats eating the roots of the plants, acclimatization of the remaining six cultivars was not possible. Also, due to the nature of the biolistic equipment, infection of the cultivars with EACMV and ACMV was not achieved as the plantlets were not robust enough to survive the pressure.

Maintenance of genomic integrity is dependent on the duplication of chromosomes, only once per cell cycle. Highly conserved mechanisms for the regulation of chromosome replication exists to ensure that the genome is copied only once. The Cdc45-MCM-GINS (CMG) DNA helicase which is the core of the eukaryotic replication complex, has been shown to be extensively regulated by post translational modifications, during its assembly. Therefore, it is not inconceivable that the process to unload the replication complex would also be a conserved and regulated process. In 2014, our lab discovered that the CMG complex undergoes post-translational modification in the form of ubiquitylation on one of the subunits of CMG, leading to its disassembly from the chromatin. Though the main players in the disassembly of CMG were known, viz the E3 ligase SCFDia2 and segregase Cdc48, very little was known about the mechanism of CMG disassembly. In the process of learning more about the disassembly of the replicative helicase from chromatin, I reconstituted the ubiquitylation of CMG and thereafter the disassembly of CMG helicase in vitro. My work resulting in the reconstitution of CMG disassembly in vitro is the first example of the disassembly of a multi-subunit physiological substrate of Cdc48. Though CMG is ubiquitylated in yeast extracts in vitro, it does not lead to its disassembly and therefore led me to find conditions necessary for the efficient ubiquitylation of CMG. I have further shown that purifying the E3 ligase associated CMG can be efficiently ubiquitylated in a semi-reconstituted system consisting of purified factors, necessary for the ubiquitylation of substrate. I investigated whether this efficiently ubiquitylated CMG can be disassembled by purified Cdc48 and associated co-factor Ufd1/Npl4 in vitro and found that disassembly is dependent on K48 linked poly-ubiquitylation of CMG. I have found that the reconstituted poly-ubiquitylation of CMG is restricted to the Mcm7 subunit of CMG, recapitulating the ubiquitylation of CMG in vivo, and my data points out that there are multiple sites of ubiquitylation on Mcm7. Through this work, I have also found that ubiquitylated Mcm7 no longer associates with the rest of the CMG components after disassembly of CMG. My assays and findings, open the door towards dissecting the molecular mechanism of the disassembly of CMG in greater detail.

It is observed that the flowing bottom-hole temperature (FBHT) changes as a result of production, injection or shutting the well down. Variations in temperature mainly occur due to geothermal gradient, injected fluid temperature, frictional heating and the Joule-Thomson effect. The latter is the change of temperature because of expansion or compression of a fluid in a flow process involving no heat transfer or work. CMG STARS thermal simulation sector model developed in this study was used to analyze FBHT changes and understand the reasons. Twenty three main and five additional cases that were developed by using this model were simulated and relation of BHT with other parameters was investigated. Indeed the response of temperature to the change of some parameters such as bottom-hole pressure and gas-oil ratio was detected and correlation was tried to set between these elements. Observations showed that generally FBHT increases when GOR decreases and/or flowing bottom-hole pressure (FBHP) increases. This information allows estimating daily gas-oil ratios from continuously measured BHT. Results of simulation were compared with a real case and almost the same responses were seen. The increase in temperature after the start of water and gas injection or due to stopping of neighboring production wells indicated interwell communications. Additional cases were run to determine whether there are BHT changes when initial temperature was kept constant throughout the reservoir. Different iteration numbers and refined grids were used during these runs to analyze iteration errors / however no significant changes were observed due to iteration number differences and refined grids. These latter cases showed clearly that variations of temperature don&rsquo / t occur only due to geothermal gradient, but also pressure and saturation changes. On the whole, BHT can be used to get data ranging from daily gas-oil ratios to interwell connection if analyzed correctly.

ABSTRACT MODELING OF CARBON DIOXIDE SEQUESTRATION IN A DEEP SALINE AQUIFER BASBUg, BaSar M.S., Department of Petroleum and Natural Gas Engineering Supervisor : Prof. Dr. Fevzi G&uuml / mrah July 2005, 245 pages CO2 is one of the hazardous greenhouse gases causing significant changes in the environment. The sequestering CO2 in a suitable geological medium can be a feasible method to avoid the negative effects of CO2 emissions in the atmosphere. CO2 sequestration is the capture of, separation, and long-term storage of CO2 in underground geological environments. A case study was simulated regarding the CO2 sequestration in a deep saline aquifer. The compositional numerical model (GEM) of the CMG software was used to study the ability of the selected aquifer to accept and retain the large quantities of injected CO2 at supercritical state for long periods of time (200 years). A field-scale model with two injectors and six water producers and a single-well aquifer model cases were studied. In a single-well aquifer model, the effects of parameters such as vertical to horizontal permeability ratio, aquifer pressure, injection rate, and salinity on the sequestration process were examined and the sensitivity analyses were performed after simulating the field-scale model. The supercritical CO2, one-state fluid which exhibits both gas and liquid-like properties, and gaseous CO2 were sequestered in the forms of free CO2 bubble, dissolved CO2 in brine and precipitated CO2 with calcite mineral in a deep saline aquifer. The isothermal condition was assumed during injection and sequestration processes. The change in porosity and permeability values that might have occurred due to mineralization and CO2 adsorption on rock were not considered in this study. Vertical to horizontal permeability ratio and initial pressure conditions were the most dominating parameters affecting the CO2 saturation in each layer of the aquifer whereas CO2 injection rate influenced CO2 saturation in middle and bottom layers since CO2 was injected through bottom layer.

Hardware configurations, a control law, and a steering law are developed for a mixed hardware spacecraft that uses both control moment gyros and reaction wheels. Replacing one or more gyros in a spacecraft with a reaction wheel has potential for cost savings while still achieving much greater performance than using reaction wheels alone. Several simulated tests are run to compare the performance to a traditional all reaction wheel or all control moment gyro spacecraft, including analysis of failure modes and singular configurations. The mixed system performed similarly to all gyro systems, responding within 6% of the gyro system’s time for all nominal cases. It far exceeds the performance of reaction wheel systems, taking only a fourth of the time. It also handles failures better than reduced size gyro systems. As such, it can be an effective cost saving measure for certain satellite missions.