The problem of relative spacecraft motion estimation is considered with application to various reference and relative orbits. Mean circular and elliptic orbits are analyzed, with relative orbits ranging in size from 1 km to 10 km. Estimators are built for three propagation models: (i) Gim-Alfriend State Transition Matrix, (ii) the J2-Linearized Equations of Motion for Circular Orbits, and (iii) the Clohessy-Wiltshire Equations of Motion. Two alternative models were developed in an attempt to ac- count for unmodeled nonlinearities: (i) Biased Clohessy-Whiltshire Equations, and (ii) J2 -Linearized State Transition Matrix. Two estimation techniques are presented in an attempt to explore and determine which propagation model minimizes the error residual: the linear Kalman filter is presented under the assumption of vector based, GPS-type measurements; the extended Kalman filter is analyzed assuming angle-range, optical-type measurements. Sampling time is varied to look at the effect of measurement frequency. It is assumed that the orbit of one of the satellites, the chief, is known reasonably well. This work showed that the error residuals from the state estimates were minimized when the propagation technique utilized was the Gim-Alfriend State Transition Matrix. This supports conclusions that are obtained outside of the estimation problem. Additionally, the error residuals obtained when the propagation technique was the Clohessy-Wiltshire Equations is comparable to the more complicated models. Unmodeled nonlinearities affect the magnitude of the error residuals. As expected, the Gim-Alfriend STM comes closest to the truth; for smaller eccentricities (0.005), the Clohessy-Wiltshire EOM show minor deviations from the truth. As the eccentricity increases, the linear models begin to diverge greatly from the true response. The additional two models (the biased CW equations, and the linear STM) show decent performance under specific conditions. The former accounts for some of the unaccounted for nonlinearities. The latter exhibits comparable performance to the Gim-Alfrien STM for circular reference orbits. However, in each case, as the nonlinearity of the problem increases, the accuracy of the model decreases.

The complexity of technical systems has increased significantly in order to address evolving customer needs and environmental concerns. From a product development process viewpoint, the pervasive nature of multi-disciplinary systems (i.e. mechanical, electrical, electronic, control, software) has brought some important integration challenges to overcome conventional disciplinary boundaries imposed by discipline specific approaches. This research focuses on functional reasoning, aiming to develop a structured framework based on the System State Flow Diagram (SSFD) for function modelling of complex multidisciplinary systems on a practical and straightforward basis. The framework is developed at two stages. 1) The development of a prototype for the SSFD framework. The proposed SSFD framework are tested and validated through application to selected desktop case studies. 2) Further development and extension of the SSFD framework for the analysis of complex multidisciplinary systems with multiple operation modes and functional requirements. The developed framework is validated on real world case studies collaborated with industrial partners. The main conclusion of this research is that the SSFD framework offers a rigorous and coherent function modelling methodology for the analysis of complex multidisciplinary systems. Further advantages of the SSFD framework is that 1) the effectiveness of the Failure Mode Avoidance (FMA) process can be enhanced by integrating the SSFD framework with relevant tools of the FMA process, and 2) the integration of the SSFD with the SysML systems engineering diagrams is doable, which can promote the take-up of the approach in industry.

The complexity of technical systems has increased significantly in order to address evolving customer needs and environmental concerns. From a product development process viewpoint, the pervasive nature of multi-disciplinary systems (i.e. mechanical, electrical, electronic, control, software) has brought some important integration challenges to overcome conventional disciplinary boundaries imposed by discipline specific approaches. This research focuses on functional reasoning, aiming to develop a structured framework based on the System State Flow Diagram (SSFD) for function modelling of complex multidisciplinary systems on a practical and straightforward basis. The framework is developed at two stages. 1) The development of a prototype for the SSFD framework. The proposed SSFD framework are tested and validated through application to selected desktop case studies. 2) Further development and extension of the SSFD framework for the analysis of complex multidisciplinary systems with multiple operation modes and functional requirements. The developed framework is validated on real world case studies collaborated with industrial partners. The main conclusion of this research is that the SSFD framework offers a rigorous and coherent function modelling methodology for the analysis of complex multidisciplinary systems. Further advantages of the SSFD framework is that 1) the effectiveness of the Failure Mode Avoidance (FMA) process can be enhanced by integrating the SSFD framework with relevant tools of the FMA process, and 2) the integration of the SSFD with the SysML systems engineering diagrams is doable, which can promote the take-up of the approach in industry. / Automotive Research Centre

The grid of the future will be more decentralized due to the significant increase in distributed generation, and microgrids. In addition, due to the proliferation of large-scale intermittent wind power, the randomness in power system state will increase to unprecedented levels. This dissertation proposes a new state transition model for power system forecasting-aided state estimation, which aims at capturing the increasing stochastic nature in the states of the grid of the future. The proposed state forecasting model is based on time-series modeling of filtered system states and it takes spatial correlation among the states into account. Once the states with high spatial correlation are identified, the time-series models are developed to capture the dependency of voltages and angles in time and among each other. The temporal correlation in power system states (i.e. voltage angles and magnitudes) is modeled by using autoregression, while the spatial correlation among the system states (i.e. voltage angles) is modeled using vector autoregression. Simulation results show significant improvement in power system state forecasting accuracy especially in presence of distributed generation and microgrids. / Ph. D.

The main objective of this work is to demonstrate some new computational methods for estimation, optimization and modeling of dynamical systems that use automatic differentiation. Particular focus will be upon dynamical systems arising in Aerospace Engineering. Automatic differentiation is a recursive computational algorithm, which enables computation of analytically rigorous partial derivatives of any user-specified function. All associated computations occur, in the background without user intervention, as the name implies. The computational methods of this dissertation are enabled by a new automatic differentiation tool, OCEA (Object oriented Coordinate Embedding Method). OCEA has been recently developed and makes possible efficient computation and evaluation of partial derivatives with minimal user coding. The key results in this dissertation details the use of OCEA through a number of computational studies in estimation and dynamical modeling. Several prototype problems are studied in order to evaluate judicious ways to use OCEA. Additionally, new solution methods are introduced in order to ascertain the extended capability of this new computational tool. Computational tradeoffs are studied in detail by looking at a number of different applications in the areas of estimation, dynamical system modeling, and validation of solution accuracy for complex dynamical systems. The results of these computational studies provide new insights and indicate the future potential of OCEA in its further development.

Stock market plays an important role in the modern capital market. As a result, the prediction of financial assets attracts people in different areas. Moreover, it is commonly accepted that stock price movement generally follows a major trend. As a result, forecasting the market trend becomes an important mission for a prediction method. Accordingly, we will predict the long term trend rather than the movement of near future or change in a trading day as the target of our predicting approach. Although there are various kinds of analyses for trend prediction, most of them use clear cuts or certain thresholds to classify the trends. Users (or investors) are not informed with the degrees of confidence associated with the recommendation or the trading signal. Therefore, in this research, we would like to study an approach that could offer the confidence of the trend analysis by providing the probabilities of each possible state given its historical data through Dynamic Bayesian Network. We will incorporate the well-known principles of Dow¡¦s Theory to better model the trend of stock movements. Through the results of our experiment, we may say that the financial performance of the proposed model is able to defeat the buy and hold trading strategy when the time scope covers the entire cycle of a trend. It also means that for the long term investors, our approach has high potential to win the excess return. At the same time, the trading frequency and correspondently trading costs can be reduced significantly.

Un système embarqué est un système électronique et informatique autonome dédié à une tâche précise. Dans le secteur de l’automobile, le nombre de systèmes embarqués dans les voitures a considérablement augmenté au cours de ces dernières années et va certainement continuer à augmenter. Ces systèmes sont dédiés entre autres, à la sécurité, au confort de conduite,et à l’assistance à la conduite. Cette croissance des systèmes est associée avec une croissance en taille des logiciels qui les contrôlent. En conséquence, leur gestion(système et logiciel) devient de plus en plus complexe et problématique. Par ailleurs, la concurrence dans le secteur automobile est très féroce et les temps de mise sur le marché sont de plus en plus courts. Ainsi, pour garantir le bon fonctionnement des systèmes en général et du logiciel en particulier, étant donné leur complexité,et aussi les délais courts de mise sur le marché des produits automobiles, de nouvelles méthodes de développement doivent être considérées. Ainsi, de nombreuses méthodes de développement, incluant de nouveaux standards (de développement) et approches automatiques ont émergé au cours de ces dernières années. Dans le cas particulier de la vérification et validation de logiciel, une des activités critiques qui a connu une avancée significative est la génération de cas de test, avec l’avènement d’approches automatiques.Malgré cela, ces approches peinent souvent à s’imposer en milieu industriel. Une des raisons est que celles ci sont souvent peu adaptées ou peu utilisées dans un contexte industriel.Dans ce contexte, cette thèse vise à proposer une approche de vérification et de validation de logiciels embarqués, basée sur la génération automatique de cas de test. Pour cela, nous avons mis en place une approche permettant de représenter sous forme de modèles abstraits les spécifications d’un logiciel, puis de générer à partir de ces modèles un ensemble de cas de test en considérant en particulier le critère de couverture MC/DC. / An embedded system is a system that performs a specific task and has a computer embedded inside. In the automotive sector, the amount of embedded systems in the vehicle has risen dramatically in recent years and is set to increase. They deal essentially with safety, comfort, and driving assistance. Furthermore, the increase in number and complexity of the systems is associated with a growth in software. As a consequence, their management (system and software) have become more and more complex and problematic. Also, the competition and time-to-market in the automotive industry are very tough. Thus, to guarantee the efficiency and reliability of the embedded systems in the vehicle in general and the software in particular, in view of the complexity as well as the competition and time-to-market law, new development methods should be considered. Therefore, new development methods including new standards, and automatic approaches have emerged over the last years. In the particular case of embedded software verification and validation, one of the most critical activities that has experienced a significant progress is test case generation with the advent of automatic approaches. Despite this, these approaches are not widely used or are not well adapted in industrial context. In that context, our goal in this PhD. thesis is to propose a new verification and validation approach, based on automatic test case generation of embedded embedded. Thus, we have set up an approach that automatically generates test cases, with respect to the MC/DC criterion, from abstract models of the software specifications expressed in the form of state-transition models.

M42 aminopeptidases are dinuclear enzymes widely found in prokaryotes but completely absent from eukaryotes. They have been proposed to hydrolyze peptides downstream the proteasome or other related proteolytic complexes. Their description relies mainly on the pioneering work on four M42 aminopeptidases from Pyrococcus horikoshii. Their quaternary structure consists of twelve subunits adopting a tetrahedral-shaped structure. Such a spatial organization allows the compartmentalization of the active sites which are only accessible to unfolded peptides. The dodecamer assembly results from the self-association of dimers under the control of the metal ion cofactors. Both oligomers have been shown to co-exist in vivo and heterododecamers with broadened substrate specificity may even occur. Yet, the molecular determinants behind the dodecamer assembly remain unknown due the lack of a high-resolution structure of a stable dimer. In addition, the bacterial M42 aminopeptidases are still ill-described due to the paucity of structural studies. This work focuses mainly on the characterization of TmPep1050, an M42 aminopeptidase from Thermotoga maritima. As expected, TmPep1050 adopts the genuine tetrahedral-shaped structure with twelve subunits. It also displays a leucyl-aminopeptidase activity requiring Co2+ as a cofactor. In addition to its catalytic function, Co2+ has a role in the enzyme thermostability and oligomerization. The absence of Co2+ provokes the disassembly of active TmPep1050 dodecamers into inactive dimers. The process, however, is reversible since Co2+ triggers the self-association of dimers into dodecamers, as shown by native MS. The main achievement of this work is the determination of the first high-resolution structure of a dimer, allowing to better understand the dimer-dodecamer transition. Several structural motifs involved in oligomerization are displaced or highly flexible in the TmPep1050 dimer structure. Furthermore, a loop bringing two catalytic relevant residues is displaced outside the catalytic site. These residues are the catalytic base and a ligand involved in the Co2+ binding at the M1 site. The metal ion binding sites have been further investigated to define how they influence the oligomerization of TmPep1050. A mutational study shows that the M1 site strictly controls the dodecamer formation while the M2 site contributes only partly to it. A strictly conserved aspartate residue of the M2 site second shell also plays an important structural role in maintaining the active site integrity. Indeed, its substitution prevents the formation of dodecamer probably due to the lack of stabilization of the active site loop. The characterization of TmPep1050 supports that bacterial M42 aminopeptidases probably share the quaternary structures and dodecamer assembly with their archaeal counterparts. The dimer structure highlights several structural modifications occurring in the dimer-dodecamer transition. Yet, based on current knowledge, no general rules can be drawn for the role of the M1 and M2 sites in oligomerization. Besides, the physiological function of the M42 aminopeptidases is under-examined albeit the proposed link to the proteasome. In this work, this has been investigated using the Escherichia coli M42 aminopeptidases as a model. Yet, no phenotype has been associated to the deletion of their coding genes. Preliminary results have shown that the three enzymes (i) display a redundant substrate specificity, (ii) could be localized partly to the membrane, and (iii) form heterocomplexes. Further experiments are still required to crack the function of these M42 aminopeptidases. / Option Biologie moléculaire du Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Thesis (MA)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: This research study aims to analyze the illicit arms trade in states in transition. While both the study of the illicit arms trade and the study of states in transition per se, are characterized by a variety of concepts and debates within academia, this study attempts to establish a coherent and concise connection between the two. Therefore, the main research question is: How do the capacity gaps of social control, social welfare, border control and legitimacy contribute to the proliferation of the illicit arms trade in states in transition? For the purpose of this study, the researcher uses the theoretical framework based on capacity gaps and functional holes as outlined by Phil Williams (2002). Williams (2002) states that organized crime and transnational organized crime (TOC), which the illicit arms trade is a part of, flourish in states that are weakened by capacity gaps and where the accompanying functional holes open up the way for organized crime and TOC to work with impunity. The seven capacity gaps that Williams (2002) outlines are: social control, social welfare, business regulation, oversight and accountability, border control, legitimacy and electoral norms and patterns. However, this thesis does not focus on all seven capacity gaps; instead, only the capacity gaps of social control, social welfare, border control and legitimacy are analysed. This decision has been based on the literature by Williams (2002), Migdal (1988), Beck and Laeven (2006), who suggest that a state in transition cannot complete its transitional period and become a consolidated democracy if high levels of social control, social welfare, respect for the rule of law and legitimacy are not obtained. Moreover, this research study conducts a comparative analysis of two states in transition, South Africa and Croatia, which have both been experiencing difficulties with TOC and the illicit arms trade, and where both states still have not completed their transitional period, and are thus not consolidated democracies. This research does not imply that the findings of this study are applicable to all states in transition; the focus is rather on how the four capacity gaps and functional holes that this research focused on contribute to the proliferation of the illicit arms trade in South Africa and Croatia. The findings indicate that due to high levels of corruption within the judicial system and police, the citizens of South Africa and Croatia lack trust in the states’ capacity to impose social control, which in turn opens the way for organized criminal groups to work with impunity. Furthermore, the social welfare capacity gap contributes to the rise in levels of organized crime and the illicit arms trade due to the fact that levels of inequality and unemployment force the citizens of South Africa and Croatia to look for alternative survival strategies, usually those that organized criminal groups can provide them with. Moreover, the lack of resources and corruption among custom officials and police staff, serve as opportunities for organized criminal groups to traffic illicit goods over South Africa and Croatia’s borders; thus indicating a functional hole in the states interdictory capacity and an overall gap in the states capacity to control its borders. Lastly, due to the South African and Croatian citizens’ lack of trust in the institutions and the state apparatus in general, the capacity gap of legitimacy is visible. This in turn opens the way for organized criminal groups to use patron-client relationships with the citizens of South Africa and Croatia, in order to build and sustain a level of popular legitimacy that the state is lacking. / AFRIKAANSE OPSOMMING: Hierdie navorsingsprojek streef daarna om die onwettige handel in wapens as deel van transnasionale georganiseerde misdaad binne state in transisie te analiseer. Alhoewel navorsing in die onwettige handel van wapens, asook die studie van state in transisie gekenmerk word deur vele konsepte en debatte binne die velde; poog hierdie studie om die twee konsepte in ʼn duidelike en presiese manier te verbind. In die lig hiervan is die navorsings vraag: Hoe dra die kapasiteitsgapings van sosiale beheer, sosiale welvaart, grens kontrole en legitimiteit by tot die volhoubaarheid van die onwettige handel in wapens in state in transisie? Vir die doel van hierdie studie het die navorser besluit om gebruik te maak van die teoretiese raamwerk gebaseer op kapasiteitsgapings en funksionele-openinge soos beskryf deur Phil Williams (2002). Wiliams (2002) voer aan dat georganiseerde misdaad en transnasionale misdaad, waarvan die onwettige handel in wapens ʼn deel uitmaak, floreer in state wat verswak is deur kapasitietsgapings; en waar bygaande funksionele-openinge die weg baan vir transnasionale misdaad om te floreer. Die sewe kapasiteitsgapings soos deur Williams (2002) beskryf is: sosiale beheer, sosiale welvaart, besigheid-regulering, oorsig en aanspreeklikheid, grens kontrole, legitimiteit en verkiesings norme en patrone. Hierdie tesis fokus egter nie op al sewe kapasiteitsgapings nie. Daar word slegs gefokus op die kapasiteitsgapings van sosiale beheer, sosiale welvaart, grens kontrole en legitimiteit. Hierdie besluit is gebaseer op literatuur deur William (2002), Joel S. Migdal (1988), Thorsten Beck en Luc Laeven (2006) en dies meer wat voorstel dat ʼn staat in transisie nie die transisie periode kan voltooi en ʼn vaste demokrasie kan raak indien hoe vlakke van sosiale beheer, sosiale welvaart, respek vir wet en orde en legitimiteit nie verkry word nie. Verder maak hierdie navorsing gebruik van ʼn vergelykende analise tussen twee state in transisie: Suid Afrika en Kroasië. Beide hierdie state ervaar probleme met trans-nasionale misdaad en die onwettige handel in wapens. Beide het ook nog nie hul transisie periode voltooi nie en is dus nie vaste of gekonsolideerde demokrasieë nie. Hoewel die navorser nie aanvoer dat die bevindinge van hierdie studie van toepassing is op alle state in transisie nie, probeer die navorser vasstel hoe die vier kapasiteitsgapings en funksionele-openinge bydrae tot die volhoubaarheid van die onwettige handel in wapens in Suid Afrika en Kroasië. Die bevindinge dui daarop dat as gevolg van hoë vlakke van korrupsie binne die regstelsel en polisie, die bevolking van Suid Afrika en Kroasië nie die staat se kapasiteit om sosiale beheer te handhaaf, vertrou nie. Dit maak die gaping oop vir georganiseerde misdaad om sonder teenkant te handel. Verder, die sosiale welvaart gaping, dra by tot die toename in die vlakke van georganiseerde misdaad en die onwettige handel in wapens as gevolg van hoë vlakke van ongelykheid en armoede, wat die bevolking van Suid Afrika en Kroasië dwing tot alternatiewe metodes van oorlewing wat gewoonlik deur georganiseerde misdaad groepe verskaf word. Verder, die gebrek aan toerusting en ook korrupsie binne grensbeheer en polisie lede, verskaf die geleentheid vir georganiseerde misdaad groepe om in onwettige goedere te handel. Dit dui op die funksionele gaping in die staat se beheersmeganismes en oor die algemeen ʼn gaping in die staat se kapasiteit om grense te beheer. Ten laaste, as gevolg van die gebrek aan vertroue van die bevolking in die strukture van die staat Suid Afrika en Kroasië is die kapasitietsgaping van legitimiteit duidelik teenwoordig. Dit open die weg vir georganiseerde misdaad groepe om populêre gesag op te bou, wat daar nie is by die regering van die lande nie.

De nombreux systèmes complexes soumis à un ajout continu d'énergie réagissent à cet ajout par une accumulation de tension au cours du temps, interrompue par de soudaines libérations d'énergie appelées avalanches. Récemment, il a été remarqué que plusieurs propriétés élémentaires de la dynamique d'avalanche sont issues de processus de relaxation ayant lieu à une échelle microscopique, processus qui sont négligés dans la plupart des modèles. Lors de ma thèse, j'ai étudié deux modèles classiques d'avalanches, modifiés par l'ajout d'une forme de relaxation la plus simple possible. Le premier système est une interface viscoélastique tirée à travers un milieu désordonné. En champ moyen, nous prouvons que l'interface a un comportement périodique caractérisé par une nouvelle échelle temporelle (émergente), avec des avalanches qui touchent l'ensemble du système. Le calcul semi-analytique de la force de friction agissant sur la surface donne des résultats compatibles avec les expériences de friction classique. En dimension finie (2D), les événements touchant l'ensemble du système (trouvés en champ moyen) deviennent localisés, et les simulations numériques donnent des résultats en bon accord avec plusieurs caractéristiques importantes des tremblements de terre, tant qualitativement que quantitativement. Le second système incluant également une forme très simple de relaxation est un modèle jouet d'avalanche : c'est la percolation dirigée. Dans notre étude d'une variante non-markovienne de la percolation dirigée, nous avons observé que la classe d'universalité était modifiée mais seulement partiellement. En particulier, un exposant change de valeur tandis que plusieurs relations d'échelle sont préservées. Cette idée d'une classe d'universalité étendue, obtenue par l'ajout d'une perturbation non-markovienne offre des perspectives prometteuses pour notre premier système. / Many complex systems respond to a continuous input of energy by an accumulation of stress over time, interrupted by sudden energy releases called avalanches. Recently, it has been pointed out that several basic features of avalanche dynamics are induced at the microscopic level by relaxation processes, which are neglected by most models. During my thesis, I studied two well-known models of avalanche dynamics, modified minimally by the inclusion of some forms of relaxation. The first system is that of a viscoelastic interface driven in a disordered medium. In mean-field, we prove that the interface has a periodic behaviour (with a new, emerging time scale), with avalanche events that span the whole system. We compute semi-analytically the friction force acting on this surface, and find that it is compatible with classical friction experiments. In finite dimensions (2D), the mean-field system-sized events become local, and numerical simulations give qualitative and quantitative results in good agreement with several important features of real earthquakes. The second system including a minimal form of relaxation consists in a toy model of avalanches: the Directed Percolation process. In our study of a non-Markovian variant of Directed Percolation, we observed that the universality class was modified but not completely. In particular, in the non-Markov case an exponent changes of value while several scaling relations still hold. This picture of an extended universality class obtained by the addition of a non-Markovian perturbation to the dynamics provides promising prospects for our first system.