Les travaux de cette thèse portent sur l’analyse de stabilité et la synthèse de commandes robustes pour les systèmes affines à commutation en temps continu en présence d’incertitudes paramétriques constantes. On propose deux méthodes de commande permettant de garantir la stabilité asymptotique globale des systèmes affines à commutation avec paramètres inconnus. La première approche est basée sur l’estimation des paramètres inconnus et la reconstruction de l’état d’équilibre associée pour permettre d’appliquer une commande robuste adaptative. La seconde méthode est basée sur une augmentation d’état par l’ajout d’une action intégrale dans la boucle de commande qui garantit une erreur statique nulle. Pour chaque approche, deux lois de commande sont proposées. Une méthode du type « min switching » qui sélectionne la commutation la plus apte à stabiliser le système et une méthode de type « Embedded » permettant de générer une commande polytopique des différents modes possibles. Les résultats sont appliqués aux convertisseurs de puissance de topologie Flyback avec preuve de stabilité dans les deux modes de conduction (continue et discontinue) / This PhD thesis is focused on stability analysis and robust control synthesis for continuous time switching affine systems in presence of constant parametric uncertainties. Two control methods are proposed to guarantee global asymptotic stability of switching affine systems with unknown parameters. The first approach is based on the estimation of the unknown parameters and the reconstruction of the related equilibrium state to allow the application of a robust adaptive control. The second method is based on a state augmentation by adding an integral action in the control loop that guarantees a null steady state error. For each approach, two control laws are proposed. A "min switching" method that selects the most suitable mode to stabilize the system and an "Embedded" method that generates a polytopic control of the different possible modes. The results are applied to Flyback topology power converters with proof of stability in both conduction modes (continuous and discontinuous)

Avec une croissance considérable dans le domaine de la technologie multimédia et de la forte disponibilité des logiciels de traitement d'image, il est désormais facile de manipuler les images numériques. En même temps, il est devenu possible de réaliser des contrefaçons très élaborées, en laissant très peu de traces. Cela présente un grave problème, en particulier, si l'authenticité de l'image numérique est exigée. L'authentification des images devrait se baser sur leurs contenus visuels et non pas sur leurs contenus binaires. Par conséquent, pour authentifier une image, il faut tolérer quelques manipulations acceptables que pourrait subir une image telles que la compression JPEG et l'ajout de bruit Gaussien. En effet, ces manipulations préservent l'aspect visuel de l'image. En même temps un système de hachage perceptuel doit être suffisamment fragile pour détecter les manipulations malveillantes qui modifient l'interprétation du contenu sémantique de l'image comme l'ajout de nouveaux objets, la suppression ou la modification majeure d'objets existants.Dans cette thèse, nous nous intéressons aux fonctions de hachage perceptuel pour l'authentification et le contrôle d'intégrité des images numériques. Dans ce but, nous présentons tous les aspects relatifs aux fonctions de hachage perceptuel. Puis, nous exposons les contraintes qu'un système de hachage perceptuel doit satisfaire pour répondre aux exigences souhaitées au niveau de la robustesse des signatures perceptuelles. Enfin, nous présentons une méthode permettant d'améliorer la robustesse et la sécurité d'un système dehachage perceptuel. / The widespread use of multimedia technology has made it relatively easy to manipulate and tamper visual data. In particular, digital image processing and image manipulation tools offer facilities to intentionally alter image content without leaving perceptual traces. This presents a serious problem, particularly if the authenticity of the digital image is required. The image authentication should be based on their visual content and not on their binary content. Therefore, to authenticate an image, some acceptable manipulations that could undergoes an image, such as JPEG compression and Gaussian noise addition, must tolerated. Indeed, these manipulations preserve the visual appearance of the image. At the same time a perceptual hashing system should be sufficiently sensitive to detect malicious manipulations that modify the interpretation of the semantic content of the imagesuch as adding new objects, deleting or major modification of existing objects.In this thesis, we focus on perceptual hash functions for authentication and integrityverification of digital images. For this purpose, we present all aspects of perceptual hashfunctions. Then, we discuss the constraints that perceptual hashing system must satisfy tomeet desired level of robustness of perceptual signatures. Finally, we present a method toimprove the robustness and security of a system of perceptual hashing.

Arid regions tend to take careful measures to ensure water supplies are secured to consumers, to help provide the basis for further development. The distribution network is the most expensive part of the water supply infrastructure and it must maintain performance during unexpected incidents. Many aspects of performance have previously been discussed separately, including reliability, vulnerability, flexibility and resilience. This study aimed to develop a framework to bring together these aspects as found in the literature and industry practice, and bridge the gap between them. Semi-structured interviews with water industry experts were used to examine the presence and understanding of robustness factors. Thematic analysis was applied to investigate these and inform a conceptual framework including the component and topological levels. Robustness was described by incorporating network reliability and resiliency. The research focused on resiliency as a network-level concept derived from flexibility and vulnerability. To utilise this new framework, the study explored graph theory to formulate metrics for flexibility and vulnerability that combine network topology and hydraulics. The flexibility metric combines hydraulic edge betweenness centrality, representing hydraulic connectivity, and hydraulic edge load, measuring utilised capacity. Vulnerability captures the impact of failures on the ability of the network to supply consumers, and their sensitivity to disruptions, by utilising node characteristics, such as demand, population and alternative supplies. These measures together cover both edge (pipe) centric and node (demand) centric perspectives. The resiliency assessment was applied to several literature benchmark networks prior to using a real case network. The results show the benefits of combining hydraulics with topology in robustness analysis. The assessment helps to identify components or sections of importance for future expansion plans or maintenance purposes. The study provides a novel viewpoint overarching the gap between literature and practice, incorporating different critical factors for robust performance.

It is a standard practice in small area estimation (SAE) to use a model-based approach to borrow information from neighboring areas or from areas with similar characteristics. However, survey data tend to have gaps, ties and outliers, and parametric models may be problematic because statistical inference is sensitive to parametric assumptions. We propose nonparametric hierarchical Bayesian models for multi-stage finite population sampling to robustify the inference and allow for heterogeneity, outliers, skewness, etc. Bayesian predictive inference for SAE is studied by embedding a parametric model in a nonparametric model. The Dirichlet process (DP) has attractive properties such as clustering that permits borrowing information. We exemplify by considering in detail two-stage and three-stage hierarchical Bayesian models with DPs at various stages. The computational difficulties of the predictive inference when the population size is much larger than the sample size can be overcome by the stick-breaking algorithm and approximate methods. Moreover, the model comparison is conducted by computing log pseudo marginal likelihood and Bayes factors. We illustrate the methodology using body mass index (BMI) data from the National Health and Nutrition Examination Survey and simulated data. We conclude that a nonparametric model should be used unless there is a strong belief in the specific parametric form of a model.

Made available in DSpace on 2017-07-21T19:25:52Z (GMT). No. of bitstreams: 1 Roberto Antonio Vosgerau.pdf: 3034632 bytes, checksum: d2446020ebe5e27005459c7155a633b7 (MD5) Previous issue date: 2016-04-25 / In this thesis, we apply network entropy to analyze characteristics of complex networks. It is analyzed the effect of vertices removal on the structure and robustness of directed and undirected networks, as a result of failures and attacks. The variation in the structure and robustness of networks due to this removal is quantified by structural entropies with zero and one order approximation. These entropies are calculated to real networks to verify the robustness, where we have been using biological network as directed and literary network as undirected. The failures are simulated through vertices that are randomly removal, while the attacks are realized on the hubs and according to betweenness centrality. We observe that the network with failures exhibits entropies with values smaller than the original network. When the attack is on the hubs or according to the betweenness centrality we verify that the entropies decrease. However, if the attack is not on the hubs, it is possible to verify values of entropies larger than the original network. Moreover, the measure of the shortest path length showed a correlation with the structural entropy. / Nesta tese, aplicou-se a entropia de rede para analisar as características de redes complexas. Analisou-se o efeito da remoção de vértices sobre a estrutura e robustez das redes direcionadas e não direcionadas, como resultado de falhas e ataques. A variação na estrutura e robustez das redes devido a esta remoção é quantificada por entropias estruturais com aproximação de ordem zero e um. Estas entropias são calculados para redes reais para verificar a robustez, onde utilizou-se a rede biológica como direcionada e rede literária como não direcionada. As falhas são simuladas através de vértices que são removidos aleatoriamente, enquanto os ataques são realizados intencionalmente nos vértices de maiores graus e de acordo com a centralidade de intermediação. Observa-se que a rede com falhas exibe entropias com valores menores do que a rede original. Quando o ataque é nos vértices de maiores graus ou de acordo com as centralidades de intermediação verifica-se que as entropias diminuem. No entanto, se o ataque não está em vértices de maiores graus ou maiores centralidade de intermediação, é possível verificar valores de entropias maiores do que a rede original. Além disso, a medida do comprimento do menor percurso mostrou uma correlação com a entropia estrutural.

This thesis investigates network properties of natural food webs. In particular, it focuses on the e ect that external disturbances have on their substructures and robustness. The importance of a network-level methodology lies in its capacity to capture entangling species interactions and identify inter-connecting properties in heterogeneous food webs. The research rst analysed the responses of freshwater food webs under the stress of drought. A core/periphery structure was detected and its relative size was found to be unchanged after drought despite a signi cant biodiversity loss. Species extinction triggered extensive link rewiring and movement of species from the core to the periphery. These results showed that the robustness was maintained indicating that the redundancy in the core can e ectively mitigate species level perturbations. Secondly, the research further examined the e ects of Genetically Modi ed Herbicide Tolerant (GMHT) management on food web properties and robustness. Network analysis showed that such change in farming practice has no signi cant impact on the agro-ecosystems. However, crop switching, a common practice in agriculture, was found to pose much more significant changes on network properties and robustness when compared to GMHT crops. Thirdly, the research examined over 50 empirical food webs and demonstrated that the relative core size is a much more e ective indicator of food web robustness than the classical ecological measure connectance, as the latter was found to be insensitive to changes in the interaction patterns. Lastly, the research established the relationships between centrality measures and species ecological and/or functional role in food webs, and how they impact on network robustness.

A utilização de controladores preditivos multivariáveis na indústria de processos cresceu significativamente nos últimos anos principalmente devido à versatilidade e a confiabilidade que essa ferramenta proporciona em termos de controle avançado. No entanto, aspectos relacionados à aplicação prática do que vem sendo desenvolvido no meio acadêmico possui pouca difusão na indústria devido às configurações clássicas adotadas, como sistemas quadrados (com o mesmo número de variáveis controladas e manipuladas), modelos lineares, utilização de setpoint e etc. diferindo daquilo que está disponível e é amplamente utilizado industrialmente: sistemas não-quadrados (geralmente com mais variáveis controladas do que manipuladas), modelos não-lineares e utilização de soft-constraints. Esse trabalho propõe uma metodologia para ajuste dos parâmetros presentes em um controlador preditivo, atento à variedade de algoritmos presentes na indústria de processos. Essa metodologia se baseia na obtenção do melhor desempenho alcançável para cada cenário de um modelo global do processo, atendendo as restrições de Número de Desempenho Robusto relativo (rRPN), Máxima Sensibilidade e restrições nas ações de controle. Baseado em um desempenho que é alcançável, o modelo linear global é escalonado (assim como a planta não-linear) e os pesos que levam o sistema para a melhor condição operacional são estimados. Essa técnica abrange controladores operando em faixas e/ou setpoint e configurações não-quadradas, i.e., com mais variáveis controladas do que manipuladas. A abordagem proposta foi testada em uma planta de quatro tanques esféricos com aquecimento apresentando resultados coerentes, corroborando seu potencial de aplicação industrial. / Due to their versatility and reliability, Model Predictive Controllers (MPCs) are the standard solution for advanced process control in the process industry. However, there is a gap between the academic developments and the actual industrial applications, since the most academic studies focus on systems working with set-points and same number of manipulated and controlled variables, whereas the industrial application cope with non-squared configuration usually with several controlled variables in ranging and a reduced number of manipulated variables. This work proposes a tuning methodology for the countable parameters presents in a typical industrial predictive controller, considering the variety of the algorithms presents commercially in the process industry. This methodology is based on the estimation of the best attainable performance for each scenario of the global model of the process, constrained by the relative Robust Performance Number (rRPN), Maximal Sensitivity and restrictions in the control actions. Based on a performance that is attainable, the linear global model is scaled (and the non-linear) and the weights that lead the system to the best operational condition are estimated. This technique covers controllers operating in zones of control and/or set-point tracking and non-square configurations, i.e., with more controlled variables than manipulated. The proposed approach was tested in a Quadruple-Spherical tanks heating system presenting coherent results indicating its potential for industrial applications.

Este trabalho apresenta uma visão geral do modo de transmissão OFDM do padrão IEEE 802.16. O controle de acesso ao meio (MAC) e da camada física (PHY) são descritos em detalhes. Especialmente a estrutura do frame na camada (PHY). Além disso, as diferentes configurações da camada PHY com diferentes níveis de robustez são analisadas. Em seguida a simulação de um frame de dados com ADS (Advanced Design System) com todas as especificações da camada PHY são incluídas: Randomização, FEC, modulação adaptativa e IFFT/FFT. Um canal com multipercursos Rayleigh fading é implementada também. Finalmente são analisadas as curvas de espectro em freqüência e tempo, e a constelação no transmissor e receptor Downlink e Uplink, respectivamente. / This works presents a general overview of the mode of transmission OFDM standard IEEE 802.16. The medium access control (MAC) and physical layer (PHY) are described in detail, especially the structure of frame layer (PHY). Moreover, the different configurations PHY layers with different level strengths are analyzed. Then the simulation of a frame data with ADS (Advanced Design System) with all the specifications of PHY layer are included: Randomização, FEC, adaptive modulation and IFFT / FFT. A breaking multipath Rayleigh fading is implemented as well. In analyzes the curves of spectrum in frequency and time, and constellation in the transmitter and receiver Uplink and Downlink, respectively.

Cette thèse porte sur trois questions qui se posent en optimisation multi-objectif. Dansun premier temps, nous étudions l’existence de solutions efficaces via des techniquesde scalarisation. On étend le théorème de Benson du cas convexe à un cas général.De plus, nous examinons d’autres techniques de scalarisation. Dans un second temps,nous abordons la question de robustesse. Nous examinons les concepts proposés dansla littérature sur le sujet. On étend au cas d’optimisation multi-objectif non-linéairela définition de Georgiev et ses collaborateurs. Quelques conditions nécessaires etsuffisantes pour obtenir une solution robuste moyennant des hypothèses appropriéessont données. Les relations entre cette notion de robustesse et certaines définitionsmentionnées sont mises en évidence. Deux types de modifications des fonctions objectifsont traités et les relations entre les solutions faibles/propres/ robustes efficacessont établies. Le dernier chapitre est consacré à l’analyse de sensibilité et de stabilitéen optimisation multi-objectif paramétrée. On montre sous des conditions faibles quela multi-application de l’ensemble des solutions réalisables et des valeurs réalisablessont strictement semi-différentiables. On donne quelques conditions suffisantes pourla semi-différentiabilité de l’ensemble efficace et des valeurs efficaces. De plus, nousétudions la pseudo-Lipschitz continuité des multi-applications ci dessus citées. / In this thesis, three crucial questions arising in multi-objective optimization are investigated.First, the existence of properly efficient solutions via scalarization toolsis studied. A basic theorem credited to Benson is extended from the convex caseto the general case. Some further scalarization techniques are also discussed. Thesecond part of the thesis is devoted to robustness. Various notions from the literatureare briefly reviewed. Afterwards, a norm-based definition given by Georgiev, Lucand Pardalos is generalized to nonlinear multi-objective optimization. Necessary andsufficient conditions for robust solutions under appropriate assumptions are given.Relationships between new robustness notion and some known ones are highlighted.Two kinds of modifications in the objective functions are dealt with and relationshipsbetween the weak/proper/robust efficient solutions of the problems, before and afterthe perturbation, are established. Finally, we discuss the sensitivity analysis andstability in parametrized multi-objective optimization. Strict semi-differentiability ofset-valued mappings of feasible sets and feasible values is proved under appropriateassumptions. Furthermore, some sufficient conditions for semi-differentiability of efficientsets and efficient values are presented. Finally, pseudo-Lipschitz continuity ofaforementioned set-valued mappings is investigated

Este trabalho apresenta uma visão geral do modo de transmissão OFDM do padrão IEEE 802.16. O controle de acesso ao meio (MAC) e da camada física (PHY) são descritos em detalhes. Especialmente a estrutura do frame na camada (PHY). Além disso, as diferentes configurações da camada PHY com diferentes níveis de robustez são analisadas. Em seguida a simulação de um frame de dados com ADS (Advanced Design System) com todas as especificações da camada PHY são incluídas: Randomização, FEC, modulação adaptativa e IFFT/FFT. Um canal com multipercursos Rayleigh fading é implementada também. Finalmente são analisadas as curvas de espectro em freqüência e tempo, e a constelação no transmissor e receptor Downlink e Uplink, respectivamente. / This works presents a general overview of the mode of transmission OFDM standard IEEE 802.16. The medium access control (MAC) and physical layer (PHY) are described in detail, especially the structure of frame layer (PHY). Moreover, the different configurations PHY layers with different level strengths are analyzed. Then the simulation of a frame data with ADS (Advanced Design System) with all the specifications of PHY layer are included: Randomização, FEC, adaptive modulation and IFFT / FFT. A breaking multipath Rayleigh fading is implemented as well. In analyzes the curves of spectrum in frequency and time, and constellation in the transmitter and receiver Uplink and Downlink, respectively.