Life presents fascinating examples of self-organization and emergent phenomena. In multi-cellular organisms, a multitude of cells interact to form and maintain highly complex body plans. This requires reliable communication between cells on various length scales. First, there has to be the right number of cells to preserve the integrity of the body and its size. Second, there have to be the right types of cells at the right positions to result in a functional body layout. In this thesis, we investigate theoretical feedback mechanisms for both self-organized body plan patterning and size control. The thesis is inspired by the astonishing scaling and regeneration abilities of flatworms. These worms can perfectly regrow their entire body plan even from tiny amputation fragments like the tip of the tail. Moreover, they can grow and actively de-grow by more than a factor of 40 in length depending on feeding conditions, scaling up and down all body parts while maintaining their functionality. These capabilities prompt for remarkable physical mechanisms of pattern formation. First, we explore pattern scaling in mechanisms previously proposed to describe biological pattern formation. We systematically extract requirements for scaling and highlight the limitations of these previous models in their ability to account for growth and regeneration in flatworms. In particular, we discuss a prominent model for the spontaneous formation of biological patterns introduced by Alan Turing. We characterize the hierarchy of steady states of such a Turing mechanism and demonstrate that Turing patterns do not naturally scale. Second, we present a novel class of patterning mechanisms yielding entirely self-organized and self-scaling patterns. Our framework combines a Turing system with our derived principles of pattern scaling and thus captures essential features of body plan regeneration and scaling in flatworms. We deduce general signatures of pattern scaling using dynamical systems theory. These signatures are discussed in the context of experimental data. Next, we analyze shape and motility of flatworms. By monitoring worm motility, we can identify movement phenotypes upon gene knockout, reporting on patterning defects in the locomotory system. Furthermore, we adapt shape mode analysis to study 2D body deformations of wildtype worms, which enables us to characterize two main motility modes: a smooth gliding mode due to the beating of their cilia and an inchworming behavior based on muscle contractions. Additionally, we apply this technique to investigate shape variations between different flatworm species. With this approach, we aim at relating form and function in flatworms. Finally, we investigate the metabolic control of cell turnover and growth. We establish a protocol for accurate measurements of growth dynamics in flatworms. We discern three mechanisms of metabolic energy storage; theoretical descriptions thereof can explain the observed organism growth by rules on the cellular scale. From this, we derive specific predictions to be tested in future experiments. In a close collaboration with experimental biologists, we combine minimal theoretical descriptions with state-of-the-art experiments and data analysis. This allows us to identify generic principles of scalable body plan patterning and growth control in flatworms. / Die belebte Natur bietet uns zahlreiche faszinierende Beispiele für die Phänomene von Selbstorganisation und Emergenz. In Vielzellern interagieren Millionen von Zellen miteinander und sind dadurch in der Lage komplexe Körperformen auszubilden und zu unterhalten. Dies verlangt nach einer zuverlässigen Kommunikation zwischen den Zellen auf verschiedenen Längenskalen. Einerseits ist stets eine bestimmte Zellanzahl erforderlich, sodass der Körper intakt bleibt und seine Größe erhält. Anderseits muss für einen funktionstüchtigen Körper aber auch der richtige Zelltyp an der richtigen Stelle zu finden sein. In der vorliegenden Dissertation untersuchen wir beide Aspekte, die Kontrolle von Wachstum sowie die selbstorganisierte Ausbildung des Körperbaus. Die Dissertation ist inspiriert von den erstaunlichen Skalierungs- und Regenerationsfähigkeiten von Plattwürmern. Diese Würmer können ihren Körper selbst aus winzigen abgetrennten Fragmenten -wie etwa der Schwanzspitze- komplett regenerieren. Darüberhinaus können sie auch, je nach Fütterungsbedingung, um mehr als das 40fache in der Länge wachsen oder schrumpfen und passen dabei alle Körperteile entsprechend an, wobei deren Funktionalität erhalten bleibt. Diese Fähigkeiten verlangen nach bemerkenswerten physikalischen Musterbildungsmechanismen. Zunächst untersuchen wir das Skalierungsverhalten von früheren Ansätzen zur Beschreibung biologischer Musterbildung. Wir leiten daraus Voraussetzung für das Skalieren ab und zeigen auf, dass die bekannten Modelle nur begrenzt auf Wachstum und Regeneration von Plattwürmern angewendet werden können. Insbesondere diskutieren wir ein wichtiges Modell für die spontane Entstehung von biologischen Strukturen, das von Alan Turing vorgeschlagen wurde. Wir charakterisieren die Hierarchie von stationären Zuständen solcher Turing Mechanismen und veranschaulichen, dass diese Turingmuster nicht ohne weiteres skalieren. Daraufhin präsentieren wir eine neuartige Klasse von Musterbildungsmechanismen, die vollständig selbstorgansierte und selbstskalierende Muster erzeugen. Unser Ansatz vereint ein Turing System mit den zuvor hergeleiteten Prinzipien für das Skalieren von Mustern und beschreibt dadurch wesentliche Aspekte der Regeneration und Skalierung von Plattwürmern. Mit Hilfe der Theorie dynamischer Systeme leiten wir allgemeine Merkmale von skalierenden Mustern ab, die wir im Hinblick auf experimentelle Daten diskutieren. Als nächstes analysieren wir Form und Fortbewegung der Würmer. Die Auswertung des Bewegungsverhaltens, nachdem einzelne Gene ausgeschaltet wurden, ermöglicht Rückschlüsse auf die Bedeutung dieser Gene für den Bewegungsapparat. Darüber hinaus wenden wir eine Hauptkomponentenanalyse auf die Verformungen des zweidimensionalen Wurmkörpers während der natürlichen Fortbewegung an. Damit sind wir in der Lage, zwei wichtige Fortbewegungsstrategien der Würmer zu charakterisieren: eine durch den Zilienschlag angetriebene gleichmässige Gleitbewegung und eine raupenartige Bewegung, die auf Muskelkontraktionen beruht. Zusätzlich wenden wir diese Analysetechnik auch an, um Unterschiede in der Gestalt von verschiedenen Plattwurmarten zu untersuchen. Grundsätzlich zielen alle diese Ansätze darauf ab, das Aussehen der Plattwürmer mit den damit verbundenen Funktionen verschiedener Körperteile in Beziehung zu setzen. Schlussendlich erforschen wir den Einfluss des Stoffwechsels auf den Zellaustausch und das Wachstum. Dazu etablieren wir Messungen der Wachstumsdynamik in Plattwürmern. Wir unterscheiden drei Mechanismen für das Speichern von Stoffwechselenergie, deren theoretische Beschreibung es uns ermöglicht, das beobachtete makroskopische Wachstum des Organismus mit dem Verhalten der einzelnen Zellen zu erklären. Basierend darauf leiten wir Vorhersagen ab, die nun experimentell getestet werden. In enger Zusammenarbeit mit Kollegen aus der experimentellen Biologie führen wir minimale theoretische Beschreibungen mit modernsten Experimenten und Analysetechniken zusammen. Dadurch sind wir in der Lage, Grundlagen sowohl der skalierbaren Ausbildung des Körperbaus als auch der Wachstumskontrolle bei Plattwürmern herauszuarbeiten.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

Modelos e teorias científicas surgem da necessidade do homem entender melhor o funcionamento do mundo em que vive. Constantemente, novos modelos e técnicas são criados com esse objetivo. Uma dessas teorias recentemente desenvolvida é a da Criticalidade Auto-Organizada. No Capítulo 2 desta tese, apresentamos uma breve introdução a Criticalidade Auto-Organizada. Tendo a criticalidade auto-organizada como pano de fundo, no Capítulo 3, estudamos a dinâmica Bak-Sneppen (e diversas variantes) e a comparamos com alguns algoritmos de otimização. Apresentamos no Capítulo 4, uma revisão histórica e conceitual das redes complexas. Revisamos alguns importantes modelos tais como: Erdös-Rényi, Watts-Strogatz, de configuração e Barabási-Albert. No Capítulo 5, estudamos o modelo Barabási-Albert não-linear. Para este modelo, obtivemos uma expressão analítica para a distribuição de conectividades P(k), válida para amplo espectro do espaço de parâmetros. Propusemos também uma forma analítica para o coeficiente de agrupamento, que foi corroborada por nossas simulações numéricas. Verificamos que a rede Barabási-Albert não-linear pode ser assortativa ou desassortativa e que, somente no caso da rede Barabási-Albert linear, ela é não assortativa. No Capítulo 6, utilizando dados coletados do CD-ROM da revista Placar, construímos uma rede bastante peculiar -- a rede do futebol brasileiro. Primeiramente analisamos a rede bipartida formada por jogadores e clubes. Verificamos que a probabilidade de que um jogador tenha participado de M partidas decai exponencialmente com M, ao passo que a probabilidade de que um jogador tenha marcado G gols segue uma lei de potência. A partir da rede bipartida, construímos a rede unipartida de jogadores, que batizamos de rede de jogadores do futebol brasileiro. Nessa rede, determinamos várias grandezas: o comprimento médio do menor caminho e os coeficientes de agrupamento e de assortatividade. A rede de jogadores de futebol brasileiro nos permitiu analisar a evolução temporal dessas grandezas, uma oportunidade rara em se tratando de redes reais. / Models and scientific theories arise from the necessity of the human being to better understand how the world works. Driven by this purpose new models and techniques have been created. For instance, one of these theories recently developed is the Self-Organized Criticality, which is shortly introduced in the Chapter 2 of this thesis. In the framework of the Self-Organized Criticality theory, we investigate the standard Bak-Sneppen dynamics as well some variants of it and compare them with optimization algorithms (Chapter 3). We present a historical and conceptual review of complex networks in the Chapter 4. Some important models like: Erdös-Rényi, Watts-Strogatz, configuration model and Barabási-Albert are revised. In the Chapter 5, we analyze the nonlinear Barabási-Albert model. For this model, we got an analytical expression for the connectivity distribution P(k), which is valid for a wide range of the space parameters. We also proposed an exact analytical expression for the clustering coefficient which corroborates very well with our numerical simulations. The nonlinear Barabási-Albert network can be assortative or disassortative and only in the particular case of the linear Barabási-Albert model, the network is no assortative. In the Chapter 6, we used collected data from a CD-ROM released by the magazine Placar and constructed a very peculiar network -- the Brazilian soccer network. First, we analyzed the bipartite network formed by players and clubs. We find out that the probability of a footballer has played M matches decays exponentially with M, whereas the probability of a footballer to score G gols follows a power-law. From the bipartite network, we built the unipartite Brazilian soccer players network. For this network, we determined several important quantities: the average shortest path length, the clustering coefficient and the assortative coefficient. We were also able to analise the time evolution of these quantities -- which represents a very rare opportunity in the study of real networks.

A presente tese tem como objetivo produzir subsídios para a construção de um referencial teórico-metodológico sobre a utilização dos objetos de aprendizagem no contexto das comunidades virtuais auto-organizadas para a produção de software livre e de código aberto. Utiliza-se como metodologia a etnografia virtual (HINE, 2000) em conjunto com a teoria analítica da ação mediada (WERTSCH, 1991) e a análise de conteúdo (BARDIN, 2000). A coleta de dados foi efetuada, em duas fases, nos fóruns de discussão de quatro (4) comunidades, além de uma comunidade incubadora de desenvolvimento de projetos de software livre e de código aberto. Constata-se que os objetos de aprendizagem mediam o processo de solução de problemas, uma vez que 100% dos problemas da amostra analisada foram resolvidos, apesar da ausência de um padrão de conformidade desses objetos. Esta limitação é superada em razão do perfil específico imperante dos membros ativos da comunidade, pois estes possuem elevado nível de comportamento colaborativo/cooperativo, iniciativa voluntária, desprendimento, obstinação, capacidade de autoaprendizagem, autonomia, independência, disciplina, responsabilidade e comprometimento com prazos, qualidade dos produtos e outras exigências estabelecidas pela comunidade. Outro fator de relevância é que as comunidades são ricas em interação humana, o que qualifica o processo do significado da mediação e o ambiente de colaboração, nas ações referentes à localização, montagem e contextualização dos objetos de aprendizagem. Os significativos resultados atingidos por estas comunidades têm impactado, sobremaneira, as grandes organizações de produção de software, levando-as a rever suas estratégias corporativas, boas práticas de desenvolvimento, gestão de pessoas, equipes e projetos. Por outro lado, infere-se que a sustentabilidade de tais comunidades não pode estar assentada somente em atributos e habilidades pessoais, principalmente pelo fato de que a localização dos objetos de aprendizagem para a solução de problemas baseia-se no conhecimento tácito de seus membros. Necessário se faz agregar inovações na forma e funcionalidade de tais comunidades (padrão de conformidade, métodos e ferramentas tecnológicas), com vistas a possibilitar uma efetiva e universal acessibilidade do conhecimento produzido para a solução mais eficiente dos problemas, bem como incorporar membros com comportamentos e habilidades diversos. Os resultados desta pesquisa contribuem para as inovações futuras, no campo teórico e prático, na definição de um padrão de conformidade para a especificação, indexação, uso, combinação e avaliação dos objetos de aprendizagem, além de motivar a mudança de comportamento, cultura e forma de aprender. / The present thesis aims to produce subsidies for the development of a theoreticalmethodological referential on the use of learning objects in the context of self-organized virtual communities for the development of free and open source software. The methodologies used were the virtual ethnography (HINE, 2000), together with the mediated action analytical theory (WERTSCH, 1991) and content analysis (BARDIN, 2000). Data was collected in two phases: from the discussion forums of (4) four communities, and from an incubator community for the development of free and open source software projects. The learning objects appear to mediate the problem solution processes, since all the problems of the analyzed sample were solved, despite the lack of a standard of compliance of those objects. This limitation is overcome due to the specific dominant profile of the active members of the community, who display a high level of collaborative behavior, voluntary initiative, detachment, obstinacy, auto-learning capacity, autonomy, independence, discipline, responsibility and commitment to deadlines, product quality and other requirements established by the community. Another relevant aspect is that the communities are abundant in human interaction, what qualifies the mediation significance process and the collaborative environment in the actions referring to location, assembling and contextualization of the learning objects. The meaningful results obtained by those communities have led great software production organizations to review their corporate strategies, good developmental practices, staff, people and project management. On the other hand, it is inferred that the sustainability of those communities can not be maintained only by personal attributes and abilities, specially because the location of the learning objects for problem solution is based on the tacit knowledge of their members. It is necessary to aggregate innovation into the nature and functionality of those communities (standard compliance, technological methods and tools), to not only enable an effective and universal accessibility to knowledge leading to more efficient problem solution, but also to incorporate members with diverse behavior and abilities. The results of the present research contribute to future innovation in both theoretical and practical fields in the definition of a pattern of conformity for the specification, indexation, use, combination and evaluation of learning objects, in addition to motivating a change of behavior, culture and way of learning.

A city is considered as a complex system. It consists of numerous interactivesub-systems and is affected by diverse factors including governmental landpolicies, population growth, transportation infrastructure, and market behavior.Land use and transportation systems are considered as the two most importantsubsystems determining urban form and structure in the long term. Meanwhile,urban growth is one of the most important topics in urban studies, and its maindriving forces are population growth and transportation development. Modelingand simulation are believed to be powerful tools to explore the mechanisms ofurban evolution and provide planning support in growth management. The overall objective of the thesis is to analyze and model urban growth basedon the simulation of land-use changes and the modeling of road networkexpansion. Since most previous urban growth models apply fixed transportnetworks, the evolution of road networks was particularly modeled. Besides,urban growth modeling is an interdisciplinary field, so this thesis made bigefforts to integrate knowledge and methods from other scientific and technicalareas to advance geographical information science, especially the aspects ofnetwork analysis and modeling. A multi-agent system was applied to model urban growth in Toronto whenpopulation growth is considered as being the main driving factor of urbangrowth. Agents were adopted to simulate different types of interactiveindividuals who promote urban expansion. The multi-agent model with spatiotemporalallocation criterions was shown effectiveness in simulation. Then, anurban growth model for long-term simulation was developed by integratingland-use development with procedural road network modeling. The dynamicidealized traffic flow estimated by the space syntax metric was not only used forselecting major roads, but also for calculating accessibility in land-usesimulation. The model was applied in the city centre of Stockholm andconfirmed the reciprocal influence between land use and street network duringthe long-term growth. To further study network growth modeling, a novel weighted network model,involving nonlinear growth and neighboring connections, was built from theperspective of promising complex networks. Both mathematical analysis andnumerical simulation were examined in the evolution process, and the effects ofneighboring connections were particular investigated to study the preferentialattachment mechanisms in the evolution. Since road network is a weightedplanar graph, the growth model for urban street networks was subsequentlymodeled. It succeeded in reproducing diverse patterns and each pattern wasexamined by a series of measures. The similarity between the properties of derived patterns and empirical studies implies that there is a universal growthmechanism in the evolution of urban morphology. To better understand the complicated relationship between land use and roadnetwork, centrality indices from different aspects were fully analyzed in a casestudy over Stockholm. The correlation coefficients between different land-usetypes and road network centralities suggest that various centrality indices,reflecting human activities in different ways, can capture land development andconsequently influence urban structure. The strength of this thesis lies in its interdisciplinary approaches to analyze andmodel urban growth. The integration of ‘bottom-up’ land-use simulation androad network growth model in urban growth simulation is the major contribution.The road network growth model in terms of complex network science is anothercontribution to advance spatial network modeling within the field of GIScience.The works in this thesis vary from a novel theoretical weighted network modelto the particular models of land use, urban street network and hybrid urbangrowth, and to the specific applications and statistical analysis in real cases.These models help to improve our understanding of urban growth phenomenaand urban morphological evolution through long-term simulations. Thesimulation results can further support urban planning and growth management.The study of hybrid models integrating methods and techniques frommultidisciplinary fields has attracted a lot attention and still needs constantefforts in near future. / <p>QC 20130514</p>

In this thesis we investigate the formation of patterns in a simple activator-inhibitor model supplemented with an inhibitory nonlocal coupling term. This model exhibits a wave instability for slow inhibitor diffusion, while, for fast inhibitor diffusion, a Turing instability is found. For moderate values of the inhibitor diffusion these two instabilities occur simultaneously at a codimension-2 wave-Turing instability. We perform a weakly nonlinear analysis of the model in the neighbourhood of this codimension-2 instability. The resulting amplitude equations consist in a set of coupled Ginzburg-Landau equations. These equations predict that the model exhibits bistability between travelling waves and Turing patterns. We present a study of interfaces separating wave and Turing patterns arising from the codimension-2 instability. We study theoretically and numerically the dynamics of such interfaces in the framework of the amplitude equations and compare these results with numerical simulations of the model near and far away from the codimension-2 instability. Near the instability, the dynamics of interfaces separating small amplitude Turing patterns and travelling waves is well described by the amplitude equations, while, far from the codimension-2 instability, we observe a locking of the interface velocities. This locking mechanism is imposed by the absence of defects near the interfaces and is responsible for the formation of drifting pattern domains, i.e. moving localised patches of travelling waves embedded in a Turing pattern background and vice versa.

Το ερευνητικό αντικείμενο και ο στόχος της διδακτορικής διατριβής είναι η πρόταση μιας ολοκληρωμένης λύσης για την υποστήριξη τηλεπικοινωνιακών εφαρμογών σε ασύρματα δίκτυα τα οποία δεν στηρίζονται σε σταθερές δικτυακές υποδομές. Ένα τέτοιο δίκτυο, το οποίο αναφέρεται στη διεθνή βιβλιογραφία ως Mobile Ad-hoc Network (MANET), είναι ένα αυτο-οργανώσιμο αυτο-σχηματιζόμενο ασύρματο δίκτυο με διαδρομές πολλαπλών τμημάτων (multi-hop), όπου η δομή του δικτύου αλλάζει δυναμικά λόγω της κινητικότητας των κόμβων ή αλλαγές στην τοπολογία. Η αρχιτεκτονική που προτείνεται για την ικανοποίηση των τιθέμενων απαιτήσεων στηρίζεται στην ανάπτυξη ενός ολοκληρωμένου επικοινωνιακού αρχιτεκτονικού πλαισίου για MANET δίκτυα το οποίο περιλαμβάνει μηχανισμούς μείωσης της κατανάλωσης ενέργειας που οφείλεται σε επικοινωνιακές λειτουργίες, την ανάπτυξη ενός εξειδικευμένου πρωτοκόλλου δρομολόγησης, τροποποιήσεις του πρωτοκόλλου TCP στο επίπεδο μεταφοράς και την υλοποίηση ενός νέου πρωτόκολλου διαχείρισης δικτύου. Η απόδοση της προτεινόμενης επικοινωνιακής διαστρωμάτωσης είναι υψηλή σε περιβάλλον με μεγάλη κινητικότητα των κόμβων και δυναμική αλλαγή της τοπολογίας ενώ παράλληλα η κατανάλωση ενέργειας των κόμβων παραμένει σχετικά χαμηλή. Οι αλγόριθμοι και τα πρωτοκόλλα που παρουσιάζονται σχεδιάστηκαν και υλοποιήθηκαν λαμβάνοντας υπόψη τους περιορισμούς και τις απαιτήσεις ενός ενσωματωμένου συστήματος, ενώ η απόδοση και αξιοπιστία τους τεκμηριώνονται θεωρητικά και με εξομοιώσεις. / The research objective of this thesis is a complete solution so as to support the implementation of telecommunication applications in wireless networks that operate without the presence of fixed infrastructure. Such a network, cited as Mobile Ad-hoc Network (MANET) in international literature, is a self-organized, auto-configured wireless network with multi-hop routing paths where its structure is modified dynamically due to node mobility and topological changes. In order to meet the above requirements a new communication framework for MANET networks is presented, which consists of the adaptation of communication-related energy reduction techniques, development of a specialized routing protocol at the network layer, modifications of the TCP protocol at the transport layer and the implementation of a novel network management protocol. The performance of the proposed protocol stack is satisfactory in dynamic network topologies with increased node mobility, whereas the node energy consumption remains in low levels. The presented algorithms and protocols are designed and implemented considering the constraints and requirements of an embedded system, while their performance and reliability is proved theoretically and by simulation results.

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Η παρούσα διατριβή κινείται στο χώρο των Ασύρματα Δικτυωμένων Συστημάτων και έχει ως αντικείμενο τη μελέτη και τη σύνθεση μηχανισμών που βελτιώνουν τη λειτουργία τους. Ο όρος Ασύρματα Δικτυωμένα Συστήματα αναφέρεται στα συστήματα των οποίων τα δομικά στοιχεία συνδέονται μέσω ασύρματων δικτύων, με την έμφαση να δίνεται στα αυτό-οργανωμένα δίκτυα και στα δίκτυα αισθητήρων. Η βελτιστοποίηση και ο έλεγχος ενός Ασύρματα Δικτυωμένου Συστήματος γίνεται με γνώμονα την Ποιότητα των παρεχόμενων Υπηρεσιών του δικτύου, η οποία χρησιμοποιείται ως μέτρο αξιολόγησης και επαναπροσδιορισμού των παραμέτρων λειτουργίας αυτού. Προσεγγίζοντας το θέμα από την οπτική γωνία του δικτύου, οι μηχανισμοί που είναι υπεύθυνοι για τη βελτιστοποίηση της λειτουργίας των Ασύρματα Δικτυωμένων Συστημάτων, αποστασιοποιούνται από την ανάπτυξη νέων πρωτοκόλλων για τα διάφορα επίπεδα του μοντέλου αναφοράς Ανοιχτής Διασύνδεσης Συστημάτων. Για τον λόγο αυτό, αναφορικά με το μοντέλο αναφοράς Ανοιχτής Διασύνδεσης Συστημάτων, το ζήτημα της βελτιστοποίησης της λειτουργίας των Ασύρματα Δικτυωμένων Συστημάτων προσεγγίζεται από τα ακραία επίπεδα της στοίβας πρωτοκόλλων, και συγκεκριμένα από την οπτική γωνία του Επιπέδου Εφαρμογής και του Φυσικού Επιπέδου. Στο Επίπεδο Εφαρμογής το ενδιαφέρον επικεντρώνεται στην διασφάλιση των περιθωρίων ευστάθειας για τα Ασύρματα Δικτυωμένα Συστήματα Ελέγχου. Η διασφάλιση της ομαλής λειτουργίας του συστήματος κλειστού βρόχου βασίζεται σε διακοπτικές δομές ελέγχου, των οποίων οι παράμετροι λειτουργίας καθορίζονται από την Ποιότητα Υπηρεσίας του δικτύου, και συγκεκριμένα από το ποσοστό των επιτυχώς ληφθέντων πακέτων. Στο Φυσικό Επίπεδο εξετάζεται αρχικά το πρόβλημα αποκατάστασης της συνδεσιμότητας μεταξύ των μελών ενός Ασύρματα Δικτυωμένου Συστήματος και στην συνέχεια το πρόβλημα επαναπροσδιορισμού της ποιότητας των ασύρματων ζεύξεων. Οι κεντρικοποιημένοι και κατανεμημένοι μηχανισμοί που αναπτύσσονται για τη βελτιστοποίηση των παραμέτρων της Ποιότητας Υπηρεσίας των Ασύρματα Δικτυωμένων Συστημάτων στο Φυσικό Επίπεδο βασίζονται σε εργαλεία της Υπολογιστικής Γεωμετρίας, συνδυάζοντας τα χωρικά χαρακτηριστικά ενός Ασύρματα Δικτυωμένου Συστήματος με δημοφιλή μοντέλα διάδοσης μεγάλης κλίμακας. Τέλος, η αξιολόγηση των μεθόδων ελέγχου και βελτιστοποίησης της λειτουργίας των Ασύρματα Δικτυωμένων Συστημάτων πραγματοποιείται με την εφαρμογή τους σε κατάλληλες πειραματικές διατάξεις και σε ένα καθορισμένο σύνολο σεναρίων εξομοίωσης. / The primary objective of the present PhD thesis is the analysis and the synthesis of mechanisms and algorithms that optimize the operation of Wireless Networked Systems. The term Wireless Networked Systems is used to describe the distributed systems, whose components are interconnected over wireless networks. Referring to wireless networking, the emphasis is given at the self-organized Ad-hoc and Sensor Networks. The effort made is focused on the reconfiguration of the Quality of Service of the underlying network. From such a perspective, the mechanisms responsible for improving the Quality of Service differentiate from the design of novel, specialized communication protocols. More specifically, with respect to the Open Systems Interconnection Reference Model (OSI-RM), the optimization issues of the Wireless Networked Systems’ operation are examined at the Application and Physical Layer. At the Application Layer, problems related to the guarantee of the stability margins for Wireless Networked Controlled Systems are studied. More precisely, the assurance of the desired performance for the closed-loop controlled system is based on switching control techniques. The optimization decision variables are determined by the network’s Quality of Service parameters. At the Physical Layer the objective is twofold: (a) to establish the physical connectivity among the members of the Wireless Networked System and (b) to optimize of the wireless link’s quality. Based on the combination of the spatial characteristics of the Wireless Networked Systems with large-scale radio propagation models, the centralized and distributed mechanisms, synthesized for the optimization of the network’s Quality of Service at the Physical Layer, exploit effectively concepts adopted by the Computational Geometry. Finally, properly developed experimental testbeds and network simulation scenaria are utilized to examine the efficiency of the synthesized mechanisms for the control and optimization of the operation of Wireless Networked Systems at the Application and Physical Layer.

[pt] O objetivo desta pesquisa é classificar o perfil de pagamento dos consumidores não-residenciais de energia elétrica, considerando conhecimento armazenado em base de dados de distribuidoras de energia elétrica. A motivação para desenvolvê-la surgiu da necessidade das distribuidoras por um modelo de suporte a formulação de estratégias capazes de reduzir o grau inadimplência. A metodologia proposta consiste em um sistema inteligente híbrido composto por módulos intercomunicativos que usam conhecimentos armazenados em base de dados para segmentar consumidores e, então, atingir o objetivo proposto. O sistema inicia-se com o módulo neural, que aloca as unidades consumidoras em grupos conforme similaridades (valor fatura, consumo, demanda medida/demanda contratada, intensidade energética e peso da conta no orçamento), em sequência, o módulo bayesiano, estabelece um escore entre 0 e 1 que permite predizer o perfil de pagamento das unidades considerando os grupos gerados e os atributos categóricos (atividade econômica, estrutura tarifária, mesorregião, natureza jurídica e porte empresarial) que caracterizam essas unidades. Os resultados revelaram que o sistema proposto estabelece razoável taxa de acerto na classificação do perfil de consumidores e, portanto, constitui uma importante ferramenta de suporte a formulação de estratégias para combate à inadimplência. Conclui-se que, o sistema híbrido proposto apresenta caráter generalista podendo ser adaptado e implementado em outros mercados. / [en] The objective of this research is to classify the non-residential electricity customer payment profiles regarding the knowledge stored in electricity distribution utilities databases. The motivation for development of the work from the need of electricity distribution by a support model to formulate strategies for tackling non-payment and late payment. The proposed methodology consists of a hybrid intelligent system constituted by intercommunicating modules that use knowledge stored in database to customer segmentation and then achieve the proposed objective. The system begins with the neural module, which allocates the consuming units in groups according to similarities (bill amount, consumption, measured demand/contracted demand, energy intensity and share of the electricity bill in the customer s income), in sequence, the Bayesian module establishes a score between 0 and 1 that allows to predict what payment profile of the units considering the generated groups and categorical attributes (business activity, tariff type, business size, mesoregion and company s legal form) that characterize these units. The results showed that the proposed system provides a reasonable success rate when classifying customer profiles and thus constitutes an important tool in the formulation of strategies for tackling non-payment and late payment. In conclusion, the hybrid system proposed here is a generalist one and could usefully be adapted and implemented in other markets.