Wireless Sensor Networks (WSNs) are ad-hoc networks consisting of tiny battery- operated wireless sensors. The sensor nodes are lightweight in terms of memory, computation, energy and communication. These networks are usually deployed in unsecured, open, and harsh environments, where it is difficult for humans to perform continuous monitoring. Consequently, it is very crucial to provide security mecha- nisms for authenticating data among sensor nodes. Key management is a pre-requisite for any security mechanism. Efficient distribution and management of keys in WSNs is a challenging task. Many standard key establishment techniques have been pro- posed using symmetric cryptosystems. Unfortunately, these systems often fail to pro- vide a good trade-off between memory and security and since WSNs are lightweight in nature, these cryptosystems are not feasible. On the other hand, public key in- frastructure (PKI) is infeasible in WSNs because of its continuous requirement of a trusted third party and heavy computational demands for certificate verification. Pairing-Based Cryptography (PBC) has paved the way for how parties can agree on keys without any interaction. It has relaxed the requirement of expensive certificate verification on PKI systems. In this thesis, we propose a new hybrid identity-based non-interactive key management protocol for WSNs, which leverages the benefits of both symmetric key based cryptosystems and pairing-based cryptosystems. The pro- posed protocol is scalable, suits many applications and can be deployed in multiple types of networks without modifications. We also provide mechanisms for key refresh when the network topology changes. A security analysis is presented to prove that the scheme is resilient to many types of attacks. To validate our scheme, we have implemented it on Crossbow TelosB motes running TinyOS and analyzed the perfor- mance in terms of memory, communication, computation and energy consumption. The results indicate that our scheme can be deployed efficiently to provide high level of security in a large-scale network without increasing memory, communication and energy overheads.

This dissertation deals with smooth feedback stabilization of control-affine systems via Interconnection and Damping Assignment - Passivity-Based Control (IDA-PBC). The IDA-PBC methodology is a feedback control design technique that aims to establish or manipulate a port-Hamiltonian structure of the closed-loop system. For a mechanical control system, a port-Hamiltonian system is a natural description of the dynamics, and several effective controller designs have been presented for this class of systems. In other fields of engineering, the development of such controller design is an active area of research. In particular, applications of IDA-PBC techniques prove to be difficult in practice for process control applications where the concept of energy is usually ill-defined. This thesis seeks to extend the application of the IDA-PBC methodology beyond mechanical control systems. This is achieved by following three directions of research. First, we establish conditions under which a port-Hamiltonian system can be written as a feedback interconnection of two port-Hamiltonian system. We identify such an interconnection structure for linear control systems based on their intrinsic properties. Second, as observed in application of IDA-PBC to non-mechanical systems, several additional assumptions on the structure of the desired port-Hamiltonian system can effectively reduce the complexity of the matching problem. We establish a unified approach that considers these additional assumptions. Third, we connect the matching problem to the classical feedback equivalence approach. We show that feedback equivalence between control-affine systems can be employed to construct some feasible interconnection and damping structures. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2011-01-31 12:59:56.828

Le régulateur PID (Proportionnel-Intégral-Dérivée) est la commande par retour d'état la plus connue. Elle permet d'aborder un bon nombre de problèmes de commande, particulièrement pour des systèmes faiblement non linéaire et dont la performance requise est relativement modeste. En plus, en raison de sa simplicité, la commande PID est largement utilisée en l'industrie. Étant donnés que les méthodes de réglage de la commande PID sont basées sur la linéarisation, la synthèse d'un contrôleur autour d'un point d'équilibre est relativement simple, néanmoins, la performance sera faible dans des modes de fonctionnement loin du point d'équilibre. Pour surmonter ce désavantage, une pratique courante consiste en adapter les gains du PID, procédure connue sous le nom de séquencement de gain (ou gain-scheduling en anglais). Il y a plusieurs désavantages à cette procédure, comme la commutation des gains de la commande et la définition -non triviale- des régions de l'espace d'état dans lesquelles cette commutation aura lieu. Ces deux problèmes se compliquent quand la dynamique est fortement non linéaire. Dans d'autres méthodes, la synthèse de la commande utilise des schémas empiriques, ce qui ne permet pas l'analyse de la stabilité globale du processus. Dans ce contexte, ce travail de thèse a pour objectif de synthétiser des contrôleurs PI, basés sur la passivité, de telle sorte que la stabilité globale du système en boucle fermé soit garantie. L'un des avantages à utiliser la passivité est son attrait intuitif, qui exploite les propriétés physique des systèmes. L'idée centrale dans un système passive est que l'écoulement d'énergie entrante au système provenant de l'extérieur n'est pas inférieur à l'incrément de son énergie de stockage. Par conséquence, ces systèmes ne peuvent pas stocker plus d'énergie que celle fournie, dont la différence correspond à l'énergie dissipée. En introduisant le concept d'énergie, cette méthodologie nous permet de formuler le problème de commande en celui de trouver un système dynamique dont la fonction de stockage d'énergie prend la forme désirée. En incorporant le concept d'énergie cette méthode devient accessible à la communauté de praticiens et permets de fournir des interprétations physique de l'action de commande. Dans cette thèse, une méthodologie constructive de commande PI basée sur la passivité est présentée et motivée par des applications à des systèmes physiques. / One of the best known forms of feeding back a system is through a three-term control law called PID (Proportional-Integral-Derivative) controller. PID controllers are sufficient for many control problems, particularly when process dynamics are not highly nonlinear and the performance requirements are modest. Besides, because of its simple structure, the PID controller is the most adopted control scheme by industry and practitioners, beeing the PI the form mostly employed. Since the PI tuning methods are based on the linearization, commissioning a PI to operate around a single operating point is relatively easy, however, the performance will be below par in wide operating regimes. To overcome this drawback the current practice is to re-tune the gains of the PI controllers based on a linear model of the plant evaluated at various operating points, a procedure known as gain-scheduling. There are several disadvantages of gain-scheduling including the need to switch (or interpolate) the controller gains and the non-trivial definition of the regions in the plants state space where the switching takes place - both problems are exacerbated if the dynamics of the plant is highly nonlinear. In other common scenarios, a little information about the process dynamics or only a "good" linear approximation is taken into account when designing the control design. This impedes to analyse the global stability of the system. In this context, the current thesis work is aimed at the designing of PI controllers, based on the passivity theory, such that the stability of the closed-loop system is guarantied. One of the main advantages of passivity concepts is that they offer a physical and intuitive appeal. The primary idea in passive systems is that the power flowing into the system is not less that the increase of storage. Thus, they cannot store more energy than is supplied to it from the outside, with the difference being the dissipated energy. Thus, introducing the concept of energy, this methodology allows to recast the control problem as finding a dynamical system such that system energy function takes the desired form. Also, with this formulation, the communication between practitioners and control theorists is facilitated, incorporating prior knowledge of the system and providing physical interpretations of the control action. In this thesis, a constructive methodology for deriving PI passivity-based controllers is presented and motivated by the application to physical systems.

In the models analyzed in this paper, there exists an incumbent politician with one objective, two choices, and voters who remember the past differently. The politician's primary goal is to get reelected, which is done by maximizing the number of votes on the day of election. The politician can increase their chances of reelection if they influence the state of the economy over time and ensure the economy is in its 'best' state on the days leading up to the election. In conducting this research, I wanted to study how different rates of memory decay influences the choices the politician makes during the course of their term. Also, I wanted to explore how long a politician would wait to have an election if that were a choice they could make. I found that voters who remember more of the past place a greater constraint on the incumbent leading to moderate fluctuations in the economy and frequent elections.

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Abstract Based upon the Nordhaus' model, we can analyze the political business cycle (PBC) of parliamentarian system. This is our point in this paper. Adding an uncertain factor in the Nordhaus' assumptions, we can get unemployment rate of optimal control path by using the dynamic optimal control theory. Comparing these two results, the model of political business cycle of parliamentarian system has higher elective frequency and lower amplitude in the unemployment rate of optimal control path. From the social welfare point of view, which one is better is hard to say? The social welfare is decided by voters' preferences when voters face these two type of PBC. Keywords: Political business cycle (PBC). Parliamentarian system. The optimal

Στις μέρες μας, οι ολοένα αυξανόμενες ενεργειακές ανάγκες καθώς και οι η μόλυνση του περιβάλλοντος είναι οι κύριοι λόγοι που η χρήση των ανανεώσιμων πηγών ενέργειας στα σύγχρονα συστήματα ενέργειας έχει αυξηθεί τις τελευταίες δεκαετίες. Τα φωτοβολταϊκά συστήματα είναι μια από τις πιο συνήθεις και αποτελεσματικές ανανεώσιμων πηγών για συνδεδεμένα στο δίκτυο ή αυτόνομα συστήματα. Ο σκοπός της παρούσας εργασίας είναι η μελέτη και προσομοίωση έλεγχου σε μετατροπέα δυο βαθμίδων για σύνδεση φωτοβολταικού συστήματος. Αρχικά, θα μελετήσουμε θεωρητικά διάφορους τύπους τοπολογιών που περιλαμβάνουν αντιστροφέα, στην περίπτωση μας, θα μοντελοποιήσουμε και προσομοιώσουμε ένα DC-DC μετατροπέα σε σύνδεση αλυσίδας με έναν τριφασικό DC-AC αντιστροφέα σε ένα απομονωμένο σύστημα. Ειδικότερα θα παρουσιάσουμε θεωρητικά και πειραματικά αποτελέσματα έλεγχου της τάσης εξόδου του μετατροπέα. Το βασικό κομμάτι αυτής της εργασίας είναι τα αποτέλεσμα του ελεγκτή που είναι βασισμένος στην παθητικότητα διασύνδεσης και εκχώρηση απόσβεσης (IDA PBC). Τέλος, θα μοντελοποιήσουμε και προσομοιώσουμε τον DC-AC μετατροπέα, του οποίου ελέγχουμε την τάση εξόδου από τους γνωστούς μας σε όλους αναλογικούς-ολοκληρωτικούς (PI) ελεγκτές. / Nowadays, increased energy needs and the increasing pollution levels of the environment are the main reasons that usage of renewable energy sources to modern power systems has significantly increased in the last decades. Photovoltaic (PV) generator systems are one of the most common and efficient renewable energy applications for grid-connected or stand-alone systems. The aim of the present thesis is the study and the simulation of control of a two level power converter used in photovoltaic systems. Firstly, we will study theoretically different types of topologies that include inverters, in our case, we model and simulate a DC-DC boost power converter string connected with a three phase DC-AC inverter to a stand-alone system. Especially we will present theoretical and experimental results controlling the DC-DC converter output voltage. The basic part of this thesis are the results of the controller, which is designed following the passivity-based interconnection and damping assignment methodology (IDA PBC). Finally, we will model and simulate the DC-AC inverter, where its output voltage is controlled by the well-known, proportional-integral (PI) controllers.

The diploma thesis examines the hypothesis that monetary policy can be an instrument of international policy, or a component of economic power. The case study focuses on the monetary policy of the PRC in terms of its potential international projection.

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Comment le plan d’organisation d’un organisme est-il mis en place est une question centrale de la biologie du développement. Les séquençages complets de plusieurs génomes de métazoaires ont montré qu’un nombre restreint de molécules régulatrices soutiennent la diversité des plans d’organisation des animaux, suggérant que ces molécules sont utilisées de manière répétée dans des contextes différents. Cela soulève la question de la diversité d’action : comment ces molécules acquièrent-elle une diversité fonctionnelle ? De plus, la plupart des molécules régulatrices partagent des motifs (fonctionnels/structuraux) communs, soulevant la question de la spécificité : comment des molécules partageant des propriétés biochimiques similaires contrôlent-elles des programmes développementaux spécifiques ?Mon équipe d’accueil s’intéresse à ces questions en utilisant les facteurs de transcription Hox de la Drosophile comme paradigme d’étude.Durant ma thèse, j’ai développé trois lignes de recherches : (1) J’ai adapté la technique de complémentation bi-moléculaire de fluorescence (BiFC) de visualisation des interactions protéines-protéines à l’embryon de drosophile en développement.(2) J’ai employé la BiFC pour disséquer la formation des complexes Hox-protéines PBC. Mes résultats remettent en question le paradigme établit : (a) en soulignant la multiplicité des modes d’interaction Hox-PBC existants, (b) en démontrant que cette diversité peut être source de spécificité d’action.(3) La BiFC a ensuite été exploitée dans un crible par approche gènes candidats pour identifier de nouveaux partenaires des protéines Hox. / My current laboratory aims to tackle the issue of specificity and diversity of regulatory molecules, taking the Drosophila Hox transcription factors as a paradigm for the analysis. During my PhD, I developed three connected research lines.Project 1: Visualization of protein interactions in living Drosophila embryos by the BiFC assayOur results establish the general suitability of BiFC for revealing and studying protein interactions in their physiological context during the rapid course of Drosophila embryonic development.Project 2: Investigation of Hox/PBC complex formation in vivo using BiFC Our findings challenge the current paradigm of Hox/Pbx complex assembly: (a) highlighting the existence of alternative modes of Pbx recruitment, (b) demonstrating that unique Hox-PBC interaction modes can provide specific regulatory function in absence of DNA-binding selectivity.To achieve this project BiFC was also performed with vertebrate Hox proteins in chicken embryos.Project 3: Realization of a candidate interaction screen based on BiFC to identify novel Hox protein partners in vivo(a) We have revealed that Hox proteins establish specific interactions with different subunits of the general mediator complex. These results constituted one of the rare studies making a direct link between the Hox regulators and components of the basal transcriptional machinery, in a physiological context.(b) We have discovered that Hox proteins can interact with importin proteins. This result allows us to assess the importance of controlling the nuclear localization of Hox proteins for controlling their regulatory activities during embryogenesis.