The present thesis is devoted to an application of the ideas of complex networks theory for analysing, modelling, and, finally, optimising different processes that occur in transportation networks.

In order to serve hundreds of millions of users, contemporary content providers employ tens of thousands of servers to scale their systems. The system software in these environments, however, is struggling to keep up with the increase in demand: contemporary network and storage stacks, as well as related APIs (e.g., BSD socket API) follow a `one-size-fits-all' design, heavily emphasising generality and feature richness at the cost of performance, leaving crucial hardware resources unexploited. Despite considerable prior research in improving I/O performance for conventional stacks, substantial hardware potential still remains unexploited because most of these proposals are fundamentally limited in their scope and effectiveness, as they still have to fit in a general-purpose design. In this dissertation, I argue that specialisation and microarchitectural awareness are necessary in system software design to effectively exploit hardware capabilities, and scale I/O performance. In particular, I argue that trading off generality and compatibility, allows us to radically re-architect the stack emphasising application-specific optimisations and efficient data movement throughout the hardware to improve performance. I first demonstrate that conventional general-purpose stacks fail to effectively utilise contemporary hardware while serving critical Internet workloads, and show why modern microarchitectural properties play a critical role in scaling I/O performance. I then identify core decisions in Operating Systems design that, although they were originally introduced to optimise performance, are now proven redundant or even detrimental. I propose clean-slate, specialised architectures for network and storage stacks designed to exploit modern hardware properties, and application domain-specific knowledge in order to sidestep historical bottlenecks in systems I/O performance, and achieve great scalability. With thorough evaluation of my systems, I illustrate how specialisation and greater microarchitectural awareness could lead to dramatic performance improvements, which could ultimately translate to improved scalability and reduced capital expenditure simultaneously.

Thesis (M. App. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 82-87). Also available in electronic format on the Internet.

Thesis (M.S.)--Georgia State University, 2005. / Title from title screen. Yi Pan, committee chair; Anu G. Bourgeois, A. P. Preethy, committee members. Electronic text (84 p. : i;;. (some col.)) : digital, PDF file. Description based on contents viewed July 2, 2007. Includes bibliographical references (p. 67-68).

In this thesis, we develop scalable frameworks to (re)design a class of large-scale network systems with built-in control mechanisms, including electric power systems and the Internet, in order to improve their economic efficiency and performance while guaranteeing their stability and robustness. After a detailed introduction relating to power system control and optimization, as well as network congestion control, we turn our attention to merging primary and secondary frequency control for the power grid. We present modifications in the conventional generation control using a consensus design approach while considering the participation of controllable loads. The optimality, stability and delay robustness of the redesigned system are studied. Moreover, we extend the proposed control scheme to (i) networks with more complexity and (ii) the case where controllable loads are involved in the optimization. As a result, our controllers can balance power flow and drive the system to an economically optimal operating point in the steady state. We then study a real-time control framework that merges primary, secondary and tertiary frequency control in power systems. In particular, we consider a transmission level network with tree topology. A distributed dynamic feedback controller is designed via a primal-dual decomposition approach and the stability of the overall system is studied. In addition, we introduce extra dynamics to improve system performance and emphasize the trade-off when choosing the gains of the extra dynamics. As a result, the proposed controller can balance supply and demand in the presence of disturbances, and achieve optimal power flow in the steady state. Furthermore, after introducing the extra dynamics, the transient performance of the system significantly improves. A redesign framework for network congestion control is developed next. Motivated by the augmented Lagrangian method, we introduce extra terms to the Lagrangian, which is used to redesign the primal-dual, primal and dual algorithms. We investigate how the gains resulting from the extra dynamics influence the stability and robustness of the system. Moreover, we show that the overall system can achieve added robustness to communication delays by appropriately tuning these gains. Also, the meaning of these extra dynamics is investigated and a distributed proportional-integral-derivative controller for solving network congestion control problems is further developed. Finally, we concentrate on a reverse- and forward-engineering framework for distributed control of a class of linear network systems to achieve optimal steady-state performance. As a typical illustration, we use the proposed framework to solve the real-time economic dispatch problem in the power grid. On the other hand, we provide a general procedure to modify control schemes for a special class of dynamic systems. In order to investigate how general the reverse- and forward-engineering framework is, we develop necessary and sufficient conditions under which an linear time-invariant system can be reverse-engineered as a gradient algorithm to solve an optimization problem. These conditions are characterized using properties of system matrices and relevant linear matrix inequalities. We conclude this thesis with an account for future research.

Submitted by Maria Aparecida (cidazen@gmail.com) on 2017-08-31T14:44:32Z No. of bitstreams: 1 Rayane.pdf: 4026589 bytes, checksum: 7e6066416420555456030ab6db3a1231 (MD5) / Made available in DSpace on 2017-08-31T14:44:32Z (GMT). No. of bitstreams: 1 Rayane.pdf: 4026589 bytes, checksum: 7e6066416420555456030ab6db3a1231 (MD5) Previous issue date: 2015-06-24 / Many security mechanisms, such as Intrusion Detection Systems (IDSs) have been developed to approach the problem of information security attacks but most of them are traditional information systems in which their threats repositories are not represented semantically. Ontologies are knowledge representation structures that enable semantic processing of information and the construction of knowledge-based systems, which provide greater effectiveness compared to traditional systems. This paper proposes an application ontology called “Application Ontology for the Development of Case-based Intrusion Detection Systems” that formally represents the concepts related to information security domain of intrusion detection systems and “Case Based Reasoning”. The “Case Based Reasoning” is an approach for problem solving in which you can reuse the knowledge of past experiences to solve new problems. The evaluation of the ontology was performed by the development of an Intrusion Detection System that can detect attacks on computer networks and recommend solutions to these attacks. The ontology was specified using the “Ontology Web Language” and the Protégé ontology editor and. It was also mapped to a cases base in Prolog using the “Thea” tool. The results have shown that the developed Intrusion Detection System presented a good effectiveness in detecting attacks that the proposed ontology conceptualizes adequately the domain concepts and tasks. / Muitos mecanismos de segurança, como os Sistemas de Detecção de Intrusão têm sido desenvolvidos para abordar o problema de ataques à Segurança da Informação. Porém, a maioria deles são sistemas de informação tradicionais nos quais seus repositórios de ameaças não são representados semanticamente. As ontologias são estruturas de representação do conhecimento que permitem o processamento semântico das informações bem como a construção dos sistemas baseados em conhecimento, os quais fornecem uma maior efetividade em relação aos sistemas tradicionais. Neste trabalho propõe-se uma ontologia de aplicação denominada “Application Ontology for the Development of Case-based Intrusion Detection Systems” que representa formalmente os conceitos relacionados ao domínio de Segurança da Informação, dos sistemas de detecção de intrusão e do “Case-Based Reasoning”. O “Case-Based Reasoning” é uma abordagem para resolução de problemas nos quais é possível reutilizar conhecimentos de experiências passadas para resolver novos problemas. A avaliação da ontologia foi realizada por meio do desenvolvimento de um Sistema de Detecção de Intrusão que permite detectar ataques a redes de computadores e recomendar soluções a esses ataques. A ontologia foi especificada na linguagem “Ontology Web Language” utilizando o editor de ontologias Protegé e, logo após, mapeada a uma base de casos em Prolog utilizando o ferramenta “Thea”. Os resultados mostraram que o Sistema de Detecção de Intrusão desenvolvido apresentou boa efetividade na detecção de ataques e portanto, conclui-se que a ontologia proposta conceitualiza de forma adequada os conceitos de domínio e tarefa abordados.

No description available.

No description available.

Thesis (M.S. in Systems Engineering)--Naval Postgraduate School, June 2010. / Thesis Advisor(s): Goshorn, Rachel ; Goshorn, Deborah. "June 2010." Description based on title screen as viewed on June 24, 2010. Author(s) subject terms: Anomaly Detection, Artificial Intelligence, Automation, Behavior Analysis, Distributed Artificial Intelligence, Intelligence-Surveillance-Reconnaissance, Maritime Domain Awareness, Maritime Force Protection, Multi-agent Systems, Network-centric Operations, Network-centric Systems Engineering, Network-centric Warfare, Smart Sensor Networks, Systems Engineering, Systems Integration, System of Systems. Includes bibliographical references (p. 209-212). Also available in print.

Les systèmes audios incluent les instruments de musique traditionnels (percussions, cordes, vents, voix) et les systèmes électro-acoustiques (amplificateurs de guitares, pédales d’effets, synthétiseurs analogiques). Ces systèmes multi-physiques possèdent une propriété commune : hors des sources d’excitation (les générateurs), ils sont tous passifs. Nous présentons dans cette thèse un ensemble de méthodes automatiques dédiées à leur modélisation, leur simulation et leur contrôle, qui garantissent explicitement et exploitent la passivité du système original. Nous utilisons dans ce travail le formalisme des systèmes hamiltoniens à ports (SHP), introduits en automatique et théorie des systèmes au début des années 1990. Pour la modélisation, on exploite le fait que la connexion de systèmes décrits dans ce formalisme préserve explicitement la dynamique de la puissance dissipée de l'ensemble, pour développer une méthode automatique de modélisation d'instruments complets à partir de modèles élémentaires rassemblés dans un dictionnaire. Pour la simulation, une méthode numérique qui préserve la structure passive des SHP à temps discret a été développée, garantissant ainsi la stabilité des simulations (pour lesquelles le code C++ est généré automatiquement). Concernant le contrôle, on exploite la structure d'interconnexion afin de déterminer automatiquement une forme découplée (sous-systèmes hiérarchisés) pour une certaine classe de SHP. Les systèmes de cette classe sont dits systèmes hamiltonien à ports plats, au sens de la propriété de platitude différentielle, à partir de laquelle une loi de commande en boucle ouverte exacte sur le modèle est générée. / The class of audio systems includes traditional musical instruments (percussion, string, wind, brass, voice) and electro-acoustic systems (guitar amplifiers, analog audio processing, synthesizers). These multi-physical systems have a common property: out of excitation sources (generators), they are all passive. We present a set of automatic methods dedicated to their modeling, simulation and control, which explicitly guarantee and exploit the passivity of the original system. This class of systems is that of port-Hamiltonian systems (PHS), introduced in system theory in the early 1990s. Regarding the models, we exploit the fact that the interconnection of systems described in this formalism explicitly preserves the dynamics of total dissipated power. This enabled the development of an automated method that builds models of complete instruments based on a dictionary of elementary models. Regarding the simulations, we developed a numerical method that preserves the passive structure of PHS in discrete-time domain. This ensures the stability of simulations (for which the C++ code is automatically generated). Regarding the control, we exploit the interconnection structure to automatically build an input-to-output decoupled form for a class of PHS. Systems of this class are flat, within the meaning of the differential flatness approach. A formula that yields the (open loop) control law for these systems is provided.