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Modern societies are fully dependent on critical infrastructures networks to support the economy, security, and prosperity. Energy infrastructure network is of paramount importance to our societies. As a pillar of the economy, it is necessary that energy infrastructure networks continue to operate safely and be resilient to provide reliable power to other critical infrastructure networks. Nonetheless, frequent large-scale blackouts in recent years have highlighted the vulnerability in the power grids, where disruptions can trigger cascading failures causing a catastrophic regional-level blackout. Such catastrophic blackouts call for a systemic risk assessment approach whereby the entire network/system is assessed against such failures considering the dynamic power flow within. However, the lack of detailed data combining both topological and functional information, and the computational resources typically required for large-scale modelling, considering also operational corrective actions, have impeded large-scale resilience studies. In this respect, the research in the present dissertation focuses on investigating, analyzing, and evaluating the vulnerability of power grid infrastructure networks in an effort to enhance their resilience. Through a Complex Network Theory (CNT) lens, the power grid robustness has been evaluated against random and targeted attacks through evaluating a family of centrality measures. The results shows that CNT models provide a quick and potential indication to identify key network components, which support regulators and operators in making informed decisions to maintain and upgrade the network, constrained by the tolerable risk and allocated financial resources. Furthermore, a dynamic Cascade Failure Model (CFM) has been employed to develop a Physical Flow-Based Model (PFBM). The CFM considers the operational corrective actions in case of failure to rebalance the supply and demand (i.e., dispatch and load shedding). The CFM was subsequently utilized to construct a grid vulnerability map function of the Link Vulnerability Index (LVI), which can be used to rank the line maintenance priority. In addition, a Node Importance Index (NII) has been developed for power substations ranking according to the resulting cascade failure size. The results from CNT and CFM approaches were compared to address the impact of considering the physical behavior of the power grid. The comparison results indicate that relying solely on CNT topology-based model could result in erroneous conclusions pertaining to the grid behavior. Moving forward, a systemic risk mitigation strategy based on the Intentional Controlled Islanding (ICI) approach has been introduced to suppress the failure propagation. The proposed mitigation strategy integrated the operation- with structure-guided strategies has shown excellent capabilities in terms of enhancing the network robustness and minimizing the possibility of catastrophic large-scale blackouts. This research demonstrates the model application on a real large-scale network with data ranging from low to high voltage. In the future, the CFM model can be integrated with other critical infrastructure network systems to establish a network-of-networks interaction model for assessing the systemic risk throughout and between multiple network layers. Understanding the interdependence between different networks will provide stakeholders with insight on enhancing resilience and support policymakers in making informed decisions pertaining to the tolerable systemic risk level to take reliable actions under abnormal conditions. / Thesis / Doctor of Philosophy (PhD)

La thèse repose sur une étude longitudinale d’une technologie de réseau émergente (le logiciel MESH Commotion) et des agencements d’actants qui l’entourent (personnes, objets, organisations, discours, etc.). Ce dispositif, parce qu’il revendique explicitement qu’il est politique au sein de différents plis socio-historiques, produit différentes versions de lui-même qui articulent de manière singulière les notions d’agentivité, d’infrastructures et de biens communs. Par cette politique ouverte et assumée, il nous invite à comprendre la notion de médiation sous un jour nouveau : la médiation infrastructurelle. L’enquête menée rend compte des différentes interprétations de ce logiciel ; elle cherche à comprendre si cette technologie représente une forme de démonstrateur qui permet de penser différemment les forces des infrastructures de télécommunications et leurs emprises sur le lien social. Pour ce faire, ce travail se caractérise par un parcours ethnographique particulier qui, par le milieu, saisit les manières dont différentes versions de ce dispositif sociotechnique sont instaurées. Les résultats de la recherche rendent compte des tâtonnements successifs des acteurs qui visent à faire émerger une forme sociotechnique encore peu reconnue, mais ils dévoilent également les éléments nécessaires à une opération de médiation infrastructurelle. / This dissertation is concerned with a longitudinal study of a computer network technology referred to as the Commotion wireless MESH software, and the assemblages of actants that come into contact with it (such as people, objects, organizations, discourses, etc.). I argue that this apparatus produces different versions of itself that uniquely relates the concepts of agency, infrastructure and the Commons because it explicitly claims to be both technical and political within different socio-historical folds. By assuming such an overt political stance, it invites us to think through the notion of mediation in a new light (infrastructural mediation). My research methods reflect different interpretations of this software by seeking to understand whether this wireless mesh network technology represents a compromise solution to redefining the forces that constitute telecommunications infrastructure and its hold on the social bond. To do so, my dissertation expands on a particular ethnographic path which, “by the middle”, attempts to understand the ways in which the existence of a socio-technical system is established. I argue that the establishment of a socio-technical apparatus does not amount to pulling it out of thin air, but rather to make it become what it is. The findings reflect the successive trials and errors that go into this process of developing a sociotechnical and mediatic form that has yet to be recognized, while also shoring up the constitutive elements of a mediation process between the Commons and telecommunications infrastructure.

L'extension des réseaux d'électricité, d'eau et d'assainissement dans les villes en développement est a priori compliquée par l'absence ou les déficiences de la planification urbaine. Les modalités de viabilisation des quartiers irréguliers à Delhi et Lima sont ici analysées comme des mécanismes sociotechniques révélateurs de dynamiques de fabrique urbaine. En effet, au quotidien, les entreprises installent des poteaux et des tuyaux dans les quartiers non-planifiés. Des innovations techniques, sociales et institutionnelles permettent d'y étendre les réseaux ; l'absence de planification n'est donc pas un obstacle à la viabilisation. Toutefois, ce processus est sous-optimal : la conduite des travaux est désordonnée, l'imprévisibilité limite l'élaboration de stratégies, et les injonctions politiques peuvent être contradictoires. De tels déficits de coordination génèrent des incertitudes qui sont difficiles à surmonter pour les entreprises de services. Il y a néanmoins des pistes prometteuses pour intervenir dans les quartiers non-planifiés : des dispositifs alternatifs de desserte existent qui peuvent être promus ; des données et plans informels satisfont les besoins de connaissances sur la ville et gagneraient à être valorisés ; et le dessin et la préservation de la trame viaire s'avèrent déterminants pour permettre une consolidation urbaine cohérente, progressive et durable. L'analyse de l'extension des réseaux permet d'identifier des instruments clés pour l'action publique dans les villes en développement, et offre ainsi de nouvelles perspectives à la planification urbaine pour aménager la ville existante et préparer stratégiquement l'urbanisation encore à venir / The extension of electricity, water and sanitation networks in developing cities seems to be a priori complicated by the lack or the deficiencies of urban planning. The modalities of infrastructure deployment into the irregular settlements of Delhi and Lima are here analysed as sociotechnical mechanisms, indicative of the dynamics of the urban fabric. Indeed, on a daily basis, utility firms do install pipes and poles in unplanned settlements. Some technical, social and institutional innovations make the extension of networks possible; the lack of urban planning is therefore not an obstacle to service extension. Nonetheless, this process is not optimal: the conduct of public works is disordered, unpredictability hampers the elaboration of strategies and political injunctions can be contradictory. Such coordination deficits generate uncertainties which are more difficult to overcome for utility firms. There are nevertheless some promising leads for intervention in unplanned settlements: alternative devices for servicing exist that can be promoted; some informal plans and data satisfy the needs for knowledge on the city and would be well worth valuing; and the design and the preservation of the road layout appear to be decisive to allow a coherent, progressive and sustainable urban consolidation process. The analysis of network extension helps to identify key instruments for public action in developing cities, and thus offers new perspectives for urban planning to develop the existing city as well as to strategically prepare for the urbanisation yet to come

abstract: We live in a networked world with a multitude of networks, such as communication networks, electric power grid, transportation networks and water distribution networks, all around us. In addition to such physical (infrastructure) networks, recent years have seen tremendous proliferation of social networks, such as Facebook, Twitter, LinkedIn, Instagram, Google+ and others. These powerful social networks are not only used for harnessing revenue from the infrastructure networks, but are also increasingly being used as “non-conventional sensors” for monitoring the infrastructure networks. Accordingly, nowadays, analyses of social and infrastructure networks go hand-in-hand. This dissertation studies resource allocation problems encountered in this set of diverse, heterogeneous, and interdependent networks. Three problems studied in this dissertation are encountered in the physical network domain while the three other problems studied are encountered in the social network domain. The first problem from the infrastructure network domain relates to distributed files storage scheme with a goal of enhancing robustness of data storage by making it tolerant against large scale geographically-correlated failures. The second problem relates to placement of relay nodes in a deployment area with multiple sensor nodes with a goal of augmenting connectivity of the resulting network, while staying within the budget specifying the maximum number of relay nodes that can be deployed. The third problem studied in this dissertation relates to complex interdependencies that exist between infrastructure networks, such as power grid and communication network. The progressive recovery problem in an interdependent network is studied whose goal is to maximize system utility over the time when recovery process of failed entities takes place in a sequential manner. The three problems studied from the social network domain relate to influence propagation in adversarial environment and political sentiment assessment in various states in a country with a goal of creation of a “political heat map” of the country. In the first problem of the influence propagation domain, the goal of the second player is to restrict the influence of the first player, while in the second problem the goal of the second player is to have a larger market share with least amount of initial investment. / Dissertation/Thesis / Doctoral Dissertation Computer Science 2016

abstract: The critical infrastructures of the nation are a large and complex network of human, physical and cyber-physical systems. In recent times, it has become increasingly apparent that individual critical infrastructures, such as the power and communication networks, do not operate in isolation, but instead are part of a complex interdependent ecosystem where a failure involving a small set of network entities can trigger a cascading event resulting in the failure of a much larger set of entities through the failure propagation process. Recognizing the need for a deeper understanding of the interdependent relationships between such critical infrastructures, several models have been proposed and analyzed in the last few years. However, most of these models are over-simplified and fail to capture the complex interdependencies that may exist between critical infrastructures. To overcome the limitations of existing models, this dissertation presents a new model -- the Implicative Interdependency Model (IIM) that is able to capture such complex interdependency relations. As the potential for a failure cascade in critical interdependent networks poses several risks that can jeopardize the nation, this dissertation explores relevant research problems in the interdependent power and communication networks using the proposed IIM and lays the foundations for further study using this model. Apart from exploring problems in interdependent critical infrastructures, this dissertation also explores resource allocation techniques for environments enabled with cyber-physical systems. Specifically, the problem of efficient path planning for data collection using mobile cyber-physical systems is explored. Two such environments are considered: a Radio-Frequency IDentification (RFID) environment with mobile “Tags” and “Readers”, and a sensor data collection environment where both the sensors and the data mules (data collectors) are mobile. Finally, from an applied research perspective, this dissertation presents Raptor, an advanced network planning and management tool for mitigating the impact of spatially correlated, or region based faults on infrastructure networks. Raptor consolidates a wide range of studies conducted in the last few years on region based faults, and provides an interface for network planners, designers and operators to use the results of these studies for designing robust and resilient networks in the presence of spatially correlated faults. / Dissertation/Thesis / Doctoral Dissertation Computer Science 2016