Many real word networks exhibit cascading phenomena, e.g., disease outbreaks in social contact networks, malware propagation in computer networks, failures in cyber-physical systems such as power grids. As they grow in size and complexity, their security becomes increasingly important. In this thesis, we address the problems of controlling cascading failures in various network settings. We address the cascading phenomena which are either natural (e.g., disease outbreaks) or malicious (e.g., cyber attacks). We consider the nodes of a network as being individually or collectively controlled by self-interested autonomous agents and study their strategic decisions in the presence of these failure cascades. There are many models of cascading failures which specify how a node would fail when some neighbors have failed, such as: (i) epidemic spread models in which the cascading can be viewed as a natural and stochastic process and (ii) cyber attack models where the cascade is driven by malicious intents. We present our analyses and algorithms for these models in two parts. Part I focuses on problems of controlling epidemic spread. Epidemic outbreaks are generally modeled as stochastic diffusion processes. In particular, we consider the SIS model on networks. There exist heuristic centralized approaches in the literature for containing epidemic spread in SIS/SIR models; however no rigorous performance bounds are known for these approaches. We develop algorithms with provable approximation guarantees that involve either protective intervention (e.g., vaccination) or link removal (e.g., unfriending). Our approach relies on the characterization of the SIS model in terms of the spectral radius of the network. The centralized approaches, however, are sometimes not feasible in practice. For example, targeted vaccination is often not feasible because of limited compliance to directives. This issue has been addressed in the literature by formulating game theoretic models for the containment of epidemic spread. However they generally assume simplistic propagation models or homogeneous network structures. We develop novel game formulations which rely on the spectral characterization of the SIS model. In these formulations, the failures start from a random set of nodes and propagate through the network links. Each node acts as a self-interested agent and makes strategic intervention decisions (e.g., taking vaccination). Each agent decides its strategy to optimize its payoff (modeled by some payoff function). We analyze the complexity of finding Nash equilibria (NE) and study the structure of NE for different networks in these game settings. Part II focuses on malware spread in networks. In cybersecurity literature malware spreads are often studied in the framework of ``attack graph" models. In these models, a node represents either a physical computing unit or a network configuration and an edge represents a physical or logical vulnerability dependency. A node gets compromised if a certain set of its neighbors are compromised. Attack graphs describe explicit scenarios in which a single vulnerability exploitation cascades further into the network exploiting inherent dependencies among the network components. Attack graphs are used for studying cascading effects in many cybersecurity applications, e.g., component failure in enterprise networks, botnet spreads, advanced persistent attacks. One distinct feature of cyber attack cascades is the stealthy nature of the attack moves. Also, cyber attacks are generally repeated. How to control stealthy and repeated attack cascades is an interesting problem. Dijk et. al.~cite{van2013flipit} first proposed a game framework called ``FlipIt" for reasoning about the stealthy interaction between a defender and an attacker over the control of a system resource. However, in cybersecurity applications, systems generally consists of multiple resources connected by a network. Therefore it is imperative to study the stealthy attack and defense in networked systems. We develop a generalized framework called ``FlipNet" which extends the work of Dijk et. al.~cite{van2013flipit} for network. We present analyses and algorithms for different problems in this framework. On the other hand, if the security of a system is limited to the vulnerabilities and exploitations that are known to the security community, often the objective of the system owner is to take cost-effective steps to minimize potential damage in the network. This problem has been formulated in the cybersecurity literature as hardening attack graphs. Several heuristic approaches have been shown in the litrature so far but no algorithmic analysis have been shown. We analyze the inherent vulnerability of the network and present approximation hardening algorithms. / Ph. D.

Nicholas John Spykman, né en 1893 aux Pays-Bas, naturalisé américain en 1928, mort en 1943, est considéré comme l’un des pères de la « théorie géopolitique ». Eminent professeur de Yale, où il est en 1934-35 le fondateur du premier département de Relations internationales, il marque profondément le débat intellectuel à l’orée des années 40, en se faisant l’avocat de la géographie politique comme nouvelle méthode d’analyse de politique étrangère. Son influence est importante dans le domaine, nouveau pour l’époque, de la « sécurité nationale », puisqu’il est considéré, à l’instar de George Kennan, comme l’inspirateur indirect de la théorie du containment de la doctrine Truman. Ses théories réalistes, débattues avec violence à partir de 1942 en raison de leur supposé « cynisme », marquent une rupture avec l’idéalisme des années 20 et 30. Au-delà de quelques topoi, peu de choses sont néanmoins approfondies le concernant. Une recherche bibliographique systématique permet d’établir que 80% de ses écrits n’ont pas été étudiés ; à la vérité, ils ne sont pas même connus. Il n’existe aucune biographie de Spykman à ce jour, même aux Etats-Unis, ce qui peut être regardé comme une anomalie, s’il est vraiment l’inspirateur du containment. Ce travail de recherche a pour objectif de combler une lacune de l’historiographie américaine, en réévaluant la place d’un théoricien central mais mal connu, à l’aide de nombreuses archives inédites. Cette thèse éclaire l’histoire de la formalisation de la théorie des Relations internationales aux Etats-Unis, et des rapports fonctionnels qu’entretient depuis ses origines la puissance américaine avec la notion polysémique de la « sécurité nationale ». / Nicholas John Spykman, born in 1893 in the Netherlands, a naturalized U.S. citizen in 1928, died in 1943. He is unanimously considered as one of the fathers of the "geopolitical theory." Eminent professor at Yale, where he is in 1934-35 the founder of the first Department of International Relations, he profoundly influences the intellectual debate on the edge of the 40’, becoming the advocate of political geography as a new method of foreign policy analysis. His influence is crucial in the new field of "national security", as he is considered, like George Kennan, as the indirect inspiration for the containment theory of the Truman Doctrine. His realistic theories, discussed with violence in 1942 because of their supposed « cynism », establish a break with the idealism of the '20s and '30s. Beyond some topoi, however, few things are really known about this central actor. A systematic literature review establishes that 80% of his writings have not been studied. In truth, they are not even known. There is no biography of Spykman to this day, even in the United States, which can be regarded as an anomaly if he is really the « Godfather of Containment». This thesis aims at filling a gap in American historiography, in a view to reassessing the place of a central but unfamiliar theorist. The research illuminates the history of the theoric formalization of International Relations in the United States, and also reappraises the functional relationships that America has, since its inception, with the polysemic notion of "national security."

At Oregon State University the Multi-Application Small Light Water Reactor (MASLWR) integral effects testing facility is being prepared for safety analysis matrix testing in support of the NuScale Power Inc. (NSP) design certification progress. The facility will be used to simulate design basis accident performance of the reactor's safety systems. The design includes an initially evacuated, high pressure capable containment system simulated by a 5 meter tall pressure vessel. The convection-condensation process that occurs during use of the Emergency Core Cooling System has been characterized during two experimental continuous blowdown events. Experimental data has been used to calculate an average heat transfer coefficient for the containment system. The capability of the containment system has been analytically proven to be a conservative estimate of the full scale reactor system. / Graduation date: 2013

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Det här examensarbetet inriktar sig på att med ett simuleringsprogram försöka utröna om det skulle gå att använda feedback control av löphju-let på en kaplanturbin för att reglera frekvensen ut på elnätet. Detta görs idag med hjälp av att öka eller minska magnetiseringen av generatorn. Det blir också en jämförelse för att se om det blir någon skillnad på resultatet mellan PID/PI. Resultatet mellan PID och PI är väldigt snar-lika och på frågan om det skulle gå att frekvens styra med löphjulet är svaret antagligen, det beror på hur mycket turbinens svängmassa på-verkar varvtalsändringen. Det skulle däremot ge ökat underhåll och större förslitning på lager och packningar. / This degree project focuses on using a simulation program to try to find out if it would be possible to use feedback control of the impeller on a Kaplan turbine to regulate the frequency on the power grid. This is done today by increasing or decreasing the magnetization of the genera-tor. There will also be a comparison to see if there is any difference in the result between PID/PI. The result between PID and PI is very close, and to the question of whether it would be possible to control the fre-quency with the impeller, the answer is probably, it depends on how much the turbine's swing mass affects the speed change. However, this would result in increased maintenance and greater wear and tear on bearings and seals.

Master of Science / Department of Architectural Engineering and Construction Science / Kimberly W. Kramer / This report explores the requirements for the design and analysis of concrete containment and shows how newer material technologies such as self-consolidating concrete (SCC) and fiber reinforcement could assist in the constructability and durability of new nuclear power plant facilities. SCC for example, enables concrete to flow in the forms around the reinforcement and provides a more uniform adhesion with the reinforcement. Additionally, fiber reinforcement in the concrete mix increases bonding capability, thus making the concrete less likely to fracture. In particular, the ease of constructability benefits offshore floating nuclear power plants and preapproved modular power plants. To differentiate, the offshore plant would employ the assembly line to make all the plants the same while the modular plant, designed to be used anywhere, is not site specific and is typically smaller. Regarding research method, the report starts with the history of the nuclear industry in the United States, including the last nuclear power plant constructed, clarifying that nuclear energy was first harnessed for a submarine propulsion system before being employed to generate electricity. After these early endeavors, two major accidents, Three Mile Island (March 28, 1979) and Chernobyl (April 26, 1986), provided information regarding the lack of safety of nuclear power plant design and operation. Since the containment building is the focus of this report, recognizing the loads and the load combinations for design was the next step in research. Following that, the next step was to determine the design considerations and analyze the containment structure. New material technologies clearly have opened the door to new construction techniques, and the combination of new materials and methods offers structural engineers opportunity to build inherently safer nuclear power plants.

As a critical public safety-related structure, the long-term integrity of post-tensioned concrete containment buildings (PCCs) is necessary for continued operation of the reactors they house. In 2009, during preparations for a steam generator replacement, extensive subsurface laminar cracking was identified in a portion of the Crystal River 3 (CR3) PCC in Florida, and the plant was permanently shut down in 2013. This study investigates potential contributing factors to the identified cracking with particular focus on the effects of high early-age temperatures on the cracking risk of the concrete, on the development of the concrete properties, and on the late-age structural behavior of the concrete. Two planar, full-scale mock-ups of a portion of the CR3 PCC were constructed and instrumented with temperature and strain gauges to monitor the thermal and mechanical behavior during representative concrete curing and post-tensioning loading. Standard- and match-cured concrete specimens were tested for determination of the time- and temperature-dependent development of thermal and mechanical concrete properties, and hydration parameters were determined for the mock-up cement paste for modeling the heat generation in the concrete. These properties and parameters were utilized in 3D finite element analysis of the mock-ups in COMSOL Multiphysics and compared with experimental results. Non-destructive evaluation via shear wave tomography was conducted on the mock-ups to identify flaws and determine the effectiveness of the methods for identifying delaminations between post-tensioning ducts approximately 10 inches beneath the concrete surface. Though early-age thermal stresses were determined not to have caused cracking in the mock-ups, the high early-age concrete temperatures resulted in decreased late-age mechanical properties that were shown to contribute to greater concrete cracking risk when the mock-up was post-tensioned. Tensile stresses exceeding the tensile strength of the concrete were identified along the post-tensioning ducts when biaxial post-tensioning loads were applied in finite element analysis, but the stresses decreased rapidly with increased distance from the ducts. Through parametric modeling, increasing the tensile strength of the concrete was identified as an effective means of reducing the cracking risk in PCCs. Additionally, relationships between the mechanical properties for the standard- and match-cured specimens were identified that could enable prediction of in-place or match-cured concrete properties based only on the results of tests on fog-cured specimens.

This dissertation focuses on the significance of containment relations between the above mentioned classes of ideals. The main problem considered in Chapter II is determining conditions which lead a ring to be a P-ring, D-ring, or AM-ring when every regular ideal is a P-ideal, D-ideal, or AM-ideal, respectively. We also consider containment relations between classes of regular ideals which guarantee that the ring is a quasi-valuation ring. We continue this study into the third chapter; in particular, we look at the conditions in a quasi-valuation ring which lead to a = Jr, sr - f, and a = v. Furthermore we give necessary and sufficient conditions that a ring be a discrete rank one quasi-valuation ring. For example, if R is Noetherian, then ft = J if and only if R is a discrete rank one quasi-valuation ring.

La réaction sulfatique interne (RSI) dans les ouvrages en béton est une pathologie susceptible de se développer lorsque des conditions particulières portant sur la composition du béton, les conditions thermiques au jeune âge et l'environnement sont réunies. Ce phénomène est attribué à la formation d'ettringite différée qui provoque un gonflement du matériau et une fissuration dans la structure. Deux types de béton sont concernés par cette pathologie : les bétons préfabriqués traités thermiquement et les bétons coulés en place dans les pièces massives. Bien que largement étudiée depuis une dizaine d'années, la RSI n'est pas à ce jour parfaitement connue du fait de la complexité du phénomène au niveau des mécanismes mis en jeu, des paramètres influents et de ses conséquences tant à l'échelle microscopique qu'à l'échelle de l'ouvrage. Ce travail vise donc à apporter des éléments de réponse à plusieurs interrogations concernant cette pathologie, en se focalisant sur l'étude de l'impact de certains facteurs intervenant lors de la réaction et sur l'application nucléaire. De nombreuses études expérimentales ont été ainsi mises en œuvre. Une large étude est consacrée à évaluer le risque de développement de la RSI dans une enceinte de confinement d'une centrale nucléaire, du fait de la présence de structures massives dans ce type d'ouvrages. Ces travaux ont permis de mettre en évidence dans quelle mesure la pathologie influe sur les caractéristiques mécaniques et sur les propriétés de transfert du béton, et ainsi de vérifier si les exigences de sûreté attendues par ces structures sont mises en cause. Ensuite, nous nous sommes intéressés à étudier l'impact de l'hygrométrie du béton sur le développement de la RSI. Nous avons pu identifier le couplage qui existe entre l'humidité environnante et le gonflement. Le rôle joué par la lixiviation des alcalins a été également mis en évidence. Des suivis des propriétés de transfert ont été menés et confrontés aux gonflements observés. Enfin, nous nous sommes intéressés à caractériser le rôle joué par le squelette granulaire sur la cinétique et l'amplitude du gonflement par RSI. Les paramètres étudiés concernent la taille et la fraction volumique des inclusions granulaires. De plus, un exemple d'application d'une modélisation numérique mésoscopique du gonflement est proposé / Delayed ettringite formation (DEF) in concrete structures is a pathology that can develop when special conditions on the concrete composition, the thermal conditions at the young age and the environment are met. This phenomenon provokes swelling of the material and cracking in the structure. It affects two types of concrete : the concrete heat-treated and the concrete cast in place in massive parts. Although many studies were done before in order to better understand this pathology, the DEF is still not well known. This is due to its complex mechanism, the influential parameters and its consequences on microscopic and structural scales. For that purpose, the thesis work was designed in order to better understand this pathology. Experimental studies were done to evaluate the impact of certain factors during the reaction, by focusing on nuclear application. An important part of this study was dedicated to assess the risk of DEF development in a nuclear power plant, and to understand how this pathology affects the mechanical characteristics and transfer properties of the concrete. Then, we have studied the impact of the hygrometry on the development of DEF. This has lead to identify a relation between environmental humidity and swelling. We have also examined the role of alkali leaching. A follow up study of the transfer properties was also done and was confronted to the observed swelling. Finally, we were interested in the characterization of the aggregates effect on the kinetics and the amplitude of DEF swelling. So, we have examined the parameters related to the size and the volume fraction of granular inclusions. Furthermore, an application of a mesoscopic numerical modeling of swelling is proposed