Dans cette thèse, nous étudions la structure asymptotique de la gravité à trois dimensions d’espace-temps avec et sans constante cosmologique.La première partie de la thèse présente en détails les propriétés fondamentales de la gravité à trois dimensions pour des espaces à constante cosmologique négative, ou espaces de types Anti-de Sitter (AdS). Nous introduisons le formalisme de Chern-Simons pour la gravité en utilisant la formulation dite du premier ordre pour cette dernière. Nous présentons également les conditions aux bords dites de Brown-Henneaux et le calcul associé de l’algèbre des charges de surface. Enfin, nous décrivons les étapes de la réduction du modèle de Chern-Simons à un modèle de Wess-Zumino-Witten puis à celui d’une théorie de Liouville. La relevance de cette théorie dans le calcul microscopique de l’entropie d’un trou noir à trois dimensions est également discutée.La seconde partie de la thèse contient les contributions originales. Tout d’abord, nous étendons l’analyse de la dynamique asymptotique de la supergravité à trois dimensions au cas d’une constante cosmologique nulle. Nous montrons que l’algèbre des charges de surface associée est une extension supersymétrique de l’algèbre BMS, et construisons la théorie bidimensionnelle située au bord de l’espace-temps qui possède cette symétrie. Le second résultat est l’obtention d’une symétrie de dimension infinie au voisinage de l’horizon d’événements d’un trou noir tridimensionnel non extrême. Troisièmement, nous discutions le cas d’une constante cosmologique positive et montrons l’existence d’une théorie de Liouville euclidienne duale à la gravité d’Einstein avec des conditions aux bords de Dirichlet dans le patch statique. Enfin, nous explorons un autre cadre dans lequel des symétries de dimension infinie apparaissent pour des espaces temps qui non sont pas du type Anti-de Sitter. Nous considérons pour cela des déformations de ces derniers, connus sous le nom d’espaces-temps Warped Anti-de Sitter. Nous montrons que ces déformations admettent une algèbre de surface donnée par une somme semi-direct entre une algèbre de Virasoro et une algèbre affine de Kac-Moody, avec extensions centrales non nulles. Nous montrons que les configurations du trou noir hôte des espaces-temps Warped s’organisent en termes de deux algèbres de Virasoro. Nous identifions les générateurs associés qui décrivent les représentations de la théorie duale et, en appliquant une formule de Cardy, nous prouvons qu’un calcul microscopique reproduit correctement l’entropie de ces trous noirs. Nous étendons ce résultat à des conditions aux bords plus générales qui incluent de nouvelles solutions associés à des degrés de liberté locaux, des gravitons massifs contenus dans le volume d’espace-temps. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

We show the scattering of electromagnetic radiation on a rotating cylinder and a rotating sphere using formalism of the vector spherical harmonics in this thesis. If a specific condition is satisfied then we can observe the rotational superradiance, phenomena originally discovered by Y. B. Zel'dovich in 1970s saying that the radiation can gain power by scattering on a rotating body. In this particular case there is an underlying principle of the rotational superradiance, the energy dissipation in the form of Joule heating created due to the induction of surface currents on the conductor. Superradiance can occur in the radiation scattering on the rotating black hole background, although there is no dissipation present. We summarize the results of scattering on the Kerr black hole from the literature, including an application called Black hole bomb, when the black hole is enclosed into a perfectly reflecting mirror. We show that for the lowest modes of the radiation at specific intervals the general relativity results can be approximated by scattering on the flat spacetime.

The flexibility of Mobile Ad hoc networks (MANET) and its characteristics introduce new security risks. One possible attack is the Black Hole attack which received recent attention. In the Black Hole attack, a malicious node uses the routing protocol to declare itself as having the shortest path to the node whose packets it wants to intercept. It is needed to understand this risk with a view to extract preventive and corrective protections against it. We introduce an approach that could stop this attack from happening in such a network by using an algorithm which controls the communications between nodes and let each node becomes identified and authorized in a group of nodes. In this algorithm, stable nodes, which called leaders, are responsible for routing and forwarding packets from source to destination nodes. This research reviews the black hole attack, and, explains the algorithm that helps throughput to be increased as a consequence. / Graduate / manar.alnaghes@hotmail.com

Closure phases along different baseline triangles carry a large amount of information regarding the structures of the images of black holes in interferometric observations with the Event Horizon Telescope. We use long time span, high cadence, GRMHD+radiative transfer models of Sgr A* to investigate the expected variability of closure phases in such observations. We find that, in general, closure phases along small baseline triangles show little variability, except in the cases when one of the triangle vertices crosses one of the small regions of low visibility amplitude. The closure phase variability increases with the size of the baseline triangle, as larger baselines probe the small-scale structures of the images, which are highly variable. On average, the funnel-dominated MAD models show less closure phase variability than the disk-dominated SANE models, even in the large baseline triangles, because the images from the latter are more sensitive to the turbulence in the accretion flow. Our results suggest that image reconstruction techniques need to explicitly take into account the closure phase variability, especially if the quality and quantity of data allow for a detailed characterization of the nature of variability. This also implies that, if image reconstruction techniques that rely on the assumption of a static image are utilized, regions of the u-v space that show a high level of variability will need to be identified and excised.

I study linear waves on higher dimensional Schwarzschild black holes and Schwarzschild de Sitter spacetimes. In the first part of this thesis two decay results are proven for general finite energy solutions to the linear wave equation on higher dimensional Schwarzschild black holes. I establish uniform energy decay and improved interior first order energy decay in all dimensions with rates in accordance with the 3 + 1-dimensional case. The method of proof departs from earlier work on this problem. I apply and extend the new physical space approach to decay of Dafermos and Rodnianski. An integrated local energy decay estimate for the wave equation on higher dimensional Schwarzschild black holes is proven. In the second part of this thesis the global study of solutions to the linear wave equation on expanding de Sitter and Schwarzschild de Sitter spacetimes is initiated. I show that finite energy solutions to the initial value problem are globally bounded and have a limit on the future boundary that can be viewed as a function on the standard cylinder. Both problems are related to the Cauchy problem in General Relativity.

This thesis deals with the problems of exploration and map construction of a dangerous network by mobile agents, and it introduces new general mechanisms for inter-agent communication, which could be applied to other mobile agents' problems. A dangerous network contains a harmful process called Black Hole that destroys all agents entering the node where it resides, without leaving any observable trace. The task for the agents, which are moving asynchronously, is to construct a map of the network with edges incident on the black hole unambiguously identified. Two types of communication mechanisms are considered: whiteboards and tokens. In the whiteboard model every node provides a shared memory on which agents can read and write. When communication occurs through tokens, instead, the agents have some pebbles that can be placed on and picked up from the nodes. Four different costs for comparing the efficiency of the protocols are taken into account: the number of agents required, the number of moves performed, the size of the whiteboard (or the token capacity at a node), and time. The black hole search problem is considered first in ring networks with whiteboards, and optimal exact time and move complexities are established improving all existing results. The same problem is then studied in arbitrary unknown graphs and it is solved in the token model by using a constant number of tokens in total. The protocol improves on existing results and is based on a novel technique for communicating using tokens. Finally, the new method of communicating using tokens described in the context of black hole search is generalized to propose a novel communication mechanism among the agents that could possibly be employed for any distributed algorithm by mobile agents.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22252号 / 理博第4566号 / 新制||理||1656(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 上田 佳宏, 准教授 岩室 史英, 教授 長田 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Thesis advisor: Mary Ann Glynn / This dissertation examines the construction of entrepreneurial possibilities, i.e., opportunities for entrepreneurial action (Lounsbury & Glynn, 2019: 37) in an institutional field. In particular, I conceptualize the field as a relational space (Wooten & Hoffman, 2008) made up of multiple actors and their identities, and set out to unpack the relational and cultural dynamics that shape what actors imagine and construe as possible. I conduct an historical ethnography (Vaughan, 2004) situated in the context of the U.S. specialty coffee segment. Building from a wealth of data, including archival, interview, and observational data, I trace the actions of a particular group within the field—roasters—and ask how, when, and why different sets of roasters spearheaded the assembly of new entrepreneurial possibilities in the field. My findings situate the actual construction of an entrepreneurial possibility as resulting from a two-part process involving: (1) the revealing of relational and cultural holes through field-level events, and (2) the bridging of these symbolic holes by actors in distinct field-level positions (e.g., insiders, outsiders, and ‘outsiders within’). Relational spaces referred to the symbolic void existing between actors who did not relate with one another (e.g., between farmers and roasters). Cultural spaces, or holes (Lizardo, 2014; Pachucki & Breiger, 2010; Vilhena et al., 2014 West, Evans & Bergstrom, 2014) referred to gaps or absences of shared meanings, tastes, or interests that led to impoverished relations between actors. As such, the dissertation offers insights on the cultural embeddedness of assembling entrepreneurial possibilities (e.g., Weber, Heinze, & DeSoucey, 2008) and especially, on the collective nature of revealing and seizing spaces of opportunity. Importantly, my work complements current research examining the link between identity and the flexibility of new ventures (Zuzul & Tripsas, 2019) by showing how, early on, when the field was dominated by one type of actor (e.g., commercial roasters), the spaces of opportunity that opened up revealed essential differences regarding the identity component of ‘who we are.’ As the field evolved, the ‘who we are’ varied less, but differences regarding ‘what we do’ became central to the assembly of new entrepreneurial possibilities. Overall, the dissertation extends the reach of cultural entrepreneurship (Gehman & Soublière, 2017; Lounsbury, Gehman, & Ann Glynn, 2019b; Lounsbury & Glynn, 2001) by casting it as a lens that can deepen our understanding of multiple facets of the entrepreneurial process, especially of its early stages where so much of what entrepreneurs do is riddled with uncertainty. / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Carroll School of Management. / Discipline: Management and Organization.

Historians have long recognized the tendency of communities to embrace tourism when extractive practices like agriculture, mining, and ranching fail as a dominant economic strategy. Jackson Hole, Wyoming, is a prime example of this phenomenon in the American West. From its origins as a Mormon farming community in the late-nineteenth century, the valley evolved into an extensively developed tourist mecca by the end of the next. While this industry was initially supported by hotel-dwelling auto tourists, by the 1960s wealthy second-home buyers began to descend on Jackson Hole, buying up scenic property and constructing vacation homes. Over the next few decades these neo-natives moved to the valley by the hundreds, initiating dramatic economic, physical, and social consequences which were a direct product of the pace, pattern, and location of development. This thesis explores that relationship, making extensive use of Geographic Information Systems (GIS) to identify spatial themes of development in an effort to enlighten historical themes of Jackson Hole's rapidly changing landscape. On a basic level, this process presents a local history of tourist development in Jackson Hole between 1967 and 2002, documenting where development occurred and the consequences and controversy that resulted. Its greater contribution, however, is methodological. The use of GIS as a tool of historical research is still in its infancy, and this project suggests another application of the technique involving the spatial integration of historical and contemporary data. Together, these contributions create an informative and inventive examination of Jackson Hole tourism that expands the potential of historical research.

Six cross-hole packer tests were conducted at the Big Hole fault, a dip-slip normal fault in the northern San Rafael Swell of east-central Utah. Three tests were conducted at each of two locations along the fault, each location having a different total displacement. Water was injected in the footwall, hanging wall, and fault core and pressure changes were monitored in isolated intervals in the adjoining wells. Response curves were analyzed using the type curves developed by Hsieh and Neuman, and Theis, in order to evaluate the hydraulic properties of the fault and its associated damage zone. The tests were not quantitatively interpretable. Response curves were a poor match for Hsieh type curves and failed to give a positive definite hydraulic conductivity tensor. Theis analysis showed transmissivity varied over four orders of magnitude. The fault was both a barrier to and a conduit for fluid flow, indicating it was both heterogeneous and anisotropic with regard to flow. No correlation was seen between the fault displacement and the hydraulic properties of the fault. The lack of consistent results indicates a high variability in the hydraulic properties of the fault, possibility resulting from changes in fault core thickness and slip surface density over small distances. Injection testing at this intermediate scale is not an effective method in determining hydraulic properties of faults in sandstone reservoirs with deformation band style faulting.