Active matter theory studies the collective behaviour of self-propelled organisms or objects. Although the field has made great progress in the past decade, little is known of the role played by confinement and surfaces. This thesis analyses the self-organisation of dense bacterial suspensions in three different microchambers: flattened drops, racetracks and lattices of cavities. Suspensions of swimming bacteria are well-known to spontaneously form macroscopic quasi-turbulent patterns such as jets and swirls. Confinement inside flattened drops and racetracks stabilises their motion into a spiral vortex and wavy streams, respectively. We have quantitatively measured and analysed bacterial circulation and discovered cells at the interfaces to move against the bulk. To understand this phenomenon, we developed a method able to measure simultaneously the directions of swimming and of motion. Experiments in drops reveal that cells align in a helical pattern, facing outward and against the main bulk circulation. Likewise, bacteria in racetracks share a biased orientation against the overall stream. Particle-based simulations confirm these results and identify hydrodynamic interactions as the main driving force: bacteria generate long-range fluid flows which advect the suspension in the bulk against its swimming direction, resulting in the double-circulation pattern. We have finally injected dense suspensions of bacteria into lattices of cavities. They form a single vortex in each cavity, initially spinning clockwise or counterclockwise with equal probabilities. Changing the topology of the lattice and the geometry of connections between cavities allows us to control the lattice state (random, ferromagnetic, antiferromagnetic, or unstable). Edge currents along interfaces and connections appear to determine the lattice organisation. We finally propose an Ising model to understand experimental results and estimate Hamiltonian and interactions parameters. This work opens new perspectives for the study of active matter and, we hope, will have a great impact on the field.

Avec la dramaturgie colombienne des trente dernières années, nous nous trouvons devant deux itinéraires qui semblent s’entrecroiser, ou mieux, se superposer : le réel, qui correspond au contexte socio-politique colombien et le fictionnel, qui nous permet d’entrevoir un paysage de fiction singulier se dessiner à travers certaines pièces contemporaines colombiennes. Cet entrecroisement entre le réel et le fictionnel nous amène à la figure récurrente de l’enfermement. Nous assistons à la représentation d’un monde où les prisons n’ont plus de barreaux, où l’enfermement est présent au quotidien. Sur scène les personnages sont clôturés leurs espaces physiques et métaphoriques, intérieurs ou extérieurs, qui leurs interdisent toute possibilité d’issue et de conciliation entre les forces opposées qui maintiennent leurs conflits. L’enfermement conduit donc les personnages au sentiment tragique, à la perte du monde et de soi, c'est-à-dire que le tragique perd dans ces pièces le sens transcendant de l’humain. D’où les questions initiales dont nous sommes partis : comment l’enfermement dans un espace dramatique contemporain nous permet-il de retrouver le tragique ? Et où va ce tragique, aujourd’hui, quand la tragédie n’existe plus ? Cette forme actuelle du tragique ne pourrait-elle pas être une nouvelle façon de retrouver l’essence de la tragédie et le « sens de l’humain » ? Ce sont ces interrogations qui donnent leurs lignes directrices à notre recherche. / With Colombian drama of the last thirty years, we face two routes intersect that appear, or better, overlap: the real, which corresponds to the socio-political context of Colombia and the fictional, which allows us to glimpse a singular landscape of fiction to emerge through some contemporary pieces Colombia. This interplay between reality and fiction, brings us to the recurring figure of confinement. Thus we attend the performance of a world where prisons have no bars, where the confinement is daily. On stage the characters are enclosed in their physical and metaphorical, indoor or outdoor spaces, which prohibit any possibility of completion and reconciliation between the oposite forces that maintains their conflicts. Then, confinement leads characters to a tragic feeling, the loss of the world and oneself, that is to say that the tragic lost in these pieces, meaning transcending the human. Hence the initial questions which we started: how to confinement in a dramatic contemporary space enable us to find the tragic? And where will this tragic go, when the tragedy is over? The current form of tragedy could it not be a new way to recapture the essence of the tragedy and the « sense of humanity » ? These are questions that give their guidance in our research.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15612号 / 工博第3301号 / 新制||工||1498(附属図書館) / 28139 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 木本 恒暢, 教授 藤田 静雄, 准教授 山田 啓文 / 学位規則第4条第1項該当

An oppressor-oppressed nature exists between adults and children. Children are not considered as individuals in the planning of cities but are rather treated as universal, homogenous beings. Their rights as competent social actors are confiscated until they are deemed competent according to adult standards. Unable to represent themselves, they are given sterile child spaces by adults, who are too conditioned to be able to appropriately represent them. Paranoia for child safety results in confined, rather than alert and surveyed spaces with carefully treated edges. Current child spaces are made to condition children with the rules that will result in their ability to be adequate and well functioning adults. They are treated as pre-adults, rather than as children - beings already adequate as themselves and not tending towards adequacy. The dissertation will deal with the dissolving of boundaries and control brought on by confined child spaces in the form of an inner-city primary school. The Museum Precinct part of the city presents itself as rich adult-biased and educational environment in which to house children. / Dissertation MArch(Prof)--University of Pretoria, 2014 / Architecture / MArch(Prof) / Unrestricted

Previous research into microbial colonies and biofilms shows a significant gap in our current understanding of how bacterial structures develop. Despite the huge body of research undertaken into the formation, genetic makeup, composition, and optimal growth conditions of colonies, no study has been successful in identifying all individual bacteria in a colony in three-dimensions as a function of time. This lack of bacterial cell lineage in such a simple class of organisms is conspicuous in the light of what is known about other organisms, such as Caenorhabditis elegans [1]. In this thesis I show that using laser scanning confocal microscopy in conjunction with developments in sample preparation and post acquisition image analysis, it is possible to fully reconstruct all individual bacteria within an Escherichia coli (E. coli ) microcolony grown in viscoelastic media. Additionally, I show that by further pushing the resolution of confocal microscopes, commercial systems are capable of extracting three-dimensional information on protein structures inside bacteria at early stages of growth. This thesis is in three parts. The first part shows that by pushing the resolution of a commercial laser scanning confocal microscope system it is possible to achieve single cell resolution of a bacterial colony growing in three dimensions in a viscoelastic medium (agarose) from a seed bacterium. The growth of individual bacteria is examined as the concentration of agarose in the media is altered. Results show there is a nonlinear dependence between the rate of growth of a bacterium and the concentration of the agarose in the media with a peak in growth rate at 3% (weight) concentrations of agarose in M9 media. The second part of this work presents a study of how an initially two-dimensional colony growing between a glass slide and agarose gel suddenly invades the third spatial dimension by buckling. The results show that the cells within the centre of the colony flex and buckle, due to confinement by their neighbours, creating additional layers. Indeed, flexing is not limited to the buckling event but occurs throughout the early growth cycle of a colony. The final part of this thesis shows that by further pushing the resolution of confocal microscopes, commercial systems are capable of extracting three-dimensional information about the temporal evolution of the spatial distribution of the FtsZ septation ring within the cell. As the bacterial colony grows from a seed bacterium to a microcolony, the error in placing the division accurately at the cell centre is seen to increase as the number of bacteria within the colony increases and spatial confinement occurs.

M.Ing. / 50 Hz technology has led the plasma torch converters up to now. This technology was used. The high power levels of plasma torches made it difficult to implement high frequency technology. At this stage it is possible to use high-frequency technology in plasma torch applications. This thesis implements a high frequency converter suitable for plasma applications. The converter used for this application is the Partial Series Resonant Converter. A study launched to get the properties of plasmas showed that the control method used at this stage namely current control is not the ideal control method. Changing the control method of the converter made it possible to see what influence it has on the plasma. A thorough large signal analisis of the Partial Series Resonant Converter was done. From this analisis a transfer function of the converter was developed and the control parameters were calculated. This control parameters made it possible to change the control and to investigate the different control methods. The design of the plasma torch converter was based on the design of a distributed transformer, input and output filter and a non-linear controller. The results of the Partial Series Resonant Converter showed that power control leads to a more stable plasma. This thesis made a positive contribution to the knowledge of plasma torches and the knowledge of plasma torch converters. The thesis forms a summarry of plasmas and plasma-related topics, and futher study fields are defined by this thesis.

Multifunctional nanocomposites are promising for a variety of applications ranging from microwave devices to biomedicine. High demand exists for magnetically tunable nanocomposite materials. My thesis focuses on synthesis and characterization of novel nanomaterials such as polymer nanocomposites (PNCs) and multi-walled carbon nanotubes (MWCNTs) with magnetic nanoparticle (NP) fillers. Magnetite (Fe3O4) and cobalt ferrite (CoFe2O4) NPs with controlled shape, size, and crystallinity were successfully synthesized and used as PNC fillers in a commercial polymer provided by the Rogers Corporation and poly(vinylidene fluoride). Magnetic and microwave experiments were conducted under frequencies of 1-6 GHz in the presence of transverse external magnetic fields of up to 4.5 kOe. Experiments confirm strong magnetic field dependence across all samples. When incorporated in to a cavity resonator device, tangent losses were reduced, quality factor increased by 5.6 times, and tunability of the resonance frequency was demonstrated, regardless of NP-loading. Work on PNC materials revealed the importance of NP interactions in confined spaces and motivated the study of confinement effects of magnetic NPs in more controlled environments, such as MWCNTs with varying diameters. MWCNTs were synthesized with diameters of 60 nm, 100 nm, 250 nm, and 450 nm to contain magnetic NP fillers (~10 nm) consisting of ferrites of the form MFe2O4, where M = Co2+, Ni2+, or Fe2+. All confined samples exhibit superparamagnetic-like behavior with stronger magnetic response with respect to increasing MWCNT diameter up to 250 nm due to the enhancement of interparticle interactions. This thesis provides the first systematic study of this class of nanocomposites, which paves the way to inclusion of novel nanostructured materials in real-world applications.

Le confinement des poteaux en béton a fait l’objet de plusieurs recherches dans les années précédentes et l’influence des différents paramètres sur l’efficacité du confinement a été aussi soigneusement étudiée, à savoir : la limite élastique de l’acier de confinement, l’espacement entre les barres transversales, la contrainte maximale du béton, l’inclusion des fibres dans le béton. Plusieurs modèles de confinement ont été proposés dans la littérature et l’examen de ces derniers a souligné le besoin de développer un modèle de confinement pour le béton à hautes performances. Ce dernier est caractérisé par son comportement fragile surtout dans les zones à forte sismicité ce qui réduit son utilisation. Il s’est avéré que l’utilisation des fibres, ne serait-ce qu’en petite quantité (0,0% à 1,0% du volume de béton), dans la matrice de béton est très bénéfique pour palier à ce problème de fragilité des BHP. Dans le cadre de ce projet nous allons effectuer une étude expérimentale qui consiste à effectuer des tests de compression centrée sur douze poteaux de dimensions : diamètre : 303 mm, hauteur : 1400 mm, afin d’examiner l’effet de plusieurs paramètres sur le comportement structural des poteaux en béton armé, à savoir : la résistance en compression du béton, l’espacement des étriers, la quantité de fibres utilisée, la présence de l’enrobage du béton, la présence de supports servant à retenir l’enrobage du béton. Les spécimens ont été fabriqués avec des bétons dont la résistance en compression spécifiée varie de 30MPa à 90MPa, selon le cas. Deux pas de spirales sont utilisés, 50 mm et 100 mm. La quantité de fibres variait de 0,0% à 1,0%. Les résultats de l’étude expérimentale montrent que la présence des fibres synthétiques dans la matrice de béton permet de remédier au problème de fragilité des BHP et que des gains de résistance sont observés au niveau du béton confiné et non confiné. L’ajout des fibres a permis à l’enrobage du béton d’atteindre sa résistance théorique et de se rompre par écrasement de matériaux et non par flambage. Des niveaux de ductilité importants sont atteints en fournissant un confinement adéquat aux BHP. Le nombre de spécimens pour analyser les variables : présence de l’enrobage et de supports, était insuffisant pour pouvoir tirer des conclusions fiables à ce sujet. Une bonne corrélation est observée lors de la comparaison des résultats expérimentaux et de ceux obtenus avec le modèle analytique proposé par Eid et Paultre qui est dérivé du modèle Cusson et Paultre.

In this dissertation, I enumerate several privacy problems in online social networks (OSNs) and describe a system called Footlights that addresses them. Footlights is a platform for distributed social applications that allows users to control the sharing of private information. It is designed to compete with the performance of today's centralised OSNs, but it does not trust centralised infrastructure to enforce security properties. Based on several socio-technical scenarios, I extract concrete technical problems to be solved and show how the existing research literature does not solve them. Addressing these problems fully would fundamentally change users' interactions with OSNs, providing real control over online sharing. I also demonstrate that today's OSNs do not provide this control: both user data and the social graph are vulnerable to practical privacy attacks. Footlights' storage substrate provides private, scalable, sharable storage using untrusted servers. Under realistic assumptions, the direct cost of operating this storage system is less than one US dollar per user-year. It is the foundation for a practical shared filesystem, a perfectly unobservable communications channel and a distributed application platform. The Footlights application platform allows third-party developers to write social applications without direct access to users' private data. Applications run in a confined environment with a private-by-default security model: applications can only access user information with explicit user consent. I demonstrate that practical applications can be written on this platform. The security of Footlights user data is based on public-key cryptography, but users are able to log in to the system without carrying a private key on a hardware token. Instead, users authenticate to a set of authentication agents using a weak secret such as a user-chosen password or randomly-assigned 4-digit number. The protocol is designed to be secure even in the face of malicious authentication agents.

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