A teoria das transforma»ções de superfícies de curvatura constante começou, no fim do século XIX, com o trabalho [3] de A.V. Bäcklund e, em seguida, recebeu importantes contribuições por parte de diversos geômetras, entre eles, L. Bianchi e C. Guichard (veja, por exemplo, [5, 6, 7, 17]). Nessa dissertação apresentamos alguns dos mais importantes resultados desse tópico da geometria diferencial que estão relacionados às superfícies de curvatura média (ou gaussiana não nula) constante. Tais superfícies estão associadas a soluções de equações diferenciais parciais de segunda ordem e não lineares. A interpretação analítica da teoria das transformações de superfícies de curvatura constante nos capacita obter soluções dessas equações diferenciais parciais a partir de uma outra dada, mediante integração de um sistema de equações diferenciais, chamado transformação de Bäcklund. Então, os teoremas de permutabilidade fornecem uma \"fórmula de superposição\" para a construção algébrica de novas soluções / The theory on transformations of surfaces with constant curvature begins, in the late nineteen century, with the article [3] of A.V. Bäcklund and, after, received important contributions from various geometricians, among others, L. Bianchi and C. Guichard (see, for example, [5, 6, 7, 17]). In this dissertation we outline some of the most important results on the theory of surfaces of constant mean (or gaussian) curvature. Such surfaces are associated to the solutions of nonlinear partial differential equations of second order. The analytic interpretation of the theory on transformations of constant curvature surfaces provides a method of obtaining, from a given solution of these partial differential equations, a new solution of the same equation, by integrating a system of differential equations, called Bäcklund transformation. Then, the permutability theorems give a \"superposition formula\" to construct, algebraically, new solutions

This study develops a utopia, named distopia, positioned as a utopia of dissidence and cultural pluralism, also described as difference. The term distopia is a neologism formulated to invoke productive elements of utopia (such as a vision for an improved sociocultural sphere), with aspects of dystopia (namely, scepticism regarding the prevalent), whilst evading the potential naiveté of utopia as well as the hopeless resignation that dystopia can encourage. The term also denotes the political expedience of dissent. Utopia is analysed in terms of its form, content, or function, and according to its underlying sociocultural dynamic, which is, in turn, determined by intersecting permutations of space and time. This study furthermore categorises utopias as either representative of the same (that is, of the institutional, political, discursive, ideological and sociocultural status quo), or of the other. The other is defined here as an agent marginalised along the vectors of race, class, gender, and sexuality. Distopia is, accordingly, a dissenting utopia of the other, formulated to address, in particular, sociocultural exclusion and human rights violations linked to the parallel projects of neocolonial exploitation and of destabilising globalisation practices driven by neoliberal ideology. The utopias of three Dutch visual artists, namely Piet Mondrian (1872-1944), Constant Nieuwenhuys (1920-2005), and Jonas Staal (b. 1981) in collaboration with Moussa Ag Assarid (b. c.1975), are critiqued through the lens of distopia. This is done in order to assess the status of productive difference and engagement with the other in their respective utopias, created over the course of a century. / Thesis (PhD)--University of Pretoria, 2017. / Visual Arts / PhD / Unrestricted

Current stoichiometric spark-ignited engine technologies require costly catalytic converters for reductions in tailpipe emissions. Load control is achieved by using a throttle, which is a leading contributor to reductions in efficiency. Spark-ignited lean burn natural gas engines have been proven to be more efficient and emit fewer pollutants than their stoichiometric counterparts. Load reduction in these engines can be achieved by regulating the air/fuel ratio of the intake charge thereby reducing the efficiency penalties inherent to throttling. Partially stratified charge (PSC) can provide further reductions in emissions and improvements in efficiency by extending the lean limit of operation. PSC is achieved by the ignition of a small quantity of natural gas in the vicinity of the spark plug. This creates an easily ignitable mixture at the spark plug electrodes, thereby providing a high energy ignition source for the ultra-lean bulk charge. Stratified charge engine operation using direct injection (DI) has been proposed as a method of bridging the throttleless load reduction gap between idle and ultra-lean conditions. A previous study was conducted to determine if PSC can provide a high-energy ignition source in a direct injected stratified charge engine. Difficulties with igniting the PSC injections in an air-only bulk charge were encountered. This study focuses on a fundamental Schlieren image-based analysis of PSC combustion. Natural gas was injected through a modified spark plug located in an optically accessible combustion bomb. The relationships between PSC injection timing, fuel supply pressure and spark timing were investigated. Spark timing is defined as the duration between commanded start of injection and the time of spark. As the fuel supply pressure was increased, the minimum spark timing that lead to successful combustion also increased. The largest spark timing window that led to successful combustion was determined to be 80 ms wide at an injection fuel supply pressure of 300 psi. The amount of unburned natural gas increased with increasing spark timing. A cold flow study of the PSC injection system was also conducted. The PSC injection solenoid was found to have a consistent average injection delay of 1.95 ms. The slope of the linear response region of observed injection duration to commanded injection duration was 8.4. Due to plenum effects, the average observed injection duration of the entire PSC system was an order of magnitude longer than the commanded injection duration and was found to vary significantly with fuel supply pressure. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Spectroscopic measurements of the helium atom are performed to high precision using an atomic beam apparatus and electro-optic laser techniques. These measurements, in addition to serving as a test of helium theory, also provide a new determination of the fine structure constant α. An apparatus was designed and built to overcome limitations encountered in a previous experiment. Not only did this allow an improved level of precision but also enabled new consistency checks, including an extremely useful measurement in 3He. I discuss the details of the experimental setup along with the major changes and improvements. A new value for the J = 0 to 2 fine structure interval in the 23P state of 4He is measured to be 31 908 131.25(30) kHz. The 300 Hz precision of this result represents an improvement over previous results by more than a factor of three. Combined with the latest theoretical calculations, this yields a new determination of α with better than 5 ppb uncertainty, α-1 = 137.035 999 55(64).

Orientador: Gilberta Sampaio de Martino Jannuzzi / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Educação / Made available in DSpace on 2018-07-19T11:43:09Z (GMT). No. of bitstreams: 1 Cartolano_MariaTeresaPenteado_D.pdf: 18196652 bytes, checksum: 51b47484ad9ee107b8da38ff56976995 (MD5) Previous issue date: 1994 / Doutorado / Filosofia e História da Educação / Doutor em Educação

Ce travail de thèse s’intéresse au problème d’optimisation séquentielle d’une fonction inconnue définie sur un ensemble continu et borné. Ce type de problème apparaît notamment dans la conception de systèmes complexes, lorsque l’on cherche à optimiser le résultat de simulations numériques ou plus simplement lorsque la fonction que l’on souhaite optimiser ne présente aucune forme de régularité évidente comme la linéarité ou la convexité. Dans un premier temps, nous nous focalisons sur le cas particulier des fonctions lipschitziennes. Nous introduisons deux nouvelles stratégies ayant pour but d’optimiser n’importe quelle fonction de coefficient de Lipschitz connu puis inconnu. Ensuite, en introduisant différentes mesures de régularité, nous formulons et obtenons des résultats de consistance pour ces méthodes ainsi que des vitesses de convergence sur leurs erreurs d’approximation. Dans une seconde partie, nous nous proposons d’explorer le domaine de l’ordonnancement binaire dans le but de développer des stratégies d’optimisation pour fonctions non régulières. En observant que l’apprentissage de la règle d’ordonnancement induite par la fonction inconnue permet l’identification systématique de son optimum, nous faisons le lien entre théorie de l’ordonnancement et théorie de l’optimisation, ce qui nous permet de développer de nouvelles méthodes reposant sur le choix de n’importe quelle technique d’ordonnancement et de formuler différents résultats de convergence pour l’optimisation de fonctions non régulières. Enfin, les stratégies d’optimisation développées au cours de la thèse sont comparées aux méthodes présentes dans l’état de l’art sur des problèmes de calibration de systèmes d’apprentissages ainsi que sur des problèmes synthétiques fréquemment rencontrés dans le domaine de l’optimisation globale. / This work addresses the sequential optimization of an unknown and potentially non-convex function over a continuous and bounded set. These problems are of particular interest when evaluating the function requires numerical simulations with significant computational cost or when the objective function does not satisfy the standard properties used in optimization such as linearity or convexity. In a first part, we consider the problem of designing sequential strategies which lead to efficient optimization of an unknown function under the only assumption that it has finite Lipschitz constant. We introduce and analyze two strategies which aim at optimizing any function with fixed and unknown Lipschitz constant. Consistency and minimax rates for these algorithms are proved, as well as fast rates under an additional Hölder like condition. In a second part, we propose to explore concepts from ranking theory based on overlaying level sets in order to develop optimization methods that do not rely on the smoothness of the function. We observe that the optimization of the function essentially relies on learning the bipartite rule it induces. Based on this idea, we relate global optimization to bipartite ranking which allows to address the cases of functions with weak regularity properties. Novel meta algorithms for global optimization which rely on the choice of any bipartite ranking method are introduced and theoretical properties are provided in terms of statistical consistency and finite-time convergence toward the optimum. Eventually, the algorithms developed in the thesis are compared to existing state-of-the-art methods over typical benchmark problems for global optimization.

In this thesis, we capitalize on the two-dimensional (2D) nature of MXenes by using them as precursors for the synthesis of 2D functional material. MXenes are easily intercalated with monovalent cations K, Na, Li due to their expanded d-spacing after etching. Based on these ideas, we have developed new synthesis processes of texture functional materials using MXenes as precursors. We have successfully synthesized two-dimensional Nb2C MXene based high aspect ratio ferroelectric potassium niobate (KNbO3) and well-oriented photoluminescent rare earth doped lithium niobate (LiNbO3:Pr3+) crystals, which have great potential in opto-electronics applications. In addition, this thesis demonstrates that poly(vinylidene fluoride) (PVDF)-based percolative composites using two-dimensional (2D) MXene nanosheets as fillers exhibit significantly enhanced dielectric permittivity. Furthermore, we fabricated MXene/in-plane aligned PVDF photo-thermo-mechanical solar tracking actuator for energy harvesting applications.

Humic acids are natural substances belonging to the group of humic substances. They arise mainly decomposition of plant residues. They are contained in soils, peat, sediments, young coal, water and even in the air. Humic acids are only partially soluble in water with increasing pH increases their solubility. Diploma thesis focuses on the use of chronopotentiometric titration of humic research. This method is mainly used for the determination of trace concentrations of analytes. This work is focused on the determination of acidity by potentiometric titration and the determination of dissociation constants using chronopotentiometry with measurement of pH of prepared samples.

abstract: Point of Load (POL) DC-DC converters are increasingly used in space applications, data centres, electric vehicles, portable computers and devices and medical electronics. Heavy computing and processing capabilities of the modern devices have ushered the use of higher battery supply voltage to increase power storage. The need to address this consumer experience driven requirement has propelled the evolution of the next generation of small form-factor power converters which can operate with higher step down ratios while supplying heavy continuous load currents without sacrificing efficiency. Constant On-Time (COT) converter topology is capable of achieving stable operation at high conversion ratio with minimum off-chip components and small silicon area. This work proposes a Constant On-Time buck dc-dc converter for a wide dynamic input range and load currents from 100mA to 10A. Accuracy of this ripple based converter is improved by a unique voltage positioning technique which modulates the reference voltage to lower the average ripple profile close to the nominal output. Adaptive On-time block features a transient enhancement scheme to assist in faster voltage droop recovery when the output voltage dips below a defined threshold. UtilizingGallium Nitride (GaN) power switches enable the proposed converter to achieve very high efficiency while using smaller size inductor-capacitor (LC) power-stage. Use of novel Superjunction devices with higher drain-source blocking voltage simplifies the complex driver design and enables faster frequency of operation. It allows 1.8VComplementary Metal-Oxide Semiconductor (CMOS) devices to effectively drive GaNpower FETs which require 5V gate signal swing. The presented controller circuit uses internal ripple generation which reduces reliance on output cap equivalent series resistance (ESR) for loop stability and facilitates ripples reduction at the output. The ripple generation network is designed to provide ai optimally stable performance while maintaining load regulation and line regulation accuracy withing specified margin. The chip with ts external Power FET package is proposed to be integrated on a printed circuit board for testing. The designed power converter is expected to operate under 200 MRad of a total ionising dose of radiation enabling it to function within large hadron collider at CERN and space satellite and probe missions. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2019

The (BMN) bulk materials were sintered at 1050°C, 1100°C, 1150°C, 1200°C by the conventional ceramic process, and their microstructure and dielectric properties were investigated by Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM) (including the X-ray energy dispersive spectrometry EDS and high resolution transmission electron microscopy HRTEM) and dielectric impedance analyzer. We systematically investigated the structure, dielectric properties and voltage tunable property of the ceramics prepared at different sintering temperatures. The XRD patterns demonstrated that the synthesized BMN solid solutions had cubic phase pyrochlore-type structure when sintered at 1050°C or higher, and the lattice parameter (a) of the unit cell in BMN solid solution was calculated to be about 10.56Å. The vibrational peaks observed in the Raman spectra of BMN solid solutions also confirmed the cubic phase pyrochlore-type structure of the synthesized BMN. According to the Scanning Electron Microscope (SEM) images, the grain size increased with increasing sintering temperature. Additionally, it was shown that the densities of the BMN ceramic tablets vary with sintering temperature. The calculated theoretical density for the BMN ceramic tablets sintered at different temperatures is about 6.7521 . The density of the respective measured tablets is usually amounting more than 91% and 5 approaching a maximum value of 96.5% for sintering temperature of 1150°C. The microstructure was investigated by using Scanning Transmission Electron Microscope (STEM), X-ray diffraction (XRD). Combined with the results obtained from the STEM and XRD, the impact of sintering temperature on the macroscopic and microscopic structure was discussed. The relative dielectric constant ( ) and dielectric loss ( ) of the BMN solid solutions were measured to be 161-200 and (at room temperature and 100Hz-1MHz), respectively. The BMN solid solutions have relative high dielectric constant and low dielectric loss. With increasing sintering temperature, the dielectric constant showed the maximum at 1150°C. The leakage current of BMN ceramic material is extraordinary small. When the voltage and thickness of the BMN capacitor are 4000V and 300um, the leakage current amounts only about 0.13-0.65 . The excellent physical and electrical properties make BMN thin films promising for potential tunable capacitor applications.