Esta tese está dirigida ao estudo das propriedades elétricas e ópticas das camadas cúbicas de InN, GaN (intrínseco), GaN:Si (tipo-p), GaN:Si (tipo-n) e AlGaN. Por meio da técnica de efeito Hall e utilizando a configuração de Van der Pauw foram obtidas as curvas de resistividade, concentração e mobilidade em função da temperatura das camadas e através destas curvas é determinada a energia de ativação dos aceitadores e doadores. Também através das mesmas curvas são estudados os principais mecanismos que predominam no espalhamento dos portadores. Em alguns casos um comportamento anômalo foi observado (curvas de concentração e mobilidade do InN e GaN:Si (tipo-p)) e os resultados foram corrigidos utilizando-se o modelo de duas camadas e/ou modelo de duas bandas. Para o material c-InN medimos sua resistividade, concentração e mobilidade na região de baixas temperaturas para investigar um possível caráter supercondutor da amostra. Abordaremos também nesta tese o estudo teórico e experimental sobre a transição metal-semicondutor nos nitretos. Para o estudo das propriedades ópticas das camadas foi utilizada a técnica de caracterização de Raman. Por meio desta técnica e utilizando a configuração de retro espalhamento foram caracterizadas as camadas cúbicas de GaN (intrínseco), GaN:Si (tipo-p), GaN:Si (tipo-n) e AlGaN. Dos espectros, foram obtidas as posições dos picos pertencentes aos fônons transversal-ópticos (TO) e longitudinal-ópticos (LO). Verificou-se o caráter cúbico das camadas e estudou-se a origem da banda que aparece entre as posições dos modos TO e LO do material. / The thesis is devoted to the study of electrical and optical properties of cubic InN, GaN (undoped), GaN:Si (type-p), GaN:Si (type-n) and AlGaN epitaxial films. For the study of the electrical properties were measured the resistivity, concentration and mobility curves as a function of the temperature by means of Hall effect and Van der Pauw configuration technique. From these curves were obtained the activation energy of donor and acceptors levels and were studied the main dominant mechanisms for the electron scattering. In some cases an anomalous behavior of the curves was observed and was corrected using the two layer model. For the study of the superconductivity character of the cubic InN sample was measured its resistivity, concentration and mobility in the low temperature region. The thesis is also devoted to the theoretical and experimental studies of the metal-non-metal transitions in the nitrites.The optical studies of the GaN (undoped), GaN:Si (type-p), GaN:Si (type-n) and AlGaN films were done by means of Raman characterization according to a backscattering configuration. From the spectra were obtained the position of the TO and LO phonon peaks, was verified the cubic character of the films and was studied the behavior of the band found between the TO and LO phonon peaks.

Neste trabalho uma nova equação cúbica de estado é proposta baseada no princípio de superposição temperatura-pressão. A equação trata de novas expressões para a determinação dos termos atrativo e co-volume sem dependência de propriedades críticas, podendo ser aplicada a qualquer forma cúbica. Neste estudo foi associada aos parâmetros da equação de Peng-Robinson e é chamada aqui de PR-S. A predição do comportamento pressão-volume-temperatura (PVT) de polímeros puros e o equilíbrio líquidovapor (VLE) de soluções poliméricas foram avaliados. Os resultados se mostraram muito bons quando comparados a dados experimentais. Com base no bom desempenho da nova equação, expandiu-se a aplicação da PR-S para a predição de VLE de misturas envolvendo biodiesel. Para os sistemas estudados a PR-S apresentou uma boa capacidade preditiva frente a outras alternativas, aproximando sua resposta aos dados reais sem a necessidade de ajustes experimentais. Por fim, foi realizado um estudo preliminar de aplicação da equação proposta para sistemas de óleos vegetais com solventes supercríticos. Algumas dificuldades foram encontradas principalmente decorrentes da caracterização dos mesmos através de um único pseudocomponente. Os resultados foram promissores e servirão como base para futuros desenvolvimentos, uma vez que na literatura a maioria dos trabalhos a cerca de misturas de óleos vegetais faz uso de parâmetros de interação binária abrindo mão de modelos puramente preditivos. / In this work a new cubic equation of state (CEOS) is proposed based on the temperaturepressure superposition principle. Called here as PR-S, it has a generic CEOS form with the Peng-Robinson parameters. A temperature-dependent attractive term a(T) is developed along with a new covolume expression, allowing an easy calculation of thermodynamic properties and vapor-liquid equilibrium. Firstly, the new equation was applied to pure polymer and polymer solutions and its results were compared with those of other equations of state and with experimental data. The PR-S equation was also applied to predict the vapor-liquid equilibrium (VLE) of biodiesel related systems and vegetable oils with supercritical solvent mixtures. The results of VLE predictions for polymer and biodiesel systems showed good agreement with experimental data as well as the pressure-volume-temperature (PVT) behavior of pure polymer liquids, attesting the appropriate form of the new equation proposed. For the vegetable oil systems the initial study showed some difficulties raised from the poor caracterization of oils as pseudocomponents. Despite this fact the first outcome was satisfying once there is no work in literature using predictive tools for these kind of mixtures with success.

A composição do clínquer controla a cinética da hidratação do cimento, devido às fases potencialmente mais reativas. O aluminato tricálcico (C3A) é a fase que reage mais rápido quando em contato com a água, formando rapidamente os aluminatos de cálcio hidratado (C3AH6, C4AH19 e C2AH8), com a liberação de elevada quantidade de calor. Para casos práticos, o sulfato de cálcio é adicionado ao clínquer para retardar esta reação. Na presença do sulfato de cálcio, o produto formado da reação com o C3A é o trissulfoaluminato de cálcio hidratado (etringita). Geralmente, a forma cristalina do C3A sintetizado durante o processo de clinquerização é cúbica. No entanto, o íon Na+, pode ser incorporado na estrutura cristalina do C3A, em substituição ao Ca2+, levando à modificação da forma cristalina de cúbica para ortorrômbica. Alguns estudos realizados apresentam interessantes resultados sobre a interferência desta fase modificada na hidratação do cimento, afetando o início de pega e a trabalhabilidade da matriz cimentícia. Os maiores problemas são observados em cimentos Portland branco onde, em função da necessidade de redução da quantidade de ferroaluminato tetracálcico (C4AF), ocorre um incremento na quantidade de C3A. Existe uma grande lacuna referente às características específicas de cada aluminato na ausência e na presença de gipsita e hidróxido de cálcio. Desta forma, mostra-se interessante a observação das características das fases do clínquer, principalmente quando se trata dos aluminatos, visto que este seria um passo importante no entendimento dos problemas de início de pega. O presente estudo utiliza fases puras (C3A cúbico e ortorrômbico) sintetizadas em laboratório, para, desta forma, focar as reações independentemente, isolando-as das demais. A associação de diferentes técnicas que possibilitam avaliar a hidratação in situ, com dois métodos originais de análise, utilizando radiações síncrotron, bem como análise de características reológicas e utilização de técnicas clássicas possibilitaram traçar algumas contribuições. Os resultados mostraram que existem grandes diferenças na hidratação de cada aluminato, sendo o ortorrômbico mais reativo nas primeiras idades quando em presença de gipsita, formando primeiramente a etringita. Na ausência de gipsita, o C3A cúbico se mostrou mais reativo, formando primeiro os aluminatos de cálcio hidratados e com maior liberação de calor. O hidróxido de cálcio, saturando a água da mistura, retardou as reações iniciais do C3A ortorrômbico na ausência de gipsita e, em maiores idades, retardou a formação de etringita em pastas de C3A com gipsita e 10% de hidróxido de cálcio. / The clinker composition controls the kinetics of cement hydration mainly due to the presence of potentially more reactive phases. The reaction of tricalcium aluminate C3A with water is almost immediate. Crystalline hydrates, such as C3AH6, C4AH19 and C2AH8 are quickly formed with generation of a large amount of heat. In presence of calcium sulfate, the product formed from the C3A reaction is ettringite or high-sulfate calcium aluminate. The alkalis can be incorporated into a number of phases in the clinker and often Na2O is taken up by the C3A. When C3A is synthesized in the presence of these elements, it changes its crystal lattice and the formation of the orthorhombic phases occurs. Earlier studies have already shown interesting interference from this phase on the cement hydration. Significant problems are found in white Portland cement, where the necessity of reducing the amount of tetracalcium ferroaluminate (C4AF) leads to an increase of the C3A content. There is a large gap in understanding the specific characteristics of each crystalline form of C3A in presence and absence of gypsum and calcium hydroxide. Therefore, characterization of the cement phases is important, especially when it is related to the aluminates (cubic and orthorhombic), since this would be a step to further understand the setting problems. The present study uses pure phases (cubic and orthorhombic C3A) synthesized in laboratory, to focus on the reactions independently, isolating the reactions of the others phases. The experimental research integrated two different synchrotron radiation techniques that enable the study of the hydration in situ with rheological analysis and classical techniques allowing to obtain contributions in the hydration of each C3A. The results showed that there are significant differences in the hydration of each aluminate, and the orthorhombic C3A is more reactive in early ages when in presence of gypsum, by forming ettringite first. In absence of gypsum the cubic C3A was more reactive, forming first calcium aluminates hydrates and generating a higher amount of heat. The ettringite formation and the heat evolution of pastes in presence and absence of gypsum were delayed when calcium hydroxide was present in the mixture.

O conceito de taxa de variação é muito útil no estudo das funções reais de uma variável real e, por ser elementar, pode ser apresentado e discutido no Ensino Médio. A proposta deste trabalho é fazer um estudo detalhado e criterioso do uso da taxa de variação no estudo das funções afins, quadráticas e cúbicas. Com isso, pretende-se desenvolver resultados e apresentar diversas aplicações deste conceito a estas classes de funções que incluem, por exemplo, novas formas de obtenção dos seus gráficos, a interpretação geométrica de seus coeficientes, bem como resolver problemas simples e interessantes de otimização. Quanto às funções quadráticas, como aplicação do estudo feito sobre estas funções, apresentamos uma maneira matematicamente rigorosa de conceituar o Movimento Retilíneo Uniformemente Variado (MRUV), bem como, obtemos as equações horárias deste movimento. A definição que apresentamos é equivalente a usual, mas não faz uso dos Cálculos Infinitesimal e Integral. Como nosso objetivo é eminentemente matemático, não apresentamos qualquer interpretação Física deste conceito na forma que o introduzimos. Já o estudo das funções cúbicas pode ser visto como uma interessante aplicação das funções quadráticas, uma vez que, através do uso das taxas de variação, a descrição (traçado do gráfico) de uma função cúbica é reduzida ao estudo do sinal de uma função quadrática associada. / The concept of rate of change is very useful in the study of real functions of one real variable. Since this is a simple concept it can be presented and discussed in high school. The purpose of this work is to make a comprehensive study use of the rate of change in the study of the affine, quadratic and cubic functions. We prove results and present several applications of this concept to these classes of functions that include, for example, new ways of obtaining their graphs, geometric interpretation of their coefficients, and the solution of simple and interesting optimization problems. As for the quadratic functions, as an application of our study about these functions, we obtain in a mathematically rigorous definition of Uniformly Varied Rectilinear Motion and obtain the equations of the motion without using the Infinitesimal or Integral Calculus. Since we were essentially concerned with the mathematical aspect of this phenomenon, we did not present a discussion about the physical interpretation of our definition. The study of cubic functions can be seen as an interesting application of the quadratic functions, since through the use of rate changing, the description of the graph of a cubic function is reduced to the study of the sign of a quadratic function associated to the given cubic.

In the past years the so-called body-centered cubic grid (bcc) has been examined and proved to be superior over Cartesian lattices for certain applications. Our work deals with parallel thinning on these bcc grids. We introduce conditions which are sufficient for retaining topology and suggest additional conditions to influence the shape of the resulting skeleton. We further developed an algorithm to extract curve skeletons out of 3d objects in parallel which we also present here. We show in our results that the developed thinning approach on bcc grids is extremely efficient.

The varied properties of Silicon Carbide (SiC) are helping to launch the material into many new applications, particularly in the field of novel semiconductor devices. In this work, the cubic form of SiC is of interest as a basis for developing integrated optical components. Here, the formation of a suitable SiO2 buried cladding layer has been achieved by high dose oxygen ion implantation. This layer is necessary for the optical confinement of propagating light, and hence optical waveguide fabrication. Results have shown that optical propagation losses of the order of 20 dB/cm are obtainable. Much of this loss can be attributed to mode leakage and volume scattering. Mode leakage is a function of the effective oxide thickness, and volume scattering related to the surface layer damage. These parameters have been shown to be controllable and so suggests that further reduction in the waveguide loss is feasible. Analysis of the layer growth mechanism by RBS, XTEM and XPS proves that SiO2 is formed, and that the extent of formation depends on implant dose and temperature. The excess carbon generated is believed to exit the oxide layer by a number of varying mechanisms. The result of this appears to be a number of stable Si-C-O intermediaries that form regions to either depth extreme of the SiO2 layer. Early furnace tests suggest a need to anneal at temperatures approaching the melting point of the silicon substrate, and that the quality of the virgin material is crutial in controlling the resulting oxide growth.

This thesis involves systems for virtual presence in remote locations, a field referred to as telepresence. Recent image-based representations such as Google map's street view provide a familiar example. Several areas of research are open; such image-based representations are huge in size and the necessity to compress data efficiently for storage is inevitable. On the other hand, users are usually located in remote areas, and thus efficient transmission of the visual information is another issue of great importance. In this work, real-world images are used in preference to computer graphics representations, mainly due to the photorealism that they provide as well as to avoid the high computational cost required for simulating large-scale environments. The cubic format is selected for panoramas in this thesis. A major feature of the captured cubic-panoramic image datasets in this work is the assumption of static scenes, and major issues of the system are compression efficiency and random access for storage, as well as computational complexity for transmission upon remote users' requests. First, in order to enable smooth navigation across different view-points, a method for aligning cubic-panorama image datasets by using the geometry of the scene is proposed and tested. Feature detection and camera calibration are incorporated and unlike the existing method, which is limited to a pair of panoramas, our approach is applicable to datasets with a large number of panoramic images, with no need for extra numerical estimation. Second, the problem of cubic-panorama image dataset compression is addressed in a number of ways. Two state-of-the-art approaches, namely the standardized scheme of H.264 and a wavelet-based codec named Dirac, are used and compared for the application of virtual navigation in image based representations of real world environments. Different frame prediction structures and group of pictures lengths are investigated and compared for this new type of visual data. At this stage, based on the obtained results, an efficient prediction structure and bitstream syntax using features of the data as well as satisfying major requirements of the system are proposed. Third, we have proposed novel methods to address the important issue of disparity estimation. A client-server based scheme is assumed and a remote user is assumed to seek information at each navigation step. Considering the compression stage, a fast method that uses our previous work on the geometry of the scene as well as the proposed prediction structure together with the cubic format of panoramas is used to estimate disparity vectors efficiently. Considering the transmission stage, a new transcoding scheme is introduced and a number of different frame-format conversion scenarios are addressed towards the goal of free navigation. Different types of navigation scenarios including forward or backward navigation, as well as user pan, tilt, and zoom are addressed. In all the aforementioned cases, results are compared both visually through error images and videos as well as using the objective measures. Altogether free navigation within the captured panoramic image datasets will be facilitated using our work and it can be incorporated in state-of-the-art of emerging cubic-panorama image dataset compression/transmission schemes.

Le cloud computing permet d'offrir un accès à la demande à des ressources de calcul et de stockage. Le succès du cloud computing nécessite la maîtrise d'aspects système et réseau. Dans cette thèse, nous nous sommes intéressés aux performances du protocole TCP Cubic, qui est la version par défaut de TCP sous Linux et donc présent dans de nombreux serveurs opérationnels dans les data centers actuels. Afin de comprendre les performances d'un environnement cloud, qui offre un faible produit bande passante-délai pour le cas intra-data center, et un fort produit dans le cas inter-data center, nous avons développé des modèles analytiques pour les cas d'une ou plusieurs connexions TCP Cubic. Nos modèles se sont révélés précis dans le cas intra-datacenter, mais ne capturaient pas la synchronisation des pertes indiquée par les simulations ns-2 dans le cas inter-datacenter. Nous avons complété les simulations par des tests en environnements réels avec (i) un réseau expérimental à l'I3S ; et (ii) une solution cloud interne à Orange : Cube. Les études dans Cube nous ont démontré la forte corrélation qui pouvait exister entre performances réseau et système, et la complexité d'analyser les performances des applications dans des contextes cloud. Les études dans l'environnement I3S ont confirmé la forte synchronisation qui peut exister entre connexions TCP Cubic et nous ont permis de définir les conditions d'apparition de cette synchronisation. Nous avons étudié deux types de solution pour lutter contre la synchronisation: des solutions niveau client, avec des modifications de TCP Cubic, et des solutions réseau avec l'utilisation de politiques de gestion de tampon, notamment PIE et Codel. / Cloud computing enables a flexible access to computation and storage services. This requires, for the cloud service provider, mastering network and system issues. During this PhD thesis, we focused on the performance of TCP Cubic, which is the default version of TCP in Linux and thus widely used in today's data centers. Cloud environments feature low bandwidth-delay products (BPD) in the case of intra data center communications and high BDP in the case of inter data center communications. We have developed analytical models to study the performance of a Cubic connection in isolation or a set of competing Cubic connections. Our models turn out to be precise in the low BDP case but fail at capturing the synchronization of losses that ns-2 simulations reveal in the high BDP case. We have complemented our simulations studies with tests in real environments: (i) an experimental network at I3S and (ii) a cloud solution available internally at Orange: Cube. Studies performed in Cube have highlighted the high correlation that might exist between network and system performance and the complexity to analyze the performance of applications in a cloud context. Studies in the controlled environment of I3S have confirmed the existence of synchronization and enabled us to identify its condition of appearance. We further investigated two types of solution to combat synchronization: client level solutions that entail modifications of TCP and network level solutions based on queue management solutions, in particular PIE and Codel.

Suppose a group G can be generated by two subgroups, P1 and P2, both isomorphic to S4 which have intersection isomorphic to D8- the dihedral group of order 8. Then G is known as a faithful completion of the Goldschmidt G3-amalgam. In this thesis we consider the alternating groups as faithful completions of the Goldschmidt G3-amalgam.

An expression for the dielectric susceptibility tensor of a cubic ionic crystal has been derived using the classical Liouville operator. The effect of cubic anharmonic forces is included as a perturbation on the harmonic crystal solution, and a series expansion for the dielectric susceptibility is developed. The most important terms in the series are identified and summed, yielding an expression for the complex susceptibility with an anharmonic contribution which is linearly dependent on temperature. A numerical example shows that both the real and imaginary parts of the susceptibility are continuous, finite functions of frequency.