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Today the multisensor array signal processing of noisy measurements has received much attention. The classical problem in array signal processing is determining the location of an energy-radiating source relative to the location of the array, in other words, direction-of-arrival (DOA) estimation. One is considering the signal estimation problem when together with the signal(s) of interest some noise and interfering signals are present. In this report a direction-of-arrival estimation system is described based on an antenna array for detecting arrival angles in azimuth plane of signals pitched by the antenna array. For this, the Multiple Signal Classication (MUSIC) algorithmis first of all considered. Studies show that in spite of its good reputation and popularity among researches, it has a certain limit of its performance. In this subspace-based method for DOA estimation of signal wavefronts, the term corresponding to additive noise is initially assumed spatially white. In our paper, we address the problem of DOA estimation of multiple target signals in a particular noise situation - in correlated spherically isotropic noise, which, in many practical cases, models a more real context than under the white noise assumption. The purpose of this work is to analyze the behaviour of the MUSIC algorithm and compare its performance with some other algorithms (such as the Capon and the Classical algorithms) and, uppermost, to explore the quality of the detected angles in terms of precision depending on different parameters, e.g. number of samples, noise variance, number of incoming signals. Some modifications of the algorithms are also done is order to increase their performance. Program MATLAB is used to conduct the studies. The simulation results on the considered antenna array system indicate that in complex conditions the algorithms in question (and first of all, the MUSIC algorithm) are unable to automatically detect and localize the DOA signals with high accuracy. Other algorithms andways for simplification the problem (for example, procedure of denoising) exist and may provide more precision but require more computation time.

Laminar burning velocity is very useful for both combustion modeling and kinetic scheme validationand improvement. Accurate experimental data are needed. To achieve this, the spherical flame method was chosen. However various expression for burning velocity from the spherically expanding flame can be found. A theorical review details all the expressions and models for the burning veolcity and shows how they can be obtained experimentally. These models were comparated considering basic fuels - various Lewis numbers. As a result, it is shown that the pure kinematic measurement method is the only one thet does not introduce any assumptions. This kinematic measurement had needed the development and validation of an original post-processing tool. Following the theorical review, a parametric experimental study is presented. The new technique is extended to extract burning velocity and Markstein length relative to the fresh gas for pure ethanol, isooctane and blended fuels at high pressure.

Submitted by Biblioteca do Instituto de Física (bif@ndc.uff.br) on 2017-06-05T18:59:28Z No. of bitstreams: 1 Dissertação_Fernanda.pdf: 596584 bytes, checksum: 88a0a09efaf23dc12638307533c93da0 (MD5) / Made available in DSpace on 2017-06-05T18:59:28Z (GMT). No. of bitstreams: 1 Dissertação_Fernanda.pdf: 596584 bytes, checksum: 88a0a09efaf23dc12638307533c93da0 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho, estudamos algumas soluções estáticas e esfericamente simétricas para uma teoria de gravidade induzida por uma teoria de Yang-Mills no regime de baixas energias. Tal estudo foi feito na situação de vácuo e na presença de uma fonte descrita pelo tensor energia-momento para as equações de campo da gravidade induzida e associada a condição de torção nula. Assim, para a situação de vácuo analisamos duas soluções, uma perturbativa e outra exata. Desta forma, encontramos uma solução perturbativa em torno da solução de Schwarzschild-de Sitter, enquanto a solução exata é uma solução de espaço-tempo de de Sitter modificado. Também discutimos sobre as singularidades para este caso. Na presença do tensor energia-momento das equações de campo da gravidade induzida, analisamos uma solução para uma fonte eletricamente carregada e uma solução associada a um tensor energia-momento de um fluido perfeito. Neste caso, encontramos uma solução perturbativa em torno da solução de Reissner - Nordström - de Sitter e expressões perturbativas para as soluções dentro de um modelo de estrela. Por fim, analisando as equações de campo para uma geometria estática e esfericamente simétrica acoplada a um tensor energia-momento de um fluido perfeito, encontramos uma equação de equilíbrio hidrostático para a densidade de energia e pressão. Onde obtemos uma equação perturbativa em torno equação de Tolman - Oppenheimer - Volkoff - de Sitter. / In this work, we study some static and spherically symmetric solutions to a gravity theory induced by a Yang-Mills theory in the low-energy regime. This study was done in vacuum condition and in the presence of a source described by the energy-momentum tensor to the field equations of induced gravity and associated null torsion condition. Thus, for vacuum situation we analyzed two solutions, one perturbative and another exact. In this way, we find a perturbative solution around the Schwarzschild-de Sitter solution. While the exact solution is a solution of spacetime of de Sitter modified. We also discussed about the singularities in this case. In the presence of the energymomentum tensor of the field equations of induced gravity, we analyze a solution to an electrically charged source and a solution associated with an energy-momentum tensor of a perfect fluid. In this case, we find a perturbative solution around the Reissner - Nordström - de Sitter solution and perturbative expressions for the solutions within a star model. Finally, analyzing the field equations for a static and spherically symmetric geometry coupled to an energy-momentum tensor of a perfect fluid, we found a hydrostatic equilibrium equation for the energy density and pressure. Where we get a perturbation equation around equation Tolman- Oppenheimer - Volkoff - de Sitter.

In recent years, Polarimetric Synthetic Aperture Radar (PolSAR) has been one of the most important instruments for earth observation, and is increasingly used in various remote sensing applications. Statistical modelling and scattering analysis are two main ways for PolSAR data interpretation, and have been intensively investigated in the past two decades. Moreover, spatial analysis was applied in the analysis of PolSAR data and found to be beneficial to achieve more accurate interpretation results. This thesis focuses on extracting typical spatial information, i.e., edges and regions by exploring the statistical characteristics of PolSAR data. The existing spatial analysing methods are mainly based on the complex Wishart distribution, which well characterizes the inherent statistical features in homogeneous areas. However, the non-Gaussian models can give better representation of the PolSAR statistics, and therefore have the potential to improve the performance of spatial analysis, especially in heterogeneous areas. In addition, the traditional fixed-shape windows cannot accurately estimate the distribution parameter in some complicated areas, leading to the loss of the refined spatial details. Furthermore, many of the existing methods are not spatially adaptive so that the obtained results are promising in some areas whereas unsatisfactory in other areas. Therefore, this thesis is dedicated to extracting spatial information by applying the non-Gaussian statistical models and spatially adaptive strategies. The specific objectives of the thesis include: (1) to develop reliable edge detection method, (2) to develop spatially adaptive superpixel generation method, and (3) to investigate a new framework of region-based segmentation. Automatic edge detection plays a fundamental role in spatial analysis, whereas the performance of classical PolSAR edge detection methods is limited by the fixed-shape windows. Paper 1 investigates an enhanced edge detection method using the proposed directional span-driven adaptive (DSDA) window. The DSDA window has variable sizes and flexible shapes, and can overcome the limitation of fixed-shape windows by adaptively selecting homogeneous samples. The spherically invariant random vector (SIRV) product model is adopted to characterize the PolSAR data, and a span ratio is combined with the SIRV distance to highlight the dissimilarity measure. The experimental results demonstrated that the proposed method can detect not only the obvious edges, but also the tiny and inconspicuous edges in heterogeneous areas. Edge detection and region segmentation are two important aspects of spatial analysis. As to the region segmentation, paper 2 presents an adaptive PolSAR superpixel generation method based on the simple linear iterative clustering (SLIC) framework. In the k-means clustering procedure, multiple cues including polarimetric, spatial, and texture information are considered to measure the distance. Since the constant weighting factor which balances the spectral similarity and spatial proximity may cause over- or under-superpixel segmentation in different areas, the proposed method sets the factor adaptively based on the homogeneity analysis. Then, in heterogeneous areas, the spectral similarity is more significant than the spatial constraint, generating superpixels which better preserved local details and refined structures. Paper 3 investigates another PolSAR superpixel generation method, which is achieved from the global optimization aspect, using the entropy rate method. The distance between neighbouring pixels is calculated based on their corresponding DSDA regions. In addition, the SIRV distance and the Wishart distance are combined together. Therefore, the proposed method makes good use of the entropy rate framework, and also incorporates the merits of the SIRV distance and the Wishart distance. The superpixels are generated in a homogeneity-adaptive manner, resulting in smooth representation of the land covers in homogeneous areas, and well preserved details in heterogeneous areas. / <p>QC 20171123</p>

Bien qu'étudiée depuis plus de 100 ans, la détermination expérimentale de la vitesse de combustion reste compliquée. Dans ce travail de thèse, la configuration de flamme sphérique en expansion a été choisie. Cependant, il apparait plusieurs formulation pour cette vitesse de combustion. Ces dernières sont liées au référentiel de mesure qui est lié 1) au laboratoire, 2) au front de flamme et 3) au taux de réaction. Ces 3 formulations, bien que différentes par définition, doivent cependant converger vers une seule et unique valeur correspondant à la vitesse de combustion laminaire à étirement nul. Une étude comparant ces formulations pour des mélanges gazeux au nombre de Lewis bien défini a été menée. Il est montré que la formulation associée au front de flamme permet d'extraire une vitesse de combustion s'abstenant de toute hypothèse. Cette technique a été ensuite appliquée pour déterminer la vitesse de combustion de mélanges issoctane/éthanol et leur dépendance en pression (10 bars). / Laminar burning velocity is very useful for both combustion modeling and kinetic scheme validationand improvement. Accurate experimental data are needed. To achieve this, the spherical flame method was chosen. However various expression for burning velocity from the spherically expanding flame can be found. A theorical review details all the expressions and models for the burning veolcity and shows how they can be obtained experimentally. These models were comparated considering basic fuels - various Lewis numbers. As a result, it is shown that the pure kinematic measurement method is the only one thet does not introduce any assumptions. This kinematic measurement had needed the development and validation of an original post-processing tool. Following the theorical review, a parametric experimental study is presented. The new technique is extended to extract burning velocity and Markstein length relative to the fresh gas for pure ethanol, isooctane and blended fuels at high pressure.

This study focusses on modelling important aspects of the evolution of pulsar wind nebulae using two different approaches. The first uses a hydrodynamic model to simulate the morphological evolution of a spherically-symmetric composite supernova remnant that is expanding into a homogeneous interstellar medium. In order to extend this model, a magnetic field is included in a kinematic fashion, implying that the reaction of the fluid on the magnetic field is taken into account, while neglecting any counter-reaction of the field on the fluid. This approach is valid provided that the ratio of electromagnetic to particle energy in the nebula is small, or equivalently, for a large plasma β environment. This model therefore allows one to not only calculate the evolution of the convection velocity but also, for example, the evolution of the average magnetic field. The second part of this study focusses on calculating the evolution of the energy spectra of the particles in the nebula using a number of particle evolution models. The first of these is a spatially independent temporal evolution model, similar to the models that can be found in the literature. While spatially independent models are useful, a large part of this study is devoted to developing spatially dependent models based on the Fokker-Planck transport equation. Two such models are developed, the first being a spherically-symmetric model that includes the processes of convection, diffusion, adiabatic losses, as well as the non-thermal energy loss processes of synchrotron radiation and inverse Compton scattering. As the magnetic field geometry can lead to the additional transport process of drift, the previous model is extended to an axisymmetric geometry, thereby allowing one to also include this process. / PhD (Space Physics), North-West University, Potchefstroom Campus, 2014

This study focusses on modelling important aspects of the evolution of pulsar wind nebulae using two different approaches. The first uses a hydrodynamic model to simulate the morphological evolution of a spherically-symmetric composite supernova remnant that is expanding into a homogeneous interstellar medium. In order to extend this model, a magnetic field is included in a kinematic fashion, implying that the reaction of the fluid on the magnetic field is taken into account, while neglecting any counter-reaction of the field on the fluid. This approach is valid provided that the ratio of electromagnetic to particle energy in the nebula is small, or equivalently, for a large plasma β environment. This model therefore allows one to not only calculate the evolution of the convection velocity but also, for example, the evolution of the average magnetic field. The second part of this study focusses on calculating the evolution of the energy spectra of the particles in the nebula using a number of particle evolution models. The first of these is a spatially independent temporal evolution model, similar to the models that can be found in the literature. While spatially independent models are useful, a large part of this study is devoted to developing spatially dependent models based on the Fokker-Planck transport equation. Two such models are developed, the first being a spherically-symmetric model that includes the processes of convection, diffusion, adiabatic losses, as well as the non-thermal energy loss processes of synchrotron radiation and inverse Compton scattering. As the magnetic field geometry can lead to the additional transport process of drift, the previous model is extended to an axisymmetric geometry, thereby allowing one to also include this process. / PhD (Space Physics), North-West University, Potchefstroom Campus, 2014