A teoria de Compressive Sensing proporciona uma nova estratégia de aquisição e recuperação de dados com bons resultados na área de processamento de imagens. Esta teoria garante recuperar um sinal com alta probabilidade a partir de uma taxa reduzida de amostragem por debaixo do limite de Nyquist-Shanon. O problema de recuperar o sinal original a partir das amostras consiste em resolver um problema de otimização. O método de Gradiente Espectral Projetado é um método para minimizar funções suaves em conjuntos convexos que tem sido aplicado com frequência ao problema de recuperar o sinal original a partir do sinal amostrado. Este trabalho dedica-se ao estudo da aplicação do Método do Gradiente Espectral Projetado ao problema de Compressive Sensing. / The theory of compressive sensing has provided a new acquisition strategy and data recovery with good results in the image processing area. This theory guarantees to recover a signal with high probability from a reduced sampling rate below the Nyquist-Shannon limit. The problem of recovering the original signal from the samples consists in solving an optimization problem. The Spectral Projected Gradient (SPG) is a method to minimize continuous functions over convex sets which often has been applied to the problem of recovering the original signal from sampled signals. This work is dedicated to the study and application of the Spectral Projected Gradient method to Compressive Sensing problems.

Cette thèse traite de la conception de récepteurs radiofréquences basés sur l'acquisition compressée pour de l'estimation paramétrique en radio cognitive.L'acquisition compressée est un changement de paradigme dans la conversion analogique-numérique qui permet de s'affranchir de la fréquence d'échantillonnage de Nyquist.Dans ces travaux, les estimations sont effectuées directement sur les échantillons compressés vu le coût prohibitif de la reconstruction du signal d'entrée.Tout d'abord, l'aspect architecture du récepteur est abordé,avec notamment le choix des codes de mélange pour le convertisseur modulé à large bande (MWC).Une analyse haut niveau des propriétés de la matrice d'acquisition, à savoir la cohérence pour réduire le nombre de mesures et l'isométrie pour la robustesse au bruit,est menée puis validée par une plateforme de simulation.Enfin l'estimation paramétrique à partir des échantillons compressés est abordée à travers la borne de Cramér-Rao sur la variance d'un estimateur non biaisé.Une forme analytique de la matrice de Fisher est établie sous certaines hypothèses et permet de dissocier les effets de la compression et de la création de diversité.L'influence du processus d'acquisition compressée, notamment le couplage entre paramètres et la fuite spectrale, est illustré par l'exemple. / This work deals with the topic of radiofrequency receivers based on Compressive Sampling for feature extraction in Cognitive Radio.Compressive Sampling is a paradigm shift in analog to digital conversion that bypasses the Nyquist sampling frequency.In this work, estimations are carried out directly on the compressed samples due to the prohibitive cost of signal reconstruction.First, the receiver architecture is considered, in particular through the choice of the mixing codes of the Modulated Wideband Converter.A high-level analysis on properties of the sensing matrix, coherence to reduce the number of measurement and isometry for noise robustness,is carried out and validated by a simulation platform.Finally, parametric estimation based on compressed samples is tackled through the prism of the Cram'{e}r-Rao lower bound on unbiased estimators.A closed form expression of the Fisher matrix is established under certain assumptions and enables to dissociate the effects of compression and diversity creation.The influence of Compressive Sampling on estimation bounds, in particular coupling between parameters and spectral leakage, is illustrated by the example.

Masonry is a layered composite consisting of mortar and the masonry unit. Perfect bond between the masonry unit and the mortar is essential for the masonry to perform as one single entity in order to resist the stresses due to various loading conditions. Nature of stresses developed in the masonry unit and the mortar and the failure pattern of masonry subjected to compression greatly depends upon the relative stiffness of the masonry unit and the mortar. The thesis is focused on (a) some issues pertaining to masonry unit – mortar bond strength and its influence on masonry compressive strength, and (b) developing a finite element (FE) model to predict the compressive strength of masonry. Importance of masonry bond strength and masonry behaviour is highlighted in chapter 1. Characteristics of masonry units and mortars used in the investigations are presented in Chapter 2. Two types of soil-cement blocks with widely varying strength and elastic properties and cement-lime mortars of two different proportions were used in the investigations. Results of stress-strain relationships and other characteristics were determined for the blocks as well as for mortars. Block-mortar combinations were selected to have block modulus to mortar modulus ratio of <1.0, ~1.0 and >1.0. Different artificial methods of enhancing the shear bond strength of masonry couplets have been discussed in chapter 3. Shear bond strength of the masonry couplets was determined through a modified direct shear box test apparatus. Without altering the block and mortar properties, bond strength values for three block-mortar combinations were generated through experiments. Effect of pre-compression on shear bond strength has also been examined for certain block-mortar combinations. Considering five different bond strength values and three block-mortar combinations, compressive strength and stress-strain characteristics of masonry was obtained through the tests on masonry prisms. A detailed discussion on influence of shear bond strength on masonry compressive strength is presented. Major conclusions of the investigation are: (a) without altering the block and mortar characteristics shear bond strength can be enhanced considerably through the manipulation of surface texture and surface coatings, (b) masonry compressive strength increases linearly as the shear bond strength increases only for the combination of masonry unit modulus less than that of mortar modulus, (c) masonry compressive strength is not sensitive to bond strength variation when the modulus of masonry unit is larger than that of the mortar. Chapter 4 is dedicated to the development of a 3D FE model to predict the masonry compressive strength. Literature review of empirical methods/formulae and some failure theories developed to predict masonry strength are presented. Existing FE models for masonry dealing with both macro and micro modelling approaches are reviewed. The proposed FE model considers (a) 3D non-linear analysis combined with a failure theory, (b) uses multi-linear stress-strain relationships to model the non-linear stress-strain behaviour of masonry materials, (c) adopting Willam-Warnke’s five parameter failure theory developed for modelling the tri-axial behaviour of concrete, and (d) application of orthotropic constitutive equations based on smeared crack approach. The predicted values of masonry compressive strength are compared with experimental values as well as those predicted from other failure theories. The thesis ends with a summary of conclusions in chapter 5.

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The Bushveld Igneous Complex (BIC) in South Africa holds approximately three quarters of the world’s viable chromite ore deposits. Most chromite is used for the production of ferrochromium (FeCr), which is a relatively crude alloy. Several chromite seams exist in the BIC. The most economically viable seams are the lower group 6 (LG6), the middle group 1 and 2 (MG1 and 2) and the upper group 2 (UG2) seams. The LG and MG seams are exploited specifically for their chromium content, whereas the UG2 seam is mainly exploited for platinum group minerals (PGM). However, the upgraded UG2 chromite in the PGM tailing is increasingly being used as a feedstock for FeCr production. Many different process variations exist for FeCr production. However, the process option applied in most green and brown field FeCr expansion projects during the last two decades in South Africa has been the oxidative sintered process (also referred to as the Outotec or Outokumpu process). Notwithstanding the common application of the oxidative sintered pelletised feed technology in the South African FeCr industry, and the increased utilisation of beneficiated UG2 ore, a direct comparison of the physical properties of oxidative sintered pellets produced from UG2 with the physical properties of that produced with conventional metallurgical grade chromite ore is currently lacking in the peer-reviewed scientific literature. Therefore, the physical properties of oxidative sintered pellets produced from a typical beneficiated South African UG2 ore were compared with the physical properties of that produced with conventional South African metallurgical grade chromite ore in this study. The results indicated that the case study metallurgical grade chromite ore required 13 kWh/t more energy to mill than the case study UG2 ore prior to pelletisation, which can lead to substantial cost savings. The compressive strength of the oxidative sintered pellets of both case study ores statistically showed that oxidative sintered pellets made from UG2 ore Abstract were the same or better than those prepared from metallurgical grade chromite ore. A comparison of the abrasion strengths of the oxidative sintered pellets of both case study ores indicated that the pellets prepared from UG2 ore were superior compared to the metallurgical grade pellets. The reasons for the superior UG2 pellet strength were investigated with backscatter-, secondary electron- and elemental X-ray mapping scanning electron microscopy (SEM), which indicated that differences in crystalline structures at least partially contributed to the differences observed. Results presented here can be utilised by FeCr producers to better quantify the advantages and disadvantages associated with the use of UG2 ore for FeCr production. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

The Bushveld Igneous Complex (BIC) in South Africa holds approximately three quarters of the world’s viable chromite ore deposits. Most chromite is used for the production of ferrochromium (FeCr), which is a relatively crude alloy. Several chromite seams exist in the BIC. The most economically viable seams are the lower group 6 (LG6), the middle group 1 and 2 (MG1 and 2) and the upper group 2 (UG2) seams. The LG and MG seams are exploited specifically for their chromium content, whereas the UG2 seam is mainly exploited for platinum group minerals (PGM). However, the upgraded UG2 chromite in the PGM tailing is increasingly being used as a feedstock for FeCr production. Many different process variations exist for FeCr production. However, the process option applied in most green and brown field FeCr expansion projects during the last two decades in South Africa has been the oxidative sintered process (also referred to as the Outotec or Outokumpu process). Notwithstanding the common application of the oxidative sintered pelletised feed technology in the South African FeCr industry, and the increased utilisation of beneficiated UG2 ore, a direct comparison of the physical properties of oxidative sintered pellets produced from UG2 with the physical properties of that produced with conventional metallurgical grade chromite ore is currently lacking in the peer-reviewed scientific literature. Therefore, the physical properties of oxidative sintered pellets produced from a typical beneficiated South African UG2 ore were compared with the physical properties of that produced with conventional South African metallurgical grade chromite ore in this study. The results indicated that the case study metallurgical grade chromite ore required 13 kWh/t more energy to mill than the case study UG2 ore prior to pelletisation, which can lead to substantial cost savings. The compressive strength of the oxidative sintered pellets of both case study ores statistically showed that oxidative sintered pellets made from UG2 ore Abstract were the same or better than those prepared from metallurgical grade chromite ore. A comparison of the abrasion strengths of the oxidative sintered pellets of both case study ores indicated that the pellets prepared from UG2 ore were superior compared to the metallurgical grade pellets. The reasons for the superior UG2 pellet strength were investigated with backscatter-, secondary electron- and elemental X-ray mapping scanning electron microscopy (SEM), which indicated that differences in crystalline structures at least partially contributed to the differences observed. Results presented here can be utilised by FeCr producers to better quantify the advantages and disadvantages associated with the use of UG2 ore for FeCr production. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Master of Science / Department of Mechanical and Nuclear Engineering / Kevin B. Lease / The purpose of this study was to experimentally characterize the compressive and shear behavior of square cell titanium honeycomb cores according to the American Society of Testing and Materials Standards C 365-05 and C 273-06. By varying the honeycomb cell size and height as well as the foil thickness, many configurations of titanium honeycomb were manufactured utilizing a laser welding and expansion method. The test matrix consisted of 1080 compression and 1080 shear specimens. The compression specimens were split evenly into stabilized and unstabilized tests, and the shear specimens were split evenly to test three different shear orientations. At the conclusion of the characterization, a comprehensive statistical analysis was performed on the data. It was determined that both the compressive and shear strengths have a strong dependence on the relative density of the honeycomb. The compressive strength was found to be slightly affected by the presence of a stabilizing face sheet, and largely unaffected by specimen core height. The compressive modulus was affected by both the core height and the presence of a face sheet. Shear strength was found to decrease with increasing core height and was influenced by the shear orientation. Additionally, the rate of increase of shear modulus with respect to relative density was proportional to core height. Although no clear trend was observed, orientation did seem to have an effect on shear modulus. The compression and shear behavior of the honeycomb was compared with experimental results of honeycomb from existing publications and found to be consistent.

Thesis (PhD (Sport Sc) (Sport Science))--University of Stellenbosch, 2011. / Please refer to full text to view abstract.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / In this paper, we propose a new, low complexity approach for the design of laser radar (LIDAR) systems for use in applications in which the system is wirelessly transmitting its data from a remote location back to a command center for reconstruction and viewing. Specifically, the proposed system collects random samples in different portions of the scene, and the density of sampling is controlled by the local scene complexity. The range samples are transmitted as they are acquired through a wireless communications link to a command center and a constrained absolute-error optimization procedure of the type commonly used for compressive sensing/sampling is applied. The key difficulty in the proposed approach is estimating the local scene complexity without densely sampling the scene and thus increasing the complexity of the LIDAR front end. We show here using simulated data that the complexity of the scene can be accurately estimated from the return pulse shape using a finite moments approach. Furthermore, we find that such complexity estimates correspond strongly to the surface reconstruction error that is achieved using the constrained optimization algorithm with a given number of samples.

<p>This dissertation studies the coding strategies of computational imaging to overcome the limitation of conventional sensing techniques. The information capacity of conventional sensing is limited by the physical properties of optics, such as aperture size, detector pixels, quantum efficiency, and sampling rate. These parameters determine the spatial, depth, spectral, temporal, and polarization sensitivity of each imager. To increase sensitivity in any dimension can significantly compromise the others. </p><p>This research implements various coding strategies subject to optical multidimensional imaging and acoustic sensing in order to extend their sensing abilities. The proposed coding strategies combine hardware modification and signal processing to exploiting bandwidth and sensitivity from conventional sensors. We discuss the hardware architecture, compression strategies, sensing process modeling, and reconstruction algorithm of each sensing system. </p><p>Optical multidimensional imaging measures three or more dimensional information of the optical signal. Traditional multidimensional imagers acquire extra dimensional information at the cost of degrading temporal or spatial resolution. Compressive multidimensional imaging multiplexes the transverse spatial, spectral, temporal, and polarization information on a two-dimensional (2D) detector. The corresponding spectral, temporal and polarization coding strategies adapt optics, electronic devices, and designed modulation techniques for multiplex measurement. This computational imaging technique provides multispectral, temporal super-resolution, and polarization imaging abilities with minimal loss in spatial resolution and noise level while maintaining or gaining higher temporal resolution. The experimental results prove that the appropriate coding strategies may improve hundreds times more sensing capacity. </p><p>Human auditory system has the astonishing ability in localizing, tracking, and filtering the selected sound sources or information from a noisy environment. Using engineering efforts to accomplish the same task usually requires multiple detectors, advanced computational algorithms, or artificial intelligence systems. Compressive acoustic sensing incorporates acoustic metamaterials in compressive sensing theory to emulate the abilities of sound localization and selective attention. This research investigates and optimizes the sensing capacity and the spatial sensitivity of the acoustic sensor. The well-modeled acoustic sensor allows localizing multiple speakers in both stationary and dynamic auditory scene; and distinguishing mixed conversations from independent sources with high audio recognition rate.</p> / Dissertation