Reduced-control antenna arrays reduce the number of controls required for beamforming while maintaining a given array aperture. A reduced-control array for direction finding (DF), inspired by the concept of compressive sensing (CS), was recently proposed which uses random compression weights for combining antenna-element signals into fewer measurements. However, this compressive array had not been studied in terms of traditional characteristics such as directivity, sidelobe level (SLL) or beamwidth. In this work, random compression weights are shown to be suboptimal and a need for the optimisation of compressive arrays is expressed. Existing codebook optimisation algorithms prove to be the best starting point for the optimisation of compressive arrays, but are computationally complex. A computationally efficient codebook optimisation algorithm is proposed to address this problem, which inspires the compressive-array optimisation algorithm to follow. Compressive antenna arrays are formulated as a generalisation of reduced-control arrays and a framework is presented for their optimisation in terms of SLL. By allowing arbitrary compression weights, compressive arrays are shown to improve on existing reduced-control techniques. A feed network consisting of interconnected couplers and fixed phase shifters is proposed, enabling the implementation of compressive arrays in microwave hardware. The practical feasibility of compressive arrays is illustrated by successfully manufacturing a 3-GHz prototype compressive array with integrated antenna elements. / Thesis (PhD)--University of Pretoria, 2020. / Electrical, Electronic and Computer Engineering / PhD / Unrestricted

Introduction: Glass ionomers are available in sets of powder and liquid constituents, which are dispensed using a scoop and dropper bottle system prior to hand-mixing by an operator. Glass ionomers are also available in capsulated form, which is mixed in a suitable mechanical mixing machine prior to clinical use. Capsulation enables uniform proportioning of the powder and liquid. In this context, mixing time will be correct as an automated process is utilised, resulting in a cement mixture that is optimal and reproducible, with minimal air entrapment. Manufacturers promote the capsulated form as being time saving, and easy to dispense, with more accurate adaptation because of the use of an applicator to place the material. Aim: The aim of this in vitro study was to compare the performance of hand-mixed glass ionomer materials with their capsule-mixed equivalents in terms of compressive strength, surface hardness and porosity. Materials and Methods: Four groups of 10 cylindrical specimens were manufactured for each of the four specified hand-mixed posterior glass ionomers for each test that was performed: Riva Self Cure (RSCH) (SDI Limited); GC Fuji IX GP (FIXH) (GC Corp); Ketac Universal (KUH) (3M ESPE) and Ketac Molar Easymix (KMH) (3M ESPE). Similarly, four groups of 10 cylindrical specimens were manufactured for each of the four equivalent capsule-mixed posterior glass ionomers for each test that was performed: Riva Self Cure (RSCC) (SDI Limited); GC Fuji IX GP (FIXC) (GC Corp); Ketac Universal Aplicap (KUC) (3M ESPE) and Ketac Molar Aplicap (KMC) (3M ESPE). The compressive fracture strength of each specimen was determined after 24 hours using a universal testing apparatus. A compressive load of 1 mm/min was applied to the 6 mm long axis of each specimen. The load to fracture was recorded and the compressive fracture strength was calculated. Within one hour after compressive strength testing, a selection of fragments from each specimen was examined by Scanning Electron Microscope (SEM). Fragments were vacuum gold-sputter-coated prior to SEM examination. The fragments were observed at an operating voltage of 10kV, and over a range of magnifications to investigate crack propagation. The surface hardness of each specimen was measured with a digital micro-hardness tester with Vickers diamond indenter. The indenter was set at a load of 500mN at five predetermined regions of each specimen, with a dwell-time of five seconds. The five readings for each specimen were computed and the mean VHN in N/mm2 for each specimen was determined. Each specimen was observed and analysed for porosity using Micro-CT. Three-dimensional reconstructions were made of each specimen and the number of voids per volume (mm3) of specimen, the total volume of voids (mm3) per volume of specimen and the volume percentage of voids per volume of specimen were calculated. Results: RSCH and RSCC showed statistically significant differences when compressive strength (p=0.027), volume of voids (p=0.005) and volume percentage of voids (p=0.005) were compared. No statistically significant differences were found between RSCH and RSCC when surface hardness (p=0.124) and number of voids (p=0.221) were compared. When compressive strength (p=0.254) and number of voids (p=0.210) of FIXH and FIXC were compared, no statistically significant differences were found. Statistically significant differences were found when surface hardness (p=0.031), volume of voids (p<0.001) and volume percentage of voids (p<0.001) of FIXH and FIXH were compared. No statistically significant difference was found when compressive strength (p=0.090) of KUH and KUC were compared. Statistically significant differences were found when surface hardness (p<0.001), number of voids (p<0.001), volume of voids (p=0.004) and volume percentage of voids (p=0.004) of KUH and KUC were compared. Statistically significant differences were found between KMH and KMC when compressive strength (p<0.001), surface hardness (p=0.006), number of voids (p=0.001), volume of voids (p=0.010) and volume percentage of voids (p=0.010) were compared. Conclusion: The current study suggests that RSCC is more advantageous for clinical use compared to RSCH. The results as to whether the capsule-mix or the hand-mix product are superior for the examined properties for GC Fuji IX GP are inconclusive. KUC surpassed KUH in tests performed and is therefore recommended for clinical use. KMC out-performed KMH in all tests conducted, and is therefore advocated for use in clinical practice. / Dissertation (MSc)--University of Pretoria, 2019. / Community Dentistry / MSc / Unrestricted

High resolution transient/3D imaging technology is of high interest in both scientific research and commercial application. Nowadays, all of the transient imaging methods suffer from low resolution or time consuming mechanical scanning. We proposed a new method based on TCSPC and Compressive Sensing to achieve a high resolution transient imaging with a several seconds capturing process. Picosecond laser sends a serious of equal interval pulse while synchronized SPAD camera's detecting gate window has a precise phase delay at each cycle. After capturing enough points, we are able to make up a whole signal. By inserting a DMD device into the system, we are able to modulate all the frames of data using binary random patterns to reconstruct a super resolution transient/3D image later. Because the low fill factor of SPAD sensor will make a compressive sensing scenario ill-conditioned, We designed and fabricated a diffractive microlens array. We proposed a new CS reconstruction algorithm which is able to denoise at the same time for the measurements suffering from Poisson noise. Instead of a single SPAD senor, we chose a SPAD array because it can drastically reduce the requirement for the number of measurements and its reconstruction time. Further more, it not easy to reconstruct a high resolution image with only one single sensor while for an array, it just needs to reconstruct small patches and a few measurements. In this thesis, we evaluated the reconstruction methods using both clean measurements and the version corrupted by Poisson noise. The results show how the integration over the layers influence the image quality and our algorithm works well while the measurements suffer from non-trival Poisson noise. It's a breakthrough in the areas of both transient imaging and compressive sensing.

El concreto es uno de los materiales más utilizados en el mundo de la construcción, de las cuales cada material en la mezcla depende de la resistencia que se requiera de acuerdo al análisis estructural. Dentro del proceso de producción de concreto debemos garantizar que el cemento reaccione químicamente y desarrolle la resistencia para la cual fue diseñada, para esto es importante mantenerlo hidratado en ese tiempo mediante el proceso de curado. Una técnica aún no tan conocida es el auto-curado del concreto, por lo cual es una necesidad saber cuál es su influencia en el desarrollo de la resistencia y en la disminución del porcentaje de agrietamiento del concreto en estado plástico. El objetivo de esta tesis es determinar la influencia que tiene el reemplazar un cierto porcentaje de ladrillo triturado como reemplazo del agregado grueso; evaluando la resistencia a la compresión, resistencia a la flexión, y el agrietamiento por contracción plástica del concreto. Se desarrolló con 3 diferentes porcentajes de reemplazo de ladrillo triturado que son: 15%, 21%, 27% del peso del agregado grueso para la resistencia a la compresión (f’c) de 280 kg/cm2. Se concluyó que reemplazo del agregado grueso por ladrillo triturado es efectivo cuando es usado hasta un máximo de 21%. Los resultados obtenidos son óptimos y viables en el tiempo, mostrándonos un aumento en la resistencia a la compresión, resistencia a la flexión y la disminución del porcentaje de fisuras en estado plástico. / Concrete is one of the most used materials in the world of construction, of which each material in the mixture depends on the strength required according to the structural analysis. Within the concrete production process, we must ensure that the cement reacts chemically and develops the resistance for which it was designed, for this it is important to keep it hydrated at that time through the curing process. A technique not yet so well known is the self-curing of concrete, so it is a necessity to know what its influence is in the development of resistance and in the reduction of the percentage of cracking of concrete in the plastic state. The objective of this thesis is to determine the influence of replacing a certain percentage of crushed brick as a replacement for coarse aggregate; evaluating the compressive strength, flexural strength, and cracking by plastic shrinkage of concrete. It was developed with 3 different percentages of crushed brick replacement that are: 15%, 21%, 27% of the weight of the coarse aggregate for the compressive strength (f’c) of 280 kg / cm2. It was concluded that replacement of coarse aggregate with crushed brick is effective when used up to a maximum of 21%. The results obtained are optimal and viable over time, showing an increase in compressive strength, flexural strength and a decrease in the percentage of cracks in the plastic state. / Tesis

Ces dernières années, la théorie mathématique de l'échantillonnage compressé (CS) a émergé en tant que nouvel outil en traitement d'images, permettant notamment de dépasser certaines limites établies par la théorie de l'échantillonnage de Nyquist. En particulier, la théorie du CS établit qu'un signal (une image, une séquence vidéo, etc.) peut être reconstruit à partir d'un faible nombre de mesures linéaires non-adaptatives et aléatoires, pourvu qu'il présente une structure parcimonieuse. Dans la mesure où cette hypothèse se vérifie pour une large classe d'images naturelles, plusieurs applications d'imagerie ont d'ores-et-déjà bénéficié à des titres divers des résultats issus de cette théorie. Le but du travail doctoral présent est d'étudier comment la théorie du CS - et plus généralement les idées et méthodes en relation avec les problèmes de reconstruction de signaux parcimonieux - peuvent être utilisés pour concevoir des dispositifs d'acquisition optiques à haute-résolution spatiale et temporelle pour des applications en imagerie biologique. Nous étudions tout d'abord quelques questions pratiques liées à l'étape de reconstruction nécessairement associée aux systèmes d'acquisition exploitant le CS, ainsi qu'à la sélection des paramètres d'échantillonnage. Nous examinons ensuite comment le CS peut être utilisé dans le cadre d'applications d'échantillonnage de signaux vidéo. Enfin, avec dans l'idée l'utilisation dans des problèmes de débruitage de méthodes inspirées du CS, nous abordons la question de l'estimation d'erreur dans les problèmes de débruitage d'images acquises en conditions de faible luminosité, notamment dans le cadre d'applications de microscopie. / In the past few years, the mathematical theory of compressed sensing (CS) has emerged as a new tool in the image processing field, leading to some progress in surpassing the limits stated by the Nyquist sampling theory. In particular, the CS theory establishes that a signal (image, video, etc.) can be reconstructed from a relatively small subset of non-adaptive linear random measurements, assuming that it presents a sparse structure. As this hypothesis actually holds for a large number of natural images, several imaging applications have already benefited from this theory in various aspects. The goal of the present PhD work is to investigate how the CS theory - and more generally the ideas and methods developed in relation with sparse signal reconstruction problematics - can be used to design efficient optical sensing devices with high spatial and temporal resolution for biological imaging applications. We first investigate some practical issues related to the post-processing stage required by CS acquisition schemes, and to the selection of sampling parameters. We then examine how CS can benefit to video sampling applications. Finally, with the application of CS methods for denoising tasks in mind, we focus on the error estimation issue in image denoising problems for low-light microscopy applications.

The influence of tricalcium silicate content of cement on concrete durability has long been a topic of discussion in the literature. The objective of this investigation was to determine whether increasing tricalcium silicate content of cement has a negative effect on concrete sulfate durability. Several mill certificates were reviewed to select cements with similar tricalcium aluminate content and variable tricalcium silicate contents. Cements selected for this study were randomly labeled as cements C, D, D2, E, and P. The following properties were assessed for the as-received cements: Blaine fineness, particle size distribution, chemical oxide content, and mineralogical content. Three different methods were employed to determine the mineralogical composition of the as-received cements: Bogue calculation, internal standard method, and Rietveld refinement analysis. Despite the attempt to select cements with similar composition, it was determined that the as-received cements had compositional differences other than their C3S content. These cements had a variable tricalcium aluminate and alkali content, as well as differences in the amount and form of calcium sulfates. In order to eliminate these variances, doped cements were prepared by increasing the C3S content of the as received cements to 69 % by Bogue calculation. Durability of as-received cements and doped cements was assessed through several measurements including length change, compressive strength, and phase transformation in sodium sulfate solution. For as-received cements, compressive strength of mortar cubes stored in saturated lime solution was evaluated as well. Semiquantitative x-ray diffraction analysis and scanning electron microscopy observations were performed on mortar bars to evaluate the relative amounts and morphology of the hydrated phases. It was concluded at the end of this study that cements with high tricalcium silicate content generally have poor durability in sodium sulfate environment. All the cements experienced higher expansion with increased C3S content. High C3S content combinedwith high C3A content was particularly detrimental to mortar resistance to sodium sulfate attack.

In situ planetary effective thermal conductivity measurements are typically made using a long needle-like probe, which measures effective thermal conductivity in the probe‟s radial (horizontal) direction. The desired effective vertical thermal conductivity for heat flow calculations is assumed to be the same as the measured effective horizontal thermal conductivity. However, it is known that effective thermal conductivity increases with increasing compressive pressure on granular beds and horizontal stress in a granular bed under gravity is related to the vertical stress through Jaky‟s at-rest earth pressure coefficient. No research has been performed previously on determining the anisotropic effective thermal conductivity of dry granular beds under compressive uniaxial pressure. The objectives of this study were to examine the validity of the isotropic property assumption and to develop a fundamental understanding of the effective thermal conductivity of a dry, noncohesive granular bed under uniaxial compression. Two experiments were developed to simultaneously measure the effective vertical and horizontal thermal conductivities of particle beds. One measured effective thermal conductivities in an atmosphere of air. The second measured effective thermal conductivities in a vacuum environment. Measurements were made as compressive vertical pressure was increased to show the relationship between increasing pressure and effective vertical and horizontal thermal conductivity. The results of this experiment show quantitatively the conductivity anisotropy for different materials. Based on the effective thermal conductivity models in the literature and results of the two experiments, a simple model was derived to predict the increase in effective vertical and horizontal thermal conductivity with increasing compressive vertical applied pressure of a granular bed immersed in a static fluid. In order to gain a greater understanding of the anisotropic phenomenon, finite element simulations were performed for a vacuum environment. Based on the results of the finite element simulations, the simple derived model was modified to better approximate a vacuum environment. The experimental results from the two experiments performed in this study were used to validate both the initial simple model and the modified model. The experimental results also showed the effects of mechanical properties and size on the anisotropic effective thermal conductivity of granular beds. This study showed for the first time that compressive pressure-dependent effective thermal conductivity of granular beds is an anisotropic property. Conduction through the fluid has been shown to have the largest contribution to the effective thermal conductivity of a granular bed immersed in a static fluid. Thermal contact resistance has been shown to have the largest influence on anisotropic effective thermal conductivity of a granular bed in a vacuum environment. Finally, a discussion of future work has been included.

The work in this dissertation is focused on two areas within the general discipline of statistical signal processing. First, several new algorithms are developed and exhaustively tested for solving the inverse problem of compressive sensing (CS). CS is a recently developed sub-sampling technique for signal acquisition and reconstruction which is more efficient than the traditional Nyquist sampling method. It provides the possibility of compressed data acquisition approaches to directly acquire just the important information of the signal of interest. Many natural signals are sparse or compressible in some domain such as pixel domain of images, time, frequency and so forth. The notion of compressibility or sparsity here means that many coefficients of the signal of interest are either zero or of low amplitude, in some domain, whereas some are dominating coefficients. Therefore, we may not need to take many direct or indirect samples from the signal or phenomenon to be able to capture the important information of the signal. As a simple example, one can think of a system of linear equations with N unknowns. Traditional methods suggest solving N linearly independent equations to solve for the unknowns. However, if many of the variables are known to be zero or of low amplitude, then intuitively speaking, there will be no need to have N equations. Unfortunately, in many real-world problems, the number of non-zero (effective) variables are unknown. In these cases, CS is capable of solving for the unknowns in an efficient way. In other words, it enables us to collect the important information of the sparse signal with low number of measurements. Then, considering the fact that the signal is sparse, extracting the important information of the signal is the challenge that needs to be addressed. Since most of the existing recovery algorithms in this area need some prior knowledge or parameter tuning, their application to real-world problems to achieve a good performance is difficult. In this dissertation, several new CS algorithms are proposed for the recovery of sparse signals. The proposed algorithms mostly do not require any prior knowledge on the signal or its structure. In fact, these algorithms can learn the underlying structure of the signal based on the collected measurements and successfully reconstruct the signal, with high probability. The other merit of the proposed algorithms is that they are generally flexible in incorporating any prior knowledge on the noise, sparisty level, and so on. The second part of this study is devoted to deployment of mobile sensors in circumstances that the number of sensors to sample the entire region is inadequate. Therefore, where to deploy the sensors, to both explore new regions while refining knowledge in aleady visited areas is of high importance. Here, a new framework is proposed to decide on the trajectories of sensors as they collect the measurements. The proposed framework has two main stages. The first stage performs interpolation/extrapolation to estimate the phenomenon of interest at unseen loactions, and the second stage decides on the informative trajectory based on the collected and estimated data. This framework can be applied to various problems such as tuning the constellation of sensor-bearing satellites, robotics, or any type of adaptive sensor placement/configuration problem. Depending on the problem, some modifications on the constraints in the framework may be needed. As an application side of this work, the proposed framework is applied to a surrogate problem related to the constellation adjustment of sensor-bearing satellites.

Les travaux présentés dans ce manuscrit ont été consacrés à la compréhension du procédé de fabrication des mousses phénoliques et de la chimie associée, dans le but de proposer des modifications de la formulation permettant l’amélioration de ses propriétés mécaniques (friabilité et comportement en compression). Dans un second temps, les propriétés mécaniques en compression, en flexion et la friabilité ont été caractérisées en fonction de la densité relative de la mousse. Les caractéristiques de compression ont été modélisées et comparées aux modèles de Gibson et Ashby. Les résultats montrent que le module d’Young et la contrainte au plateau de compression sont des fonctions quadratiques de la densité relative. Le comportement thermique de la mousse phénolique a été également étudié. L’évolution de la structure chimique des résidus obtenus après différents traitement thermique a été suivie par IRTF. Les observations spectrales ont été interprétées en fonction des réactions de dégradat ion proposées dans la littérature. Les paramètres cinétiques de dégradation de la mousse phénolique ont été déterminés grâce à différentes méthodes dites « model-free kinetic» développées par Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose et Friedman. Finalement, dans une première approche, nous avons essayé de déterminer les paramètres cinétiques, en condition isotherme, du phénomène d’oxydation qui apparait à faible température / The following work has been devoted to the understanding of the phenolic foam manufacturing process and the associated chemistry, to propose modifications of the formulation itself that allows an enhancement in mechanical properties (friability and compression behavior). In addition, these mechanical properties in compression, bending and brittleness were characterized as a function of the foam relative density. Compression properties were modeled and compared to the Gibson and Ashby models. Results show that Young's modulus and collapse plateau stress are quadratic functions of the relative density. Moreover, the thermal behavior of the phenolic foam was also studied. The evolution of the chemical structure of the obtained residues after different thermal treatment was followed by FTIR. Spectral observations were interpreted according to the degradation reactions proposed in the literature. The kinetic parameters of phenolic foams degradation have been determined using different "mo del-free kinetic" approaches, developed by Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose and Friedman. Finally, in a first approach, we tried to determine the kinetic parameters, in isothermal condition, of the oxidation phenomenon that appears at low temperature

The present dissertation contributes to advancing methods of determining the elastic and inelastic buckling resistance of compressive members with single angle and back-to-back double angle cross-sections with end conditions representative of those commonly used in steel construction. The first contribution develops an elastic buckling solution for members with asymmetric sections, such as unequal-leg angle members, connected to gusset plates at both ends and subjected to pure compression. In this case, the gusset plate connections at the member ends provide a fixity restraint to the member within the plane of the gusset and nearly a pin restraint in a plane normal to the gusset. Since both directions do not coincide with the principal directions of the member, the classical flexural-torsional buckling solutions provided in standards become inapplicable. In this context, a variational principle is formulated based on non-principal directions and then used to derive the governing differential equations and associated boundary conditions for the problem. The coupled equations are then solved analytically subject to the boundary conditions, and the characteristic equations are recovered and solved for the flexural-torsional buckling load of the member. The validity of the solutions derived is assessed against 3D shell elastic eigen-value buckling models based on ABAQUS for benchmark cases and the solution is shown to accurately predict the elastic buckling load and mode shapes. The effect of non-principal end restraints on the buckling load of compression members is then investigated for members with angle and zed cross-sections in a parametric study. It is observed that when a member end is fixed about a non-principal direction and pinned about the orthogonal direction, the flexural-torsional buckling load of the member is significantly influenced by the angle of inclination between the fixity axis and the minor principal axis. The second contribution aims to obtain the inelastic buckling resistance for single angle compression members with end gusset plate connections by taking into consideration the effects of material and geometric nonlinearity, initial out-of-straightness, residual stresses, and load eccentricity induced by the offset of the member centroidal axis from the end gusset plate connection. Towards this goal, a series of 3D shell models based on ABAQUS are developed and validated through comparisons against experimental results by others and then used to generate a database of compressive capacities for over 900 eccentrically loaded angle members with various geometrical dimensions and load eccentricities. The database is then used to investigate the effect of slenderness ratio, leg width ratio, connected leg width-to-thickness ratio and gusset plate-to-angle thickness ratio on the compressive resistance of the members, assess the accuracy of solutions available in present design standards, and develop improved design expressions for the compressive resistance for the members. The third contribution develops solutions for predicting the elastic buckling resistance of back-to-back double angle assemblies with end gusset plates and intermediate interconnectors subjected to compressive loads. Towards this goal, two novel models are developed. (1) A thin-walled finite element buckling solution is formulated and implemented into a MATLAB code. The formulation treats each angle member as a line of 1D thin-walled beam elements where then both angle members are connected at intermediate points along the span at the locations of interconnectors. The formulation is equipped with a multi-point constraint feature to enforce the kinematic constraints at the interconnector locations and at both extremities of the member. The model captures the tendency of both angles to open relative to one another in between interconnectors while undergoing flexural-torsional buckling. (2) An analytical buckling solution is developed for the limiting case where enough interconnectors are provided between members to force the two angles to essentially behave as a monolithic entity. The resistance predicted by the former model was then shown to asymptotically approach that predicted by the later model as the number of interconnectors is increased. The validity of the finite element model is assessed against 3D shell models based on ABAQUS and published experimental results, and then used to assess the validity of present design rules based on the effective slenderness concept. The present models are then used to carry out a parametric study of 1250 runs while varying the member slenderness ratio, leg width ratio, connected leg width-to-thickness ratio, and angle spacing-to-thickness ratio. The database of results generated is used to develop a simple expression to characterize the elastic buckling load/stress of the assembly. The possible integration of the new expression with present design provisions in standards to predict the inelastic buckling resistance of the member is illustrated through a design example.