<div>Near-Field Acoustical Holography (NAH) is an inverse process in which sound pressure measurements made in the near-field of an unknown sound source can be used to reconstruct the sound field so that source locations can be identified. Usually a large number of measurements is required for the usual NAH methods since a large number of parameters in the source or field model need to be determined. However, a large-scale microphone measurement is costly and hard to perform, so the use of NAH is limited by practical experimental conditions. In the present work, with the motivation of decreasing the number of microphone measurements required, and thus facilitating the measurement process, two sparse Equivalent Source Method (ESM) algorithms were studied: i.e., Wideband Acoustical Holography (WBH) and l_1-norm minimization. Based on these two algorithms, a new hybrid NAH procedure was proposed and demonstrated.To study and verify the above mentioned algorithms, simulations of different sources were conducted and then experiments were conducted on different sources: i.e., a loudspeaker cabinet and a diesel engine.</div>

Recentemente, uma quantidade de informação/computação quântica chamada complexidade computacional tem adquirido mais e mais importância no estudo de buracos negros.Resumidamente, complexidade mede a dificuldade de alguma tarefa. No contexto de mecânica quântica (ou mesmo para estados em uma CFT), qualquer estado tem uma complexidade associada, uma vez que o processo de preparar algum estado, usando operações unitárias, é uma tarefa por sí só. Propostas holográficas para o cálculo de complexidade tem sido desenvolvidas nos anos recentes. Há duas delas que estão mais desenvolvidas: as conjecturas complexidade=volume e complexidade=ação. No contexto da correspondência AdS/CFT é sabido que o buraco negro de Schwarzschild em AdS é dual à um estado térmico que descreve duas CFTs emaranhadas. Para esse caso em específico, a conjectura complexidade=volume iguala a complexidade do estado que descreve esse par de CFTs emaranhadas com o volume da máxima superfície de codimensão um no espaço-tempo dual. Por outro lado, a conjectura complexidade=ação iguala a complexidade da borda com a ação gravitacional calculada sobre uma região do espaço-tempo conhecida como Wheeler-DeWitt patch. O objetivo dessa tese é proporcionar os requisitos necessários para entender as conjecturas relacionadas com complexidade, monstrando alguns resultados importantes proporcionados pelos cálculos holográficos no lado gravitacional. / In recent years, a quantity from quantum information/computation called computational complexity has been acquiring more and more importance in the study of black holes. Briefly, complexity measures the hardness of some task. In the context of quantum mechanics (or even for states in a CFT), any state has an associated complexity, once the process of to preparing some state, using unitary operations, is a task by itself. Holographic proposals for the computation of complexity have been developed in recent years. There are two of them that are more developed: the complexity=volume and complexity=action conjectures. In the context of the AdS/CFT correspondence, it is known that the two sided AdS-Schwarzschild black hole is dual to some thermal state that describes two entangled CFTs. For this specific case, the complexity=volume conjecture equates the complexity of the state that describes this pair of entangled CFTs with the volume of the maximal codimension-one surface in the dual space-time. On the other hand, the complexity=action conjecture equates the boundary complexity with the gravitational action evaluated on a region of space-time known as the Wheeler-DeWitt patch. The goal of this thesis is to provide the necessary requisites to understand the conjectures related to complexity, showing some important results provided by holographic computations on the gravitational side.

A Microscopia Holográfica Digital (MHD) é uma poderosa ferramenta para análise não destrutiva de superfícies e caracterização morfológica e estrutural de materiais. Várias técnicas microscópicas têm sido utilizadas com esses objetivos, mas, em todas elas, a visualização de campo completo não é permitida em uma única aquisição da informação do sistema analisado, além disso, a necessidade de uso de corantes, o processo de varredura, entre outros fatores, dificulta a aquisição das imagens. A Microscopia Holográfica Digital permite contornar essas dificuldades através de um método simples e rápido. Com uma modificação em seu arranjo original, é possível revelar as diferenças na absorção e nos índices de refração experimentados por um campo transmitido por um material anisotrópico. Este método, neste trabalho, foi nomeado como Microscopia Holográfica de Polarização, o qual permite medir as diferenças de fase e de intensidade relacionadas com a birrefringência e com o dicroísmo do material, respectivamente. Dessa forma, A MHD se mostra uma ferramenta promissora na análise de problemas em diversas áreas, pois possibilita, através de uma única captura, obter informações sobre as propriedades ópticas e estruturais dos sistemas de interesse. O objetivo desse trabalho foi, além do desenvolvimento instrumental, analisar variações nas propriedades ópticas e morfológicas de eritrócitos através da quantificação dos índices de refração e perfis topográficos destes quando submetidos aos principais agentes de fixação de amostras. Essas variações são determinantes na escolha do método de análise, já que estes podem alterar significativamente os resultados, assim como a sua interpretação. Também foi descrito um novo método, baseado na técnica holográfica, de análise do dicroísmo linear através de uma varredura executada sobre os padrões de difração das componentes ortogonais do campo transmitido pela amostra. A aplicação da MHD ao estudo de processos dinâmicos também foi realizada, utilizando células cardíacas vivas e proteínas em solução. Somados, estes resultados demonstraram a possibilidade de se utilizar as técnicas holográficas como métodos de estudo amplo de microssistemas biológicos. / The Digital Holographic Microscopy (DHM) is a powerful tool for nondestructive analysis of surfaces and for morphological and structural characterization of materials. Several microscopic techniques have been used with these purposes, but in all cases, the complete field reconstruction is not allowed in a single acquisition of information of the analyzed system, moreover, the requirements of staining and scanning procedures, among other factors, difficult the image acquisition. Digital Holographic Microscopy allows to overcome these difficulties through a simple and quick method. With a modification in its original setup, is possible to reveal the differences in absorption and refractive index experienced by a wavefield transmitted by an anisotropic material. This method, in this thesis, is named Polarization Holographic Microscopy, which allows to measure differences in phase and intensity related to the birefringence and the dichroism of the material, respectively. Thereby, the DHM is shown as a promising tool for the study of problems in several fields, because it allows, through a single capture, to obtain information related to optical and morphological properties of the systems of interest. The objective of this work was, besides instrumental development, to evaluate changes in optical and morphological properties of erythrocytes through quantification of their refractive index and topographic profiles when submitted to the main fixating agents. These changes are crucial once the method of analysis is chosen, as they can significantly alter the results, as well as their interpretation. A new method was also described based on the holographic technique, for analysis of linear dichroism, through scans performed on the diffraction patterns of the orthogonal components of the field transmitted by the sample. The application of the DHM to the study of dynamic processes was also performed, using live cardiac cells and proteins in solution. Together, these results demonstrate the possibility of using holographic techniques such as extensive methods for studying biological microsystems.

No description available.

The objective of this project is to develop a shape-based image analysis system, which allows classification and identification of holographic images of marine particles and plankton recorded by an underwater digital holographic camera. In order to achieve this goal, the first step is to extract shape regions of objects from images and to describe the regions by polygonal boundaries. After extraction of the polygonal boundary curve of an object, affine-invariant curve normalisation is implemented on the curve to reduce the influence of object shape deformations on object identification and classification. Six numeric features are then selected to describe shape properties of an object. Before these six shape features are used as a numeric interpretation of an object for image analysis, some processing of them is necessary, consisting of selecting the number of items in each feature and rescaling the selected feature vectors. Afterwards, Gaussian rescaling is adopted to rescale the feature data. Lastly, a shape-based image classification and identification system is built. The system contains two components: semi-automatic image classification (imCLASS) and automatic image identification (imIDENT). In imCLASS, an image retrieval method based on the support vector machine with a feedback mechanism has been developed. The function of imCLASS is to classify given images into different folders with the corresponding labels from the user. These labelled folders can be used to train the artificial neural network in imIDENT. A set of analyses of effects of the proposed methods in the process chain on image analysis are carried out. The whole performance of the system for classifying and identifying marine particles and plankton is also evaluated in terms of the time-cost and accuracy performance. In the end, some main conclusions are listed. The areas of weakness of the system are also highlighted for future work.

This thesis improves on the design of the leaky-mode spatial light modulator, LMW-SLM, presented by Dr. Smalley[1]. Improvements include: input coupling gratings, a pulsed laser input, output coupling gratings, and a 3D printed adjustable module for the stabilization of critical alignments. First, input coupling gratings reduce the cost of the LMW-SLM from $500 to around $2, a drop in cost of over two orders of magnitude. This enables multiple modulators to be used in a single display and allows for an inexpensive modular design to be created. Second, a pulsed laser input allows for image creation without the use of a polygon for derotation. Removal of the polygon allows for direct viewing of the LMW-SLM output enabling near-eye and flat panel displays. Third, output coupling gratings allow for bottom exit devices that are essential for thin substrates and flat panel displays. Fourth, the 3D printed module allows for the critical alignments of the LMW-SLM to become permanent. This in turns allows for transportation of the created displays without a trained technician by abstracting away the complexities of the device. The resulting changes simplify hardware, reduce cost, and enable the LMW-SLM to be modularized and the resulting 3D displays to be transportable. These improvements are made possible by the addition of a one new mask step during fabrication, a simple circuit design, and a 3D printed module designed in SOLIDWORKS. Included in this thesis as attachments are the MATLab, Eagle, and SOLIDWORKS files used to create the improved LMW-SLM.

Gabor's original holography, which is the basic theory of modern microwave holographic techniques, is introduced. By computer simulations, it is demonstrated that the conventional holographic approach can be used as a tool to reconstruct aperture field distributions of an antenna with some constraints. Computer simulations of the theory and technique of the improved microwave holographic approach originally introduced by Rahmat-Samii et al. are carried out. The results show that it can be used for surface distortion diagnosis of large reflector antennas. The physical optics integral formulation is derived by general solutions of the vector wave equations. The necessary theory , which is needed to reconstruct the aperture field from near-field measurements both in a rectangular coordinate system and in a cylindrical coordinate system is developed. It is based on the plane wave spectrum and the vector wave modal expansion of an electromagnetic field. By using a simple dipole and other well-defined antennas, computer simulations have been performed. The results show that the technique is rigorous and applicable. It is also demonstrated that the sampling intervals and the number of sampling points should be chosen carefully in order to obtain a satisfactory resolution of the reconstructed aperture field. Furthermore, the simulations carried out in this work reveal that the real aperture field distribution of a dipole antenna has a maximum point at each end of the antenna. This characteristic can only be obtained at a very close distance to the antenna. This study also reveals the significant contributions of the evanescent waves to the aperture reconstruction. A simple but effective method for examining the evanescent waves from the measured near-field is also presented. By using dipoles and other well known antennas and antenna arrays, the experiments were carried out. The experimental results provide reasonable good agreements with the simulations. The technique proposed is effective and accurate. / Doctor of Philosophy (PhD)

The increasing demand for high density storage devices has led to innovative data recording paradigms like optical holographic memories that record and read data in a two-dimensional page-oriented manner. In order to overcome the effects of inter-symbol-interference and noise in holographic channels, sophisticated constrained modulation codes and error correction codes are needed in these systems. This dissertation deals with the information-theoretic and signal processing aspects of holographic storage. On the information-theoretic front, the capacity of two-dimensional runlength-limited channels is analyzed. The construction of two-dimensional runlength-limited codes achieving the capacity lower bounds is discussed. This is a theoretical study on one of the open problems in symbolic dynamics and mathematical physics. The analysis of achievable storage density in holographic channels is useful for building practical systems. In this work, fundamental limits for the achievable volumetric storage density in holographic channels dominated by optical scattering are analyzed for two different recording mechanisms, namely angle multiplexed holography and localized recording. Pixel misregistration is an important signal processing problem in holographic systems. In this dissertation, algorithms for compensating two-dimensional translation and rotational misalignments are discussed and analyzed for Nyquist size apertures with low fill factors. These techniques are applicable for general optical imaging systems

No description available.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaf 99).