Ulm, Univ., Diss., 2008.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Michaels, Jennifer; Committee Member: Jacobs, Laurence; Committee Member: Michaels, Thomas. Part of the SMARTech Electronic Thesis and Dissertation Collection.

In the indoor environment, multipath fading causes the received signal amplitude to fluctuate rapidly over space and frequency. Multiple-in multiple-out (MIMO) systems overcome this phenomenon through the use of multiple antennas on transmitters and receivers. This establishes multiple independent MIMO sub-channels between antenna pairs, which allows a theoretical increase in capacity which is linear with the number of antennas, while requiring no additional power or bandwidth expenditure. The capacity increase is reliant upon MIMO sub-channels being well decorrelated. Decorrelation may be achieved by separating antennas in space. On devices where space is limited, an alternative approach is to use antennas with orthogonal polarisations, which may be positioned closer together. Existing literature states that the performance of polarisation MIMO systems is typically inferior to that of spatial MIMO systems under diversity applications, but can be superior in multiplexing applications. These statements are based on the analysis of a statistical channel model, using channel conditions assumed to be typical of an ideal polarisation MIMO system. There is little existing literature which examines how close these assumptions are to a practical polarisation MIMO channel, or whether the above statements remain true of practical systems. This thesis presents a novel end-to-end, predominantly deterministic approach to the modelling of polarisation MIMO systems. A bespoke MIMO channel model is used to estimate capacity and error rate under diversity and spatial multiplexing applications in the indoor environment. The parameters of the channel model are obtained deterministically from a ray launching propagation model, using antenna patterns of orthogonally polarised small antenna systems positioned in the indoor environment. The individual differences in the channel gains and K-factors of each sub-channel are accounted for. Correlation is accounted for using a full correlation matrix, rather than the Kronecker model. Particular attention is paid to mutual coupling of closely spaced antennas. Using this analysis, it is shown that for practical antennas and systems conditions of the polarisation MIMO channel may differ from those assumed in literature. The effect of this in terms of channel capacity and system bit error rate is directly determined and presented. Performance of polarisation MIMO systems, using co-located and spatially separate orthogonally polarised antennas, is compared to that of spatial MIMO systems, which use co-polar antennas with limited spatial separation. Additionally, comparison is made between compact polarisation MIMO systems which use orthogonal linear polarised antennas and those using orthogonal circular polarised antennas. Further analysis examines the significant effect of objects in the antenna near-field regions. The effects of the presence of a metal case on antenna performance are presented, before its impact on the channel conditions and ultimately the resultant MIMO performance is shown.

One feature of the brain is that different parts of it respond to different stimuli. This means not all brain regions or neurons within those regions are active at a given moment. This feature of the brain gives it the ability to encode and store a wide range of stimuli that are then used to make predictions about a changing external environment. Activation of non-overlapping neural populations is fundamental to the ability to encode a wide range of stimuli to represent a changing environment. To examine the limits of this idea we used genetic tools to label active cell populations following a neutral stimulus presentation or a learned negative association with the same stimulus. The study examined the degree of similarity between these active populations by comparing key features of the active neurons including gene expression and monosynaptic inputs. Another feature of the brain is its ability to store information. In a neural population recently activated by a salient stimulus, molecular processes occur that result in the formation and maintenance of a memory. Collectively these processes are referred to as plasticity, and act on short and long time scales to strengthen the connections between active neurons and weaken the connections between inactive ones. Plasticity processes are not only necessary for the formation and storage of memories but also for wiring up the nervous system during development. A molecule called ZIP has been shown to erase memories months after formation and specifically affects plasticity on longer time scales. However, the effects of ZIP on the developing brain are not well understood and difficult to study using ZIP’s typical delivery method of injection into the brain. To facilitate a developmental study of ZIP’s effects, we made a genetic tool that can specify where and when ZIP is delivered to the brain. Results of the study indicated that males were particularly vulnerable to ZIP during early development while females were unaffected. Together these results provide insight into the limits of information coding potential at the anatomical level and reveal a fundamental difference in plasticity processes in males and females. / 10000-01-01

The behaviour of very low frequency (V.L.F.) radio waves propagating in an ionlzed medium, such as the ionosphere and exosphere, may exhibit markedly different characteristics from those of frequencies such as are used for communication in the short-wave bands. The anisotropy introduced into the medium by the presence of the earth's magnetic field has a significant effect, while at frequencies below about 5KHz the presence of heavy positive ions may further affect propagation. In particular it is found that, under suitable conditions, V.L.F. signals may propagate along paths closely following the lines of force of the earth's magnetic field. The study of such signals has a practical interest in that, from consideration of their propagation times and dispersion properties, they can provide an inexpensive method of determining electron densities at well beyond the range of satellite investigation. For this reason, if for no other, theoretical investigation of the paths traced in a model exosphere may indicate how closely the model exosphere approximates the true one. A powerful method of tracing out these paths is by the use of "ray-tracing", provided the properties of the medium vary slowly in space, a condition not always fulfilled in practice. It has been the subject of this thesis to carry out ray-tracing studies, in particular noting the effects of the positive ions in the exosphere; effects which have not received much notice before as they were thought to be unimportant. Intro., p. 1-2.

With the push to exascale, in situ visualization and analysis will play an increasingly important role in high performance computing. Tightly coupling in situ visualization with simulations constrains resources for both, and these constraints force a complex balance of trade-offs. A performance model that provides an a priori answer for the cost of using an in situ approach for a given task would assist in managing the trade-offs between simulation and visualization resources. In this work, we present new statistical performance models, based on algorithmic complexity, that accurately predict the run-time cost of a set of representative rendering algorithms, an essential in situ visualization task. To train and validate the models, we create data-parallel rendering algorithms within a light-weight in situ infrastructure, and we conduct a performance study of an MPI+X rendering infrastructure used in situ with three HPC simulation applications. We then explore feasibility issues using the model for selected in situ rendering questions.

[pt] Dentre as diversas técnicas, modelos e procedimentos desenvolvimentos para a produção de imagens realistas em computador, há um subconjunto que tem como objetivo a síntese de texturas. O presente trabalho realiza um estudo sobre a geração de texturas em imagens realistas produzidas por computador. Abordam-se os conceitos teóricos fundamentais e os principais parâmetros de textura com seus modelos e mapeamentos. Desenvolve-se um sistema de visualização de texturas utilizando-se o algoritmo de produção de imagens Ray-tracing aliado ao paradigma da programação orientada a objetos. Com esta plataforma, executou-se uma série de testes que permitiram uma análise dos assuntos tratados. / [en] Among the many techniques, models and procedures developed to produce computer generated realistic images, there is a subset which is concerned with synthesis. The present work surveys the area of texture in computer generated realistics images. It covers theoretical concepts and the main texture paramenters with their respective models and mapping. It has been deleoped a texture visualization system based on an object-oriented ray-tracing algorithm. A series of testes have been perfomed which allowed an evalution of the discussed methods and techniques.

A síntese de imagens é uma ferramenta valiosa na compreensão de diversos fenômenos da natureza. Nos últimos anos várias abordagens têm sido propostas para sintetizar tais fenômenos. A grande maioria de tais abordagens têm se centralizado no desenvolvimento de modelos procedurais. Porém, cada uma destas técnicas simula exclusivamente um fenômeno natural. Um dos métodos de síntese de imagens fotorealísticas mais proeminente é denominado de Traçado de Raios (Ray Tracing). Contudo, apesar de produzir imagens de excelente qualidade, este método é computacionalmente muito oneroso. A síntese de fenômenos naturais utilizando-se o traçado de raios é um desafio. É importante que este problema seja abordado, apesar da sua complexidade, pois a simulaçao fotorealista da natureza é muito importante para os cientistas e pesquisadores desde o surgimento dos computadores. Um algoritmo versátil e rápido para a síntese de fenômenos da natureza através do traçado de raios utilizando campos de altitude é proposto. O algoritmo utiliza uma modificação do algoritmo do Analisador Diferencial Digital de Bresenham para atravesar uma matriz bidimensional de valores de altitude. A determinação das primitivas geométricas a serem interseccionadas por um raio é obtida num tempo ( N ) , sendo N o número de altitudes no campo de altitude. Este trabalho faz uma comparação em termos de velocidade e realismo deste método com outras abordagens convencionais; e discute as implicações que a implementação deste método traz. Finalmente, destaca-se a simplicidade e versatilidade que este método proporciona devido à pequena quantidade de parâmetros necessária para a síntese de fenômenos naturais utilizando o traçado de raios. Para a criação de animações basta a especificação de novos parâmetros num intervalo de tempo diferente. / Visualization is a powerful tool for better undestanding of several natural phenomena. In recent years, several techniques have been proposed. Considerable interest in natural scene synthesis has focused on procedural models. However, these techniques produce synthetic scenes of only one natural phenomenon. Ray tracing is one of the most photorealistic methods of image syntesis. While providing images of excellent quality, ray tracing is a computationally intensive task. Natural scene synthesis is a challenging problem within the realm of ray tracing. It is important to tackle this problem, despite of its complexity, because photorealistic simulation have been important to scientific community since the appearance of computers. A fast and versatile algorithm for ray tracing natural scenes through height fields is presented. The algorithm employs a modified Bresenham DDA to traverse a two dimensional array of values. The objects tested for intersection are located in ( N ) time where N is the number of values in the field. This work compares the speed-up and photorealism achieved in natural scene synthesis using this method with other algorithms and discusses the implications of implementing this approach. As a final point, the simplicity and versatility of synthesizing complex natural scenes from a few parameters and data is especially attractive. Animated sequences require only the additional specifications of time modified parameters or data.

An important aspect of upcoming fifth-generation (5G) cellular communication systems is to improve the accuracy with which user equipments can be positioned. Accurately knowing the position of a user equipment is becoming increasingly important for a wide range of applications, such as automation in industry, drones, and the internet of things. Contrary to how existing techniques for outdoor cellular positioning deal with multipath propagation, in this study the aim is to use, rather than mitigate, the multipath propagation prevalent in dense urban environments. It is investigated whether it is possible to position a user equipment using only a single transmitting base station, by exploiting position-related information in multipath components inherent in the received signal. Two algorithms are developed: one classical point-estimation algorithm using a grid search to find the cost function-minimizing position, and one Bayesian filtering algorithm using a point-mass filter. Both algorithms make use of BEZT, a set of 3D propagation models developed by Ericsson Research, to predict propagation paths. A model of the signal received by a user equipment is formulated for use in the positioning algorithms. In addition to the signal model, the algorithms also require a digital map of the propagation environment. The algorithms are evaluated first on synthetic measurements, generated using BEZT, and then on real-world measurements. For both the synthetic and real-world measurement sets, the Bayesian point-mass filter outperforms the classical algorithm. It is observed how, given synthetic measurements, the algorithms yield better estimates in non-line-of-sight regions than in regions where the user equipment has line-of-sight to the transmitting base station. Unfortunately, these results do not generalize well to the real-world measurements, where, overall, neither algorithm is able to provide reliable and robust position estimates. However, as multipath-assisted positioning, to the best of our knowledge, has not been used for outdoor cellular positioning before, there are plenty of algorithm extensions, modifications, and problem aspects left to be studied - some of which are discussed in the concluding chapters.

A síntese de imagens é uma ferramenta valiosa na compreensão de diversos fenômenos da natureza. Nos últimos anos várias abordagens têm sido propostas para sintetizar tais fenômenos. A grande maioria de tais abordagens têm se centralizado no desenvolvimento de modelos procedurais. Porém, cada uma destas técnicas simula exclusivamente um fenômeno natural. Um dos métodos de síntese de imagens fotorealísticas mais proeminente é denominado de Traçado de Raios (Ray Tracing). Contudo, apesar de produzir imagens de excelente qualidade, este método é computacionalmente muito oneroso. A síntese de fenômenos naturais utilizando-se o traçado de raios é um desafio. É importante que este problema seja abordado, apesar da sua complexidade, pois a simulaçao fotorealista da natureza é muito importante para os cientistas e pesquisadores desde o surgimento dos computadores. Um algoritmo versátil e rápido para a síntese de fenômenos da natureza através do traçado de raios utilizando campos de altitude é proposto. O algoritmo utiliza uma modificação do algoritmo do Analisador Diferencial Digital de Bresenham para atravesar uma matriz bidimensional de valores de altitude. A determinação das primitivas geométricas a serem interseccionadas por um raio é obtida num tempo ( N ) , sendo N o número de altitudes no campo de altitude. Este trabalho faz uma comparação em termos de velocidade e realismo deste método com outras abordagens convencionais; e discute as implicações que a implementação deste método traz. Finalmente, destaca-se a simplicidade e versatilidade que este método proporciona devido à pequena quantidade de parâmetros necessária para a síntese de fenômenos naturais utilizando o traçado de raios. Para a criação de animações basta a especificação de novos parâmetros num intervalo de tempo diferente. / Visualization is a powerful tool for better undestanding of several natural phenomena. In recent years, several techniques have been proposed. Considerable interest in natural scene synthesis has focused on procedural models. However, these techniques produce synthetic scenes of only one natural phenomenon. Ray tracing is one of the most photorealistic methods of image syntesis. While providing images of excellent quality, ray tracing is a computationally intensive task. Natural scene synthesis is a challenging problem within the realm of ray tracing. It is important to tackle this problem, despite of its complexity, because photorealistic simulation have been important to scientific community since the appearance of computers. A fast and versatile algorithm for ray tracing natural scenes through height fields is presented. The algorithm employs a modified Bresenham DDA to traverse a two dimensional array of values. The objects tested for intersection are located in ( N ) time where N is the number of values in the field. This work compares the speed-up and photorealism achieved in natural scene synthesis using this method with other algorithms and discusses the implications of implementing this approach. As a final point, the simplicity and versatility of synthesizing complex natural scenes from a few parameters and data is especially attractive. Animated sequences require only the additional specifications of time modified parameters or data.