No description available.

Echolocation in bats is a subject that has received much attention over the last few decades. Bat echolocation calls have evolved over millions of years and can be regarded as well suited to the task of active target-detection. In analysing the time-frequency structure of bat calls, it is hoped that some insight can be gained into their capabilities and limitations. Most analysis of calls is performed using non-parametric techniques such as the short time Fourier transform. The resulting time-frequency distributions are often ambiguous, leading to further uncertainty in any subsequent analysis which depends on the time-frequency distribution. There is thus a need to develop a method which allows improved time-frequency characterisation of bat echolocation calls. The aim of this work is to develop a parametric approach for signal analysis, specifically taking into account the varied nature of bat echolocation calls in the signal model. A time-varying harmonic signal model with a polynomial chirp basis is used to track the instantaneous frequency components of the signal. The model is placed within a Bayesian context and a particle filter is used to implement the filter. Marginalisation of parameters is considered, leading to the development of a new marginalised particle filter (MPF) which is used to implement the algorithm. Efficient reversible jump moves are formulated for estimation of the unknown (and varying) number of frequency components and higher harmonics. The algorithm is applied to the analysis of synthetic signals and the performance is compared with an existing algorithm in the literature which relies on the Rao-Blackwellised particle filter (RBPF) for online state estimation and a jump Markov system for estimation of the unknown number of harmonic components. A comparison of the relative complexity of the RBPF and the MPF is presented. Additionally, it is shown that the MPF-based algorithm performs no worse than the RBPF, and in some cases, better, for the test signals considered. Comparisons are also presented from various reversible jump sampling schemes for estimation of the time-varying number of tones and harmonics. The algorithm is subsequently applied to the analysis of bat echolocation calls to establish the improvements obtained from the new algorithm. The calls considered are both amplitude and frequency modulated and are of varying durations. The calls are analysed using polynomial basis functions of different orders and the performance of these basis functions is compared. Inharmonicity, which is deviation of overtones away from integer multiples of the fundamental frequency, is examined in echolocation calls from several bat species. The results conclude with an application of the algorithm to the analysis of calls from the feeding buzz, a sequence of extremely short duration calls emitted at high pulse repetition frequency, where it is shown that reasonable time-frequency characterisation can be achieved for these calls.

Escoamentos turbulentos têm sido por muitos anos o objetivo de importantes estudos para descobrir sua dinâmica. Dentre as características mais significativas, destaca-se a multiplicidade de escalas que os caracterizam, desde as maiores estruturas (baixas freqüências) controladas pela geometria que as geram, até as menores estruturas (altas freqüências) limitadas pela viscosidade do fluido. Uma idéia importante é o conceito de vórtices que está ligado a melhorias nas técnicas de visualização, tanto em laboratório quanto em experimentos numéricos. Estes vórtices têm um importante papel em numerosas aplicações tecnológicas, sendo necessário entender a dinâmica da organização de seus movimentos para controlar mecanicamente sua produção ou supressão. Neste contexto, a análise de um misturador de ar em um escoamento em tê é o principal objetivo de estudo deste trabalho. A geometria em tê é bastante simples, mas propicia o aparecimento de um escoamento com passagem de vórtices. Testes experimentais do escoamento, com duas entradas de ar com temperaturas diferentes, foram realizados no Laboratório de Engenharia Térmica e Fluidos da Escola de Engenharia de São Carlos da Universidade de São Paulo (LETeF - EESC - USP). As medidas de temperatura foram obtidas com termopares instalados ao longo da tubulação. Com o software CFX foram realizados estudos com métodos numéricos LES e DES aplicados ao escoamento. Estes resultados computacionais foram comparados com os dados experimentais, através da análise tempo-freqüência. Estudos preliminares do escoamento mostram regiões com passagem de vórtices, e a habilidade da técnica de análise tempo-freqüência em caracterizar a existência e a forma destas estruturas turbulentas. / Turbulent flows have been the objective of important studies to discover its dynamics. One important characteristic of these flows is the multiplicity of scales, since the large structures (low frequencies) controlled by the geometry that generates them, until the small structures (high frequencies) limited by the fluid viscosity. An important idea is the concept of vortices that it is associated with the improvements in the visualization techniques, in laboratory or numerical experiments. These vortices have an important function in many technological applications. In each one of these fields, it is necessary to understand the dynamics of its movements to control the mechanisms for producing or suppressing these vortices. In this context, the analysis of an air mixing in a tee junction is the main objective of this work. The tee geometry is sufficiently simple, but contributes for the appearance of a flow with vortices transition. Experimental tests with two different air temperatures inlets were done at the Thermal and Fluid Engineering Laboratory of the University of São Paulo at São Carlos (LETeF - EESC - USP). The measures of temperature were acquired with thermocouples installed along the pipe. Numerical studies with LES and DES methods using CFX software were applied to the flow. These computational results were compared with the experimental data through the time-frequency analysis. Preliminary studies of the flow show vortices transition regions and the ability of time-frequency technique in describing the existence and shape of turbulent structures.

Escoamentos turbulentos têm sido por muitos anos o objetivo de importantes estudos para descobrir sua dinâmica. Dentre as características mais significativas, destaca-se a multiplicidade de escalas que os caracterizam, desde as maiores estruturas (baixas freqüências) controladas pela geometria que as geram, até as menores estruturas (altas freqüências) limitadas pela viscosidade do fluido. Uma idéia importante é o conceito de vórtices que está ligado a melhorias nas técnicas de visualização, tanto em laboratório quanto em experimentos numéricos. Estes vórtices têm um importante papel em numerosas aplicações tecnológicas, sendo necessário entender a dinâmica da organização de seus movimentos para controlar mecanicamente sua produção ou supressão. Neste contexto, a análise de um misturador de ar em um escoamento em tê é o principal objetivo de estudo deste trabalho. A geometria em tê é bastante simples, mas propicia o aparecimento de um escoamento com passagem de vórtices. Testes experimentais do escoamento, com duas entradas de ar com temperaturas diferentes, foram realizados no Laboratório de Engenharia Térmica e Fluidos da Escola de Engenharia de São Carlos da Universidade de São Paulo (LETeF - EESC - USP). As medidas de temperatura foram obtidas com termopares instalados ao longo da tubulação. Com o software CFX foram realizados estudos com métodos numéricos LES e DES aplicados ao escoamento. Estes resultados computacionais foram comparados com os dados experimentais, através da análise tempo-freqüência. Estudos preliminares do escoamento mostram regiões com passagem de vórtices, e a habilidade da técnica de análise tempo-freqüência em caracterizar a existência e a forma destas estruturas turbulentas. / Turbulent flows have been the objective of important studies to discover its dynamics. One important characteristic of these flows is the multiplicity of scales, since the large structures (low frequencies) controlled by the geometry that generates them, until the small structures (high frequencies) limited by the fluid viscosity. An important idea is the concept of vortices that it is associated with the improvements in the visualization techniques, in laboratory or numerical experiments. These vortices have an important function in many technological applications. In each one of these fields, it is necessary to understand the dynamics of its movements to control the mechanisms for producing or suppressing these vortices. In this context, the analysis of an air mixing in a tee junction is the main objective of this work. The tee geometry is sufficiently simple, but contributes for the appearance of a flow with vortices transition. Experimental tests with two different air temperatures inlets were done at the Thermal and Fluid Engineering Laboratory of the University of São Paulo at São Carlos (LETeF - EESC - USP). The measures of temperature were acquired with thermocouples installed along the pipe. Numerical studies with LES and DES methods using CFX software were applied to the flow. These computational results were compared with the experimental data through the time-frequency analysis. Preliminary studies of the flow show vortices transition regions and the ability of time-frequency technique in describing the existence and shape of turbulent structures.

In this thesis we study the short-time Fourier transform. The short-time Fourier transform of a function f(x) is obtained by restricting our function to a short time segment and take the Fourier transform of this restriction. This method gives information locally of f in both time and frequency simultaneously.To get a smooth frequency localization one wants to use a smooth window, whichmeans that the windows will overlap. The continuous short-time Fourier transform is not appropriate for practical purpose, therefore we want a discrete representation of f. Using Gabor theory, we can write a function f as a linear combination of time- and frequency shifts of a fixed window function g with integer parameters a; b > 0. We show that if the window function g has compact support, then g generates a Gabor frame G(g; a; b). We also show that for such a g there exists a dual frame such that both G(g; a; b) and its dual frame has compact support and decay fast in the Fourier domain. Based on [2], we show that B-splines generates a pair of Gabor frames.

In this dissertation, multicarrier schemes are reviewed within the framework of Gabor Systems. Their fundamental elements; what to transmit, i.e., symbols, how to transmit, i.e., filters or pulse shape, and where/when to transmit, i.e., lattices are investigated extensively. The relations between different types of multicarrier schemes are discussed. Within the framework of Gabor systems, a new windowing approach, edge windowing, is developed to address the out-of-band (OOB) radiation problem of orthogonal frequency division multiplexing (OFDM) based multicarrier schemes. To the best of our knowledge, for the first time, the diversity on the range of the users is exploited to suppress the sidelobes of OFDM. In addition to that, the concept of using different filters in OFDM structure is proposed. Besides the improvement on the OOB radiation performance of OFDM via edge windowing, conventional lattice structure of OFDM frame is enhanced considering the diversity in the network. The lattice structure of an OFDM frame is designed based on the statistical characteristics of the range of the users and the mobility. The concept of channel-aware frame structure is developed, which allows more efficient and reliable transmission. In addition to the aforementioned improvements on OFDM, interference issues in uncoordinated networks are addressed in this dissertation considering different multicarrier schemes. It is stressed that the interference from other links in the network sharing the same spectrum might degrade the link performance between the devices in an uncoordinated network, significantly. Considering the degradation due to other-user interference, the concept of partially overlapping tones (POT) is proposed. With the concept of partially overlapping tones, the interference energy observed at the victim receiver is mitigated via an intentional frequency offset between the links. The usefulness of intentional frequency offset to combat with the asynchronous nature of other-user interference without any timing constraint between interfering signals is emphasized. To the best of our knowledge, for the first time, the efficacy of non-orthogonal schemes are shown along with POT to address the other-user interference, which relies on the fact that self-interference problem is easier than other-user interference problem in an uncoordinated network. In the last part of this dissertation, required number of equalizer taps for multicarrier schemes is investigated to address the potential self-interference problems (e.g. due to the non-orthogonal multicarrier schemes with the concept of POT). Composite impact of transmit pulse shape, communication medium, and receive filter on the characteristics of the interference among the symbols in time and frequency is analyzed. It is emphasized that while taking less number of taps into account for the channel estimation causes lack of description of the composite effect, using more number of taps folds the noise into the estimated channel. The number of interfering symbols and their locations are obtained in both time and frequency for a given multicarrier scheme and signal-to-noise ratio. It is shown that correct number of taps yields not only improvement on BER performance but also less complex equalizer structures in practice.

No description available.

In our daily lives, we often make decisions that require the use of self-control, weighing trade-offs between various attributes: for example, selecting a food based on its health rather than its taste. Previous research suggests that re-weighting attributes may rely on selective attention, associated with decreased neural oscillations over posterior brain regions in the alpha (8-12 Hz) frequency range. Here, we utilized the high temporal resolution and whole-brain coverage of electroencephalography (EEG) to test this hypothesis in data collected from hungry human subjects exercising dietary self-control. Prior analysis of this data has found time-locked neural activity associated with each food’s perceived taste and health properties from approximately 400 to 650 ms after stimulus onset (Harris et al., 2013). We conducted time-frequency analyses to examine the role of alpha-band oscillations in this attribute weighting. Specifically, we predicted that there would be decreased alpha power in posterior electrodes beginning approximately 400 ms after stimulus onset for the presentation of healthy food relative to unhealthy food, reflecting shifts in selective attention. Consistent with this hypothesis, we found a significant decrease in alpha power for presentations of healthy relative to unhealthy foods. As predicted, this effect was most pronounced at posterior occipital and parietal electrodes and was significant from approximately 450 to 700 ms post-stimulus onset. Additionally, we found significant alpha-band decreases in right temporal electrodes during these times. These results extend previous attention research to multi-attribute choice, suggesting that the re-weighting of attributes can be measured neuro-computationally.

Este trabalho trata de conceitos relacionados à qualidade da Energia Elétrica (EE) e, neste contexto, apresenta a proposta de técnicas para a compressão da representação de transitórios rápidos e da análise tempo-frequência de distúrbios elétricos em geral. A qualidade da Energia Elétrica é medida pelo coeficiente de desvios que os sinais de tensão e corrente apresentam em relação ao sinal senoidal ideal. Tais desvios são denominados de distúrbios, podendo ser classificados como quase estacionários (e.g. distorção de harmônicas) e eventos (e.g. transitórios rápidos). No contexto de EE, os transitórios rápidos possuem pequena duração (i.e. na ordem dos microssegundos), são detectados por altas taxas de amostragem (i.e. na ordem dos MHz) e possuem difícil parametrização. Portanto, as representações das formas de onda geralmente são armazenadas para auxiliar a avaliação subjetiva dos transitórios e dos parâmetros de interesse. Consequentemente, a compressão destas formas de onda torna-se de extrema importância para armazenar dados adquiridos por longos períodos de tempo, e estes modos de compressão são tratados nesta dissertação. Em virtude das altas taxas de amostragem utilizadas, uma técnica baseada em Análise de Componentes Principais (PCA – Principal Component Analysis) é proposta para esta representação mais compacta de transitórios. Resultados mostram que o desempenho em compressão versus qualidade de reconstrução é semelhante ao de trabalhos relacionados com a vantagem de atender aos requisitos de altas taxas de amostragem. A análise tempo-frequência é um mecanismo que auxilia na classificação e caracterização dos distúrbios elétricos. Neste trabalho, a Transformada de Hilbert-Huang é estudada e uma proposta de melhoria na Decomposição Empírica de Modos (EMD – Empirical Mode Decomposition) é apresentada. Nossos resultados mostram que a técnica proposta economiza o custo computacional se comparada com o estado da arte. Em virtude disso, a técnica proposta apresenta uma taxa de redução no tempo médio de execução de 99,76 % em relação à técnica do estado da arte. Além disso, uma verificação acerca do desempenho em eficiência de compressão versus qualidade de reconstrução de trabalhos anteriores é também desenvolvida nesta dissertação. Foi utilizada uma sistemática de avaliação experimental com base em amostras de sinais AC, de forma a avaliar as taxas de compressão atingidas pelas técnicas estudadas, como a Transformada Wavelet Discreta. Resultados mostram que a Transformada Wavelet falha para compressão de todo e qualquer tipo de distúrbio elétrico quando analisado o compromisso entre acuidade de reconstrução versus eficiência de compressão. / This work deals with concepts related to the AC Power Quality theoretical framework and, in this scope, proposes techniques for the representation of fast transient data compression and for the power line disturbances time-frequency analysis. The AC power quality is measured by the differences between actual and ideal sinusoidal voltage/current signals. These differences are known as electrical disturbances, which can be classified as quasi-stationary (e.g. harmonic distortion) or events (e.g. surge or fast transients) disturbances. In the AC Power Quality scope, the fast transients have short duration (i.e. typically on the order of microseconds), are detected by high sampling rates (i.e. typically on the order of MHz), and are hard to characterize and parameterize. Hence, the resultant representation of the waveforms is in general stored to help in the subjective evaluation of these fast transients and their parameters of interest. As a consequence the compression turns out to be of main concern, in order to store this information acquired over long periods of time (like weeks or months). In this work, a compression technique is proposed taking into account the high sampling rates. The proposed technique makes use of the Principal Component Analysis (PCA) for such compact representation of fast transients. The Compression efficiency versus reconstruction accuracy results show a similar performance for the proposed technique when compared to the related works. On the other hand, the proposed technique can handle the large amount of data provided by the high sampling rates. The time-frequency analysis helps in the classification and characterization of AC power quality disturbances. In this work, the Hilbert-Huang Transform is studied and a modification is proposed in order to improve the Empirical Mode Decomposition (EMD) performance. Our results show that the proposed modification can save computational cost when compared to the state-of-the-art. Therefore, the average execution time is reduced to 99.76 % in comparison with the state-of-the-art technique. Besides that, this work also revisits previous techniques based on the Discrete Wavelet Transform (DWT) in order to verify the trade-off between reconstruction accuracy versus compression efficiency under a more systematic experimental evaluation setup, considering samples of real AC signals. Results show that DWT fails as a general-purpose technique in AC Power Quality scope.

Este trabalho trata de conceitos relacionados à qualidade da Energia Elétrica (EE) e, neste contexto, apresenta a proposta de técnicas para a compressão da representação de transitórios rápidos e da análise tempo-frequência de distúrbios elétricos em geral. A qualidade da Energia Elétrica é medida pelo coeficiente de desvios que os sinais de tensão e corrente apresentam em relação ao sinal senoidal ideal. Tais desvios são denominados de distúrbios, podendo ser classificados como quase estacionários (e.g. distorção de harmônicas) e eventos (e.g. transitórios rápidos). No contexto de EE, os transitórios rápidos possuem pequena duração (i.e. na ordem dos microssegundos), são detectados por altas taxas de amostragem (i.e. na ordem dos MHz) e possuem difícil parametrização. Portanto, as representações das formas de onda geralmente são armazenadas para auxiliar a avaliação subjetiva dos transitórios e dos parâmetros de interesse. Consequentemente, a compressão destas formas de onda torna-se de extrema importância para armazenar dados adquiridos por longos períodos de tempo, e estes modos de compressão são tratados nesta dissertação. Em virtude das altas taxas de amostragem utilizadas, uma técnica baseada em Análise de Componentes Principais (PCA – Principal Component Analysis) é proposta para esta representação mais compacta de transitórios. Resultados mostram que o desempenho em compressão versus qualidade de reconstrução é semelhante ao de trabalhos relacionados com a vantagem de atender aos requisitos de altas taxas de amostragem. A análise tempo-frequência é um mecanismo que auxilia na classificação e caracterização dos distúrbios elétricos. Neste trabalho, a Transformada de Hilbert-Huang é estudada e uma proposta de melhoria na Decomposição Empírica de Modos (EMD – Empirical Mode Decomposition) é apresentada. Nossos resultados mostram que a técnica proposta economiza o custo computacional se comparada com o estado da arte. Em virtude disso, a técnica proposta apresenta uma taxa de redução no tempo médio de execução de 99,76 % em relação à técnica do estado da arte. Além disso, uma verificação acerca do desempenho em eficiência de compressão versus qualidade de reconstrução de trabalhos anteriores é também desenvolvida nesta dissertação. Foi utilizada uma sistemática de avaliação experimental com base em amostras de sinais AC, de forma a avaliar as taxas de compressão atingidas pelas técnicas estudadas, como a Transformada Wavelet Discreta. Resultados mostram que a Transformada Wavelet falha para compressão de todo e qualquer tipo de distúrbio elétrico quando analisado o compromisso entre acuidade de reconstrução versus eficiência de compressão. / This work deals with concepts related to the AC Power Quality theoretical framework and, in this scope, proposes techniques for the representation of fast transient data compression and for the power line disturbances time-frequency analysis. The AC power quality is measured by the differences between actual and ideal sinusoidal voltage/current signals. These differences are known as electrical disturbances, which can be classified as quasi-stationary (e.g. harmonic distortion) or events (e.g. surge or fast transients) disturbances. In the AC Power Quality scope, the fast transients have short duration (i.e. typically on the order of microseconds), are detected by high sampling rates (i.e. typically on the order of MHz), and are hard to characterize and parameterize. Hence, the resultant representation of the waveforms is in general stored to help in the subjective evaluation of these fast transients and their parameters of interest. As a consequence the compression turns out to be of main concern, in order to store this information acquired over long periods of time (like weeks or months). In this work, a compression technique is proposed taking into account the high sampling rates. The proposed technique makes use of the Principal Component Analysis (PCA) for such compact representation of fast transients. The Compression efficiency versus reconstruction accuracy results show a similar performance for the proposed technique when compared to the related works. On the other hand, the proposed technique can handle the large amount of data provided by the high sampling rates. The time-frequency analysis helps in the classification and characterization of AC power quality disturbances. In this work, the Hilbert-Huang Transform is studied and a modification is proposed in order to improve the Empirical Mode Decomposition (EMD) performance. Our results show that the proposed modification can save computational cost when compared to the state-of-the-art. Therefore, the average execution time is reduced to 99.76 % in comparison with the state-of-the-art technique. Besides that, this work also revisits previous techniques based on the Discrete Wavelet Transform (DWT) in order to verify the trade-off between reconstruction accuracy versus compression efficiency under a more systematic experimental evaluation setup, considering samples of real AC signals. Results show that DWT fails as a general-purpose technique in AC Power Quality scope.