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.

[pt] Estudam-se as formas de resolução do campo-livre e obtenção das funções de transferência adotadas pelo programa SASSI2000 na análise de problemas de interação solo-estrutura, no domínio da freqüência, no caso de uma excitação sísmica. Propõem-se composições do campo-livre no que tange à natureza e ângulo de incidência das ondas que o compõem. Para tal, avalia-se o comportamento de um sistema simples, constituído por uma estrutura superficial com cinco graus de liberdade, apoiada em um terreno estratificado sobre um semiespaço em rocha. Analisa-se a influência, na resposta do sistema, da variação dos seguintes parâmetros definidores do campo-livre: natureza e ângulo de incidência das ondas, propriedades topográficas e constitutivas do terreno, direção do movimento de controle e posição relativa do ponto de controle ao nó de interação. Cria-se um banco de dados em funções de transferência. Com relação à obtenção dessas funções, faz-se a análise de um sistema similar, para o qual são fornecidos diferentes conjuntos de freqüências de análise e, examinando-se as soluções encontradas, propõe-se um roteiro para definição das freqüências de análise utilizando exclusivamente o programa em questão, comprovando sua eficiência em estruturas reais das usinas nucleares de Angra 3 e Angra 1. / [en] One examines a series of SASSI2000 runs to develop sensibility regarding the behavior of the program general solution in order to propose adequate analyst aptitudes in the choice of the analysis frequencies, as well as in the free-field wave composition and body wave incident angle selection. The control motion point localization and control motion direction options are also considered. A five degree of freedom superficial structure model is used founded over a horizontally layered site overlaying a rock halfspace. The study is made on a large set of acceleration transfer functions to the only one interaction node obtained by the variation of the above mentioned parameters. Recommendations are proposed to clarify and to extend the user manual chapters on the determination of the analysis frequencies and on the free-field wave composition. The efficiency of this proposal is checked on a group of examples on nuclear power plant structural models.

<p>The importance of control systems and diagnostics in vehicles are increasing and has resulted in several new methods to calculate better control signals. The performance can be increased by calculating these signals close to optimum, but that also require more and precise information regarding the system.</p><p>One of the wanted control signals are the crankshaft torque and the thesis presents two different methods to estimate this torque using engine speed variations. These methods are Modeling of the Crankshaft and Frequency Analysis. The methods are evaluated and implemented on for a four cylinder SAAB engine. Measurements are made in an engine test cell as well as a vehicle.</p><p>The results show that the Modeling of the Crankshaft method does not produce a satisfying estimation, with a difference of about 200% between estimated and calculated torque. On the other hand, the Frequency Analysis provides an accurate estimation of both mean and instantaneous indicated torque, with a maximum difference of ±20% between estimated and calculated torque.</p>

Tracking and quantifying hydrologic change in urbanizing watersheds is a complex problem which can vary spatially and temporally throughout the effective catchment area as change occurs. Hydromodification due to urbanization usually results in a larger peak event stream discharge, a change in typical event volume, a reduced lag time between rainfall and stream discharge events, and a more complex falling hydrograph. Recently extracted Environment Canada data have allowed the creation of a high resolution instantaneous stream flow dataset dating to the late 1960s for many Ontario gauge stations. Hydrometric data were obtained for fifteen urban and semi-urban catchments within Southern Ontario ranging in size from ~50km² to 300 km² with urbanized land use assemblages varying from <5% to 80%. Utilizing automated methods, each individual runoff event from the hydrographic record was identified and characterized. Temporal changes to urban land area, land use, and road length were quantified for each watershed from aerial photography spanning the period of record at approximately 8 year intervals allowing identified trends in event hydrograph parameters to be correlated quantitatively with the alteration of the catchment over time. <br> Increasing trends in event peak discharge were identified in all but one study catchment. Event volume was found to be consistently increasing in most of the urban watershed, while trends in event duration were observed but with no clear increasing or decreasing trend. The lack of consistent trends in the timing and distribution of flow during runoff events suggest that build-out, drainage network design, and stormwater management systems play differing roles in the neighbouring urban catchments. Changes to flood recurrence intervals through the period of urbanization were also investigated; peak magnitude of high frequency events is affected to a greater extent than low frequency or flood events. The relative change in return frequency distribution is not consistent between catchments, also the degree of alteration can differ between various recurrence intervals at a gauge. Peak discharge of some return periods appeared to decrease with urban development suggesting that the increased detention brought with urban stormwater management systems have effectively offset the increased runoff due to additional impervious area and improved drainage efficiency. A consistent relationship defining the change in geomorphically significant return periods (i.e. channel forming flow) with urbanization was identified in neighbouring urban catchments.

Dans cette thèse, nous présentons des méthodes asymptotiques <br />mathématiquement justifiées permettant de connaître les champs <br />électromagnétiques dans des milieux à couches minces hétérogènes. <br />La motivation de ce travail est le calcul du champ électrique dans des <br />cellules biologiques composées d'un cytoplasme conducteur entouré <br />d'une fine membrane très isolante. <br />Nous remplaçons la membrane, lorsque son épaisseur est infiniment <br />petite, par des conditions de transmission ou des conditions aux <br />limites appropriées et nous estimons l'erreur commise par ces <br />approximations.<br /> Pour les basses fréquences, nous considérons l'équation quasistatique<br />donnant le potentiel dont dérive le champ. A l'aide d'un <br />calcul en géométrie circulaire nous obtenons les expressions explicites<br /> du potentiel et nous en déduisons les asymptotiques du champ <br />électrique, en fonction de l'épaisseur de la couche mince, avec des <br />estimations de l'erreur. Nous estimons ensuite la différence entre le <br />champ réel et le champ statique. Puis nous généralisons notre <br />développement asymptotique à une géométrie quelconque. <br /> La deuxième partie de cette thèse traite des moyennes fréquences : <br />nous donnons le développement asymptotique de la solution de <br />l'équation de Helmholtz lorsque l'épaisseur de la membrane tend vers <br />0. Tous ces précédents résultats sont illustrés par des calculs par <br />éléments finis.<br /> Enfin, pour les hautes fréquences, nous construisons une condition <br />d'impédance pseudodifférentielle permettant de concentrer l'effet de <br />la couche sur son bord intérieur. Nous concluons cette thèse par un <br />problème de diffraction à haute fréquence d'une onde incidente par <br />un disque de petite taille. A l'aide d'une analyse pseudodifférentielle, <br />nous bornons la norme de la trace du champ diffracté à distance fixe <br />de l'inhomogénéité en fonction de la taille de l'objet et de l'onde <br />incidente.

Wetlands are nominally characterized by, vegetation, presence of saturated soils and/or period and depth of standing water (inundation). Wetland hydroperiod, traditionally defined by the period or duration of inundation, is considered to control the ecological function and resultant plant community. This study seeks to redefine "hydroperiod" to incorporate both surface and subsurface water-level fluctuations, to identify predominant hydroperiod of different wetland types, and to find the range of the water-level fluctuations during the predominant hydroperiod durations. The motivation being that wetland ecological condition is controlled not just by the period of inundation but also by the proximity and depth to water-table and period of water-level fluctuation. To accomplish this, a frequency distribution analysis of water-table and stage levels in wetlands is performed. The conclusions of this study suggest a need to rethink current definitions and methodologies in determining hydroperiod. Redefining wetland hydroperiod taking into consideration depth to water-table, namely water-level periods and depths below ground surface, may also aid in the understanding of how fluctuations in water-levels in a wetland affect plant ecology.

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.

Hydraulic geometry relationships and regional curves are used in natural channel design to assist engineers, biologists, and fluvial geomorphologists in the efforts undertaken to ameliorate previous activities that have diminished, impaired or destroyed the structure and function of stream systems. Bankfull channel characteristics were assessed for 14 United States Geological Survey (USGS) gaged sites in the Inner Bluegrass and 15 USGS gaged sites in the Outer Bluegrass Regions of Kentucky. Hydraulic geometry relationships and regional curves were developed for the aforementioned regions. Analysis of the regression relationships showed that bankfull discharge is a good explanatory variable for bankfull parameters such as area, width and depth. The hydraulic geometry relationships developed produced high R2 values up to 0.95. The relationships were also compared to other studies and show strong relationships to both theoretical and empirical data. Regional curves, relating drainage area to bankfull parameters, were developed and show that drainage area is a good explanatory variable for bankfull parameters. R2 values for the regional curves were as high as 0.98.