O presente trabalho aborda uma análise das deformações residuais que ocorrem em painéis estruturais soldados compostos de chapas de aço com espessura de até 10 mm. Baseando-se em resultados experimentais, obtidos através da realização sistemática de ensaios de soldagem em corposde prova, o autor utiliza-se da análise dimensional para tentar encontrar o melhor correlacionamento entre as variáveis envolvidas no processo. Em seguida, utilizando-se dos recursos da análise de regressão, tenta-se obter algorítimos que facilitem a tarefa de prever as deformações nos referidos painéis. / This study deals with an analysis of residual distortion on welded structural panels with plate thickness up to 10 mm. From a systematic set of experiments conducted for welded test panels, tentative correlations were done in order to relate the major variables involved in the welding process by means of dimensional analysis. Futhermore, by utilizing regression analysis, appropriate equations were developed so that they could be used in the prediction of the residual distortion of the above mentioned panels.

Two kinds of low distortion switching power amplifiers are presented in this thesis. In the first power amplifier, we use feedback and low voltage low power circuits to improve the distortion and power efficiency. In the second power amplifier, we use ring oscillator and Noise shaping to construct the circuit and filters are added in the feedback loop to reduce the quantization noise. HSPICE simulations and experimental results verify the proposed circuits. Experimental results show that the THDs of both circuits are all lower than 0.27% at 1.5V supply voltage. This result shows that the proposed power amplifiers have superior performance in THD, and these circuits are applicable to low-distortion, high-efficiency, and low-voltage applications, such as the hearing instruments.

Rapid Distortion Theory is used to perform calculations of unsteadily-forced initially isotropic turbulence so that the physics of such flows can be better understood. The results of these calculations show that there are three distinct regimes of physical behavior for the kind of turbulence that we are considering: (1) turbulence that is forced at a relatively low frequency in which the kinetic energy settles down to a constant value at later times, (2) turbulence that is forced at a slightly higher frequency in which the kinetic energy value oscillates for a time, but then increases dramatically, and (3) turbulence that is forced at a relatively high frequency in which the kinetic energy evolution exhibits a periodic behavior. To better understand the role of the rapid pressure-strain correlation, these results are also compared to Inertial Model results for the same set of forcing frequencies. The results of this comparison show that the rapid pressure plays a key role in determining the stability characteristics of unsteadily-forced turbulence. The evolution equation for kinetic energy is then used to propose a model that describes the behavior approximately in terms of a time lag between applied mean strain and the Reynolds stress. This model suggests that the different responses under the different frequencies of forcing correspond to different stress-strain time lags. Overall, then the results indicate that rapid pressure serves to create a time lag between applied stress and strain, and it is the extent of this time lag that causes turbulence to respond differently under various frequencies of forcing.

Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2004. / Xiaoming Huo, Committee Member ; J. Stevenson Kenney, Committee Member ; Douglas Williams, Committee Member ; Erik Verriest, Committee Member ; G. Tong Zhou, Committee Chair. Vita. Includes bibliographical references (leaves 170-179).

The use of Community Antenna Television Network (CATV) cable systems are a very common way that subscribers use to access the internet and download data. The transmitters that send the signals to subscribers must conform to a very stringent specification known as DOCSIS. Using traditional high frequency design techniques to meet this specification often lead to a lengthy and difficult production process where several calibrations have to be made. In order to send a digitally modulated signal that conforms to the DOCSIS specification some sort of conversion between the discrete digital domain and the analog domain must occur. To accomplish this a Digital to Analog converter is used. In recent years, the clocking or sampling frequency that can be used for Digital to Analog converters (DACs) has been rapidly increasing. The clocking frequency is directly proportional to the bandwidth that can be transmitted. DAC's that have exceptionally high clocking frequencies can be referred to as Radio Frequency DAC's. The clocking frequency of these devices has now progressed to the point where direct digital synthesis can be used for a DOCSIS transmitter without any analog frequency conversion stages. Since Radio Frequency DAC's are real devices the output is not a perfect representation of the discrete signal that is sent to it. Unwanted distortion is added that can be measured at the analog output. Removal of this distortion or at least significantly reducing it could be the difference meeting or or not meeting the DOCSIS specification. This thesis will explore the usage of these devices in this application. The basic structure of DAC's as well as the distortion signals themselves will be investigated in order to develop a method where the distortion can be removed. Ideally this can be done in a way that is suitable to be integrated into a transmitter architecture and meet the specification. The frequency response of the major distortion products across the DOCSIS band is measured. Once this is done a way to match these frequency responses is needed so a cancellation signal can be created that removes the distortion. A method is developed that uses an iterative algorithm to find filter coefficients whose frequency response matches that of the distortion signals as closely as possible. Since these cancellation signals are added to the discrete signal to be transmitted before the interface with the Radio Frequency DAC the process is known as pre-distortion. The generated coefficients are used in digital filters as part of a pre-distortion design. Tests are performed with discrete signals that are close approximates to a DOCSIS signal that would be sent to a subscriber. Measured results show a decrease in the power of targeted distortion signals. The reduction of the distortion level is enough that the DOCSIS specification is met for all test signals.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 155-157). Also available via the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 140-147). Available also in a digital version from Dissertation Abstracts.

O presente trabalho aborda uma análise das deformações residuais que ocorrem em painéis estruturais soldados compostos de chapas de aço com espessura de até 10 mm. Baseando-se em resultados experimentais, obtidos através da realização sistemática de ensaios de soldagem em corposde prova, o autor utiliza-se da análise dimensional para tentar encontrar o melhor correlacionamento entre as variáveis envolvidas no processo. Em seguida, utilizando-se dos recursos da análise de regressão, tenta-se obter algorítimos que facilitem a tarefa de prever as deformações nos referidos painéis. / This study deals with an analysis of residual distortion on welded structural panels with plate thickness up to 10 mm. From a systematic set of experiments conducted for welded test panels, tentative correlations were done in order to relate the major variables involved in the welding process by means of dimensional analysis. Futhermore, by utilizing regression analysis, appropriate equations were developed so that they could be used in the prediction of the residual distortion of the above mentioned panels.

Ces dernières décennies ont vu émerger de nombreuses applications utilisant la technologie 3D, telles que les écrans auto-stéréoscopiques, les écrans de télévisions 3D ou encore la visio-conférence stéréoscopique. Ces applications requièrent des techniques adaptées afin que leur flux de données soit compressé efficacement. En particulier, dans le cas des images stéréoscopiques, ces dernières étant composées de deux vues de la même scène, elles nécessitent à ce titre deux fois plus d’informations à transmettre ou à stocker que dans le cas des images 2D traditionnelles. Nos travaux se situent dans le cadre de la compression des images stéréoscopiques. Plus précisément, ils concernent l’amélioration de l’estimation de la carte de disparité dans le but d’obtenir un meilleur compromis entre le débit binaire nécessaire au codage de la carte de disparité et la qualité de l’image prédite.Généralement, la carte de disparité est estimée en minimisant la distorsion de l’image prédite. Cette minimisation peut être sujette à une contrainte de lissage. L’idée étant qu’une carte de disparité plus lisse nécessitera un débit binaire moindre en supposant que les mêmes vecteurs de disparités seront sélectionnés plus souvent. Néanmoins cette contrainte de lissage ne permet pas toujours de diminuer le coût binaire de la carte. Le lissage peut entraîner par ailleurs une augmentation notable de la distorsion de l’image prédite. Dans le premier chapitre de la thèse, nous présentons un algorithme d’estimation de carte de disparité minimisant une métrique conjointe entropie-distorsion. Le coût binaire finale de la carte de disparité est estimée à chaque étape de l’algorithme et est intégré dans le calcul de la métrique. La distorsion globale de la carte de disparité est aussi mise à jour au fur et à mesure du traitement de l’image. Par ailleurs, cette algorithme repose sur la construction séquentiel d’un arbre dont on ne garde qu’un nombre défini de branches à chaque profondeur de l’arbre. Ainsi, l’algorithme développé apporte une solution sous-optimale en minimisant le coût binaire de la carte de disparité tout en assurant une bonne qualité de l’image prédite. Le chapitre deux étend l’algorithme précédent au cas des images non rectifiées. Dans le troisième chapitre, nous nous intéressons au fait de trouver une solution au problème d’optimisation du compromis débit-distorsion en réduisant la complexité numérique par rapport à l’algorithme précédent. De ce fait, nous avons développé le R-algorithme qui se base sur une solution initiale de Référence (celle minimisant la distorsion de l’image prédite) et la modifie successivement tant qu’une amélioration est constatée en termes de compromis débit-distorsion. Le quatrième chapitre s’intéresse toujours au fait d’accroître les performances de l’algorithme développé tout en réduisant le coût en complexité numérique et donc en temps de traitement. Nous proposons deux approches afin de tirer profit d’un grand espace de recherche sans avoir à tester pour chaque bloc à apparier l’ensemble des disparités qui composent cet espace de recherche. En effet, un espace de recherche plus grand permet plus de choix de disparités et donc potentiellement une meilleur reconstruction de l’image prédite. En contrepartie, il se peut que le coût binaire de la carte de disparité augmente si l’ensemble des disparités sélectionnées constituent un ensemble plus divers qu’auparavant. Les deux approches proposées permettent de restreindre l’espace de recherche à un ensemble composées de certaines disparités permettant de minimiser la distorsion de l’image prédite pour un débit donné. Le dernier chapitre de la thèse s’intéresse à l’utilisation des blocs de taille variable pour la compression des images stéréoscopiques. / During the last decades, a wide range of applications using stereoscopic technology has emerged still offering an increased immersion to the users such as video games with autostereoscopic displays, 3D-TV or stereovisio-conferencing. The raise of these applications requires fast processing and efficient compression techniques. In particular, stereoscopic images require twice the amount of information needed to transmit or store them in comparison with 2D images as they are composed of two views of the same scene. The contributions of our work are in the field of stereoscopic image compression and more precisely, we get interested in the improvement of the disparity map estimation. Generally, disparities are selected by minimizing a distortion metric which is sometimes subjected to a smoothness constraint, assuming that a smooth disparity map needs a smaller bitrate to be encoded. But a smoother disparity map does not always reduce significantly the bitrate needed to encode it but can increase the distortion of the predicted view. Therefore, the first algorithm we have proposed minimizes a joint entropy-distortion metric to select the disparities. At each step of the algorithm, the bitrate of the final disparity map is estimated and included in the metric to minimize. Moreover, this algorithm relies on a tree where a fixed number of paths are extended at each depth of the tree, ensuring good rate-distortion performance. In the second part of the work, we have proposed a sub-optimal solution with a smaller computational complexity by considering an initial solution -the one minimizing the distortion of the predicted view- which is successively modified as long as an improvement is observed in terms of rate-distortion. Then, we have studied how to take advantages of large search areas in which the disparities are selected as one can easily supposed that enlarging the search area will increase the distortion performance as there will be more choices of disparities. In the other hand, the larger is the range of the selected disparities, the higher is supposed to be the cost of the disparity map in terms of bitrate. We have proposed two approaches allowing to take advantage of a large search area by selecting only sets of disparities belonging to it enabling to achieve a given bitrate while minimizing the distortion of the predicted image. The last part of the work concerns variable block sizes which undeniably allows to improve the bitrate-distortion performance as the block size suits to the image features. We have thus proposed a novel algorithm which jointly estimates and optimizes the disparity and the block length maps.

Auditory nerve fiber models provide further insight into the inner workings of the ear and brain. These models have helped us to develop physiologically based speech intelligibility metrics, to assess the difficulty of understanding speech objectively. Several metrics have been developed, but they have been developed using a range of auditory nerve (AN) fiber models. A full comparison of different metrics on even footing should be performed to evaluate the accuracy of their predictions. Speech intelligibility is understood to be dependant on both temporal fine structure and envelope cues in the acoustic speech signal, which are however linked in a way where they are very difficult to split. This makes the evaluation of speech intelligibility metrics tricky, as metrics often aim to analyze mean rate and fine timing information in the auditory nerve representation of the acoustic cues. In this study, a method of phase distortion was developed, with the goal of degrading the fine timing information of a speech signal to the point where only the mean rate representation in the AN is contributing to the speech intelligibility. Also, the neural cross correlation coefficients developed in Heinz & Swaminathan (2009) were adapted from the Zilany & Bruce (2007) auditory nerve model to the Bruce, Erfani & Zilany (2018) AN model. / Thesis / Master of Applied Science (MASc)