Дисертації з теми "Ordered Transmissions"

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.
Includes bibliographical references (p. 114-116).
by Douglas S. Brungart.
M.S.

Given an algebra of pseudo-differential operators on a manifold, an elliptic element is said to be a reduction of orders, if it induces isomorphisms of Sobolev spaces with a corresponding shift of smoothness. Reductions of orders on a manifold with boundary refer to boundary value problems. We consider smooth symbols and ellipticity without additional boundary conditions which is the relevant case on a manifold with boundary. Starting from a class of symbols that has been investigated before for integer orders in boundary value problems with the transmission property we study operators of arbitrary real orders that play a similar role for operators without the transmission property. Moreover, we show that order reducing symbols have the Volterra property and are parabolic of anisotropy 1; analogous relations are formulated for arbitrary anisotropies. We finally investigate parameter-dependent operators, apply a kernel cut-off construction with respect to the parameter and show that corresponding holomorphic operator-valued Mellin symbols reduce orders in weighted Sobolev spaces on a cone with boundary.

Although the neural mechanisms responsible for the orderly recruitment of motor units have been investigated extensively, the flexibility of the underlying neural circuitry remains unclear. For example, the effects of electrical stimulation on the recruitment order of motor units is not well understood. This project was designed to study the recruitment order of motor units in man during different stimulation protocols. Examination of the compound-twitch characteristics of electrically evoked responses allowed an indirect determination of motor-unit recruitment order. The results demonstrate that the recruitment order of quadriceps femoris and triceps surae motor units differs according to the stimulation protocols used. Analysis of the compound-twitch characteristics indicated that the recruitment order of motor units during Hoffmann reflexes is similar to that of volitional muscle contractions but effectively the reverse of that during direct-motor responses. Moreover, the results suggest that cutaneous-afferent stimulation alters the recruitment thresholds of different motor unit types during the Hoffman reflex.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 119-121).
High power applications require an accurate calculation of the losses on overmoded corrugated cylindrical transmission lines. Previous assessments of power loss on these lines have not considered beam polarization or higher order mode effects. This thesis will develop a theory of transmission that includes the effect of linearly polarized higher order modes on power loss in overmoded corrugated transmission line systems. This thesis derives the linearly polarized basis set of modes for corrugated cylindrical waveguides. These modes are used to quantify the loss in overmoded transmission line components, such as a gap in waveguide or a 900 miter bend. The dependence of the loss in the fundamental mode on the phase of higher order modes (HOMs) was investigated. In addition, the propagation of a multi-mode beam after the waveguide was quantified, and it was shown that if two modes with azimuthal (m) indices that differ by one propagate in the waveguide, the resultant centroid and the tilt angle of radiation at the guide end are related through a constant of the motion. These theoretical calculations are useful for high-power applications, such as the electron cyclotron heating in plasma fusion reactors. In addition, this thesis develops a low-power S-Parameter Response (SPR) technique to accurately measure the loss in ultra-low loss overmoded waveguide components. This technique is used to measure the loss of components manufactured to ITER (an experimental fusion reactor) specifications, operated at 170 GHz with a diameter of 63.5 mm and quarter-wavelength corrugations. The loss in a miter bend was found to be 0.022+0.08 dB. This measurement is in good agreement with theory, which predicts 0.027 dB loss per miter bend, and past measurements [18]. The SPR was used to measure the loss in a gap of waveguide and the results were in good agreement with the well-established theoretical loss due to gap, which demonstrates the accuracy of the SPR technique. For both of these measurements, a baseline analysis determined the effects of a small percentage (1-2%) of higher order modes in the system.
by Elizabeth J. Kowalski.
S.M.

Scanning transmission electron microscopy (STEM) has been widely used for characterization of materials; to identify micro- and nano-structures within a sample and to analyze crystal and defect structures. High-angle annular dark field (HAADF) STEM imaging using atomic number (Z) contrast has proven capable of resolving atomic structures with better than 2 A lateral resolution. In this work, the HAADF STEM imaging mode is used in combination with multislice simulations. This combination is applied to the investigation of the temperature dependence of the intensity collected by the HAADF detector in silicon, and to convergent beam electron diffraction (CBED) to measure the degree of chemical order in intermetallic nanoparticles. The experimental and simulation results on the high–angle scattering of 300 keV electrons in crystalline silicon provide a new contribution to the understanding of the temperature dependence of the HAADF intensity. In the case of 300 keV, the average high-angle scattered intensity slightly decreases as the temperature increases from 100 K to 300 K, and this is different from the temperature dependence at 100 keV and 200 keV where HAADF intensity increases with temperature, as had been previously reported by other workers. The L10 class of hard magnetic materials has attracted continuous attention as a candidate for high-density magnetic recording media, as this phase is known to have large magnetocrystalline anisotropy, with magnetocrystalline anisotropy constant, Ku, strongly dependent on the long-range chemical order parameter, S. A new method is developed to assess the degree of chemical order in small FePt L10 nanoparticles by implementing a CBED diffraction technique. Unexpectedly, the degree of order of individual particles is highly variable and not a simple function of particle size or sample composition. The particle-to-particle variability observed is an important new aspect to the understanding of phase transformations in nanoparticle systems.
Ph.D.
Department of Physics
Sciences
Physics

Unsteady heat transfer by natural convection in a closed square cavity is investigated numerically. A new finite-volume approach is developed and applied to the two-dimensional continuity, vorticity, and energy equations. The variation of the field variables is approximated by bi-quadratic interpolation formulas over the space occupied by the finite volume and the region surrounding it. These are used in the integral conservation laws for energy, vorticity and mass. The convective transport is modelled using a new upstream-weighting approach which uses volume averages for the vorticity and the energy transported across the boundaries of the finite volume. The weighting is dependent on the skewness of the velocity field to the surfaces of the finite volume as well as its strength. It is adaptive to local flow conditions. The velocities are obtained from the application of the velocity induction law. Use is made of an image system for the free vorticity of fluid. In this way, the no-penetration condition is enforced at the cavity boundaries, but at the same time it may allow a slip condition to exist. This is not permitted in a viscous flow analysis, and the slip velocity is reduced to zero by the production of free vorticity at the boundaries. Two test cases are treated which have exact solutions. The first is not new and involves a rotating shaft. The errors are less than.06% for this case. The second case is new and involves convection past a source and sink. The maximum error is 2.3%. For both test cases, the maximum error occurs at moderate values of the cell Peclet number and diminishes at the extreme low and high values. The time-development of the profiles of the vorticity, horizontal velocity, and temperature is examined at different locations within the cavity for Rayleigh numbers equal to 10³, 10⁴, and 10⁵. For these calculations, a 21 x 21 grid was used. The flow is found to approach a steady-state condition. The steady-state results are compared with a benchmark solution. In general, the agreement is excellent. The discrepancy is found to be less than 2% for the vast majority of the results for this relatively coarse grid.

Includes abstract.
Includes bibliographical references.
Despite two decades of studies of mother to child transmission of HIV, very little data is available regarding vertical transmission in twin pregnancies. There is uncertainty whether discordance of HIV transmission exists between the first born (Twin A) and second born (Twin B) infant. Primary aim of the study was to examine if there is any discordance of HIV transmission in twin pregnancies when comparing Twin A to Twin B. Secondary objectives were to identify possible additional risk factors for HIV transmission in twin pregnancies. We assessed antenatal care, antiretroviral therapy, birth order, delivery route and feeding options as risk factors for mother to child transmission of HIV in twin pregnancies.

Wir untersuchen die Phasenbildung von Festkörperlösungen von (InxGa1-x)2O3 experimentell mittels Transmissionselektronenmikroskopie und stützen uns bei der Modellierung auf die Clusterexpansion. Epitaktische (InxGa1-x)2O3 Schichten auf kristallinen Substrate sind durch ausgeprägte Ordnung auf den Kationenuntergittern gekennzeichnet, bei welchem In und Ga sich auf Gitterplätze einbauen auf denen sie die energetisch günstigste Koordination zum Sauerstoff einnehmen. Ausgehend von diesem Befund, modifizieren wir das Modells der idealen Mischung so dass wir die Konfigurationsentropie auf den kationischen Untergittern mit spezifischer Koordinations getrennt betrachten um diese realistisch zu berechnen. Das resultierende Phasendiagramm ist durch enge thermodynamisch Stabilitätsbereiche für die jeweiligen Phasen gekennzeichnet, weil sich gleichzeitig große metastabile Zusammensetzungsbereiche ergeben bei Temperaturen die typisch für epitaktisches Wachstum sind: so ist die monokline Phase im Zusammensetzungsbereich x<0.5 metastabil, die hexagonale Phase für 0.550.91. Wird amorphes (InxGa1-x)2O3 kristallisiert in-situ im TEM, bildet sich im Zusammensetzungbereich bis x<0.22 die Spinellphase, die als ungeordnete Variante der monoklinen Phase beschrieben wird. Oberhalb dieser Zusammensetzung ist die kubische Phase stabil. Ursache hierfür ist der Einfluss der maximale Menge an Konfiguartionsentropie auf die Bildungsenthalpie in Strukturen mit vielfältigem Koordinationsumgebungen der Kationen. Der letzte Teil der Arbeit befasst sich mit dem Einflusses der Gitterordnung auf den Materialkontrast bei der Abbildung mittels HAADF (High Angle Annular Dark Field) STEM. Hier wird gezeigt, dass die Anregung des 2s-Bloch-Wellen-Zustands zu langperiodsichen Kontrastoszillationen führt, die die quantitaive Bestimmung der Zusammensetzung mittels Z-Kontrast erschwert es aber erlaubt den Ordnungsparameter bei bekaannter Zusammensetzung zu messen.
We investigate the phase formation in (InxGa1-x)2O3 solid solutions experimentally by means of transmission electron microscopy (TEM) and with computational support using cluster expansion. In the case of epitaxial growth on crystalline substrates, we find strong ordering on the cation sublattices of (InxGa1-x)2O3, energetically driven by the tendency of In and Ga to each assume their preferred coordination environment. Based on this experimental finding, we modify the model of the ideal mixture by considering the configurational entropy on the respective cation sublattices with different coordination separately in order to calculate it realistically. The resulting phase diagram is characterized by narrow thermodynamically stable ranges for each phase, while wide composition ranges of metastable compounds are predicted, which can be achieved at temperatures typical for epitaxy: the monoclinic phase is metastable in the composition range x<0.5, the hexagonal phase for 0.550.91. If amorphous (InxGa1-x)2O3 is crystallized in-situ in the TEM, the spinel phase, which is described as a disordered variant of the monoclinic phase, is formed in the composition range up to x<0.22, while above this composition, the bixbyite phase is stable. This shift in stability is explained by the maximum amount of configurational entropy present during crystallization, which strongly influences the formation enthalpy in structures with diverse coordination environments of the cations. The last part of the work deals with the influence of the lattice order on the material contrast when imaging by HAADF (High Angle Annular Dark Field) STEM. It is shown that the excitation of the 2s-Bloch wave state leads to long-period contrast oscillations, which complicate the quantitative determination of the composition by Z-contrast but allows to quantify the order parameter for a given composition.

Coherent optical detection has drawn a considerable interest in the past few years. This is mainly due to its high tolerance towards linear and non-linear fiber impairments and improved spectral efficiency, enabled by the use of polarization multiplexing (PM) and multilevel modulation formats. Using digital signal processing, coherent optical detection has made it possible to increase the spectral efficiency (SE) of optical systems well beyond the 1 b/s/Hz achievable in intensity modulated direct detection (IMDD) systems. Combined with polarization multiplexing (PM) and multilevel M-ary quadrature amplitude modulation (QAM) formats, coherent optical detection is considered to be the best candidate for future high capacity 100 and 400 Gbps wavelength-division multiplexing (WDM) systems. A critical part of coherent optical communication systems is the phase sensitive coherent receiver whose performance is limited by the phase noise that exists on the recovered data samples. Major source of phase noise is the finite linewidth of both transmitter (Tx) laser and receiver (Rx) local oscillator. Amplified Spontaneous Emission (ASE) creating nonlinear phase noise that interacts with the nonlinear Kerr effect, can also add in the phase noise of recovered data signal. This phase noise causes distortion and hence random rotation of the received constellation points. As a consequence, design of efficient carrier phase estimation (CPE) algorithms has become very important, especially while implementing high order modulation formats. This thesis presents several novel CPE algorithms for phase noise detection and compensation of high order QAM formats. Some algorithms make a phase estimation by increasing the number of symbols that took part in CPE while others use novel multistage architectures. The algorithms are based on a classic feed forward Viterbi&Viterbi (V&V) scheme. Performance of the algorithms in terms of complexity and linewidth times symbol duration product with other standard CPE algorithms is also given. It was observed that some of the proposed schemes give even better performance than the best available algorithms present in the literature. Also in optical communication systems frequency offset compensation (FOC) and carrier phase estimation (CPE) techniques require a prior knowledge of the modulation format but owing to the flexible transceivers, it is no longer guaranteed that the signals arriving at the receiver side would have the same, known in advance, modulation format (MF). The receiver thus needs to have some 'blind' or 'flexible' algorithms to adapt to these changes. Modulation format identification (MFI) is of high interest for the next generation fiber-optic networks as it could grant more autonomy and flexibility to the network. Elastic optical networks (EON) and cognitive optical networks (CON), with rate-adaptive transceivers supporting multiple modulation formats, have recently drawn a considerable interest as future optical networks. Although MFI for wireless systems has been thoroughly investigated, not much work has been done for the recognition/identification of modulation formats in fiber-optic networks. For MFI, a digital coherent receiver should be able to identify the MF of the incoming signals to ensure proper demodulation. Since FOC and CPE techniques require a prior knowledge of the modulation format, this makes blind MFI on-the-fly more difficult. As a consequence, we either need to develop FOC or CPE algorithms that are MF oblivious or develop some schemes that do MFI before entering the FOC or CPE blocks in the DSP receiver. This thesis also gives a simple and novel MFI scheme based on the evaluation of the peak-to-average-power ratio (PAPR) of the received data samples. To the best of our knowledge the proposed scheme is the simplest among all the schemes present in the literature. At a particular optical signal to noise ratio (OSNR) value, different modulation formats have distinct PAPR which can be used as defining parameter for their correct identification. Simulation and experimental results demonstrate successful identification of four commonly used modulation formats. Furthermore, the propose technique can also be extended to other lower or higher order formats. In order to practically generate these QPSK and QAM formats, the most commonly used modulator is the Dual Parallel Mach-Zender (DPMZ) modulator. DPMZ modulators are also used in a wide variety of radio-over-fiber (ROF) links. A stable biasing condition of these modulators is very important for high gain and low noise figure (NF) of these links. Being technologically mature and due to the fact that it has a linear Pockels effect, LiNBO3 is commonly used as a manufacturing material for MZ modulators. However, a change in temperature, radio-frequency (RF) heating or aging, can result in a drift of operating bias of LiNBO3 modulators. To cope with it, a close-loop control technique has to be developed that will follow this drift of the operating bias and will keep the DPMZ modulators under their optimal condition. This thesis also presents a close loop control technique for the automatic bias control of both the inner and outer MZ's of the DPMZ structure. This technique requires the generation of three separate low amplitude pilot tones at three different frequencies. These pilot tones are then clamped with the dc biasing voltage, at biasing ports of the MZ's. The pilot tones should have low amplitude so that they will not interfere with the RF signal data of the modulators. By carefully monitoring the beating between these tones, a close-loop control technique can be developed that will automatically monitor and follow the drift of the dc biasing voltage from its optimum and will enable the modulators to exhibit long term stability. In summary, this thesis makes important contributions by designing ad-hoc algorithms for performance optimization of high-order modulation formats in coherent optical transmission systems.

For heat transfer through building insulations such as fiberglass, radiation and conduction are important modes of heat transfer. Moreover, materials like fiberglass scatter radiation in a highly anisotropic manner. The equations for heat transfer by simultaneous conduction and radiation are a coupled pair, one of which is of the nonlinear integrodifferential type. Exact solution for transient heat transfer in this case is not available, and the approximate solution available is the two-flux model. The two-flux model does not give good results for transient, combined mode heat transfer, through an absorbing, emitting, and anisotropically scattering medium. In this thesis a higher order approximate solution has been developed. It is found that this model gives appreciably better results than the two-flux model.

Master of Science

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2013
The demand for electrical energy has kept on increasing, thus causing power systems to be more complex and bringing the challenging problems of electrical energy generation, transmission, stability, as well as storage to be examined more thoroughly. With the advent of high-speed computation and the desire to analyze increasingly complex behaviour in power systems, simulation techniques are gaining importance and prevalence. Nevertheless, while simulations of large, interconnected complex power systems are feasible, they remain time-consuming. Moreover, the models and parameters used in simulations are uncertain, due to measurement uncertainty, the need to represent a complex behaviour with low-order models, and the inherent changing nature of the power system. This research explores the use of a model reduction technique and the applications of a Real-Time Digital Simulator (RTDS) to reduce the uncertainty in large-scale complex power system models. The main goal of the research is to develop a reduced order model and to investigate the applications of the RTDS simulator in reduction of large, interconnected power systems models. The first stage of the study is to build and simulate the full model of the power system using the DigSILENT and RTDS simulators. The second phase is to apply model reduction technique to the full model and to determine the parameters in the reduced-order model as well as how the process of reduction increases this model uncertainty. In the third phase the results of the model reduction technique are compared based on the results of the original model - IEEE standard benchmark models has been used. The RTDS was used for comparative purposes. The thesis investigations use a particular model reduction technique as Coherency based Method. Though the method ideas are applicable more generally, a concrete demonstration of its principles is instructive and necessary. Further, while this particular technique is not relevant to every system, it does apply to a broad class of systems and illustrates the salient features of the proposed methodology. The results of the thesis can be used in the development of reduced models of complex power systems, simulation in real-time during power system operation, education at universities, and research. Keywords: IEEE benchmark models, reduced models, Coherency based Method, DigSILENT, RTDS, model uncertainty, power system stability

This thesis presents the study of the model order reduction for power grids and transmission networks. The specific focus has been the transient dynamics. A mathematical viewpoint has been adopted for model reduction. Power networks are huge and complex network, simulation for power grid analysis and design require large non-linear models to be solved. In the context of developing "Smart Grids" with the distributed generation of power, real time analysis of complex systems such as these needs fast, reliable and accurate models. In the current study we propose model order reduction methods both a-priori and a-posteriori suitable for dynamic models of power grids. The model that describes the transient dynamics of the power grids is complex non-linear swing dynamics model. The non-linearity of the swing dynamics model necessitates special attention to achieve maximum benefit from the model order reduction techniques. In the current research, POD and LATIN methods were applied initially with varying degrees of success. The method of TPWL has been proved as the best-suited model reduction method for swing dynamics model; this method combines POD with multiple linear approximations. For the transmission lines, a distributed parameters model in frequency-domain is used. PGD based reduced-order models are proposed for the DP model of transmission lines. A fully parametric problem with electrical parameters of transmission lines included as coordinates of the separated representation. The method was extended to present the solution of frequency-dependent parameters model for transmission lines.
Cette these présente l'étude de la réduction de modeles pour les réseaux électriques et les réseaux de transmission. Un point de vue mathématique a été adopté pour la réduction de modeles. Les réseaux électriques sont des réseaux immenses et complexes, dont l'analyse et la conception nécessite la simulation et la résolution de grands modeles non-linéaires. Dans le cadre du développement de réseaux électriques intelligents (smart grids) avec une génération distribuée de puissance, l'analyse en temps réel de systemes complexes tels que ceux-ci nécessite des modeles rapides, fiables et précis. Dans la présente étude, nous proposons des méthodes de réduction de de modeles a la fois a priori et a posteriori, adaptées aux modeles dynamiques des réseaux électriques. Un accent particulier a été mis sur la dynamique transitoire des réseaux électriques, décrite par un modele oscillant non­linéaire et complexe. La non-linéarité de ce modele nécessite une attention particuliere pour bénéficier du maximum d'avantages des techniques de réduction de modeles. lnitialement, des méthodes comme POD et LATIN ont été adoptées avec des degrés de succes divers. La méthode de TPWL, qui combine la POD avec des approximations linéaires multiples, a été prouvée comme étant la méthode de réduction de modeles la mieux adaptée pour le modele dynamique oscillant. Pour les lignes de transmission, un modele de parametres distribués en domaine fréquentiel est utilisé. Des modeles réduits de type PGD sont proposés pour le modele DP des lignes de transmission. Un probleme multidimensionnel entierement paramétrique a été formulé, avec les parametres électriques des lignes de transmission inclus comme coordonnées additionnelles de la représentation séparée. La méthode a été étendue pour étudier la solution du modele des lignes de transmission pour laquelle les parametres dépendent de la fréquence.
Esta tesis presenta un estudio de la reducción de modelos (MOR) para redes de transmisión y distribución de electricidad. El enfoque principal utilizado ha sido la dinámica transitoria y para la reducción de modelos se ha adoptado un punto de vista matemático. Las redes eléctricas son complejas y tienen un tamaño importante. Por lo tanto, el análisis y diseño de este tipo de redes mediante la simulación numérica, requiere la resolución de modelos no-lineales complejos. En el contexto del desarrollo de redes inteligentes, el objetivo es un análisis en tiempo real de sistemas complejos, por lo que son necesarios modelos rápidos, fiables y precisos. En el presente estudio se proponen diferentes métodos de reducción de modelos, tanto a priori como a posteriori, adecuados para modelos dinámicos de redes eléctricas. La dinámica transitoria de redes eléctricas, se describe mediante modelos dinámicos oscilatorios no-lineales. Esta no-linearidad del modelo necesita ser bien tratada para obtener el máximo beneficio de las técnicas de reducción de modelos. Métodos como la POD y la LATIN han sido inicialmente utilizados en esta problemática con diferentes grados de éxito. El método de TPWL, que combina la POD con múltiples aproximaciones lineales, ha resultado ser el mas adecuado para sistemas dinámicos oscilatorios. En el caso de las redes de transmisión eléctrica, se utiliza un modelo de parámetros distribuidos en el dominio de la frecuencia. Se propone reducir este modelo basándose en la PGD, donde los parámetros eléctricos de la red de transmisión son incluidos como coordenadas de la representación separada del modelo paramétrico. Este método es ampliado para representar la solución de modelos con parámetros dependientes de la frecuencia para las redes de transmisión eléctrica

A computationally efficient, discrete model is presented for transmission line analysis and passive model order reduction of high-speed interconnect systems. The development of this model was motivated by the on-going efforts in chip/package co-design to route a major portion of the on-chip clock and high-speed data buses through the package in order to overcome the bandwidth reduction and delay caused by the high ohmic loss of on-chip wiring. The geometric complexity of the resulting interconnections is such that model order reduction is essential for rapid and accurate signal integrity assessment to support pre-layout design iteration and optimization. The modal network theory of the skin effect in conjunction with the theory of compact differences is used for the development of discrete models for dispersive, multi-conductor interconnects compatible with passive model order reduction algorithms. The passive reduced-order interconnect modeling algorithm, PRIMA, is then used on the resulting discrete model to generate a low-order, multi-port macromodel for interconnect networks. Numerical examples are used to demonstrate the validity and efficiency of the proposed model.

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Joshi, Yogendra; Committee Member: Gallivan, Martha; Committee Member: Graham, Samuel; Committee Member: Yeung, Pui-Kuen; Committee Member: Zhang, Zhuomin. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Neste trabalho, é apresentado e discutido um novo modelo para proteção de Linhas de Transmissão. O sistema proposto executa, individualmente, as etapas tradicionais da filosofia de proteção de distância: detecção, classificação e localização. Este modelo emprega Estatísticas de Ordem Superior (EOS) como ferramenta de extração de características, para posterior aplicação das Redes Neurais Artificiais (RNAs). As RNAs são responsáveis pelas tomadas de decisões do sistema, no sentido de identificar a ocorrência da falta e o tipo da mesma, além de localizar a falta no que tange às zonas de proteção consideradas. O processamento com tais estatísticas é responsável pela transformação dos dados para um domínio onde as diferentes faltas são evidenciadas através de agrupamentos de dados (padrões). O banco de dados disponível com sinais elétricos de LTs em condições de falta é utilizado para cálculo das estatísticas e o posterior treinamento supervisionado (e validação) das redes. A junção das etapas de proteção em um único modelo permitiu o desenvolvimento de um protótipo de relé, sendo executada uma bateria extensiva de testes, com as mais diversas condições de faltas possíveis. Apesar de operar apenas com sinais de corrente, o método proposto alcançou resultados que, em comparação com a técnica tradicional de proteção de distância, baseada na impedância aparente, aumenta consideravelmente o desempenho da proteção de LTs. Especialmente para as faltas monofásicas, de ocorrência mais comum, o desempenho obtido com o algoritmo proposto é largamente superior ao obtido com um relé de distância tradicional normalmente empregado em proteção de LTs, evidenciando a relevância da técnica empregada em aplicações de proteção.
A novel method of Transmission Lines (TLs) protection is presented and discussed in this work. The proposed algorithm performs the traditional steps of distance relaying, such as: fault detection, classification and location. The new method applies the Higher Order Statistics (HOS), also known as cumulants, as a tool for feature extraction in order to apply Artificial Neural Networks (ANN) for pattern classification. These networks are responsible for the processing of information, identifying a possible fault condition, the type of fault and, finally, its location in terms of fault zones considered for the problem. The application of HOS in a protection scheme is responsible for the transformation of electrical data, such as current signals, to a different domain where the different types of faults are highlighted by different classes of samples. The available database was obtained by simulating an Electric Power System and it is used for computing the statistics and training/validating the distinct neural networks of each step of the distance protection. A relay prototype is obtained by combining these steps in a synchronized operation. This prototype allowed the execution of extensive tests, simulating the operation of a protective system in real-time. Despite the use of currents signals only, the proposed method provided efficient protection for the EPS under study. In fact, comparing the results with a traditional method applied to distance protection, based on apparent impedance, an improvement of the protection performance was demonstrated. Especially for faults involving one phase and the ground, the most common in power systems, the results of the new methodology was significantly superior to that of the conventional relay. It can be concluded that the technique presents a high relevance for applications in transmission line protection.

Analyse des microstructures de deformation dans l'alliage de structure l1::(2) en fonction de la temperature afin de comprendre les causes du comportement plastique anormal. A basse temperature, les superdislocations dominent. Analyse de leur structure fine et de leur role de verrou en glissement octaedrique. Etude de l'evolution des structures des dislocations lors de l'augmentation de la temperature d'essai

The reliability and data rate of wireless communication have traditionally been limited by the presence of multipath fading in wireless channels. However, dramatic performance improvements can be obtained by the use of multiple transmit and receive antennas. Specifically, multiple antennas increase reliability by providing diversity gain, namely greater immunity to deep channel fades. They also increase data rates by providing multiplexing gain, i.e., the ability to multiplex multiple symbols in one signaling interval. Harvesting the potential benefits of multiple antennas requires the use of specially designed space-time codes at the transmitter front-end. Space-time codes introduce redundancy in the transmitted signal across two dimensions, namely multiple transmit antennas and multiple signaling intervals. In this work, we focus on linear space-time codes, which linearly combine the real and imaginary parts of their complex inputs to obtain transmit vectors for multiple signaling intervals. We aim to design optimum linear space-time codes. Optimality metrics and design principles for space-time codes are shown to depend strongly on the codes' function in the overall transmitter architecture. We consider two cases, depending on whether or not the space-time code is complemented by a powerful outer error-control code. In the absence of an outer code, the multiplexing gain of a space-time code is measured by its rate, while its diversity gain is measured by its raw diversity order. To maximize multiplexing and diversity gains, the space-time code must have maximum possible rate and raw diversity order. We show that there is an infinite set of maximum-rate codes, almost all of which also have maximum raw diversity order. However, different codes in this set have different error rate for a given input alphabet and SNR. Therefore, we develop analytical and numerical optimization techniques to find the code in this set which has the minimum union bound on error rate. Simulation results indicate that optimized codes yield significantly lower error rates than unoptimized codes, at the same data rate and SNR. In a concatenated architecture, a powerful outer code introduces redundancy in the space-time code inputs, obtaining additional diversity. Thus, the raw diversity order of the space-time inner code is only a lower limit to the total diversity order of the concatenated transmitter. On the other hand, we show that the rate of the space-time code places an upper limit on the multiplexing ability of the concatenated architecture. We conclude that space-time inner codes should have maximum possible rate but need not have high raw diversity order. In particular, the serial-to-parallel converter, which introduces no redundancy at all, is a near-optimum space-time inner code. This claim is supported by simulation results. On the receiver side, we generalize the well known sphere decoder to develop new detection algorithms for stand-alone space-time codes. These new algorithms are extended to obtain efficient soft-output decoding algorithms for space-time inner codes.

Orientador: Ariovaldo Verandio Garcia, Ruben Augusto Romero Lazaro
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
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Resumo: Neste trabalho são propostos modelos matemáticos e técnicas de solução para resolver o problema de planejamento da expansão de sistemas de transmissão através de três enfoques. a) Usando o modelo de corrente alternada do sistema de transmissão e um algoritmo heurístico construtivo especializado para resolver o problema de planejamento, e, ainda, realiza-se uma primeira tentativa de alocação de fontes de potência reativas; b) Usando o modelo de corrente contínua e técnicas de programação não-linear especializadas. Nesse caso emprega-se uma versão relaxada do problema de planejamento da expansão de sistemas de transmissão usando o modelo de corrente contínua, onde a integralidade das variáveis de investimento é desprezada. Resolve-se o problema de programação não-linear, modelado de forma matricial com um algoritmo de otimização especializado e, além disso, um algoritmo heurístico construtivo especializado é utilizado para resolver o problema de planejamento. c) Usando o modelo de corrente contínua e um algoritmo Branch and Bound (B&B) sem empregar técnicas de decomposição. Para isso foram redefinidos os chamados testes de sondagem no algoritmo B&B e em cada nó da árvore de B&B tem-se um problema de programação não-linear que são resolvidos usando a metodologia desenvolvida no item (b). Os ítens (a), (b) e (c) requerem a solução de problemas de programação não-linear diferenciados. Uma revisão das características principais da resolução iterativa dos métodos de pontos interiores é apresentada. Foi desenvolvida uma técnica baseada em uma combinação de métodos de pontos interiores de alta ordem (MPI-AO) para resolver os problemas de programação não-linear de forma rápida, eficiente e robusta. Essa combinação dos MPI-AO tem como objetivo colocar num único método as características particulares de cada um dos MPI-AO e melhorar o desempenho computacional comparado com os MPI-AO de forma individual
Abstract: In this work mathematical models and solution techniques are proposed to solve the power system transmission expansion planning problem through three approaches: a) Using the nonlinear model ofthe transmission system (AC model) and a specialized constructive heuristic algorithm to solve the problem and, yet, a first attempt to allocate reactive power sources is also considered; b) Using the direct-current (DC) model and specialized techniques of nonlinear programming. In this case a version of the power system transmission expansion planning problem using the DC model where the integrality of the investment variables is relaxed is used. The nonlinear programming problem is solved with a specialized optimization algorithm and, moreover, a constructive heuristic algorithm is employed to solve the planning problem. c) Using the DC model and Branch and Bound (B&B) algorithm without the use of decomposition techniques. The so called fathoming tests of the B&B were redefined and at each node of the tree a nonlinear programming problem is solved using the method developed in b). Items a), b) and c) require the solution of distinct problems of nonlinear programming. A revision of the main characteristics of the iterative solution of the interior points methods is presented. An optimization technique based on a combination of the higher order interior point methods (HO-IPM) had been developed to solve the nonlinear programming problems in a fast, efficient and robust way. This combination of the HO-IPM has as objective to explore the particular characteristics of each method in a single one and to improve the comparative computational performance with the HO-IPM of individual form
Doutorado
Energia Eletrica
Doutor em Engenharia Elétrica

Cette thèse porte sur la modélisation des ondes élastodynamiques dans deux situations particulières qui pénalisent les méthodes numériques utilisées pour simuler ces phénomènes. Dans la première partie, on se place dans le cas où les ondes de pression (ondes P) se propagent à une vitesse beaucoup plus grande que celle des ondes de cisaillement (ondes S). Les modèles numériques utilisés habituellement pour traiter cette configuration sont pénalisés par la plus petite vitesse qui dicte le choix du pas du schéma. Nous proposons ici un schéma qui découple numériquement, dans le volume, les ondes P et les ondes S, pour deux types de conditions de bord en utilisant la décomposition du déplacement en potentiels de Lamé, en deux dimensions. Les conditions aux limites de Dirichlet homogènes, qui sont des conditions essentielles pour la formulation classique en déplacement, deviennent des conditions naturelles, mais non standard, pour la formulation en potentiels qui se présente comme un système de deux équations d'ondes couplées par les conditions aux limites. Cette formulation préserve une énergie équivalente à l'énergie élastodynamique. Nous construisons un schéma éléments finis en espace et utilisons un thêta-schéma en temps sur les termes de bord afin de ne pas pénaliser la CFL et mener à une condition sur le pas de temps indépendante des termes de couplage au bord. Ce schéma préserve une énergie discrète. Le cas des conditions de surface libre mène à des instabilités. Nous les avons traitées comme des perturbations des conditions de Dirichlet, ce qui permet d'obtenir de bons résultats dans le domaine fréquentiel mais donne naissance à de sévères instabilités après discrétisation en temps. La seconde partie de la thèse est consacrée à la construction, l'analyse et la validation de conditions de transmission effectives (CTE) à travers une couche mince de matériau homogène et isotrope d'épaisseur constante h. Ici, la finesse de la couche affecte les schémas explicites usuels car le maillage de la couche avec des éléments suffisamment petits entraîne une diminution analogue du pas de temps critique via la condition CFL, tandis que l'on espère avec les CTE obtenir un pas de temps indépendant de l'épaisseur de la couche. Une analyse complète du cas de la bande mince rectiligne est donnée en deux et trois dimensions. Les conditions obtenues sont stables via la conservation d'une énergie et l'ordre de l'erreur d'approximation par rapport à l'épaisseur de la couche pour les conditions d'ordre 2 est de O(h^3). Des résultats numériques sont présentés pour les configurations bi et tridimensionnelles, ils valident les résultats de stabilité, d'estimation d'erreur et de conditions de stabilité de schémas en temps proposés, qui sont des modifications du schéma explicite utilisé en l'absence de couche mince. Enfin, le traitement d'une couche curviligne est effectué dans le cas bidimensionnel. Sa stabilité est à nouveau vérifiée par conservation d'énergie et des résultats numériques sont également présentés.

Dans un intervalle de composition étroit autour de Cu3Al, le système Cu-Al présente des caractéristiques particulièrement intéressantes concernant les phénomènes ordre-désordre. Tout d'abord, il existe à basse température une phase d'équilibre ordonnée à longue période : la phase 2. Cette phase peut être obtenue par trempe à partir de l’état à haute température suivie d'un revenu prolongé. Par ce procédé, l'évolution structurale passe, à la trempe, par une première transformation ordre-désordre, interrompue par une transformation martensitique, puis, au revenu, par une deuxième transformation ordre-désordre conduisant à la phase métastable x, contenant des parois d'antiphase périodiques. La phase 2 apparait ensuite, par modification du mode d'empilement des plans compacts de la phase x. Le présent travail a pour objet l'étude, en MET, des tout premiers stades de mise en ordre par revenu des martensites de ce système. Au cours de ce travail, nous avons été amené à distinguer deux scenarios différents, suivant que la martensite de départ est désordonnée ou partiellement ordonnée. La formation de la phase x, à partir de martensites désordonnées, passe par des stades caractérisés en diffraction électronique par des figures diffuses. Une interprétation de ces figures est donnée, ainsi que la cinétique de formation de la phase x. La mise en ordre des martensites partiellement ordonnées, peut s'accompagner ou non de la destruction de l'ordre initial. Dans le cas où celui-ci n'est pas détruit, la formation de la phase x met en jeu des mécanismes collectifs permettant la formation de parois d'antiphase périodiques. Ce travail devrait permettre de mieux comprendre les propriétés mécaniques des martensites du système Cu-Al, et expliquer le comportement d'alliages ternaires Cu-Al-x, qui sont à la base d'un certain nombre alliages à mémoire de forme.

Ces bronzes de titane de type hollandite sont des composes a vfalence mixte de formule generale a::(x)tio::(2), avec a=k, rb, cs et 0,125