Dynamics of non-Abelian Aharonov-Bohm systems

This thesis examines several examples of systems in which non-Abelian magnetic flux and non-Abelian forms of the Aharonov-Bohm effect play a role. We consider the dynamical consequences in these systems of some of the exotic phenomena associated with non-Abelian flux, such as Cheshire charge holonomy interactions and non-Abelian braid statistics. First, we use a mean-field approximation to study a model of U(2) non-Abelian anyons near its free-fermion limit. Some self-consistent states are constructed which show a small SU(2)-breaking charge density that vanishes in the fermionic limit. This is contrasted with the bosonic limit where the SU(2) asymmetry of the ground state can be maximal. Second, a global analogue of Chesire charge is described, raising the possibility of observing Cheshire charge in condensedmatter systems. A potential realization in superfluid He-3 is discussed. Finally, we describe in some detail a method for numerically simulating the evolution of a network of non-Abelian (S₃) cosmic strings, keeping careful track of all magnetic fluxes and taking full account of their non-commutative nature. I present some preliminary results from this simulation, which is still in progress. The early results are suggestive of a qualitatively new, non-scaling behavior.

Control mechanisms in the human binocular oculomotor system

A study of human eye movements was made in order to elucidate the nature of the control mechanism in the binocular oculomotor system.

We first examined spontaneous eye movements during monocular and binocular fixation in order to determine the corrective roles of flicks and drifts. It was found that both types of motion correct fixational errors, although flicks are somewhat more active in this respect. Vergence error is a stimulus for correction by drifts but not by flicks, while binocular vertical discrepancy of the visual axes does not trigger corrective movements.

Second, we investigated the non-linearities of the oculomotor system by examining the eye movement responses to point targets moving in two dimensions in a subjectively unpredictable manner. Such motions consisted of hand-limited Gaussian random motion and also of the sum of several non-integrally related sinusoids. We found that there is no direct relationship between the phase and the gain of the oculomotor system. Delay of eye movements relative to target motion is determined by the necessity of generating a minimum afferent (input) signal at the retina in order to trigger corrective eye movements. The amplitude of the response is a function of the biological constraints of the efferent (output) portion of the system: for target motions of narrow bandwidth, the system responds preferentially to the highest frequency; for large bandwidth motions, the system distributes the available energy equally over all frequencies. Third, the power spectra of spontaneous eye movements were compared with the spectra of tracking eye movements for Gaussian random target motions of varying bandwidths. It was found that there is essentially no difference among the various curves. The oculomotor system tracks a target, not by increasing the mean rate of impulses along the motoneurons of the extra-ocular muscles, but rather by coordinating those spontaneous impulses which propagate along the motoneurons during stationary fixation. Thus, the system operates at full output at all times.

Fourth, we examined the relative magnitude and phase of motions of the left and the right visual axes during monocular and binocular viewing. We found that the two visual axes move vertically in perfect synchronization at all frequencies for any viewing condition. This is not true for horizontal motions: the amount of vergence noise is highest for stationary fixation and diminishes for tracking tasks as the bandwidth of the target motion increases. Furthermore, movements of the occluded eye are larger than those of the seeing eye in monocular viewing. This effect is more pronounced for horizontal motions, for stationary fixation, and for lower frequencies.

Finally, we have related our findings to previously known facts about the pertinent nerve pathways in order to postulate a model for the neurological binocular control of the visual axes.

Direito Internacional em matéria de água doce: conteúdo, formas e efetividade

Este trabalho objetiva analisar diversos aspectos do Direito Internacional Público em matéria de recursos hídricos de água doce superficiais e subterrâneos. Geração de energia, abastecimento, pesca, navegação, lazer, agricultura e indústria, são múltiplos os usos que os seres humanos fazem da água doce, mas antes disso a água é essencial para manutenção de todo e qualquer tipo de vida na Terra. São complexas e passíveis de várias análises as relações entre os Estados e as relações que se concretizam no interior dos Estados com objetivo de utilizar, controlar e preservar as fontes de água doce, a que se pretende fazer é uma análise jurídica, inserida no contexto político de expansão do capitalismo liberal. Pretende-se identificar e analisar normas jurídicas produzidas no âmbito internacional multilateral, considerando a sua forma, conteúdo e possíveis efeitos: na resolução de conflitos entre os Estados pelo controle e utilização da água doce, no estabelecimento de parâmetros para solução da crise ambiental e na superação dos problemas de acesso à água. Na primeira parte do trabalho, são identificadas as normas de Direito Internacional Público atinentes à matéria, descrevendo-se, primeiramente, a evolução histórica do Direito Internacional Fluvial até os estudos da doutrina de Direito Internacional e a Convenção de Nova York de 1997. O capítulo segundo objetiva apresentar o tema da água doce no contexto de surgimento do Direito Internacional do Meio Ambiente, de realização de conferências e criação de fóruns internacionais para a questão da água e do desenvolvimento de um direito humano à água. O capítulo terceiro propõe-se a ingressar na incipiente questão da regulamentação dos usos das águas subterrâneas, analisando os trabalhos da Comissão de Direito Internacional da Organização das Nações Unidas que culminaram com a adoção de uma Resolução sobre o Direito dos Aquíferos Transfronteiriços por parte da Assembleia Geral daquela organização. A segunda parte do trabalho objetiva analisar a aplicação das regras e princípios ensaiados nos textos de Direito Internacional aos casos concretos, confrontando-as com as soluções propostas em casos paradigmáticos de conflitos pela água, como o caso Gabcikovo-Nagymaros e o caso das Papeleras, envolvendo Argentina e Uruguai, ambos julgados pela Corte Internacional de Justiça. Na segunda parte do trabalho, também é analisado o caso do aquífero Guarani, um sistema de aquíferos interligados que se estende sob os subsolos de Argentina, Brasil, Paraguai e Uruguai, que em agosto de 2010 foi objeto de um tratado internacional assinado no âmbito do Mercosul. Por fim, a pesquisa objetiva desenvolver ideias e explicações para a existência (ou não) e a efetividade (ou a falta dela) das normas de Direito Internacional sobre recursos hídricos, considerando o conceito de soberania estatal que ora é o bode expiatório para a falta de assinaturas nos tratados ou de votos em declarações, ora é o próprio fundamento para a adoção de compromissos por parte dos Estados. Conclui-se tentando responder as seguintes questões: Existe Direito Internacional da água doce? São as normas de Direito Internacional efetivas? Para que servem essas normas de Direito Internacional, além da afirmação de sua própria existência como metas a serem atingidas?

I. Site effects and exciton structure in molecular crystals - Benzene. II. The first and second triplet states of solid benzene

The effect of intermolecular coupling in molecular energy levels (electronic and vibrational) has been investigated in neat and isotopic mixed crystals of benzene. In the isotopic mixed crystals of C₆H₆, C₆H₅D, m-C₆H₄D₂, p-C₆H₄D₂, sym-C₆H₃D₃, C₆D₅H, and C₆D₆ in either a C₆H₆ or C₆D₆ host, the following phenomena have been observed and interpreted in terms of a refined Frenkel exciton theory: a) Site shifts; b) site group splittings of the degenerate ground state vibrations of C₆H₆, C₆D₆, and sym-C₆H₃D₃; c) the orientational effect for the isotopes without a trigonal axis in both the ¹B_2u electronic state and the ground state vibrations; d) intrasite Fermi resonance between molecular fundamentals due to the reduced symmetry of the crystal site; and e) intermolecular or intersite Fermi resonance between nearly degenerate states of the host and guest molecules. In the neat crystal experiments on the ground state vibrations it was possible to observe many of these phenomena in conjunction with and in addition to the exciton structure.

To theoretically interpret these diverse experimental data, the concepts of interchange symmetry, the ideal mixed crystal, and site wave functions have been developed and are presented in detail. In the interpretation of the exciton data the relative signs of the intermolecular coupling constants have been emphasized, and in the limit of the ideal mixed crystal a technique is discussed for locating the exciton band center or unobserved exciton components. A differentiation between static and dynamic interactions is made in the Frenkel limit which enables the concepts of site effects and exciton coupling to be sharpened. It is thus possible to treat the crystal induced effects in such a fashion as to make their similarities and differences quite apparent.

A calculation of the ground state vibrational phenomena (site shifts and splittings, orientational effects, and exciton structure) and of the crystal lattice modes has been carried out for these systems. This calculation serves as a test of the approximations of first order Frenkel theory and the atom-atom, pair wise interaction model for the intermolecular potentials. The general form of the potential employed was V(r) = Be^-Cr - A/r⁶ ; the force constants were obtained from the potential by assuming the atoms were undergoing simple harmonic motion.

In part II the location and identification of the benzene first and second triplet states (³B_1u and ³E_1u) is given.

Museos y parques naturales: comunidades locales, administraciones públicas y patrimonialización de la cultura y la naturaleza

Cap. 1. Patrimonialización cultural y natural: un proceso, múltiples aproximaciones. Cap. 2. Comment un musée de ville peut-il être au service des citoyens? Un parcours et quelques pistes d’action. Jean-François Leclerc. Cap. 3. Los museos comunitarios de Kuna Yala y la memoria histórica. Anelio Merry López Cap. 4. Turismo y museos en la ciudad de Valencia. Javier Martí. Cap. 5. La Red de Museos Etnográficos de Asturias: proyecto y realidad. Juaco López Álvarez. Cap. 6. Culturas campesinas y conservación del patrimonio natur-rural. Jaime Izquierdo. Cap. 7. Faire et savoir faire un « territoire patrimonial » : Parc naturel régional du Haut-Jura (France). Olivier Givre. Cap. 8. Espacios naturales y especies salvajes. La construcción de la naturaleza como patrimonio en el Pallars Sobirà, Pirineo catalán. Oriol Beltran e Ismael Vaccaro. Cap. 9. L’histoire au cœur de la cité : l’exemple du laboratoire d’histoire et de patrimoine de Montréal. Joanne Burgess.

Beam splitting of low-contrast binary gratings under second Bragg angle incidence

Beam splitting of low-contrast rectangular gratings under second Bragg angle incidence is studied. The grating period is between lambda and 2 lambda. The diffraction behaviors of the three transmitted propagating orders are illustrated by analyzing the first three propagating grating modes. From a simplified modal approach, the design conditions of gratings as a high-efficiency element with most of its energy concentrated in the -2nd transmitted order (similar to 90%) and of gratings as a 1 x 2 beam splitter with a total efficiency over 90% are derived. The grating parameters for achieving exactly the splitting pattern by use of rigorous coupled-wave analysis verified the design method. A 1 x 3 beam splitter is also demonstrated. Moreover, the polarization-dependent diffraction behaviors are investigated, which suggest the possibility of designing polarization-selective elements under such a configuration. The proposed concept of using the second Bragg angle should be helpful for developing new grating-based devices. (C) 2008 Optical Society of America.

Distributed Optimal Control of Cyber-Physical Systems: Controller Synthesis, Architecture Design and System Identification

The centralized paradigm of a single controller and a single plant upon which modern control theory is built is no longer applicable to modern cyber-physical systems of interest, such as the power-grid, software defined networks or automated highways systems, as these are all large-scale and spatially distributed. Both the scale and the distributed nature of these systems has motivated the decentralization of control schemes into local sub-controllers that measure, exchange and act on locally available subsets of the globally available system information. This decentralization of control logic leads to different decision makers acting on asymmetric information sets, introduces the need for coordination between them, and perhaps not surprisingly makes the resulting optimal control problem much harder to solve. In fact, shortly after such questions were posed, it was realized that seemingly simple decentralized optimal control problems are computationally intractable to solve, with the Wistenhausen counterexample being a famous instance of this phenomenon. Spurred on by this perhaps discouraging result, a concerted 40 year effort to identify tractable classes of distributed optimal control problems culminated in the notion of quadratic invariance, which loosely states that if sub-controllers can exchange information with each other at least as quickly as the effect of their control actions propagates through the plant, then the resulting distributed optimal control problem admits a convex formulation.

The identification of quadratic invariance as an appropriate means of "convexifying" distributed optimal control problems led to a renewed enthusiasm in the controller synthesis community, resulting in a rich set of results over the past decade. The contributions of this thesis can be seen as being a part of this broader family of results, with a particular focus on closing the gap between theory and practice by relaxing or removing assumptions made in the traditional distributed optimal control framework. Our contributions are to the foundational theory of distributed optimal control, and fall under three broad categories, namely controller synthesis, architecture design and system identification.

We begin by providing two novel controller synthesis algorithms. The first is a solution to the distributed H-infinity optimal control problem subject to delay constraints, and provides the only known exact characterization of delay-constrained distributed controllers satisfying an H-infinity norm bound. The second is an explicit dynamic programming solution to a two player LQR state-feedback problem with varying delays. Accommodating varying delays represents an important first step in combining distributed optimal control theory with the area of Networked Control Systems that considers lossy channels in the feedback loop. Our next set of results are concerned with controller architecture design. When designing controllers for large-scale systems, the architectural aspects of the controller such as the placement of actuators, sensors, and the communication links between them can no longer be taken as given -- indeed the task of designing this architecture is now as important as the design of the control laws themselves. To address this task, we formulate the Regularization for Design (RFD) framework, which is a unifying computationally tractable approach, based on the model matching framework and atomic norm regularization, for the simultaneous co-design of a structured optimal controller and the architecture needed to implement it. Our final result is a contribution to distributed system identification. Traditional system identification techniques such as subspace identification are not computationally scalable, and destroy rather than leverage any a priori information about the system's interconnection structure. We argue that in the context of system identification, an essential building block of any scalable algorithm is the ability to estimate local dynamics within a large interconnected system. To that end we propose a promising heuristic for identifying the dynamics of a subsystem that is still connected to a large system. We exploit the fact that the transfer function of the local dynamics is low-order, but full-rank, while the transfer function of the global dynamics is high-order, but low-rank, to formulate this separation task as a nuclear norm minimization problem. Finally, we conclude with a brief discussion of future research directions, with a particular emphasis on how to incorporate the results of this thesis, and those of optimal control theory in general, into a broader theory of dynamics, control and optimization in layered architectures.

The oculomotor system: (1) Vertical-horizontal interaction and signal recognition, (2) Time delays and power spectra

In the first section of this thesis, two-dimensional properties of the human eye movement control system were studied. The vertical - horizontal interaction was investigated by using a two-dimensional target motion consisting of a sinusoid in one of the directions vertical or horizontal, and low-pass filtered Gaussian random motion of variable bandwidth (and hence information content) in the orthogonal direction. It was found that the random motion reduced the efficiency of the sinusoidal tracking. However, the sinusoidal tracking was only slightly dependent on the bandwidth of the random motion. Thus the system should be thought of as consisting of two independent channels with a small amount of mutual cross-talk.

These target motions were then rotated to discover whether or not the system is capable of recognizing the two-component nature of the target motion. That is, the sinusoid was presented along an oblique line (neither vertical nor horizontal) with the random motion orthogonal to it. The system did not simply track the vertical and horizontal components of motion, but rotated its frame of reference so that its two tracking channels coincided with the directions of the two target motion components. This recognition occurred even when the two orthogonal motions were both random, but with different bandwidths.

In the second section, time delays, prediction and power spectra were examined. Time delays were calculated in response to various periodic signals, various bandwidths of narrow-band Gaussian random motions and sinusoids. It was demonstrated that prediction occurred only when the target motion was periodic, and only if the harmonic content was such that the signal was sufficiently narrow-band. It appears as if general periodic motions are split into predictive and non-predictive components.

For unpredictable motions, the relationship between the time delay and the average speed of the retinal image was linear. Based on this I proposed a model explaining the time delays for both random and periodic motions. My experiments did not prove that the system is sampled data, or that it is continuous. However, the model can be interpreted as representative of a sample data system whose sample interval is a function of the target motion.

It was shown that increasing the bandwidth of the low-pass filtered Gaussian random motion resulted in an increase of the eye movement bandwidth. Some properties of the eyeball-muscle dynamics and the extraocular muscle "active state tension" were derived.

Como inventar uma nação: o ensaio de interpretação do Brasil em Varnhagen, Joaquim Nabuco e Euclides da Cunha

A presente tese representa um esforço no sentido de contextualizar a caminhada do ensaio de interpretação do Brasil, durante o século XIX, com base em três aspectos: a construção do tema nacional, em Varnhagen; a aquisição de uma linguagem de corte subjetivo, em Joaquim Nabuco; e o relacionamento entre ciência e literatura, em Euclides da Cunha. Na introdução, ocorrem aproximações de natureza conceitual acerca das características mais salientes do ensaio como gênero na literatura e da noção de identidade nacional. No primeiro capítulo, os objetivos se transferem para a investigação dos antecedentes da interpretação do Brasil, principalmente aqueles localizados nos textos de não ficção, a exemplo da carta de Pero Vaz Caminha e dos relatos de viagem durante o período colonial. O segundo capítulo descreve os esforços para a criação de uma língua literária correspondente ao novo estatuto de independência política, tendências inventariadas pela prosa e poesia do período, em textos como a História Geral do Brasil, de Francisco Adolfo de Varnhagen. O influxo de uma nova subjetividade sobre a linguagem constitui o escopo do terceiro capítulo que também reproduz parte da fortuna crítica do ensaio O Abolicionismo, de Joaquim Nabuco. Em quarto, o diálogo entre ciências sociais e a interpretação do Brasil servem de contraponto ao levantamento de obras que já aproximam a questão social (o caso de Os Sertões, de Euclides da Cunha). No quinto capítulo, uma breve reconstituição da passagem do ensaio de interpretação do Brasil no século XX. Por último, na coda, a trajetória do ensaio de interpretação do Brasil, até meados de 1900

Computer system support for data analysis

This thesis is an investigation into the nature of data analysis and computer software systems which support this activity.

The first chapter develops the notion of data analysis as an experimental science which has two major components: data-gathering and theory-building. The basic role of language in determining the meaningfulness of theory is stressed, and the informativeness of a language and data base pair is studied. The static and dynamic aspects of data analysis are then considered from this conceptual vantage point. The second chapter surveys the available types of computer systems which may be useful for data analysis. Particular attention is paid to the questions raised in the first chapter about the language restrictions imposed by the computer system and its dynamic properties.

The third chapter discusses the REL data analysis system, which was designed to satisfy the needs of the data analyzer in an operational relational data system. The major limitation on the use of such systems is the amount of access to data stored on a relatively slow secondary memory. This problem of the paging of data is investigated and two classes of data structure representations are found, each of which has desirable paging characteristics for certain types of queries. One representation is used by most of the generalized data base management systems in existence today, but the other is clearly preferred in the data analysis environment, as conceptualized in Chapter I.

This data representation has strong implications for a fundamental process of data analysis -- the quantification of variables. Since quantification is one of the few means of summarizing and abstracting, data analysis systems are under strong pressure to facilitate the process. Two implementations of quantification are studied: one analagous to the form of the lower predicate calculus and another more closely attuned to the data representation. A comparison of these indicates that the use of the "label class" method results in orders of magnitude improvement over the lower predicate calculus technique.

Esporte contemporâneo: um novo templo do capital monopolista

Esta pesquisa teve por objetivo abrir uma discussão sobre o papel do esporte contemporâneo junto ao processo de alienação humana em tempos de domínio do capitalismo monopolista e do fortalecimento da ideologia dominante. Para tal, no primeiro capítulo, analisou-se as principais transformações vividas historicamente pelo capitalismo com a intenção de identificar o impacto do capitalismo monopolista sobre o novo ordenamento da humanidade. No segundo capítulo, demonstrou-se como o esporte contemporâneo constituiu-se como uma instituição burguesa, socialmente determinada e integrada ao conjunto de normas, ideias e estratégias inerentes ao modo de produção capitalista, participando do processo de mascaramento da questão social. Destaca-se neste capítulo o uso de fontes documentais que demonstraram como o esporte contemporâneo tem ocupado lugar estratégico tanto junto à produção da ideologia dominante, quanto junto ao controle da queda da taxa de lucro. Identificou-se que sob tais condições o esporte contemporâneo compõe os processos compensatórios frente à queda tendencial da taxa de lucro e, ao mesmo tempo, integra-se ao processo de alienação humana, tendo por maior expressão a sua materialização sob a forma dos megaeventos esportivos. Neste ponto, a pesquisa concentra-se na análise dos megaeventos esportivos no Brasil e na criação das políticas do esporte, desde o primeiro governo Lula da Silva até os dias atuais. Identificou-se que os projetos de desenvolvimento do esporte no país, no período em tela, têm participado do processo de gerenciamento da crise do capital e do refluxo das lutas dos trabalhadores. O último capítulo abordou as particularidades que envolvem a ideologia pós-moderna, tendo por objetivo identificar as relações desta com fenômeno esportivo. Constatou-se que, em tempos de domínio do capitalismo monopolista e de suas políticas neoliberais, as contradições que aguçam o processo de alienação sob o qual encontra-se a classe trabalhadora de todo o mundo, coloca a humanidade em um novo patamar de alienação, ainda mais brutal e desumanizador. Nesta conjuntura, o esporte contemporâneo destaca-se por ser funcional tanto ao mercado globalizado, quanto ao projeto imperialista, impondo-se como instrumento da contenção de conflitos em nome da tolerância e da paz no mundo. A presente pesquisa pôde concluir que as condições impostas pela fase monopolista do capitalismo ocultam a natureza dialética do esporte transforma-o num instrumento eficiente ao projeto dominante de incremento da alienação humana. O esporte, sob a forma assumida na contemporaneidade, não contribui para o avanço da consciência da classe trabalhadora, pois vem colaborando para adiamento do projeto de emancipação da humanidade. Projeto este que só será produzido pela organização consciente da classe trabalhadora em busca da superação do modo de produção capitalista.

The microbiological quality of water: the nature of the problem

Improvements in methods for the detection and enumeration of microbes in water, particularly the application of techniques of molecular biology, have highlighted shortcomings in the ”standard methods” for assessing water quality. Higher expectations from the consumer and increased publicity associated with pollution incidents can lead to an uncoupling of the cycle which links methodological development with standard-setting and legislation. The new methodology has also highlighted problems within the water cycle, related to the introduction, growth and metabolism of microbes. A greater understanding of the true diversity of the microbial community and the ability to transmit genetic information within aquatic systems ensures that the subject of this symposium and volume provides an ideal forum to discuss the problems encountered by both researcher and practitioner.

Influence of the second cladding on the properties of four-layer large flattened mode fibers

A theoretical method to analyze four-layer large flattened mode (LFM) fibers is presented. The influence of the second cladding on the properties of four-layer LFM fiber, including the fundamental and higher-order modal fields, effective area, bending loss, and dispersion, are studied by comparison. At the same time, the reasons for the different characteristics are considered. The obtained results indicate that the effective area of the four-layer LFM fiber is about 1.6 times larger than that of the conventional standard step-index fiber and the fibers have better bend-induced filtering ability than three-layer LFM fibers. (C) 2007 Society of Photo-Optical Instrumentation Engineers.

Influência da posição sócio-econômica ao longo da vida nas desigualdades de cor/raça na ocorrência de miomas uterinos: Estudo Pró-Saúde

Os miomas uterinos (MU) são considerados os tumores mais comuns do sistema reprodutor feminino. Estudos norte-americanos demonstram que mulheres negras são mais acometidas pelos MU que as de outros grupos étnico-raciais. No entanto, as causas da desigualdade racial na ocorrência dos tumores permanecem desconhecidas e possíveis mecanismos são pouco explorados na literatura. Em outra direção, devido às características dos MU (crescimento lento e longo período de latência) parte considerável dos estudos epidemiológicos utilizam um delineamento transversal, o que pode gerar problemas metodológicos, como os relacionados à utilização da idade coletada transversalmente (posteriormente a ocorrência dos MU) como proxy da idade do surgimento dos tumores. Assim, este trabalho de tese foi dividido em três partes, como se segue. A primeira, com características descritivas, teve por objetivo estimar a ocorrência de MU autorelatados segundo categorias demográficas e sócio-econômicas na população de estudo (compôs o artigo 1). A segunda, com componente analítico, propôs-se a avaliar o papel da PSE ao longo da vida como mediadora do efeito da cor/raça na ocorrência de MU auto-relatados (compôs o artigo 2). A terceira, com caráter metodológico, teve por objetivo comparar medidas de associação, entre variáveis aferidas transversalmente, em análises que incluem a co-variável idade no momento da coleta de dados e análises que consideram a idade ao diagnóstico dos MU (compôs o artigo 3). Para tanto, foram analisados dados transversais da população feminina participante das duas etapas da linha de base do Estudo Pró-Saúde, referentes à história auto-relatada de diagnóstico médico de MU e ainda a características sócio-demográficas, da vida reprodutiva e de acesso a serviços de saúde. Os resultados evidenciaram o aumento de ocorrência de MU em mulheres de maior idade e com a cor da pele mais escura (artigo 1); que a PSE ao longo da vida não medeia as associações entre cor/raça e MU (artigo 2); e que apesar das diferenças de pequena magnitude, a idade referida no momento da coleta de dados parece ser menos indicada para fins de especificação dos modelos analíticos do que a idade ao diagnóstico dos MU(artigo 3).

Stability analysis of RF amplifiers based on MIMO pole-zero identification

Spurious oscillations are one of the principal issues faced by microwave and RF circuit designers. The rigorous detection of instabilities or the characterization of measured spurious oscillations is still an ongoing challenge. This project aims to create a new stability analysis CAD program that tackles this chal- lenge. Multiple Input Multiple Output (MIMO) pole-zero identification analysis is introduced on the program as a way to create new methods to automate the stability analysis process and to help designers comprehend the obtained results and prevent incorrect interpretations. The MIMO nature of the analysis contributes to eliminate possible controllability and observability losses and helps differentiate mathematical and physical quasi-cancellations, products of overmodeling. The created program reads Single Input Single Output (SISO) or MIMO frequency response data, and determines the corresponding continuous transfer functions with Vector Fitting. Once the transfer function is calculated, the corresponding pole/zero diagram is mapped enabling the designers to analyze the stability of an amplifier. Three data processing methods are introduced, two of which consist of pole/zero elimina- tions and the latter one on determining the critical nodes of an amplifier. The first pole/zero elimination method is based on eliminating non resonant poles, whilst the second method eliminates the poles with small residue by assuming that their effect on the dynamics of a system is small or non-existent. The critical node detection is also based on the residues; the node at which the effect of a pole on the dynamics is highest is defined as the critical node. In order to evaluate and check the efficiency of the created program, it is compared via examples with another existing commercial stability analysis tool (STAN tool). In this report, the newly created tool is proved to be as rigorous as STAN for detecting instabilities. Additionally, it is determined that the MIMO analysis is a very profitable addition to stability analysis, since it helps to eliminate possible problems of loss of controllability, observability and overmodeling.