1,720,994 research outputs found
Implementation and analysis of control techniques by sliding modes and nonlinear predictive
No full textThis work presents an implementation and analysis of traction control and linear trepidation techniques, driven by a six - pulse fully controlled three - phase rectifier. The methodology addresses the construction of real reality, modeling by method of system identification, design and tuning of optimization processes. The comparisons between the techniques are their characteristics and their performances when performing statistics, verifying the robustness of the series in non-linear systems. Both techniques perform satisfactory in the execution of the control, correlating with the.Este trabalho apresenta a implementação e análise das técnicas de controle por modos deslizantes e preditivo não linear, aplicados no controle de velocidade de motor de corrente contínua de excitação independente, acionado por retificador trifásico totalmente controlado de seis pulsos. A metodologia aborda a construção da bancada real, modelagem por método de identificação de sistemas, projeto e sintonia dos controladores utilizando processo de otimização. São realizadas comparações entre as referidas técnicas destacando suas características e desempenhos quando executadas em condições semelhantes, verificando a robustez das mesmas atuando em sistemas não lineares. Ambas as técnicas apresentam desempenho satisfatório na execução do controle, dependendo portanto, da análise do sistema a ser implementado para a determinação do método apropriado
Mathematical and computational methods applied to geoelectrical prospection with tridimensional stratification
No full textThis work presents two optimization methods to obtain the parameters of strati-
cation of the soil represented by a multilayer structure superimposed horizontally.
From of the optimization methodologies applied the geoelectrical stratication is
developed a method of three-dimensional stratication. The optimization methodology
uses a resistivity experimental apparent curve obtained from measurements
made on the soil to be stratied. The experimental curve is then compared with the
resistivity theoretical apparent curve. The resistivity theoretical apparent curve is
developed from the algorithm Sunde, using equations of wave propagation in strati
ed ways. This algorithm takes as input the parameters of the stratied soil and
as output data a resistivity theoretical apparent curve. With both experimental and
theoretical curves, it is calculated the error produced in the process of horizontal
soil stratication. A main feature of this model compared to the methods already
developed is the optimization of the number of layers. Some errors and misconceptions
committed in the horizontal soil stratication in several layers are discussed
and an apparatus to assist in large scale three-dimensional soil stratication and
a mathematical operator to assist in the optimization process are proposed. The
results obtained with this new model are also presented and discussed.Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorDoutor em CiênciasEste trabalho apresenta duas metodologias de otimização para obtenção dos parâmetros
da estratificação do solo representado por uma estrutura de múltiplas camadas
horizontalmente sobrepostas. A partir das metodologias de otimização aplicadas a estratificação geoelétrica, é desenvolvido um método de estratificação tridimensional.
A metodologia de otimização utiliza uma curva de resistividade aparente experimental
obtida a partir de medições feita no próprio solo a ser estratificado. Esta
curva experimental é depois comparada com uma curva de resistividade aparente
teórica. A curva de resistividade aparente teórica é desenvolvida a partir do algoritmo
de Sunde, que utiliza equações de propagação de onda em meios estratificados.
Este algoritmo tem como dados de entrada os parâmetros do solo estratificado e de
saída a curva de resistividade aparente teórica. Com ambas as curvas, experimental
e teórica, calcula-se o erro produzido no processo de estratificação horizontal do
solo. Uma das principais características desta modelagem em relação aos métodos
já desenvolvidos, é a otimização do número de camadas. Alguns erros e equívocos
cometidos na estratificação do solo em viárias camadas horizontais são discutidos e
um Dispositivo para auxiliar na estratificação tridimensional do solo em larga escala
e um operador matemático para auxiliar no processo de otimização são propostos.
Os resultados obtidos com esta nova modelagem são então apresentados e discutidos
Aplicação do mapeamento conforme no cálculo do fator de Carter
No full textThe present work proposes a numeric formulation for the determination of Carter's
factor as a function of the geometry of the slot of electric machines. This task is made by the
use of the Schwarz-Christoffel transformation. In order to reach the objective, there is the
need to calculate the Schwarz-Christoffel inverse transformation. This represents a non-linear
optimization problem. Therefore, it is proposed a methodology to calculate the parameters of
the Schwarz-Christoffel inverse transformation using genetic algorithms. The assessment of
Carter s factor is achieved considering polygonal domains with many vertices. The
transformation leads to a rectangular domain approach. Moreover, some case studies are
proposed and the methodology results are compared to traditional formulation results for the
Carter s factor, yielding some disparities.O presente trabalho propõe obter uma formulação numérica para a determinação do
fator de Carter em função da geometria da ranhura de máquinas elétricas, utilizando o cálculo
numérico da transformação de Schwarz-Christoffel. Com este objetivo, verifica-se a
necessidade do cálculo da transformação inversa de Schwarz-Christoffel. Este problema
representa um problema de otimização não linear. Desta forma, propõe-se uma metodologia
que implementa um algoritmo genético para resolver o problema de cálculo dos parâmetros da
Transformação inversa de Schwarz-Christoffel, considerando domínios poligonais com
muitos vértices. Em seguida, obtém-se um domínio retangular para o qual o problema do
cálculo do fator de Carter é resolvido. Desta forma, apresentam-se vários casos de estudos
onde a metodologia proposta é comparada com as formulações tradicionalmente utilizadas
para o cálculo do fator de Carter. Os resultados obtidos pelas diferentes metodologias são
confrontados, mostrando certas disparidades
Methodology to correlate the humidity, compaction and soil apparent electrical conductivity
No full textThis work presents the study of the relationship between soil apparent electrical
resistivity ρa and the moisture content, clay content and soil compaction, for use of
the ρa as a mapping tool of spatial soil variability. The values of apparent electrical
resistivity are obtained by geoelectrical prospecting methods that detect the effects
produced by the flow of electrical current in the soil. It is used the Wenner array
and the technique of Lateral Profiling for data collection. It was held measures of
ρa in different soil types, varying moisture content gradually while maintaining a
constant compaction, and then varying the compaction and relating it to a constant
humidity. To the study of spatial variability, it was chose two areas that would enable
the change of moisture and compaction content, in order to verify the measurement
capacity of ρa as methodology of identification of change in soil dynamics. The results
obtained are presented and discussed.Este trabalho apresenta o estudo das rela¸c˜oes entre a resistividade el´etrica aparente
do solo ρa e o teor de umidade, teor de argila e compacta¸c˜ao do solo, para utiliza¸c˜ao
de ρa como ferramenta de mapeamento da variabilidade espacial do solo. Os valores
da resistividade el´etrica aparente s˜ao obtidos atrav´es de m´etodos de prospec¸c˜ao
geoel´etricos que detectam os efeitos produzidos pelo fluxo de corrente el´etrica no solo.
Utilizam-se o arranjo de Wenner e a t´ecnica do Caminhamento El´etrico para coleta
dos dados. Realizaram-se medidas de ρa em diferentes tipos de solo, variando-se
gradualmente o teor de umidade, mantendo-se constante a compacta¸c˜ao, e posteriormente
variando a compacta¸c˜ao em fun¸c˜ao de valor constante de umidade. Para
o estudo da variabilidade espacial, escolheram-se duas ´areas que possibilitassem a
altera¸c˜ao dos teores de umidade e compacta¸c˜ao, a fim de verificar a capacidade da
medi¸c˜ao de ρa como metodologia de identifica¸c˜ao de altera¸c˜oes na dinˆamica do solo.
Os resultados obtidos s˜ao apresentados e discutidos
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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