1,720,957 research outputs found
Funcionais de Tikhonov e penalização com distâncias de Bregman
Full text linkDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-graduação de Matemática e Computação CientíficaUma técnica de regularização que vem ganhando destaque na comunidade de problemas inversos é a regularização de Tikhonov com termo de penalização dado pela seminorma de variação limitada. Esse método de regularização busca aproximar a solução "exata"' do problema por funções em BV, um espaço de Banach. O método de Tikhonov é largamente utilizado para problemas inversos formulados em espaços de Hilbert, situação para qual vários resultados teóricos são conhecidos. Esse método de regularização tem como característica fornecer soluções suaves, o que se torna uma desvantagem em certas aplicações em processamento de imagens, quando a imagem a ser reconstruída apresenta grandes gradientes ou quando é descontínua. Neste trabalho apresentamos um método tipo Tikhonov que visa obter soluções de problemas inversos mal-postos num contexto mais geral. Com essa generalização procuramos resultados teóricos para o tratamento de uma equação mal-posta em que o operador envolvido é definido entre espaços de Banach, além de utilizar uma penalização não diferenciável. Dessa maneira, o método investigado corresponde a uma generalização da teoria clássica de Tikhonov, a qual pode ser utilizada no espaço de funções de variação limitada. Após introduzirmos as condições necessárias para garantir a existência de uma solução para o problema regularizado, damos início ao estudo da qualidade das soluções obtidas por esse método. Exibimos resultados de estabilidade e taxas de convergência entre uma solução regularizada e uma solução "exata" do problema inverso. Tal análise de convergência é obtida com base na distância de Bregman. Operadores lineares e não lineares são considerados. Para problemas não lineares, investigamos também um método de Tikhonov iterado
Um algoritmo de pontos interiores para o sub-problema tangencial em métodos de filtros para programação não linear
Full text linkTCC (graduação) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Curso de Matemática.Neste trabalho procuramos relembrar alguns conceitos e revisar métodos necessários para a solução do nosso problema, tais como região de confiança e trajetória primal-dual, com o intuito de usá-los para a elaboração de um novo algo-ritmo para a solução do sub-problema tangencial, problema proveniente do segundo passo do algoritmo de PQS com métodos de filtro, o que completou nosso objetivo para este trabalho
Novel regularization methods for ill-posed problems in Hilbert and Banach spaces
No full textPeer reviewe
An alternating iterative minimisation algorithm for the double-regularised total least square functional
Full text linkThe total least squares (TLS) method is a successful approach for linear problems if both the right-hand side and the operator are contaminated by some noise. For ill-posed problems, a regularisation strategy has to be considered to stabilise the computed solution. Recently a double regularised TLS method was proposed within an infinite dimensional setup and it reconstructs both function and operator, reflected on the bilinear forms Our main focuses are on the design and the implementation of an algorithm with particular emphasis on alternating minimisation strategy, for solving not only the double regularised TLS problem, but a vast class of optimisation problems: on the minimisation of a bilinear functional of two variables.Peer reviewe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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