1,720,961 research outputs found
Anomalous dynamics and the choice of Poincaré recurrence set
No full textWe investigate the dependence of Poincaré recurrence-time statistics on the choice of recurrence set by sampling the dynamics of two- and four-dimensional Hamiltonian maps. We derive a method that allows us to visualize the direct relation between the shape of a recurrence set and the values of its return probability distribution in arbitrary phase-space dimensions. Such a procedure, which is shown to be quite effective in the detection of tiny regions of regular motion, allows us to explain why similar recurrence sets have very different distributions and how to modify them in order to enhance their return probabilities. Applied to data, this enables us to understand the coexistence of extremely long, transient powerlike decays whose anomalous exponent depends on the chosen recurrence set
Records and occupation time statistics for area-preserving maps
Full text linkA relevant problem in dynamics is to characterize how deterministic systems
may exhibit features typically associated to stochastic processes. A widely
studied example is the study of (normal or anomalous) transport properties for
deterministic systems on a non-compact phase space. We consider here two
examples of area-preserving maps: the Chirikov-Taylor standard map and the
Casati-Prosen triangle map, and we investigate transport properties, records'
statistics and occupation time statistics. While the standard map, when a
chaotic sea is present, always reproduces results expected for simple random
walks, the triangle map -- whose analysis still displays many elusive points --
behaves in a wildly different way, some of the features being compatible with a
transient (non conservative) nature of the dynamics.Comment: 8 pages and 7 figure
Extensive numerical investigations on the ergodic properties of two coupled Pomeau-Manneville maps
Full text linkWe present extensive numerical investigations on the ergodic properties of two identical Pomeau-Manneville maps interacting on the unit square through a diffusive linear coupling. The system exhibits anomalous statistics, as expected, but with strong deviations from the single intermittent map: Such differences are characterized by numerical experiments with densities which do not have singularities in the marginal fixed point, escape and Poincaré recurrence time statistics that share a power-law decay exponent modified by a clear dimensional scaling, while the rate of phase-space filling and the convergence of ensembles of Lyapunov exponents show a stretched instead of pure exponential behavior. In spite of the lack of rigorous results about this system, the dependence on both the intermittency and the coupling parameters appears to be smooth, paving the way for further analytical development. We remark that dynamical exponents appear to be independent of the (nonzero) coupling strength
Duas partículas clássicas confinadas num bilhar unidimensional e interagindo via potencial de Yukawa
Full text linkOrientador: Marcus Werner BeimsDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Curso de Pós-Graduaçao em Física. Defesa: Curitiba, 2006Inclui bibliografi
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
Estudo das propriedades de Caos Fraco em Sistemas Conservativos e Intermitentes
Full text linkOrientador: Prof. Dr. Marcus Werner BeimsTese (doutorado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Física. Defesa: Curitiba, 22/07/2010Bibliografia: fls. 91-95Resumo: O tema desta Tese consiste na caracterização do efeito de aprisionamento de trajetórias caóticas por estruturas de regularidade, chamadas quase-armadilhas dinâmicas. Geralmente, o espaço de fases de sistemas conservativos é composto por domínios onde a dinâmica pode ser regular, caótica ou uma mistura de ambos. A proposta deste trabalho visa investigar, principal- mente, o que acontece na interface entre estes domínios. Sabe-se que quando trajetórias caóticas se aproximam de regiões de regularidade, elas são aprisionadas por um intervalo de tempo fi- nito fazendo com que seu movimento se torne localmente quase-regular. Este processo é de essencial importância pois influencia diretamente as propriedades de transporte e decaimento das correlações temporais. Com o intuito de detectar estas estruturas de regularidade e esti- mar o decaimento das correlações temporais através dos expoentes de Lyapunov a tempo finito, investigamos numericamente diferentes classes de sistemas dinâmicos ao longo deste trabalho. Inicialmente utilizamos a distribuição dos expoentes de Lyapunov a tempo finito para analisar- mos a dinâmica de duas partículas interagentes aprisionadas num bilhar unidimensional, como função da razão entre as suas massas. Mostramos que o número de ocorrências do expoente de Lyapunov a tempo finito mais provável, extraído da distribuição destes, é sensível à existência de trajetórias aprisionadas no espaço de fases. Em seguida, também baseados na teoria dos grandes desvios das distribuições dos expoentes de Lyapunov a tempo finito, determinamos o decaimento algébrico das correlações e recorrências de Poincaré para o mapa de Pikovsky, para uma família de mapas intermitentes e para um ensemble de mapas padrão modificados. Todos os resultados numéricos obtidos reproduziram de forma satisfatória o decaimento das quantidades citadas. E finalmente, através da investigaçõo sistemática de uma rede de mapas simpléticos, caracterizamos a existência de trajetórias prisionadas no espaço de fases de altas dimensções. Nesta investigação utilizamos quatro quantidades associadas à caracterização das distribuições dos expoentes de Lyapunov a tempo finito: o número de ocorrências do expoente de Lyapunov mais provável, a variáncia, a assimetria e a curtose. Através destas quantidades mostramos que conforme o parâmetro de não-linearidade aumenta podemos dentificar a transição da dinâmica quase-regular para a caótica, que ocorre simultaneamente em todas as direções instáveis. Deste modo, os resultados discutidos ao longo desta Tese contribuem para um melhor entendimento da dinâmica de sistemas que apresentam propriedades de caos fraco.Abstract: The main idea of this Thesis is to characterize the presence of trapped trajectories close to structures of regularity, called quasi-traps. Generally, the phase space of conservative systems is composed of regions where the dynamics can be regular, chaotic or a coexistence of both. The purpose of this work aims to investigate, mainly, what happens at the interface between these regions. It is known that when the chaotic trajectories come close to regions of regularity, they are trapped by a finite time interval and its motion becomes locally quasi-regular. This process is of relevance since it directly influences the transport properties and correlations decay. With the aim of detecting these quasi-traps and estimating the decay of correlations via the distributi- ons of finite time Lyapunov exponents, we investigate numerically different classes of dynamical systems throughout this work. Initially we used the distributions of finite time Lyapunov ex- ponents to analyze the dynamics of interacting particles trapped in a two-dimensional billiards as a function of their masses ratio. We showed that the number of occurrences of the most probable finite time Lyapunov exponent, obtained from their distribution, is very sensitive to the existence of trapped trajectories in phase space. Then, based on the theory of large deviati- ons of the distributions of finite time Lyapunov exponents, we determine the algebraic decay of correlations and Poincar'e recurrences for the Pikovsky map, for a family of intermittent maps and an ensemble of modified standard maps. All numerical results reproduce satisfactorily the decay of correlations and Poincar'e recurrences. Finally, through the systematic investigation of coupled symplectic maps, we characterize the existence of trapped trajectories in phase space of higher dimensions. In this investigation we use four quantities associated with the characteri-
zation of the distributions of finite time Lyapunov exponents: the number of occurrences of the most probable finite time Lyapunov exponent, variance, skewness and kurtosis. Through these quantities we showed that as the parameter of non-linearity increases, it is possible to identify the transition from quasi-regular dynamics to the chaotic one which occurs simultaneously in all unstable directions. Thus, the results discussed throughout this Thesis give an important contribution to better understand the dynamics of systems that exhibit properties of weak chaos
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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