1,720,959 research outputs found
Dinamica del gruppo di rinormalizzazione dei modelli di Potts gerarchici
No full textOggetto di questa tesi è il comportamento analitico delle funzioni termodinamiche di sistemi particolari, denominati modelli gerarchici.
Si tratta di modelli di Potts su reticoli che sono invarianti per una opportuna procedura di coarse-graining. Questa proprietà permette il calcolo esatto del gruppo di rinormalizzazione, dal quale si può ottenere una descrizione dei domini di analiticità delle funzioni termodinamiche dei sistemi ad essi associati. Tale descrizione è legata alla dinamica delle iterazioni di una opportuna mappa razionale in più variabili complesse che esprime l'operatore di rinormalizzazione associato al modello.
Si tratta di un argomento di ricerca estremamente nuovo e molti dei risultati ottenuti sono originali. All'esposizione dei risultati generali rigorosi si abbina inoltre una parte esemplificativa anche numerica, con il doppio fine di chiarire la trattazione e di esplicitare la sua generalità
Dynamics of Some Fermi–Ulam Models
Get PDFFermi acceleration is a mechanism which allows an interacting particle to extract arbitrarily large amounts of energy from a stationary environment. In the early 1940s, Fermi and Ulam designed simple dynamical systems to model this phenomenon, conducted numerical experiments, and obtained results supporting the ideas used to explain high-energy cosmic rays (cf. Fermi, 1949). In this talk, I will describe the dynamics of a number of dynamical systems inspired by their work. I will report on recent and ongoing work based on a combination of ideas from classical KAM (Kolmogorov–Arnold–Moser) theory and modern techniques in hyperbolic dynamics. This is part of a joint project with D. Dolgopyat
Abundance of escaping orbitsin a family of anti-integrable limitsof the standard map
Get PDFWe give quantitative results about the abundance of escaping orbits in a family of exact twist maps preserving Lebesgue measure on the cylinder T × R; geometrical features of maps of this family are quite similar to those of the well-known Chirikov-Taylor standard map, and in fact we believe that the techniques presented in this work can be further improved and eventually applied to studying ergodic properties of the standard map itself.
We state conditions which assure that escaping orbits exist and form a full Hausdorff dimension set. Moreover, under stronger conditions we can prove that such orbits are not charged by the invariant measure. We also obtain prove that, generically, the system presents elliptic islands at arbitrarily high values of the action variable and provide estimates for their total measure
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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