1,721,010 research outputs found
Renormalization group flow and fixed point of the lattice topological charge in the 2-d O(3) sigma-model
No full textWe study the renormalization group evolution up to the fixed point of the
lattice topological susceptibility in the 2-d O(3) non-linear sigma-model. We
start with a discretization of the continuum topological charge by a local
charge density, polynomial in the lattice fields. Among the different choices
we propose also a Symanzik--improved lattice topological charge. We check step
by step in the renormalization group iteration the progressive dumping of
quantum fluctuations, which are responsible for the additive and multiplicative
renormalizations of the lattice topological susceptibility with respect to the
continuum definition. We find that already after three iterations these
renormalizations are negligible and an excellent approximation of the fixed
point is achieved. We also check by an explicit calculation that the assumption
of slowly varying fields in iterating the renormalization group does not lead
to a good approximation of the fixed point charge operator
Scaling and topology in the 2-d O(3) -model on the lattice with the fixed point action
No full textWe study scaling properties and topological aspects of the 2--d O(3)
non--linear --model on the lattice with the parametrized fixed point
action recently proposed by P.~Hasenfratz and F.~Niedermayer. The behavior of
the mass gap confirms the good properties of scaling of the fixed point action.
Concerning the topology, lattice classical solutions are proved to be very
stable under local minimization of the action; this outcome ensures the
reliability of the cooling method for the computation of the topological
susceptibility, which indeed reproduces the results of the field theoretical
approach. Disagreement is instead observed with a different approach in which
the fixed point topological charge operator is used: we argue that the
discrepancy is related to the ultraviolet dominated nature of the model
Scaling and topology in the 2-d O(3) sigma-model on the lattice with the fixed point action.
No full textWe study scaling properties and topological aspects of the 2-d 0(3) non-linear sigma-model on the lattice with the fixed point action recently found by P. Hasenfratz and F. Niedermayer. The behavior of the mass gap confirms the good properties of scaling of the fixed point action. Concerning the topology, lattice classical solutions are proved to be very stable under local minimization of the action; this outcome ensures the reliability of the cooling method for the computation of the topological susceptibility, which indeed reproduces the results of the field theoretical approach. Disagreement is instead observed with a different approach in which the fixed point topological charge operator is used: we argue that the discrepancy is related to the ultraviolet dominated nature of the model
Renormalization group flow and fixed point of the lattice topological charge in the 2D O(3) sigma model
No full textWe study the renormalization group evolution up to the fixed point of the lattice topological susceptibility in the 2D O(3) nonlinear sigma model. We start with a discretization of the continuum topological charge by a local charge density polynomial in the lattice fields. Among the different choices we propose also a Symanzik improved lattice topological charge. We check step by step in the renormalization group iteration the progressive damping of quantum fluctuations, which are responsible for the additive and multiplicative renormalizations of the lattice topological susceptibility with respect to the continuum definition. We find that already after three iterations these renormalizations are negligible and an excellent approximation of the fixed point is achieved. We also check by an explicit calculation that the assumption of slowly varying fields in iterating the renormalization group does not lead to a good approximation of the fixed point charge operator
TOPOLOGICAL SUSCEPTIBILITY ON THE LATTICE - THE 2-DIMENSIONAL O(3) SIGMA-MODEL
No full textAs a test of the procedures used in lattice gauge theories, we study the topological susceptibility chi in a two-dimensional O(3) sigma or CP1 model. We determine chi by defining the density of topological charge as a local operator on the lattice. Following the prescriptions of field theory we perform the additive and multiplicative renormalizations needed to extract chi from Monte Carlo data. We also determine chi by the cooling method, finding consistent results. A combined use of cooling and field theory again gives the same result and insight into the renormalization mechanism. Finally we give a direct determination, by Monte Carlo techniques, of both the multiplicative and additive renormalizations, by heating configurations with a definite number of instantons. The results are consistent with perturbation theory
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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