1,720,961 research outputs found
Hamiltonian analysis in Lie-Poisson gauge theory
No full textLie-Poisson gauge formalism provides a semiclassical description of noncommutative U(1) gauge theory with Lie algebra type noncommutativity. Using the Dirac approach to constrained Hamiltonian systems, we focus on a class of Lie-Poisson gauge models, which exhibit an admissible Lagrangian description. The underlying noncommutativity is supposed to be purely spatial. Analyzing the constraints, we demonstrate that these models have as many physical degrees of freedom as there are present in the Maxwell theory
Jacobi sigma models
No full textWe introduce a two-dimensional sigma model associated with a Jacobi manifold. The model is a generalisation of a Poisson sigma model providing a topological open string theory. In the Hamiltonian approach first class constraints are derived, which generate gauge invariance of the model under diffeomorphisms. The reduced phase space is finite-dimensional. By introducing a metric tensor on the target, a non-topological sigma model is obtained, yielding a Polyakov action with metric and B-field, whose target space is a Jacobi manifold
Poisson-Lie T-Duality of WZW Model via Current Algebra Deformation
Full text linkPoisson-Lie T-duality of the Wess-Zumino-Witten (WZW) model having the group
manifold of as target space is investigated. The whole construction
relies on the deformation of the affine current algebra of the model, the
semi-direct sum ,
to the fully semisimple Kac-Moody algebra
. A two-parameter family of models
with as target phase space is obtained so that Poisson-Lie
T-duality is realised as an rotation in the phase space. The dual
family shares the same phase space but its configuration space is
, the Poisson-Lie dual of the group . A parent action
with doubled degrees of freedom on is defined, together with
its Hamiltonian description.Comment: Final amended version. References added. 50 page
Topological and dynamical aspects of Jacobi sigma models
Full text linkThe geometric properties of sigma models with target space a Jacobi manifold
are investigated. In their basic formulation, these are topological field
theories - recently introduced by the authors - which share and generalise
relevant features of Poisson sigma models, such as gauge invariance under
diffeomorphisms and finite dimension of the reduced phase space. After
reviewing the main novelties and peculiarities of these models, we perform a
detailed analysis of constraints and ensuing gauge symmetries in the
Hamiltonian approach. Contact manifolds as well as locally conformal symplectic
manifolds are discussed, as main instances of Jacobi manifolds.Comment: 36 pages, Latex file. Text enlarged with introduction and final
discussion 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
Soluble complement receptor type 1 (sCR1) in chronic liver diseases: Serum levels at different stages of liver diseases
No full textComplement receptor type 1 (CR1) is an integral membrane protein of many haematopoietic cells and plays an important role in the clearance of complement-associated immune complexes, favouring their transport to liver and spleen macrophages. A small amount of soluble CR1 (sCR1) is also found in plasma and might originate directly from release of leucocytes and other circulating cells. In previous studies, an increase in serum sCR1 level has been observed in liver cirrhosis and end-stage renal failure. High levels have also been found in patients with some haematologic malignancies. sCR1 serum levels were measured using a specific double sandwich ELISA assay. The present study demonstrates the correlation between mean serum sCR1 concentrations and disease severity in patients with chronic liver disease. In patients with liver cirrhosis, grouped according to the Child-Pugh classification, sCR1 rose as liver function decreased. The presence of neoplastic growth in the liver apparently does not play a role in the increase of sCR1. Serum sCR1 was not elevated in other solid malignancies. Since sCR1 accumulates in liver diseases, evaluation of its serum levels could be useful as a liver function test
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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