1,721,027 research outputs found
A normalized solitary wave solution of the Maxwell-Dirac equations
Full text linkWe prove the existence of a L2-normalized solitary wave solution for the Maxwell-Dirac equations in (3+1)-Minkowski space. In addition, for the Coulomb-Dirac model, describing fermions with attractive Coulomb interactions in the mean-field limit, we prove the existence of the (positive) energy minimizer
Existence and asymptotics for self-dual periodic vortices of topological-type
No full textWe consider vortices of topological-type for a class of selfdual gauge models, with periodic
boundary conditions and as the ratio of the vortex core size to the separation distance between vortex
points (the scaling parameter) tends to zero. We use a gluing technique (shadowing lemma) for solutions
to the corresponding semilinear elliptic equation on the plane, where the vortex points are periodically
arranged. This approach is particularly convenient and natural for the study of the asymptotics as the
scaling parameter tends to zero. In particular, we prove a factorization ansatz for multivortex solutions,
up to an error which is exponentially small
Multi-peak periodic semiclassical states for a class of nonlinear Schrödinger equations
No full textGround state for the relativistic one electron atom in a self-generated electromagnetic field
No full textWe study the Dirac-Maxwell system coupled with an external potential of Coulomb type. We prove the existence of a ``ground state" solution using the Foldy-Wouthuysen (unitary) transformation of the Dirac operator and its realization as an elliptic problem in the 4-dim half space R^4_+ with a Neumann boundary condition
Topological "observables" in semiclassical field theories
No full textWe give a geometrical set-up for the semiclassical approximation to euclidean field theories having families of minima (instantons) parametrized by suitable moduli spaces M. The standard examples are of course Yang-Mills theory and non-linear Ï\u83-models. The relevant space here is a family of measure spaces N Ì\u83â\u86\u92M, with standard fibre a distribution space, given by a suitable extension of the normal bundle to M in the space of the smooth fields. Over N Ì\u83 there is a probability measure dμ given by the twisted product of the (normalized) volume element on M and the family of gaussian measures with covariance given by the tree propagator CÏ\u86 in the background of an instanton Ï\u86εlunateM. The space of "observables", i.e., measurable functions on ( N Ì\u83, dμ), is studied and it is shown to contain a topological sector, corresponding to the intersection theory on M. The expectation value of these topological "observables" does not depend on the covariance; it is therefore exact at all orders in perturbation theory and can moreover be computed in the topological regime by setting the covariance to zero. © 1992
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
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