1,720,972 research outputs found
Dirac-Coulomb Operators with Infinite Mass Boundary Conditions in Sectors
Full text linkWe investigate the properties of self-adjointness of a two-dimensional Dirac
operator on an infinite sector with infinite mass boundary conditions and in
presence of a Coulomb-type potential with the singularity placed on the vertex.
In the general case, we prove the appropriate Dirac-Hardy inequality and
exploit the Kato-Rellich theory. In the explicit case of a Coulomb potential,
we describe the self-adjoint extensions for all the intensities of the
potential relying on a radial decomposition in partial wave subspaces adapted
to the infinite-mass boundary conditions. Finally, we integrate our results
giving a description of the spectrum of these operators
Singular perturbations of the dirac hamiltonian
Full text link114 p.This thesis is devoted to the study of the Dirac Hamiltonian perturbed by delta-type potentials andCoulomb-type potentials. We analysed on the delta-shell interaction on bounded and smooth domainsand its approximation by the coupling of the free Dirac operator with shrinking short rangepotentials.Under certain hypothesis of smallness of a regular potential, we prove that the Dirac operatorin R^3 coupled with a suitable rescaling of the potential converges in the strong resolvent sense to theHamiltonian coupled with a delta-shell potential supported on a bounded C^2 surface. Nevertheless, thecoupling constant depends non-linearly on the potential: the Klein's Paradox comes into play.Furthermore, we pay focus on the Dirac Operator with spherical delta-shell interactions. We characterizethe eigenstates of those couplings by finding sharp constants and minimizers of some precise inequalitiesrelated to an uncertainty principle and we explore the spectral relation between the shell interaction andits approximation by short range potentials with shrinking support, improving previous results in thespherical case. Finally, we investigate the Dirac operator perturbed by a certain class of Coulomb-typespherically symmetric potentials. We describe the self-adjoint realizations of this operator in terms of thebehaviour of the functions of the domain in the origin, and we provide Hardy-type estimates on them.Finally, we give a description of the distinguished extension
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
Singular perturbations of the dirac hamiltonian
Full text link114 p.This thesis is devoted to the study of the Dirac Hamiltonian perturbed by delta-type potentials andCoulomb-type potentials. We analysed on the delta-shell interaction on bounded and smooth domainsand its approximation by the coupling of the free Dirac operator with shrinking short rangepotentials.Under certain hypothesis of smallness of a regular potential, we prove that the Dirac operatorin R^3 coupled with a suitable rescaling of the potential converges in the strong resolvent sense to theHamiltonian coupled with a delta-shell potential supported on a bounded C^2 surface. Nevertheless, thecoupling constant depends non-linearly on the potential: the Klein's Paradox comes into play.Furthermore, we pay focus on the Dirac Operator with spherical delta-shell interactions. We characterizethe eigenstates of those couplings by finding sharp constants and minimizers of some precise inequalitiesrelated to an uncertainty principle and we explore the spectral relation between the shell interaction andits approximation by short range potentials with shrinking support, improving previous results in thespherical case. Finally, we investigate the Dirac operator perturbed by a certain class of Coulomb-typespherically symmetric potentials. We describe the self-adjoint realizations of this operator in terms of thebehaviour of the functions of the domain in the origin, and we provide Hardy-type estimates on them.Finally, we give a description of the distinguished extension
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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