1,720,968 research outputs found
Microscopic calculations of charge-exchange nuclear modes
No full textMicroscopic calculations of nuclear states excited by means of charge-exchange reactions and
involving spin and isospin degrees of freedom, in particular, of the Gamow–Teller and the spin–dipole
resonances, are discussed. The framework is a fully self-consistent nonrelativistic spherical quasiparticle
random-phase approximation constructed on top of the Hartree–Fock–Bardeen–Cooper–Schrieffer approach.
Our results are compared with available experimental data, and a critical discussion is attempted
Spin-isospin nuclear response using the existing microscopic Skyrme functionals
No full textOur paper aims at providing an answer to the question of whether one can reliably describe the properties of the
most important spin-isospin nuclear excitations by using the available nonrelativistic Skyrme energy functionals.
Our method, which has been introduced in a previous publication devoted to the isobaric analog states, is the
self-consistent quasiparticle random-phase approximation (QRPA). The inclusion of pairing is instrumental for
describing a number of experimentally measured spherical systems which are characterized by open shells. We
discuss the effect of isoscalar and isovector pairing correlations. Based on the results for the Gamow-Teller
resonance in 90Zr, 208Pb, and a few Sn isotopes, we draw definite conclusions on the performance of different Skyrme parametrizations, and we suggest improvements for future fits. We also use the spin-dipole resonance as a benchmark of our statement
The fully self-consistent charge-exchange QRPA and its application to the Isobaric Analog Resonances
No full textA microscopic model aimed at the description of charge-exchange nuclear excitations along isotopic chains which include open-shell systems is developed. It consists of the quasiparticle random phase approximation (QRPA) made on top of Hartree-Fock-Bardeen-Cooper-Schrieffer (HF-BCS). The calculations are performed by using the Skyrme interaction in the particle-hole channel and a zero-range, density-dependent pairing force in the particle-particle channel. At variance with the (many) versions of QRPA which are available in the literature, in our work special emphasis is put on the full self-consistency. Its importance, as well as the role played by the charge-breaking terms of the nuclear Hamiltonian, like the Coulomb interaction, the charge symmetry and charge independence breaking (CSB-CIB) forces and the electromagnetic spin-orbit, are elucidated by means of numerical calculations of the isobaric analog resonances (IAR). The theoretical energies of these states along the chain of the Sn isotopes agree well with the experimental data in the stable isotopes. Predictions for unstable systems are presented
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
Spin-orbit splitting and the tensor component of the Skyrme interaction
No full textWe study the role of the tensor term of the Skyrme effective interactions on the spin–orbit splittings in the N = 82 isotones and Z = 50 isotopes.
The different role of the triplet-even and triplet-odd tensor forces is pointed out by analyzing the spin–orbit splittings in these nuclei. The experimental
isospin dependence of these splittings cannot be described by Hartree–Fock calculations employing the usual Skyrme parametrizations,
but is very well accounted for when the tensor interaction is introduced. The capability of the Skyrme forces to reproduce binding energies and
charge radii in heavy nuclei is not destroyed by the introduction of the tensor term. Finally, we also discuss the effect of the tensor force on the
centroid of the Gamow–Teller states
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
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