1,721,233 research outputs found
Microscopic calculations of spin polarized neutron matter at finite temperature
No full textThe properties of spin polarized neutron matter are studied both at zero and finite temperature within the framework of the Brueckner-Hartree-Fock formalism, using the Argonne v 18 nucleon-nucleon interaction. The free energy, energy and entropy per particle are calculated for several values of the spin polarization, densities and temperatures together with the magnetic susceptibility of the system. The results show no indication of a ferromagnetic transition at any density and temperature. (c) 2005 Elsevier B.V. All rights reserved
Neutrino trapping effects on beta-stable neutron matter
No full textWe investigate in the framework of the Brueckner-Hartree-Fock approximation, the influence of neutrino trapping on the composition, equation of state, and structure of neutron stars immediately after birth. We explore also the consequences of neutrino trapping on the early evolution of a neutron star and on the final remnant left by the supernova explosion
Estimation of the effect of hyperonic three-body forces on the maximum mass of neutron stars
No full textA model based on a microscopic Brueckner-Hartree-Fock approach of hyperonic matter supplemented with additional simple phenomenological density-dependent contact terms is employed to estimate the effect of hyperonic three-body forces on the maximum mass of neutron stars. Our results show that although hyperonic three-body forces can reconcile the maximum mass of hyperonic stars with the current limit of 1.4-1.5M(circle dot), they are unable to provide the repulsion needed to make the maximum mass compatible with the observation of massive neutron stars, such as the recent measurements of the unusually high masses of the millisecond pulsars PSR J1614-2230 (1.97 +/- 0.04M(circle dot)) and PSR J1903+0327 (1.667 +/- 0.021M(circle dot))
Microscopic study of neutrino trapping in hyperon stars
No full textEmploying the most recent parametrization of the baryon-baryon interaction of the Nijmegen group, we investigate, in the framework of the Brueckner-Bethe-Goldstone many-body theory at zero temperature, the influence of neutrino trapping on the composition, equation of state, and structure of neutron stars, relevant to describe the physical conditions of a neutron star immediately after birth (protoneutron star). We find that the presence of neutrinos changes significantly the composition of matter delaying the appearance of hyperons and making the equation of state stiffer. We explore the consequences of neutrino trapping on the early evolution of a neutron star and on the nature of the final compact remnant left by the supernova explosion
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
Spin-orbit and tensor interactions in homogeneous matter of nucleons: accuracy of modern many-body theories
No full textWe study the energy per particle of symmetric nuclear matter and pure neutron matter using realistic nucleon-nucleon potentials having noncentral tensor and spin-orbit components, up to three times the empirical nuclear matter saturation density, rho(0) = 0.16 fm(-3). The calculations are carried out within the frameworks of the Brueckner-Bethe-Goldstone (BBG) and correlated basis functions (CBF) formalisms, in order to ascertain the accuracy of the methods. The two hole-line approximation, with the continuous choice for the single particle auxiliary potential, is adopted for the BBG approach, whereas the variational Fermi hypernetted chain/single operator chain theory, corrected at the second order perturbative expansion level, is used in the CBF one. The energies are then compared with the available quantum and variational Monte Carlo results in neutron matter and with the BBG, up to the three hole-line diagrams. For neutron matter and potentials without spin-orbit components all methods, but perturbative CBF, are in reasonable agreement up to rho similar to 3 rho(0). After the inclusion of the LS interactions, we still find agreement around rho(0), whereas it is spoiled at larger densities. The spin-orbit potential lowers the energy of neutron matter at rho(0) by similar to 3-4 MeV per nucleon. In symmetric nuclear matter, the BBG and the variational results are in agreement up to similar to 1.5 rho(0). Beyond this density, and in contrast with neutron matter, we find good agreement only for the potential having spin-orbit components. (c) 2005 Elsevier B.V. All rights reserved
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
- …
