1,721,021 research outputs found
Muon capture on the deuteron and the neutron-neutron scattering length
Full text linkBackground: We consider the muon capture reaction mu(-) + H-2 -> nu(mu) + n + n, which presents a "clean" two-neutron (nn) system in the final state. We study here its capture rate in the doublet hyperfine initial state (Gamma(D)). The total capture rate for the muon capture mu(-) + He-3 -> nu(mu) + H-3 (Gamma(0)) is also analyzed, although, in this case, the nn system is not so clean anymore. Purpose: We investigate whether Gamma(D) (and Gamma(0)) could be sensitive to the nn S-wave scattering length (a(nn)), and we check on the possibility to extract a(nn) from an accurate measurement of Gamma(D). Method: The muon capture reactions are studied with nuclear potentials and charge-changing weak currents, derived within chiral effective field theory. The next-to-next-to-next-to-leading-order chiral potential with cutoff parameter Lambda = 500 MeV is used, but the low-energy constant (LEC) determining a(nn) is varied so as to obtain a(nn) = -18.95, -16.0, -22.0, and +18.22 fm. The first value is the present empirical one, while the last one is chosen such as to lead to a di-neutron bound system with a binding energy of 139 keV. The LEC's c(D) and c(E), present in the three-nucleon potential and axial-vector current (c(D)), are constrained to reproduce the A = 3 binding energies and the triton Gamow-Teller matrix element. Results: The capture rate Gamma(D) is found to be 399(3) s(-1) for a(nn) = -18.95 and -16.0 fm; and 400(3) s(-1) for a(nn) = -22.0 fm. However, in the case of a(nn) = +18.22 fm, the result of 275(3) s(-1) [135(3) s(-1)] is obtained, when the di-neutron system in the final state is unbound (bound). The total capture rate Gamma(0) for muon capture on He-3 is found to be 1494(15), 1491(16), 1488(18), and 1475(16) s(-1) for a(nn) = -18.95, -16.0, -22.0, and +18.22 fm, respectively. All the theoretical uncertainties are due to the fitting procedure and radiative corrections. Conclusions: Our results seem to exclude the possibility of constraining a negative a(nn) with an uncertainty of less than similar to +/- 3 fm through an accurate determination of the muon capture rates, but the uncertainty on the present empirical value will not complicate the interpretation of the (forthcoming) experimental results for Gamma(D). Finally, a comparison with the already available experimental data discourages the possibility of a bound di-neutron state (positive a(nn))
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
How well does the chiral expansion converge in nuclear and neutron matter
Full text linkThe equations of state of nuclear and neutron matter (and, more generally, neutron-rich matter) play a fundamental role towards the understanding of a broad spectrum of systems, ranging from the skins of neutron-rich nuclei to the structure of compact stars. After a brief review of different approaches to predict the properties of nuclear and neutron matter, we will focus on error quantification in effective field theory. The various sources of uncertainty and their impact in infinite matter will be explored. We will then report on recent calculations of the nuclear and neutron matter equations of state at different orders of the chiral expansion as well as changing resolution scale. We will discuss the significance of such predictions as a foundation for future studies of convergence of the chiral perturbation series
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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