1,720,964 research outputs found
Optical Potentials: Microscopic vs. Phenomenological Approaches
No full textIn this work we study the performances of our microscopic optical potential [1, 2], derived from nucleon-nucleon chiral potentials at fifth order (N4LO), in comparison with those of a successful non-relativistic phenomenological optical potential in the description of elastic proton scattering data on tin and lead isotopes at energies around and above 200 MeV. Our results indicate that microscopic optical potentials derived from nucleon-nucleon chiral potentials at N4LO can provide reliable predictions for observables of stable and exotic nuclei, even at energies where the robustness of the chiral expansion starts to be questionable
Neutron density distribution and neutron skin thickness of Pb208
No full textWe present and discuss numerical predictions for the neutron density distribution of Pb208 using various nonrelativistic and relativistic mean-field models for the nuclear structure. Our results are compared with the very recent pion photoproduction data from Mainz. The parity-violating asymmetry parameter for elastic electron scattering at the kinematics of the PREX experiment at JLab and the neutron skin thickness are compared with the available data. We consider also the dependence between the neutron skin and the parameters of the expansion of the symmetry energy
Optical potentials derived from nucleon-nucleon chiral potentials at N4LO
No full textBackground: Elastic scattering is probably the main event in the interactions of nucleons with nuclei. Even if
this process has been extensively studied in the past years, a consistent description, i.e., starting from microscopic
two- and many-body forces connected by the same symmetries and principles, is still under development.
Purpose: In a previous paper [M. Vorabbi, P. Finelli, and C. Giusti, Phys. Rev. C 93, 034619 (2016)] we derived
a theoretical optical potential from N N chiral potentials at fourth order (N 3 LO). In the present work we use N N
chiral potentials at fifth order (N 4 LO), with the purpose to check the convergence and to assess the theoretical
errors associated with the truncation of the chiral expansion in the construction of an optical potential.
Methods: Within the same framework and with the same approximations as the previous paper [M. Vorabbi,
P. Finelli, and C. Giusti, Phys. Rev. C 93, 034619 (2016)], the optical potential is derived as the first-order
term within the spectator expansion of the nonrelativistic multiple scattering theory and adopting the impulse
approximation and the optimum factorization approximation.
Results: The pp and np Wolfenstein amplitudes and the cross section, analyzing power, and spin rotation of
elastic proton scattering from 16 O, 12 C, and 40 Ca nuclei are presented at an incident proton energy of 200 MeV.
The results obtained with different versions of chiral potentials at N 4 LO are compared.
Conclusions: Our results indicate that convergence has been reached at N 4 LO. The agreement with the
experimental data is comparable with the agreement obtained in the previous paper [M. Vorabbi, P. Finelli,
and C. Giusti, Phys. Rev. C 93, 034619 (2016)]. We confirm that building an optical potential within chiral
perturbation theory is a promising approach for describing elastic proton-nucleus scattering
Elastic and quasi-elastic electron scattering off isotopic and isotonic chains
No full textWe present theoretical predictions for electron scattering on Z = 20 isotopic and N = 20 isotonic chain. The calculations are done within the framework of the distorted-wave Born approximation for elastic scattering and the plane-wave Born approximation for the QE one. The proton and neutron density distributions are evaluated adopting a relativistic Dirac- Hartree model. We present results for the elastic and quasi-elastic cross sections and for the parity-violating asymmetry and investigate the evolution of nuclear properties as a function of the neutron and proton number. We also present a comparison with the parity-violating asymmetry parameter obtained by the PREX Collaboration on 208Pb
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
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
- …
