1,721,005 research outputs found
Theoretical optical potential derived from nucleon-nucleon chiral potentials
Full text linkBackground: Elastic scattering is probably the main event in the interactions of nucleons with nuclei. Even if this
process has been extensively studied over the last 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 this work we study the domain of applicability of microscopic two-body chiral potentials in the
construction of an optical potential.
Methods: We basically follow the Kerman, McManus, and Thaler approach [Ann. Phys. (NY) 8, 551 (1959)] to
build a microscopic complex optical potential, and then we perform some test calculations on 16O at different
energies.
Results:. Our conclusion is that a particular set of potentials with a Lippmann–Schwinger cutoff at relatively
high energies (above 500 MeV) reproduces best the scattering observables.
Conclusions: Our work shows that building an optical potential within chiral perturbation theory is a promising
approach for describing elastic proton scattering; in particular, in view of the future inclusion of many-body
forces that naturally arises in such a framework
Determination of Nuclear Matter Radii by Means of Microscopic Optical Potentials: The Case of Kr
Full text linkIn this work we use microscopic Nucleon–Nucleus Optical Potentials (OP) to analyze elastic scattering data for the differential cross section of the 78Kr (p,p) 78Kr reaction, with the goal of extracting the
matter radius and estimating the neutron skin, quantities that are both needed to determine the slope parameter
L of the nuclear symmetry energy. Our analysis is performed with the factorized version of the microscopic
OP obtained in a previous series of papers within the Watson multiple scattering theory at the first order of the
spectator expansion, which is based on the underlying nucleon–nucleon dynamics and is free from phenomenological inputs. Differently from our previous applications, the proton and neutron densities are described with
a two-parameter Fermi (2pF) distribution, which makes the extraction of the matter radius easier and allows
us to make a meaningful comparison with the original analysis, that was performed with the Glauber model.
With standard minimization techniques we performed data analysis and extracted the matter radius and the
neutron skin. Our analysis produces a matter radius of R(rms) m = 4.12 fm, in good agreement with previous
matter radii extracted from 76Kr and 80Kr, and a neutron skin of Rnp −0.1 fm, compatible with a previous
analysis. Our factorized microscopic OP, supplied with 2pF densities, is a valuable tool to perform the analysis
of the experimental differential cross section and extract information such as matter radius and neutron skin.
Without any free parameters it provides a reasonably good description of the experimental differential cross
section for scattering angles up to ≈ 40 degrees. Compared to the Glauber model our OP can be applied to a
wider range of scattering angles and allows one to probe the nuclear systems in a more internal regio
Toward a Microscopic Description of Nucleus-Nucleus Collisions
Full text linkWe present the first results of a comprehensive microscopic approach to describe nucleus-nucleus elastic collisions by means of an optical potential derived at first order in multiple-scattering theory and computed by folding the projectile and target nuclear densities with the nucleon-nucleon t matrix, which describes the interaction between each nucleon of the projectile and each nucleon of the target. Chiral interactions are consistently used in the calculation of the t matrix and of the nonlocal nuclear densities, which are computed within the ab initio no-core shell model. Cross sections calculated for α collisions on ^{12}C and ^{16}O at projectile energies in the range 100-300 MeV are presented and compared with available data. For momentum transfer q up to about 1.0 fm^{-1} our results are in good agreement with the experimental data, whereas for higher momenta a reduction of the imaginary contributions is needed
Neutron density distribution and neutron skin thickness of Pb 208
No full textWe present and discuss numerical predictions for the neutron density distribution of Pb-208 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
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
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