1,720,968 research outputs found
lukeshingles/pynonthermal: V2024.07.04
No full textMassively increase performance with new artistools rust atomic data reader and use of polars library. Full Changelog: https://github.com/lukeshingles/pynonthermal/compare/v2024.4.29...V2024.07.04:::::::::::::::pynonthermal is a non-thermal energy deposition (Spencer-Fano equation) solver.When high-energy leptons (electron and positrons) are injected into a plasma, they slow down by ionising and exciting atoms and ions, and Coulomb scattering with free (thermal) electrons. Keeping track of the rates of the processes is important for example, when modelling Type Ia supernovae at late times (>100 days). At late times, ionisation by high-energy non-thermal leptons (seeded by radioactive decay products) generally overtakes photoionisation, and the non-thermal contribution to ionisation is needed to obtain reasonable agreement with observed emission lines of singly- and doubly-ionised species.The numerical details of the solver are similar to the Spencer-Fano solver in the ARTIS radiative transfer code (Shingles et al. 2020), which itself is an independent implementation of the Kozma & Fransson (1992) solution to the Spencer & Fano (1945) equation. A similar solver is also applied in the CMFGEN code.The impact ionisation cross sections are formula fits from Arnaud & Rothenflug (1985) and Arnaud & Raymond (1992).If the internal set of levels and transitions are applied (e.g., using add_ion_ltepopexcitation()), these are imported from the CMFGEN atomic data compilation. See the individual source files for atomic data references
Neutron-Capture Nucleosynthesis and the Chemical Evolution of Globular Clusters
Full text linkElements heavier than iron are almost entirely produced in stars through neutron captures
and radioactive decays. Of these heavy elements, roughly half are produced by the slow
neutron-capture process (s-process), which takes place under extended exposure to low
neutron densities. Most of the s-process production occurs in stars with initial masses
between roughly 0.8 and 8 M , which evolve through the Asymptotic Giant Branch (AGB)
phase.
This thesis explores several topics related to AGB stars and the s-process, with a focus on
comparing theoretical models to observations in the literature on planetary nebulae, post-
AGB stars, and globular cluster stars. A recurring theme is the uncertainty of 13C-pocket
formation, which is crucial for building accurate models of s-process nucleosynthesis.
We first investigated whether neutron-capture reactions in AGB stars are the cause of
the low sulphur abundances in planetary nebulae and post-AGB stars relative to the
interstellar medium. Accounting for uncertainties in the size of the partial mixing zone
that forms 13C pockets and the rates of neutron-capture and neutron-producing reactions,
our models failed to reproduce the observed levels of sulphur destruction. From this, we
concluded that AGB nucleosynthesis is not the cause of the sulphur anomaly. We also
discovered a new method to constrain the extent of the partial mixing zone using neon
abundances in planetary nebulae.
We next aimed to discover the stellar sites of the s-process enrichment in globular clusters
that have inter- and intra-cluster variation, with the examples of M4 (relative to M5) and
M22, respectively. Using a new chemical evolution code developed by the candidate, we
tested models with stellar yields from rotating massive stars and AGB stars. We compared
our model predictions for the production of s-process elements with abundances from
s-poor and s-rich populations. We found that rotating massive stars alone do not explain
the pattern of abundance variations in either cluster, and that a contribution from AGB
stars with 13C pockets is required. We derived a minimum enrichment timescale from
our best-fitting chemical evolution models and, although the value depends on the
assumptions made about the formation of 13C pockets, our estimate of 240–360 Myr for
M22 is consistent with the upper limit of 300 Myr inferred by isochrone fitting.
Lastly, there is accumulating evidence that some stars (e.g., in ! Centauri) have been born
with helium mass fractions as high as 40%. This motivated us to explore the impact of
helium-rich abundances on the evolution and nucleosynthesis of intermediate-mass (3–6
M ) AGB models. We found that the stellar yields of s-process elements are substantially
lower in He-rich models, largely as a result of less intershell material being mixed into the
envelope. We also found evidence that high He abundances could restrict the s-process
production by 13C pockets to stars with lower initial masses
lukeshingles/pynonthermal: v2024.4.29
No full text<ul>
<li>Remove warnings in notebook</li>
<li>Remove dependencies on argcomplete, coveralls, and flake8</li>
<li>Fix markdown readme in PyPI
<strong>Full Changelog</strong>: https://github.com/lukeshingles/pynonthermal/compare/v2024.02.17...v2024.4.29</li>
</ul>
lukeshingles/pynonthermal: 2024-02-17
No full text<p><strong>Full Changelog</strong>: https://github.com/lukeshingles/pynonthermal/compare/v2021.04.21...v2024.02.17</p>
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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