1,721,112 research outputs found
Non-ideal simulations of neutron star mergers
No full textAs gravitational wave astronomy begins to mature, the need for precise and efficient numerical modelling of compact object mergers grows. Simulations of mergers require relativistic models capable of capturing complex dynamics that act over disparate length and time scales, where improving the quality of the solution always comes at the cost of additional computation. In the vast majority of merger simulations, the equations defining the interaction of the matter and electromagnetic fields make a number of specific assumptions. In this work, we provide several means of efficiently evolving systems of equations that move away from this ideal framework. So-called non-ideal models of magnetohydrodynamics (MHD) may be dissipative or describe the evolution of multiple fluid species. Here, we present both kinds, describe why they are more physically accurate than the models that are generally used for merger simulations, and demonstrate the drawbacks inherent in their use. To alleviate the computational cost incurred by some non-ideal models, we develop a number of methods. First, we demonstrate how resistive and multiple fluid models of MHD can be accelerated by 21× by executing the most computationally expensive tasks on graphics processing units. We then focus our attention on resistive MHD, developing an approximation that can extend the ideal models that are currently used, emulating a full resistive model within a fraction of the time. After modifying this approximation to work in general relativity, we then use it for resistive simulations of neutron star mergers. These simulations demonstrate conclusively that a physically realistic magnitude of resistivity for neutron star matter can have dramatic effects upon the evolution of merger simulations, with large impacts on key observables. Finally, we present two novel, hybrid models of MHD that allow for significantly improved accuracy and computational efficiency when evolving resistive MHD. With all these tools, the computational costs preventing the widespread adoption of non-ideal models for merger simulations have been dramatically reduced, allowing for higher resolution and more realistic, resistive descriptions of neutron star matter for future merger simulations
A resistive extension for ideal MHD
No full textWe present an extension to the special relativistic, ideal magnetohydrodynamics (MHD) equations, designed to capture effects due to resistivity. The extension takes the simple form of an additional source term which, when implemented numerically, is shown to emulate the behaviour produced by a fully resistive MHD description for a range of initial data. The extension is developed from first principle arguments, and thus requires no fine tuning of parameters, meaning it can be applied to a wide range of dynamical systems. Furthermore, our extension does not suffer from the same stiffness issues arising in resistive MHD, and thus can be evolved quickly using explicit methods, with performance benefits of roughly an order of magnitude compared to current methods
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
