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Simulation Study of Trapped Electron Effects on Positron Acceleration by a Shock Wave in an Electron–Ion–Positron Plasma
No full textA theoretical study for parallel electric field in nonlinear magnetosonic waves in three-component plasmas
No full textSimulation Study of Trapped Electron Effects on Positron Acceleration by a Shock Wave in an Electron–Ion–Positron Plasma
Full text link0000-0003-2691-5068Positron acceleration by a shock wave in an electron–ion–positron plasma is studied with two-dimensional (2D), relativistic, electromagnetic particle simulations with special attention to effects of electrons trapped in the shock wave. It is demonstrated that ultrarelativistic positron acceleration can occur even when the fluctuations along the shock front, which we call 2D fluctuations, excited by the trapped electrons grow to large amplitudes. Further, by comparing the results of the simulation and the calculation of test positrons not influenced by the 2D fluctuations, we show that the positrons influenced by the 2D fluctuations are accelerated to higher energies than the positrons not influenced by them. In addition to the parallel electric field formed in the shock transition region, the perpendicular electric field in the shock wave greatly contributes to the ultrarelativistic positron acceleration under the influence of the 2D fluctuations. Effects of the accelerated positrons on the 2D fluctuations are also discussed.journal articl
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
Effects of trapped electrons on electromagnetic fields in an oblique shock wave
Full text linkA magnetosonic shock wave propagating obliquely to an external magnetic field can trap electrons and accelerate them to ultrarelativistic energies. The effect of trapped electrons on electromagnetic fields in a shock wave is studied by theory and particle simulations. The expressions for field strengths are analytically obtained, including the number of trapped electrons nt as a factor. It is shown that as nt increases, the magnitude of F increases, where F is the integral of the parallel electric field, E∥ = (E⋅B)/B, along B. Theoretical analysis also suggests that the increase in F causes the electrons to be trapped deeper and accelerated to higher kinetic energies. These theoretical predictions are verified with relativistic electromagnetic particle simulations.journal articl
The maximum energy of 3He ions accelerated by current-driven instabilities
Full text linkNonlinear development of strong current-driven instabilities can cause selective acceleration of 3He ions through H cyclotron waves with frequencies ω≃2Ω_{3He} (Ω_{3He} is the cyclotron frequency of 3He). Energies of these ions are studied theoretically and numerically. Theoretical expressions for the wave numbers, k_|| and k_⊥, of the H cyclotron waves with ω≃2Ω_{3He} and for the maximum energy of 3He ions are presented. As initial electron drift speed υ_d increases, the value of k_⊥ decreases; which leads to the increase in the maximum 3He energy. Simulation results for the wave numbers and for the maximum 3He energy obtained by a two-dimensional, electrostatic, particle code are quantitatively in good agreement with the theory. It is also shown that when the initial electron drift energy is of the order of 10 keV, many 3He ions can be accelerated to energies of the order of MeV/n.journal articl
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