1,720,963 research outputs found
Solar Flares as Electron Accelerators: Toward a Resolution of the Acceleration Efficiency Issue
No full textA major open issue concerning the active Sun is the effectiveness with which magnetic reconnection accelerates electrons in flares. A paper published by Nature in 2022 used microwave observations to conclude that the Sun is an almost ideal accelerator, energizing nearly all electrons within a coronal volume to nonthermal energies. Shortly thereafter, a paper published in Astrophysical Journal Letters used hard X-ray measurements of the same event to reach the contradictory conclusion that less than 1% of the available electrons were accelerated. Here we address this controversy by using spatially resolved observations of hard X-ray emission and a spectral inversion method to determine the evolution of the electron spectrum throughout a set of flares. We use the spatial variation of the electron spectrum to deduce the density of the medium where electrons propagate and, from this and the total intensity of the flare, the ratio of accelerated to ambient electron densities. Results show that this ratio never exceeds 1% or so in all the events analyzed
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
Variation of the electron flux spectrum along a solar flare loop as inferred from STIX hard X-ray observations
No full textContext. Regularized imaging spectroscopy was introduced for the construction of electron flux images at different energies from count visibilities recorded by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). In this work we seek to extend this approach to data from the Spectrometer/Telescope for Imaging X-rays (STIX) on board the Solar Orbiter mission. Aims. Our aims are to demonstrate the feasibility of regularized imaging spectroscopy as a method for analysis of STIX data, and also to show how such an analysis can lead to insights into the physical processes affecting the nonthermal electrons responsible for the hard X-ray emission observed by STIX. Methods. STIX records imaging data in an intrinsically different manner from RHESSI. Rather than sweeping the angular frequency plane in a set of concentric circles (one circle per detector), STIX uses 30 collimators, each corresponding to a specific angular frequency. For this work, we derived an appropriate modification to the previous computational approach for the analysis of the visibilities observed by STIX. This approach also allows for the observed count data to be placed into nonuniformly spaced energy bins. Results. We show that the regularized imaging spectroscopy approach is not only feasible for an analysis of the visibilities observed by STIX, but also more reliable. The application of the regularized imaging spectroscopy technique to several well-observed flares reveals details of the variation of the electron flux spectrum throughout the flare sources. Conclusions. We conclude that the visibility-based regularized imaging spectroscopy approach is well suited for the analysis of STIX data. We also used STIX electron flux spectral images to track, for the first time, the behavior of the accelerated electrons during their path from the acceleration site in the solar corona toward the chromosphere
RIS: Regularized imaging spectroscopy for STIX on board Solar Orbiter
No full textContext. The generation of spatially resolved count spectra and of cubes of count maps at different energies via imaging spectroscopy is one of the main goals of solar hard X-ray missions based on Fourier imaging. Thus, so far, for these telescopes, this goal has been realized via the generation of either count maps that are independently reconstructed in the different energy channels or electron flux maps reconstructed via a deconvolution of the approximate forms for the bremsstrahlung cross-section. Aims. Our aim is to introduce a regularized imaging spectroscopy method (RIS), whereby the regularization implemented in the count space imposes a smoothing constraint across contiguous energy channels, without the need for computing any deconvolution of the bremsstrahlung effect. Methods. STIX records imaging data, while computing the visibilities in the spatial frequency domain. Our RIS is a sequential scheme in which part of the information coded in the image is reconstructed at a specific energy channel and transferred to the reconstruction process at a contiguous channel via a visibility interpolation computed by means of variably scaled kernels (VSKs). Results. In the case of STIX visibilities recorded during the November 11, 2022 flaring event, we show that RIS is able to generate hard X-ray maps, whose morphology is seen to smoothly evolve from one energy channel to the contiguous one; accordingly, from these maps, it is possible to infer spatially resolved count spectra characterized by a notable numerical stability. We also show that the performance of this approach is robust with respect to both the image reconstruction method and the count energy channel utilized to trigger the sequential process. Conclusions. We conclude that RIS is not only an appropriate, but also an effective and necessary approach to constructing image cubes from STIX visibilities that are characterized by smooth behavior across count energies. Thus, it allows for the generation of numerically stable (and, thus, physically reliable) local count spectra
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
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