1,721,079 research outputs found
Unraveling the Effects of Dense Medium on a Near to Bohm-Limit Acceleration in Kepler's SNR
Full text linkThe maximum energy of electrons accelerated by supernova remnants (SNR) is
typically limited by radiative losses. In this scenario, the synchrotron
cooling time scale is equal to the acceleration time scale. On the other hand,
the low propagation speed of a shock in a dense medium is expected to result in
an extended acceleration time scale, thus inducing a decrease in the maximum
electron energy for a given SNR age and in the X-ray nonthermal flux. The young
Kepler's SNR shows an enhanced efficiency of the acceleration process, which is
close to the Bohm limit in the north of its shell, where the shock is slowed
down by a dense circumstellar medium. Conversely, in the south, where no
interaction with a dense medium is evident and the shock speed is high, the
acceleration proceeds with a higher Bohm factor. To investigate this scenario,
we studied the temporal evolution of the non-thermal emission, taking advantage
of two Chandra X-ray observations of Kepler's SNR (performed in 2006 and 2014).
We analyzed the spectra of different filaments both in the north and south of
the shell, and measured their proper motion. We found a region with low shock
velocity where we measured a significant decrease in flux from 2006 to 2014.
This could be the first evidence of fading synchrotron emission in Kepler's
SNR. This result suggests that under a certain threshold of shock speed the
acceleration process could exit the loss-limited regime
A Spatially Resolved Study of Hard X-Ray Emission in Kepler???s Supernova Remnant: Indications of Different Regimes of Particle Acceleration
Full text linkSynchrotron X-ray emission in young supernova remnants (SNRs) is a powerful diagnostic tool to study the population of high-energy electrons accelerated at the shock front and the acceleration process. We performed a spatially resolved spectral analysis of NuSTAR and XMM-Newton observations of the young Kepler's SNR, aiming to study in detail its nonthermal emission in hard X-rays. We selected a set of regions all around the rim of the shell and extracted the corresponding spectra. The spectra were analyzed by adopting a model of synchrotron radiation in the loss-limited regime, to constrain the dependence of the cutoff energy of the synchrotron radiation on the shock velocity. We identify two different regimes of particle acceleration, characterized by different Bohm factors. In the north, where the shock interacts with a dense circumstellar medium (CSM), we found a more efficient acceleration than in the south, where the shock velocity is higher and there are no signs of shock interaction with the dense CSM. Our results suggest an enhanced efficiency of the acceleration process in regions where the shock-CSM interaction generates an amplified and turbulent magnetic field. By combining hard X-ray spectra with radio and gamma-ray observations of Kepler's SNR, we modeled the spectral energy distribution. In the light of our results we propose that the observed gamma-ray emission is mainly hadronic and originates in the northern part of the shell
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
A diagnostic to trace shocked ejecta in SN 1987A using XRISM - Resolve
No full textSupernova (SN) 1987A is one of the best candidates to exploit the capabilities of the upcoming XRISM satellite, offering the unique opportunity to observe the rapid evolution of the non-equilibrium ionisation (NEI) plasma in a very early stagesupernova remnant.
Recent studies provide compelling evidence that in the forthcoming years, the X-ray emission from SN 1987A will increasingly stem from the ejecta.
Our aim is to assess the proficiency of XRISM-Resolve high resolution spectrometer in pinpointing signatures of the shocked ejecta in SN 1987A.
Taking advantage of a self consistent state-of-art magneto-hydrodynamic simulation, we synthesized the XRISM-Resolve spectrum, simulating the allocated observation during the performance verification (PV) phase, which is expected to occur in 2024.
Our forecast suggests that the bulk motion Doppler broadening from the fast moving ejecta will dominate over thermal broadening in all the visible ion emission lines.
Therefore we can strongly link the broadened line emission to the freshly shocked ejecta, using it as a diagnostic tool to retrieve the ejecta dynamics from the X-ray emission
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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