1,721,096 research outputs found
Coherent light sources and optical techniques for Thomson scattering and Laser-Plasma experiments
Full text linkRecent progress in accelerators and lasers technology opens new perspectives in terms of particle-photon colliders luminosity: low cross section processes can be therefore utilized to create specific radiation sources. Indeed, exploiting the inverse Compton scattering or Thomson back-scattering process, the interaction between relativistic electron beams (γ >> 1) and near-infrared laser pulses (λ ≈ 1μm) yields electromagnetic waves in the X-ray and γ-ray range. The energy, the flux and the spectrum of such kind of generated radiation are suitable for many purposes, e.g. dynamical studies and imaging of solid, molecular and biological systems.
Nevertheless, the big development in the high power laser field, begun in the ’80s thanks to the chirped pulse amplification (CPA) scheme [66], has provided
systems to be employed in the study of the laser wakefield acceleration (LWFA). As stated by Tajima and Dawson in 1979, an intense laser pulse, propagating through a plasma, can stimulate plasma waves able to accelerate electrons with accelerating gradients greater than 100 GV/m, i.e. some orders of magnitude more than the conventional RF-based LINAC. Moreover, with TW-class laser systems and intensity more than 10^18 W/cm^2, the relativistic regime occurs and electrons can be self-injected into the plasma accelerating structure. This opens the possibility to build much more compact particle accelerators, even though the beam quality, in terms of emittance and energy spread, is not yet comparable to the standard linear accelerator.
In this work, the activity related to Thomson back-scattering and laser-plasma interaction pursued at SPARC_LAB Facility in Frascati (Italy) will be presented. SPARC_LAB (Sources for Plasma Accelerators and Radiation Compton with Lasers and Beams) is a multi-disciplinary facility aiming to test new radiation source
(THz, XUV, X-Ray) exploiting different phenomena such Free Electron Laser (FEL), Coherent Transition Radiation (CTR) and Thomson back-scattering, thank to the high brightness electron beam that it can provide. The peculiarity of SPARC_LAB is the presence of 300 TW FLAME laser together with the high brightness LINAC. This kind of laser represents a powerful tool to study Thomson back-scattering, when combining it with the linear accelerator, as well as the interaction with the matter, mainly to perform experiments related to LWFA, both in self-injection and external-injection regime. Furthermore, a development of a new diagnostics tool able to measure electron beam emittance in a single shot way will be presented. This novel technique seems to be very useful for beam from plasma accelerators, since they suffer shot-by-shot instabilities. Therefore, a statistical measurement would me meaningless while a single shot diagnostics can provide a more useful description of electron beam parameters. Simulations and some preliminary results will be provided. In addiction, also a research activity on interaction with solid target has been conducted in order to study the possibility to optimize the ion acceleration without increasing the laser energy but opportunely shaping the target itself
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
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