1,720,964 research outputs found
Target Normal Sheath Acceleration at ultrahigh intensities: A theoretical parametric investigation
No full textIons can be effectively accelerated during the interaction of an ultra-intense ultra-short laser pulse irradiating a thin solid target via the so-called Target Normal Sheath Acceleration (TNSA) mechanism. One of the crucial issues at this stage of the research is how to predict the properties of the accelerated ions, both from a fundamental point of view and in the light of foreseen applications. Thus, it is desirable to have a simple but reliable description, to be used to extrapolate current results to regimes likely to be reached in the near future, thanks to developments in laser technology. In this work we theoretically investigated the maximum ion energy achieved in TNSA as a function of laser properties, with special focus to the ranges I_L (pulse intensity) 10^20 -10^22 W/cm^2 and E_L (pulse energy) 1-30 J, which appear to be the most interesting for future facilities. Particular attention will be devoted to elucidate the effective dependence of the maximum ion energy on the laser intensity for different combinations of laser parameters
Energetic ions from next generation ultraintense ultrashort lasers: Scaling laws for Target Normal Sheath Acceleration
No full textLaser-driven ion acceleration represents one of the most exciting topics related to the physics of laser-plasma interaction. Ions can be effectively accelerated up to multi-MeV energies via the so-called Target Normal Sheath Acceleration (TNSA) mechanism. The possibility of predicting the properties of the accelerated ions is definitely a crucial issue, both from a fundamental point of view and in the light of foreseen applications. In this work the problem of the dependence of the maximum ion energy achieved in TNSA on the laser properties is theoretically investigated. Particular attention is devoted to elucidate the role played by the various laser parameters, like power, intensity, energy and focal spot, in determining the maximum ion energy, with special focus to values relevant for the present and next generation of Ti:Sa laser systems
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
Proton maximum energy cutoff scaling laws for bulk targets
No full textIn this work we experimentally and theoretically report on the energy cutoff scaling law for proton generation from bulk targets over one decade of intensity ranging from 5x10^18 to 5x10^19 W/cm2 in the ultra-short pulse duration regime (25 fs). Assuming the same experimental conditions and that the physics does not change for higher intensities, we extrapolate that 100 MeV could be reached using 500 TW ultra-high-contrast-ultra short laser pulses
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
Target normal sheath acceleration: theory, comparison with experiments and future perspectives
No full textIons can be effectively accelerated during the interaction of an ultraintense ultra-short laser pulse irradiating a thin solid target via the so-called target normal sheath acceleration (TNSA) mechanism. One of the pivotal questions at this stage of the research is how to predict the properties of the accelerated ions, both from a fundamental point of view and in the light of foreseen applications.
In this context, it is desirable to have a simple but reliable description to be used to extrapolate current results to future regimes, which will be made available in the near future, thanks to developments in laser technology. In this paper, the possible approaches for an analytical description of TNSA are discussed, and
a theoretical TNSA model is developed. This model is then used to investigate the maximum ion energy as a function of laser parameters. Detailed comparisons with available experimental data and scaling laws are presented. In particular, the relative role played by both the laser pulse energy and irradiance in determining
the ion features is investigated
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
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