1,720,960 research outputs found
High-order harmonic generation from a linear chain of ions
No full textThe high-order harmonic generation process due to the interaction of a multi-well quantum system with an intense laser field is examined. A plateau extension up to a photon energy of I-p + 8U(p) and the generation of attosecond pulses are demonstrated
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
Line spectroscopy with spatial resolution of laser-plasma X-ray emission
No full textHigh dynamic range, space-resolved X-ray spectra of an aluminum laser-plasma in the 5.5-8 Angstrom range were obtained using a TIAP crystal and a cooled CCD camera as a detector. This technique was used to investigate the emission region in the longitudinal direction over a distance of approximately 350 mum from the solid target surface. These data show that the electron density profile varies by two orders of magnitude with the temperature ranging from about 180 eV in the overdense region to about 650 eV in the underdense region. Accordingly, different equilibria take place across the explored region which can be identified with this experimental technique. Derailed studies on highly ionized atomic species in different plasma conditions can therefore be performed simultaneously under controlled conditions
Analysis of space-resolved X-ray spectra from laser plasmas
No full textHigh dynamic range, space-resolved X-ray spectra, obtained using a TIAP crystal and a cooled CCD camera as a detector, were used to investigate the electron density and temperature profiles of an aluminum laser plasma with micrometer resolution. The electron density profile retrieved from the measurements is compared with numerical predictions from the two hydrodynamics codes MEDUSA (1D) and POLLX (2D). It is shown that 2D density profiles can be successfully reproduced by 1D simulations using a spherical geometry with an ad hoe initial radius, leading to similar electron temperature profiles
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
Application of novel techniques for interferogram analysis to laser-plasma ferntosecond probing
No full textRecently, two novel techniques for the extraction of the phase-shift map (Tomassini et al. (2001). Applied Optics 40, 35) and the electronic density map estimation (Tomassini P. & Giulietti A. (2001). Optics Communication 199, 143-148) have been proposed. In this article, we apply both methods to a sample laser-plasma interferogram obtained with fetmoseconds probe pulse, in an experimental setup devoted to laser particle acceleration studies
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