1,721,054 research outputs found
Time of flight profile of multiply-charged ion currents produced by a pulse laser
No full textAbstract
The ion emission from a Cu-plasma produced by a 308 nm excimer laser is analysed by time-of-flight spectroscopy and by deconvolution of measured ion currents. The ion current signals recorded by an ion collector outside the critical zone, where the charge-states of ions of the expanding plasma are frozen, have been deconvoluted by the use of the Kelly and Dreyfus equation.
The meaningful recovered currents recorded for Cu+ and Cu2+ ions have been compared with the current signals reconstructed from the ion energy analyser spectra. A velocity distribution and the abundance of the above ions are presented. A time-resolved average charge-state of ions is also determined.
The application of the law Q ∝ l −2, based on the dilution of the total charge, Q, carried out by ions at long distances, l, from the target, is shown to be fundamental for a characterization of the laser-produced plasma
Measurements of equivalent ion temperature in plasma pulse laser-generated at INFN-LNS and PALS
No full textCharge losses in expanding plasma created by a XeCl laser
No full textThe emission of multiply charged Cuq+ ions from a plasma produced by 308-nm excimer laser is analysed with respect to the distance from the irradiated target. The critical zone, outside which the charge states of ions of the expanding plasma are frozen, was determined to be about 20 cm from the target. This value was estimated using a charge-freezing criterion expressed by a distance dependence of the total charge carried by the ions QL-2, which describes the dilution of plasma by its expansion into a vacuum without collisional recombination processes
Significant role of the recombination effects for a laser ion source
No full textThis study is devoted to characterize a free expansion laser plasma produced by an excimer laser with respect to recombination phenomena. The plasma was ejected from a Cu target after the laser pulse. The diagnostic system was a Faraday cup located at different distances from the target in order to collect the ions carried by the plasma. Ion recombination effects were clearly observed at distances close to the target, due to the high density of the laser-produced plasma at the beginning of its expansion. The recombination range and critical distance were experimentally estimated measuring the ion charge variation on the distance from the target. Beyond it, the charge loss due to the recombination effects was negligible and the freezing of the charge states set in. In this region the plasma dilution, which was due to its free expansion into the vacuum, occurred, and the collected ion charge, Q, followed the law QL-2 as a function of the distance from the target, L. The assessment of recombination processes is very important for the optimization of a laser ion source
Recombination effects during the laser-produced plasma expansion
No full textThe precise characterization of plasmas generated by laser irradiation is needed for the development of ion sources. Since the characteristic parameters of the expanding plasma vary on both the distance and the time, an experimental study of their evolution is appropriate for a deeper knowledge of the plasma. The purpose of this work is to study same characteristics of laser plasma produced by ablation of a pure Cu target as function of the distance from the target along the propagation axis of the plasma plume. We irradiated the target by a KrF laser and a lens of 15 cm focal length. As the diagnostic system, a small Faraday cup array and an axial Faraday cup were utilized to study the spatial variation in the total charge carried by plasma ions. Charge loss during the plasma expansion was observed due to the recombination of charged species, which occurs within a critical distance, relatively close to the target, where the plasma density is high enough. The critical distance was determined for different laser fluences; beyond the critical distance the collisions among plasma particles are negligible and the ion charge remains frozen. It was observed that the critical distance increases as the laser fluence increases
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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