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Injection of photoelectrons into dense argon gas
No full textThe injection of photoelectrons into a gaseous or liquid sample is a widespread technique that is used to produce a cold plasma in a weakly ionized system to study the transport properties of electrons in a dense gas or liquid. We report here the experimental results of the collection efficiency of photoelectrons injected into dense argon gas at T = 142.6 K as a function of the externally applied electric field and gas density. We show that the experimental data can be interpreted in terms of the so-called Young-Bradbury model, only if multiple scattering effects due to the dense environment are taken into account when computing the scattering properties and energetics of the electrons
Collection efficiency of photoelectrons injected into dense ar gas at low and intermediate temperatures
No full textWe measured the collection efficiency of electrons injected by means of photoelectric effect into argon gas at high density at temperatures T=177.3 K, above the critical temperature, and T=142.6 K, below it, for several densities as a function of the applied electric field. We show that the experimental data can be interpreted in terms of the Young-Bradbury model if we take into account the multiple scattering effects that affect the electron-atom scattering cross section
Excess Electron-mobility In High-density Argon Gas
No full textWe report accurate measurements of excess electron mobility in high-density Ar gas at a temperature T congruent-to 163 K in the density range (4 < N < 70) x 10(20) cm-3 as a function of the electric-field strength. The positive-density effect shown by the zero-field density-normalized mobility mu0N can be explained within the same theoretical framework recently used for neon gas, where mu0N shows a negative-density effect. Thus the analysis of our present measurements indicates that there is no need for two separate theories for both negative- and positive-scattering-length gases
Collection efficiency of photoelectrons injected into near- and supercritical argon gas
No full textInjection of photoelectrons into gaseous or liquid dielectrics is a widely used technique to produce cold plasmas in weakly ionized systems for investigating the transport properties of electrons. We report measurements of the collection efficiency of photoelectrons injected into dense argon gas for T = 152.7 K, close to the critical temperature Tc ≈ 150.9 K, and for T = 200.0 K. The high-field data agree with the Young-Bradbury model and with previous measurements below Tc and at an intermediate temperature above Tc. The effective, density-dependent electron-atom momentum transfer scattering cross section can be deduced. However, the weak-field data near Tc show large deviations from the theoretical model. We show that the electron behavior at weak field is influenced by electrostriction effects that are only important near the critical point
Collection efficiency of photoelectrons injected into dense argon gas at low temperature
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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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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