1,721,031 research outputs found
The role of the adsorbed gases on the photoelectron performance of Mg-based photocathodes
No full textThe influence of the adsorbed gases on the photoelectron performance of Mg thin film-based photocathodes was investigated. Mg thin
films were deposited on Silicon and Copper substrates by pulsed laser ablation technique. The samples deposited on Silicon substrate
were used to deduce the morphology, the structure and the thickness by using different diagnostic techniques. On the contrary, the
samples deposited on Copper substrate were tested as photocathodes in a DC photodiode cell. The quantum efficiency of the Mg
photocathodes was systematically improved by laser cleaning treatments, which appears to be necessary before any use of a metallic
photocathode. The role of the hydrogen and oxygen absorption process on the emission properties is presented and discussed
Effects of prepoling and polarization on photoemission from ferroelectric ceramics
No full textWe describe the photoemission of lanthanum-doped lead zirconate titanate when illuminated with 355 nm radiation, with/without prepoling and with/without the application of a polarizing field. To explain the different behaviors observed, we propose a physical picture based on the defects moving toward the surface and the donor electrons squeezing into a very thin layer at the surface. The model and the experimental results indicate that ferroelectric ceramics could become interesting photoemitters
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
Photoemission Characteristics of PLD Grown Mg Films under UV Laser Irradiation
No full textIn this paper we report a detailed description of the laser cleaning procedure
and emission performance measurement on a pulsed laser deposited Mg
film. During the tests performed after the end of each cleaning operation we
have observed an increase in quantum efficiency (QE) in time. Then the QE
apparently stabilizes at a remarkably higher value. The study of this
phenomenon and its relation to chemical composition of the residual gases
of vacuum environment is important because it determines both the
achievable QE value and the lifetime of the Mg film based cathode.
Moreover, the stability of the QE at remarkably high values has been
revealed for a time scale of several days after each laser cleaning process, in
our vacuum conditions. The adsorption of reactive chemical species leading
to the lowering of the Mg work function is discussed
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