1,720,964 research outputs found
Chalcogenide glass thin films: Z-Scan measurements of refractive index changes
No full textNonlinear properties of chalcogenide glass As2S3 thin films have been measured with a self-diffraction (Z-Scan) technique. Photostructural changes and dynamical effects have been measured
Nonlinearity and photostructural changes in glassy As2S3 thin films
No full textMeasurements are reported of the refractive index and absorption coefficient changes of amorphous As2S3 (chalcogenide glass) thin films due to cw laser light irradiation. We have measured the transmittance through a thin film in the Z-scan technique configuration. Two different contributions to refractive index changes are demonstrated, showing the existence of a permanent and a dynamical effect. The first effect was demonstrated performing usual normal incidence transmittance measurements. The second dynamical change, revealed by the Z-scan technique, disappears once the light source is turned off: measured in the latter case is a maximum change of the refractive index Δn=-8×10-3 in the cw regime at λ=514.5 nm
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
Optical hysteresis and ultrafast transmission switching in chalcogenide glasses
No full textDynamics of optical nonlinearity are investigated experimentally in different time scales, from microsecond to nano-, pico-, and femtosecond domains. In addition Z-Scan measurements carried out the competition between permanent photodarkening and electronic nonlinearities in photoinduced absorption and refraction
Creation of long-living ordered electron-hole structures in a disordered system: Slow nonlinear response and formation of a beam channel by weak pumping
No full textExperimental and theoretical studies of an amorphous As2S5 semiconductor show the appearance of a
nonlinear variation of the refractive index An, produced by a weak He-Ne laser beam. The refractiveindex
variation needs long-time exposure (hours) and survives for a long time {afew days) after the laser
is switched off. The main feature of the theoretical model proposed here is the existence of electron and
hole trapped states resulting in slow relaxation and recombination, and the dependence of generation
and recombination rates in a given trap on the space distribution of electron-hole ordering. This dependence
results in spatial electron-hole ordering: the ordered state is long living and gives a contribution
to the refractive-index variation. Some experimental results supporting the presented model are also reported
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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