1,721,096 research outputs found
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
Exciton dynamics in ZnSe/ZnSxSe1-x superlattices
No full textTime-resolved photoluminescence experiments in a wide carrier density range up to and beyond the threshold for stimulated emission in ZnSe/ZnSxSe1-x. superlattices are presented. Different localisation mechanisms of free excitons are identified giving rise to different radiative recombination channels. At high carrier density localised energy states merge into miniband that allows for exciton-exciton interaction, such as screening of the free-exciton absorption and inelastic exciton-exciton scattering
EXCITON DYNAMICS AND RECOMBINATION IN ZNSE ZNSE0.82S0.18 SUPERLATTICES
No full textWe report time-resolved optical transmission and photoluminescence measurements of exciton dynamics and recombination in a ZnSe/ZnSe0.82S0.18 superlattice which displays low-threshold lasing. The carrier densities in our experiments are below threshold for stimulated emission. We find clear evidence for strong exciton-LO phonon scattering which gives rise to emission at the same wavelength where stimulated emission is reported to occur
Time-resolved study of stimulated emission in ZnSe/Zn(S,Se) superlattices
No full textThe time evolution of the stimulated emission in ZnSe/Zn(S,Se) superlattices has been studied by picosecond photoluminescence spectroscopy. ?The threshold of the stimulated emission is characterised by a sharp decrease of the transition lifetime from 150 ps to less than 30 ps at a carrier density of about 10(12) cm(-2). While the experimental results are consistent with a stimulated emission process due to excitons, they show no evidence of electron-hole plasma recombination
EXCITONIC PROCESSES AND LANSING IN ZNSSE/ZNSE SUPERLATTICES
No full textWe report the results of a systematic investigation of the stimulated emission in ZnSSe/ZnSe superlattices, by time resolved luminescence and high excitation intensity magnetoluminescence. The stimulated emission is found to have excitation origin from localized states around the thresold, and free-carrier origin at carrier densities well above the phase space filling thresold of the exciton
TIME-RESOLVED PHOTOLUMINESCENCE STUDIES OF STIMULATED-EMISSION AND EXCITON DYNAMICS IN ZNSE/ZNS0.18SE0.82 SUPERLATTICES
No full textWe report measurement of time resolved photoluminescence from ZnSe/ZnSSe superlattices. We observe an anomalous fast-decay component in the luminescence at an energy corresponding to that at which stimulated emission is observed at higher pump densities. From consideration of the risetimes and spectral position of the lasing line, we infer an excitonic scattering mechanism to be responsible for lasing in these samples
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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