1,720,959 research outputs found
Pulsed thulium-doped fiber laser at 1.94 μm based on a seed diode
No full textA fiber laser operating at 1.94μm in pulsed regime has been developed in a MOPA configuration. The seed consists of a custom-developed board hosting a laser diode, whose current is modulated to achieve the desired pulse shape, duration and repetition rate. The pulses are amplified through a thulium-doped fiber amplifier pumped at 793 nm. Thedesign of the amplifier stage has been performed by dynamic simulation of a rate-equationsmodel and compared to the experimental measurements. Simulations and experimental measurements have exhibited comparable results,
devising the realization of an effective pulsed laser system whose parameters can be easily tuned through the seed
Modeling and optimization of multimode fused fiber combiners
Full text linkAn effective method to predict the performance of multimode fused fiber combiners is presented. The realization of high power devices is strongly affected by the specific application, for instance whether used in fiber or in direct-diode lasers, and thus usually requires costly and time-consuming trial-and-error procedures. The proposed approach, which is based on ray tracing and statistical analysis, allows analyzing a-priori the impact of fiber dimensions, combiner geometry, glass material properties and laser beam quality on the coupling efficiency, therefore reducing the fabrication runs. Examples of application to 7-to-1 and 19-to-1 combiners are given and compared with experimental results
Caratterizzazione spettroscopica di fibre ottiche per la realizzazione di laser di media e alta potenza
No full textIl lavoro presentato riguarda la realizzazione di un banco di misura per la caratterizzazione di fibre ottiche drogate con ioni di terre rare, che trovano applicazione nella realizzazione di laser e amplificatori in fibra ottica di media e alta potenza (decine-centinaia di W). Il banco è composto da un monocromatore in grado di separare le componenti spettrali di un generico segnale ottico applicato al suo ingresso e di indirizzarle verso un sistema di rivelazione/visualizzazione. Eccitando mediante opportuna radiazione ottica la fibra sotto test, è possibile ricavare la sua risposta spettrale, ossia determinarne le caratteristiche di emissione e assorbimento in funzione della lunghezza d'ond
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
All-fiber kilowatt signal combiners for high power fiber lasers
No full textThe fabrication of multi-kilowatt fiber-fused signal combiners for fiber laser power scaling is presented. Characterization results up to 2kW have validated the manufacturing procedure and highlight the suitability for further power increase
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
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