1,720,971 research outputs found
Theoretical and experimental investigation of a resonantly pumped thulium doped fluorozirconate fiber amplifier at around 810 nm
No full textWe have investigated the potential of thulium doped fluorozirconate fibers to provide an efficient AlGaAs diode pumped traveling wave amplifier at wavelengths around 810 nm. We present here calculations and experimental measurements of the small signal gain when excitation is resonant with the upper laser level. Amplification over the range 800-830 nm has been achieved in multimoded fiber with a best observed gain of 22 dB at 806 nm. Optimization of the fiber parameters is expected to provide an amplifier slope efficiency in excess of 0.7 dB/mW
A 20dB gain thulium-doped fluorozirconate fibre amplifier operating at around 0.8µm
No full textA thulium-doped fluorozirconate fibre amplifier pumped at 785 nm is described. Amplification is observed from 800 nm to 830nm. with a small signal gain in excess of 20dB at 806 nm
CW room temperature operation of praseodymium-doped fluorozirconate glass fibre lasers in the blue-green, green and red spectral regions
No full textWe report room temperature, continuous-wave oscillation of Pr3+-doped fluorozirconate fibre lasers at around 491 nm, 520 nm, 605 nm, 635 nm and 715 nm. An output power of 250 mW has been obtained at 635 nm for 800 mW of pump power from an argon ion laser operating at 476.5 nm. Tunable operation of the red transitions has been investigated, with output powers in excess of 30 mW being obtained. Q-switched pulses of 75 ns (fwhm) and 20 W peak power at 635 nm have also been generated
A high gain Tm<sup>3+</sup> fluorozirconate fibre amplifier operating in the 0.8µm region
No full textTo date, most research on rare earth doped optical fibre amplifiers has been directed towards developing high gain amplifiers in the second and third telecommunications windows at 1.3µm and 1.55µm respectively. In this paper we describe a Tm3+-doped fluorozirconate fibre amplifier pumped at 785nm and giving 20dB gain at 806nm in the first telecommunications window
CW Room temperature upconversion lasing at blue, green and red wavelengths in infrared-pumped Pr<sup>3+</sup>-doped fluoride fibre
No full textContinuous-wave, room temperature laser oscillation at 491 nm, 520 nm, 605 nm and 635 nm in a Pr3+-doped fluoro-zirconate fibre pumped simultaneously at 1.01 µm and 0.835µm is reported. An output power of 185mW has been measured for the 635 nm transition. The thresholds obtained suggest that laser diode-pumped operation of all four transitions should be possible in an optimised fibre
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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