1,720,958 research outputs found
Transient gain dynamics in saturated counter-pumped raman amplifiers
No full textThe transient gain dynamics in saturated counter-pumped Raman amplifiers were analyzed. The strong power of the signal leading edge at the amplifier output was found to deplete the injected pump. It was shown that the gain dynamics were determined by the time behavior of a single state variable
Optimal placement of isolators in Raman amplified optical links
No full textExplicit formulae for the optimal placement of isolators inside distributed Raman
ampliers for the minimization of signal Double Rayleigh Backscattering are provided, and the
achievable improvement in optical signal to noise ratio is assessed
Impulsive pump depletion in saturated Raman amplifiers
No full textThe analytical results available for counter-propagating pump
distributed Raman amplifiers in the undepleted pump
approximation are shown to be easily extended to the signalsaturated
case by using effective values of both input pump and
sign a 1 s
Transient gain dynamics in saturated Raman amplifiers
No full textThis paper provides a detailed analysis of transient gain dynamics in saturated Raman amplifiers
fed by wavelength division multiplexed (WDM) signals. Such dynamics are due to a pump saturation
effect, known as pump-mediated signal-to-signal crosstalk, which is equivalent to the well-known
cross-gain modulation in EDFAs. We provide for the first time a simple block-diagram model of the
Raman amplifier, whose state is represented by the relative pumps depletion sensed by the signals.
With such model, we are able to prove that the time constants of the Raman gain transients are of the
same order as the pump–signal walk-off times. For counter-propagating pumps, the model is very
accurate in predicting both the steady-state gain and the transient gain dynamics, with more than an
order of magnitude improvement in computation time with respect to the direct solution of the signals
and pumps propagation equations. The value of such model is therefore in the simulation of dynamic
WDM networking scenarios in which the input powers have large swings in time. The model also
extends to the co-propagating pump and well captures the time constants involved in the transients,
although the accuracy in the predicted power levels is worse than that of the counter-propagating
pump case
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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