1,722,156 research outputs found
Effect of all-optical phase regeneration on fiber transmission capacity
No full textWe investigate theoretically the benefits of using all-optical phase regeneration in a long-haul fiber optic link. We simulate numerically the bit-error rate of a WDM optical communication system over many fiber spans with periodic re-amplification and compare the results obtained with and without the use of a phase regenerator at half the transmission distance. Our results suggest that, depending on the modulation format, a significantly improved performance by up to 1.5 orders of magnitude can be achieved
All-optical phase regeneration of multi-level amplitude and phase shift keyed signals
No full textAll-optical phase regeneration of multi-level phase shift keyed signals in fiber optic communications systems reduces the impact of phase noise induced by, e.g., self/cross-phase modulation of amplitude varying symbols, and has been previously simulated and experimentally demonstrated [1-3]. Phase regeneration is achieved through a judicious coherent addition of phase harmonics, bearing integer multiples of the signal phase, to the signal via four-wave mixing in a highly nonlinear fiber (HNLF), such that a staircase is realised in the signal phase transfer function of the HNLF. Phase regeneration may allow for greater transmission capacity and optical regeneration has the potential to work faster and consume less power than electronic compensation
Spatio-temporal collapse of ultrashort pulses in multimode optical fibers
No full textInvestigating MW peak-power ultra-short pulse propagation in multimode fibers using a multimode Schrödinger equation reveals nonlinear and dispersive effects can cause dramatic compression in space-time even for launch peak powers below the self-focussing power, Pcrit
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
Optimisation of amplitude limiters for phase preservation based on the exact solution to degenerate four-wave mixing
Get PDFAdopting an exact solution to four-wave mixing (FWM), wherein harmonic evolution is described by the sum of two Bessel functions, we identify two causes of amplitude to phase noise conversion which impair FWM saturation based amplitude regenerators: self-phase modulation (SPM) and Bessel-order mixing (BOM). By increasing the pump to signal power ratio, we may arbitrarily reduce their impact, realising a phase preserving amplitude regenerator. We demonstrate the technique by applying it to the regeneration of a 10 GBaud QPSK signal, achieving a high level of amplitude squeezing with minimal amplitude to phase noise conversion
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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