1,720,959 research outputs found
Performance evaluation of ASK phase-diversity lightwave systems
No full textPhase diversity coherent systems are gaining increasing interest with the increase of the bit rate in optical transmissions. In this work, an accurate approach for the evaluation of the error probability in ASK phase-diversity lightwave systems is presented. The approach is based on a Gaussian quadrature rule integration, which takes into account the exact characterization of the filtered phase noise through its moments. The effects of the laser linewidth on the error probability for hybrid circuits with different number of ports are derived and discussed. Also, the effects of the frequency offset are considere
Exact performance evaluation of heterodyne coherent optical systems with FSK modulation
No full textThe authors report the analysis and the performance evaluation of a coherent optical receiver with binary frequency shift keying (FSK) modulation. The receiver makes use of envelope detection with two branches for the two transmitted frequencies. The analysis is performed also in the presence of a low-pass post-detection filter. The analysis accounts for the effect of phase noise, modeled as a Brownian motion, which strongly affects the system performance. The numerical evaluation is carried out by the use of Gaussian quadrature rules and is based on previous results on the moment characterization of the phase nois
Exact performance evaluation of lightwave systems with optical preamplifier
No full textIn this paper the performances of a direct-detection receiver with optical doped fiber preamplifier are investigated. All the sources which contribute to the global noise are taken into account, namely the shot noise, the excess noise due to the randomness of the gain, the amplified spontaneous emission (ASE) noise, and finally the thermal noise generated by the receiver. The approach is based on a probabilistic model of the amplifier that enables us to give the complete statistics of the noises. Comparisons with results previously obtained by different methods are presented. The effects of the amplifier gain, the spontaneous emission factor, the optical bandwidth, and the thermal noise on the error probability are examined and discussed
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
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
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