1,721,195 research outputs found
Modulation Instability, Four-Wave Mixing and their Applications
Full text linkThis chapter presents an overview of the analysis of the nonlinear dynamics of Modulation instability (MI) by means of a simple three-mode truncation. It discusses how the coupling between two polarization modes in a birefringent optical fiber may extend the domain of MI to the normal dispersion regime. It also briefly discusses the case where the MI is induced by two pumps and occurs on top of multiple four-wave mixing. The chapter reviews the linear stability analysis of a plane wave background solution of the nonlinear Schrodinger (NLS). It generalizes the model to include pump depletion and describes a truncated three-wave model for the pump and its immediate sidebands. The chapter briefly considers an application of the four-wave mixing process in passive fiber cavities. This application relies on the fact that the growth rate of the cavity MI is purely real and can give rise to stationary periodic patterns and temporal cavity solitons
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
Multiphoton-absorption-excited up-conversion luminescence in optical fibers
Full text linkWe experimentally demonstrate a previously unforeseen nonlinear effect in optical fibers: up-conversion luminescence generation excited by multiphoton absorption of femtosecond infrared pulses. We directly estimate the average number of photons involved in the up-conversion process, by varying the wavelength of the pump source. We highlight the role of nonbridging oxygen hole centers and oxygen-deficient center defects and directly compare the intensity of side-scattered luminescence with numerical simulations of pulse propagation
Femtosecond nonlinear losses in multimode optical fibers
Full text linkMultimode optical fibers are attracting a growing interest for their capability to transport high-power laser beams, coupled with novel nonlinear optics-based applications. However, optical fiber breakdown occurs when beam intensities exceed a certain critical value. Optical breakdown associated with irreversible modifications of the refractive index, triggered by multiphoton absorption, has been largely exploited for fiber material micro- structuration. Here we show that, for light beam intensities slightly below the breakdown threshold, nonlinear absorption strongly affects the dynamics of a propagating beam as well. We experimentally analyze this subthresh- old regime and highlight the key role played by spatial self-imaging in graded-index fibers for enhancing non- linear optical losses. We characterize the nonlinear power transmission properties of multimode fibers for femtosecond pulses propagating in the near-infrared spectral range. We show that an effective N-photon absorp- tion analytical model is able to describe the experimental data well
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
Vector Solitons and XPM-Induced Polarization Scattering in Dispersion Managed Fiber Systems
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