1,720,998 research outputs found
Self-frequency blueshift of dissipative solitons in silicon-based waveguides
No full textWe analyze the dynamics of dissipative solitons in silicon on insulatorwaveguides embedded in a gain medium. The optical propagation is modeled through a cubicGinzburg-Landau equation for the field envelope coupled with an ordinary differential equation accounting for the generation of free carriers owing to two-photon absorption. Our numerical simulations clearly indicate that dissipative solitons accelerate due to the carrier-induced index change and experience a considerable blueshift, which is mainly hampered by the gain dispersion of the active material. Numerical results are fully explained by analytical predictions based on soliton perturbation theory.</p
Free-carrier-driven spatiotemporal dynamics in amplifying silicon waveguides
Full text linkWe theoretically investigate the free-carrier-induced spatiotemporal dynamics of continuous waves in silicon waveguides embedded in an amplifying medium. Optical propagation is governed by a cubic Ginzburg-Landau equation coupled with an ordinary differential equation accounting for the free-carrier dynamics. We find that, owing to free-carrier dispersion, continuous waves are modulationally unstable in both anomalous and normal dispersion regimes and chaotically generate unstable accelerating pulses.</p
Loss-compensated nonlinear modes and symmetry breaking in amplifying metal-dielectric-metal plasmonic couplers
No full textWe theoretically investigate the propagation of surface plasmon polaritons in an amplifying plasmonic coupler (metal-amplifying dielectric-metal). We study the loss-compensated nonlinear stationary modes of the system by deriving coupled-mode equations for the optical amplitudes, predicting the existence of a mode with broken symmetry for gain values higher than a characteristic threshold. We analyze the stability of symmetric, antisymmetric, and nonsymmetric modes by solving the linearized system for small perturbations and by numerically integrating coupled-mode equations in propagation. We find that, while the antisymmetric mode stays always stable or marginally stable, the stability of symmetric and nonsymmetric modes is more involved.</p
Localization of optical vortices in nonlinear hexagonal multicore fibers
No full textWe investigate the existence and stability of vortexlike collective excitations in nonlinear (NL) multicore fibers (MCFs). We focus on realistic cored and coreless hexagonal MCFs where every core operates in the single-mode regime while displaying polarization degeneracy. We model the propagation dynamics of vortex fields in such MCF structures by NL discrete Schrödinger equations, finding families of homogeneouslike NL vortex fields with constant power distribution over peripheral cores. By analyzing the stability of such collective modes with distinct topological charges against perturbations, we find that they are all unstable. We further investigate the existence and stability of inhomogeneous NL vortex fields, finding only one stable nonspinning localized NL mode with vanishing topological charge in a narrow power range only for cored hexagonal MCFs. Our results are relevant for the manipulation and control of collective excitations in NL MCFs, indicating that self-organization into stable localized collective modes can be exploited in innovative MCF-based communication systems
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
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
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