1,721,087 research outputs found
Dispersive Shock Waves: From Water Waves to Nonlinear Optics
No full textDispersive shock waves are strongly oscillating wave trains that spontaneously form and expand thanks to the action of weak dispersion, which contrasts the tendency, driven by the nonlinearity, to develop a gradient catastrophe. Here we review the basic concepts and recent progresses made in the description of such nonlinear waves, both in terms of experimental results and modelling. In particular, we discuss the formation of dispersive shocks in shallow water, which can be described in terms of Korteweg-de Vries orWhitham nonlocal equations.We contrast such results with those obtained in the field of nonlinear optics, described in terms of local or nonlocal nonlinear Schrödinger equations. Finally we show that a dispersive shock propagating under the action of small perturbations can radiate. A perturbative approach allows for the accurate prediction of the radiated frequencies
Experimental demonstration of modulation instability in dispersion oscillating fiber ring cavity
No full textDerivation of third-order nonlinear susceptibility of thin metal films as a delayed optical response
Full text linkMetals typically have very large optical nonlinearities, whose origin is mainly of thermal character. We model the cubic nonlinearity of thin metal films by means of a delayed response derived from an improved version of the classic two-temperature model. We validate our model by comparison with ultrafast pump-probe experiments on gold films
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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