1,721,005 research outputs found
Dynamical diffraction of guided electromagnetic waves by two-dimensional periodic dielectric gratings
No full textThe properties connected to the propagation of electromagnetic waves in rectangular waveguides loaded by periodic dielectric gratings have been treated by extending the theory of dynamical scattering by perfect atomic crystals. The theoretical formulation has been developed for the TE10 excitation of the periodic load, but it remains valid in the same form when a TE(n0) (n > 1) excitation takes place. The analysis was first developed for two-dimensional periodicities, and later the results were applied to one-dimensional periodicities without modifications to the formalism. The generalization of Bragg's law to guided propagation has been obtained, and the conditions and limits of applicability of the theory have been discussed. It has been shown that, when a small permittivity contrast between supporting and loaded material is present, the electromagnetic field can be approximated by either one or two waves only. The expressions of the electromagnetic field supported by the periodic medium and the dispersion relaion have been obtained. The diffraction pattern, the deviation from the generalized Bragg law, the width of the total reflection range, and the extinction length have been evaluated for a regular array of cylindrical holes on a polyethylene support. We have reported the results of an experiment carried out to verify the accuracy of the theory. The comparison between theoretical and experimental results has shown excellent agreement
Dynamical diffraction of microwaves by periodic dielectric media
No full textThe properties of microwave diffraction by periodic dielectric media have been treated by extending the theory of dynamical scattering by perfect atomic crystals. The expressions of the form factor and of the structure factor have been obtained, and the conditions and limits of applicability of the two-wave approximation have been discussed. The diffraction pattern in Bragg geometry, the extinction length, the deviation from the Bragg law, and the width of the total reflection range have been evaluated for a two-dimensional periodic medium consisting of a regular array of cylindrical holes made on a polyethylene plane slab. We have reported the results of the experiment carried out to verify the accuracy of the theory. The comparison between theoretical and experimental results has shown good agreement
Investigation by X-ray diffraction of phase transitions of the mesomorphic polymer poly(p-biphenylyl acrylate)
No full textChiral liquid crystal polymers. 7. Structural characterization of thermotropic polyesters based on 4,4'-(terephthaloyldioxy)dibenzoic acid and 1,3-butanediol
No full textX-ray analysis of chiral thermotropic liquid crystal copolyesters based on linear and nonlinear aromatic ester triads
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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
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