1,721,012 research outputs found
A RADIATION CONDITION FOR UNIQUENESS IN A WAVE PROPAGATION PROBLEM FOR 2-D OPEN WAVEGUIDES
Full text linkWe study the uniqueness of solutions of Helmholtz equation for a
problem that concerns wave propagation in waveguides. The classical
radiation condition does not apply to our problem because the
inhomogeneity of the index of refraction extends to infinity in one
direction. Also, because of the presence of a waveguide, some waves
propagate in one direction with different propagation constants and
without decaying in amplitude.
Our main result provides an explicit condition for uniqueness which
takes into account the physically significant components,
corresponding to guided and non-guided waves; this condition reduces
to the classical Sommerfeld-Rellich condition in the relevant cases.
Finally, we also show that our condition is satisfied by a solution,
already present in literature, of the problem under consideration
Optical characterization of Al(X)Ga(1-x)Sb/GaSb epitaxial heterostructures
No full textThe complex refractive index n+ik and the dielectric function e1+ie2 at room temperature
of AlxGa12xSb films with 0<x<0.5, grown by molecular beam epitaxy on a GaSb substrate, were
determined from 0.02 to 6 eV by using the complementary data from fast Fourier transform
far-infrared, dispersive, and ellipsometric spectrometry. The effect of the native oxide was
accounted for and the self-consistency of the optical functions was checked in the framework of the
Kramers–Kronig causality relations. In the restrahlen region the dielectric function was well fitted
by classical Lorentz oscillators; in the transparent region below the fundamental gap E0, the
refractive index was modeled by a Sellmeier dispersion relation, and in the interband region the
dielectric function near the critical points was analyzed through standard line shapes. Interpolating
the fitting parameters or the interband dielectric spectra, it was possible to obtain the optical
functions for any concentration x between 0.0 and 0.5
Thermoreflectance study of the direct optical gap in epitaxial AlxGa1-xSb (x<=0.5)
No full textThermoreflectance spectroscopy was used to precisely determine the direct optical gap EgΓ, as a function of composition and temperature of a series of AlxGa1-xSb layers (0.0<~x<~0.5) epitaxially grown on GaSb. The experimental line shapes were fitted with a critical-point functional form including excitonic effects, to derive the direct gap and broadening parameter values. The relation between EgΓ and x shows a x-dependent bowing, which was compared with previous results and theoretical models, leading to the conclusion that EgΓ(x) curves in AlxGa1-xSb alloys have a cubic polynomial form
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
- …
