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Abrupt transition coupling between two five-layered symmetric slab waveguides
No full textThe abrupt transition coupling between two five-layered symmetric slab waveguides is analyzed by means of an integral equation appropriate for the boundary-value problem. A complete set of modes is employed to describe the fields inside both waveguides, and the integral equation is solved by a Neumann-series iterative procedure giving highly accurate results, especially in the case of small difference (~ 1%) between the refractive indices of the core and cladding regions. The reflection and coupling coefficients of the guided waves as well as the total power of the radiation modes are computed. Numerical results are presented for several coupling geometries, and misalignment losses are also calculated. Finally, a comparison with relevant previously published papers is made. © 1998 Optical Society of America
Radiation Characteristics of a Semi-Infinite Fiber Waveguide for the Case of Transverse Magnetic Waves
No full textWe deal with the scattering phenomenon from an abruptly ended fiber waveguide by means of an integral equation appropriate for the boundary-value problem of the transverse magnetic (TM) waves. This equation is solved by applying an iterative procedure, which converges very fast, especially when the weak guidance condition is valid. The transverse electric-field distribution at the terminal plane, the reflection coefficient of the first TM guided mode, and the far-field radiation pattern are computed. Several numerical computations are performed and presented for various cases of abruptly ended fiber waveguides. The contribution of the radiation modes of the fiber waveguide to the electric-field distribution is estimated and special attention is given to the rotation of the far-field radiation pattern
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Radiation modes of a five-layer symmetric slab waveguide
No full textThe radiation modes of a five-layered symmetric slab waveguide are treated in detail. Since the slab is assumed to be infinitely extended in the yz plane, all field quantities are considered to be independent of y. The analysis is based on modal expansion formulation and the modes can be classified as TE and TM as well as even and odd ones. Applying the boundary conditions at interfaces, the expansion coefficients of the field components are easily calculated. In addition, the normalization factors and the orthogonality properties are determined by deriving appropriate integrals over the cross section of the waveguide. Finally, the validity of the orthogonality relations between the radiation modes and the guided ones, which propagate in such a waveguide, is proved explicitly. © 1995 Plenum Publishing Corporation
Radiation properties of a semi-infinite slab waveguide for the case of odd transverse electric guided waves
No full textWe examine the radiation properties of an abruptly ended symmetric slab waveguide for the case of transverse electric (TE) guided modes with odd symmetry of the electric-field distribution by employing the integral equation method. This method converges very fast, especially in the case of small relative difference Δ12 between the refractive indices of the core and cladding regions of the slab waveguide. The electric-field distribution at the terminal plane, the reflection coefficient of the first odd TE guided mode, and the far-field radiation pattern are computed. We present numerical results for several cases of abruptly ended waveguides and we examine the influence of the value of Δ12 on the guided-mode reflectivity, on the electric-field distribution at the terminal plane, as well as on the angle of the maximum value (elevation angle) and on the beamwidth of the far-field radiation pattern
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Geometry induced localization of electrons in quantum pillars
No full textWe investigate the energies and wavefunctions of a structure consisting of one small cubic box centered on top of another larger with a uniform potential inside. This model is a representation of a quantum pillar on a substrate, a nanostructure with potential device applications. We find that the eigenstates are localized in one or the other of the boxes. Those in the large box are very well localized while those in the small are moderately so. Their energy and localization are studied with respect to the ratio of sides of the two boxes and compared with the results obtained with the small box. closed by all sides
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