1,721,011 research outputs found
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
Nonlinear acousto-optics: improvements in optical spectrum analysis
Get PDFIn this work, the non-linear acousto-optical interaction is studied for the collinear
and the non-collinear cases. First, a non-linear regime of the collinear acoustooptical
interaction is considered with acoustic waves of finite amplitude
considering the acoustic loses in a crystalline acousto-optical cell. The results of
this analysis were confirmed first in a calcium molybdate (CaMoO4) acoustooptical
cell. After this, the results were extrapolated to predict the performances of
a lithium niobate (LiNbO3) acousto-optical cell oriented to the application in
astrophysical spectroscopy near the ultraviolet range. This material, specifically,
was in need of further analysis due to known phenomena within it that could
affect the capabilities of such cell.
Then, the non-collinear acousto-optical interaction is studied for the multiphonon
light scattering in the Bragg regime. This regime allows only two possible cases
of multiphonon light scattering, namely, the two- and three-phonon acoustooptical
interaction. Together with this, a specific degree of freedom for this
acousto-optical interaction is introduced to regulate the acoustic frequency
necessary for the interaction to occur. The multiphonon light scattering was
theoretically analyzed and experimented in two different crystals; calomel
(Hg2Cl2) for the two-phonon interaction and tellurium dioxide (TeO2) for the
three-phonon case.En este trabajo se estudia la interacción acusto-óptica no-lineal para los regímenes
colineal y no-colineal. Primero, un régimen no-lineal de la interacción acustoóptica
colineal está bajo consideración con ondas acústicas de amplitud finita
tomando en cuenta las pérdidas acústicas en una celda acusto-óptica cristalina.
Los resultados de este análisis fueron confirmados primero en una celda acustoóptica
de molibdato de calcio (CaMoO4). Luego de esto, los resultados fueron
extrapolados para predecir el desempeño de una celda acusto-óptica de niobato de
litio (LiNbO3) encaminada a su aplicación en espectroscopía astrofísica cerca del
rango ultravioleta. Este material en particular, necesitó de un análisis más
profundo debido a fenómenos conocidos en él que podrían afectar las capacidades
de una celda de este material.
Después, la interacción acusto-óptica no colineal se estudió para el esparcimiento
multifonón de luz en el régimen de Bragg. Este régimen sólo permite dos posibles
casos, la interacción acusto-óptica de dos y de tres fonones. Junto con esto, un
grado de libertad específico de esta interacción acusto-óptica se introdujo para
regular la frecuencia acústica necesaria para que ocurra la interacción. El
esparcimiento multifonón de luz se analizó teoréticamente en dos cristales
diferentes; cloruro de mercurio (Hg2Cl2) para el caso de la interacción de dos
fonones y dióxido de telurio (TeO2) para el caso de tres fonones
Acousto-optical interaction and its advanced applications
Get PDFIn this this work, the acousto-optical interaction is studied. Since its
inception, in 1922, it has been widely studied and applied. Here, the
development of three advanced application of this branch of physics is
considered.
First, is analyzed the potential use of an acousto-optical cell for be included as
a dynamic diffraction grating, in order to improve in many ways the actual
static gratings used, in the Guillermo Haro astrophysical observatory. For
this, it was necessary to estimate the performance of several acousto-optical
materials available today.
Second, a specific mechanism of the acousto-optical nonlinearity is studied to
regulate the performance of the collinear acousto-optical filter. The theory of
this phenomenon is analyzed and confirmed experimentally using and
advanced filter based on calcium molybdate (CaMoO 4 ) single-crystal. The
transmission function of electronically tunable filter exhibits a dependence on
the applied acoustic power density, and as a result, it is possible to squeeze
the transmission function at the cost of decreasing the device efficiency
partially.
And at final, the triple product processor is studied for its potential
application in spectroscopy designed for 3-inch optics and analyzing all the
materials needed for its realization. The need to use 3-inch optics is mainly
oriented to exploit an acousto-optical cells with large aperture windows to get
a large time-bandwidth product
Some aspects of acousto-optical spectrum analysis
Get PDFAcousto-optics is the branch of physics devoted to the study of the effects of
the interaction between acoustic and optical waves. For signal analysis systems,
that allow the interaction of sound and light waves, acousto-optical devices are
needed. The advent of lasers made possible, among other things, the practical
use of acousto-optical effect to modulate light for signal transmission and manipulation. It is necessary to characterize the materials, in which the acousto-optical
interaction will be hold, for the proper functioning of these systems.
To determine the usefulness of acousto-optical devices it is necessary to understand the properties of acousto-optical materials, which are desirable to make
acousto-optical devices. This thesis presents the study of two acousto-optical cells
for optical signal and radio signal analysis, namely calcium molybdate and KRS-5
single crystals, respectively.La acusto-óptica es la rama de la Física que estudia los efectos de la interacción entre ondas acústicas y ópticas. Existen sistemas destinados al análisis de
señales, tales sistemas necesitan dispositivos que permitan la interacción de ondas
de sonido y de luz. La llegada del láser a principios de la década de los años 60
hizo posible, entre otras cosas, el uso del efecto acusto-óptico para modular la luz
en casos de transmisión de señales. Sin embargo, para el correcto funcionamiento
de dichos sistemas es necesario caracterizar los materiales en los cuales se llevará
a cabo la interacción acusto-óptica.
Es necesario analizar los materiales, con los que se desea fabricar dispositivos
acusto ópticos, para determinar si serán útiles en el análisis de señales. En este
trabajo se presenta el estudio realizado sobre dos celdas acusto-ópticas destinadas
al análisis de señales ópticas y señales de radio, dichas celdas acusto-ópticas están
fabricadas de molibdato de calcio y KRS-5, respectivament
Application of acousto-optical interactions in crystals to performing the spectrum analysis of radio-signals and shaping the multi-wave coupled states
Get PDFAcoustic waves were studied extensively in the 19th century; surface acoustic waves were first described by Lord Rayleigh in 1885 as they pertained to earthquakes [1]. The acousto-optical effect was first studied or predicted by Brillouin in 1922 [2]. Physically, this effect describes the interaction between light and sound waves. This interaction produces the diffraction of light from the medium which was first perturbed by an acoustic wave. Later, in 1932 Debye and Sears [3] and Lucas and Biquard [4] verified it experimentally when optical sources of sufficiently high coherence become available. Surprisingly, a large number of diffracted orders were observed, symmetrically spaced about the undiffracted beam. Brillouin proposed that this effect was due to rescattering of light from the acoustic beam, it was quantified until a theoretical treatment using Feynman diagrams was presented in 1980 by Korpel and Poon [5]. This established a rigorous physical description of the multiple scattering of plane waves; a similar concept had been employed in a mathematical formalism first presented in 1960 [6].
The presence of multiple diffracted orders was first explained in a classic series of papers by Raman and Nath in 1935-1936 [7], who modeled the sound column as a phase grating acting in transmission to give rise to many diffracted orders by interference. They also considered the problem of oblique and arbitrary angle of incidence of light on the acoustic beam. Debye and Sears [3], who also derived a criteria for single- and multiple-order diffraction phenomena (Debye-Sears ratio)
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
- …
