1,720,981 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
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Experimental characterization of drift-wave turbulence in the sheared, cylindrical slab
No full texttextPlasma turbulence on a uniform density gradient with unfavorable magnetic curvature is investigated extensively in the Helimak device. The turbulence is strong with density and electrostatic potential fluctuation levels in excess of 40%. Measurements of the dispersion relation, k[subscript z], and k[subscript parallel lines] identify the the fluctuations with drift-waves, which propagate in the poloidal direction at the diamagnetic drift velocity and have a small, but nite parallel wavenumber. A non-zero phase shift between the density and potential fluctuations gives rise to turbulent cross-eld particle transport, which is measured using spectral techniques. In addition, the electrostatic drift-wave fluctuations have a small magnetic component that is driven by the turbulent parallel current [scientific symbols]. An examination of nonlinear processes associated with the plasma turbulence uncovers high levels of intermittency near the plasma edge and long-time persistence of the density fluctuations on the order of the parallel confinement time. An analysis of the bispectrum conrms the existence local and nonlocal three-wave interactions between unstable drift-waves although the turbulent saturation of the density fluctuation spectrum is likely due nonlinear processes acting in the time domain.Physic
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
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Investigation of the shear layer versus the last closed flux surface on TEXT-upgrade
No full texttextThe Texas Experimental Tokamak Upgrade (TEXT-Upgrade) has a set of
41 magnetic sensor coils that are used to determine the magnetic flux surface
configuration of plasma discharges. These reconstructions include the x-points
and the separatrix. These magnetic flux surface reconstructions and simultaneous
data from several Langmuir probes are used to determine the locations of features
in the shear layer, specifically the flux surface where Er=0, and of the last closed
flux surface (LCFS). This is done for several different magnetic configurations.
These results are then compared to results obtained from other tokamaks.Physic
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Spectroscopic measurement of ne and Te profiles using atomic and kinetic models for Argon in the Texas Helimak
Get PDFtextProfiles for electron density and temperature were determined in a self-consistent way using line emission spectroscopy and collisional radiative models for neutral and singly ionized Argon (Ar I and Ar II) in the Texas Helimak. Neutral Argon density profiles were calculated using a kinetic gas model. Electron-impact excitation and Ionization rates were corrected to account for the electron velocity distribution deviating slightly from a true Maxwellian distribution due to inelastic electron-neutral collisions. Results show an electron temperature which roughly agrees with probe diagnostics. This method gives an electron density that is about twice as high, which may be possible from a power balance perspective.Physic
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Electron cyclotron emission measurements of coherent and broadband density fluctuations in the Alcator C-Mod tokamak
Get PDFtextA novel technique for measuring density fluctuations using a heterodyne
ECE radiometer has been developed. Although ECE radiometry is typically
used for electron temperature measurements, the unique viewing geometry of
this system’s quasi-optical antenna has been found to make the detected emission
extremely sensitive to refractive effects under certain conditions. This
sensitivity gives the diagnostic the ability to measure very low levels of density
fluctuations in the core of the Alcator C-Mod tokamak. The refractive
effects have been modeled using ray-tracing methods, allowing estimates of
the density fluctuation magnitude and spatial localization to be obtained.
This new diagnostic technique has been used to observe density fluctuations
in a variety of plasmas. The bulk of the observations have been
during internal transport barriers (ITBs) generated by off-axis ICRF heating
at 5.4 T and 4.5 T toroidal fields. Density fluctuations during pellet injection
into L-mode plasmas have been detected as well. A coherent mode with both
temperature and density oscillations was observed in the 5.4 T ITB plasmas.
Estimates of the magnitude of the temperature and density oscillations, their
radial structure, and some information on their relative phases is discussed.
Broadband fluctuations have been observed in ITBs generated at 4.5 T. Estimates
of their magnitude and localization is presented. Directions for future
work is also discussed.Physic
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
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