1,721,120 research outputs found
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
A broadband photolithographic polariser for millimetre wave applications
No full textCircular polarisers are used to convert linear- into circular-polarisation, and vice versa.This is achieved by introducing a phase-shift of 90° between two orthogonal polarisations passing through the device.These devices can be designed using slabs of birefringent material with the appropriate thicknesses (Quarter-Wave Plates).An interesting alternative solution consists of designing planar metallic grids with sub-wavelength geometries that exhibits different behaviour along two orthogonal axes.In this work we present a broadband dielectrically embedded quasi-optical polariser built using photolithographic techniques.The device was experimentally tested using a Vector Network Analyser working in W-band (75-110 GHz).The presented results are in excellent agreement with finite-element analysis simulations: across a 30% bandwidth the transmission along the two axes and the very flat differential phase-shift are respectively: T C = 0:92, T L= 0:95 and Δ℘LC = 89:3 ± 1:5°
Dielectrically embedded mesh half wave plate beam impact studies
No full textAn alternative solution to classic birefringent Half Wave Plates (HWP), based on the photolithographic techniques, has been recently developed. This new device can offer a very good alternative as a polarisation modulator for future CMB polarisation instruments. However, the systematic effects that this HWP will introduce in the overall instrument need to be investigated. We present a preliminary study of the impact of this dielectrically embedded HWP on the beam shape of a corrugated horn and its performance across the beam. Using a W-band Vector Network Analyser, we measured the co- and cross-polarisation beams of the HWP-horn system and the differential phase-shift introduced by the HWP across the beam. © 2012 SPIE
Effects of quasi-optical components on feed-horn co- And cross-polarisation radiation patterns
No full textAstrophysical experiments dedicated to the study of the Cosmic Microwave Background are in needs of very well defined beam shape in order to get an accurate re-construction of the anisotropies power spectrum. These beams have to be carefully designed, but also properly characterised. Some of these instruments will be located in a cryostat for which filters and windows are necessary, and the effects of these additional optical components on the beam shape need to be taken into account. We present here, measurements of such effects on the co- and cross-polarisation radiation patterns of corrugated horns using a Vector Network Analyser
Metal-mesh achromatic half-wave plate for use at submillimeter wavelengths
No full textA metal-mesh achromatic half-wave plate (HWP) has been designed, manufactured, and tested for potential use in millimeter and submillimeter astronomical instruments. The prototype device presented here is based on a 12-grid Shatrow [IEEE Trans. Antennas Propag. 43,109 (1995)] recipe to operate over the frequency range of 120-180 GHz. Transmission line modeling and finite-element analysis [Ansoft HFSS website: http://www.ansoft.com/hfss/1 were used to optimize the design geometrical parameters in terms of the device transmission, reflection, absorption, phase-shift, and cross-polarization as a function of frequency. The resulting prototype device was constructed and characterized using incoherent radiation from a polarizing Fourier transform spectrometer to explore its frequency and polarization behavior. These measurements are shown to be in excellent agreement with the models. Lists of the achieved HWP performance characteristics are reported. © 2008 Optical Society of America
Experimental performance comparison of two polarimeter techniques for CMB applications
No full textPolarisation modulators are necessary for present and next generations of CMB polarisation experiments. Because of the very faint B-mode signal expected, these instruments have not only to be extremely sensitive but also to have low and well-characterised systematic effects. The beam RF characterisation in the W-band (75-110 GHz) of two polarimeter pixels using the same corrugated horn has been performed using two different modulators: a waveguide rotator modulator and a quasi-optical half-wave plate. Co- and cross-polarisation beam measurements are presented together with the systematic effects introduced by both modulators. © 2012 SPIE
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