1,720,998 research outputs found
Neutron diffraction from macroscopic objects and transverse coherence of the wavefunction: The Fresnel zone plates
No full textA new high resolution (400 nm) Fresnel Zone Plate (ZP) of 1 mm diameter has been designed and produced in order to accurately measure its spatial resolution and efficiency. This experiment is an extension of the previous tests performed to measure the efficiency of these devices. The measurements were carried out on the diffractometer Morpheus at PSI using a new ZP designed to obtain a small focal length of 0.833 m at 4.7 (A) over circle. In this experiment a 0.8 mm edge square neutron source at 4.7 (A) over circle was demagnified by the ZP by a factor 2 down to about 0.4 mm at 1.24 m distance from the ZP. With this configuration, using a Gd knife edge, we determined the transverse profile of the image with a spatial accuracy of 0.01 mm. In addition an appropriate configuration was used to measure the efficiency of the ZP, which was equal to 0.28 +/- 0.02, to be compared to 0.325, that is the ideal value at 4.7 (A) over circle. The result for the ZP resolution suggests that the image has a broadening in the range of 0.01 mm, corresponding to an effective wave front coherence over a distance greater than 50 mu m, to be compared to some 0.2 mu m as deduced from the indetermination principle, according to the beam divergence. Numerical simulations of the ZP are performed with a partially coherent wave front to show the effect of the phase variation on the intensity at different positions
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
Fresnel zone plates as neutron optical elements for neutron imaging
No full textWe present the operation of a matrix of Fresnel zone plates consisting of 900 individual zone plates. The individual efficiency of the zone plate lenses is close to 30% for lambda = 13.7 angstrom. We discuss the use of such a matrix as an optical element for performing high-resolution neutron imaging (at a sub 50 mu m resolution)
Zone plate for thermal neutron focusing: design, fabrication and first experimental tests
No full textThe aim of this paper is to present the design, the fabrication and the first experimental tests of neutrons focussing for our fabricated phase zone plates. Two different diffractive optical elements will be presented in the article. One is a 5 mm zone plate with a resolution of 400 nm and the other is a matrix (30 x 30) different Zone Plates, each one 300 mum in diameter, with an outermost zone width of 1 micron. A 4.8 mum thick natural nickel was used as phase shifter. This translates in High Aspect Ratios of similar to12 and similar to5, respectively, for these two devices. A series of test measurements carried out on a monochromatic neutrons beam have successfully demonstrated the ability of zone plates in focussing neutrons, thus opening a wide range of possible applications
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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