1,721,006 research outputs found
Influence of Al(2)O(3) nanoparticles on the thermal stability of ultra-fine grained copper prepared by high pressure torsion
No full textUltra-fine grained (UFG) Cu (grain size 80 nm) containing 0.5 wt.% Al(2)O(3) nanoparticles (size 20nm) was prepared by high pressure torsion (HPT). Positron lifetime spectroscopy was employed to characterize the microstructure of this material, especially with respect to types and concentration of lattice defects. The evolution of microstructure with increasing temperature was studied by positron lifetime spectroscopy and X-ray diffraction measurements. The thermal stability of the Cu + 0.5 wt.% Al(2)O(3) nanocomposite was compared with that of pure UFG Cu prepared by the same technique. The processes taking place during thermal recovery of the initial nanoscale structure in both studied materials are described
Positron-lifetime investigation of thermal stability of ultra-fine grained nickel
No full textThermal stability of ultra-fine grained (UFG) nickel (mean grain size 114 nm) prepared by high pressure torsion was studied by means of positron-lifetime spectroscopy (PLS) combined with TEM. The experimental results obtained by PLS are interpreted using the diffusion trapping model, which allows for determination of important physical parameters characterizing the specimens. The microstructure of the material studied is strongly inhomogeneous. The grain interiors with low dislocation density are separated by distorted regions with high numbers of dislocations. We have found that positrons are trapped at dislocations inside the distorted regions and in the microvoids situated inside the grains. Structure evolution with increasing temperature was studied in details using isochronal annealing of the specimen. We have found that recovery of the UFG structure involves the abnormal grain growth followed by further recrystallization in the whole volume of samples. It was shown that PLS is sensitive to structure changes, caused by the magnetostriction phenomenon
Dark Counts in Superconducting Single-photon NbN/NiCu Detectors
No full textNanostripes of hybrid superconductor/ferromagnetic (S/F) NbN/NiCu bilayers and pure superconducting NbN nanostripes have been investigated in dark count experiments. Presence of a ferromagnetic layer influences the superconducting properties of the S/F bilayer, such as the critical current density and the transient photoresponse. The observed significant decrease of the dark-count rate is discussed in terms of vortex-related fluctuation models to shed more light in the intriguing question of the basic mechanism responsible for dark counts in superconducting nanostripe single photon detectors
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
Hydrogen-induced defects in niobium studied by positron annihilation
No full textChanges of the defect structure of niobium induced by hydrogen loading are presented in this work. It was found that annealing of virgin bulk Nb (99.9%) at 1000degreesC for 1h leads to a complete recovery of defects. Subsequently, the defect-free samples were step-by-step electrochemically loaded with hydrogen up to x(H) - 0.06 [H/Nb atom ratio], i.e. in the alpha-phase region, where the Nb-H system represents a single-phase solid solution. The evolution of the microstructure with increasing hydrogen concentration was studied by X-ray diffraction and two complementary techniques of positron annihilation spectroscopy (PAS), namely positron lifetime spectroscopy and slow positron implantation spectroscopy with measurement of Doppler broadening. It was found that new defects were created due to hydrogen loading. The concentration of these hydrogen-induced defects increases with increasing hydrogen concentration. A comparison of PAS results with theoretical calculations revealed that complexes consisting of a vacancy, surrounded likely by four hydrogen atoms, were introduced into the samples due to hydrogen loading
Hydrogen-induced defects in niobium studied by positron annihilation
No full textChanges of the defect structure of niobium induced by hydrogen loading are presented in this work. It was found that annealing of virgin bulk Nb (99.9%) at 1000degreesC for 1h leads to a complete recovery of defects. Subsequently, the defect-free samples were step-by-step electrochemically loaded with hydrogen up to x(H) - 0.06 [H/Nb atom ratio], i.e. in the alpha-phase region, where the Nb-H system represents a single-phase solid solution. The evolution of the microstructure with increasing hydrogen concentration was studied by X-ray diffraction and two complementary techniques of positron annihilation spectroscopy (PAS), namely positron lifetime spectroscopy and slow positron implantation spectroscopy with measurement of Doppler broadening. It was found that new defects were created due to hydrogen loading. The concentration of these hydrogen-induced defects increases with increasing hydrogen concentration. A comparison of PAS results with theoretical calculations revealed that complexes consisting of a vacancy, surrounded likely by four hydrogen atoms, were introduced into the samples due to hydrogen loading
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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