1,720,966 research outputs found
Out- and in-diffusion of oxygen in YBa2Cu3O7 - x oxide
No full textIn situ resistance measurements have been used to investigate the oxygen out- and in-diffusion in YBa2Cu3O7 - x oxide. The oxygen content has been measured by nuclear reaction and by weighing; X-ray diffraction has been used to determine the crystalline structure. Polycrystalline sintered material has been used. Out-diffusion has been investigated by heating samples with x = 0.1 in argon atmosphere at fixed temperature and as a function of the time. The resistance increases exponentially and reaches saturation after 5000 min at 550 °C. The oxygen content, after an initial decrease which occurs in the first 100 min, remains constant. Order-disorder transformation can be responsible for the exponential increase in resistance. The in-diffusion has been studied with a material having x = 0.65 heated in oxygen. As a function of the time the resistance curves continuously decrease and present two slopes: fast at the beginning and slow after a certain time. At first the material is tetragonal and non-superconducting. The sharp decrease in resistivity can be attributed to the presence of a thin continuous conductive skin around the grain or, more likely, to a disorder-order transformation activated by the presence of oxygen and involving a large part of the material. © 1989
YBCO-bulk tunnel junctions with cadmium sulphide artificial barriers
No full textTunnel junctions consisting of a YBCO pellet electrode, a cadmium sulphide film as artificial barrier and an indium layer as counterelectrode have been fabricated. Results concerning the effect of the YBCO surface treatment and of the cadmium sulphide film thickness, both on the dV/dI characteristics and the Josephson effect occurrence are reported
Structure determination by electron diffraction and HREM of the incommensurate modulated phase BaxCuO2 (0.67
No full textOxygen in-diffusion processes in tetragonal YBa2Cu3O7-x oxide
No full textIn situ resistance measurements have been used to investigate the oxygen in diffusion in tetragonal YBa2Cu3O7-x oxide. The oxygen content has been measured by nuclear reaction and by weighing; x-ray diffraction has been used to determine the crystalline structure. The polycrystalline bulk material with x=0.65 has been heated in oxygen to 200370°C. As a function of time the resistance curves continuously decrease and present two slopes: fast at the beginning and slow later. At first the material is tetragonal and nonsuperconducting. Complementary weight measurements indicate a significant increase only after a delay, and the oxygen uptake is associated with the slow variation of resistance. The initial slopes of the isothermal resistance versus time curves follow, in an Arrhenius plot, a straight line, suggesting a process with an activation energy of 0.400.05 eV. The sharp decrease in resistivity can be attributed to the presence of a thin continuous conductive skin around the grains or, more likely, to a disorder-order transformation activated by the presence of oxygen and involving a large part of the material. A process having an activation energy of 0.90.1 eV is responsible for the slow variation of the resistance. This is in agreement with published data obtained for oxygen in diffusion in similar conditions. © 1989 The American Physical Society
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
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