1,720,965 research outputs found
Control of Interfacial Reactivity Between ZrB2 and Ni-Based Brazing Alloys
Full text linkTransition metals diborides (Ti,Zr,Hf)B2 play a key role in applications where stability at extremely high
temperatures and damage tolerance are required; however, much research has still to be done to optimize
the joining of these materials to themselves or to other high-temperature materials. In this study, the
reactivity at the solid-liquid interface between ZrB2 ceramics and Ni-based brazing alloys has been
addressed; it is shown how the reactivity and the dissolution of the solid phase can be controlled and even
suppressed by adjusting the brazing alloy composition on the basis of thermodynamic calculations. Wetting
experiments on ZrB2 ceramics by Ni, Ni-B 17 at.%, and Ni-B 50 at.% were performed at 1500 and 1200 C
by the sessile drop technique. The obtained interfaces were characterized by optical microscopy and SEMEDS,
and interpreted by means of the ad hoc-calculated B-Ni-Zr ternary diagram. A correlation among
microstructures, substrate dissolution, shape of the drops, spreading kinetics, and the phase diagram was
found. The effect on the interfacial reactivity of Si3Ni4 used as a sintering aid and issues related to Si
diffusion into the brazing alloy are discussed as well
Experimental investigations and thermodynamic modeling in the ZrB2-Ni section of the B-Ni-Zr system
No full textAbstract
An investigation of melting equilibria in the Ni-rich part of the Bsingle bondNisingle bondZr system was carried out by means of a combined experimental and computational approach, in order to improve the interpretation of wetting experiments of Bsingle bondNi alloys on ZrB2 substrates. Several samples along the Nisingle bondZrB2 vertical section, close to the Zr2(Ni21−xZrx)B6 ternary phase, were prepared by arc-melting the pure metals; the samples were thoroughly studied by means of powder X-ray diffraction and SEM–EDS, and then analyzed by DTA in order to obtain their transition temperatures. The results were used to improve the CALPHAD thermodynamic modeling of the Bsingle bondNisingle bondZr system. A solubility range of the ternary phase between x = 0.14 and x = 0.68 was detected, due to the mixing of Zr and Ni in the 4a crystallographic site
Isothermal solid-liquid transitions in the (Ni,B)/ZrB2 system as revealed by sessile drop experiments
No full textIn the framework of joining processes of Ultra High Temperature Ceramics (UHTCs), sessile drop experiments were performed in the Ni-B/ZrB2 system in the range 1110°≤T≤1200°C. They show that, at temperatures between 1110 and 1150°C, isothermal solid-liquid transitions occur in a sequence; while in fact at T≥1200°C the drop melts without any further phase transition, at lower temperatures complete melting is followed by a solidification stage and final re-melting. This complex behaviour, which can be very relevant when utilizing Ni-B alloys for brazing processes (e.g. by the Transient Liquid Phase Bonding technique), is successfully interpreted on the basis of the complete B-Ni-Zr phase diagram newly computed by CALPHAD: isothermal sections, calculated between 1110 and 1150°C, show that the composition of the drop enters, crosses and leaves the primary solidification region of the Zr2Ni21B6 ternary compound. The use of thermodynamic modelling for the explanation of experimental data sets a link between wetting and joining experiments, and phase diagrams assessment
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
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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