1,720,961 research outputs found
Ultra high temperature high-entropy borides: effect of graphite addition on oxides removal and densification behaviour
Full text linkThe introduction of 0.5–1.0 wt.% graphite to the powders prepared by Self-propagating High-temperature Synthesis (SHS) is found to be highly beneficial for the removal of oxide impurities (from 2.7-8.8 wt.% to 0.2–0.5 wt.%) during spark plasma sintering (1950°C/20 min, 20 MPa) of (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B2 and (Hf0.2Mo0.2Ta0.2Zr0.2Ti0.2)B2 ceramics. Concurrently, the consolidation level achieved is enhanced from about 92.5% and 88%, respectively, to values exceeding 97%. While a further increase of graphite slightly improves samples densification, final products become progressively richer of the unreacted carbon.
It is assumed that graphite plays a double role during SPS, e.g. not only as a reactant during the carbothermal reduction of oxides contaminant, but also as lubricating agent for the powder particles. The latter phenomenon is likely the main responsible for the densification improvement when 3 wt.% or larger amounts of additive are used. Another positive effect is the crystallite size refinement of the high-entropy phases with the progressive abatement of oxides, to confirm that their presence promotes grain coarsening during the sintering process.ARCHIMEDES project sponsored by Regione Autonoma della Sardegna (Italy) - Fondo di Sviluppo e Coesione (FSC) 2014–2020 (Cod. RAS: RASSR88309, Cod. CUP: F76C18000980002). One of the authors (S.B.) performed his activity in the framework of the International PhD in Innovation Sciences and Technologies at the University of Cagliari, Italy. One of us (G.C.) acknowledges the results obtained in this manuscript as quite important for the “Ithermal” and “Generazione E” projects, sponsored by Sardegna Ricerche, Italy (Cod. CUP: F21I18000130006) and by the Italian Ministry of Education, University and Research, Italy (Cod. CUP: B96G18000560005
Optical Properties of Bulk High-Entropy Diborides for Solar Energy Applications
No full textSo far, the studies regarding the innovative High-Entropy Borides (HEBs), which belong to the more general class of Ultra-high temperature ceramics (UHTCs), have been entirely confined to their fabrication or characterization from the microstructural, mechanical and oxidation resistance viewpoints.
In this work, the optical properties of two members of HEBs, i.e. (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 and (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, are evaluated for the first time to assess their possible utilization in the thermal solar energy field. The bulk samples (96.5 and 97.4% dense, respectively) are obtained as single-phase products by Spark Plasma Sintering (1950 °C/20 min/20 MPa) starting from powders previously synthesized by Self-propagating High-temperature Synthesis (SHS). The optical characterization, whose results are discussed by comparing HEBs to the individual borides, shows that they are characterized by intrinsic spectral selectivity and low thermal emittance, resulting therefore interesting for high-temperature solar absorbers applications
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Processing and characterization of Ultra High Temperature High‐Entropy (Ti0.2Zr0.2Hf0.2Mo0.2W0.2)B2-based Ceramics: Effect of W granulometry, graphite, and SiC addition
Full text linkA highly dense and single phase (Ti0.2Zr0.2Hf0.2Mo0.2W0.2)B2 ceramic product is obtained in this work at 1950°C (20 min, 20 MPa) by Spark Plasma Sintering (SPS) from powders prepared by Self-propagating High-temperature Synthesis (SHS). The formation of the (W,Mo)B2 secondary phase is avoided using fine W precursors and adding 1 wt% graphite to the SHS powders before SPS. Kinetic limitations responsible for hindering the synthesis of the high entropy boride are correspondingly eliminated. The resulting 98.5 % dense sample exhibits a homogeneous microstructure, with Vickers hardness of 26.8 GPa. The introduction of 20 vol% SiC produces an increase of the KIC values from 2.32 to 5.11 MPa m1/2. Very relevant is that the volatilization of Mo- and W-oxides occurring during sample oxidation at high temperature, which leads to its rapid degradation with the formation of a very porous oxide scale, can be strongly inhibited by the silicate phases generated in the composite ceramic
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