1,721,012 research outputs found
Effect of porosity of cordierite preforms on microstructure and mechanical strength of co-continuous ceramic composites
No full textA facile method to oxidize carbon nanotubes in controlled flow of oxygen at 350 °C
Full text linkThe functionalization of carbon nanotubes (CNTs) is a very important step in many applications but it is still a very complex and variable task. This work shows an efficient, easily reproducible and optimal method to introduce oxygenated functional groups to CNTs by treating them for 60′ at 350 °C with a mixture of 2% oxygen in argon. The oxidized nanotubes were characterized through FT-IR, Raman and TGA to verify the quality of the oxidation and the lattice integrity of the treated CNTs. The results demonstrate that the treated nanotubes are not damaged even after introducing a significant number of new groups. This methodology could be easily tuned to functionalize other types of graphitic materials
Synergistic Effect of Carbon-Based Reinforcements on the Mechanical Properties of Cement-Based Composites
Full text linkCarbon reinforcements are used to improve the mechanical properties of cement, allowing the preparation of a strengthened and toughened composite. Functionalization through a reaction with acid is necessary to guarantee both a good dispersion in water and a strong interaction with cement. Different functionalized reinforcements improve the mechanical properties of the composites in comparison with pristine cement. The use of a combination of carbon fibers, carbon nanotubes, and graphene nanoplatelets were analyzed in order to verify their synergistic effect. The use of functionalized carbon nanotubes and carbon fibers demonstrates an improvement of 71% in flexural strength and 540% in fracture energy
Dissimilar friction stir welding of AA2198 and AA7475: Effect of solution treatment and aging on the microstructure and mechanical strength
Full text linkA post-weld heat treatment consisting of solution treatment and subsequent aging (STA) is widely applied to aluminum joints fabricated by friction stir welding (FSW) to improve the mechanical strength via precipitation hardening. In this study, aerospace aluminum alloys of AA2198 and AA7475 were FSWed in similar and dissimilar states. Differential scanning calorimetry (DSC) was used to trace the precipitation strengthening during the aging of welded specimens. The post-weld aging procedures were designed based on the DSC outputs. Accordingly, welded sheets were solution treated at 480 °C and 540 °C for 10–90 min, air-cooled and aged at 155 °C and 170 °C for 2–40 h, respectively. Optical micrographs revealed that due to the faster kinetics of the recrystallization, higher homogenizing temperature led to nucleation of the finer grains from highly stress localized points in the stir zone (SZ) and TMAZ by faster growth rate. Higher time and temperature of the solution-treatment eventuated in accumulation of Cu-enriched intermetallic phases in the grain boundaries at SZ and TMAZ of AA7475, attenuation of the grains adhesion and failure of the sample. Hardness test results showed that the hardness increased in AA7475 alloy while decreasing in AA2198 alloy in the as-welded state. Post weld heat treatment enhanced the hardness in AA2198 and reduced it in AA7475. However, it had no significant effect on the grain size
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
Polyvinyl butyral-based composites with carbon nanotubes: Efficient dispersion as a key to high mechanical properties
Full text linkEven if the carbon nanotubes (CNTs) and their derivatives are commonly used as reinforcing phase in composite materials, also in commercial products, their tendency to agglomerate generally determines a scarce dispersion, thus not maximizing the effect due to the second phase. In this article, a perfect dispersion of highly entangled nanotubes was achieved by using a very simple approach: exploiting the dispersing effect of a low-cost polymer, polyvinyl butyral (PVB), coupled with standard ultrasound sonication. Several dispersion approaches were tested in order to develop a consistent and widely applicable dispersion protocol. The tape casting technology was subsequently used to produce 100 to 300 μm thick PVB-matrix composite tapes, reinforced by multiwall CNTs dispersed according to the optimized protocol. Their mechanical properties were evaluated, and a simple model was used to demonstrate that the effective dispersion of CNTs is the key to obtain significantly improved properties
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