1,721,014 research outputs found
Graphene oxide membranes on ceramic hollow fibers - Microstructural stability and nanofiltration performance
No full textGraphene oxide (GO) membranes have demonstrated great potential in liquid filtration. With the aim of real applications, GO membranes in a hollow fiber shape are of particular interest because of the high-efficiency and easy-assembly features at the module level. We report here that GO membranes on ceramic hollow fiber substrates are unstable at the dry state, mainly due to the drying-related shrinkage. And we demonstrate that these GO hollow fiber membranes can be stabilized by keeping them wet after initial controlled formation of the membranes. The GO hollow fiber membranes show higher permeation fluxes of acetone and methanol than most commercial membranes, and reject molecules larger than 300. Da, showing a great potential in the use of value-added organic solvent nanofiltration processes.</p
Fabrication of graphene-covered micro-tubes for process intensification
No full textGraphene is known for its high surface-area-to-mass ratio. However, for using graphene in engineering processes such as catalytic reactors or heat exchangers, a high surface-area-to-volume ratio is essential. Currently, graphene is only prepared in sheet form, which limits its surface-area-to-volume ratio to around 200 m2 m−3. Herein, a technique based on chemical vapor deposition (CVD) to realize graphene on a micro-tubular substrate to not only substantially increase its surface-area-to-volume ratio to a value over 2000 m2 m−3 but also to eliminate the maldistribution of flows commonly unavoidable in flat-sheet configurations is proposed and demonstrated. This approach uses a dual-layer micro-tubular substrate fabricated by a phase-inversion technique. In the substrate, a thin copper outer layer is used to enable the CVD growth of graphene, and an inner Cu–Fe layer is adopted to provide a strong mechanical support. This approach is feasible to produce graphene with a very high surface-area-to-volume ratio for possible applications in catalytic reactors or heat exchangers, although problems such as inter-diffusion between the two metal layers and defects in graphene need to be addressed. To the best of our knowledge, this study is the first attempt to prepare graphene with high surface-area-to-volume ratios by a CVD route.</p
Effect of substrate surface defects on the Fe film morphology deposited on graphite
No full textWe have studied Fe films on Ar+ ion sputtered highly oriented pyrolitic graphite (HOPG) using scanning tunnelling microscopy
(STM). The adsorbed Fe atoms form nanoparticles uniformly distributed over the substrate surface with narrow size distribution. Comparing
these data with Fe deposited on non-sputtered HOPG indicates the role of substrate defects, acting as nucleation sites, on the
overall film structure. However, the shape and size of individual defects do not seem to influence the shape of the nanoparticles. The correlation between the Fe film morphology and the sputtered substrate morphology is discussed taking into account the different capturing properties of sputtering-induced defects
Dynamic microstructure of graphene oxide membranes and the permeation flux
Full text linkGraphene oxide (GO) membranes have been reported to be a promising separation barrier that can retain small molecules and multi-valent salts because of the well-defined interlayer space between GO flakes. However, while some studies suggested fast liquid transport through the extremely tortuous transport path, contradictory observations (e.g. low permeation flux) have also been obtained. This paper revealed the dynamic microstructure of GO membranes, which affected the membrane performance significantly. We showed that all GO membranes prepared by varied methods and on different substrates presented a severe reduction in water permeability during filtration, due to the compaction of their original loose microstructure. The water flux could drop continuously from tens of LMH bar−1 to <0.1 LMH bar−1 after more than ten hours. This result demonstrated that the structure of GO membranes prepared by current approaches was far from the ideal laminar structure. The high permeability of GO membranes observed could be contributed by the disordered membrane microstructure. Therefore, the transport mechanisms assuming perfect laminar structure in GO membranes, and the fast transport hypothesis may not fully describe the water transport in GO membranes. Interestingly, the loosely packed microstructure of GO membranes was also found reversible depending on the storage conditions
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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