1,720,958 research outputs found
Bidirectional Superionic Conduction in Surface-Engineered 2D Hexagonal Boron Nitrides
No full textWe designed functionalized hexagonal boron nitride (FhBN) nanoflakes with high proton conductivity in both in- and through-plane directions as next generation polymer electrolyte membranes (PEMs) for energy storage and conversion systems. The synthesis and functionalization of hBN nanoflakes with sulfonic acid (SA) groups are obtained by one-step and in situ liquid-phase exfoliation with excellent dispersibility and stability over a period of three months. The physico/chemical properties of FhBN nanoflakes were investigated by different spectroscopic and microscopic characterization, confirming chemical interactions between hBN lattice and SA groups. High concentrations (65 and 75 wt %) of FhBN nanoflakes composed with Nafion solution formed stable FhBN-Nafion nanocomposite PEMs, offering extra proton conduction sites, doubling ion-exchange capacity, and reducing the swelling ratio compared to those of Nafion. Our results demonstrate that both the in-plane and through-plane proton conductivities of FhBN-Nafion PEMs significantly improve under various conditions comparative to that of Nafion. The maximum values of both in- and through-plane conductivities for FhBN75%-Nafion PEM at 80% of humidity and 80 °C are 0.41 and 0.1 S·cm–1, respectively, which are 7 and 14 times higher than those of Nafion. The bidirectional superionic transport in highly concentrated FhBN PEMs is responsible for outstanding properties, useful for electrochemical energy devices
Novel Polymer Electrolyte Nano-Composite Membranes for Fuel Cell Applications
Full text linkFuel cells are electrochemical devices which have been established to lead in the transition to clean energy technology and will become the energy efficient power source of the future. Among all the fuel cell systems, anion exchange membrane fuel cells (AEMFCs) and solid polymer electrolyte membrane fuel cells (PEMFCs) are qualified of achieving high power densities (>l W cm-2) that is required for many applications. Mainly, operation of AEMFCs and PEMFCs at higher temperatures (100-130 °C) would considerably enhance their kinetic performance over the current lower temperature operation technologies. However, due to the type of materials used in each fuel cell there is an associated set of challenges including cost and lifetime which require innovative engineering solutions. One of the important challenges is the fabrication of a cost effective solid electrolyte with high efficiency and durability for both PEMFCs and AEMFCs.
Concerning PEMFCs, the state of the art perfluorosulfonic acid (PFSA) membrane (Dupont Nafion®) has high ionic conductivity and good mechanical and chemical stability. However, its high performance and durability is limited to the operational conditions (e.g., temperature, humidity, and pH). In the case of AEMFCs, the dilemma between high ionic conductivity and physicochemical stability for membranes is an important issue, i.e., maximizing one will minimize the other. Thus, for both PEMFCs and AEMFCs, there is a desire to develop a solid electrolyte material capable of maintaining both ion-conductivity and durability at the same time for various operational conditions, especially elevated temperature conditions.
The main goal of this research project has been the design and fabrication of novel nano-composite electrolyte membranes that fulfills all the aforementioned requirements for a cost effective solid electrolyte membrane in both PEMFCs and AEMFCs. To accomplish this, different approaches have been effectively integrated and improved by understanding and combination of organic chemistry, electrochemistry, chemical engineering and nano-materials science. Hygroscopic nano-fillers made of titanium oxide nanotubes (TiO2-NT) or graphene oxide (GO) nanosheets were first functionalized with highly ion-conductive groups, and then composed with the commercial membrane or another type of polymeric backbone. The latter was morphologically modified to favor higher electrolyte and water absorption capacity. Combining the benefits of a nano-filler with a morphologically modified polymer electrolyte effectively led to the development of a highly ion-conductive, water-retentive, and durable electrolyte membrane. Electrochemical, thermal, physical and chemical properties of proposed membranes were tested, analyzed and reported by various characterization methods. For PEMFC applications, the developed nano-composite PFSA membranes demonstrated significant ion conductivity and single fuel cell performance improvement (~4 times) over commercial PEM at the humidity of 30 % and temperature of 120 °C. For AEMFCs, the selected nano-filler (e.g., GO) composed with morphologically modified polymer (e.g., porous polybenzimidazole) notably increased both performance and durability of AEMs in harsh alkaline conditions. This work offered promising solid electrolyte replacements synthesized by simple and cost effective techniques, able to meet the fuel cell market demands.4 month
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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