1,720,955 research outputs found
Organic protic ionics based on Nitrilo(trimethylenephosphonic acid) as water-free, proton-conducting materials
No full textWe produced two solid protic ionics by stoichiometric acid-base reaction between Nonafluorobutanesulfonic or p-Toluenesulfonic acid with Nitrilotri(methylenephosphonic acid). The latter behaves as a Bronsted base by means of the nucleophilic nitrogen atom which captures the proton from the Nonafluorobutanesulfonic or p-Toluenesulfonic acid. Moreover, the Nitrilotri(methylenephosphonic acid) moiety possesses six POH terminating units. 1H MAS NMR evidenced hydrogen-bonding activity of these units, which enables proton transport through the lattice by a hopping-site mechanism. Homogeneous, transparent and mechanically and thermally robust disks from these materials were obtained by sintering the powders under mild pressure and temperature. We showed, using electrochemical impedance spectroscopy, that these protic ionics possess good proton conductivity, in excess of 10–2 –1 cm–1, under fully anhydrous conditions at 190 °C. As such, these materials appear potentially attractive for application in high-temperature electrochemical devices, such as polymer electrolyte fuel cells and water electrolyzers operating at elevated temperature, typically above 130 °C and up to 200 °C for fuel cells. The proton-transport mechanism is also discussed in the light of the NMR- and impedance-spectroscopy results
Water-free, Proton-Conducting Hybrid Materials for Elevated-Temperature Electrochemical Systems
No full textBy reacting TiCl4 with nitrilo tris(methylenphosphonic acid) (NTMPA) in water solution, a titanium complex gel (Ti-NTMPA) has been prepared. After drying, this gel was powdered and mixed with benzimidazole. The resulting hybrid material, which is insoluble in water and thermally stable up to at least 210 °C, possesses proton conductivity on the order of 10-2 Ω-1 cm-1 in fully anhydrous conditions. Due to these characteristics, such Ti-NTMPA/benzimidazole hybrid may be considered for application as a proton conductor in fuel cells or water electrolyzers operating under elevated-temperature and low-humidity conditions. X-ray diffraction, thermogravimetric analysis, and FT-IR spectroscopy show the presence of hydrogen-bonding interaction between Ti-NTMPA and benzimidazole in the hybrid. It appears that the Ti-NTMPA/benzimidazole system forms a solid protic ionic with the "free" (not coordinated to Ti) phosphonic acid moieties and benzimidazole acting, respectively, as Brà ̧nsted acid and base. In this way the imidazolic rings can vehiculate the protons provided by the phosphonic groups, thereby conferring hopping-site proton conduction upon this hybrid material even in the absence of water. This work provides proof of the above concepts, thereby demonstrating a general paradigm to design a whole class of hybrid materials with effective water-free proton conductivity. (Figure Presented)
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
Development of Functional Materials For Electrochemical Systems, Particularly Fuel Cells
No full textThe main objective of present thesis is to develop novel and inexpensive solid polymeric electrolytes capable of conducting protons at intermediate temperatures and anhydrous conditions. Such materials are interesting in view of potential applications for a variety of emerging electrochemical technologies such as high-temperature-polymer-electrolyte-membrane fuel cells (HT-PEMFC).
Polymer electrolytes are prepared based on proper acid-base interactions between host polymers and guest molecules as an effective route to distribute modifier within the matrix structure. In anhydrous condition protons hop from site to site in a dense hydrogen bonding network formed among amphoteric jumping sites (Grotthhus mechanism). According to amphoteric nature, these jumping sites can be simply divided into two main categories: amine based- and phosphonic based sites. Solid electrolytes of both categories are prepared.
All samples are systematically characterized as to morphological, thermal and structural properties. IR spectroscopy and X-ray diffraction (XRD) are applied to reveal any considerable structural interactions between functional groups. By means of thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), important information is collected on thermal stabilities and glass transition temperatures (Tg) of composite membranes. Proton conductivity is investigated by means of electrochemical impedance spectroscopy (EIS), which allows determination of proton conductivity and the activation energy of proton transfer in anhydrous state. An extended investigation is carried out in order to establish a correlation between proton conductivity and the content of modifiers in prepared materials. Additionally, compositional information of material is obtained from solid state nuclear magnetic resonance (SSNMR).
Based on preparation and processing conditions, following important values are achieved: I. All composite membranes were thermally stable within intermediate temperature range (100-200 °C), II. Proton conductivities in excess of 0.01 Ω-1 cm-1 at 190 °C and anhydrous condition are obtained, III. For the first time, positive effect of phosphonic condensation reaction on proton conductivity is reported and IV. Phosphonic groups and aromatic amines are recommended as the most efficient proton conductive functional groups for intermediate temperatures applications
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