1,720,969 research outputs found
New inorganic-organic proton conducting membranes based on Nafion and hydrophobic fluoroalkylated silica nanoparticles
No full textIn this report, a new nanofiller consisting of silica "cores" bearing fluoroalkyl surface functionalities is synthesized and adopted in the preparation of a series of hybrid inorganic-organic proton conducting membranes based on Nation. The hybrid materials are obtained by a solvent-casting procedure and include between 0 and 10 wt.% of nanofiller. The resulting systems are extensively characterized by Thermogravimetry (TG), Modulated Differential Scanning Calorimetry (MDSC) and Dynamic Mechanical Analysis (DMA), showing that the hybrid materials are stable up to 240°C and that their overall thermal and mechanical properties are affected both by the polar groups on the surface of the silica "cores" and by the fluoroalkyl surface functionalities of the nanofiller. The electric properties of the hybrid materials are investigated by broadband dielectric spectroscopy (BDS). It is shown that proton conductivity of the materials is not compromised by the lower water uptake arising from the hydrophobic character of the nanofiller. With respect to a pristine Nation recast membrane, the hybrid material characterized by 5 wt.% of nanofiller, [Nafion/(Si80F)0.7], shows the highest conductivity in all the investigated temperature range (5 <= T <= 155°C). Indeed, [Nafion/(Si80F)0.7] features the lowest water uptake and presents a conductivity of 0.083 S/cm at 135°C. This result is consistent with the good performance of the membrane in single fuel cell tests
'Membrane ibride inorganico-organiche a scambio protonico a base di PTFE e nanofiller a carattere acido per applicazioni in celle a combustibile ad elettrolita polimerico ed elettrolizzatori', brevetto italiano depositato il 17-06-2010
No full textL'invenzione descrive la preparazione di membrane ibride a scambio protonico per applicazione in celle a combustibile ad elettrolita polimerico ed elettrolizzatori di H2O. L’obbiettivo dell’invenzione è la preparazione di membrane a scambio protonico nelle quali la matrice è a base di politetrafluoroetilene (PTFE) mentre i portatori di carica sono forniti da un componente inorganico o ibrido inorganico-organico allo stato solido contenente gruppi funzionali acidi
'Membrane ibride contenenti biossido di titanio drogato con fluoro', brevetto italiano depositato il 09/08/2010
No full textVengono descritte membrane ibride a base di biossido di titanio cristallino, contenente atomi di fluoro all’interno del reticolo cristallino costituito da atomi di titanio e ossigeno, ed avente formula [(TiO2)Fn], dove n varia tra 0.09 e 0.35; tali membrane ibride sono particolarmente adatte per la produzione di celle a combustibile ed elettrolizzatori. Il biossido di titanio in esse contenuto viene prodotto con un processo comprendente i seguenti passaggi:
(a) un minerale di titanio contenente ferro viene fatto reagire con una soluzione acquosa di NH4HF2;
(b) la dispersione acquosa così ottenuta è filtrata con conseguente separazione di un residuo solido ed una soluzione acquosa contenente sali di titanio;
(c) la soluzione acquosa così ottenuta viene sottoposta a idrolisi, detta idrolisi comprendente una prima fase a pH 7,0 - 8,0 ed una seconda fase a pH 9 - 11;
(d) la dispersione acquosa così ottenuta è filtrata ed il residuo solido è sottoposto a piroidrolisi ad una temperatura massima di circa 500° C, preferibilmente di circa 450° C
Platinum-free Carbon Nitride Electrocatalysts for PEMFCs Based on Pd, Co and Ni: Effect of Nitrogen on the Structure and Electrochemical Performance
No full textThis report describes two new synthesis protocols for the preparation of “core-shell” platinum-free electrocatalysts consisting of graphite cores covered by carbon nitride shells embedding the active sites. The resulting systems are characterized by a well-controlled chemical composition with different wt% of nitrogen in their supports. The protocols rely on the thermal decomposition of precursors obtained by networking suitable metal coordination complexes with an organic binder over active carbon nanoparticles. The resulting electrocatalysts showed a higher thermal stability in oxidizing conditions with respect to a reference system. The materials provided a remarkable performance in the oxygen reduction reaction (ORR), even if a lower selectivity towards the desired 4-electron pathway is observed. Membrane electrode assemblies (MEAs) tested in operative conditions with the proposed materials applied at the cathode required a lower mass of noble metal (up to 0.46 g/kW) to achieve the same electrical power as the platinum-based reference (1.1 g/kW)
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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