1,720,996 research outputs found
Event location and vagueness
No full textMost event-referring expressions are vague it is utterly difficult, if not impossible, to specify the exact spatiotemporal location of an event from the words that we use to refer to it. We argue that in spite of certain prima facie obstacles, such vagueness can be given a purely semantic (broadly supervaluational) account
PtRu supported on mesoporous carbons for DMFC application
No full textWe prepared cryogel mesoporous carbons of different pore-size distribution by sol-gel synthesis. On one selected carbon we deposited PtRu by the colloidal method and the resulting electrocatalytic system, C656/PtRu-A, was characterized in passive and active DMFCs by V-I and P-I plots. The results are reported and compared to those of PtRu supported by impregnation on the same carbon (C656/PtRu-B) and to those of a commercial Vulcan XC72R/PtRu electrocatalytic system. Both C656/PtRu-A and C656/PtRu-B performed better than Vulcan/PtRu. Although the colloidal syntheses should give catalysts with improved properties compared to those obtained by simpler impregnation methods, we obtained a catalytic system with a lower Ru content than expected, which would explain the non-optimized performance of C656/PtRu-A. Indeed, the C656/PtRu-B system performed better, providing 28 W g-1 in active DMFC at 60°C
Supported PtRu on mesoporous carbons for direct methanol fuel cells
No full textdoi: 10.1016/j.jowsour.2008.09.022
We prepared and characterized several cryogel mesoporous carbons of different pore-size distribution and report the catalytic activity of PtRu supported on mesoporous carbons of pore size > 15 nm in passive and in active DMFCs. At room temperature (RT), the specific maximum power of the passive DMFCs with mesoporous carbon/PtRu systems as anode was in the range 3-5 W g-1. Passive DMFC assembly and RT tests limit the performance of the electrocatalytic systems and the anodes were thus tested in active DMFCs at 30, 60 and 80°C. Their responses were also compared to those of commercial Vulcan carbon/PtRu. At 80°C, the specific maximum power of the active DMFC with C656/PtRu was 37 W g-1 and the required amount of Pt per kW, estimated at 0.4 V cell voltage was 31 g kW-1, a value less than half that of Vulcan carbon/PtRu
PtRu supportato su carboni mesoporosi per applicazioni in celle a combustibile a metanolo
No full textIl PtRu è il catalizzatore di scelta per gli anodi delle celle a combustibile a metanolo diretto (DMFC) in quanto il Ru gioca un ruolo chiave nella rimozione del CO adsorbito sul Pt. Lo sviluppo di elettrodi con elevata attività catalitica e a basso contenuto di metalli nobili è una delle principali sfide nell'ambito delle DMFC, assieme al miglioramento delle membrane polimeriche per ridurre il crossover del metanolo. A parità di contenuto di metalli nobili, carboni di supporto ad alta area superficiale evitano l'agglomerazione del catalizzatore e consentono una elevata superficie attiva. Elevate aree superficiali dei supporti carboniosi non sono però sufficienti a garantire buone attività catalitiche in quanto il catalizzatore deve essere in contatto con gli ionomeri del Nafion ed è pertanto fondamentale la distribuzione della dimensione dei pori che contribuiscono all'area superficiale totale.
A tale scopo abbiamo preparato e caratterizzato carboni mesoporosi sui quali abbiamo depositato PtRu per riduzione chimica. Nel presente contributo mostreremo i risultati di attività catalitica di un carbone con dimensione dei pori centrata intorno a 20 nm e con un carico del 30% p/p di Pt (Pt:Ru 1:1) ottenuti sulla base di misure condotte a temperatura ambiente in configurazione di DMFC passiva alimentata da CH3OH 1 M e aria. Le prestazioni di tali anodi, in termini di potenza, densità di corrente e a lunghi tempi di funzionamento saranno confrontate con quelle di anodi realizzati con carbone Vulcan/PtRu commerciale valutati nella stessa configurazione di cella e nelle stesse condizioni
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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