1,720,971 research outputs found
Hydrogen sorption by nanostructured materials under thermal and mechanical activation
No full textThe hydrogen sorption properties of nanostructured materials prepared by ball milling are described and discussed
Sorption properties of dispersed MBH4-MgH2 (M=Na, Li) systems in nano-mesoporous scaffolds
No full textThe sorption properties of MBH4-MgH2 (M=Na, Li) composites dispersed in nano-mesoporous scaffolds are evaluated by manometric, calorimetric and thermal programmed desorption analyses
Hydrogenation of carbon monoxide over nanostructured systems: mechanochemical approach
No full textThe hydrogenation of CO by mechanical milling under hydrogen in presence of Mg-Ni and Ti-based materials as catalysts is studied. Hydrocarbons as CH4 and C2H6 are obtained, in different amounts depending on the hydrogen pressure and the chemical nature of the catalysts
Ordered mesoporous scaffolds for the confinement of nanosized complex and metal hydrides
No full textRising attention has been recently addressed to the sorption properties of nanosized materials confined into different mesoporous matrices. The reduction to nanometer scale and the control of grain size of hydrides particles could, at least in principle, induce an enhancement of the hydrogen release and uptake through the tuning of thermodynamic and kinetic properties [1]. While grain growth and particle agglomeration can be avoided, ordered scaffolds can also allow to obtain homogeneous size distribution of active phases. Most of the works recently published concern C based porous materials [2], whereas less attention has been addressed to chemically different scaffolds which, in turn, could offer further opportunities in tuning the sorption properties of hydrogen rich phases.
In this study we focus on the properties of nanosized hydrides confined into mesoporous scaffolds. Highly ordered Si-, C-, and transition metal-based mesoporous structures were prepared by sol-gel methods, and then embedded with mixtures of MgH2 and different complex borohydrides, by resorting to wet chemical impregnation and melting infiltration processes.
Structural characterization was performed by X-Ray diffraction (XRD), small angle neutron scattering (SANS) and transmission electron microscopy (TEM), in order to estimate the efficiency of confinement pathways. The thermodynamics and kinetics of the hydrogen absorption and desorption processes, as well as the chemical nature of the released gas, were then investigated by high-pressure differential scanning calorimetric device (HP-DSC), Sievert apparatus (PCT-Pro2000) and mass spectroscopy (MS).
Preliminary results indicate evident improvement in the sorption properties of the nanoconfined hydrides with regard to the corresponding materials in bulk conditions. The decrease of desorption temperatures in the multistep processes were tentatively related to the structural characteristics of the studied systems [3].
[1] M. Fichtner, Nanotechnology, 20, (2009) 204009.
[2] P. Adelhelm, J. Gao, M.H.W. Verkuijlen, C. Rongeat, M. Herrich, P.J.M. van Bentum, O. Gutfleisch, A.P.M. Kentgens, K.P. de Jong, P.E. de Jongh, Chemistry of Materials 22 (2010) 2233-2238.
[3] G. Mulas, R. Campesi, S. Garroni, E. Napolitano, C. Milanese, F. Dolci, E. Pellicer, D. Baró, A. Marini, Journal of Alloys and Compounds (2012) doi:10.1016/j.jallcom.2011.12.04
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
- …
