1,721,006 research outputs found
Hybrid membranes based on sulfated titania nanoparticles as low-cost proton conductors
No full textThis work reports on a novel, hybrid solid-state membrane based on sulfated titania nanoparticles stabilized by a polyvinylidene fluoride-hexafluoropropylene copolymer. A fast solvent-casting technique was adopted as a valid alternative to a fully dry, hot-pressing preparation procedure. Self-standing, flexible membranes with high proton conductivity were obtained
An advanced lithium-ion battery based on a nanostructured Sn-C anode and an electrochemically stable LiTFSi-Py24TFSI ionic liquid electrolyte
No full textWe report here a detailed impedance analysis of the interface between a selected IL electrolyte, i.e. a solution of lithium N, N-bis(trifluoromethane sulfon) imide in N-n-butyl-N-ethyl pyrrolidinium and a N, N-bis(trifluoromethane sulfon) imide, LiTFSI-Py24TFSI, and two electrodes, namely a conventional lithium metal and an advanced nanostructured Sn-C alloy, respectively. We show that the Sn-C alloy, in virtue of a specific formation of a surface protecting film, has an interface much more stable than that of the Li electrode. This favourable property is exploited for using Sn-C as a new anode for the development of an advanced lithium-ion battery based on LiTFSI-Py24TFSI as the electrolyte and on olivine LiFePO4 as the cathode. The results demonstrated that this battery has very promising performances in terms of cycle life and rate capability. (C) 2009 Elsevier B. V. All rights reserved
Mixtures of ionic liquid - Alkylcarbonates as electrolytes for safe lithium-ion batteries
No full textMixtures of alkylcarbonate electrolytes with an ionic liquid (IL) and a lithium salt have been studied in order to develop new electrolytes for lithium-ion cells with enhanced safety profiles. In this work the influence of the addition of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Py14TFSI) on the electrochemical properties of commercial carbonate-based electrolytes, i.e. 1 M LiPF6 in EC:DMC (LP30) and in EC:DMC:DEC (LP71) is reported. Four new electrolyte compositions have been prepared and characterized. The addition of the ionic liquid in the electrolyte carbonate-based solution results in (i) an ionic conductivity comparable with that of the pristine IL-free carbonate-based electrolyte, (ii) the enlargement of the electrochemical stability window, and (iii) a large reduction of the self-extinguish time (SET) of the electrolyte mixture when exposed to a free flame. All the newly developed electrolytes have been tested in lithium cells versus LiFePO4 and Li4Ti5O12 electrodes: the cells show good performances in galvanostatic cycling. The best performing electrolyte i.e. LP30/Py14TFSI 70/30 wt/wt has been also successfully tested in a full Li-ion cell realized by coupling LiFePO4 and Li4Ti5O12 electrodes. (C) 2012 Elsevier B.V. All rights reserved
Composite Poly(ethylene oxide) Electrolytes Plasticized by N-Alkyl-N-butylpyrrolidinium Bis(trifluoromethanesulfonyl)imide for Lithium Batteries
No full textWe report a new class of quaternary polymer electrolyte membranes that comprise poly(ethylene oxide) (PEO), lithium trifluoromethanesulfonylimide (LiTFSI), N-alkyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PyrA,4TFSI) as an ionic liquid, and a SiO2 filler. The results of differential scanning calorimetry indicate that the addition of SiO2 and different ionic liquids induces a decrease in the PEO melting enthalpy, which thereby increases the ionic conductivity and the Li transference number. The electrochemical stability is proved by using impedance spectroscopy and cyclic voltammetry. Galvanostatic cycling of Li/LiFePO4 cells, which comprise the quaternary polymer electrolytes, revealed their superior performance compared to conventional PEO-Li salt electrolytes. In the course of this investigation, a synergistic effect of the combined ionic liquid-ceramic filler modification could be proved at temperatures close to 50 degrees C
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
Preparation and Characterization of Nanocomposite Polymer Membranes Containing Functionalized SnO2 Additives
Full text linkIn the research of new nanocomposite proton-conducting membranes, SnO2 ceramic powders with surface functionalization have been synthesized and adopted as additives in Nafion-based polymer systems. Different synthetic routes have been explored to obtain suitable, nanometer-sized sulphated tin oxide particles. Structural and morphological characteristics, as well as surface and bulk properties of the obtained oxide powders, have been determined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) and Raman spectroscopies, N2 adsorption, and thermal gravimetric analysis (TGA). In addition, dynamic mechanical analysis (DMA), atomic force microscopy (AFM), thermal investigations, water uptake (WU) measurements, and ionic exchange capacity (IEC) tests have been used as characterization tools for the nanocomposite membranes. The nature of the tin oxide precursor, as well as the synthesis procedure, were found to play an important role in determining the morphology and the particle size distribution of the ceramic powder, this affecting the effective functionalization of the oxides. The incorporation of such particles, having sulphate groups on their surface, altered some peculiar properties of the resulting composite membrane, such as water content, thermo-mechanical, and morphological characteristics
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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