1,720,973 research outputs found
Mechanism of ionic conductivity in poly(ethylene glycol 400)/(MgCl2)(x) polymer electrolytes: studies based on electrical spectroscopy
No full textIn this paper, eight solvent-free polymer electrolytes PEG400/(MgCl2)x (0.00329 less than or equal to x less than or equal to 0.7000) were prepared in order to investigate the mechanism of ionic motion and the interactions existing in these systems. The study was carried out by impedance spectroscopy in the 20-Hz to 1-MHz range at different temperatures. Real and imaginary components of conductivity spectra in terms of equivalent circuit analysis (EC) and correlated ionic motion analysis based on a generalized universal power law (UPL) were investigated. Results revealed that in the PEG400/(MgCl2)x, the ionic species formed in the bulk materials are crucial for the overall conductivity. Indeed, in PEG400/(MgCl2)x, conductivity is ionic and takes place through hopping of the cationic species Mg2+ and [MgCl]+ between the coordination sites present along the polyethereal chains
Two new siloxanic proton-conducting membranes - Part I. Synthesis and structural characterization
No full textThe development of stable polymer electrolytes having good proton conductivity, low cost and operating at medium temperatures represent a crucial step in the evolution of polymer electrolyte fuel cells. We describe two new siloxanic proton-conducting membranes that were synthesized through a two-stage protocol. In the first stage, a poly(methyl hydrosiloxane) precursor (P) bearing siloxane side chains with sulfonic acid groups was prepared. In the second step, the hydrolysis of pristine precursor or its derivative obtained by grafting siloxane chains on P yielded two types of membranes with the formulas {Si(CH3)3O[Si(CH3)HO]21.26–[Si(CH3)((CH2)3SO3H)O]1.8–[Si(CH3)((CH2)3Si(CH3)2O–)–O]14–Si(CH3)3}n (A) and {Si(CH3)3O[Si(CH3)HO]21.26–[Si(CH3)((CH2)3SO3H)O]1.8–[Si(CH3)((CH2)3–(Si(CH3)2O–)w)–O]v[Si(CH3)((CH2)3Si(CH3)2O–)-O]14− vSi(CH3)3}n (B), with w = 20.31. Polymer membranes of A and B were prepared
by means of a hot-pressing process at 80 °C and 10 t/cm2. Scanning electron microscopy showed that A and B are rubbery materials with rough and transparent surfaces. Thermogravimetric investigations performed under air atmosphere disclosed that A and B are thermally stable
up to at least 198 °C. DSC measurements yielded Tg(s) of −44 and −60 ◦C for A and B, respectively. The polymers exhibit ionic exchange capacities of 0.33 (A) and 0.15 meq/g (B). FT-IR and FT-Raman investigations revealed that the polymers consist of reticulated siloxane networks with pendant silicone chains having sulfonic acid groups
SCIATIC-NERVE ATPASE ACTIVITY IS UNAFFECTED IN DIABETIC MUTANT C57BL/KS (DB/DB) MICE
No full textWe investigated composite (total), Mg2+ (ouabain-resistant), and Na+-K+-(ouabain-inhibited) ATPase in sciatic nerves of diabetic mutant C57BL/Ks (db/db) and age-related littermate (db/+) control mice at various ages (16, 26, and 40 wk). This is the first report indicating that nerve ATPase activities measured in vitro showed no deficit in mice with spontaneous diabetes. Thus, diabetic neuropathy in the genetically diabetic mouse may occur in the absence of Na+-K+-ATPase abnormalities, which were previously described in association with polyol pathway impairment in experimental diabetic and BB Wistar rats. Control and diabetic groups treated with ganglioside mixture for 30 days before death presented statistically insignificant differences. Therefore, the beneficial effect of gangliosides described in C57BL/Ks (db/db) mice on electrophysiological and morphometrical parameters must be due to different pharmacological activites rather than to prevention of the decay or better maintenance of ATPase activity
Spectroscopic conductivity studies of ionic motion in poly(ethyleneglycol 600)/(LiCl)x electrolytic complexes
No full text
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
Synthesis and structure of electrolytic complexes based on a-hydro-w-oligo(oxyethylene)hydroxy-poly[oligo(oxyethylene)oxydimethylsililene] and d-MgCl2
No full textVariations 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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