1,720,986 research outputs found
Redox mechanism and cycling behaviour of nonylbenzo-hexaquinone electrodes in Li cells
No full textNonylbenzo-hexaquinone (NBHQ), a quinonoid polymer of low molecular weight, has been reinvestigated as a cathode material for Li cells. Its reduction mechanism gives rise at first, in a 3-electron process, to an irreversible species involving the formation of radical anion. Successively, a direct two-electron reduction of other quinone groups occurs. This second step, witch involve 4 e- in quasi-thermodynamic conditions, is reversible and allows cells of the type Li/LiClO4-PC.DME/NBHQ,C to be cycled for more than 500 cycles at the c/2 rate between 3.5 and 2.0 V. The average energy density during this cycling was 160 Wh/kg, based on the weight of the cathode material (additive included)
A Stereoselective Total Synthesis of (±)-Maritimol, (±)-2-Deoxystemodinone, (±)-Stemodinone, and (±)-Stemodin
No full textIncreased conformational rigidity of humic substances by oxidative biomimetic catalysis
Full text linkA synthetic water-soluble meso-tetra(2,6-dichloro-3-sulfonatophenyl)porphyrinate of iron(III) chloride, Fe-(TDCPPS)Cl, was employed as a biomimetic catalyst in the oxidative coupling of terrestrial humic materials.
High-performance size-exclusion chromatography (HPSEC), solid-state nuclear magnetic resonance (CPMAS13CNMR), electron paramagnetic resonance (EPR), and diffuse reflectance infrared spectroscopy (DRIFT) were used to follow conformational and structural changes brought about in different humic materials by the oxidative coupling. Increase in apparent weight-average molecular weight (Mwa) occurred invariably for all humic substances with the oxidative polymerization catalyzed by Fe(TDCPPS)Cl. HPSEC further showed that the polymerization reaction turned the loosely bound humic supramolecular structures into more stable conformations which could no longer be disrupted by the disaggregating effect of acetic acid.
DRIFT spectroscopy suggested the formation of new alkyl and aromatic ethers following the oxidative coupling with the biomimetic catalyst. CPMAS-13C NMR and EPR spectra suggested a reduced molecular mobility of humic components and enhanced stabilization of free radicals in larger oxidized fragments. All findings concur in indicating that the biomimetic catalysis by Fe(TDCPPS)Cl increased the molecular mass and chemical rigidity of humic materials by formation of intermolecular covalent bonds via a free-radical mechanism. The development of a technology ased on oxidative polymerization by biomimetic catalysis may be of importance in controlling the properties and reactivity of humic matter for industrial and environmental applications
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
Edge functionalization of Graphene Nano-Plates: multi-step carboxylation and Friedel-Crafts reaction
Full text linkGraphene is a material of recent discovery that shows excellent properties even if its preparation is rather difficult and complex. Graphene Nano-Plates (GNPs),
made by few tenths of graphene layers, have similar properties but their preaparation is easier. Nevertheless, their employment in the field of nanocomposite materials is
not widely applied due to the difficulty to disperse their in solvent or polymeric matrix. The purpose of this work is the selective functionalization of the edges
of the GNP, in order to preserve the internal aromatic structure of the plans, preserving the peculiar physical-chemical properties of the graphene materials.
In this regard, two synthetic routes have been applied: bromination, lithiation and subsequent carboxylation; Friedel-Crafts reaction, using succinic anhydride as an
acylating agent
Synthesis and reactivity towards nucleophiles of bis(isocyanide)(porphyrinato)rhodium(III) complexes. Crystal and molecular structure of a novel carbene complex: {(TPP)Rh(PhCH2NC)[:C(NHCH2Ph)2]PF6}
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