1,720,957 research outputs found
Electro-insertion of Mn2+ions into V2O5·: N H2O on MWCNTs coated carbon felt for binder-free Na+ion battery electrodes
Full text linkIn the present article, we report the electrochemical deposition of hydrated and amorphous V2O5·nH2O nanostructures and related Mn2+ cations insertion during anodic polarization. The hydrated phase was synthesized on hydrophilic carbon felt substrates coated by defective multiwall carbon nanotubes (MWCNTs). From the combined data of micro-Raman scattering and X-ray photoelectron spectroscopy (XPS), it was possible to see that the Mn2+ cations were intercalated into V2O5 under anodic polarization. When MnOOH is inserted between atomic bilayers of V2O5·nH2O (V5+), a 3D complex monoclinic-MnxV2O5 system arises. This novel method of Mn doping into V2O5·nH2O/MWCNT produces an amorphous MnxV2O5/MWCNT but without hydration. The resulting binder-free MnxV2O5/MWCNT/felt composite electrode provides remarkable Na+ reversible specific capacities of 400 mA h g-1 and 224 mA h g-1 in the 3.5-1.0 V and 3.5-1.5 V ranges, respectively, while the V2O5·nH2O/MWCNT/felt provides only 120 mA h g-1 between the smaller cut-off potential limits. The MnxV2O5/MWCNT nanostructures synthesis onto fibers of graphitic felt does not present a fading capacity during the polarization of 100 discharge/charge cycles
Pd catalysts supported on different hydrophilic or hydrophobic carbonaceous substrate for furfural and 5-(hydroxymethyl)-furfural hydrogenation in water
No full textWe hydrogenated furfural and 5-(hydroxymethyl)furfural (HMF) in water in
a reaction catalyzed by Pd nanoparticles on carbonaceous materials with
different morphology and hydrophobic degree. The different Pd catalysts
were prepared by dipping the carbonaceous material into a Pd-0
micro-emulsion. The catalyst support affected the catalytic
hydrogenation of furfural and HMF. By using micrometric active carbon
(AC) combined with cup-stacked carbon nanotubes (CSCNTs) and Pd0/2+
nanoparticles (Pd), we obtained a micro/nanostructured material
designated Pd/CSCNT-AC, which performed better than the other
carbonaceous materials containing similar Pd nanoparticle loading.
Pd/CSCNT-AC produced tetrahydrofurfuryl alcohol from furfural with
excellent selectivity (>99 %). Unlike Pd on hybrophobic spheroid
graphite or hydrophilic AC, Pd/CSCNT-AC hydrogenated both the C=O and
C=C double bonds of furfural and catalyzed HMF hydrogenation at the C=O
double bond more selectively: between 85 % and 99 % selectivity toward
2,5-dihydroxymethylfuran. We also investigated how temperature, hydrogen
pressure, and reaction time affected HMF hydrogenation in water.
Finally, Pd/CSCNT-AC was recycled several times without significant
catalytic activity loss
Nanostructured V2O5.nH2O/cup-stacked carbon nanotube composite with remarkable Li+ specific capacity
No full textNanostructures for lithium intercalation can be obtained by combining carbon nanotubes with nanoparticles, to achieve a composite that can be applied as electrochemical energy storage device. Depending on the chemical composition and architecture of the nanostructure, it can be used to develop batteries, supercapacitors, or hybrid battery-supercapacitor devices. Here, we study how the V2O5.nH2O concentration affects lithium intercalation into the V2O5.nH2O/cup-stacked carbon nanotube (CSCNTs) nanostructure. First, CSCNTs were directly grown on the surface of a nonwoven carbon fiber felt (CF). Then, ε/δ-V2O5.nH2O was electrodeposited on the CF/CSCNT composite. Between 4.2 and 1.5 V, 34 wt% V2O5.nH2O load provided lithium specific capacity of 633 mAhg−1 at 0.5 Ag−1 for 300 discharge/charge cycles with lower fading capacity. Higher or lower V2O5.nH2O load diminished this performance. Depending on the V2O5.nH2O load and scan rate, this new nanostructure can also operate as a pseudo-capacitor, to deliver 610 F g−1 at a scan rate of 10 mV s−1 between 4.0 and 1.5 V. We discuss this dependence in terms of V2O5.nH2O morphology and the presence of a junction between CSCNTs and V2O5.nH2O
The role of nanoparticle concentration and CNT coating in high-performance polymer-free micro/nanostructured carbon nanotube-nanoparticle composite electrode for Li intercalation
No full textWe investigate how Li intercalation into composite electrodes resulting
from the combination of graphitic carbon felt (CF) with carbon nanotubes
(CNTs) functionalized with electroactive nanoparticles (NPs) depends on
NP concentration. To this end, we study CF electrodes coated or not with
hydrophilic CNTs containing electrodeposited beta/gamma-MnO(2)NPs (wt%
25, 42, and 69) with hollow-nanotube structure. Galvanic coupling
between the CNTs and the NPs is the reason why the electrochemical
performance of CNT-NP nanocomposites varies with the NP concentration.
The CNT coating on the CF electrode also avoids capacity fading of the
CF/MnO2NP electrodes and prevents carbon fibers from interconnecting
with SEL More specifically, the CNTs stabilize the solid electrolyte
interphase and prevent NP detachment, thereby producing electrodes with
long-term cyclability. The best electrochemical performance occurs for
CNT/MnO2NP mass wt% 25 (1114 mAh g(-1), 1st discharge/charge Faradaic
efficiency similar to 80% at 1 A g(-1), cut-off potential = 4-0.005 V
vs Li+ /Li). (C) 2020 Elsevier B.V. All rights reserved
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
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