1,720,999 research outputs found
Macroscopic and microscopic electron transfer kinetics of HOPG and graphite intercalated compound investigated by cyclic voltammetry and SECM
Full text linkHighly oriented pyrolytic graphite (HOPG) is one of the most used host materials for obtaining and investigating graphite intercalated compounds, because of the high degree structural order of this polycrystal. Experiments on electrochemically intercalated HOPG in sulphuric acid have a model character, as the results obtained can be usefully generalised, not only with respect to other graphite compounds but also for the intercalation of other layered host lattices. In addition, the HOPG/H2SO4 system has an attractive potential for the possibility of electrochemically producing graphite oxide, ideally, by reversible oxidation/reduction cycles, which is of interest for energy storage and graphene production on an industrial scale. However, the oxidation/reduction cycles in such electrochemical intercalation process are not reversible and topotactic, so that the HOPG structure is considerably altered. This alteration may affect, for instance, the quality of the electrochemically produced graphene. In particular, the impact the electrochemical intercalation has on the conductivity of basal planes of HOPG, and so on graphene sheets, is still debated. In this work, we investigated both the macroscopic and microscopic electron transfer (ET) kinetics of the HOPG surface, before and after the intercalation of 1 M H2SO4 to obtain graphite intercalated compound, by using cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM), respectively. The heterogeneous kinetic constant (k0) of the HOPG was evaluated quantitatively by using the redox systems [Fe(CN)6]3–/4– and [Ru(NH3)6]3+/2+. The morphology of the samples was also investigated by atomic force microscopy (AFM), which revealed a widespread formation of blisters and precipitates during the HOPG intercalation process. The CV and SECM results indicate that, upon intercalation, the electrochemical behaviour of the HOPG changes sensibly and the ET decreases sensibly. However, this effect depends on the redox mediators employed and it results more dramatic for the [Fe(CN)6]3–/4– system, for which a decrease of k0 by orders of magnitude was obtained. The decrease of ET can be correlated to the blisters and precipitates, which occur during the HOPG intercalation, as observed by AFM
Pt Nanoelectrodes Sealed in Quartz Capillaries Modified with Underpotential-Deposited Bismuth for Formic Acid Electrooxidation
No full textPlatinum disk nano- and micro-electrodes with radii in the range 40 nm-12.5 mu m were fabricated using quartz capillaries and the laser-puller assisted approach. The hydrogen underpotential deposition (H-UPD), performed in a 0.5 M H2SO4 aqueous solution, revealed that the nanoelectrodes, with radii of 160 nm and less, displayed extraordinarily large surface areas, which in terms of roughness factors (RFs, i. e., the ratio of the real surface areas to the geometric surface areas) were in the range 1030-3600. This finding was attributed to diffusion of adsorbed species at the Pt/quartz interface along portions of the Pt wires sealed within the glass. RFs between 2 and 3 were instead found at the microelectrodes. Similar results were also obtained with underpotential-deposited metallic bismuth. In this case, diffusion of Bi adatoms onto the Pt surface was hindered to some extent, providing a RF value of 172. Bi-modified Pt nano- and micro-electrodes were employed to study the electrooxidation of HCOOH, which is of interest in the field of fuel cells. It was found that the nanoelectrode displayed higher activity towards the electrooxidation of HCOOH and tolerance to CO poisoning, compared to the microelectrode
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
Fecal biomarkers in Italian anthropogenic soil horizons and deposits from Middle Ages and bronze age
Full text linkArchaeological excavations in urban and rural contexts often uncover dark homogeneous anthropogenic deposits, soils and soil horizons, known as Dark Earths, Cultural Layers and Anthrosols. Major scientific questions arise about the processes that lead to the formation of these soils and deposits, as they are often related to a complex combination of environmental, climatic, and anthropogenic factors. Many studies focused on the morphological and physical-chemical investigation of the archaeological remains found as well as the inorganic constituent of the soil. The organic fraction has been only roughly investigated and studies carried out on a molecular level are very limited. However, a more refined investigation of the chemical constituents of these soils can potentially reveal pivotal insights on the archaeological context such as past domestic habits and/or urban organization. It has been demonstrated that, among organic matter constituents, fecal steroids are promising biomarkers to track fecal input in many environmental matrixes such as water, soils, and sediments. In this paper we determine the fecal sterols and stanols content in dark homogeneous anthropogenic deposits and soils found in seven archaeological sites in Italy (from Verona, Como, Florence, Mel and Conegliano) dated from the Late Bronze Age and the Medieval Period, aiming to assess the major contribution of the fecal input using diagnostic fecal indexes obtained from specific fecal sterol proportions. To this purpose, a baseline was established by identifying the fecal fingerprint of domestic herbivores (caprids, ovines, equines and bovines) and omnivores (pigs). Based on their fecal fingerprint, we classified the deposits of seven studied sites into four distinct categories: i) the medieval sites of Verona, presented a strong mixed fecal input from both herbivores and humans; ii) the medieval sites of Como and Florence which showed a similar pattern, with a predominance of human fecal input over livestock; iii) the late medieval soils of Mel and the late bronze age Cultural Layers of Castellar di Leppia (Verona) which exhibited a generally scarce fecal contamination while iv) the final bronze age site of Conegliano (Treviso), a strong fecal contamination from herbivores was detected. These results thus demonstrate that for the Medieval Dark Earth the socio-cultural processes leading to the formation of the Dark Earth differ in terms of sewage and waste management and/or in animal husbandry practices
Abiotic factors affecting the bacterial and fungal diversity of permafrost in a rock glacier in the Stelvio Pass (Italian Central Alps)
No full textThe impact of climate change in the European Alps has been roughly twice the global average, dramatically reducing permafrost extent and thickening of its active layer. Therefore, the study of the abiotic factors (i.e. chemical/physical parameters) affecting the microbial diversity inhabiting Alpine permafrost appears to be of dramatic relevance. Within the European Alps, the Stelvio area exhibits these effects in a particularly evident way, with important consequences on microbial ecosystems. Therefore, microbial communities inhabiting a permafrost core collected in the Scorluzzo active rock glacier (Stelvio Pass, Italian Central Alps) were investigated along a depth gradient (410 to 524 cm from the surface). The taxonomic structures of bacterial and fungal communities were investigated via a next-generation sequencing (NGS) approach (Illumina MiSeq), targeting the bacterial V3-V4 regions of 16S rDNA and the fungal ITS2 region. Abiotic soil factors (grain size, electrical conductivity, ice/water content, pH, Loss-on-Ignition - LOI, total and organic carbon, nitrogen and phosphorous) were analysed. Richness and Shannon-H diversity indices were correlated to abiotic factors. Bacterial diversity was significantly (p < 0.05) correlated with LOI, while fungal diversity was significantly (p < 0.05) correlated with the depth gradient. The Constrained Analysis of Principal (CAP) coordinates were used to study the correlation between abiotic parameters and the taxonomic structure of bacterial and fungal communities. Among all tested variables, the depth gradient, water content, pH and LOI affected the taxonomic structure of bacterial communities (in particular, the abundance of bacterial amplicon sequence variants - ASVs - assigned to Afipia sp., Chloroflexi, Gaiella sp., Oryzihumus sp. and Serratia, sp.), while fungal communities (ASVs assigned to Naganishia sp., Rhodotorula sp., Sordariomycetes and Taphrinales) were affected by the depth gradient. Co-occurrences (calculated by Pearson correlation coefficient) among microbial taxa (i.e. bacteria vs bacteria, bacteria vs fungi, fungi vs fungi) were investigated: the prevalence of significant (p < 0.05) positive co-occurrences was found, suggesting that the coexistence of different microbial taxa could play a crucial role in maintaining the ecological and taxonomic balance of both bacterial and fungal communities inhabiting the Alpine permafrost ecosystem. These findings suggest that the bacterial and fungal diversity of Alpine permafrost are affected in different ways by some abiotic factors
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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