1,721,008 research outputs found
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
Ta doped nanostructured TiO2 for liquid phase photodegradation reactions
No full textTitanium dioxide has been widely studied as a photocatalyst. One of the main applications lies in the environmental remediation, both in gas and liquid phases. Especially, degradation of VOCs has been investigated. In more recent years, research in this field has been focused on the detection and the degradation of new emergent pollutants, such as pharmaceutical compounds and their metabolites. Moreover, structural properties of titanium dioxide deeply influence its photocatalytic performance. It is well-known in the literature that among the three natural crystalline phases (anatase, brookite and rutile) anatase is the most promising for this application, thanks to the more favourable position of its conduction band, even if its band gap is larger (3.2 eV) than those of brookite and rutile (3.0 eV). Nonetheless, the compresence of two different crystalline phases can be very useful, promoting the trapping of the photogenerated electrons from one to the other, lowering the possibilities of electronhole
recombination. Moreover, doping with transition metals is widely used to promote TiO2 photocatalytic activity under UV light. In particular, theoretical results have forecast tantalum as efficient dopant of TiO2 for UV photodegradation, thanks to the electronic states generated in the conduction band. Here, pristine and Ta doped TiO2 nanomaterials were prepared, characterized and photocatalytically tested in three different degradation reaction, both in gas and liquid phase
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
Structural and electronic properties of N-doped TiO2/SnO2 photocatalysts for air pollutant remediation
Full text linkIntroduction
TiO2/SnO2 heterojunctions bear relevance to numerous research fields, such gas sensors, fuel cells and photocatalysis [1]. Actually, the isomorphism of SnO2 cassiterite and TiO2 rutile (both P42/mnm) makes them suitable for developing stable junctions. Moreover, the relative positions of the two semiconductors’ Fermi energies favour electron transfer from the TiO2 conduction band to the SnO2 one, promoting charge carrier separation and increasing the e–-h+ life-time. In turn, this improves the device efficiency in photo-electrochemical applications with respect to N-doped TiO2, one of the most investigated visible-light active photocatalysts, which suffers from enhanced recombination of photo-generated charges [2].
Results and Discussion
N-doped TiO2-SnO2 photocatalysts were prepared in a broad range of Sn:Ti ratios (0-20%) by three different synthetic approaches (mechanical mixing, seeded growth and co-synthesis), followed by calcination at 400°C. Samples were characterized from the structural, morphological and electronic point of view, also via in situ synchrotron radiation-based XAS studies. Structural properties are remarkably modified by the adopted synthetic procedure (Fig.1a). Mechanical mixing leads to mixed phases in almost stoichiometric ratios. The seeded growth gives rise to partial segregation of SnO2, while for co-synthesis, the only appreciable component is rutile TiO2, despite the low calcination temperature. Such a tailoring of the structural features reflects in tuneable optical properties (Fig.1b), which show synergistic effects when both N and Sn diffuse in bulk TiO2. The samples’ photocatalytic activity was tested toward the gas phase degradation of VOCs, under both UV and visible light irradiation, monitoring the pollutant disappearance, the main intermediates’ formation and the mineralization degree.
Conclusions
By tuning the synthetic procedure, mixed phases or Sn doping within the TiO2 matrix could be obtained, leading to different optical and electronic properties. High-resolution XRPD and XAS analyses shed light on (i) the actual location and chemical nature of Sn species, (ii) the defectivity of the TiO2 lattice, and (iii) the interplay between the dopants. Structural and spectroscopic results were correlated with the photocatalytic activity in the visible region.
References
[1] G. Kelp et al., Nanoscale, 2016, 8, 7056; H. An et al., Electrochim. Acta, 2013, 92, 176.
[2] Asahi et al. Chem Rev, 2014, 114, 9824; Rimoldi et al. J Phys Chem C, 2015, 119, 24410
Photocatalytic removal of gaseous ethanol, acetaldehyde and acetic acid: from a fundamental approach to real cases
No full textThe photocatalytic oxidation of volatile organic compounds (VOCs) has been extensively investigated. With respect to water treatment, photocatalytic degradation of air pollutants is still less understood, but this has not prevented photocatalytic building materials and air purifiers to reach the market. Here, we provide a selective overview of the current understanding on VOC photocatalytic oxidation, focusing on ethanol, acetaldehyde, and acetic acid. Among the main indoor pollutants, these molecules are also oxidation intermediates of numerous VOCs. Their adsorption at the photocatalyst surface is first presented, based on theoretical and experimental evidence. Reaction intermediates are discussed, comparing proposed reaction mechanisms. The role of the photocatalyst features in directing adsorption and oxidation phenomena is highlighted, encompassing both TiO2 and emerging photocatalysts. We then critically discuss gaps in our knowledge, such as the effect of air humidity, multi-pollutant interactions and deactivation pathways. Finally, attempts to model VOC degradation in realistic conditions are reviewed
VOCs Photocatalytic Degradation By Oxidic Materials In Films. Achieving Enhanced Activity By Creating Heterostructures
No full textIn this work, different photoactive oxides (both binary and ternary) were synthesized and deposited as films, both singularly and as composites and photocatalytically tested towards the degradation of volatile organic compounds (VOCs) in the gas phase. In particular, TiO2 and WO3 were selected as binary oxides, while copper vanadate (Cu2V2O7) was chosen as the ternary visible light active oxide.
Colloidal syntheses performed under nitrogen pressure on Schlenk ramp were adopted to obtain both WO3 and Cu2V2O7 materials.
The effects provided by the creation of heterojunctions on the final photocatalytic performance are investigated
Green and low cost tetracycline degradation processes by nanometric and immobilized TiO2 systems
Full text linkTetracycline accumulation in surface waters, due to its extensive use and ineffective removal by traditional remediation treatments, represents a major environmental problem, leading e.g. to increasedantibiotic resistance. Here, photocatalysis by TiO2, both as nanostructured powders and macroscopic immobilized systems, is proposed as an efficient procedure to totally degrade tetracycline to harmless compounds. Home-made TiO2 powders were studied to clarify the role of synthetic and process parameters (light pre-treatment, calcination temperature) and to shed light on the role of radical species in promoting the reaction (tests with radical scavengers). The control of phase composition and wetting features appears to be essential in producing photocatalysts able to completely mineralize tetracycline in a short time scale (6 h). The knowledge acquired on the powder system was preparatory to the development of low cost, mechanically robust and highly active TiO2 immobilized systems. Two different substrate geometries (laminas and pellets) were investigated to ease the photocatalyst removal from the treated effluent. Both immobilized systems proved efficient: in particular, the TiO2-coated pellets promoted tetracycline degradation and mineralization on a time scale that is very competitive when compared to similar literature immobilized systems
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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