1,720,967 research outputs found
Divergent [ONNNMg–Cl] complexes in highly active and living lactide polymerization
No full textChloro-magnesium complexes of divergent tetradentate-monoanionic {ONNN}-type ligands which formed as either mononuclear or dinuclear complexes are reported. These complexes catalyze the ring-opening polymerization of lactide with high activity and in a living manner, and enable the synthesis of well-defined stereo-diblock copolymers with Mn > 200 kDa, as well as stereo-n-block copolymers (n = tri, tetra) with high molecular weights by sequential monomer addition. Thermal and crystallographic characterizations revealed that even the very high molecular weight PLA copolymers crystallized in a stereocomplex phase, and that their degradation temperature was as high as 354 °C
Block–Stereoblock Copolymers of Poly(ε-Caprolactone) and Poly(Lactic Acid)
No full textA magnesium complex of the type ONNNMg-HMDS wherein ONNN is a sequential tetradentate monoanionic ligand is introduced. In the presence of an alcohol initiator this complex catalyzes the living and immortal homopolymerization of the lactide enantiomers and ε-caprolactone at room-temperature with exceptionally high activities, as well as the precise block copolymerization of these monomers in a one-pot synthesis by sequential monomer addition. Copolymers of unprecedented microstructures such as the PCL-b-PLLA-b-PDLA and PDLA-b-PLLA-b-PCL-b-PLLA-b-PDLA block–stereoblock microstructures that feature unique thermal properties are readily accessed
Removal of phenol in aqueous media by N-doped TiO2based photocatalytic aerogels
No full textIn this work, composite monolithic aerogels based on syndiotactic polystyrene (s-PS) and N-doped TiO2(NdT) photocatalyst characterized by high surface areas (up to 280 m2/g) and low density (0.1 g cmâ3) are presented. These aerogels are obtained by supercritical carbon dioxide extraction of NdT/s-PS gels prepared by s-PS dissolution with NdT in suitable organic solvent. X-ray diffraction measurements and SEM analysis showed that a highly efficient dispersion of NdT nanoparticles can be achieved in the composite aerogels avoiding thus the aggregation phenomena that typically occur when the photocatalyst is used in slurry reactors. The optimization of NdT amount dispersed in s-PS was evaluated using phenol as model pollutant both under UV and visible light irradiation. The photoactivity of NdT/s-PS samples increased with increase of the amount of NdT dispersed in aerogel matrix up to NdT/s-PS weight ratio equal to 10/90 (10NdT/s-PS), for which the highest phenol degradation and TOC removal were achieved both under UV and visible light irradiation. Moreover, the photocatalytic activity of the optimized photocatalyst 10NdT/s-PS did not change significantly after several reuses underlining that any NdT particles are removed from the polymeric matrix
Influence of aggregate size on photoactivity of N-doped TiO2 particles in aqueous suspensions under visible light irradiation
No full textThis work is focused on the study of the correlation between the photocatalytic activity of N-doped TiO2 particles, achieved by a designed synthesis, and their degree of aggregation in aqueous suspension. N-doped TiO2 photocatalyst particles, suspended in bidistilled water, presented a trimodal (in the nano-micro metric range) aggregate size distribution. This distribution resulted monomodal, in the nanometric range, when in the aqueous solution was added an organic dispersing agent (azulene). This behavior was associated to the presence, on the N-doped TiO2 particle surfaces, of an organic phase which was detected by thermal and infrared analysis. This organic phase was assumed to have a stabilizing function for nanoparticles. The influence of aggregate size of N-doped TiO2 photocatalyst on the photocatalytic degradation of methylene blue has been studied. The aggregate size distribution of photocatalyst influenced the amount of methylene blue adsorbed on catalyst surface and increased the photocatalytic activity. The influence of operating parameters such as the amount of dispersing agent and the amount of photocatalyst in aqueous suspensions has also been examined
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Combined adsorption and solar driven photocatalysis processes for the removal of persistent contaminants from water by highly porous nanocomposite aerogels
Get PDF2019 - 2020Water is a very important resource for human and ecosystem. However, in recent years the presence of pollutants, such as pharmaceuticals, cosmetics, personal cares, dyes, and pesticides deriving from industrial, agricultural, and human practices is object of growing concern as these substances persist in the environment and are not removed by wastewater treatment plants (WWTPs). In fact, the latter are among the main sources of such pollution since they are not designed to remove persistent organic contaminants that are eventually discharged into receiving water bodies.
Thus, many substances, their metabolites and/or transformation products once in the environment, can propagate through different environmental compartments or can accumulate in plants and others organism posing a risk to the environment and human health, as the ecotoxicological effects of the presence of these molecules in the environment are often unknown.
Advanced oxidation processed (AOPs) are the most promising techniques that could solve this problem. In fact, during AOPs processes are generate hydroxyl radicals (OH•) highly reactive and capable of oxidising these contaminants. Among all these processes, heterogeneous photocatalysis has been widely investigated for this purpose due to its ability to mineralize many organic compounds using the solar light as light source.
The photocatalysts is generally dispersed in a slurry reactor as suspended powder resulting in disadvantages, such as the necessity to separate particles from the treated water, the damage of the recirculation pumps used for the process and toxicity problems related either to the release of the metal in solution or to the generation of by-products or intermediates that are more toxic than the starting materials. Therefore, possible solutions could include dispersing the
photocatalyst into highly porous nanocomposite aerogels (HP-NcAs) and conducting ecotoxicological experiments to assess the materials and solutions compatibility undergoing photocatalytic treatment. The process will be then optimised to develop a sustainable, low environmental impact technology for the degradation of organic pollutants using UV, VIS and sunlight. The HP-NcAs are easy-to-handle, highly efficient composite materials to be used as an alternative to conventional catalysts in solar driven-photocatalysis with the benefit of maximising the specific photo-activatable surface area compared with other media (ceramics, films and sponge) and preventing the nanoparticles aggregation in aqueous matrix. Therefore, in this work, aerogel/photocatalyst composite systems based on syndiotactic polystyrene (sPS) and semiconductors such as N-TiO2 (NdT), ZnO, ZnO/NdT and Fe0-ZnS were prepared and tested in the degradation processes of model pollutants, such as atrazine (ATZ), thiacloprid (THI) and tetrachloroethylene (PCE) under UV, Visible and solar irradiation. In addition, ecotoxicological experiments were carried out to evaluate the adverse toxicity effects of materials and solutions generated by the degradation process. [edited by Author]XXXIII cicl
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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