1,721,024 research outputs found
Guanidine functionalized porous SiO2 as heterogeneous catalysts for microwave depolymerization of PET and PLA
No full text<p>Chemical recycling is an important strategy to tackle the growing global problem of plastic waste pollution. The development of metal-free catalysts for depolymerization of plastics is attractive as it avoids the use of metal salts, which are potentially damaging to the environment. Here we report a metal-free heterogeneous catalyst for the glycolysis of polyethylene terephthalate (PET) and methanolysis of polylactic acid (PLA). The catalysts are synthesized by covalent surface modification of mesoporous silica (SiO2) with guanidine ligands and evaluated under conventional thermal and microwave-assisted heating. A surface bound cyanoguanidine ligand was found to be the best catalyst giving 100% PET conversion with 80% BHET yield. The nature of the catalyst support material influenced the catalytic performance of the guanidine ligands with porous SiO2 supports outperforming activated carbon under conventional thermal glycolysis, while the opposite trend was observed with microwave assisted glycolysis. Dedicated density functional theory (DFT) computations were performed to simulate the depolymerization processes, characterize the free energy profiles of the reaction mechanisms, and identify the important role of hydrogen bonding in the reaction mechanism. </p>
Ligand-Aided Glycolysis of PET Using Functionalized Silica-Supported Fe2O3 Nanoparticles
No full text<p>The development of efficient catalysts for the chemical recycling of poly(ethylene terephthalate) (PET) is essential to tackling the global issue of plastic waste. There has been intense interest in heterogeneous catalysts as a sustainable catalyst system for PET depolymerization, having the advantage of easy separation and reuse after the reaction. In this work, we explore heterogeneous catalyst design by comparing metal-ion (Fe3+) and metal-oxide nanoparticle (Fe2O3 NP) catalysts immobilized on mesoporoussilica (SiO2) functionalized with different N-containing amine ligands. Quantitative solid-state nuclear magnetic resonance (NMR) spectroscopy confirms successful grafting and elucidates the bonding mode of the organic ligands on the SiO2 surface. The surface amine ligands act as organocatalysts, enhancing the catalytic activity of the active metal species. The Fe2O3 NP catalysts in the presence of organic ligands outperform bare Fe2O3 NPs, Fe3+ ion-immobilized catalysts and homogeneous FeCl3 salts, with equivalent Fe loading. X-ray photoelectron spectroscopy analysis indicates charge transfer between the amine ligands and Fe2O3 NPs and the electron donating ability of the N groups and hydrogen bonding may also play a role in the higher performance of the amine-ligand-assisted Fe2O3 NP catalysts. Density functional theory (DFT) calculations also reveal that the reactivity of the ion-immobilized catalysts is strongly correlated to the ligand−metal binding energy and that the products in the glycolysis reaction catalyzed by the NP catalysts are stabilized, showing a significant exergonic character compared to single ion-immobilized Fe3+ ions.</p>
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
Reflections on the Enforcement of Labour Law : A Review of Re-inventing Labour Law Enforcement. A Socio-Legal Analysis by Louise Munkholm, Hart 2020
No full text‘… technical law by itself is useless, at best an arid game played by keen minds in courtrooms and academic ivory towers. To understand its significance we must look at its historical and social setting'. (K. W. Wedderburn, The Worker and the Law 7 (Penguin Books 1965)). ‘… ultimately the point of labour law is to do something'. (Hugh Collins, Gillian Lester & Virginia Mantouvalou, Introduction, in Philosophical Foundations of Labour Law 1, 2 (Hugh Collins, Gillian Lester & Virginia Mantouvalou eds., OUP 2018))
Reflections on the Enforcement of Labour Law A Review of Re-inventing Labour Law Enforcement. A Socio-Legal Analysis by Louise Munkholm, Hart 2020
No full text‘… technical law by itself is useless, at best an arid game played by keen minds in courtrooms and academic ivory towers. To understand its significance we must look at its historical and social setting'. (K. W. Wedderburn, The Worker and the Law 7 (Penguin Books 1965)). ‘… ultimately the point of labour law is to do something'. (Hugh Collins, Gillian Lester & Virginia Mantouvalou, Introduction, in Philosophical Foundations of Labour Law 1, 2 (Hugh Collins, Gillian Lester & Virginia Mantouvalou eds., OUP 2018))
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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