1,720,961 research outputs found
Synthesis and characterization of novel hybrid perovskites featuring quaternary organoammonium cations with extended conjugation
Full text linkThe last decade has seen an unprecedented interest in hybrid metal halide perovskites semiconductors, as active layers in photovoltaic cells, with extraordinarily high efficiency values achieved, and for various different optoelectronic applications, especially light emission and radiation detection.
In fact, these materials have the advantage of being synthesized from affordable precursors by solution techniques, and of allowing a fine tuning of their photophysical properties through the modification of their composition. Regretfully, their utilization on a large scale is still hindered by their poor environmental stability, owed to the ammonium cations contained in them, which undergo hydrolysis reactions in the presence of water; for this reason, the main goal of the current research in the field of hybrid perovskites is represented by the improvement of their tolerance to moisture and other environmental agents (such as high temperature and O2).
The aim of this work was therefore the study of the possibility to enhance perovskite stability and performances, through the introduction of novel organic cations featuring the following characteristics: an extendedly conjugated structure, in order to modulate the optoelectronic properties of the materials, and the absence of hydrolysable protons, to avoid decomposition in the presence of moisture.
In particular, the synthesis and characterization of two novel water-insensitive and thermally stable hybrid metal halide perovskites, containing 4,4′-(anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium), (C30H22N2)2+ cation, is described in Chapters 3 and 4. The two materials, both of which showed intense photoluminescence, were prepared using different metals, lead in the first case and bismuth in the second, with the aim of exploring the possibility of replacing a toxic element such as lead (which is however the most frequently used metal in hybrid perovskites) with a safer alternative.
Moreover, the synthesis of a series of additional environmentally stable lead-based and bismuth-based hybrid materials, sharing the presence of quaternary conjugated bipyridinium cations is described in Chapter 5, together with a preliminary evaluation of their potentialities for applications
Brightly Luminescent and Moisture Tolerant Phenyl Viologen Lead Iodide Perovskites for Light Emission Applications
Full text linkLead halide perovskites are outstanding materials for optoelectronics, but they typically feature low stability against external agents. To overcome this drawback, LHPs based on quaternary ammonium cations, such as phenyl viologen lead iodide (PhVPI), were found to be promising candidates, being water-resistant and thermally stable. In this Letter, the optoelectronic properties of the PhVPI are investigated by a combined experimental-theoretical approach. Although the as-prepared material is photoluminescence-inactive, a short thermal (5 min @ 290 °C) or laser annealing turns PhVPI into a highly luminescent material, in the 600-1000 nm range. The PhVPI PL emission was characterized at different annealing conditions, and the structural evolution following thermal treatments was investigated by means of X-ray diffraction, Raman, and NMR spectroscopies. Besides this, the electronic structure and emission properties were investigated by density functional theory simulations. The intense optical emission and high stability make PhVPI an intriguing material for applications related to light-emitting devices
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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