1,720,956 research outputs found
Molecular shape, elastic constants and spontaneous twist in chiral and achiral nematics: insights from a generalised Maier–Saupe framework
No full textOrdinary nematic liquid crystals have a uniform director field as ground state. However, there are relevant examples of spontaneously twisted nematic states, not only in chiral, but also in achiral materials. Different twist configurations can be found, with the director modulation along the twist axis, as in the cholesteric and in the twist-bend nematic phase, or perpendicular to it, as in blue phases and in skyrmion structures. Here, we develop a generalised Maier–Saupe theory to calculate the thermodynamic and elastic properties, included saddle-splay, of nematics made of particles whose shape can be described as a distorted rod. This turns out to be a powerful approach for screening the relation between the molecular shape and the formation of modulated nematic phases. Application to the paradigmatic models of banana-shaped and helical particles allows us to identify the role of distinct shape features, such as curvature and chirality, and the distinct mechanisms by which these promote twisted configurations
From Bend to Splay Dominated Elasticity in Nematics
Full text linkIn the past decade, much evidence has been provided for an unusually low cost for bend deformations in the nematic phase of bent-core mesogens and bimesogens (liquid crystal dimers) having a bent shape on average. Recently, an analogous effect was observed for the splay mode of bent-core mesogens with an acute apical angle. Here, we present a systematic computational investigation of the Frank elastic constants of nematics made of V-shaped particles, with bend angles ranging from acute to obtuse. We show that by tuning this angle, the elastic behavior switches from bend dominated (K33>K11) to splay dominated (K11>K33), with anomalously low values of the splay and the bend constant, respectively. This is related to a change in the shape polarity of particles, which is associated with the emergence of polar order, longitudinal for splay and transversal for bend deformations. Crucial to this study is the use of a recently developed microscopic elastic theory, able to account for the interplay of mesogen morphology and director deformations
Artificial Neural Networks Applied to Colorimetric Nanosensors: AnUndergraduate Experience Tailorable from Gold NanoparticlesSynthesis to Optical Spectroscopy and Machine Learning
Full text linkNowadays, technologies involving nanoparticles, colloids,sensors, and artificial intelligence are widespread in society, media, andindustry. It is thus mandatory to integrate them into the curricula ofstudents enrolled in chemistry and materials science. To this purpose, wedesigned a simple assay for the detection of glutathione (GSH) usingsurface-clean gold nanoparticles (Au NPs). The alteration of the electricdouble layer of the Au NPs with increasing GSH concentration causes theparticles to aggregate, producing a measurable change in color. Thisbehavior, which is widely exploited for optical sensing, has been introducedin an undergraduate course to familiarize the students with the concepts ofnanoparticles, colloids, colloidal stability, and sensor features (selectivity,sensitivity, detection range). Nonetheless, there are no analytical models toquantitatively relate the absorption of Au NP colorimetric sensors toanalyte concentration, which is the ideal condition for resorting to machinelearning (ML). Hence, an artificial neural network was instructed in a students'collective data-sharing experiment about machinelearning. Overall, the laboratory experience is safe and highly tailorable to students'background, course duration, availableinstruments, and teacher's didactic objectives. For instance, it can be lifted to the Master's or Ph.D. level by improving thespectroscopic and ML contents or shifted toward the industrial ground by focusing on the nanoparticle synthesis. We propose theintegration of this laboratory experience in the undergraduate and Master's academic programs to stimulate the students with acollection of hot topics that at the same time can consolidate their preparation on arguments of great relevance for their professionallif
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
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