1,720,968 research outputs found
Mechanical Transitions in Crystals: The Low-Temperature Thermosalient Transition of a Mesogenic Polyphenyl
Get PDFThermosalient transitions are a subset of single-crystal-to-single-crystal (SCSC) transitions, in which the change of lattice parameters is highly anisotropic and very fast. As a result, crystals at the transition undergo macroscopic dynamical effects (hopping, jumping, and shattering). These transitions feature a conversion of heat to mechanical energy that can be exploited in the realization of advanced materials. Most thermosalient transitions are observed at temperatures higher than room temperature. Examples of low-temperature thermosalient transitions are rare. We describe a new example of a low-temperature thermosalient transition in a sexiphenyl compound. At about −40 °C, the parent single crystal (phase I) shatters into single crystal fragments of the new phase (phase II). The two phases have been studied by single-crystal X-ray analysis using a synchrotron source, variable-temperature Raman spectroscopy, and computational analysis of lattice normal vibration modes. A mechanism of the transition is proposed. We confirm colossal thermal expansion coefficients and supercells as reliable features of thermosalient transitions and add as a third feature a low-frequency principal optical vibration of the crystal lattice prompting the transition. Based on this, a roadmap for the automated prediction of thermosalient transitions in molecular crystals is also outlined
In Situ Observation of the Structure of Crystallizing Magnesium Sulfate Heptahydrate Solutions with Terahertz Transmission Spectroscopy.
Get PDFTerahertz time-domain spectroscopy in a transmission geometry combined with visual analysis was used to investigate the crystallization process of MgSO4 solution. Careful spectral analysis of both a feature at 1.6 THz and the overall magnitude of absorption allowed the extraction of information about the liquid phase before and during crystallization, aiding the investigation of solvation dynamics and the behavior of molecular species at phase boundaries. The method was reproducibly applied to a number of measurements on a series of solutions of three chosen concentrations at different temperatures. When increasing temperature at the end of the measurement, the dissolution of crystals was observed as well. The temperature-dependent absorption data of the semicrystalline systems were converted to the solvent concentrations using a recently developed method. Solutions of a series of concentrations were also investigated in the temperature range of 4-25 °C. The results were compared to the theoretical calculated values, and the consistent differences proved the existence of a hydration shell around the salt ions whose behavior is different from bulk water. Future work will focus on triggering nucleation at specific positions in order to study the very beginning of the crystallization process. MgSO4 heptahydrate is used as a model system in this study, while the concept and the setup can be applied to other systems
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
ENVIRONMENTALLY INDUCED CHANGES IN THE BARRIERS TO INTERNAL
No full textAuthor Institution: Department of Chemistry, University of PittsburghThe rotationally resolved fluorescence excitation spectra of N-methyl-, 3-methyl-, and 5-methylindole and their Ar van der Waals complexes have been obtained. Analyses of these spectra show that the torsional barrier for methyl group rotation is significantly influenced by the attachment of a single Ar atom to the isolated molecule. For example, N-methylindole has and ; upon complexation, these values changes to and . Possible reasons for this behavior will be discussed; including (a) simple steric effects, (b) Ar atom induced changes in the electronic distribution of the parent molecule, and/or (c) changes in the nature of the motion itself. Work supported by NSF
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
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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