1,720,974 research outputs found
Organic chemistry applications
No full textStructures are at the heart of organic chemistry. The brains
are in using structures and structural theory to achieve
desired chemical transformations. Before the 1920s, the only
way to determine the way that the constituent atoms in an
organic molecule are bonded together was by degradation and
synthesis. For complex molecules, the process of determining
structures was often arduous, particularly when there were
few functional groups as with many steroids. Nonetheless,
extraordinary progress was made, even if slowly, by a
combination of experimental and deductive skills
Crystal structure determination by the combined analysis of NMR and powder diffraction data
No full textPowder diffraction and solid-state NMR are complementary approaches for probing the structural properties of solids, and provide complementary types of information. There are thus considerable potential benefits to be gained by employing these techniques in tandem in the structural characterization of solids. This article is focused on the combined analysis of solid-state NMR data and powder X-ray diffraction data during the process of crystal structure determination. The article covers both the wide-ranging uses of solid-state NMR in providing information to assist the process of structure determination from powder X-ray diffraction data, as well as recent advances toward ab initio crystal structure determination from solid-state NMR data (which generally relies on the combined use of information from powder X-ray diffraction data for the material of interest)
Oxygen-17 NMR of Inorganic Materials
No full textOxygen is one of the most naturally abundant elements, making it a key constituent in many materials, including some of central technological importance. 17O solid-state NMR can provide unique insight into the local environment around oxygen and hence the local structure, including the atomic ordering of solid materials. The background for improving the observation of 17O by solid-state NMR and determining the NMR interaction parameters including the combination of experimental data with first-principles density functional theory calculations is presented. The utility of this approach is illustrated here for a range of inorganic systems: highly crystalline ordered samples (including some important in the earth sciences), disordered materials, both crystalline solid solutions and glasses, as well as oxygen ion conducting material
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
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