1,720,959 research outputs found
The perils of large 'small' molecules - successful refinement of metallosupramolecular grid-like assemblies
No full textWith recent advances in diffractometers and as computers grow ever more powerful, it is possible to collect and solve several data sets every day. Thus the technique is now being used as alternative form of characterisation. This also has meant that the size of crystals required to obtain data has decreased, and the size of the molecules involved has increased, which can lead to a severe shortfall in data to parameter ratio. A recent area which has gained from these advancements is that of molecular grid and tape structures, although the successful solution and refinement may often be problematic due to the generally large asymmetric units. As chemists design and prepare these larger structures, the composition is generally known, but the geometry is still vital to determine. Most programs for full structure determinations were designed for small molecules with up to 100 non-hydrogen atoms. Although they can cope with larger numbers, quite a few crash once more than 500 atoms become involved. This does cause problems not only in attempts to solve structures, but also (especially for the chemist) when trying to visualise them later. Through our work with the UK National Service it has been necessary to address some of the problems described. For example the application of focussing mirrors to a rotating anode generator significantly increases the number of observed reflections for small crystals and for those of the above type of compound which are often weakly diffracting. This increase in quantity of experimental data coupled with the large number of variables provides a real test for the software. Generally, of the initial solution refinement programs, it is often only Shelxs-97 which produces a reasonable solution, although the assignment of the atoms is tedious. Most of the 'brute-force' programs give a nonsensical solution, if at all. For refinements Shelxh-97 does work, although sometimes the source code needs to be tweaked to cope with the largest structures (4000 parameters might be ample for most systems but 8000 is often a better limit). This poster will present successful structure determination of a number of these cases and the pitfalls and method of treatment will be outlined
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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