1,721,032 research outputs found
The failure of asymmetric synthesis in cholesteric liquid crystals. New examples of bimolecular reactions
No full textA set of bimolecular reactions was carried out in cholesteric solvents in order to obtain asymmetric syntheses. In all cases the products did not show significant optical rotation
Circular dichroism for studying gel-like phases
No full textChiroptical spectroscopies, optical rotatory dispersion (ORD) and circular dichroism (CD) [1], were developed in the 1960s to study mainly steroidal ketones [2] and octahedral metal complexes [3]. Subsequently, several different chromophores were investigated by CD using different theoretical analyses [4]; the exciton approach, in particular, has been very successful for studying molecular systems containing two or more absorbing chromophores, for example, biaryls [4, 5] and proteins [6]. At the present time, the outstanding sensitivity of CD is employed mainly to study biological macromolecules and their perturbations by external factors. In the field of supramolecular chemistry, CD has several interesting applications. In particular, assembly processes leading to the formation of helical superstructures can be investigated [7]. In those cases where gels are formed by chiral monomers through self-assembly processes, it seems natural to use CD to monitor the progress of the process and, hopefully, to obtain information on the assembled structures that complements that from other techniques (see Chapters 10-12)
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
The circular dichroism of (-)-(S)-3-methylthian: a study of the electronic transitions and stereochemistry of cyclic sulphur derivatives
No full textThe self-assembly of a lipophilic deoxyguanosine derivative and the formation of a liquid crystalline phase in hydrocarbon solvents
No full textVariations 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
Induction of cholesteric mesophases in nematic liquid crystals and correlation of absolute configurations of some chiral oxiranes and thiiranes
No full textThe self-assembly of dideoxyguanosine (3-3') and (5-5') monophosphates.
No full textThe title compounds show a pronounced cation-directed ability to self-assemble in water and to gives columnar structures similar to four-stranded helices; for compound (5'-->5')-d(GpG), this leads to the formation of cholesteric and hexagonal liquid crystalline phases. Both phases are columnar and the cholesteric phase is left handed. This behaviour is a further confirmation of the tendency of guanine derivatives to self-assemble to give stacked columnar structures whenever not impossible for structural reasons. The CD spectra of the aggregates in isotropic solutions are dominated by a negative exciton couplet centred around 250 nn associated to a left-handed columnar chirality. The shapes of the profiles, in the 220-300-nm region, for (5'-->5')-d(GpG) (in water or in saline solutions) and for (3'-->3')-d(GpG) (in KCI solution) are quasi-mirror images of those of poly(G) and (3'-->5')-d(GpG). The appearance of relatively intense CD signals around 280-300 nm in solution of (3'-->3')-d(GpG) in the presence of NaCl resembles that of (3'-->5')-d(GpG) in the presence of Rb+ or Na+. In the compounds investigated in this work, which present two equivalent ends, one observes the two CD features that have been associated, in the current literature, with the signature of four-stranded parallel and antiparallel structures: hence the origin of these CD bands cannot be found in the polarity of the strands. Self-assembly is favoured by the addition of extra salt and the stabilising effect of K+ is greater than that of Na+ in the case of (3'-->3')-d(GpG), an assembled species could be detected by CD only in the presence of extra salt
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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