1,720,958 research outputs found
H-2-NMR of the induced Chiral Phases of Acrylate-Metacrylate Liquid Crystalline Polymers
No full textIt is shown that the addition of 2 to 6 wt.%of a chiral dopant (CD) to a series of nematic copolymers (Pn) induces blue and cholesteric mesophases. The mesomorphic behaviour of various CD + Pn mixtures is investigated by polarized optical microscopy and the phase transition temperatures are determined by DSC measurements. Deuterium NMR spectra are recorded as a function of temperature within the mesophases and the spectral line shapes characteristic of different local orientational order parameters and orientational ordering processes of molecules in a magnetic field are observed depending on temperature, heating or cooling process, chiral dopant concentration, copolymer composition, and magnetic field strength
Internal and overall molecular dynamics in a chiral smectogen through H-2 NMR relaxation
No full textThe dynamics of a chiral polymorphic liquid crystal smectogen (8BEF5), partially deuterated on the aromatic core and on the chiral chain, has been investigated in its smectic A and C' phases. The H-2 T-1Q and T-1z spin-lattice relaxation times. and. consequently, the spectral densities J(1) (omega(o)) and J(2)(2omega(o)) have been determined for the aromatic as well as methylene deuterons of the chiral chain closer to the aromatic core. The interpretation of the relaxation behaviour has been carried out by means of the available motional models in the SmA phase. Contrary to what is usually observed for other mesogens, in the case of 8BEF5 the internal rotations are much better described by the strong collision model rather than by the small step rotational diffusion one
Study of the ferroelectric liquid crystal 11EB1M7 by means of H-2 NMR
No full textIn this work, a new procedure for the synthesis of the selectivity deuterium-labeled chiral liquid crystal (+)-(S)-4-[4′-(1-methylheptyloxy)] biphenyl 4(10-undecenylox)benzoate (11EB1M7) has been developed, aimed to the study of its structure, orientational ordering, and dynamic behavior by means of 2H NMR. 11EB1M7 was investigated throughout its mesophasic range, formed by a very rich variety of chiral liquid crystalline phases including blue, cholesteric, TGBA*, and smectic C*. Two isotopomers were synthesized by labeling 11EB1M7 on either the phenyl or the biphenyl moiety of the mesogenic core. This allowed structural information (such as the tilt angle of the rigid fragments of the molecule and the angle between their para axes), orientational order parameters, and individual diffusional coefficients for the various overall and internal motions to be obtained from 2H NMR spectra and relaxation measurements by applying suitable data analyses based on several theoretical models
H-2 NMR spectroscopy of liquid crystals: structure and orientational order of a chiral smectogen in its A, C* and J* phases
No full text2H NMR spectroscopy is employed to investigate the orientational order, molecular structure and phase transitions of the chiral smectic liquid crystal 1-methylheptyl 43⁄4-(4-n-decyloxy- benzoyloxy)biphenyl-4-carboxylate (10B1M7), showing smectic A, C* and J phases, as well as several sub-smectic C* phases. Two optically pure, diŒerently deuteriated isotopomers have been purposely synthesized and studied
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
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
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