1,720,956 research outputs found
Molecular dynamics in a blue phase liquid crystal: a H-1 fast field-cycling NMR relaxometry study
No full textLiquid crystals exhibiting Blue Phases (BPs) have been the focus of academic and commercial research interest in the last few years due to their highly interesting properties in the fields of optics and photonics. In order to better understand the properties of the BPs, it is important to study molecular dynamics in these phases, including molecular rotations/reorientations, diffusion, and collective motions. Here, we present the first study of molecular dynamics in a BP system by means of H-1 fast field-cycling relaxometry. The investigated sample, called 10BBL, was a lactate derivative, containing two chiral centers, exhibiting BP, TGBA*, TGBC*, and SmC* phases stable in rather large temperature ranges. Molecular dynamics was investigated by analyzing the temperature- and frequency-dependencies of spin-lattice relaxation. We compare the dynamics in the TGB phases with the one in the BP and with the TGB phases investigated in previous studies
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
Estudo da Dinamica Molecular em Cristais Liquidos com Polimorfismos Peculiares
No full textIn this work we studied by proton NMR spectroscopy the molecular dynamics in the S_A_d mesophases of the compounds 4-(4'-#eta#-hexadecyloxybenzylidene)-amino) benzonitrile (16CN) and binary mixture of 30% of 4-#eta#-dodeciloxybenzylidene- 4'-#eta#-cyanoaniline (DOBCA) with 70% of 4-cyanobenzylidene-4'-#eta#-octyloxyaniline (CBOOA), in the N and S_A_2 mesophases of the compound 4-pentyl-phenyl 4'-cyanobenzoyloxy-benzoate (DB5CN) and in the N, S_A_d, N_r_e and S_A_1 mesophases of the compound 4-cyanobenzoate-4'-octylbenzoxyphenyl (DB8CN Sym). The studies of the molecular dynamics were based on frequency, temperature and angular dependent measurements of the proton spin-lattice relaxation rate (1/#TAU#_1). For all the compounds the 1/#TAU#_1 measurements for frequencies between 5.6 MHz were performed on conventional NMR spectrometers. On the compounds DB5CN and DB8CN Sym adicional Fast-field Cycling NMR 1/#TAU#_1 measurements were performed for frequencies below 1 MHz. The molecular dynamics in the nematic mesophases (N and N_r_e) is quit different from the molecular dynamics in the smetic ones (S_A_1, S_A_d and S_A_2). In the nematic mesophases the spin-lattice relaxation can be explained essentially in terms of collective motions associated with order director fluctuations, characterized by the frequency dispersion law 1/#TAU#_1#approx##nu#"-"1"/"2, and non-collective molecular ratation/reorientational motions. It is found that the contribution of the translational self-diffusion movements in the modulation of the inter-proton spin interactions is very small. On the other hand, in the smetic mesophases self-diffusion and the rotation/reorientations are the main relaxation mechanisms. Collective motions which in these mesophases have to be associated with layer undulations described by the frequency dispersion law 1/#TAU#_1#approx##nu#"-"1, have a small contribution to the spin-lattice relaxation in the S_A mesophases. The inclusion in the relaxation model of a contribution from the cross-relaxation mechanism between protons and nitrogen nuclei improves the quality of the 1/#TAU#_1 data fits in both kinds of mesophases. In the S_A_d mesophases an additional relaxation mechanism associated with the dynamic process of dissociation and recombination of molecules in dimers can be present. The combined study of the molecular dynamics in the N, S_A_d, N_r_e and S_A_1 mesophases of DB8CN Sym assuming that the rotation/reorientational motions are thermally activated reveals that, in fact, one more relaxation mechanism has to be considered in the analysis of the 1/#TAU"_1 data in this kind of mesophasesAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga
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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