1,720,981 research outputs found
Director configuration in the twist-bend nematic phase of CB11CB
Full text linkThe director distribution in the nematic phases exhibited by the 1",11"-bis(4-cyanobiphenyl-4'-yl)undecane (CB11CB) liquid crystal has been studied in the bulk using the EPR spin probe technique. EPR spectra confirmed the presence of a higher temperature uniaxial nematic phase and of a lower temperature nematic phase in which the director distribution is not uniform. Spectra recorded in the lower temperature nematic phase were not fully compatible with theoretical EPR spectra calculated according to the recently proposed model for the twist-bend phase in which the local domain director twists around an axis with a fixed tilt angle, theta_0, but were well described by a ‘‘distributed-tilt’’ model in which the director has a relatively narrow distribution, centred at theta_0
Nematic Director Configuration, Local Order and Microviscosity in a PSLC Cell
No full textThe director configuration, the local order and the molecular-level reorientational dynamics (microviscosity) of the 5CB liquid crystal (LC) inside a polymer-stabilized LC (PSLC) cell prepared with the 4,4-bis(6-(acryloyloxy)hexyloxy)biphenyl (BAB6) diacrylic monomer have been studied with the EPR spin probe technique across the nematic and the isotropic phase of the LC. The cells made from glass slides, either clean or coated with an aligning layer, were filled with pure 5CB or with 0.5, 1.0 or 2.0 wt% of BAB6, either in the monomeric state or polymerized. Local orientational order parameter () in the non treated cells was always slightly lower than in the coated ones and both were lower than in the bulk LC. Order appeared to be independent of polymerization state or BAB6 concentration up to 1.0 wt%. Reorientational dynamics was essentially bulk-like in all cases, indicating that in our PSLC cells a full molecular mobility is retained. At the concentration of 2.0 wt%, in the coated cell with polymerized BAB6, the monodomain did not reform after a 90 • rotation of the cell in the magnetic field, suggesting that the polymer network is, as expected, stabilizing the preexisting director configuration
A comparison of the effects of dispersed hydrophobic or hydrophilic aerosil nanoparticles on the order and dynamics of the 5CB liquid crystal
Full text linkWe report on a comparison between the random disorder effects of an hydrophobic (R812) or an hydrophilic (A380) aerosil on the order and dynamics of the 3beta-DOXYL-5alpha-cholestane spin probe in the liquid crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) using the ESR technique. Increasing the aerosil concentration up to 3 wt% the probe order parameter is depressed with a larger effect for the hydrophilic aerosil. The dynamics in the isotropic phase is of Arrhenius type and essentially concentration and aerosil-type independent. Deviations from this behavior are observed in the nematic even at 0.3 wt% of hydrophilic aerosil and are well represented by a Vogel-Fulcher-Tammann type law, suggesting that a glass-like state can be induced by a very small amount of random disorder
EPR study of the polydomain structure of the twist-bend nematic phase of CB9CB in the bulk
Full text linkEPR spin probe spectra of the liquid crystal phases exhibited, in the bulk, by the 1″,9″-bis(4-cyanobiphenyl-4’-yl)nonane (CB9CB) bent-shape dimer showed that, on cooling from the isotropicphase, this material forms a uniaxial nematic phase with a uniform director macroscopicallyaligned along the spectrometer field. Upon further cooling, a transition into the twist-bendnematic phase is observed after a biphasic region of approximately 4 K. In this lower temperaturenematic phase, the director does not appear to be macroscopically aligned. The non-uniformdirector distribution is modelled as a collection of monodomains tilted with respect to themagnetic field and orientationally distributed around the tilt direction
Director configuration in the twist-bend nematic phase of CB11CB
Full text linkThe director distribution in the nematic phases exhibited by the 100,1100-bis(4-cyanobiphenyl-40-
yl)undecane (CB11CB) liquid crystal has been studied in the bulk using the EPR spin probe technique.
EPR spectra confirmed the presence of a higher temperature uniaxial nematic phase and of a lower
temperature nematic phase in which the director distribution is not uniform. Spectra recorded in the
lower temperature nematic phase were not fully compatible with theoretical EPR spectra calculated
according to the recently proposed model for the twist-bend phase in which the local domain director
twists around an axis with a fixed tilt angle, y0, but were well described by a ‘‘distributed-tilt’’ model in
which the director has a relatively narrow distribution, centred at y_0
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
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