1,720,978 research outputs found
Fabrication and characterization of hybrid liquid crystal devices
No full textThis thesis describes new characterization techniques that can be used to investigate nematic liquid crystal (LC) materials and systems, and experimental studies of new hybrid LC devices.The characterization techniques include an all-optical method for determining nematic viscosities, a multi-spectrum analysis (VTF) of the electro-optic response of an LC device subject to an AC field, and a measurement of two-beam coupling (TBC) in photorefractive LC systems subject to an AC field. The time response measurement is the first experimental study of fast director oscillations seen when a modulated field is applied to a cell, and it has been shown that Erickson-Leslie theory can be used to determine the rotational viscosity by fitting to these oscillations. The VTF has been used to show that the conductivity of the LC E7 is 2 x that of TL205, and can explain the origin of higher beam coupling in E7 photorefractive devices. The AC driven TBC and its analysis has proved that a non-ohmic photoconductor will lead to two distinct beam coupling regimes in frequency space, and has shown that optimum beam coupling efficiency can be obtained by tuning the AC frequency.The range of new hybrid LC devices investigated here include cells using an LC doped with multiferroic nanoparticles, and photorefractive cells that use a new electrode material (PEDOT) to reduce injection barriers in standard photorefractive devices, a photorefractive polymer (JTDA16) as an aligning layer, and a photoaligning layer (PAAD) to enhance the modulation depth of induced photorefractive gratings. The multiferroic nanoparticle study showed that a magneto-optic response could be observed at low fields (< 500 Gauss), and that the sol-gel process for growing nanoparticles is not appropriate for creating ferroelectric layers with thicknesses below ~ 15 nm. The new materials for photorefractive cells have shown promising results, with observed diffraction efficiencies up to 13 x higher than a benchmark cell using polyvinyl carbazole as a photoconductor
Liquid crystals under the spotlight: light based measurements of electrical and flow properties of liquid crystals
No full textOptical light modulation in photorefractive liquid crystal cells depends strongly on the relative voltage drop across the photoconductive and liquid crystal layers. This quantity can be estimated using the Voltage Transfer Function, a generalization of the standard cross polarized intensity measurements. Another advantage of this new measurement technique is that we can use it to estimate dynamical parameters of the liquid crystal and of the device, either through simple black-box models or using a full Ericksen-Leslie theory. In this latter case we can obtain estimates of some of the viscosities of the liquid crystal
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
Voltage transfer function as an optical method to characterize electrical properties of liquid crystal devices
No full textThe voltage transfer function is a rapid and visually effective method to determine the electrical response of liquid crystal (LC) systems using optical measurements. This method relies on cross-polarized intensity measurements as a function of the frequency and amplitude of the voltage applied to the device. Coupled with a mathematical model of the device it can be used to determine the device time constants and electrical properties. We validate the method using photorefractive LC cells and determine the main time constants and the voltage dropped across the layers using a simple nonlinear filter model
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
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