1,720,955 research outputs found
Mathematical models of some nematic and cholesteric liquid crystal devices
No full textThis thesis describes the mathematical modelling and analysis of liquid crystal systems when an electric field is applied. This analysis is performed for Nematic, Twisted nematic, and Super-twisted nematic cells and for Polymer Gels. The mathematical techniques employed are: linear and non-linear stability analysis; perturbation theory; and the method of matched asymptotic expansions. For conventional nematic systems analytic expressions are obtained which describe the distortion of the liquid crystal and the coupled electric field at low, intermediate, and high applied voltages. Aspects of the dynamics are considered for both strong and weak anchoring and also with the inclusion of a coupled flow. It is shown that certain weakly anchored nematic systems admit travelling wave solutions. This is particularly relevant to the relaxation of polymer gels. For these systems a model is proposed which treats the polymer matrix as comprising thin orientated fibrils which act as weak anchoring sites distributed throughout the liquid crystal. The model is shown to correctly predict many of the experimentally observed properties of polymer gels. Specifically it predicts the enhanced critical voltage for such systems and also indicates that they saturate at a voltage proportionately close to the critical voltage. The model predicts that the decay of a polymer gel from a highly distorted state occurs via a travelling wave. This in turn implies that the decay constant will depend linearly on the width of the cell containing the gel
Experimental characterization of velocity and acoustic fields of single-stream subsonic jets
No full textThe characterization of velocity and acoustic fields from a single-stream free jet operating at subsonic regimes is essential for aeronautical applications. For instance, the investigation of exhaust gases from single or coaxial nozzles or from bleed valve in turbojets and turbofan engines is crucial for understanding the mechanisms of noise generation and propagation and eventually for finding ways to reduce aircraft noise. This article evaluates the velocity and acoustic fields of an isothermal single jet discharging from a circular 38.1 mm conical nozzle at three different Mach and Reynolds numbers of 0.25 (Re = 2.5 × 105), 0.50 (Re = 4.9 × 105) and 0.75 (Re = 6.8 × 105), respectively. Pitot-tube and hot-wire probes were used to identify the mean velocity profiles in longitudinal and transversal directions in the wake of the jet. The hot-wire anemometry system was also used to evaluate the turbulence intensity distribution over eleven axial lines, from the centerline to the edge of the nozzle. The accuracy of hot-wire anemometers for turbulent intensities lower than 15% at low and high subsonic Mach numbers was evaluated by comparing the experimental measurements with available data from the literature. An acoustic investigation was carried out by analyzing the sound pressure level obtained at six positions in the far field, with viewing angles ranging from 40° to 110°. The results were integrated to a database with sound pressure level as a function of Strouhal number, aiming to provide a benchmark for further RANS-based methods applied to aeroacoustic simulations of single jets
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
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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