1,721,025 research outputs found
Refractive indices of liquid crystals E7 and K15 in the mid- and near-IR regions
No full textThis paper presents the results of refractive-index measurements of the extraordinary and ordinary rays in nematic liquid crystals (NLCs) using a refractometric technique in the mid-IR (gimel = 10.6 mu m) and near-IR (gimel = 1550 nm) regions for NLC E7 and at (gimel = 1550 nm) regions for NLC K15. The optical anisotropy of NLC E7 at 10.6 mu m is determined independently by means of the interferometric method in order to compare it with the results obtained by the refractometric technique. (c) 2006 Optical Society of America
An innovative neutron spectrometer for soil moisture measurements
Full text linkSoil moisture is a crucial variable in evaluating soil properties and its interaction with the atmosphere, yet none of the techniques currently employed is fully adequate for evaluating the water content in soil over an area of hectares and depth of tens of centimeters. In recent times, it has been shown how the water content over this volume can be accurately assessed measuring changes in the epithermal flux of cosmic neutrons, which is extremely sensitive to the moderation caused by hydrogen. The instruments employed for neutron flux measurements are usually neutron counters, covered with moderator coatings for enhancing their sensitivity in the epithermal energy range. On the other hand, the worldwide shortage of 3He caused a considerable increase in the costs associated with the manufacturing of proportional counters based on this gas, which were widely employed for their great sensitivity and noise rejection capability. In this work, we developed a 3He-free neutron spectrometer for performing these measurements, which detects neutrons in the energy range from 0.01 ev to 1 GeV. The reconstruction of the energy spectrum allows a more accurate evaluation of the epithermal neutron flux and provides other information which improves the quality of soil moisture measurements. Irradiations performed with neutron sources of 241Am and AmBe allowed to evaluate the spectrometric capability of the instrument, whereas the measurements of cosmic neutrons were employed to assess its sensitivity to cosmic radiation. The sensitivity of the instrument is slightly less than the one of the neutron counters currently employed, yet the access to the spectrometric information should provide greater accuracy in the epithermal flux measurements
Measurement of refractive indices of the liquid crystal mixtures Merck 10400-000 and 10400-100 at the infrared wavelength lambda=1550 nm
No full textIn this work the extraordinary and ordinary refractive indices of different commercial liquid crystal (LC) compounds have been measured at the wavelength lambda = 1550nm. Four samples have been investigated. Two of them are LCs Merck 10400-000 and 10400-100. The other two have been obtained mixing the previous LCs in different proportions. The method used for the measurement is based on a refractometric technique that takes advantage of refraction of a narrow laser beam by a wedged shaped LC cell. The method allows the measurement of both the extraordinary and ordinary refractive indices of the LC. The measurement of the angle of the wedged cell is a very critical point and it has been performed by means of an optical method. The refractive indices have been measured at different temperatures
Mid-infrared refractive indices of the nematic mixture E7
No full textE7 is a room temperature nematic liquid crystal mixture with a high positive dielectric anisotropy and a high chemical stability. Because of its relatively high nematic-to-isotropic transition temperature, it is suitable for mid-infrared laser applications, where the absorption of laser light is not negligible and gives rise to a certain heating of the medium. In this paper we give a measurement of the refractive indices of the liquid crystal E7 at a wavelength of 10.6mum as a function of temperature. An empirical formula to represent the experimental data is also provided
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
Infrared refractive indices of liquid crystals
No full textThe refractive indices of E7 liquid-crystal mixture were measured at six visible and two infrared (lambda=1.55 and 10.6 mu m) wavelengths at different temperatures, using Abbe and wedged cell refractometer methods, respectively. The experimental data of the visible wavelengths fit the extended Cauchy equations well. Using the extended Cauchy equations, we can extrapolate the refractive indices of E7 to IR. The extrapolated results almost strike through the measured data. Thus, the extended Cauchy equations can be used to link the visible refractive indices to infrared, where the refractive index measurements are more difficult. (C) 2005 American Institute of Physics
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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