1,720,958 research outputs found
Interrogation of optical pH sensor based on sol-gel doped new luminescent europium chelate with compact photon counting system
No full textSummary: This paper presents recent measurements of novel Eu3+-complex doped sol gel layers (ref 1) which are intended for use as pH indicators, with interrogation by monitoring their fluorescent decay with a compact photon-counting receiver (ref 2). The basic chemistry is outlined and the instrumental arrangement and experimental results are described.Requirements and basic concept of indicator chemistry. Luminescent lanthanide chelates have many applications, being useful alternatives to standard fluorescent dyes especially when there is significant autofluorescence. They are also useful donors for use in energy transfer experiments to determine static inter-molecular distances. These applications arise because of the chelates' excellent solubility and unusual spectral characteristics, including narrow (<10 nm) spectral emission, large Stokes shifts (>150 nm), potentially high quantum yields. Selvin et al. have synthesized several lanthanide chelates but all show inconvenient excitation maxima around 340 nm. In contrast, our novel long-wave luminescent dye, based on europium luminescence initiated by a covalently-bonded antenna fluorophor, shows excitation maxima at 370 nm where low cost LEDs are now available. To design sensors of high stability and long lifetime, the sensor matrix and sensor technology are of prime interest. Sol-gel technology enables the production of proton-permeable glassy layers at room temperature and offers simple methods for manipulation of the basic composition, molecular structure, and hence the chemical characteristics of organic matrices. Time-resolved fluorometry is preferable to conventional fluorometry, since there are no intensity related problems due to turbid samples, self-filter effect, and cuvette geometry. Also, the fluorescence decay time is usually independent of the concentration of the indicator, even when it has been partially modified by leaching out, by decomposition, or by photo bleaching. In the current work, the Eu3+-complex has been successfully entrapped into tetramethoxysilane (TMOS)-based sol-gel matrices. It was initially found that a Eu3+-complex, which showed useful pH sensitivity in aqueous solution, lost this sensitivity when immobilized in sol-gel matrices. In order to recover this property, the pH indicator bromothymol blue (BTB) was added to the starting sol-gel components and it was found that the useful pH response that was present in water was not only restored, but was actually improved upon. Instrumentation and experiment for interrogation of Eu3+-complex-doped sol-gel coated layer. The arrangement shown in fig 1 was used for rapid interrogation of fluorescence lifetime. The arrangement improves signal to noise because the sol-gel coating is illuminated directly with a filtered UV LED source, rather than via an optical fibre probe. This increases illumination intensity by removing optical power loss in the launch optics, illuminates a large coating area, and reduces the background auto-fluorescence signal generated from combined launch and return optics. The main excitation peak occurs at 370 nm, which falls in the absorption band of the pH-sensing layer. It should be noted that this arrangement, which was used to improve signal to noise and reduce self-fluorescence in our measurement, was considered to be only an interim step on the way to developing an all-fibre system for illumination and collection of light. Clearly similar gains in signal can be achieved by using larger input and output fibres or fibre bundles, and self-fluorescence can be reduced by use of separate fibre cables for incident and fluorescent light.<br/
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
Prediction of digestible organic matter in dry matter in vivo from the chemical composition, in vitro and in situ measurements on native mountain forages.
No full textAuthor-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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