1,721,003 research outputs found
Determination of cadmium (II) and zinc (II) in olive oils by derivative potentiometric stripping analysis
Full text linkA method for the determination of cadmium (II) and zinc (II) in olive oils by derivative potentiometric stripping analysis after dry ashing of the sample is described. The metal ions were concentrated as their amalgams on a glassy carbon working electrode that was previously coated with a thin mercury film and then stripped by a suitable oxidant. Potential and time data were digitally converted into dt dE−1, and E was plotted vs. dt dE−1, thus increasing sensitivity of the method and improving resolution of the analysis. Quantitative analysis was carried out by the method of standard additions; a good linearity was obtained in the range of concentrations examined. Recoveries of 92–102% for cadmium (II) and of 89–99% for zinc (II) were obtained from an olive oil spiked at different levels. The detection limits were 5.1 ng g−1 for cadmium (II) and 7.6 ng g−1 for zinc (II)
Characterisation of Columbite-Tantalite (Coltan) ore from Congo. Elemental composition by total reflection X-ray fluorescence analysis
Full text linkThe paper describes the analysis of a columbite-tantalite (coltan) mineral ore from
Congo by using total reflection X-ray fluorescence (TRXRF) analysis. The sample was
mineralised with a lithium tetraborate and lithium metaborate flux mixture. TRXRF allows
multi-element analysis in a wide range of concentrations. The results were in good
agreement with those obtained by using another alkaline fusion with sodium peroxide
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
Determination of cadmium (II) and lead (II) in whole and skim milk by stripping chronopotentiometric analysis
Full text linkA method for the determination of cadmium (II) and lead (II) in whole and skim milk
by stripping chronopotentiometric analysis is described. The metal ions were concentrated
as their amalgams on a glassy carbon working electrode that was previously coated with
a thin mercury film and then stripped by a suitable oxidant. Potential and time data were
digitally converted into dt dE-1, and E was plotted vs. dt dE-1, thus increasing both
sensitivity of the method and resolution of the analysis. Quantitative analysis was carried
out by the method of standard additions. A good linearity was obtained in the range of
concentrations examined. Recoveries of 94-100% for cadmium (II) and of 91-98% for
lead (II) were obtained from a sample spiked at different levels. The detection limits were
4.4 ng g-1 for cadmium (II) and 8.6 ng g-1 for lead (II) and the relative standard deviations
(mean of nine determinations) were 4.1 and 5.6%, respectively. Results obtained on
commercial whole and skim milk were not significantly different from those obtained by
inductively coupled plasma atomic emission spectrometry
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
Unusual nighttime impulsive<i>fo</i>F2 enhancement below the southern anomaly crest under geomagnetically quiet conditions
Full text linkAn unusual nighttime impulsive electron density enhancement was observed on 6 March 2010 over a wide region of South America, below the southern crest of the equatorial anomaly, under low solar activity and quiet geomagnetic conditions. The phenomenon was observed almost simultaneously by the F2 layer critical frequency ( foF2) recorded at three ionospheric stations which are widely distributed in space, namely Cachoeira Paulista (22.4°S, 44.6°W, magnetic latitude 13.4°S), São José dos Campos (23.2°S, 45.9°W, magnetic latitude 14.1°S), Brazil, and Tucumán (26.9°S, 65.4°W, magnetic latitude 16.8°S), Argentina. Although in a more restricted region over Tucumán, the phenomenon was also observed by the total electron content (TEC) maps computed by usingmeasurements from 12 GPS receivers. The investigated phenomenon is very particular because besides being of brief duration, it is characterized by a pronounced compression of the ionosphere. This compression was clearly visible both by the virtual height of the base of the F region (h′F) recorded at the aforementioned ionospheric stations, and by both the vertical electron density profiles and the slab thickness computed over Tucumán. Consequently, neither an enhanced fountain effect nor plasma diffusion from the plasmasphere can be considered as the single cause of this unusual event. A thorough analysis of isoheight and isofrequency ionosonde plots suggest that traveling ionospheric disturbances (TIDs) caused by gravity wave (GW) propagation could have likely played a significant role in causing the phenomenonFil: Pezzopane, M.. Istituto Nazionale di Geofisica e Vulcanologia; ItaliaFil: Fagundes, P. R.. Física E Astronomia, Universidade Do Vale Do Paraiba; BrasilFil: Ciraolo, L.. Ifac-crn; ItaliaFil: Correia, E.. Física E Astronomia, Universidade Do Vale Do Paraiba; BrasilFil: Cabrera, Miguel Angel. Laboratorio de Telecomunicaciones; ArgentinaFil: Ezquer, Rodolfo Gerardo. Centro de Investigación de Atmósfera Superior y Radiopr; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentin
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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