1,720,999 research outputs found
Measuring stellar temperatures : an astrophysical laboratory for undergraduate students
No full textWhile astrophysics is a fascinating subject, it hardly lends itself to laboratory experiences accessible to undergraduate students. In this paper we describe is presented a feasible astrophysical laboratory experience, in which students are guided to take several stellar spectra, using a telescope, a spectrograph and a CCD camera, and perform a full data analysis using the equivalent widths method on some spectral lines. This allows them to derive stellar temperatures after a suitable calibration and fitting procedure. On average the estimated stars temperatures agree with known results within an error margin of 5 to 10% for cold stars, and 20 to 25% for hot stars
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
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
Stellar temeratures by Wien's law : not so simple
No full textA star’s surface temperature is among the most important features that can be deduced from its
light. We have made measurements to see how reliably we could determine the surface
temperatures of some A to K stars using Wien’s Displacement Law. We took spectra, corrected
them for atmospheric extinction and instrumental response, found the wavelengths of their
intensity maxima, and then from Wien’s law found the surface temperatures of the observed stars.
For F to early K stars, our results agree with temperatures determined in other ways. For A and
later K stars, the agreement is poor because the spectra are appreciably different from ideal
blackbody spectra and because our equipment responds poorly to the deep red and blue
wavelengths where the spectra of these stars have their peak intensities. This paper points out
several interesting concepts in and outside the astrophysical domain that can be instructive for
undergraduate students
Immobilization of reagents and catalysts by photochemical grafting onto polymers
No full textThe possibility of immobilizing reagents and catalysts by photochemical grafting of their composites with an epoxy-diacrylate resin has been investigated. Two model systems have been examined: (i) the catalytic decomposition of aqueous sodium hypochlorite by cobalt peroxide, with oxygen production; (ii) the reaction of alkali metals with alcohols. For case (i) the catalyst was embedded, in the form of a mixture with 90% of zeolite 13X, into the photografted polymer matrix; while for case (ii) the alkali metal reagent, supported onto 90% of zeolite 13X, was incorporated into the microporous membrane. Kinetics of reaction (i) were studied in standard conditions (1.0 M NaOCl; 1.0 M NaCl; 0.25 M NaOH) between 288.2 to 318.2 K, and the relation between pseudp-first order kinetic constants and amount of catalyst incorporated into the membrane determined. Isotope effects for reaction (ii), relative to H2, D2, HD production, were measured with mixtures of deuterated and non-deuterated CH3OH(D), C2H5OH(D), n-C3H7OH(D), and i-C3H7OH(D) at 25 °C, as a function of volume percent of non-deuterated alkanols in the liquid phase. For reaction (i) reactivity was found to be substantially the same in the membrane reactor as in ordinary chemical conditions: loss of catalytic activity did not exceed 15%. For reaction (ii) isotope effects, the origin of which is discussed, fully coincided with those measured in the absence of the polymer matrix
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