1,721,116 research outputs found
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
Gas-to-Particle Partitioning of Major Oxidation Products from Monoterpenes and Real Plant Emissions
Get PDFSecondary organic aerosol (SOA), formed through the oxidation of volatile organic compounds (VOCs) in the atmosphere, play a key role in climate change and air quality. Due to thousands of individual compounds involved in SOA formation, the chemical characterization of organic aerosols (OA) remains a huge analytical challenge. Defining the fundamental parameters that distribute these organic molecules between the gas and particle phases is essential, as atmospheric lifetime and their impacts change drastically depending on their phase state. In this work, an instrument called aerosol collection module (ACM) was redeveloped and automated to allow a better characterization of SOA originating from the oxidation of biogenic precursors. An inter-comparison of the ACM to different aerosol chemical characterization techniques was performed with a focus on the partitioning of major biogenic oxidation products between the gas- and particle-phase. In particular, the ACM, the collection thermal desorption unit (TD) and the chemical analysis of aerosol on-line (CHARON) are different aerosol sampling inlets utilizing a Proton-Transfer-Reaction Timeof- Flight Mass Spectrometer (PTR-ToF-MS). These techniques were deployed at the atmosphere simulation chamber SAPHIR to study SOA formation and aging from different monoterpenes (β-pinene, limonene) and real plant emissions (). The capabilities of the PTR-based techniques were compared among each other and to results from an Aerodyne Aerosol Mass Spectrometer (AMS) and a Scanning Mobility Particle Sizer (SMPS). Gas-to-particle partitioning values were determined based on the saturation mass concentration (C*) of individual ions by performing simultaneous measurement of their signal in the gas- and particle-phase. Despite significant differences in the aerosol collection and desorption methods of the PTR based techniques, the determined chemical composition was comparable, i.e. the same major contributing ions were found by all instruments for the different chemical systems studied. These ions could be attributed to known products expected from the oxidation of the examined monoterpenes. Averaged over all experiments, the total aerosol mass recovery compared to an SMPS was 80 ± 10%, 51 ± 5% and 27 ± 3% for CHARON, ACM and TD, respectively. Comparison to the oxygen to carbon ratios (O:C) obtained by AMS showed that all PTR based techniques observed lower O:C ratios indicating a loss of molecular oxygen either during aerosol sampling or detection. Differences in total mass recovery and O:C between the three instruments was found to result predominately from differences in the electric field strength (V cm) to buffer gas density (molecules cm) (E/N) ratio in the drifttube reaction ionization chambers of the PTR-ToF-MS instruments and from dissimilarities in the collection/desorption of aerosols. A method to identify and exclude ions affected by thermal dissociation during desorption and ionic dissociation in the ionization chamber of the PTRMS was developed and tested. Determined species were mapped onto the two dimensional volatility basis set (2D-VBS) and results showed a decrease of the C* with increasing oxidation state. For compounds measured [...
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
Multi-stress interaction effects on BVOC emission fingerprints from oak and beech: A cross-investigation using Machine Learning and Positive Matrix Factorization
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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
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