1,720,983 research outputs found
Loss of methane and ethene from long-lived gaseous xylenium ions (protonated xylene) after "composite" scrambling
No full textMormann M, Kuck D. Loss of methane and ethene from long-lived gaseous xylenium ions (protonated xylene) after "composite" scrambling. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY. 2002;219(3):497-514.The unimolecular fragmentation of long-lived gaseous xylenium ions, CH3-C6H5+-CH3, has been studied in detail using C-13-labeling, in addition to deuterium labeling, in combination with mass-analyzed ion kinetic energy (MIKE) spectrometry. Metastable xylenium ions generated from the EI-induced loss of (COOR)-C-circle (R=H, CH3) from 1,4-dimethyl-1,4-dihydrobenzoic acid or its methyl ester or by protonation of para-xylene under CI(CH4) conditions eliminate H-2, CH4 and, most remarkably, C2H4. The kinetic energy release characteristics of these fragmentation processes are reported. H-2-labeling reveals that the loss of methane occurs by protonolytic cleavage of the C-alpha-C-lpso bonds, excluding intra-complex benzylic hydride abstraction by CH3+ ions. C-13-labeling confirms the composite scrambling behavior preceding both methane and ethene losses. CH4 loss of a major fraction (92%) of xylenium ions occurs without C scrambling but with some concomitant hydrogen exchange (H-alpha/H-ring) via nonclassical tolylmethonium ions, whereas a minor fraction (8%) undergoes complete C and H scrambling. C2H4 loss is preceded by different sequences of reversible ring expansion and ring contraction reactions involving methyldihydrotropylium ions (protonated methylcycloheptatriene) which, by irreversible ring contraction, eventually form ethylbenzenium ions (protonated ethylbenzene). A major fraction (66-75%) of the ions exhibits "specific" behavior, with the one of the methyl carbons being incorporated specifically into the ethene fragment and the other only after randomization with the carbons of the tolyl unit. A minor fraction (34-25%) of the ions undergoes complete C and H scrambling prior to ethene loss, involving both methyl groups. 1,2-CH3 shifts are invoked to occur in the xylenium and/or dihydrotropylium ions
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
A three base pair gene variation within the distal 5 '-flanking region of the interleukin-10 (IL-10) gene is related to the in vitro IL-10 production capacity of lipopolysaccharide-stimulated peripheral blood mononuclear cells
No full textInterleukin-10 (IL-10) is an important multifunctional immunmodulator. There is evidence that IL-10 secretion is associated with certain genetic elements of the proximal IL-10 gene 5'-flanking region. The allelic and genotypic comparison of IL-10 expression by lipopolysaccharide (LPS)-stimulated leukocytes (PBMC) with a recently discovered distal "indel" DNA-sequence variation at - 7400 by revealed significant inter-individual differences in the IL-10 in vitro production capacity. Homozygotes lacking the three base pairs "GGA" (- 7400del) at this gene locus are characterised by high expression of IL-10 with a median of 1690pg/ml (P less than or equal to 0.009). The allelic comparison supports this finding (P less than or equal to 0.002). Further analysis of the haplotype - 7400/- 1087 showed that homozygotes for - 7400del/- 10876 may be classified as very strong IL-10 responders with a median IL-10 secretion of 2378 pg/ml (P less than or equal to 0.025). When leukocytes were stimulated in vitro by dibutyryl-cAMP or infected with Epstein-Barr virus no significant inter-individual differences between the - 7400indel alleles or genotypes and the IL-10 in vitro production capacity were observed. Our findings further the understanding of the complexity of IL-10 gene regulation in relation to defined regulatory gene variations
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
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