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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
Strong Metal-Adsorbate Interactions Increase the Reactivity and Decrease the Orientational Order of OH-Functionalized N-Heterocyclic Carbene Monolayers
No full textFundamental understanding of the correlation between the structure and reactivity of chemically addressable N-heterocyclic carbene (NHC) molecules on various surfaces is essential for the design of functional NHC-based self-assembled monolayers. In this work, we identified the ways by which the deposition of chemically addressable OH-NHCs on Au(111) or Pt(111) surfaces modified the anchoring geometry and chemical reactivity of surface-anchored NHCs. The properties of surface-anchored NHCs were probed by conducting X-ray photoelectron spectroscopy and polarized near-edge X-ray absorption fine structure measurements. While no preferred orientation was identified for OH-NHCs on Pt(111), the anchored molecules adopted a preferred flat-lying position on Au(111). Dehydrogenation and aromatization of the imidazoline ring along with partial hydroxyl oxidation were detected in OH-NHCs that were anchored on Au(111). The dehydrogenation and aromatization reactions were facilitated, along with partial decomposition, for OH-NHCs that were anchored on Pt(111). The spectroscopic results reveal that stronger metal-adsorbate interactions increase the reactivity of surface-anchored OH-NHCs while decreasing their molecular orientational order
Identifying site-dependent reactivity in oxidation reactions on single Pt particles
Get PDFCatalytic nanoparticles are heterogeneous in their nature and even within the simplest particle various surface sites exist and influence the catalytic reactivity. Thus, detailed chemical information at the nanoscale is essential for understanding how surface properties and reaction conditions direct the reactivity of different surface sites of catalytic nanoparticles. In this work, hydroxyl-functionalized N-heterocyclic carbene molecules (NHCs) were anchored to the surface of Pt particles and utilized as chemical markers to detect reactivity variations between different surface sites under liquid and gas phase oxidizing conditions. Differences in the chemical reactivity of surface-anchored NHCs were identified using synchrotron-radiation-based infrared nanospectroscopy with a spatial resolution of 20 nanometers. By conducting IR nanospectroscopy measurements, along with complementary spatially averaged IR and X-ray spectroscopy measurements, we identified that enhanced reactivity occurred on the particles' periphery under both gas and liquid phase oxidizing conditions. Under gas phase reaction conditions the NHCs' hydroxyl functional groups underwent preferential oxidization to the acid along the perimeter of the particle. Exposure of the sample to harsher, liquid phase oxidizing conditions induced modification of the NHCs, which was mostly identified at the particle's periphery. Analysis of X-ray absorption spectroscopy measurements revealed that exposure of the sample to oxidizing conditions induced aromatization of the NHCs, presumably due to oxidative dehydrogenation reaction, along with reorientation of the NHCs from perpendicular to parallel to the Pt surface. These results, based on single particle measurements, demonstrate the high reactivity of surface sites that are located at the nanoparticle's periphery and the influence of reaction conditions on site-dependent reactivity
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
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Enantioselective Functionalizations of Alkenes Using Chiral Phosphoric Acids
Get PDFNew organocatalytic enantioselective reactions were developed, focusing on using new modes of reactivity with chiral phosphoric acids. Prochiral alkenes and styrenes were explored as substrates for various transformations, including enyne cycloisomerization, hydroamination, halocyclization, and fluorination. The enantioenriched chiral products generated by these methods include heterocycles and allylic fluorides
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Gold(I)-Mediated Nucleophilic Additions to Allenes: from Enantioselective Catalysis to Supramolecular Chemistry
Get PDFThe ability of gold(I) complexes to activate carbon-carbon multiple bonds for the addition of nitrogen and oxygen nucleophiles has emerged as an attractive synthetic method in organic chemistry. While many transformations catalyzed by gold(I) have been reported in recent years, few studies provide insight into the mechanism of gold(I) mediated processes. The first half of this thesis will discuss the development of an enantioselective gold(I)-catalyzed hydroamination of allenes with hydroxylamine and hydrazine nucleophiles and mechanistic studies of this and related systems. The second half of this thesis will cover our efforts to incorporate gold(I) catalysts into supramolecular host-guest complexes and will highlight potential advantages of this novel approach to gold(I) reactions.Chapter 1. In this chapter, we report a novel enantioselective method for formation of isoxazolidines, pyrazolidines and tetrahydrooxazine heterocycles catalyzed by dinuclear bisphosphine gold(I) complexes. Furthermore, we discuss our efforts toward the development of a dynamic kinetic resolution of chiral allenes via intermolecular asymmetric hydroamination. Chapter 2. We perform detailed kinetic studies to elucidate the mechanism of two transformations: the gold(I)-catalyzed hydroamination of allenes with hydrazine nucleophiles and the intramolecular hydroamination of dienes in the presence of alcohol co-catalysts. While the hydroamination of allenes proceeds via an outer sphere ¥ð-acid mechanism, the related reaction with dienes likely proceeds via a Lewis-acid assisted-Br©ªnsted acid pathway. Chapter 3. This chapter will focus on our efforts to incorporate catalytically active gold(I) complexes into tetrahedral supramolecular guest of the form Ga4L6. Using such a complex, we catalyze the intramolecular hydroalkoxylation of allenes. We demonstrate that encapsulation of gold(I) increases the rate of reaction relative to Me3PAuBr and also leads to improved catalyst lifetime. Chapter 4. Herein we apply the supramolecular host-guest complex with gold(I) and Ga4L6 to tandem reactions with enzymes. The encapsulated complex performs as well, if not better than the ¡°free¡± gold(I) complex in chemoenzymatic processes with a variety of esterase and lipases. In some cases the free gold(I) cations significantly reduce the rate of enzyme catalysis while the encapsulated complex has no effect on enzyme activity
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