1,721,022 research outputs found
Crystal structure of Au-pseudocarbyne(C6)
Get PDFCarbyne-related materials permit exploring the potentially extraordinary properties of this long-sought but still elusive carbon allotrope. However, accurate understanding of these materials is challenging. Here we report the crystal structure of a Au-pseudocarbyne, a representative of a possible new family of materials consisting of sp-hybridized carbon chains and stabilizing metal atoms. Au-pseudocarbyne(C6), the representative pseudocarbyne containing six-membered carbon chains, has space group P6/mmm191 and unit-cell parameters a = b = 0.60 nm, c = 0.896 nm, α = β = 90°, γ = 120°. Its long-range structure can be understood as intimately intergrown bundles, each consisting of six parallel, infinite carbon chains surrounding a column of gold atoms. This compound, together with its eight-membered counterpart Au-pseudocarbyne(C8), shows that interesting new materials resembling the carbyne structure and sharing some of its properties can be designed and developed. The current work raises serious questions regarding recent reports of carbyne synthesis
High resolution transmission electron microscopy of two stony meteorites : Murchison and Kenna
No full textStabilization of reactive sp carbon chains
No full textWe describe a novel strategy for stabilizing the long-elusive, condensed-state materials consisting of sp carbon chains. High-level ab initio calculations indicate that covalent attachment of such carbon chains to gold thiolate clusters stabilizes the cumulenic (double bonded --C--C--C--) form, whereas a non-covalent interaction stabilizes the polyynic (alternating single/triple bonded -C---C-C---C-) form. The Raman-active CC stretching mode is a sensitive probe of these bonding differences. This mode occurs at the same frequencies as that of isolated polyynes in non-covalent complexes, but it appears at lower wavenumbers in the covalent complexes. The current work provides a new direction for the synthesis and stabilization of materials containing sp carbon chains
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
Pseudocarbynes: Linear Carbon Chains Stabilized by Metal Clusters
No full textPseudocarbynes, defined as linear carbon chains stabilized by noncovalent bonding to a metal cluster, were synthesized via laser ablation of a liquid/metal interface, in this case, gold (Au) in ethanol. We present UV-vis, Raman, and IR spectra that collectively demonstrate the formation of Au-pseudocarbynes. The Au-pseudocarbynes presented here likely consist of polyynes containing fewer than 16 carbon atoms associated with subnanometer Au clusters. Their characteristic spectral signatures are supported by density functional theory calculations that highlight the interaction between the Au clusters and the πnetwork of-CC-chains. This class of molecules represents a synergy between sp-hybridized carbon chains and small metal clusters that stabilize one another
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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