1,721,019 research outputs found
Ba6P12N17O9Br3 - A Column-Type Phosphate Structure Solved from Single-Nanocrystal Data Obtained by Automated Electron Diffraction Tomography
No full textOxonitridophosphate Ba6P12N17O9Br3 was synthesized by heating a multicomponent mixture of BaBr2, BaS, phosphoryl triamide and thiophosphoryl triamide in an evacuated and sealed silica-glass ampoule to 750 degrees C. Ba6P12N17O9Br3 was obtained as the main product as a nanocrystalline powder. The crystal structure was determined ab initio on the basis of electron diffraction data acquired from a single needle-shaped nanocrystal by automated diffraction tomography. Ba6P12N17O9Br3 crystallizes in the hexagonal space group P6(3)/m (no. 176) with unit cell parameters alpha = 14.654(19), c = 8.255(9) angstrom and Z = 2. Its structure includes triangular, column-shaped anions of (1)(infinity){(P12N17O9)(9-)}, which are built from vertex-sharing P(O,N)(4) tetrahedra with 3-rings and three-coordinate nitrogen atoms. The 1D anions are separated by Ba2+ and Br- ions, which are arranged in channels parallel to the phosphate anions along [001]. The Ba2+ ions are eight- and nine-coordinated by Br- and O/N atoms, respectively. RI Kolb, Ute/A-2642-2011; Mugnaioli, Enrico/E-6237-2011; Sedlmaier, Stefan/K-6868-201
SrP3N5O: A Highly Condensed Layer Phosphate Structure Solved from a Nanocrystal by Automated Electron Diffraction Tomography
No full textThe oxonitridophosphate SrP3N5O has been synthesized by heating a multicomponent reactant mixture that consisted of phosphoryl triamide OP(NH2)(3), thiophosphoryl triamide SP(NH2)(3), SrS, and NH4Cl enclosed in evacuated and sealed silica-glass ampoules up to 750 degrees C. The compound was obtained as nanocrystalline powder with needle-shaped crystallites. The crystal structure was solved ab initio on the basis of electron diffraction data by means of automated electron diffraction tomography (ADT) and verified by Rietveld refinement with X-ray powder diffraction data. SrP3N5O crystallizes in the orthorhombic space group Pnma (no. 62) with unit-cell data of a = 18.331(2), b = 8.086(1), c = 13.851(1) angstrom and Z = 16. The compound is a highly condensed layer phosphate with a degree of condensation kappa = 1/2. The corrugated layers (2)(infinity){(P3N5O)(2-)} consist of linked, triangular columns built up from P(O, N)(4) tetrahedra with 3-rings and triply binding nitrogen atoms. The Sr2+ ions are located between the layers and exhibit six-, eight-, and ninefold coordination. FTIR and solid-state NMR spectra of SrP3N5O are discussed as well. RI Mugnaioli, Enrico/E-6237-2011; Kolb, Ute/A-2642-2011; Sedlmaier, Stefan/K-6868-201
High-temperature synthesis, single-crystal X-ray and neutron powder diffraction, and materials properties of Sr(3)Ln(10)Si(18)Al(12)O(18)N(36) (Ln = Ce, Pr, Nd)-novel sialons with an ordered distribution of Si, Al, O, and N
No full textThe novel oxonitridoaluminosilicates (sialons) Sr(3)Ln(10)Si(18)Al(12)O(18)N(36) (Ln = Ce, Pr, Nd) were obtained by the reaction of the respective lanthanide metals with Si(NH)(2), SrCO3, and AlN using a radiofrequency furnace at temperatures between 1550-1650 degrees C. The crystal structures of the isotypic sialons were determined by single-crystal X-ray investigations (Sr3Ce10Si18Al12O18N36: I (4) over bar 3m, Z = 2, a = 1338.2(2) pm, R1 = 0.0333; Sr3Pr10Si18Al12O18N36: a = 1334.54(6) pm, R1 = 0.0296; Sr3Nd10Si18Al12O18N36: a = 1332.85(6) pm, R1 = 0.0271) and in the case of Sr3Pr10Si18Al12O18N36 with powder neutron diffraction as well. The three-dimensional sialon network is built up by SiON3, SiN4, and AlON3 tetrahedra. Besides the bridging O and N atoms of the sialon network there are isolated O2- which are tetrahedrally coordinated by Sr and Ln. The crystallographic differentiation of Si/Al and O/N seemed to be possible by a careful evaluation of the single-crystal X-ray diffraction data combined with lattice energy calculations using the MAPLE concept (Madelung Part of Lattice Energy). In the case of Sr3Pr10Si18Al12O18N36 the differentiation of O and N and the proposed ordering was completely confirmed by powder neutron diffraction
Crystal structure of barium oxonitridophosphate, Ba3P6O6N8
Full text linkBa3N8O6P6, trigonal, P3 (no. 147), a = 7.40227(9) Å, c = 6.3144(1) Å, V = 299.6 Å3, Z = 1, R(I) = 0.008, R(P) = 0.041, T = 297(2) K
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
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