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T- and P-stability and thermo-elastic behavior of the ABW-compounds TlAlSiO4 and CsAlSiO4
No full textT- and P-stability and thermo-elastic behavior
of the ABW-compounds TlAlSiO4 and CsAlSiO4
Paolo Lotti,a G. Diego Gattaa,b, Domenico Caputoc, Marco Merlinia,
Paolo Apreac, Andrea Lausid, Carmine Colellac
aDipartimento di Scienze della Terra, Università degli Studi di Milano, Milano, Italy
bCNR - Istituto di Cristallografia, Sede di Bari, Bari, Italy
cDipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università degli Studi di Napoli “Federico II”, Napoli, Italy
dSincrotrone Trieste S.C.p.A. di Interesse Nazionale, Basovizza, Trieste, Italy
[email protected]
A large number of microporous compounds sharing the ABW framework topology have so far been reported in the literature. These compounds show a significant chemical variability, leading to interesting magnetic, optical or structural properties (see e.g. [1] and references therein). The ABW framework can be described as made by sheets of six-membered rings of tetrahedra, in which three tetrahedra have apical oxygen atoms pointing upward (U) and three downward (D), according to a “UUUDDD” scheme. The sheets are interconnected through the apical oxygen atoms, giving rise to elliptical 8-membered ring channels, where the extraframework population is hosted. The latter is generally represented by monovalent cations, with (as Li-ABW) or without (as Rb-, Cs- or Tl-ABW) H2O molecules. Only a few studies have so far been devoted to the phase-stability fields and thermo-elastic behavior of ABW compounds, in response to T and P.
In this study, we focused our attention to two synthetic ABW compounds: TlAlSiO4 and CsAlSiO4, which gain interest for the pollutant and/or toxic nature of the hosted extraframework cations (Tl+ or Cs+). TlAlSiO4 has been investigated up to 950 °C (at room-P) and up to 8 GPa (at room-T) by means of in-situ synchrotron powder diffraction with a diamond anvil cell and with a high-temperature furnace [2]. No phase transition has been observed within the T- and P-range investigated. A II-order Birch-Murnaghan equation of state (II-BM EoS) fit of the P-V data led to a refined bulk modulus KV0 = 48.8(2) GPa. A polynomial fit of the T-V data led to a refined volume thermal expansion coefficient αV,25°C = 4.44(3)*10-5 K-1. CsAlSiO4 has been investigated up to 1000 °C (at room-P) and up to 10 GPa (at room-T) by means of in-situ synchrotron powder diffraction [3]. As for the Tl-analogue, no phase transitions have been observed within the T- and P-range investigated. A II-BM EoS fit of the P-V data gave a refined KV0 = 41.3(3) GPa. A polynomial fit of the T-V data led to a refined αV,20°C = 3.63(1)*10-5 K-1. Both the studied ABW-compounds show a remarkably anisotropic thermo-elastic pattern, resembling that of “layered materials” (e.g. phyllosilicates), where the stacking direction of the 6mR-sheets is significantly more compressible and expandable than the sheets plane. Such a behavior appears to be governed by the nature of the ABW topology of the framework. The high stability and flexibility of TlAlSiO4 and CsAlSiO4 at high-T (at room-P) and high-P (at room-T) suggest these compounds as functional materials for the fixation and storage of the Tl+ and Cs+.
[1] V. Kahlenberg, R.X. Fischer, W.H. Baur, Z. Kristallogr. 2001, 216, 489-494.
[2] G.D. Gatta, P. Lotti, M. Merlini, D. Caputo, P. Aprea, A. Lausi, C. Colella, Micropor. Mesopor. Mater. 2014, submitted.
[3] G.D. Gatta, M. Merlini, P. Lotti, A. Lausi, M. Rieder, Micropor. Mesopor. Mater. 2013, 163, 147-152
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
The structure of K-hydrosodalite
No full textHydrosodalite, Na-6[AlSiO4](6)center dot 8H(2)O, is a synthetic modification of natural sodalite with water molecules replacing for the anion at the centre of the beta cage. Hydrosodalite has a cubic structure with space group P (4) over bar 3n and a approximate to 8.9 angstrom. Cation ordering and framework distortions leading to symmetry reduction were observed for synthetic sodalites but have never been reported for hydrosodalite. This work reports the first experimental evidence of a symmetry reduction in hydrosodalite. The investigated sample is a K-exchanged hydrosodalite with chemical formula K-6[AlSiO4](6)center dot 7.8H(2)O. The structure refinement was performed using synchrotron powder diffraction data in space group P1 with a = 9.196(1) angstrom, b = 9.188(1) angstrom, and c = 9.205(1) angstrom, alpha = 89.69(1)degrees, beta = 90.43(1)degrees, and gamma = 89.791(9)degrees. K+ strongly interacts with all the framework oxygen atoms of the hexagonal ring and provokes anisotropic distortion of the framework. In the distorted framework, the only possible distribution scheme for the K+ ions is ordered, to prevent any Coulomb repulsion between adjacent ions. In addition, the ordered scheme is the only to ensure even distribution of the positive cation charges with respect to the Al atoms (AI:K ratio is 1: 1). In fact, each of the six Al atoms has three K+ ions at a distance of 3.5-3.9 angstrom and in turn, each of the six K+ ions has three Al atoms at a distance of 3.5-3.9 angstrom. K+ ions display a coordination number from 8 to 10 and mean K-O distance, including the water molecules, of 2.921-3.043 angstrom. (c) 2006 Elsevier Inc. All rights reserved
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
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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