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Pressure-induced over-hydration and water ordering in gismondine: A synchrotron powder diffraction study
No full textThis paper reports the results of an in situ HP synchrotron X-ray powder diffraction investigation on the natural zeolite gismondine (ideal chemical formula Ca4Al8Si8O32·16H2O, space group P21/c). The study was performed from Pamb to 7.9 GPa, and upon decompression, using methanol:ethanol:water (16:3:1) mixture (m.e.w.) as a nominally penetrating hydrostatic P-transmitting medium. No complete X-ray amorphization is observed up to the highest investigated pressure, and the original unit-cell parameters are almost completely recovered upon decompression. From 0.6 GPa, the water content is slightly higher than at ambient pressure, as a result of a moderate over-hydration. Moreover, at about 2 GPa, a significant water molecule system re-arrangement occurs, characterized by an ordering of part of the water molecules from four partially occupied sites to only two fully occupied ones. The over-hydration, but not the water ordering, is substantially irreversible upon pressure release. The Rietveldstructural refinements of the powder patterns converged successfully up to 2.8 GPa; above this pressure, a phase transition to triclinic symmetry was observed and only the unit-cell parameters were refined. The comparison of the overall cell volume reductions and of the bulk modula of gismondine compressed between Pamb and 7.9 GPa in m.e.w. and in silicone oil, reveals that this is the unique zeolite with a higher compressibility in penetrating vs. non-penetrating P-transmitting media. This is ascribed to the re-organization of the water molecule system upon compression in m.e.w., which leaves a larger free volume inside the pores with respect to the phase compressed in silicone oil
Pressure-induced structural deformation and elastic behavior of wairakite
No full textThe elastic behavior and the high-pressure structural evolution of the zeolite wairakite [ideal chemical formula Ca(Al2Si4O12)⋅2H2O, space group I2/a], the Ca-analog of analcime, have been investigated by means of in-situ synchrotron X-ray powder diffraction from ambient pressure to 7.8 GPa, and upon decompression. No complete X-ray amorphization is observed up to the highest investigated pressure, and the original unit-cell parameters are recovered upon decompression. The Rietveld structural refinements of the powder patterns converged successfully up to 2.5 GPa; above this pressure, a phase transition to triclinic symmetry is observed and only the unit-cell parameters were refined. An overall reduction of about 14% of the unit-cell volume between 0.0001 and 7.0 GPa is observed, demonstrating that wairakite is much more flexible upon compression than upon heating. The pressure dependence of the cell parameters is strongly anisotropic and larger after the transition to the triclinic space group. The elastic parameters refined with a second-order Birch-Murnaghan Equation of State are V0 = 2536(4) Å3, K0 = 39(3) GPa, and V0 = 2632(38) Å3, K0 = 24(3) GPa, for the monoclinic and triclinic phases, respectively.The structure distortion of monoclinic wairakite, proceeding via tetrahedral tilting, induces deformationsin the 4-, 6-, and 8-membered rings and an increase in the extra-framework Ca coordination number.A comparative discussion of the compressibility behavior of wairakite and analcime is reported
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
Russian-German cooperation in education and science in the sope of polar and marine sciences at St. Petersburg State University (in Russian)
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