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The high temperature P21/c-C2/c phase transition in Fe-free Ca-rich P21/c clinopyroxenes
No full textTHE HIGH TEMPERATURE P21/C-C2/C PHASE TRANSITION IN Fe-FREE CA-RICH P21/C CLINOPYROXENES
No full text
The high-pressure and high-temperature P21/c - C2/c phase transitions in clinopyroxenes along the join diopside-enstatite
No full textAbstract n° EAE03-A-0355
Water incorporation in synthetic and natural MgAl2O4 spinel
Full text linkThe solubility and incorporation mechanisms of water in synthetic and natural MgAl2O4 spinel have been investigated in a series of high-pressure/temperature annealing experiments. In contrast to most other nominally anhydrous minerals, natural spinel appears to be completely anhydrous. On the other hand, non-stoichiometric Al-rich synthetic (defect) spinel can accommodate several hundred ppm water in the form of structurally-incorporated hydrogen. Infrared (IR) spectra of hydrated defect spinel contain one main O-H stretching band at 3343-3352 cm(-1) and a doublet consisting of two distinct O-H bands at 3505-3517 cm(-1) and 3557-3566 cm(-1). IR spectra and structural refinements based on single-crystal X-ray data are consistent with hydrogen incorporation in defect spinel onto both octahedral and tetrahedral O-O edges. Fine structure of O-H bands in IR spectra can be explained by partial coupling of interstitial hydrogen with cation vacancies, or by the effects of Mg-Al disorder on the tetrahedral site. The concentration of cation vacancies in defect spinel is a major control on hydrogen affinity. The commercial availability of large single crystals of defect spinel coupled with high water solubility and similarities in water incorporation mechanisms between hydrous defect spinel and hydrous ringwoodite (Mg2SiO4) suggests that synthetic defect spinel may be a useful low-pressure analogue material for investigating the causes and consequences of water incorporation in the lower part of Earth's mantle transition zone. (c) 2009 Elsevier Ltd. All rights reserved. <br/
The real topological configuration of the extra-framework content in alkali-poor beryl: a multi methodological study
No full textThe crystal structure of alkali/water-poor beryl (1120 + Na2O + Cs2O 4 sigma(F-0). The topological configuration of the H2O molecule into the channel is confirmed by the spectroscopic investigation. Polarized single-crystal IR spectra show that the H2O molecule is oriented with the molecular symmetry axis perpendicular to the hexagonal axis and (HH)-H-... vector parallel (or quasi-parallel) to [001]
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
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