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Local structure and spin transition in Fe2O3 hematite at high pressure
No full textThe pressure evolution of the local structure of Fe2O3 hematite has been determined by extended x-ray
absorption fine structure up to ∼79 GPa. Below the phase-transition pressure at ∼50 GPa, no increasing of FeO6
octahedra distortion is observed as pressure is applied. Above the phase transition, an abrupt decrease of the
nearest-neighbor Fe-O distance is observed concomitantly with a strong reduction in the FeO6 distortion. This
information on the local structure, used as a test-bench for the different high-pressure forms proposed in the
literature, suggests that the orthorhombic structure with space group Aba2, recently proposed by Bykova et al.
[Nat. Commun. 7, 10661 (2016)], is the most probable, but puts into question the presence of the P21/n form in
the pressure range 54–67 GPa. Finally, the crossover from Fe high-spin to low-spin states with pressure increase
has been monitored from the pre-edge region of the Fe K-edge absorption spectra. Its “simultaneous” comparison
with the local structural changes allows us to conclude that it is the electronic transition that drives the structural
transition and not vice versa
Experimental measurements of viscosity and melt structure of CO2-bearing melts at high pressure and temperature
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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
Viscosity and melt structure of CO2-bearing melts in the earth’s upper mantle. Implications for the mobilization, ascent rate and emplacement of carbonatite rocks over time
Full text linkVariations 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
Experimental Study of the System Mg3Al2Si3O12-Mg3Cr2Si3O12 at High Pressure and High Temperature
Full text linkPhase relation between pyrope Mg3Al2Si3O12 and knorringite Mg3Cr2Si3O12 is determined experimentally under high pressure and temperature condition. The solubility limit of the knorringite molecule expands with increasing pressure, and knorringite end member is stable at pressures higher than 105 kbar at 1200℃. A low pressure phase assemblage of garnet s.s. + pyroxene s.s. + spinel s.s. + quartz (coesite) appears on the pyrope-rich side, while this assemblage is replaced by that of garnet s.s. + pyroxene s.s + corundum s.s. on the knorringite-rich side at the pressures above ca. 67 kbar at 1200℃. Measurement of chemical compositions of these phases is carried out, and the distribution of Cr3+ among the coexisting phases is determined. As a result, it is confirmed that the Cr content of the garnet, as well as that of the spinel, is a useful indicator of the equilibrium pressure between spinel and garnet lherzolites. Melting experiment is made for the pyrope end member and also for the garnet solid solution between pyrope and knorringite at high pressures. It is observed that Cr3+ strongly prefers the garnet to the melt at relatively low pressures. However, such a preference is almost absent at the higher pressures around 90 kbar. On the other hand, an anomalous change of the quenched phase from the garnet melt is observed at pressures a round 70 kbar; the quench crystal changes from aluminous pyroxene with garnet stoichiometry to garnet at these pressures. Further, notable decrease in slope of the melting curve is observed for the pyrope end member at around this pressure. It is strongly suggested that these changes would be caused by a pressure-induced structural change, from pyroxene-like structure with tetrahedrally coordinated Al to garnet-like one in which every Al is in an octahedral site, in the pyrope melt at the pressures about 70 kbar. This interpretation is confirmed by the X-ray emission spectroscopic measurement, which shows structural similarity between pyrope glass and the quench crystal. Origin of Cr-rich pyrope and distribution of Cr in the upper mantle are discussed on the basis of the present experimental results. The Cr-rich pyrope, which commonly occurs as an inclusion in diamond, is estimated to be formed as a residual crystal caused by partial melting of the mantle material at pressures corresponding to 120-240 km in depth. It is also suggested that the garnet would be almost a unique phase which accommodates Cr3+ in the upper mantle from ca. 600 km to ca. 100 km depth, above which Cr3+ would be accommodated mainly in spinel and pyroxene. However, the notably high concentration of Cr3+ observed in the garnet inclusions (Cr/Cr+Al=0.2-0.5) is considered to be a local phenomenon limited in the shallower horizons above ca. 240 km
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