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Shogo Tachibana Shinnosuke Tamada Haruka Kawasaki Kazuhito Ozawa Hiroko Nagahara 《Physics and Chemistry of Minerals》2013,40(6):511-519
The interdiffusion coefficient of Mg–Fe in olivine (D Mg–Fe) was obtained at 1,400–1,600 °C at the atmospheric pressure with the oxygen fugacity of 10?3.5–10?2 Pa using a diffusion couple technique. The D Mg–Fe shows the anisotropy (largest along the [001] direction and smallest along the [100] direction), and its activation energy (280–320 kJ/mol) is ~80–120 kJ/mol higher than that estimated at lower temperatures. The D Mg–Fe at temperatures of >1,400 °C can be explained by the cation-vacancy chemistry determined both by the Fe3+/Fe2+ equilibrium and by the intrinsic point defect formation with the formation enthalpy of 220–270 kJ/mol depending on the thermodynamical model for the Fe3+/Fe2+ equilibrium in olivine. The formation enthalpy of 220–270 kJ/mol for the point defect (cation vacancy) in olivine is consistent with that estimated from the Mg self-diffusion in Fe-free forsterite. The increase in the activation energy of D Mg–Fe at >1,400 °C is thus interpreted as the result of the transition of diffusion mechanism from the transition metal extrinsic domain to the intrinsic domain at the atmospheric pressure. 相似文献
2.
G. V. Gibbs M. B. Boisen F. C. Hill O. Tamada R. T. Downs 《Physics and Chemistry of Minerals》1998,25(8):574-584
The topological properties of the electron density distributions for more than 20 hydroxyacid, geometry optimized molecules
with SiO and GeO bonds with 3-, 4-, 6- and 8-coordinate Si and Ge cations were calculated. Electronegativities calculated
with the bond critical point (bcp) properties of the distributions indicate, for a given coordination number, that the electronegativity
of Ge (∼1.85) is slightly larger than that of Si (∼1.80) with the electronegativities of both atoms increasing with decreasing
bond length. With an increase in the electron density, the curvatures and the Laplacian of the electron density at the critical
point of each bond increase with decreasing bond length. The covalent character of the bonds are assessed, using bond critical
point properties and electronegativity values calculated from the electron density distributions. A mapping of the (3, −3)
critical points of the valence shell concentrations of the oxide anions for bridging SiOSi and GeOGe dimers reveals a location
and disposition of localized nonbonding electron pairs that is consistent with the bridging angles observed for silicates
and germanates. The bcp properties of electron density distributions of the SiO bonds calculated for representative molecular
models of the coesite structure agree with average values obtained in X-ray diffraction studies of coesite and danburite to
within ∼5%.
Received: 18 August 1997 / Revised, accepted: 19 February 1998 相似文献
3.
Yuichiro Yamada Shinnosuke Kaga Yoshimasa Kaga Kimiaki Naiki Shiho Watanabe 《Journal of Oceanography》2017,73(1):11-24
Ofunato Bay was a semi-closed area because of the breakwater effect at the entrance; however, the breakwater was destroyed by a massive tsunami generated by the 2011 off the Pacific coast of Tohoku Earthquake. Consequently, the physical environment of Ofunato Bay has been changed significantly, i.e., the modification of the stratified structure of seawater inside the bay and the intermittent intrusion of seawater outside the bay. These alterations of physical environment are considered to have an influence on the chemical and biological environment in Ofunato Bay. To elucidate the influence of the tsunami on the aquatic environment, we measured dissolved nutrients, chlorophyll a and dissolved oxygen concentrations, and heterotrophic bacteria abundance inside and outside of Ofunato Bay from 2012 to 2014, and compared these data with those obtained before the earthquake. As compared with before the earthquake, significant changes after the earthquake were (1) decrease of ammonium and phosphate concentrations, (2) increase of chlorophyll a concentration, (3) increase of dissolved oxygen concentration in the bottom, and (4) decrease of heterotrophic bacteria abundance. The collapse of the breakwater and consequential enhanced water exchange were considered to have brought the decrease of nutrient concentration inside the bay. Furthermore, washout of shellfish mariculture rafts by the tsunami decreased the shellfish biodeposits along with the elution of nutrients by heterotrophic bacteria. Decrease of cultivated shellfish further caused a decline in feeding pressure on phytoplankton and, subsequently, increased the phytoplankton biomass that contributed to the decrease of nutrients inside the bay. 相似文献
4.
The bonded radii of anions obtained in topological analyses of theoretical and experimental electron density distributions
differ from atomic, ionic and crystal radii in that oxide-, fluoride-, nitride- and sulfide-anion radii are not constant for
a given coordination number. They vary in a regular way with bond length and the electronegativity of the cation to which
they are bonded, exhibiting radii close to atomic radii when bonded to a highly electronegative cation and radii close to
ionic radii when bonded to a highly electropositive cation. The electron density distributions show that anions are not spherical
but exhibit several different radii in different bonded directions. The bonded radii of cations correlate with ionic and atomic
radii. But unlike ionic radii, the bonded radius of a cation shows a relatively small increase in value with an increase in
coordination number. In contrast to atomic and ionic radii, the bonded radius of an ion in a crystal or molecule can be used
as a reliable and well-defined estimate of its radius in the direction of its bonds.
Received April 16, 1996 / Revised, accepted August 6, 1996 相似文献
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