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1.
The crystal structure of hydrous wadsleyite, Mg1.75SiH0.5O4 synthesized in an MA 8-type apparatus at conditions of 1300°C and 15.5 GPa, has been analyzed and refined in space group Imma, using the X-ray intensities measured on a 60X60X10 μm single crystal. The composition (Z=8) and unit cell are Mg1.74Si0.97H0.65O4 by E.P.M.A. analysis and a=5.663(1) Å, b= 11.546(2) Å, c=8.247(4) Å, V=539.2(5) Å3. The partial M-site occupancies were determined; vacancies associated with the incorporation of water are strongly concentrated on the Mg 3 site. The OH in the structure was confirmed by Raman and FTIR spectroscopies. The result of valence sum calculation based on the refined bond lengths indicates that O1 is a hydroxyl. The formula of hydrous wadsleyite can be expressed as Mg2-xSiH2xO4, where 0≤x≤0.25. When x=0.25, all of the O1 site is hydroxyl and the maximum solubility of 3.3 wt% H2O is realized. Structural relations to other dense hydrous phases are discussed. 相似文献
2.
The crystal structures of the two hydrous wadsleyite crystals with formulae, Mg1.75SiH0.50O4 (0.5H–β) and Mg1.86SiH0.28O4 (0.3H–β) have been analyzed in this study. The single-crystal X-ray diffraction data showed that the unit cells of the 0.3H–β
and the 0.5H–β are metrically monoclinic with a slight distortion from the orthorhombic cell but their intensity distributions
conform to the orthorhombic symmetry within the limit of experimental errors. The Fourier and the difference Fourier syntheses
were calculated. Small but significant Fourier peaks were found at the site, Si2, in a normally vacant tetrahedral void adjacent
to Mg3 site as reported for the monoclinic hydrous wadsleyite by Smyth et al.. From the comparison of the hydrous and anhydrous
wadsleyite structures, the Mg-vacant structural modules were found to be the building units for the structure of hydrous wadsleyite.
The dilution of symmetry from orthorhombic to monoclinic in the hydrous wadsleyite structure is interpreted qualitatively
due to lack of mirror perpendicular to the a axis in the module. The mode of arrangement of the Mg-vacant structural modules
interprets the symmetry and hydrogen content of the hydrous wadsleyite and gives the structural relationship between hydrous
wadsleyite and hydrous ringwoodite.
Received: 8 May 1998 / Revised, accepted: 3 October 1998 相似文献
3.
Fuminori Hashihama Toru Hirawake Sakae Kudoh Jota Kanda Ken Furuya Yukuya Yamaguchi Takashi Ishimaru 《Polar Science》2008,2(2):109-120
We investigated the size fraction and pigment-derived class compositions of phytoplankton within the euphotic zone of the Antarctic marginal ice zone between 63.3°S and 66.5°S along the 140°E meridian on two consecutive cruises in the late austral summer and early austral autumn of 2003. We observed significant temporal and spatial variations in phytoplankton size and taxonomic composition, although chlorophyll a concentrations were generally below 1 μg l−1 during both periods. Microphytoplankton (>20 μm), mainly diatoms, were prominent in the euphotic zone in the southernmost area around 66.5°S during late summer. In the rest of the study area during both cruises, the phytoplankton community was dominated by pico- and nano-sized populations (<20 μm) throughout the euphotic zone. The small-size populations mostly consisted of diatoms and haptophytes, although chlorophytes were dominant in extremely cold water (−1.5°C) below the overlying warm water around 65.5°S during late summer. From late summer to early autumn, chlorophytes declined in abundance, probably due to increasing temperature within the euphotic zone (−1 to 0°C). These pico- and nano-phytoplankton-dominated populations were often accompanied by relatively high concentrations of ammonium, suggesting the active regeneration of nutrients within the small-size plankton community. 相似文献
4.
Takahiro Kudoh Shantanu Basu Youichi Ogata Takashi Yabe 《Monthly notices of the Royal Astronomical Society》2007,380(2):499-505
We employ the first fully three-dimensional simulation to study the role of magnetic fields and ion–neutral friction in regulating gravitationally driven fragmentation of molecular clouds. The cores in an initially subcritical cloud develop gradually over an ambipolar diffusion time while the cores in an initially supercritical cloud develop in a dynamical time. The infalling speeds on to cores are subsonic in the case of an initially subcritical cloud, while an extended (≳0.1 pc) region of supersonic infall exists in the case of an initially supercritical cloud. These results are consistent with previous two-dimensional simulations. We also found that a snapshot of the relation between density (ρ) and the strength of the magnetic field ( B ) at different spatial points of the cloud coincides with the evolutionary track of an individual core. When the density becomes large, both the relations tend to B ∝ρ0.5 . 相似文献
5.
Jun Shoji Takaya Kudoh Hideyuki Takatsuji Osamu Kawaguchi Akihide Kasai 《Estuarine, Coastal and Shelf Science》2010,86(3):485-490
Biological and physical surveys were conducted in order to investigate the relationship between environmental conditions and the distribution of moon jellyfish Aurelia aurita in Hiroshima Bay, western Seto Inland Sea, Japan. Moon jellyfish and ichthyoplankton were collected at 13 stations in Hiroshima Bay during monthly surveys from July to September in 2006 and 2007. Surface temperature in 2006 was significantly lower during the August and September cruises and surface salinity was lower during all cruises than in 2007. Moon jellyfish was the most dominant gelatinous plankton collected, accounting for 89.7% in wet weight. Mean moon jellyfish abundance in 2006 was higher than that in 2007 from July through September, with significant inter-year differences for July and September. Variability in precipitation and nutritional input from the Ohta River, northernmost part of Hiroshima Bay, were suggested as possible factors affecting the inter-annual variability in moon jellyfish abundance in the coastal areas of northern Hiroshima Bay. Moon jellyfish were more abundant in the coastal areas of northern Hiroshima Bay, where the dissolved oxygen (DO) concentration was lower, while low in the central part of the bay. Japanese anchovy Engraulis japonicus eggs were most dominant (58.1% in number) among the ichthyoplankton and were abundant in the central area of Hiroshima Bay. Explanatory analysis was conducted to detect possible effects of environmental conditions on the abundance of moon jellyfish and Japanese anchovy eggs during the summer months in Hiroshima Bay. Of the environmental conditions tested (temperature, salinity and DO of surface and bottom layers at each sampling station), bottom DO had the most significant effect on the moon jellyfish abundance: there was a negative correlation between the bottom DO and the moon jellyfish abundance in Hiroshima Bay during summer. 相似文献
6.
Y. Kudoh 《Physics and Chemistry of Minerals》2001,28(8):523-530
The sequential displacement mechanism based on the oxygen-lattice cubic closest packing (c.c.p.) in the < 2 0 1 > direction was proposed in this study. All displacements of cations are within the OT and the O layers with the length of displacement vector being around 1.7 or 2.9 Å, contrary to displacement of around 5.0 Å for models proposed previously. The difference in atomic arrangement between hydrous wadsleyite and hydrous ringwoodite is small. The atomic arrangement of the O layer of hydrous wadsleyite is essentially the same as that of hydrous ringwoodite when Mg vacancies preferentially exist in the O layer. The partial occupancies of normally vacant tetrahedral sites reported in the hydrous-β and hydrous-γ structures may possibly be caused by the existence of Mg vacancies at the octahedral sites through phase transition from hydrous-β to hydrous-γ or from hydrous-γ to hydrous-β phases. 相似文献
7.
Y. Kudoh T. Nagase S. Sasaki M. Tanaka M. Kanzaki 《Physics and Chemistry of Minerals》1995,22(5):295-299
The structure of phase F, a non-stoichiometric hydrous silicate synthesized in a uniaxial, split-sphere, multi-anvil apparatus at conditions of 17 GPa and 1000° C, has been solved and refined in space group P63cm, using synchrotron X-ray data for a single crystal of a size 18 × 24 × 30 μm. The composition and unit cell for phase F are Mg3.35Si5.51H7.26O18, a=5.073(3) Å, c=14.013(9) Å, 7= 312.3(5) Å3. The structure contains layers with many similarities to superhydrous phase B. The layers of oxygen atoms are stacked in the ABCBAC-type double cubic closest packing arrangement. The bulk modulus of phase F was estimated from the structural and compositional relationship to superhydrous phase B and periclase. 相似文献
8.
Combining a miniature diamond-anvil pressure cell with a single crystal four-circle diffractometer, the crystal structure of a synthetic ZrO2 has been studied in situ up to 51 kbar at room temperature. The space group of the unquenchable orthorhombic high pressure phase is Pbcm. The directions of the b and c axes are preserved through the transition and the transformation is displacive. The coordination configurations of the Zr atoms and oxygen atoms are the same in the high pressure and low pressure phases. The orthorhombic high pressure phase has a higher entropy than that of low pressure monoclinic phase. 相似文献
9.
We perform numerical simulations of nonlinear MHD waves in a gravitationally stratified molecular cloud that is bounded by a hot and tenuous external medium, within a 1.5-dimensional approximation. Under the influence of a driving source of Alfvénic disturbances, the cloud is lifted up by the pressure of MHD waves and reaches a steady state characterized by oscillations about a new time-averaged equilibrium state. The nonlinear effect results in the generation of longitudinal motions and many shock waves. Models of an ensemble of clouds show that, for various strengths of the input energy, the velocity dispersion in the cloud σ ∝ Z 0.5, where Z is a characteristic size of the cloud. Furthermore, σ is always comparable to the mean Alfvén velocity of the cloud, consistent with observational results. 相似文献
10.
A-HIGHERS—The System to Produce the High Spatial Resolution Sea Surface Temperature Maps of the Western North Pacific Using the AVHRR/NOAA 总被引：1，自引：0，他引：1
To study on the oceanic variations in the western North Pacific, we developed a system to produce a high spatial resolution sea surface temperature (SST) map from the data obtained by the Advanced Very High Resolution Radiometer (AVHRR) aboard the National Oceanic and Atmospheric Administration (NOAA) satellites. As the system has been improved on the HIGHERS (Sakaida and Kawamura, 1996), it is called the Advanced-HIGHERS (A-HIGHERS). The A-HIGHERS has been developed on the super computer in the Tohoku University, which is favorable for handling of a large volume of data. Mainly because of improvements in the cloud detection algorithm, the A-HIGHERS can deal with the data obtained at dawn and dusk around the year, and at daytime in summer more effectively. The A-HIGHERS are used to produce SST maps spanning from (60°N, 120°E) to (20°N, 160°E) with a grid size of 0.01 degree. 相似文献