High-pressure behavior of MnGeO3 and CdGeO3 perovskites and the post-perovskite phase transition     

Shigehiko Tateno  Kei Hirose  Nagayoshi Sata  Yasuo Ohishi 《Physics and Chemistry of Minerals》2006,32(10):721-725

The stability and high-pressure behavior of perovskite structure in MnGeO₃ and CdGeO₃ were examined on the basis of in situ synchrotron X-ray diffraction measurements at high pressure and temperature in a laser-heated diamond-anvil cell. Results demonstrate that the structural distortion of orthorhombic MnGeO₃ perovskite is enhanced with increasing pressure and it undergoes phase transition to a CaIrO₃-type post-perovskite structure above 60 GPa at 1,800 K. A molar volume of the post-perovskite phase is smaller by 1.6% than that of perovskite at equivalent pressure. In contrast, the structure of CdGeO₃ perovskite becomes less distorted from the ideal cubic perovskite structure with increasing pressure, and it is stable even at 110 GPa and 2,000 K. These results suggest that the phase transition to post-perovskite is induced by a large distortion of perovskite structure with increasing pressure.  相似文献   

Numerical Simulation of Accretion Discs in Close Binary Systems andDiscovery of Spiral Shocks     

Takuya Matsuda  Makoto Makita  Hidekazu Fujiwara  Takizo Nagae  Kei Haraguchi  Eiji Hayashi  H.M.J. Boffin 《Astrophysics and Space Science》2000,274(1-2):259-273

The history of hydrodynamic numerical simulations for accretion disks in close binary systems is reviewed, in which emphasis is placed, in particular, on the facts that spiral shock waves were numerically found in 1986 by researchers including one of the present authors and that spiral structure was discovered in IP Pegasi in 1997 by Steeghs et al. The results of our two and three-dimensional numerical simulations in recent years are then summarized, with comparison being made with observations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Projected 21st century climate change on snow conditions over Shasta Dam watershed by means of dynamical downscaling          下载免费PDF全文

Toan Trinh  M. Levent Kavvas  Kei Ishida  Kara Carr  Noriaki Ohara 《水文研究》2017,31(16):2887-2901

Snow is an important component of the Earth's climate system and is particularly vulnerable to global warming. It has been suggested that warmer temperatures may cause significant declines in snow water content and snow cover duration. In this study, snowfall and snowmelt were projected by means of a regional climate model that was coupled to a physically based snow model over Shasta Dam watershed to assess changes in snow water content and snow cover duration during the 21st century. This physically based snow model requires both physical data and future climate projections. These physical data include topography, soils, vegetation, and land use/land cover, which were collected from associated organizations. The future climate projections were dynamically downscaled by means of the regional climate model under 4 emission scenarios simulated by 2 general circulation models (fifth‐generation of the ECHAM general circulation model and the third‐generation atmospheric general circulation model). The downscaled future projections were bias corrected before projecting snowfall and snowmelt processes over Shasta Dam watershed during 2010–2099. This study's results agree with those of previous studies that projected snow water equivalent is decreasing by 50–80% whereas the fraction of precipitation falling as snowfall is decreasing by 15% to 20%. The obtained projection results show that future snow water content will change in both time and space. Furthermore, the results confirm that physical data such as topography, land cover, and atmospheric–hydrologic data are instrumental in the studies on the impact of climate change on the water resources of a region.  相似文献   

Slip Distribution of the 1963 Great Kurile Earthquake Estimated from Tsunami Waveforms     

Kei Ioki  Yuichiro Tanioka 《Pure and Applied Geophysics》2011,168(6-7):1045-1052

The 1963 great Kurile earthquake was an underthrust earthquake occurred in the Kurile?CKamchatka subduction zone. The slip distribution of the 1963 earthquake was estimated using 21 tsunami waveforms recorded at tide gauges along the Pacific and Okhotsk Sea coasts. The extended rupture area was divided into 24 subfaults, and the slip on each subfault was determined by the tsunami waveform inversion. The result shows that the largest slip amount of 2.8?m was found at the shallow part and intermediate depth of the rupture area. Large slip amounts were found at the shallow part of the rupture area. The total seismic moment was estimated to be 3.9?×?10²¹?Nm (M_w 8.3). The 2006 Kurile earthquake occurred right next to the location of the 1963 earthquake, and no seismic gap exists between the source areas of the 1963 and 2006 earthquakes.  相似文献   

Stabilities of NAL and Ca-ferrite-type phases on the join NaAlSiO<Subscript>4</Subscript>-MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> at high pressure     

Saori Imada  Kei Hirose  Yasuo Ohishi 《Physics and Chemistry of Minerals》2011,38(7):557-560

Stabilities of hexagonal new aluminous (NAL) phase and Ca-ferrite-type (CF) phase were investigated on the join NaAlSiO₄-MgAl₂O₄ in a pressure range from 23 to 58 GPa at approximately constant temperature of 1,850 K, on the basis of in situ synchrotron X-ray diffraction measurements in a laser-heated diamond-anvil cell. The results show that NAL is formed as a single phase up to 34 GPa, NAL + CF between 34 and 43 GPa, and only CF at higher pressures in 40%NaAlSiO₄-60%MgAl₂O₄ bulk composition. On the other hand, both NAL and CF coexist below 38 and 36 GPa, and only CF was obtained at higher pressures in 60%NaAlSiO₄-40%MgAl₂O₄ and 20%NaAlSiO₄-80%MgAl₂O₄ composition, respectively. These results indicate that NAL appears only up to 46 GPa at 1,850 K, and CF forms continuous solid solution at higher pressures on the join NaAlSiO₄-MgAl₂O₄. NAL has limited stability in subducted mid-oceanic ridge basalt crust in the Earth’s lower mantle and undergoes a phase transition to CF in deeper levels.  相似文献   

Hayabusa‐returned sample curation in the Planetary Material Sample Curation Facility of JAXA     

Toru YADA  Akio FUJIMURA  Masanao ABE  Tomoki NAKAMURA  Takaaki NOGUCHI  Ryuji OKAZAKI  Keisuke NAGAO  Yukihiro ISHIBASHI  Kei SHIRAI  Michael E. ZOLENSKY  Scott SANDFORD  Tatsuaki OKADA  Masayuki UESUGI  Yuzuru KAROUJI  Maho OGAWA  Shogo YAKAME  Munetaka UENO  Toshifumi MUKAI  Makoto YOSHIKAWA  Junichiro KAWAGUCHI 《Meteoritics & planetary science》2014,49(2):135-153

Abstract– The Planetary Material Sample Curation Facility of JAXA (PMSCF/JAXA) was established in Sagamihara, Kanagawa, Japan, to curate planetary material samples returned from space in conditions of minimum terrestrial contaminants. The performances for the curation of Hayabusa‐returned samples had been checked with a series of comprehensive tests and rehearsals. After the Hayabusa spacecraft had accomplished a round‐trip flight to asteroid 25143 Itokawa and returned its reentry capsule to the Earth in June 2010, the reentry capsule was brought back to the PMSCF/JAXA and was put to a series of processes to extract recovered samples from Itokawa. The particles recovered from the sample catcher were analyzed by electron microscope, given their ID, grouped into four categories, and preserved in dimples on quartz slide glasses. Some fraction of them has been distributed for initial analyses at NASA, and will be distributed for international announcement of opportunity (AO), but a certain fraction of them will be preserved in vacuum for future analyses.  相似文献   

Crystallization temperature determination of Itokawa particles by plagioclase thermometry with X‐ray diffraction data obtained by a high‐resolution synchrotron Gandolfi camera     

Masahiko Tanaka  Tomoki Nakamura  Takaaki Noguchi  Aiko Nakato  Hatsumi Ishida  Toru Yada  Kei Shirai  Akio Fujimura  Yukihiro Ishibashi  Masanao Abe  Tatsuaki Okada  Munetaka Ueno  Toshifumi Mukai 《Meteoritics & planetary science》2014,49(2):237-244

The crystallization temperatures of Itokawa surface particles recovered by the space probe Hayabusa were estimated by a plagioclase geothermometer using sodic plagioclase triclinicity. The Δ131‐index required for the thermometer, which is the difference in X‐ray diffraction peak positions between the 131 and 11 reflections of plagioclase, was obtained by a high‐resolution synchrotron Gandolfi camera developed for the third generation synchrotron radiation beamline, BL15XU at SPring‐8. Crystallization temperatures were successfully determined from the Δ131‐indices for four particles. The observed plagioclase crystallization temperatures were in a range from 655 to 660 °C. The temperatures indicate crystallization temperatures of plagioclases in the process of prograde metamorphism before the peak metamorphic stage.  相似文献   

3-D Spatial Variation of b-Values of Magnitude-Frequency Distribution Beneath the Kanto District, Japan     

Yosihiko Ogata  Masajiro Imoto  Koichi Katsura 《Geophysical Journal International》1991,104(1):135-146

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Surface water chemistry and nitrate pollution in Shimabara,Nagasaki, Japan     

Hiroki Amano  Kei Nakagawa  Ronny Berndtsson 《Environmental Earth Sciences》2018,77(9):354

Groundwater is a finite resource that is threatened by pollution all over the world. Shimabara City, Nagasaki, Japan, uses groundwater for its main water supply. During recent years, the city has experienced severe nitrate pollution in its groundwater. For better understanding of origin and impact of the pollution, chemical effects and surface–groundwater interactions need to be examined. For this purpose, we developed a methodology that builds on joint geochemical analyses and advanced statistical treatment. Water samples were collected at 42 sampling points in Shimabara including a part of Unzen City. Spatial distribution of water chemistry constituents was assessed by describing Stiff and Piper diagrams using major ions concentrations. The nitrate (NO₃?+?NO₂–N) concentration in 45% of water samples exceeded permissible Japanese drinking level of 10 mg L^??1. Most of the samples showed Ca–HCO₃ or Ca–(NO₃?+?SO₄) water types. Some samples were classified into characteristic water types such as Na–Cl, (Na?+?K)–HCO₃, (Na?+?K)–(SO₄?+?NO₃), and Ca–Cl. Thus, results indicated salt water intrusion from the sea and anthropogenic pollution. At the upstream of Nishi River, although water chemistry was characterized as Ca–HCO₃, ion concentrations were higher than those of other rivers. This is probably an effect of disinfection in livestock farming using slaked lime. Positive correlation between NO₃^? and SO₄^2?, Mg²⁺, Ca²⁺, Na⁺, K⁺, and Cl^? (r?=?0.32–0.64) is evidence that nitrate pollution sources are chemical fertilizers and livestock waste. Principal component analysis showed that chemistry of water samples can be explained by three main components (PCs). PC1 depicts general ion concentration. PC2 and PC3 share influence from chemical fertilizer and livestock waste. Cluster analyses grouped water samples into four main clusters. One of these is the general river chemistry mainly affected by PC1. The others reflect anthropogenic activities and are identified by the combination of the three PCs.  相似文献   

Effects of solar and view angles on reflectance for paddy field canopies     

Masaaki Shikada  Kei Miyakita 《国际地球制图》2013,28(3):9-17

It is very important to know the spectral characteristics for the sake of understanding the remote sensing data. The reflectance characteristics of paddy field canopies vary with time or observational conditions (solar zenith angle, solar azimuth angle, and view zenith angle). A number of field studies have clarified the effects of these conditions on grain canopy reflectance. Most of the field data used in these study, however, were conducted only through the growing season in one year or by grains planted in pots. A series of authors’ experiments were initiated in 1982 and continued from the spring to the autumn every year to 1987. In this study we describe that the remotely sensed spectral data measured on the ground are influenced not only by the grain type, observational conditions, and growing season but also by the solar zenith angle, solar azimuth angle and view zenith angle in relation to scene. In this paper we report the results from the investigation of these various fundamental properties.  相似文献