Rare-earth and trace elements in the Quaternary volcanic rocks of Hokkaido,Japan     

Yasuyuki Masuda  Susumu Nishimura  Takashi Ikeda  Yoshio Katsui 《Chemical Geology》1975,15(4):251-271

Seven rare-earth elements (La, Ce, Sm, Eu, Tb, Yb, Lu) and Co, Cr, Sc, Ba, Hf and Th have been determined by non-destructive neutron activation analysis on the Quaternary volcanic rocks in Hokkaido, Japan. The trace-element abundances are discussed in terms of the petrological problems, particularly the origin of calc-alkali magma. On the basis of the La/Sm ratio and the contents of K, Ba, Th and La, lateral variations in the contents of trace elements exist across the Kurile and the northern Honshū arcs. The calc-alkali rocks can be classified into three types which correspond to Kuno's three basalt-magma types. There is no essential difference in the rare-earth patterns between the basaltic rocks and the associated calc-alkali rocks in each petrographic province. This suggests that the calcalkali rocks may be derived from the basaltic magmas by fractional crystallization under certain conditions.  相似文献   

Observation of cosmic soft X-rays     

S. Hayakawa  T. Kato  T. Kohno  K. Nishimura  Y. Tanaka  K. Yamashita 《Astrophysics and Space Science》1972,17(1):30-38

Cosmic X-rays in the energy range between 0.210 keV were observed with polypropylene window proportional counters on board a sounding rocket. The field of view crossed the galactic plane in the Sgr region and reached galactic latitudes of 50° and –90°. A new soft X-ray source was found in the Aries-Taurus region. The soft X-ray flux from the direction of NGC 1275 was conspicuous, whereas that of Sgr region source were very weak. The distribution of the intensity of diffuse soft X-rays over the scanned region indicates the galactic emission of soft X-rays.  相似文献   

X-ray emission associated with gamma-ray bursts     

J. Nishimura  M. Fujii  T. Yamagami 《Astrophysics and Space Science》1983,93(1):87-96

The energy spectra of gamma-ray bursts differ from those of black-body radiation and are similar to the thermal bremsstrahlung spectra of optically thin plasma. This could be realized if the source is located in the outer atmosphere of a neutron star. In this case, almost one half of the emitted photons hit the surface of the star. The surface of the star is heated to a temperature of the order 10⁷ K, and a dominant flux of X-rays with a black-body spectrum would be expected. The X-rays produced by this mechanism are detectable in the energy range from a few keV to 10 keV. This model is discussed in relation to the recent observations in the X-ray region at the time of gamma-ray bursts, and modifications of this model are also presented. The observation in this energy range will bring us valuable information on the nature of gamma-ray burst sources.  相似文献   

Melt inclusion analysis of the Unzen 1991–1995 dacite: implications for crystallization processes of dacite magma     

Koshi Nishimura  Tatsuhiko Kawamoto  Tetsuo Kobayashi  Takeshi Sugimoto  Shigeru Yamashita 《Bulletin of Volcanology》2005,67(7):648-662

Dacitic magma, a mixture of high-temperature (T) aphyric magma and low-T crystal-rich magma, was erupted during the 1991–1995 Mount Unzen eruptive cycle. Here, the crystallization processes of the low-T magma were examined on the basis of melt inclusion analysis and phase relationships. Variation in water content of the melt inclusions (5.1–7.2 wt% H₂O) reflected the degassing history of the low-T magma ascending from deeper levels (250 MPa) to a shallow magma chamber (140 MPa). The ascent rate of the low-T magma decreased markedly towards the emplacement level as crystal content increased. Cooling of magma as well as degassing-induced undercooling drove crystallization. With the decreasing ascent rate, degassing-induced undercooling decreased in importance, and cooling became more instrumental in crystallization, causing local and rapid crystallization along the margin of the magma body. Some crystals contain scores of melt inclusions, whereas there are some crystals without any inclusions. This heterogeneous distribution suggests the variation in the crystallization rate within the magma body; it also suggests that cooling was dominant cause for melt entrapment. Numerical calculations of the cooling magma body suggest that cooling caused rapid crystal growth and enhanced melt entrapment once the magma became a crystal-rich mush with evolved interstitial melt. The rhyolitic composition of melt inclusions is consistent with this model.Editorial responsibility: H Shinohara  相似文献   

A model with rigid rotations and slip deficits for the GPS-derived velocity field in Southwest Japan     

Sou Nishimura  Manabu Hashimoto   《Tectonophysics》2006,421(3-4):187-207

We interpret the GPS-derived velocity field in southwest Japan by a superposition of the elastic deformation caused by fault interactions (slips or slip deficits) on the rigid motion of tectonic blocks (or plates). Based on the strain rate field and crustal seismicity, we apply a model with three blocks (Inner Arc, Outer Arc, and the northern Ryukyu block) and slip deficits along the block boundaries.Several characteristics of the synthesized contributions are found:

(1) Westward motion of the outer arc relative to the Amurian plate and the inner arc,

(2) southeastward motion of the northern Ryukyu block relative to the Amurian plate,

(3) 2−4 mm/yr deficits of left lateral slip rates along the boundary at 32°N in southern Kyushu,

(4) 0−8 mm/yr deficits of right lateral slip rates along the Median Tectonic Line and the Beppu-Shimabara Graben,

(5) slip deficit rates on the plate interface smaller than those in the case without any consideration for rigid block motions,

(6) clockwise deflection of slip deficit rate vector on the plate interface from that estimated when not taking rigid block motions into consideration.

Microbial responses using denaturing gradient gel electrophoresis to oil and chemical dispersant in enclosed ecosystems     

Yoshida A  Nomura H  Toyoda K  Nishino T  Seo Y  Yamada M  Nishimura M  Wada M  Okamoto K  Shibata A  Takada H  Kogure K  Ohwada K 《Marine pollution bulletin》2006,52(1):89-95

Microbial responses to the addition of oil with or without a chemical dispersant were examined in mesocosm and microcosm experiments by using denaturing gradient gel electrophoresis of bacterial ribosomal DNA and direct cell counting. When a water-soluble fraction of oil was added to seawater, increases in cell density were observed in the first 24h, followed by a decrease in abundance and a change in bacterial species composition. After addition of an oil-dispersant mixture, increases in cell density and changes in community structure coincided, and the amount of bacteria remained high. These phenomena also occurred in response to addition of only dispersant. Our results suggest that the chemical dispersant may be used as a nutrient source by some bacterial groups and may directly or indirectly prevent the growth of other bacterial groups.  相似文献   

Paleohydrological processes revealed by n-alkane δD in lacustrine sediments of Lake Pumoyum Co,southern Tibetan Plateau,and their response to climate changes during the past 18.5 cal ka     

Yong Wang  Liping Zhu  Junbo Wang  Jianting Ju  Ping Peng  Xiao Lin  Jianfang Hu  Mitsugu Nishimura 《Journal of Paleolimnology》2016,56(2-3):223-238

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Dipolarization fronts in the magnetotail plasma sheet   总被引：1，自引：0，他引：1  

A. Runov  V. Angelopoulos  V.A. Sergeev  Y. Nishimura  H.U. Frey  D. Larson  K.-H. Glassmeier  M. Connors  C.T. Russell 《Planetary and Space Science》2011,59(7):517-525

We present a THEMIS study of a dipolarization front associated with a bursty bulk flow (BBF) that was observed in the central plasma sheet sequentially at X=−20.1, −16.7, and −11.0R_E. Simultaneously, the THEMIS ground network observed the formation of a north-south auroral form and intensification of westward auroral zone currents. Timing of the signatures in space suggests earthward propagation of the front at a velocity of 300 km/s. Spatial profiles of current and electron density on the front reveal a spatial scale of 500 km, comparable to an ion inertial length and an ion thermal gyroradius. This kinetic-scale structure traveled a macroscale distance of 10R_E in about 4 min without loss of coherence. The dipolarization front, therefore, is an example of space plasma cross-scale coupling. THEMIS observations at different geocentric distances are similar to recent particle-in-cell simulations demonstrating the appearance of dipolarization fronts on the leading edge of plasma fast flows in the vicinity of a reconnection site. Dipolarization fronts, therefore, may be interpreted as remote signatures of transient reconnection.  相似文献   

Synthesis of coda wave envelopes in randomly inhomogeneous elastic media in a half-space: single scattering model including Rayleigh waves     

Takuto Maeda  Haruo Sato  Takeshi Nishimura 《Geophysical Journal International》2008,172(1):130-154

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Hysteresis and Surface Shear Stresses During Snow-Particle Aeolian Transportation     

Niiya  Hirofumi  Nishimura  Kouichi 《Boundary-Layer Meteorology》2022,183(3):447-467

Boundary-Layer Meteorology - Surface shear stresses produced by wind and particle collision play a key role in aerodynamic entrainment and splash processes. The fluid shear stress at the surface...  相似文献