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91.
S. Takechi T. Miyachi M. Fujii N. Hasebe K. Nogami H. Ohashi S. Sasaki H. Shibata T. Iwai E. Grün R. Srama N. Okada 《Journal of Atmospheric and Solar》2009,71(2):191-193
A cosmic dust detector for installation on a satellite is currently being developed using piezoelectric lead zirconate titanate (PZT), which can possess both functions of the collector and the transducer. The characteristics of the PZT detector have been studied by bombarding it with hypervelocity particles supplied by a Van de Graaff accelerator. The front surface of the detector used in this study was covered with a white paint to reduce any increase in the temperature due to the solar radiation. There was a linear relationship between the rise time of the signal produced by the detector and the particle's velocities, which were above 10 km/s on impact. This implies that individual particle velocities on impact can be inferred through the empirical formula derived from the data obtained from the PZT detector. 相似文献
92.
Precise determination of the partitioning of Mg and Fe2+ between olivine and ultramafic melt has been made at pressures from 5 to 13 GPa using a MA-8 type multi-anvil high-pressure apparatus (PREM) installed at Earthquake Research Institute, University of Tokyo. A very short rhenium capsule (<100 μm sample thickness) was adopted to minimize temperature variation within the sample container. Synthetic gels with the composition of the upper mantle peridotite were used as starting materials to promote the homogeneity. Analyses of quenched melts and coexisting olivines were made with an electron probe microanalyzer. The obtained partition coefficient, KD [=(FeO/MgO)ol/(FeO/MgO)melt], decreases from 0.35 to 0.25 with increasing pressure from 5 to 13 GPa, suggesting a negative correlation between pressure and KD above 5 GPa. Our result is consistent with a parabolic relationship between KD and degree of polymerization (NBO/T) of melts reported by previous studies at lower pressures. The negative correlation between pressure and KD suggests that olivine crystallizing in a magma ocean becomes more Mg-rich with depth and that primary magmas generated in the upper mantle become more Fe-rich with depth than previously estimated. 相似文献
93.
Changes in the lower limit of mountain permafrost between 1973 and 2004 in the Khumbu Himal, the Nepal Himalayas 总被引:2,自引:0,他引:2
Kotaro Fukui Yoshiyuki Fujii Yutaka Ageta Katsuhiko Asahi 《Global and Planetary Change》2007,55(4):251-256
Because the Khumbu Himal of the Nepal Himalayas lacks long-term climate records from weather stations, mountain permafrost degradation serves as an important indicator of climate warming. In 1973, the permafrost lower limit was estimated to be 5200–5300 m above sea level (ASL) on southern-aspect slopes in this region. Using ground-temperature measurements, we examined the mountain permafrost lower limit on slopes with the same aspect in 2004. The results indicate that the permafrost lower limit was 5400–5500 m ASL in 2004. The permafrost lower limit was estimated to be 5400 to 5500 m on slopes with a southern aspect in the Khumbu Himal in 1991 using seismic reflection soundings. Thus, it is possible that the permafrost lower limit has risen 100–300 m between 1973 and 1991, followed by a stable limit of 5400 to 5500 m over the last decade. An increase in mean annual air temperature of approximately 0.2 to 0.4 °C from the 1970s to the 1990s has indicated a rise in the permafrost lower limit of 40 to 80 m at the Tibetan Plateau. The rise in the mountain permafrost lower limit in the Khumbu Himal exceeds that of the Tibetan Plateau, suggesting the possibility of greater climate warming in the Khumbu Himal. 相似文献
94.
Frédéric Moynier Toshiyuki Fujii Francis Albarède 《Meteoritics & planetary science》2009,44(11):1735-1742
Abstract— We explore the possibility that Te isotopic anomalies measured in Ca‐Al‐rich inclusions (Fehr et al. 2009) and in leachates of carbonaceous chondrites (Fehr et al. 2006) may be due to mass‐independent effects controlled by nuclear field shift rather than to nucleosynthetic processes. Fehr et al.'s spectrum of mass‐independent anomalies of Te isotopes shows a smooth correlation with mass number and nuclear charge distribution. Ratios of even to odd isotopes, as the 125Te/126Te ratio used by these authors for normalization are particularly prone to nuclear field shift effects. We show that the alternative normalization of isotopic ratios to 130Te/126Te strongly reduces the trend of isotopic fractionation with mass number, leaving only 125Te as truly anomalous. For both normalizations (125Te/126Te and 130Te/126Te), Fehr et al.'s results fit the theory of Bigeleisen (1996), which suggests that the nuclear field shift effect can potentially account for the observed Te isotope abundances, as an alternative to nucleosynthetic processes. We propose that these mass‐independent effects may be acquired during accretion of sulfides from the solar nebula. 相似文献
95.
Tomohiro Nakamura Takahiro Toyoda Yoichi Ishikawa Toshiyuki Awaji 《Journal of Oceanography》2004,60(2):411-423
A numerical study using a 3-D nonhydrostatic model has been applied to baroclinic processes generated by the K
1 tidal flow in and around the Kuril Straits. The result shows that large-amplitude unsteady lee waves are generated and cause
intense diapycnal mixing all along the Kuril Island Chain to levels of a maximum diapycnal diffusivity exceeding 103 cm2s−1. Significant water transformation by the vigorous mixing in shallow regions produces the distinct density and potential vorticity
(PV) fronts along the Island Chain. The pinched-off eddies that arise and move away from the fronts have the ability to transport
a large amount of mixed water (∼14 Sv) to the offshore regions, roughly half being directed to the North Pacific. These features
are consistent with recent satellite imagery and in-situ observations, suggesting that diapycnal mixing within the vicinity
of the Kuril Islands has a greater impact than was previously supposed on the Okhotsk Sea and the North Pacific. To examine
this influence of tidal processes at the Kurils on circulations in the neighboring two basins, another numerical experiment
was conducted using an ocean general circulation model with inclusion of tidal mixing along the islands, which gives a better
representation of the Okhotsk Sea Mode Water than in the case without the tidal mixing. This is mainly attributed to the added
effect of a significant upward salt flux into the surface layer due to tidal mixing in the Kuril Straits, which is subsequently
transported to the interior region of the Okhotsk Sea. With a saline flux into the surface layer, cooling in winter in the
northern part of the Okhotsk Sea can produce heavier water and thus enhance subduction, which is capable of reproducing a
realistic Okhotsk Sea Mode Water. The associated low PV flux from the Kuril Straits to the open North Pacific excites the
2nd baroclinic-mode Kelvin and Rossby waves in addition to the 1st mode. Interestingly, the meridional overturning in the
North Pacific is strengthened as a result of the dynamical adjustment caused by these waves, leading to a more realistic reproduction
of the North Pacific Intermediate Water (NPIW) than in the case without tidal mixing. Accordingly, the joint effect of tidally-induced
transport and transformation dominating in the Kuril Straits and subsequent eddy-transport is considered to play an important
role in the ventilation of both the Okhotsk Sea and the North Pacific Ocean.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
96.
Ken-ichi Hirauchi Izumi Segawa Yui Kouketsu Yumiko Harigane Yasuhiko Ohara Jonathan Snow Atlanta Sen Masakazu Fujii Kyoko Okino 《Island Arc》2021,30(1):e12419
We determined the mineralogical and petrological characteristics of ultramafic rocks dredged from two oceanic core complexes: the Mado Megamullion and 23°30′N non-transform offset massif, which are located within the Shikoku back-arc basin in the Philippine Sea. The ultramafic rocks are strongly serpentinized, but can be classified as harzburgite/lherzolite or dunite, based on relict primary minerals and their pseudomorphs. Strongly elongated pyroxene porphyroclasts with undulatory extinction indicate high-temperature (≥700 °C) strain localization on a detachment fault within the upper mantle at depths below the brittle–viscous transition. During exhumation, the peridotites underwent impregnation by magmatic or hydrothermal fluids, lizardite/chrysotile serpentinization at ≤300 °C, antigorite crystallization, and silica metasomatism that formed talc. These features indicate that the detachment fault zones formed a fluid pathway and facilitated a range of fluid–peridotite interactions. 相似文献
97.
The eruption of Unzen Volcano commenced on 17 November 1990. Phreatic and phreatomagmatic eruptions occurred by early May 1991. No large-scale explosive eruptions preceded the extrusion of lava domes. Lava domes appeared in a summit crater on 20 May 1991, and they grew on the steep slope of Mt. Fugen at Unzen Volcano. Rockfalls from the margins of the domes frequently generated pyroclastic flows. Major pyroclastic flows occurred on 3 June, 8 June, and 15 September 1991. The 3 June pyroclastic flow killed forty-three persons. Many of the pyroclastic flows seem to have resulted from the simple rockfalls, except one flow on 8 June, which was accompanied by an explosion from the crater. Many of the rockfalls that generated pyroclastic flows were witnessed. As of November 1991. Unzen Volcano was still active with a nearly constant magma-supply rate of about 0.3 × 106 m3/d. The total magma output exceeded 45 × 106 m3 by the beginning of November 1991. The volume of the lava domes is more than 23 × 106 m3. 相似文献
98.
A statistical approach is proposed for nonlinear surface ground analysis. In contrast to the conventional method which deals with only a single ground motion for equivalent linearization of soil properties, a design response spectrum defined at the upper level (bottom of the surface ground) of an engineering bedrock can be handled as the target design earthquake in the present paper. The effective shear strain in each soil layer is evaluated by means of a statistical procedure in which the mean peak shear strain is computed in terms of its standard deviation and the corresponding peak factor. The stiffness and damping ratio of each soil layer are obtained iteratively from the nonlinear relation of stiffness reduction factors and damping ratios with respect to the strain level. After the evaluation of the equivalent stiffness and damping ratio of every soil layer, the ground surface response spectrum is transformed from the design response spectrum defined at the upper level of the engineering bedrock via the one-dimensional wave propagation theory. The reliability and accuracy of the proposed analysis method is examined through the comparison with the results by the conventional method (represented by the
program) for many simulated spectrum-compatible ground motions. 相似文献
99.
Detrital zircon multi‐chronology,provenance, and low‐grade metamorphism of the Cretaceous Shimanto accretionary complex,eastern Shikoku,Southwest Japan: Tectonic evolution in response to igneous activity within a subduction zone 下载免费PDF全文
Hidetoshi Hara Yoshihiro Nakamura Kousuke Hara Toshiyuki Kurihara Hiroshi Mori Hideki Iwano Tohru Danhara Shuhei Sakata Takafumi Hirata 《Island Arc》2017,26(6)
Detrital zircon multi‐chronology combined with provenance and low‐grade metamorphism analyses enables the reinterpretation of the tectonic evolution of the Cretaceous Shimanto accretionary complex in Southwest Japan. Detrital zircon U–Pb ages and provenance analysis defines the depositional age of trench‐fill turbidites associated with igneous activity in provenance. Periods of low igneous activity are recorded by youngest single grain zircon U–Pb ages (YSG) that approximate or are older than the depositional ages obtained from radiolarian fossil‐bearing mudstone. Periods of intensive igneous activity recorded by youngest cluster U–Pb ages (YC1σ) that correspond to the younger limits of radiolarian ages. The YC1σ U–Pb ages obtained from sandstones within mélange units provide more accurate younger depositional ages than radiolarian ages derived from mudstone. Determining true depositional ages requires a combination of fossil data, detrital zircon ages, and provenance information. Fission‐track ages using zircons estimated YC1σ U–Pb ages are useful for assessing depositional and annealing ages for the low‐grade metamorphosed accretionary complex. These new dating presented here indicates the following tectonic history of the accretionary wedge. Evolution of the Shimanto accretionary complex from the Albian to the Turonian was caused by the subduction of the Izanagi plate, a process that supplied sediments via the erosion of Permian and Triassic to Early Jurassic granitic rocks and the eruption of minor amounts of Early Cretaceous intermediate volcanic rocks. The complex subsequently underwent intensive igneous activity from the Coniacian to the early Paleocene as a result of the subduction of a hot and young oceanic slab, such as the Kula–Pacific plate. Finally, the major out‐of‐sequence thrusts of the Fukase Fault and the Aki Tectonic Line formed after the middle Eocene, and this reactivation of the Shimanto accretionary complex as a result of the subduction of the Pacific plate. 相似文献
100.
Yoichi Ishikawa Toshiyuki Awaji Nobumasa Komori Takahiro Toyoda 《Journal of Oceanography》2004,60(2):293-301
A sensitivity experiment has been performed by assimilating altimetric data into a 1.5-layer primitive equation model as a
first attempt to examine the impact of initialization on forecasts of the Kuroshio path variability south of Japan. By exploiting
the advantage of an adjoint model, our approach clearly shows that a small meander off Shikoku Island has a large impact on
the prediction of meander growth in the Kuroshio region. Further, the strengthening of the Kuroshio current and its recirculation
clearly becomes an important factor in the development of the meander. These results demonstrate the effectiveness of our
assimilation approach in identifying efficient initialization schemes on numerical forecasting of the Kuroshio south of Japan
and should help in the construction of an effective observing system for improving the forecasting.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献