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741.
A theoretical study is made of the whistler mode cyclotron instability both in linear and nonlinear regimes in conjunction with the generation of VLF emissions in the magnetosphere. For the nonlinear treatment, a well-established quasilinear method is used and some physical processes of the cyclotron instability viz. energy conservation, mechanism of instability and frequency change of the excited emissions are clarified. The results are applied to some types of the triggered VLF emissions; whistler triggered emissions and artificially stimulated emissions (ASE). It is found that whistler triggered emissions excited around the upper cutoff frequencies of whistlers may be explained by the whistler mode cyclotron instability by a model distribution function inferred from satellite data. In order to see a nonlinear evolution of the whistler mode cyclotron instability, computer simulations were carried out and it is shown that the change of frequency with time of whistler triggered emissions as well as characteristics of ASE are well explained by resonant nonlinear behaviour of whistler mode cyclotron instability considered in the present paper. 相似文献
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744.
Hitoshi Yusa Masaki Akaogi Nagayoshi Sata Hiroshi Kojitani Ryo Yamamoto Yasuo Ohishi 《Physics and Chemistry of Minerals》2006,33(3):217-226
In-situ X-ray powder diffraction measurements conducted under high pressure confirmed the existence of an unquenchable orthorhombic perovskite in ZnGeO3. ZnGeO3 ilmenite transformed into perovskite at 30.0 GPa and 1300±150 K in a laser-heated diamond anvil cell. After releasing the pressure, the lithium niobate phase was recovered as a quenched product. The perovskite was also obtained by recompression of the lithium niobate phase at room temperature under a lower pressure than the equilibrium phase boundary of the ilmenite–perovskite transition. Bulk moduli of ilmenite, lithium niobate, and perovskite phases were calculated on the basis of the refined X-ray diffraction data. The structural relations among these phases are considered in terms of the rotation of GeO6 octahedra. A slight rotation of the octahedra plays an important role for the transition from lithium niobate to perovskite at ambient temperature. On the other hand, high temperature is needed to rearrange GeO6 octahedra in the ilmenite–perovskite transition. The correlation of quenchability with rotation angle of GeO6 octahedra for other germanate perovskites is also discussed. 相似文献
745.
Observation of shear zone development in ring-shear apparatus with a transparent shear box 总被引:1,自引:1,他引:1
Using a new ring-shear apparatus with a transparent shear box and video image analysis system, drained and undrained speed-controlled tests were conducted on coarse-grained silica sands to study the shear-zone formation process in granular materials. Velocity distribution profiles of grains under shear at various stages in the ring shear tests were observed through processing the video image by the Particle Image Velocimetry (PIV) program. Shear-zone thickness and type of shear mode (slide-like or flow-like) during shear were observed. Before reaching peak strength in low-speed and drained condition test, a comparatively major part of the sample in the upper shear box showed a velocity distribution profile of structural deformation and dilatancy behavior. After peak strength, the velocity profile changed into a slide-like mode and thereafter showed almost no change. In higher speed tests with drained and undrained conditions, an almost slide-like mode was observed, compared to low-speed test. Apparent shear-zone thicknesses of high-speed tests are thinner than low-speed tests. Unexpectedly, almost no difference was observed in the shear-zone thickness and mode of shear (slide or flow-like) between drained and undrained tests. This study was conducted as part of the International Programme on Landslides (IPL) M101 “Areal prediction of earthquake and rain induced rapid and long-traveling flow phenomena (APERITIF)” of the International Consortium on Landslides (ICL). These results will contribute to understanding the mechanism of shear-zone development in granular materials as a basic knowledge for disaster risk mitigation of rapid long run-out landslides. 相似文献
746.
Failure mechanism in an extremely slow rock slide at Bitchu-Matsuyama castle site (Japan) 总被引:1,自引:1,他引:1
One of the specific problems related to historical structures is the fact that they are prone to damage caused by even very
small deformations acting over a long period of time, such as creep or extremely small rock displacements. If any damage has
already occurred, the determination of the rock slope failure mechanism is one of the prerequisites for successful mitigation
technique selection. In this study a medieval castle in central Japan, suffering damage caused by deformation of the rock
mass in the subgrade of the castle, was investigated using a combination of field investigation, high-precision monitoring
and physical modeling experiments. Using these techniques an attempt to determine the failure mechanism of the rock slope
was made. Based on the field investigation a toe-slope failure seemed to be the main triggering factor activating the deformations
in the upper slope area, right below the defense walls of the castle. The displacement monitoring of the surface rock blocks
revealed a slumping failure with the backward rotational component prevailing over the sliding in the immediate vicinity of
the castle wall. This was in accordance with the expectations obtained from the structural analysis of the rock mass carried
out during the field investigation. The displacements obtained during the rock block monitoring, especially from the crack
gauges, were not sufficient for drawing a satisfactory conclusions about the failure mechanism of the blocks located in the
central part of the slope. Therefore, the failure mechanisms of rock blocks inferred from their displacements obtained from
the monitoring were correlated with the results of modeling experiments carried out on the scaled slope model. The physical
modeling revealed a possibility of toppling failure of rock blocks in the central area of the slope caused mainly by block
interlocking, which was supported by the data from surface tilt meters installed additionally in the field. Furthermore, the
possibility of the occurrence of forward and backward rock block rotations in the same sliding body at given conditions was
supported by the physical modeling experiments. 相似文献
747.
Stable carbon (δ13C) and hydrogen (δD) isotopic compositions of n-alkanes, anteiso-alkanes, n-alkanoic acids, n-alkanols, phytol and sterols in raw leaves of Acer argutum and Acer carpinifolium, their fallen leaves, mold and soils from a natural Acer forest were measured in order to: (1) understand isotopic variation of the plant biomarkers in a plant-soil system and (2) evaluate which biomarker is the most effective recorder of soil vegetation. Long-chain (> C24) n-alkanes, n-alkanoic acids and n-alkanols are gradually enriched in 13C up to 12.9‰ (average of 4.3‰) and depleted in D up to 94‰ (average of 55‰) from raw leaves to soils. However, anteiso-alkanes, phytol and sterols show little variation in both δ13C (< ± 1‰) and δD (< ± 2‰) from raw leaves to soils. These isotope signatures in a plant-soil system indicate that isoprenoid plant biomarkers such as sterols in soils faithfully preserve the isotopic compositions of dominant higher plants growing on the soils without a diagenetic effect upon the isotopic compositions. In contrast, long-chain n-alkyl molecules in soils undergo specific isotopic modification during biodegradation associated with early diagenesis and/or a significant contribution from heterotrophic reworking. 相似文献
748.
Shuai Yin Xiufeng Wang Heri Santoso Hiroshi Tani Guosheng Zhong Zhongyi Sun 《International Journal of Digital Earth》2018,11(8):825-844
We used OCO-2 products and considered three factors that potentially affect CO2 concentration in Indonesia: sea surface temperature (SST), forest fires and vegetation. From 2014 to 2016, CO2 concentration in Indonesia showed a trend of increase, which is consistent with the global increase reported by the Greenhouse Gases Observing Satellite (GOSAT) Project. As an archipelago country, the results indicate that SST has a direct effect on the CO2 concentration in Indonesia. Their changing exhibits similar fluctuations; meanwhile, CO2 concentration and SST also presented positive correlation. In 2015, the number of fire hotspots suddenly increased to 140,699, because of occurrence of the worst forest fire. Due to special geographic conditions, forest fires did not induce CO2 concentration changes in Indonesia, but CO2 concentration in the corresponding islands showed a trend of increase. CO2 concentration increased in Kalimantan during the occurrence of forest fire in September–October 2014, and CO2 concentration increased in Kalimantan and Sumatra during the occurrence of forest fire in September–October 2015. Vegetation indices were stable and presented no correlation with CO2 concentration. This study demonstrated that OCO-2 is capable of monitoring CO2 concentration at a regional scale; additionally, an effective method for using OCO-2 Level 2 products is proposed. 相似文献
749.
Towhata Ikuo Goto Satoshi Goto Shigeru Akima Takeshi Tanaka Junya Uchimura Taro Wang Gonghui Yamaguchi Hiroshi Aoyama Shogo 《Natural Hazards》2021,105(1):501-530
Natural Hazards - A volcanic slope in Izu Oshima Island in Japan experienced a profound rain-induced disaster in October 2013. Since this slope had been stable for centuries except for minor... 相似文献
750.
Yuichi Nosaka Tomonori Isada Isao Kudo Hiroaki Saito Hiroshi Hattori Atsushi Tsuda Koji Suzuki 《Journal of Oceanography》2014,70(1):91-103
We investigated the water-column light utilization efficiency (Ψ) of phytoplankton photosynthesis in the Western Subarctic Gyre (WSG) of the North Pacific during summer 2008. The Ψ values (0.64–1.86 g C [g Chl a]?1 [mol photon]?1 m2) obtained were observed to increase significantly with decreasing daily photosynthetic available radiation (PAR) and were generally higher than those of previous studies, not only from the subarctic Pacific but also from the world’s oceans. To examine the effect of iron availability on Ψ in the WSG, Ψ values were estimated from the data of two in situ iron fertilization experiments: the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study I (SEEDS-I) and II (SEEDS-II). We found that iron availability did not affect Ψ values. Overall, this study revealed that Ψ values changed remarkably in the WSG during the summer, and that higher values were found at the stations where moderate PAR levels (ca. 10–30 mol photons m?2 day?1) were observed and where autotrophic flagellates predominated in the phytoplankton assemblages. 相似文献