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排序方式: 共有105条查询结果,搜索用时 15 毫秒
1.
Shin-ichi Nishimura Toshifumi Shibata Takayuki Shuku 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2016,10(4):312-319
The spatial distribution of the strength inside the earth-fill is identified by the sounding tests. In this research, the Swedish weight sounding (SWS) is employed, and the spatial high-density test is performed to identify the spatial correlation structure. Furthermore, the synthesised approach of the SWS and surface wave method, which is one of the geophysical method, is proposed to compensate the shortage of each approach. Consequently, the correlation structure of an earth-fill could be identified accurately, and the high resolution of the spatial distribution could be visualised based on the survey results. 相似文献
2.
Noriko T. Kita Qing‐Zhu Yin Glenn J. MacPherson Takayuki Ushikubo Benjamin Jacobsen Kazuhide Nagashima Erika Kurahashi Alexander N. Krot Stein B. Jacobsen 《Meteoritics & planetary science》2013,48(8):1383-1400
High‐precision bulk aluminum‐magnesium isotope measurements of calcium‐aluminum‐rich inclusions (CAIs) from CV carbonaceous chondrites in several laboratories define a bulk 26Al‐26Mg isochron with an inferred initial 26Al/27Al ratio of approximately 5.25 × 10?5, named the canonical ratio. Nonigneous CV CAIs yield well‐defined internal 26Al‐26Mg isochrons consistent with the canonical value. These observations indicate that the canonical 26Al/27Al ratio records initial Al/Mg fractionation by evaporation and condensation in the CV CAI‐forming region. The internal isochrons of igneous CV CAIs show a range of inferred initial 26Al/27Al ratios, (4.2–5.2) × 10?5, indicating that CAI melting continued for at least 0.2 Ma after formation of their precursors. A similar range of initial 26Al/27Al ratios is also obtained from the internal isochrons of many CAIs (igneous and nonigneous) in other groups of carbonaceous chondrites. Some CAIs and refractory grains (corundum and hibonite) from unmetamorphosed or weakly metamorphosed chondrites, including CVs, are significantly depleted in 26Al. At least some of these refractory objects may have formed prior to injection of 26Al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk. Bulk aluminum and magnesium‐isotope measurements of various types of chondrites plot along the bulk CV CAI isochron, suggesting homogeneous distribution of 26Al and magnesium isotopes in the protoplanetary disk after an epoch of CAI formation. The inferred initial 26Al/27Al ratios of chondrules indicate that most chondrules formed 1–3 Ma after CAIs with the canonical 26Al/27Al ratio. 相似文献
3.
A full particle simulation study is carried out on a perpendicular collisionless shock with a relatively low Alfven Mach number (MA = 5). Recent self-consistent hybrid and full particle simulations have demonstrated ion kinetics are essential for the non-stationarity of perpendicular collisionless shocks, which means that physical processes due to ion kinetics modify the shock jump condition for fluid plasmas. This is a cross-scale coupling between fluid dynamics and ion kinetics. On the other hand, it is not easy to study cross-scale coupling of electron kinetics with ion kinetics or fluid dynamics, because it is a heavy task to conduct large-scale full particle simulations of collisionless shocks. In the present study, we have performed a two-dimensional (2D) electromagnetic full particle simulation with a “shock-rest-frame model”. The simulation domain is taken to be larger than the ion inertial length in order to include full kinetics of both electrons and ions. The present simulation result has confirmed the transition of shock structures from the cyclic self-reformation to the quasi-stationary shock front. During the transition, electrons and ions are thermalized in the direction parallel to the shock magnetic field. Ions are thermalized by low-frequency electromagnetic waves (or rippled structures) excited by strong ion temperature anisotropy at the shock foot, while electrons are thermalized by high-frequency electromagnetic waves (or whistler mode waves) excited by electron temperature anisotropy at the shock overshoot. Ion acoustic waves are also excited at the shock overshoot where the electron parallel temperature becomes higher than the ion parallel temperature. We expect that ion acoustic waves are responsible for parallel diffusion of both electrons and ions, and that a cross-scale coupling between an ion-scale mesoscopic instability and an electron-scale microscopic instability is important for structures and dynamics of a collisionless perpendicular shock. 相似文献
4.
Mitsuhiro Yoshimoto Toshitsugu Fujii Takayuki Kaneko Atsushi Yasuda Setsuya Nakada Akikazu Matsumoto 《Island Arc》2010,19(3):470-488
A buried, old volcanic body (pre‐Komitake Volcano) was discovered during drilling into the northeastern flank of Mount Fuji. The pre‐Komitake Volcano is characterized by hornblende‐bearing andesite and dacite, in contrast to the porphyritic basaltic rocks of Komitake Volcano and to the olivine‐bearing basaltic rocks of Fuji Volcano. K‐Ar age determinations and geological analysis of drilling cores suggest that the pre‐Komitake Volcano began with effusion of basaltic lava flows around 260 ka and ended with explosive eruptions of basaltic andesite and dacite magma around 160 ka. After deposition of a thin soil layer on the pre‐Komitake volcanic rocks, successive effusions of lava flows occurred at Komitake Volcano until 100 ka. Explosive eruptions of Fuji Volcano followed shortly after the activity of Komitake. The long‐term eruption rate of about 3 km3/ka or more for Fuji Volcano is much higher than that estimated for pre‐Komitake and Komitake. The chemical variation within Fuji Volcano, represented by an increase in incompatible elements at nearly constant SiO2, differs from that within pre‐Komitake and other volcanoes in the northern Izu‐Bonin arc, where incompatible elements increase with increasing SiO2. These changes in the volcanism in Mount Fuji may have occurred due to a change in regional tectonics around 150 ka, although this remains unproven. 相似文献
5.
6.
The fruticose lichen Cetrariella delisei is among the dominant lichen species in the deglaciated High Arctic areas of Svalbard. As part of a study of carbon cycling in the High Arctic, we aimed to estimate the primary production of lichen in a deglaciated area in Ny-Ålesund, Svalbard (79° N), by examining the effects of abiotic factors on the net photosynthesis ( Pn ) and dark respiration ( R ) rates of C. delisei . Experiments were conducted in the snow-free season of 2000 using an open-flow gas exchange system with an infrared gas analyser. Positive photosynthetic activities were observed on rainy days or soon after rainfall when the thallus water content was high, whereas photosynthetic activities dropped below the detectable limit on clear days because of the low thallus water content. Under a sufficiently high thallus water content and close to light saturation, Pn was nearly constant over a wide temperature range of 4–20 °C, while R increased with increasing temperature. We constructed a model for estimating the net primary production ( NPP ) of lichen based on the relationships between abiotic factors and the CO2 exchange rate. The mean, minimum and maximum NPP values in the snow-free season, estimated using meteorological data obtained from 1995–2003, were 5.1, 1.0 and 8.4 g dry wt. m−2 snow-free season−1 , respectively. These results suggest that NPP is highly variable and the contribution of lichen to carbon input is small compared with that of vascular plants and mosses in the study site. 相似文献
7.
Wataru Ootani Makoto Minowa Takayuki Watanabe Yutaka Ito Yasuhiro Kishimoto Kentaro Miuchi Yoshizumi Inoue Youiti Ootuka 《Astroparticle Physics》1998,9(4):325-329
The performance of a 21-g lithium fluoride bolometer is presented. The background spectrum was measured in the surface laboratory. We derive an exclusion plot for the spin-dependent coupled Weakly Interacting Massive Particles (WIMPs) cross section. 相似文献
8.
Dynamic spectra of S-bursts of Jovian decametric radiations are obtained by using a high time resolution radio spectrograph
which has a time resolutionof 2 msec and the bandwidth of 2 MHz.Within occurrence of 65 S-burst events observed in the period
from 1983 to 1999, 26 events have been identified as the S-N burst events, which are characterized by the interaction between
the S-burst emissions and the Narrow band emissions. In the dynamic spectra of the S-N burst, the trend of emissions with
negative and slower frequency drift named as “Trailing Edge Emission” are often observed shortly after the appearance of the
S-burst.Detailed analyses of these phenomena revealed that the Trailing Edge Emission is not a manifestation of S-burst with
slower drift rate but a variation ofN-burst. The results suggested that S-burst and the associated Trailing Edge Emission
are formed simultaneously started from a common region with different drift rates. It has been further suggested that the
appearance of the S-burstsis not controlled by the geometrical effect between the source region and theobserver, but directly
reflects the generation of the source region widelydistributed in an altitude range from a few thousands km to 30,000 km,
alongthe Io flux tube.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Takahito Mikami Tomoya Shibayama Miguel Esteban Koichiro Ohira Jun Sasaki Takayuki Suzuki Hendra Achiari Teguh Widodo 《Natural Hazards》2014,71(1):851-870
On October 25, 2010, a large earthquake occurred off the coast of the Mentawai islands in Indonesia, generating a tsunami that caused damage to the coastal area of North Pagai, South Pagai, and Sipora islands. Field surveys were conducted soon after the event by several international survey teams, including the authors’. These surveys clarified the tsunami height distribution, the damage that took place, and residents’ awareness of tsunamis in the affected islands. Heights of over 5 m were recorded on the coastal area of the Indian Ocean side of North and South Pagai islands and the south part of Sipora island. In some villages, it was difficult to evacuate immediately after the earthquake because of the lack of routes to higher ground or the presence of rivers. Residents in some villages had taken part in tsunami drills or education; however, not all villages shared awareness of tsunami threats. In the present paper, based on the results of these field surveys, the vulnerability of these islands with regards to future tsunami threats was analyzed. Three important aspects of this tsunami disaster, namely the geographic disadvantage of the islands, the resilience of buildings and other infrastructure, and people’s awareness of tsunamis, are discussed in detail, and corresponding tsunami mitigation strategies are explained. 相似文献