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排序方式: 共有147条查询结果,搜索用时 31 毫秒
11.
In this study the inelastic behavior of steel arch bridges subjected to strong ground motions from major earthquakes is investigated by dynamic analyses of a typical steel arch bridge using a three‐dimensional (3D) analytical model, since checking seismic performance against severe earthquakes is not usually performed when designing such kinds of bridge. The bridge considered is an upper‐deck steel arch bridge having a reinforced concrete (RC) deck, steel I‐section girders and steel arch ribs. The input ground motions are accelerograms which are modified ground motions based on the records from the 1995 Hyogoken‐Nanbu earthquake. Both the longitudinal and transverse dynamic characteristics of the bridge are studied by investigation of time‐history responses of the main parameters. It is found that seismic responses are small when subjected to the longitudinal excitation, but significantly large under the transverse ground motion due to plasticization formed in some segments such as arch rib ends and side pier bases where axial force levels are very high. Finally, a seismic performance evaluation method based on the response strain index is proposed for such steel bridge structures. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
12.
Chelo PASCUA Tsutomu SATO Glenn GOLLA 《《地质学报》英文版》2006,80(2):230-235
Arsenic is usually associated with sulphide minerals formed in the geothermal environment. However, sulphide minerals are prone to dissolution after contact with meteoric water under surface oxidizing conditions. Secondary precipitates that form from the dissolution of the primary sulfides exert a greater influence on arsenic mobility in the geothermal environment. Fe-hydroxides have very good affinity with dissolved arsenate and are stable under most surface oxidizing conditions. Both amorphous silica directly precipitated from geothermal fluids and possibly a kaolinite alteration can host a small significant amount of arsenic. These silicates are also more stable under a wide range of pH and redox conditions. 相似文献
13.
Biomass distribution and trophodynamics in the oceanic ecosystem in the Oyashio region are presented and analyzed, combining
the seasonal data for plankton and micronekton collected at Site H since 1996 with data for nekton and other animals at higher
trophic levels from various sources. The total biomass of biological components including bacteria, phytoplankton, microzooplankton,
mesozooplankton, micronekton, fishes/squids and marine birds/mammals was 23 g C m−2, among which the most dominant component was mesozooplankton (34% of the total), followed by phytoplankton (28%), bacteria
(15%) and microzooplankton (protozoans) (14%). The remainder (9%) was largely composed of micronekton and fish/squid. Marine
mammals/birds are only a small fraction (0.14%) of the total biomass. Large/medium grazing copepods (Neocalaus spp., Eucalanus bungii and Metridia spp.) accounted for 77% of the mesozooplankton biomass. Based on information about diet composition, predators were assigned
broadly into mean trophic level 3–4, and carbon flow through the grazing food chain was established based on the estimated
annual production/food consumption balance of each trophic level. From the food chain scheme, ecological efficiencies as high
as 24% were calculated for the primary/secondary production and 21% for the secondary/tertiary production. Biomass and production
of bacteria were estimated as 1/10 of the respective values for phytoplankton at Site H, but the role of the microbial food
chain remains unresolved in the present analysis. As keystone species in the oceanic Oyashio region, Neocalanus spp. are suggested as a vital link between primary production and production of pelagic fishes, mammals and birds. 相似文献
14.
Attenuation of compressional waves in peridotite measured as a function of temperature at 200 MPa 总被引:3,自引:0,他引:3
Hiroki Sato I. Selwyn Sacks Tsutomu Murase Gregory Muncill Hiroyuki Fukuyama 《Pure and Applied Geophysics》1988,128(1-2):433-447
A technique has been developed to determine attenuation in rocks at high temperature using a gas-media, high-pressure apparatus. A pulse transmission technique and a spectral ratio method are used to study compressional seismic properties of rocks. Seismic waves are transmitted to and from the sample through buffer rods of mullite. The effect of seismic wave reflections within the sample assembly are cancelled out by taking ratios of the spectra measured at different temperatures. In order to obtain good signal-to-noise ratio for resolving the attenuation at high pressure and temperature, special care is taken in the sample assembly and the ultrasonic coupling between the sample, buffer rods and transducers. A very tight connection of the sample-buffer rod-transducer is essential for obtaining high frequency signals (>300 kHz) at high temperature. A small mass is attached to each outside end of the transducer to drive low frequency signals (<250 kHz) into the sample. Before attenuation measurements, the sample and the buffer rods are tightly compacted in a platinum tube at high pressure and room temperature to ensure pressure seal of the sample assembly. The frequency range of measurement covers 50 to 450 kHz for the sample. Attenuation is very small in the buffer rod compared to the sample for the entire temperature range of the study. Because of the small attenuation, a wide frequency band of 50 kHz to 3.2 MHz can be covered for investigating the attenuation in the buffer rod. The technique has been used to measure attenuation at high confining pressure, and temperatures including sub- and hyper-solidus of upper mantle rocks. Therefore, effects of partial melting on attenuation can be studied.The method is applied to the attenuation measurement in a peridotite as a function of temperature to 1225°C at 200 MPa confining pressure. At high temperature, signal amplitude decays more rapidly at high frequency than at low frequency, from which attenuation (andQ) can be determined using a spectral ratio method. No frequency dependence ofQ is resolved for both the sample and the buffer rod over the entire temperature and frequency ranges of the measurement. The results show thatQ decreases rapidly with increasing temperature even in the temperature range below the solidus of peridotites. Such temperature sensitivity ofQ is probably more useful to probe thermal structure in the upper mantle than that of conductivity at temperatures below the solidus. The results in this study are compared with available seismic velocity, electrical conductivity and solidus data for peridotites, suggesting that there is no discontinuous change in both mechanical and electrical properties of peridotites at the solidus temperature. Even at hypersolidus temperatures, it appears that velocity drops and conductivity increases continuously (not abruptly) with increasing melt fraction. This implies that mechanical and electrical properties of the upper mantle will gradually change at the boundary where the geotherm crosses the solidus. 相似文献
15.
The vertical section of microearthquakes, determined accurately by using the Hokkaido University network, shows two dipping zones (the double seismic zone) 25–30 km apart in the depth range of 80–150 km beneath the middle of Hokkaido in the southwestern side of the Kurile arc. Hypocentral distribution of large earthquakes (mb > 4) based on the ISC (International Seismological Centre) bulletin also shows the double seismic zone beneath the same region. The hypocentral distribution indicates that the frequency of events occurring in the lower zone is four times greater than that in the upper zone. The difference in seismic activity between the two zones beneath Hokkaido is in contrast with the region beneath northeastern Honshu in the northeastern Japan arc.Composite focal mechanisms of microearthquakes and individual mechanisms of large events mainly characterize the down-dip extension for the lower zone as is observed beneath northeastern Honshu. For the upper zone, however, the stress field is rather complex and not necessarily similar to that beneath northeastern Honshu. This may be considered to indicate the influence of slab contortion or transformation in the Hokkaido corner between the Kurile and the northeastern Japan arcs. 相似文献
16.
Hideko Takayanagi Yasufumi Iryu Tsutomu Yamada Motoyoshi Oda Kazuyuki Yamamoto Tokiyuki Sato Shun Chiyonobu Akira Nishimura Tsutomu Nakazawa Satoshi Shiokawa 《Island Arc》2007,16(3):394-419
Abstract The lithology of shallow-water carbonates collected from 19 sites on 16 seamounts in six areas of the northwestern Pacific Ocean using the Deep-sea Boring Machine System are described. The areas include the Amami Plateau, Daito Ridge, Oki-Daito Ridge, Urdaneta Plateau, Kyushu-Palau Ridge and Ogasawara Plateau. Chronological constraint is provided by calcareous nannofossil biostratigraphy, planktonic foraminiferal biostratigraphy, larger foraminiferal biostratigraphy and strontium (Sr) isotope stratigraphy. Large amounts of shallow-water carbonates accumulated on the seamounts during the Oligocene, a relatively cool period, whereas limited carbonate deposits formed during the Early Miocene, a relatively warm period. This might indicate that deposition of shallow-water carbonates on seamounts in the northwestern Pacific Ocean was not necessarily controlled by climatic conditions, but was related to volcanism and tectonics that served as foundations for reef/carbonate-platform formation. Remarkable differences in biotic composition exist between Cretaceous and Cenozoic shallow-water carbonates. Late Cretaceous shallow-water carbonates are distinguished by the occurrence of rudists, solenoporacean algae and microencrusters. Middle Eocene to Early Oligocene shallow-water carbonates are dominated by Halimeda or nummulitid and discocyclinid larger foraminifers. Scleractinian corals became common from the Oligocene onward. Nongeniculate coralline algae and larger foraminifers were common to abundant throughout the Eocene to the Pleistocene. The replacement of major carbonate producers in the shallow-water carbonate factory during post-Cretaceous time is in accordance with previous studies and is considered to reflect a shift in seawater chemistry. 相似文献
17.
Logic-tree Approach for Probabilistic Tsunami Hazard Analysis and its Applications to the Japanese Coasts 总被引:2,自引:0,他引:2
Tadashi Annaka Kenji Satake Tsutomu Sakakiyama Ken Yanagisawa Nobuo Shuto 《Pure and Applied Geophysics》2007,164(2-3):577-592
For Probabilistic Tsunami Hazard Analysis (PTHA), we propose a logic-tree approach to construct tsunami hazard curves (relationship
between tsunami height and probability of exceedance) and present some examples for Japan for the purpose of quantitative
assessments of tsunami risk for important coastal facilities. A hazard curve is obtained by integration over the aleatory
uncertainties, and numerous hazard curves are obtained for different branches of logic-tree representing epistemic uncertainty.
A PTHA consists of a tsunami source model and coastal tsunami height estimation. We developed the logic-tree models for local
tsunami sources around Japan and for distant tsunami sources along the South American subduction zones. Logic-trees were made
for tsunami source zones, size and frequency of tsunamigenic earthquakes, fault models, and standard error of estimated tsunami
heights. Numerical simulation rather than empirical relation was used for estimating the median tsunami heights. Weights of
discrete branches that represent alternative hypotheses and interpretations were determined by the questionnaire survey for
tsunami and earthquake experts, whereas those representing the error of estimated value were determined on the basis of historical
data. Examples of tsunami hazard curves were illustrated for the coastal sites, and uncertainty in the tsunami hazard was
displayed by 5-, 16-, 50-, 84- and 95-percentile and mean hazard curves. 相似文献
18.
Tsutomu Takashima 《Astrophysics and Space Science》1973,23(1):201-204
Suppose that the atmosphere consists of homogeneous sublayers whose scattering and transmission matrices are known, then it is shown in this paper how to determine the intensity and polarization parameters of internal radiation field by the matrix method. 相似文献
19.
Masao Ohno Tsutomu Sato Kenji Notsu Hiroshi Wakita Kunio Ozawa 《Pure and Applied Geophysics》2006,163(4):647-655
Anomalous water level changes were observed at two wells associated with seismic swarm activity off Izu Peninsula on March,
1997. These are coseismic water level drops followed by gradual postseismic water level rise at the time of large earthquakes
during the swarm activity. The post-seismic water level rises, which can be fitted by an exponential function with a time
constant of about six hours, are explained in terms of the horizontal pressure diffusion due to the pressure gradient in the
aquifer induced by the coseismic static strain. 相似文献
20.
多环芳香烃由于诱发突变和致癌的性质威胁着人类的健康,近年来,其降解问题得到了广泛的关注。笔者研究了在没有光照的条件下,改变相对湿度(5%至30%之间),苯并芘(一种典型的多环芳烃物质)在石英,矾土,蒙脱石,高岭石,腐殖酸和吸附了腐殖酸的石英上的稳定性,继而可以检测出矿物表面催化多环芳烃降解的效果。苯并芘的稳定性主要是由吸附剂的物化性质决定的。石英表现出很好的催化效果,即便其表面被腐殖酸所包覆。在整个实验过程中(3天)吸附在蒙脱石和腐殖酸表面的苯并芘依然很稳定。实验装置中的湿度影响在某些特定的矿物中的苯并芘的稳定性。特… 相似文献