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141.
Hitoshi Oda Osamu Nishizawa Kin'ichiro Kusunose Takayuki Hirata 《Pure and Applied Geophysics》1990,133(1):73-85
Velocity as well as attenuation factorQ
–1 ofP-wave in a dry granitic rock sample under uniaxial compressions were measured in the range of frequency between 100 kHz and 710 kHz by using the pulse transmission technique. Above the stress of 0.5
f
, where
f
is the fracture stress, theP-wave velocity decreases with increasing axial stress, whereasQ
–1 increases. Particularly, the change ofQ
–1 is greater for high frequency than for low frequency. At a given stress level, the higher the frequency, the higher theP-wave velocity and the largerQ
–1. This result means that the velocity decrease with increasing stress is smaller for higher frequency. Because of this frequency-dependence of velocity decrease, theP-wave in the rock under dilatant state shows dispersion. The body wave dispersion is more remarkable at higher stress, and is not found in a homogeneous material with no cracks. Thus the disperison is attributed to the generation of cracks. When the frequency-dependence ofQ
–1 is approximated asf
n
in the present frequency range, the exponentn takes a value from 0.63 to 0.77. 相似文献
142.
Spring blooms of phytoplankton composed of centric diatoms developed in late February, March, and April in Otsuchi Bay on Sanriku ria coast, Japan. During this period, associated with prolonged seasonal west wind (>1 day), intense exchange of waters occurred between inside and outside the bay: outflow of nearsurface brackish water over inflow of oceanic water at depth. This circulation interrupted formation of the blooms, and transported phytoplankton populations seaward. By such water movements, a significant amount of nutrients in the bay was carried out, otherwise replenished into the bay, depending on water masses located outside the bay. Owing to irregular features of wind events, a bloom lasted from several days to a week. From February to April, supply of nutrients seemed to be replete except for the latter half of the bloom period, and estimates of the critical depth exceeded the depth of the bottom consistently. Thus, net growth of phytoplankton was expected throughout the observation period, and potentially blooms could be formed. However, the blooms were only formed under calm weather. We hypothesize that the exchange of waters dilutes populations in the bay, and that formation of the bloom, that is, accumulation of biomass depends on a balance between the growth of phytoplankton and the dilution of bay water. 相似文献
143.
John Kuo Ziyusei Kanamoto Hitoshi Iizumi Keiko Aioi & Hiroshi Mukai 《Marine Ecology》2006,27(4):290-298
The Nansei Islands in the southern Japanese Archipelago have 15 taxa of seagrasses from seven genera within three families. Seagrasses in this region grow on coral sands or coral debris in shallow reefs and on sandy or muddy substrata in the shallow areas of bays and inlets. Certain Halophila species grow in deep water off some islands. Enhalus acoroides only reaches to Ishigaki I. with winter sea water temperature (WST) at 23 °C, while Okinawa I. (WST at 21.6 °C) is the northern biogeographic limit for Halophila decipiens, H. okinawensis, H. major and H. gaudichaudii. Amami‐oshima I. (WST at 20.7 °C) is the northern border for Thalassia hemprichii, H. minor, H. ovalis, Cymodocea serrulata, Cymodocea rotundata, Syringodium isoetifolium, Halodule uninervis and Halodule pinifolia. Halophila mikii the sole seagrass collected from Yakushima I. (WST at 19.3 °C), is of volcanic origin. The distribution of tropical seagrasses in the Nansei Islands is clearly associated with the warm Kuroshio Current, WST and habitat availability. Zostera japonica is the only temperate species occurring in the region. Meadows of Z. japonica, H. ovalis and Halodule pinifolia have disappeared from certain localities in the Archipelago, due probably to human activities and natural siltation. 相似文献
144.
A critical and comprehensive literature survey of sand transport by wind on a dry sand surface is made from the perspective of engineering use. Principal findings are: (1) Most predictive expressions for the sand transport rate show a cubic dependence on the shear velocity, or obey a similar power law. (2) Some difference is found in the value of the multiplicative empirical coefficient in the various formulas, and much of the scatter may be ascribed to relative trap efficiency. (3) Verification of predictive formulas has mainly rested on laboratory measurements, and reliable but limited field verification has not been made until recently. (4) The laboratory and field data indicate that both the Bagnold and the Kawamura formulas are applicable to a well-sorted sand and can be used for estimation of wind-blown sand transport on dry natural beaches. Modifications have been made for a widely distributed sand and for fluctuating wind velocity. 相似文献
145.
Acta Geotechnica - Soil improvement techniques have been developed experimentally and empirically from various geotechnical standpoints based on physical, chemical, and biological findings. The... 相似文献
146.
基于地震的全球面波层析成像技术的发展对于探测地球深部动力学状态起着至关紧要的作用。人们很自然地认为只有大地震才会产生类似探测所需要的穿入地球深部的长周期地震波。然而,由海洋和/或大气扰动随机产生的地震"哼鸣"的发现,即地球背景自由振荡,提供了一种可供选择的方法。我们在此呈现的是利用地震"哼鸣"而非天然地震进行上地幔地震层析成像的结果。在100~400s周期,Rayleigh波的相速度异常可通过下述方式测得,即对观测得到的54个遍布全球的地震台站中每两个台站间的互相关函数进行模拟,然后对这些异常进行反演,以获取上地幔三维S波速度结构。此方法为探测具有大气和/或海洋的类地行星——特别是火星的三维内部结构提供了一种新的途径。 相似文献
147.
Hitoshi Tanaka Kosuke Kayane Mohammad Bagus Adityawan Min Roh Mohammad Farid 《Ocean Dynamics》2014,64(9):1319-1332
The relations of river morphology and tsunami propagation in rivers were studied at several rivers in the Tohoku region during The Great Chilean Tsunami of 2010 and The Great East Japan Tsunami of 2011. It was found that river mouth morphological features play an important role in the intrusion of low magnitude tsunamis in which the geological and geographical conditions are an important factor. Nevertheless, the effects of these features were not found in the case of an extreme tsunami wave. As the wave enters the river, the propagation depends on other factors. It was found that the intrusion distance correlates well to the riverbed slope. The measurements of water level and riverbed slope were analyzed to propose an empirical method for estimating the damping coefficient for the tsunami propagation in rivers based on the tsunami of 2011. The proposed empirical method was used to approximate the length of the tsunami intrusion into a river by assuming that the furthest distance is given for the ratio of local tsunami wave height to the tsunami wave height at the river entrance of 0.05 (5 %). The estimated intrusion length from the proposed method in this study shows a good comparison with measurement data. 相似文献
148.
Water mass variability in the western North Pacific detected in a 15-year eddy resolving ocean reanalysis 总被引:2,自引:0,他引:2
149.
近岸波生流数值计算的一种新方法 总被引:4,自引:5,他引:4
运用Hardy-Cross法的基本原理建立了一种波生流计算的数值模型.本方法在维持计算稳定性方面表现出色,解决了以往的计算方法所存在的计算不稳定的根本缺陷,但是运用这一方法进行实际问题计算时还明显存在计算收敛缓慢的现象,对此,在探讨计算收敛原因的基础上,提出了同心矩形回路补正、粗网格计算初始值等对策.运用这些对策成功地提高了计算的效率和精度.最后通过计算例验证表明,运用本方法既能有效地维持计算的稳定,又能有效地解决局部缓和法所固有的计算效率低的问题,从而为研究和预测海岸工程对地形及环境变化影响问题提供了合理、实用的方法. 相似文献
150.
Food sources of the pearl oyster in coastal ecosystems of Japan: Evidence from diet and stable isotope analysis 总被引:1,自引:0,他引:1
Kayoko Fukumori Misa Oi Hideyuki Doi Noboru Okuda Hitomi Yamaguchi Michinobu Kuwae Hitoshi Miyasaka Kenji Yoshino Yoshitsugu Koizumi Koji Omori Hidetaka Takeoka 《Estuarine, Coastal and Shelf Science》2008
We estimated the composition of two food sources for the cultured pearl oyster Pinctada fucata martensii using stable isotopes and stomach content analysis in the coastal areas of the Uwa Sea, Japan. The δ13C values of oysters (−17.5 to −16.8‰) were intermediate between that of particulate organic matter (POM, −20.2 to −19.1‰) and attached microalgae on pearl cages (−13.0‰). An isotope mixing model suggested that oysters were consuming 78% POM (mainly phytoplankton) and 22% attached microalgae. The attached microalgal composition of the stomach content showed a strong resemblance to the composition of that estimated through the isotope mixing model, suggesting preferential utilization of specific components is unlikely in this species. These results indicate that P. fucata martensii feed on a mixture of phytoplankton and attached microalgae, and that the attached microalgae on pearl cages can serve as an important additional food source. 相似文献