Estimation of wind drift current in the Soya Strait     

Wei Zhang  Naoto Ebuchi  Yasushi Fukamachi  Yutaka Yoshikawa 《Journal of Oceanography》2016,72(2):299-311

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Observation and estimation of daily actual evapotranspiration and evaporation on a glacierized watershed at the headwater of the Urumqi River,Tianshan, China     

Zhang Wanchang  Zhang Yinsheng  Katsuro Ogawa  Yasushi Yamaguchi 《水文研究》1999,13(11):1589-1601

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A monthly stream flow model for estimating the potential changes of river runoff on the projected global warming     

Zhang Wanchang  Katsuro Ogawa  Ye Besheng  Yasushi Yamaguchi 《水文研究》2000,14(10):1851-1868

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A quadratic element method for evaluating groundwater flow by the inversion of surface tilt with application to the Tono Area, Japan     

Koji Matsuki  Katsuya Nakatani  Takashi Arai  Kazuo Ohmura  Ryuji Takeuchi  Yasushi Arai  Shinji Takeuchi 《Journal of Hydrology》2008,360(1-4):217-229

By modifying a previous method with constant elements, we developed a quadratic element method for more accurately estimating groundwater flow by the inversion of tilt data. In this method: (1) a region of groundwater flow is divided into quadratic elements in which the change in groundwater volume per unit volume of rock (Δv) and the Skempton coefficient (B) vary in a quadratic manner with the coordinates, (2) the values of Δv are set to zero at the boundaries of the region of groundwater flow and (3) the sum of the squared second derivatives of Δv is adopted as a constraining condition that is weighted and added to the sum of the squared errors in tilt. First, analyses were performed for a flow model to determine the accuracy of this method for estimating groundwater flow and also to clarify the effect of the assumed size of a region of groundwater flow. These analyses showed that the quadratic element method proposed in this study gives a much better estimation of Δv than the constant element method and that a large region of groundwater flow should be assumed, rather than a small region, since the values of Δv at points outside of the actual region of groundwater flow are estimated to be nearly zero when a large region is assumed while these values are greatly overestimated when an excessively small region is assumed. Finally, the quadratic element method was applied to the site of the Mizunami Underground Research Laboratory in the Tono area, Japan. Inverse analyses were performed for tilt data measured by four tiltmeters with a resolution of 10⁻⁹ radians during the excavation of two shafts under the assumption that the rock mass is an isotropic and homogeneous half- space. The results showed that the method proposed in this study reproduced the tilt data very accurately. Thus, the distribution of Δv was estimated without sacrificing the reproducibility of the tilt data. The contour maps of B(1 + ν)Δv (ν: Poisson’s ratio) showed that the heterogeneous flow of groundwater occurred at the site and that groundwater volume decreased mainly in the area surrounded by two faults. The latter result is consistent with the finding obtained by previous investigations that these faults have low permeability in the direction perpendicular to the strike and may act as a flow barrier.  相似文献   

Nickel–bearing Djerfisherite in Gehlenite-Spurrite Skarn at Kushiro, Hiroshima Prefecture, Japan     

Yasushi TAKECHI  Isao KUSACHI  Yoshihiro NAKAMUTA  Katsuo KASE 《Resource Geology》2000,50(3):179-184

Abstract: Djerfisherite occurs intimately intergrown with troilite and pentlandite in gehlenite-spurrite skarn at Kushiro, mainly as inclusions in gehlenite and andradite grains. The mode of occurrence indicates that the djerfisherite formed in the culminated stage of the contact metamorphic-metasomatic process. The chemical compositions of the mineral are approximately represented by a formula of K₆Na(Fe, Ni, Cu)₂₄S₂₆Cl with Ni up to 4. 85. It is likely that high temperature condition corresponding to the formation of gehlenite-spurrite skarn as well as low f_O2 and f_S2 conditions are responsible for the formation of djerfisherite in the potassium-rich chemical environments.  相似文献   

Experimental investigation on cohesionless sandy bank failure resulting from water level rising   总被引：1，自引：1，他引：0  

Ryosuke Arai  Kazuyuki Ota  Takahiro Sato  Yasushi Toyoda 《国际泥沙研究》2018,33(1):47-56

In the last decade, sediment replenishment forming cohesionless sandy banks below dams has become an increasingly common practice in Japan to compensate for sediment deficits downstream. The erosion process of the placed cohesionless sediment is a combination of lateral toe-erosion and the following mass failure. To explore cohesionless bank failure mechanisms, a series of experiments was done in a soil tank using a compacted sandy soil mass exposed to an increasing water level. Two types of uniform sand(D_(50) = 0.40 mm and 0.17 mm) and two bank heights(50 cm and 25 cm) were used under the condition of a constant bank slope of 75°. The three dimensional(3D) geometry of the bank after failure was measured using a handheld 3D scanner. The motion of bank failure was captured using the particle image velocimetry(PIV) technique, and the matric suction was measured by tensiometers. The compacted sandy soil was eroded by loss of matric suction accompanying the rise in water level which subsequently caused rotational slide and cantilever toppling failure due to destabilization of the bank. The effect of erosion protection resulting from the slumped blocks after these failures is discussed in the light of different failure mechanisms. Tensile strength is analyzed by inverse calculation of cantilever toppling failure events. The tensile strength had non-linear relation with degree of saturation and showed a peak.The findings of the study show that it is important to incorporate the non-linear relation of tensile strength into stability analysis of cantilever toppling failure and prediction of tension crack depth within unsaturated cohesionless banks.  相似文献   

Softening effects of RC nonstructural flat walls on ductile concrete buildings          下载免费PDF全文

Yasushi Sanada  Rokhyun Yoon  Takumi Akahori  Yuto Ojio  Ho Choi  Yousok Kim 《地震工程与结构动力学》2017,46(10):1645-1665

Nonstructural reinforced concrete flat walls architecturally designed as exterior/partition walls in concrete buildings were severely damaged by the 2011 earthquake off the Pacific coast of Tohoku. This damage was observed in the monolithic nonstructural flat walls of relatively old ductile concrete buildings. Although these flat walls might affect the overall seismic performance and behavior of a building, the nonstructural wall effects have not been clarified because of the complex interactions among the structural components. To understand these effects, this paper conducts an experimental and numerical investigation of the nonstructural wall effects, focusing on a typical residential building damaged by the 2011 earthquake. A single‐story, one‐bay moment‐resisting frame model of the building with a nonstructural flat wall was tested to clarify the fundamental behavior. The results reveal that the wall significantly contributed to the seismic performance of the overall frame until it failed in shear, subsequently losing structural effectiveness. Such experimental wall behavior could be simulated by the isoparametric element model. Moreover, the structural effects of the nonstructural flat walls on the global seismic performance and behavior of the investigated building were discussed through earthquake response analyses using ground motions recorded near the building site and pushover analyses. Consequently, the building damage could be simulated in an analytical case considering the nonstructural flat walls, showing larger inter‐story drifts in the lower stories due to softening of the walls. The analytical results also indicated that the softening of the nonstructural flat walls decreased the building ductility, as defined by ultimate inter‐story drifts. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Wind- and density-driven circulation in a bay on the Sanriku ria coast,Japan: study of Shizugawa Bay facing the Pacific Ocean     

Daisuke Takahashi  Hikaru Endo  Yuki Minegishi  Yasushi Gomi  Kenji Kaneko 《Journal of Oceanography》2018,74(1):81-100

Flow fields in Shizugawa Bay on the Sanriku ria coast, which faces the Pacific Ocean, were investigated using hydrographic observations for the purpose of understanding oceanographic conditions and the process of water exchanges in the bay after the 2011 earthquake off the Pacific coast of Tohoku. In spring to summer, density-driven surface outflow is part of estuarine circulation and is induced by a pressure gradient force under larger longitudinal gradients in density along with lower salinity water in the innermost part of the bay, regardless of wind forcing. In winter to summer, another density-driven current with a thermal structure is induced by a pressure gradient force under the smaller longitudinal density gradients in calm wind conditions. Particularly in winter, Tsugaru Warm Current water can be transported in the surface layer inside the bay. Wind-driven bay-scale circulation with downwind and upwind currents in the surface and deeper layers, respectively, is induced by strong longitudinal wind forcing under the smaller longitudinal density gradients, irrespective of season. Particularly in fall to spring, this circulation can cause the intrusions of oceanic water associated with Oyashio water and Tsugaru Warm Current water in the deeper layer. These results suggest that wind- and density-driven currents can produce the active exchange of water from inside and outside the bay throughout the year.  相似文献   

Complex vertical migration of larvae of the ghost shrimp, Nihonotrypaea harmandi, in inner shelf waters of western Kyushu,Japan     

Akio Tamaki  Sumit Mandal  Yoshihiro Agata  Ikumi Aoki  Toshikazu Suzuki  Hisao Kanehara  Takashi Aoshima  Yasushi Fukuda  Hideshi Tsukamoto  Tetsuo Yanagi 《Estuarine, Coastal and Shelf Science》2010

The position of meroplanktonic larvae in the water column with depth-dependent current velocities determines horizontal transport trajectories. For those larvae occurring in inner shelf waters, little is known about how combined diel and tidally-synchronized vertical migration patterns shift ontogenetically. The vertical migration of larvae of Nihonotrypaea harmandi (Decapoda: Thalassinidea: Callianassidae) was investigated in mesotidal, inner shelf waters of western Kyushu, Japan in July–August 2006. The larval sampling at seven depth layers down to 60 m was conducted every 3 h for 36 h in a 68.5-m deep area 10 km off a major coastal adult habitat. Within a 61–65-m deep area 5–7.5 km off the adult habitat, water temperature, salinity, chlorophyll a concentration, and photon flux density were measured, and water currents there were characterized from harmonic analysis of current meter data collected in 2008. The water column was stratified, with pycnocline, chlorophyll a concentration maximum, and 2% of photon flux density at 2 m, recorded at around 22–24 m. The stratified residual currents were detected in their north component, directed offshore and onshore in the upper and lower mixed layers, respectively. More than 87% of larvae occurred between 20 m and 60 m, producing a net onshore transport of approximately 1.3 km d⁻¹. At the sunset flooding tide, all zoeal-stage larvae ascended, which could further promote retention (1.4-km potential onshore transport in 3 h). The actual onshore transport of larvae was detected by observing their occurrence pattern in a shallow embayment area with the adult habitat for 24 h in October 1994. However, ontogenetic differences in the vertical migration pattern in inner shelf waters were also apparent, with the maximum mean positions of zoeae deepening with increasing stages. Zoeae I and II performed a reverse diel migration, with their minimum and maximum depths being reached around noon and midnight, respectively. Zoeae IV and V descended continuously. Zoeae III had behaviors that were intermediate to those of the earlier- and later-stage zoeae. Postlarvae underwent a normal diel migration (nocturnal ascent) regardless of tides, with the deepest position (below 60 m and/or on the bottom) during the day. These findings give a new perspective towards how complex vertical migration patterns in meroplanktonic larvae enable their retention in inner shelf waters before the final entry of postlarvae into their natal populations.  相似文献   

Pulsation at the tip of the first giant branch?     

Yoshifusa Ita  Toshihiko Tanabé  Noriyuki Matsunaga  Yasushi Nakajima  Chie Nagashima  Takahiro Nagayama  Daisuke Kato  Mikio Kurita  Tetsuya Nagata  Shuji Sato  Motohide Tamura  Hidehiko Nakaya  Yoshikazu Nakada 《Monthly notices of the Royal Astronomical Society》2002,337(3):L31-L34

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