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151.
Naoki Yoshie Yasuhiro Yamanaka Michio J. Kishi Hiroaki Saito 《Journal of Oceanography》2003,59(5):563-571
A one-dimensional ecosystem model has been used to investigate the processes relevant to the spring diatom bloom which play
important roles in the biogeochemical cycle in the western subarctic Pacific. The model represents the plankton dynamics and
the nutrient cycles in the spring diatom bloom; its results show the importance of dilution by deep mixing in winter. It is
supposed that the vertically integrated biomass of phytoplankton decreases in the winter due to the decrease of photosynthesis,
because the deep mixing transports phytoplankton to a layer with a low light level. However, the observed integrated diatom
biomass increases as the mixed layer deepens. This is because the decrease of concentration due to dilution by mixing causes
the diatom grazed pressure to be less significant than diatom photosynthesis. In other words, the effect of dilution on the
grazed rate is more significant than the effect on the photosynthesis rate because the grazed rate depends on the concentrations
of both diatom and grazer, whereas the photosynthesis rate depends only diatom concentration. The average specific diatom
grazed rate, defined as grazed rate divided by diatom biomass, decreases by 35% associated with the deepening, while the average
specific photosynthesis rate of diatom decreases by 11%. As a result, the average specific net diatom growth rate during the
deep mixing is about 70% of its maximum during the spring diatom bloom. The deep mixing significantly affects the amplitude
of the spring diatom bloom not only by the supply of nutrients but also by the dilution which drastically decreases the grazed
pressure.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
152.
Michio Kawamiya Michio J. Kishi Yasuhiro Yamanaka Nobuo Suginohara 《Journal of Oceanography》1995,51(6):635-664
A vertical one-dimensional ecosystem model was constructed and applied to Station Papa. The model has seven compartments (phytoplankton, nitrate, ammonium, zooplankton, particulate organic matters, dissolved organic matters, dissolved oxygen) and was coupled with a mixed layer model for calculating diffusion coefficient which appears in the governing equations. The mixed layer model was driven by SST, SSS data observed at Station Papa in 1980 and ECMWF wind data for 1980, and the ecosystem model was driven by fixing nitrate concentration in deep layer to an observational value. The phytoplankton maximum in March was reproduced by the model although the maximum in fall-winter could not be reproduced. The model also suggests the importance of studying nitrification. As a whole, the model could reproduce characteristic features at Station Papa such as the summer ammonium maximum at 50 m depth, the summer dissolved oxygen maximum at 70 m depth and the absence of remarkable phytoplankton bloom. 相似文献
153.
Masateru Ishiguro Takahiro Hiroi David J. Tholen Sho Sasaki Yuji Ueda Tokuhiro Nimura Masanao Abe Beth E. Clark Aya Yamamoto Fumi Yoshida Ryosuke Nakamura Naru Hirata Hideaki Miyamoto Yasuhiro Yokota Tatsuaki Hashimoto Takashi Kubota Akiko M. Nakamura Robert W. Gaskell Jun Saito 《Meteoritics & planetary science》2007,42(10):1791-1800
Abstract— We obtained color images of near‐Earth asteroid 25143 Itokawa by the Hayabusa multiband imaging camera to characterize the regional color properties. Images were obtained for the whole disk from the gate position (GP) and home position (HP) at a spatial resolution of 0.8–3.7 m/pixel. Whole‐disk spectra are adjusted to the telescopic data obtained by the University of Hawai'i's 88‐inch telescope using the Eight Color Asteroid Survey (ECAS) system. The disk‐resolved measurements show large variations in the three visible channels. We present a map of an index related to the degree of space weathering, which has been newly developed based on laboratory measurements. We find large variations in the degree of space weathering on Itokawa. Fresh materials are observed in regions of steep slopes and craters, whereas mature materials are ubiquitously distributed. This result suggests that pristine ordinary chondrite‐like materials have been exposed through weathered layers by excavation. By also examining close‐up images obtained during touchdown rehearsal, we find that most rocks in Itokawa's rough terrains are weathered. Instead of a regolith blanket, the surface of this small asteroid is covered with weathered rocks and gravels. 相似文献
154.
Yasuhiro Kuwayama Toshimitsu Sawai Kei Hirose Nagayoshi Sata Yasuo Ohishi 《Physics and Chemistry of Minerals》2009,36(9):511-518
The phase relations of Fe-6.4 wt% Si and Fe-9.9 wt% Si have been investigated up to 130 GPa and 2,600 K based on in situ synchrotron
X-ray diffraction measurements in a laser-heated diamond-anvil cell along with chemical analysis of the quenched samples using
a field-emission electron probe microanalyzer. We found that the maximum solubility of silicon in solid hcp-iron increases
with increasing pressure. Linear extrapolation of the phase boundary between hcp + B2 and hcp phases for Fe-9.9 wt% Si suggests
that the solid hcp-iron can include more than 9.9 wt% Si at the Earth’s inner-core conditions. If silicon is a major light
element in the outer core, a substantial amount of silicon may be incorporated into the inner core during inner-core solidification. 相似文献
155.
Yasuhiro Iba 《Journal of Asian Earth Sciences》2009,34(1):46-50
An Early Albian Arctic-type ammonite Arcthoplites was discovered from the Kamiji Formation of the Yezo Group in the Nakagawa area, northern Hokkaido, northern Japan. This is the first reliable record of a hoplitid ammonite from Japan and clearly indicates the distribution of an Arctic fauna in the middle latitudes of the North Pacific at that time. Synchronously with the appearance of this Arctic-type ammonite, the tropical Tethyan biota (Mesogean taxa) disappeared from Hokkaido and elsewhere in the Northwest Pacific. These biogeographic changes suggest the existence of a “cooling” episode in the Early Albian North Pacific. 相似文献
156.
Diel tuning of photosynthetic systems in ice algae at Saroma-ko Lagoon, Hokkaido, Japan 总被引:1,自引:0,他引:1
Shimpei Aikawa Hiroshi Hattori Yasushi Gomi Kentaro Watanabe Sakae Kudoh Yasuhiro Kashino Kazuhiko Satoh 《Polar Science》2009,3(1):57-72
Ice algae are the major primary producers in seasonally ice-covered oceans during the cold season. Diurnal change in solar radiation is inevitable for ice algae, even beneath seasonal sea ice in lower-latitude regions. In this work, we focused on the photosynthetic response of ice algae under diurnally changing irradiance in Saroma-ko Lagoon, Japan. Photosynthetic properties were assessed by pulse-amplitude modulation (PAM) fluorometry. The species composition remained almost the same throughout the investigation. The maximum electron transport rate (rETRmax), which indicates the capacity of photosynthetic electron transport, increased from sunrise until around noon and decreased toward sunset, with no sign of the afternoon depression commonly observed in other photosynthetic organisms. The level of non-photochemical quenching, which indicates photoprotection activity by dissipating excess light energy via thermal processes, changed with diurnal variations in irradiance. The pigment composition appeared constant, except for xanthophyll cycle pigments, which changed irrespective of irradiance. These results indicate that ice algae tune their photosynthetic system harmonically to achieve efficient photosynthesis under diurnally changing irradiance, while avoiding damage to photosystems. This regulation system may be essential for productive photosynthesis in ice algae. 相似文献
157.
泥石流的二维数学模型 总被引:5,自引:2,他引:3
泥石流是在重力作用下,由砂粒石块和水等组成的固液混合物,是一种发生于山区的复杂的地质灾害现象。泥石流主要是由暴雨诱发引起的,它沿着复杂的三维地形高速流动,具有流体流动的特性。为了模拟泥石流的运动规律,预测降雨诱发的泥石流的到达距离和泛滥范围,减少和避免泥石流引起的灾害,把泥石和雨水组成的固液混合物假定为遵循均匀、连续、不可压缩的、非定常的牛顿流体运动规律。基于质量守恒方程和Naiver-stokes方程,采用深度积分方法,推导出了一个模拟泥石流运动的二维数学模型。所有方程式可用有限差分法来求解。结合GIS,该模型可用于预测泥石流的流动距离和泛滥范围,以及泛滥范围内的危险房屋和路段,也可以用于泥石流灾害的风险性分析。 相似文献
158.
Ying-Ya Hsu Tung-Li Hsiung H. Paul Wang Yasuhiro Fukushima Yu-Ling Wei Juu-En Chang 《Marine pollution bulletin》2008,57(6-12):873
The nitrogen-doped TiO2 nanotube (N-TNT) thin films were synthesized using ZnO nanorods as the template and doped with urea at 623 K. Under ultraviolet (UV) and visible light irradiation, the efficiencies for photocatalytic degradation of methylene blue is as high as 30%. About 10% of toluene (representing aromatics in the spill oils) in sea water can be photocatalytically degraded under visible light radiation for 120 min. The aliphatic model compound (1-hexadecene) has, on the contrary, a less efficiency (8%) on the N-TNT photocatalyst. On the average, under visible light radiation, the effectnesses of the N-TNT for photocatalytic degradation of model compounds in the spill oils in sea water are 0.38 mg toluene/gN-TNT h and 0.25 mg 1-hexadecene/gN-TNT h. It is expected that spill oils in the harbors or seashores can be adsorbed and photocatalytically degraded on the N-TNT thin films that are coated onto levee at the sea water surface level. 相似文献
159.
Ho Choi Yasushi Sanada Hisatoshi Kashiwa Yasuhiro Watanabe Jafril Tanjung Huanjun Jiang 《地震工程与结构动力学》2016,45(6):999-1018
This study proposes a procedure for identifying spectral response curves for earthquake‐damaged areas in developing countries without seismic records. An earthquake‐damaged reinforced concrete building located in Padang, Indonesia was selected to illustrate the identification of the maximum seismic response during the 2009 West Sumatra earthquake. This paper summarizes the damage incurred by the building; the majority of the damage was observed in the third story in the span direction. The damage was quantitatively evaluated using the damage index R according to the Japanese guidelines for post‐earthquake damage evaluation. The damage index was also applied to the proposed spectral response identification method. The seismic performance of the building was evaluated by a nonlinear static analysis. The analytical results reproduced a drift concentration in the third story. The R‐index decreased with an increase in the story drift, which provided an estimation of the maximum response of the building during the earthquake. The estimation was verified via an earthquake response analysis of the building using ground acceleration data, which were simulated based on acceleration records of engineering bedrock that considered site amplification. The maximum response estimated by the R‐index was consistent with the maximum response obtained from the earthquake response analysis. Therefore, the proposed method enables the construction of spectral response curves by integrating the identification results for the maximum responses in a number of earthquake‐damaged buildings despite a lack of seismic records. Copyright © 2016 The Authors. Earthquake Engineering & Structural Dynamics published by John Wiley & Sons Ltd. 相似文献
160.
Thomas Hobiger Seiichi Shimada Shingo Shimizu Ryuichi Ichikawa Yasuhiro Koyama Tetsuro Kondo 《Journal of Atmospheric and Solar》2010,72(2-3):262-270
Space geodetic applications require to model troposphere delays as good as possible in order to achieve highly accurate positioning estimates. However, these models are not capable to consider complex refractivity fields which are likely to occur during extreme weather situations like typhoons, storms, heavy rain-fall, etc. Thus it has been investigated how positioning results can be improved if information from numerical weather models is taken into account. It will be demonstrated that positioning errors can be significantly reduced by the usage of ray-traced slant delays. Therefore, meso-scale and fine-mesh numerical weather models are utilized and their impact on the positioning results will be measured. The approach has been evaluated during a typhoon passage using global positioning service (GPS) observations of 72 receivers located around Tokyo, proving the usefulness of ray-traced slant delays for positioning applications. Thereby, it is possible reduce virtual station movements as well as improve station height repeatabilities by up to 30% w.r.t. standard processing techniques. Additionally the advantages and caveats of numerical weather models will be discussed and it will be shown how fine-mesh numerical weather models, which are restricted in their spatial extent, have to be handled in order to provide useful corrections. 相似文献