Diatom Assemblage and Productivity Changes during the Last 340,000 Years in the Subarctic Pacific     

Kota Katsuki  Kozo Takahashi  Makoto Okada 《Journal of Oceanography》2003,59(5):695-707

Diatoms represent the major part of the microfossils preserved in the subarctic Pacific sediments. During the warm climate intervals the diatom accumulation rate (DAR) tended to increase, whereas it tended to decrease during the cold intervals. Principal component (PC) analysis of the fossil diatom assemblages in Piston Core KH99-3 ES samples from the subarctic Pacific was carried out to investigate the paleoceanographic conditions of the area. PC1 (59.9% of the total variance) was represented by Neodenticula seminae, a characteristic species representing the high nutrient concentrations, which dominated during the interglacial periods. The DAR and PC changes can be attributed to a global origin that is influenced by the nutrient change due to intermediate water change and to a local one that is explained by the change of upwelling region. The analysis of PC2 (17.1% of the total variance) indicates the change of water mass in the western subarctic Pacific. During Marine Isotope Stages (MIS) 2 and 3, the western subarctic Pacific region was significantly influenced by the sea-ice, which may have been derived from the coastal region or a proximal marginal sea. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Chemical and mineralogical compositions of two grains recovered from asteroid Itokawa          下载免费PDF全文

M. Ebihara  N. Shirai  S. Sekimoto  T. Nakamura  A. Tsuchiyama  J. Matsuno  T. Matsumoto  M. Tanaka  M. Abe  A. Fujimura  Y. Ishibashi  Y. Karouji  T. Mukai  T. Okada  M. Uesugi  T. Yada 《Meteoritics & planetary science》2015,50(2):243-254

Two silicate grains (RB‐QD04‐0049 and RA‐QD02‐0064, whose estimated masses are 0.050 μg and 0.048 μg, respectively) recovered from the asteroid Itokawa by the Hayabusa spacecraft were studied for their mineralogical characteristics by synchrotron X‐ray diffraction and synchrotron X‐ray microtomography and further analyzed for their bulk chemical compositions by instrumental neutron activation analysis (INAA). According to X‐ray tomography, RB‐QD004‐0049 is composed of olivine, high‐Ca pyroxene, plagioclase, Ca‐phosphate, and troilite, whereas RA‐QD002‐0064 entirely consists of olivine. INAA data are consistent with these mineral compositions except for rare earth elements (REEs). Although the grain RB‐QD004‐0049 contains measurable REEs, which seems to be consistent with the presence of Ca‐phosphate, their abundances are anomalously high. Very low abundance of Co implies less than 0.1 mass% of metals in these two grains by calculation, which is in contrast to the result for the previously analyzed grain RA‐QD02‐0049 (Ebihara et al., 2011). FeO/Sc ratios of the grains fall within the range of those for ordinary chondrite olivines, implying that these grains are extraterrestrial in origin. FeO/MnO ratios also confirm this conclusion and further suggest that the Hayabusa grains analyzed in this study are similar to material found in LL chondrites rather than CK chondrites although olivines from LL and CK chondrites have similar Fa# (molar% of Fe relative to [Fe+Mg] in olivine) (~30) to those of the Hayabusa grains including the two grains analyzed in this study.  相似文献   

40Ar/39Ar age of material returned from asteroid 25143 Itokawa          下载免费PDF全文

Jisun Park  Brent D. Turrin  Gregory F. Herzog  Fara N. Lindsay  Jeremy S. Delaney  Carl C. Swisher III  Masayuki Uesugi  Yuzuru Karouji  Toru Yada  Masanao Abe  Tatsuaki Okada  Yukihiro Ishibashi 《Meteoritics & planetary science》2015,50(12):2087-2098

The Hayabusa mission to asteroid 25143, Itokawa, brought back 2000 small particles, which most closely resemble material found in LL4‐6 chondrites. We report an ⁴⁰Ar/³⁹Ar age of 1.3 ± 0.3 Ga for a sample of Itokawa consisting of three grains with a total mass of ~2 μg. This age is lower than the >4.0 Ga ages measured for 75% of LL chondrites but close to one for Y‐790964 and its pairs. The flat ⁴⁰Ar/³⁹Ar release spectrum of the sample suggests complete degassing 1.3 Ga ago. Recent solar heating in Itokawa's current orbit does not appear likely to have reset that age. Solar or impact heating 1.3 Ga ago could have done so. If impact heating was responsible, then the 1.3 Ga age sets an upper bound on the time at which the Itokawa rubble pile was assembled and suggests that rubble pile creation was an ongoing process in the inner solar system for at least the first 3 billion years of solar system history.  相似文献   

Hortonian overland flow from Japanese forest plantations—an aberration,the real thing,or something in between?     

Roy C. Sidle  Tomonori Hirano  Takashi Gomi  Tomomi Terajima 《水文研究》2007,21(23):3237-3247

There is a growing opinion that poorly managed plantation forests in Japan are contributing to increased storm runoff and erosion. Here we present evidence to the contrary from runoff plots at two scales (hillslope and 0·5 × 2 m plots) for several forest conditions in the Mie and Nariki catchments. Runoff coefficients from small plots in untended hinoki forests were variable but typically higher than from better managed or deciduous forests during small storms at Nariki; at Mie, runoff during small events was highly variable from all small plots but runoff coefficients were similar for hinoki plots with and without understory vegetation, while the deciduous plot had lower runoff coefficients. Storm runoff was less at the hillslope scale than the plot scale in Mie; these results were more evident at sites with better ground cover. During the largest storms at both sites, differences in runoff due to forest condition were not evident regardless of scale. Dynamic soil moisture tension measurements at Nariki indicated that during a large storm, flow in the upper organic‐rich and root‐permeated soil horizons was 3·2 times higher than measured overland runoff from a small hinoki plot with poor ground cover and 8·3 times higher than runoff from a deciduous forest plot. On the basis of field observations during storms, at least a portion of the monitored ‘Hortonian overland flow’ was actually occurring in this near‐surface ‘biomat’. Therefore our field measurements in both small and large plots potentially included biomat flow in addition to short‐lived Hortonian runoff. Because overland flow decreased with increasing scale, rill erosion did not occur on hillslopes. Additionally, runoff coefficients were not significantly different among cover conditions during large storms; thus, the ‘degraded’ forest conditions appear not to greatly enhance peak flows or erosion potential at larger scales, especially when biomat flow is significant. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

A fluidized landslide on a natural slope by artificial rainfall   总被引：9，自引：5，他引：4  

Hirotaka?Ochiai  Yasuhiko?OkadaEmail author  Gen?Furuya  Yoichi?Okura  Takuro?Matsui  Toshiaki?Sammori  Tomomi?Terajima  Kyoji?Sassa 《Landslides》2004,1(3):211-219

An experiment to induce a fluidized landslide by artificial rainfall was conducted on a natural slope at Mt. Kaba-san in the village of Yamato, Ibaraki Prefecture, Japan. The experimental slope was 30 m long, 5 m wide, and the average slope gradient was 33°. A landslide initiated 24,627.5 s (410 m/27.5 s) after the start of sprinkling at a rainfall intensity of 78 mm/h. The landslide mass was 14 m long and 1.2 m deep (at maximum). It first slid, then fluidized, and changed into a debris flow. The travel distance was up to 50 m in 17s. The apparent friction angle of the fluidized landslide was 16.7°. Formation of the sliding surface was detected by soil-strain probes. Motion of the surface of the failed landslide mass was determined by stereo photogrammetry.  相似文献   

Damage detection of base‐isolated buildings using multi‐input multi‐output subspace identification     

Reiki Yoshimoto  Akira Mita  Keiichi Okada 《地震工程与结构动力学》2005,34(3):307-324

A damage detection algorithm of structural health monitoring systems for base‐isolated buildings is proposed. The algorithm consists of the multiple‐input multiple‐output subspace identification method and the complex modal analysis. The algorithm is applicable to linear and non‐linear systems. The story stiffness and damping as damage indices of a shear structure are identified by the algorithm. The algorithm is further tuned for base‐isolated buildings considering their unique dynamic characteristics by simplifying the systems to single‐degree‐of‐freedom systems. The isolation layer and the superstructure of a base‐isolated building are treated as separate substructures as they are distinctly different in their dynamic properties. The effectiveness of the algorithm is evaluated through the numerical analysis and experiment. Finally, the algorithm is applied to the existing 7‐story base‐isolated building that is equipped with an Internet‐based monitoring system. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Performance of regional distance centroid moment tensor inversion applied to the 2004 mid-Niigata prefecture earthquake, Japan     

Yoshihiro Ito  Shoji Sekiguchi  Tomomi Okada  Ryou Honda  Kazushige Obara  Sadaki Hori 《Geophysical Journal International》2006,167(3):1317-1331

  相似文献   

Modeling urban expansion scenarios by coupling cellular automata model and system dynamic model in Beijing, China   总被引：9，自引：0，他引：9  

Chunyang He  Norio Okada  Qiaofeng Zhang  Peijun Shi  Jingshui Zhang   《Applied geography (Sevenoaks, England)》2006,26(3-4):323-345

Spatially explicit urban expansion models that can trace urban development in the past and predict the expansion scenarios in the future are indispensable for examining urban planning policies. This paper demonstrates a new urban expansion scenario (UES) model by coupling one “bottom-up” cellular automata (CA)-based model and one “top-down” system dynamics (SD)-based model. By implementing the UES model in Beijing, the urban evolution from 1991 to 2004 was simulated and the UESs from 2004 to 2020 were predicted. The results suggest that a dilemma of urban expansion versus limited water resource and environment deterioration exists. Dealing with such a dilemma remains a challenge for the local government.  相似文献   

Modification of sea-salt aerosols over the coastal area in china     

Li Fang  Duan Minzheng  Lu Daren  Kikuo Okada 《大气科学进展》1998,15(4):531-540

Ｉ．ＩＮＴＲＯＤＵＣＴＩＯＮＡｅｒｏｓｏｌｃｏｍｐｏｓｉｔｉｏｎｉｓａｐｉｅｃｅｏｆｉｍｐｏｒｔａｎｔｉｎｆｏｒｍａｔｉｏｎｆｏｒｒａｄｉａｔｉｏｎｔｒａｎｓｆｅｒ．Ｔｗｏｐａｒａｍｅｔｅｒｓ,ｎａｒｎｅｌｙ,ｔｏｔａｌｌｏａｄｉｎｇａｎｄｃｈｅｍｉ...  相似文献   

Collision structure in the upper crust beneath the southwestern foot of the Hidaka Mountains, Hokkaido, Japan as derived from explosion seismic observations     

Takeo Moriya  Hiroshi Okada  Takeshi Matsushima  Shuzo Asano  Toshikatsu Yoshii  Akira Ikami   《Tectonophysics》1998,290(3-4):181-196

The P-wave velocity structure of the upper crust beneath a profile ranging from Niikappu to Samani in the southwestern foot of the Hidaka Mountains, Hokkaido, Japan was obtained through analysis of refraction and wide-angle reflection data. The mountains are characterized by high seismicity and a large gravity anomaly. The present profile crosses the source region of the 1982 Urakawa-oki earthquake (M_s 6.8). The length of the profile is 66 km striking northwest and southeast. Along the profile, 64 vertical geophones were set up and 5 shot points were chosen. For each shot, a 400–600 kg charge of dynamite was detonated. The studied area is composed of four major geological belts: Neogene sedimentary rocks, the Kamuikotan belt, the Yezo Group, and the Hidaka belt. The measurement line crosses these geological trend at an oblique angle. The structure obtained is characterized by remarkable velocity variations in the lateral direction and reflects the surface geological characteristics. A thin, high-velocity layer (HVL) was found between low-velocity materials in the central part of the profile, beneath the Kamuikotan Metamorphic Belt, at a depth ranging from 0.5 to 6 km, overthrusting toward the west on the low-velocity materials consisting of Neogene sedimentary rocks, and forming gentle folds. Outlines of the velocity structure of the Hidaka Mountains yielded by other studies have shown a large-scale overthrust structure associated with the collision of the Outer Kurile and the Outer Northern Honshu Arcs. The shallow velocity structure inferred by the present study showed a similar (although small scale) overthrust structure. The obtained structure shows that the composite tectonic force, comprising westward movement of the Outer Kurile Arc and northward movement of the Outer Northern Honshu Arc, plays an important role in the evolution of the tectonic features of the crust and upper mantle in a wide depth range beneath the Hidaka Mountains.  相似文献