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51.
Keiichi Sasaki Akio Omura Tetsuo Miwa Yoshihiro Tsuji Hiroki Matsuda Toru Nakamori Yasufumi Iryu Tsutomu Yamada Yuri Sato Hiroshi Nakagawa 《Island Arc》2006,15(4):455-467
Abstract High-resolution seismic reflection profiles delineated the distribution of mound-shaped reflections, which were interpreted as reefs, beneath the insular shelf western off Irabu Island, Ryukyus, southwestern Japan. A sediment core through one of the mounded structures was recovered from the sea floor at a depth of −118.2 m by offshore drilling and was dated by radiometric methods. The lithology and coral fauna of the core indicate that the mounded structure was composed of coral–algal boundstone suggesting a small-scaled coral reef. High-precision α-spectrometric 230 Th/234 U dating coupled with calibrated accelerator mass spectrometric 14 C ages of corals obtained reliable ages of this reef ranging from 22.18 ± 0.63 to 30.47 ± 0.98 ka. This proves that such a submerged reef was formed during the lowstand stage of marine oxygen isotope stages 3–2. The existence of low-Mg calcite in the aragonitic coral skeleton of 22.18 ± 0.63 ka provides evidence that the reef had once been exposed by lowering of the relative sealevel to at least −126 m during the last glacial maximum in the study area. There is no room for doubt that a coral reef grew during the last glacial period on the shelf off Irabu Island of Ryukyus in the subtropical region of western Pacific. 相似文献
52.
Junji Koyama 《Tectonophysics》1985,118(3-4)
Theoretical study has been made investigating the seismic source spectrum generated from a coherent and incoherent rupture. An earthquake is modeled by a finite propagating rupture on a fault plane where fault heterogeneities, fault patches, are randomly distributed. The dislocation velocity of such a fracture is assumed to be approximated by a stochastic process of random impacts of particles obeying Brownian motion. The parameters of the present stochastic source are seismic moment, fault dimension, fault patch intensity, and patch fracture time. The model predicts two corner frequencies; one originates from the fault finiteness and the other from the fracturing of fault patches. The seismic source spectrum from the model consequently shows distinct frequency dependence of ω0 − ω−2 − ω−γ − ω−2 with increasing angular frequency ω, where γ is about 1.0. The seismic moment is controlled by an average dislocation on the fault and by the fault dimension. The short-period spectrum, which is much more abundant than that of the ordinary deterministic models, is controlled by the product of the fault patch intensity and the square root of their total number. The ω−2 high frequency asymptote of the theoretical spectrum is in conformity with the white acceleration spectrum usually found in the literature, and it guarantees the finite total energy of the rupture process. 相似文献
53.
54.
Akio Makishima Katsura Kobayashi Eizo Nakamura 《Geostandards and Geoanalytical Research》2002,26(1):41-51
A simple and accurate method for the determination of Cr, Ni, Cu and Zn at μg g?1 levels in milligram‐sized bulk silicate materials is reported using isotope dilution high‐resolution inductively coupled plasma‐mass spectrometry (HR‐ICP‐MS) with a flow injection system. Silicate samples with Cr, Ni, Cu and Zn spikes were digested with HF‐HBr and Br2, and subsequently decomposed at 518 K in a Teflon bomb. In this procedure, all sulfides and chromite, major hosts of these elements, were completely decomposed, thus allowing for isotope equilibration between the sample and spike. Magnesium and Al fluorides formed after the digestion of the sample were removed by centrifugation, and the supernatant was directly aspirated into a HR‐ICP‐MS at a mass resolution of 7500, where interfering oxide ions, ArO+, CaO+, TiO+, CrO+ and VO+, were separated from Cr+, Ni+, Cu+ and Zn+. No matrix effects were observed down to a dilution factor of 50. Detection limits for these elements in silicate samples were < 0.04 μg g?1. The effectiveness of the technique was demonstrated by the analysis of 13 to 40 mg test portions of USGS and GSJ silicate reference materials with a major element composition ranging from andesite to peridotite, in addition to 8‐23 mg of the Smithsonian reference Allende. Both the reproducibility and the deviation from the reference value for most reference materials of various rock types were < 9%, and thus confirm that the method gives accurate analytical results for small sample sizes over a wide range of Cr, Ni, Cu and Zn contents. This method is, therefore, suitable for analysing small and/or precious bulk samples, such as meteorites, mantle peridotites and mineral separates, and for the characterisation of silicate and sulfide minerals for use as calibration samples in secondary ion mass spectrometry or laser ablation ICP‐MS. 相似文献
55.
Aoki Koji Sakamaki Tatsuya Ohashi Tomonori Ikeda Osamu Suzuki Akio 《Physics and Chemistry of Minerals》2020,47(6):1-9
Physics and Chemistry of Minerals - A black tourmaline sample from Seagull batholith (Yukon Territory, Canada) was established to be a schorl with concentrations of Fe2+ among the highest currently... 相似文献
56.
Ayumi Fujisaki Hajime Yamaguchi Takenobu Toyota Akio Futatsudera Masaru Miyanaga 《Journal of Oceanography》2009,65(4):487-498
The air-ice drag coefficient under neutral stratification C
DN
was measured with the eddy correlation method in the southern Sea of Okhotsk. The disturbance of the wind field caused by
the ship’s structure was evaluated by computational fluid dynamics (CFD), and two types of correction methods were applied
to estimate the error span of C
DN
: one is based on the results of CFD, and the other is based on the parameterization of C
DN
over open water suggested by Taylor and Yelland (2001). The C
DN
× 103 values finally obtained ranged from 1.9 to 5.4 with a mean value of 2.7 by the CFD correction and from 1.5 to 5.0 with a
mean value of 3.1 by the other method. This is somewhat larger than the value of 2.5 suggested by Shirasawa (1981), and in
the same range as 2.2–4.0 over rough ice and 3.1–5.0 over very rough ice, values which were complied by Guest and Davidson
(1991) for first year ice. Most of the ice conditions were characterized by broken floes with a diameter less than 100 m and
raised rims, which made the surface rougher than flat, level ice. The relation between C
DN
and ice concentration was not clear, mainly because the contribution of the form drag caused at the freeboard was undetectable
due to the great variation of ice surface condition. The roughness length z
M
was also evaluated using the model developed for snow covered ice in a previous study. 相似文献
57.
Youichi Oyama Bunkei Matsushita Takehiko Fukushima Kazuo Matsushige Akio Imai 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(1):73-85
The remote sensing of Case 2 water has been far less successful than that of Case 1 water, due mainly to the complex interactions among optically active substances (e.g., phytoplankton, suspended sediments, colored dissolved organic matter, and water) in the former. To address this problem, we developed a spectral decomposition algorithm (SDA), based on a spectral linear mixture modeling approach. Through a tank experiment, we found that the SDA-based models were superior to conventional empirical models (e.g. using single band, band ratio, or arithmetic calculation of band) for accurate estimates of water quality parameters. In this paper, we develop a method for applying the SDA to Landsat-5 TM data on Lake Kasumigaura, a eutrophic lake in Japan characterized by high concentrations of suspended sediment, for mapping chlorophyll-a (Chl-a) and non-phytoplankton suspended sediment (NPSS) distributions. The results show that the SDA-based estimation model can be obtained by a tank experiment. Moreover, by combining this estimation model with satellite-SRSs (standard reflectance spectra: i.e., spectral end-members) derived from bio-optical modeling, we can directly apply the model to a satellite image. The same SDA-based estimation model for Chl-a concentration was applied to two Landsat-5 TM images, one acquired in April 1994 and the other in February 2006. The average Chl-a estimation error between the two was 9.9%, a result that indicates the potential robustness of the SDA-based estimation model. The average estimation error of NPSS concentration from the 2006 Landsat-5 TM image was 15.9%. The key point for successfully applying the SDA-based estimation model to satellite data is the method used to obtain a suitable satellite-SRS for each end-member. 相似文献
58.
Tidal Correction of Altimetric Data in the Japan Sea 总被引:2,自引:0,他引:2
Satellite altimetric data have been very useful in the study of variation in the eddy field of the ocean. In order to investigate the variation in the eddy field, we have to remove tidal signals from altimetric data. However, global tidal models do not have sufficient accuracy in marginal seas such as the Japan Sea. In this study, we carried out harmonic analysis of temporal fluctuations of sea surface height data in the Japan Sea measured by TOPEX/POSEIDON. We could eliminate the tidal signals from altimetric data of TOPEX/POSEIDON and also from ERS-2 altimetric data with use of the harmonic constants derived from TOPEX/POSEIDON and tide gauge data along the coast. We draw co-tidal and co-range charts in the Japan Sea using the result of the harmonic analysis of TOPEX/POSEIDON altimetric data and tide gauge data along the coast. The results obtained turn out to be very useful for the tidal correction of altimetric data from satellite in the Japan Sea. 相似文献
59.
Sato Minoru Oba Takashi Hosokawa Takao Yamaguchi Toshiyasu Nakano Toshiki Saito Tadao Muramoto Koji Kahara T akashi Funayama Katsura Kobayashi Akio Nakano Takahisa 《中国海洋大学学报(英文版)》2005,4(3):209-213
Brown alga ( Undaria pinnatifida) was treated with alginate lyase and hydrolyzed using 17 kinds of proteases and the inhibitory activity of the hydrolysates for the angiotensin-I-converting enzyme (ACE) was measured. Four hydrolysates with potent ACE-inhibitory activity were administered singly and orally to spontaneously hypertensive rats (SHRs). The systolic blood pressure of SHRs decreases significantly after single oral administration of the brown alga hydrolysates by pro- tease S ' Amano' (from Bacillus stearothermophilus) at the concentration of 10 (mg protein) (kg body weight)^ - 1. In the 17 weeks of feeding experiment, 7-week-old SHRs were fed standard diet supplemented with the brown alga hydrolysates for 10 weeks. In SHRs fed 1.0 and 0.1% brown alga hydrolysates, elevating of systolic bloodpressure was significantly suppressed for 7 weeks. To elucidate the active components, the brown alga hydrolysates were fractionated by 1-butanol extraction and HPLC on a reverse-phase column. Seven kinds of ACE-inhibitory peptides were isolated and identified by amino acid composition analysis, sequence analysis, and LC-MS with the results Val-Tyr, Ile-Tyr, Ala-Trp, Phe-Tyr, Val-Trp, Ile-Trp, and Leu-Trp. Each peptide was determined to have an antihypertensive effect after a single oral administration in SHRs. The brown alga hydrolysates were also confirmed to decrease the blood pressure in humans. 相似文献
60.
The identification of substorm onset is quite important in studying the mechanism of excitation of substorm disturbances. At present, one of the most practical methods to identify accurately the onset of substorms is to use low-latitude Pi2, which is sensitively related to the plasma instability in the magnetosphere, that triggers the substorm disturbances. This method is applied to examine the onset times of three substorm events which were already defined by various methods other than the low-latitude Pi2 method. Preceding the onset times, other evident substorm onsets are clearly determined with Pi2 onsets for all the three events by examining only the H-component of rapid-run magnetogram from a single low-latitude station in the dark hemisphere. Cooperative monitoring of Pi2 at three low-latitude stations on three well-separated meridians, therefore, is really effective in detecting most substorms. 相似文献