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排序方式: 共有300条查询结果,搜索用时 31 毫秒
51.
Tomohide Ishiyama Mohammed Y. Ali Satoshi Ishikawa Gerrit Blacquiere Shotaro Nakayama 《Geophysical Prospecting》2019,67(7):1852-1866
We introduce a concept of generalized blending and deblending, develop its models and accordingly establish a method of deblended-data reconstruction using these models. The generalized models can handle real situations by including random encoding into the generalized operators both in the space and time domain, and both at the source and receiver side. We consider an iterative optimization scheme using a closed-loop approach with the generalized blending and deblending models, in which the former works for the forward modelling and the latter for the inverse modelling in the closed loop. We applied our method to existing real data acquired in Abu Dhabi. The results show that our method succeeded to fully reconstruct deblended data even from the fully generalized, thus quite complicated blended data. We discuss the complexity of blending properties on the deblending performance. In addition, we discuss the applicability to time-lapse seismic monitoring as it ensures high repeatability of the surveys. Conclusively, we should acquire blended data and reconstruct deblended data without serious problems but with the benefit of blended acquisition. 相似文献
52.
Nutrients,light and phytoplankton production in the shallow,tropical coastal waters of Bandon Bay,Southern Thailand
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Takashi Yoshikawa Kosuke Tomizawa Yuki Okamoto Kazuya Watanabe Jintana Salaenoi Kenichi Hayashizaki Hisashi Kurokura Satoshi Ishikawa 《Marine Ecology》2017,38(6)
Phytoplankton primary production and its regulation by light and nutrient availability were investigated in the shallow, tropical coastal waters of Bandon Bay, Southern Thailand. The bay was meso‐eutrophicated and highly turbid, receiving river water discharge. Water column stratification was consistently weak during both rainy and dry seasons. Dissolved inorganic nitrogen (DIN) was higher off the river mouth than in the other regions, suggesting that river water discharge was a main source of DIN. By contrast, dissolved inorganic phosphorus (DIP) showed a significant negative correlation with total water depth, implying that regeneration around the sea floor was an important source of DIP. Surface DIN and DIP showed positive correlations with surface primary production (PP) and water column primary productivity (ΣPP*), respectively. The combined correlation and model analyses indicate that total water depth had an ambivalent influence on water column primary production (ΣPP); shallower water depth induced more active regeneration of nutrients, but it also caused higher turbidity and lower light availability as a result of enhanced resuspension of sediments. Furthermore, there was a vertical constraint for phytoplankton during the rainy season: total water depth tended to be shallower than euphotic zone depth. In conclusion, light limitation and vertical constraint owing to shallow water depth appear to be more important than nutrient limitation for water column primary production in Bandon Bay. 相似文献
53.
Experimental study on the bidirectional inelastic deformation capacity of U‐shaped steel dampers for seismic isolated buildings
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Diana Ene Shoichi Kishiki Satoshi Yamada Yu Jiao Yoshinao Konishi Masao Terashima Norihisa Kawamura 《地震工程与结构动力学》2016,45(2):173-192
Hysteretic dampers are used to dissipate earthquake‐induced energy in base‐isolated structures by acquiring inelastic deformations, rendering their hysteretic behavior of vital importance. The present paper focuses on investigating the behavior of U‐shaped steel dampers under bidirectional loading; this is significantly different from their corresponding uniaxial behavior. Two main sets of loading tests on full‐scale specimens are conducted in this regard: (i) quasi‐static tests with simple histories and (ii) dynamic tests with realistic loading histories. Based on the results obtained in the quasi‐static tests, an interaction curve that accounts for the reduction of the cyclic deformation capacity is proposed. However, the fidelity of this relation must be assessed under loading conditions similar to those of a seismically isolated structure subjected to an earthquake, which represents the goal of the second set of tests. The results of the dynamic tests validate the proposed interaction curve for estimating the deformation capacity of U‐shaped steel dampers under bidirectional loading. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
54.
Keita Kodama Yoshihiro Tajima Takamichi Shimizu Satoshi Ohata Hiroaki Shiraishi Toshihiro Horiguchi 《Marine pollution bulletin》2014
We investigated effects of severe hypoxia (dissolved oxygen <1 ml l−1) on recruitment of mantis shrimp Oratosquilla oratoria in Tokyo Bay. Ten-year field surveys were conducted to examine quantitative relationships in annual mean densities of larvae and juveniles, and spatial distribution of juveniles and severe hypoxia. There was no significant correlation between annual mean densities of larvae and juveniles, suggesting that mortality during larval or juvenile stages varies among years, which might have regulated abundance of young-of-the-year juveniles. Juvenile density was low in the severely hypoxic area, implying that hypoxia could affect survivals and spatial distribution of juveniles. Meanwhile, there are yearly fluctuations in juvenile density in normoxic areas of both northern and southern part of the bay. This evidence suggests that abundance of post-settled juveniles might have been determined by not only effects of hypoxia, but also other factors influencing mortality during the early life stages. 相似文献
55.
Norihisa Usui Hiroyuki Tsujino Hideyuki Nakano Satoshi Matsumoto 《Journal of Oceanography》2013,69(6):647-670
This study investigates the long-term variability of the Kuroshio path south of Japan. Sensitivity experiments using a data-assimilative model suggest that the duration of the large meander (LM) strongly depends on the Kuroshio transport; specifically, low transport leads to a long duration of the LM. Actually, we find a good correlation between the duration of the past LMs and the Sverdrup transport estimated by a wind-driven linear baroclinic vorticity model. Then we explore favorable conditions for the LM and find a close relationship between the Kuroshio Extension (KE) state and the LM. That is, a precondition for the LM that the Kuroshio path on the Izu Ridge is fixed at a deep channel located around 34°N is achieved during a stable KE state. In addition, westward propagating signals with negative anomalies in the Kuroshio region and high sea-surface height (SSH) state east of Taiwan are key for generation of a small meander southeast of Kyushu that triggers a subsequent LM. The signals related to the above conditions change the upstream Kuroshio transport and velocity, which are consistent with features indicated by the former observational studies. Using reanalysis data, we construct long-time series of indices for the three conditions, which explain well the past LMs. The indices suggest that long-term non-LM states around 1970 and in the 1990s were attributed to a low-SSH state east of Taiwan and an unstable KE state, respectively. 相似文献
56.
Akihiro Hachikubo Oleg Khlystov Masato Kida Hirotoshi Sakagami Hirotsugu Minami Satoshi Yamashita Nobuo Takahashi Hitoshi Shoji Gennadiy Kalmychkov Jeffrey Poort 《Geo-Marine Letters》2012,32(5-6):419-426
This study reports measurements of the Raman spectra of Lake Baikal gas hydrates and estimations of the hydration number of methane-rich samples. The hydration number of gas hydrates retrieved from the southern Baikal Basin (crystallographic structure I) was approx. 6.1. Consistent with previous results, the Raman spectra of gas hydrates retrieved from the Kukuy K-2 mud volcano in the central Baikal Basin indicated the existence of crystallographic structures I and II. Measurements of the dissociation heat of Lake Baikal gas hydrates by calorimetry (from the decomposition of gas hydrates to gas and water), employing the hydration number, revealed values of 53.7–55.5?kJ?mol–1 for the southern basin samples (structure I), and of 54.3–55.5?kJ?mol–1 for the structure I hydrates and 62.8–64.2?kJ?mol–1 for the structure II hydrates from the Kukuy K-2 mud volcano. 相似文献
57.
Keiji Misawa Mika Kohno Takayuki Tomiyama Takaaki Noguchi Tomoki Nakamura Keisuke Nagao Takashi Mikouchi Kunihiko Nishiizumi 《Earth and Planetary Science Letters》2010,289(1-2):287-297
Two silicate-rich dust layers were found in the Dome Fuji ice core in East Antarctica, at Marine Isotope Stages 12 and 13. Morphologies, textures, and chemical compositions of constituent particles reveal that they are high-temperature melting products and are of extraterrestrial origin. Because similar layers were found ~ 2000 km east of Dome Fuji, at EPICA (European Project for Ice Coring in Antarctica)-Dome C, particles must have rained down over a wide area 434 and 481 ka. The strewn fields occurred over an area of at least 3 × 106 km2. Chemical compositions of constituent phases and oxygen isotopic composition of olivines suggest that the upper dust layer was produced by a high-temperature interaction between silicate-rich melt and water vapor due to an impact explosion or an aerial burst of a chondritic meteoroid on the inland East Antarctic ice sheet. An estimated total mass of the impactor, on the basis of particle flux and distribution area, is at least 3 × 109 kg. A possible parent material of the lower dust layer is a fragment of friable primitive asteroid or comet. A hypervelocity impact of asteroidal/cometary material on the upper atmosphere and an explosion might have produced aggregates of sub-μm to μm-sized spherules. Total mass of the parent material of the lower layer must exceed 1 × 109 kg. The two extraterrestrial horizons, each a few millimeters in thickness, represent regional or global meteoritic events not identified previously in the Southern Hemisphere. 相似文献
58.
The deterioration of sediments is a serious environmental problem. Controlling nutrient release fluxes from sediments is important to alleviating eutrophication and to reducing terrigenous nutrient loads. The purpose of this study was to evaluate the phosphate removal performance of granulated coal ash (GCA) from seawater, which is produced from coal thermal electric power generation. Batch experiments were carried out to investigate the removal kinetics of phosphate from seawater under both oxic and anoxic conditions. Phosphate was removed well from seawater under both oxic and anoxic conditions. The adsorption isotherm for phosphate revealed that GCA could remove phosphate effectively from seawater above a concentration of 1.7 μmol L−1. GCA can reduce the concentration of phosphate in seawater effectively under anoxic conditions where iron type adsorbents cannot be applied. Therefore, GCA could potentially be used to adsorb phosphate in the organically-enriched sediment, which generally occurs under highly reductive conditions. 相似文献
59.
Genki I. Matsumoto Yukinori Tani Koji Seto Tomoko Tazawa Masumi Yamamuro Takahiro Watanabe Toshio Nakamura Tetsuo Takemura Satoshi Imura Hiroshi Kanda 《Journal of Paleolimnology》2010,44(2):677-693
Antarctic climate changes influence environmental changes at both regional and local scales. Here we report Holocene paleolimnological
changes in lake sediment core Sk4C-02 (length 378.0 cm) from Lake Skallen Oike in the Soya Kaigan region of East Antarctica
inferred from analyses of sedimentary facies, a range of organic components, isotope ratios of organic carbon and nitrogen,
and carbon-14 dating by Tandetron accelerator mass spectrometry. The sediment core was composed of clayish mud (378.0–152.5 cm)
overlain by organic sediments (152.5 cm-surface). The age of the surface and the core bottom were 150 (AD1950-1640) and ca.
7,030 ± 73 calibrated years before present (cal BP), respectively, and the mean sedimentation rate was estimated to be 0.55 mm/year.
Multi-proxy analyses revealed that the principal environmental change in the core is a transition from marine to lacustrine
environments which occurred at a depth of 152.5 cm (ca. 3,590 cal BP). This was caused by relative sea level change brought
about by ongoing retreat of glaciers during the mid-Holocene warming of Antarctica, and ongoing isostatic uplift which outpaced
changes in global (eustatic) sea level. The mean isostatic uplift rate was calculated to be 2.8 mm/year. The coastal marine
period (378.0–152.5 cm, ca. 7,030–3,590 cal BP) was characterized by low biological production with the predominance of diatoms.
During the transition period from marine to freshwater conditions (152.5-approximately 135 cm, ca. 3,590–3,290 cal BP) the
lake was stratified with marine water overlain by freshwater, with a chemocline and an anoxic (sulfidic) layer in the bottom
of the photic zone. Green sulfur bacteria and Cryptophyta were the major photosynthetic organisms. The Cryptophyta appeared
to be tolerant of the moderate salinity and stratified water conditions. The lacustrine period (approximately 135 cm-surface,
ca. 3,290 cal BP-present) was characterized by high biological production by green algae (e.g. Comarium clepsydra and Oedegonium spp.) with some contributions from cyanobacteria and diatoms. Biological production during this period was 8.7 times higher
than during the coastal marine period. 相似文献
60.
Wataru Nishijima Yoichi Nakano Satoshi Nakai Tetsuji Okuda Tsuyoshi Imai Mitsumasa Okada 《Marine pollution bulletin》2013
We investigated the effects of river floods on the macrobenthic community of the intertidal flat in the Ohta River Estuary, Japan, from 2005 to 2010. Sediment erosion by flood events ranged from about 2–3 cm to 12 cm, and the salinity dropped to 0‰ even during low-intensity flood events. Cluster analysis of the macrobenthic population showed that the community structure was controlled by the physical disturbance, decreased salinity, or both. The opportunistic polychaete Capitella sp. was the most dominant species in all clusters, and populations of the long-lived polychaete Ceratonereis erythraeensis increased in years with stable flow and almost disappeared in years with intense flooding. The bivalve Musculista senhousia was also an important opportunistic species that formed mats in summer of the stable years and influenced the structure of the macrobenthic community. Our results demonstrate the substantial effects of flood events on the macrobenthic community structure. 相似文献