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排序方式: 共有172条查询结果,搜索用时 31 毫秒
91.
Asten Michael W. Yong Alan Foti Sebastiano Hayashi Koichi Martin Antony J. Stephenson William J. Cassidy John F. Coleman Jacie Nigbor Robert Castellaro Silvia Chimoto Kosuke Cornou Cécile Cho Ikuo Hayashida Takumi Hobiger Manuel Kuo Chun-Hsiang Macau Albert Mercerat E. Diego Molnar Sheri Pananont Passakorn Pilz Marco Poovarodom Nakhorn Sáez Esteban Wathelet Marc Yamanaka Hiroaki Yokoi Toshiaki Zhao Don 《Journal of Seismology》2022,26(4):757-780
Journal of Seismology - Site response is a critical consideration when assessing earthquake hazards. Site characterization is key to understanding site effects as influenced by seismic site... 相似文献
92.
River floods influence sedimentary environments and ecosystems from the terrestrial to the deep-marine. This study documents the occurrence conditions of hyperpycnal flows generated by river floods and related organic-matter sedimentation for Holocene sediments of the Niigata Plain, Central Japan, based on detailed sedimentary facies, total sulfur and total organic carbon content, diatom assemblages and organic-matter composition. Holocene sediments of the Niigata Plain consist of sand, mud and gravel that were deposited in estuarine and fluvial systems during a sea-level rise (15 000–6800 years BP) and stillstand (after 6800 years BP) following the Last Glacial Maximum. Hyperpycnites are present in the upper part of the estuarine lagoon sediments. The depositional age is considered to be about 5000 years BP. The hyperpycnites comprise two successions of a top fining-up unit and a basal coarsening-up unit, and include abundant terrigenous organic matter and freshwater diatoms. A large volume of freshwater is inferred to have flowed into the lagoon during deposition of the upper part of the lagoon sediments. In consequence, hyperpycnal flows may have readily formed in the lagoon, because the halocline was weak. The hyperpycnal flows also produced a layer of concentrated terrigenous organic matter in the uppermost part of the hyperpycnites. The abundant organic matter on the estuarine floor is inferred to have produced anoxic bottom conditions owing to oxidative decomposition by benthic bacteria. 相似文献
93.
The Hill Forests in Bangladesh have been depleted and degraded in volume, area, and quantity, thus requiring urgent forest
protection by identifying the causes of forest loss. This study seeks to identify the fundamental causes of the shrinking
forest cover in the Hill Forests in Bangladesh. The results indicate four sets of causes: (i) indigenous forest dwellers,
having their own types of problems; (ii) migrants, who, because of problems in their places of origin, have decided to move
to the forests; (iii) the timber industry, which, legal or not, are cutting too many trees; and (iv) the government through
its Forest Department which is not able or willing to implement suitable policies to regulate the cutting trees and to prevent
illegal cutting. Because it is a time consuming task to mitigate the first and second sets of factors, we recommend to involve
forest dwellers in forestry practices as much as possible and taking necessary steps to alleviate the third and fourth sets
and thereby reduce the rate of forest depletion. Accordingly, a number of strategies that should be adopted to halt the loss
of remaining forest cover are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
94.
Characteristics of Sea Surface Circulation and Eddy Field in the South China Sea Revealed by Satellite Altimetric Data 总被引:4,自引:0,他引:4
Temporal and spatial variations of sea surface circulation in the South China Sea were revealed with use of altimetric data provided by TOPEX/POSEIDON from December 1992 to October 1997. The estimated distribution of sea surface dynamic heights from altimetric data coincide well with the results of observation by Soong et al. (1995) and Chu et al. (1998). The RMS variability of sea surface dynamic height, which is obtained after tidal correction based on Yanagi et al. (1997), is high in the central part of the South China Sea, the Gulf of Tongking, the Sunda Shelf and the Gulf of Thailand. The high RMS variability in the Gulf of Tongking, the Sunda Shelf and the Gulf of Thailand is due to set up and set down of sea water by the East Asian monsoon, which is northeasterly during winter and southwesterly during summer. Also, the high RMS variability in the central part of the South China Sea is due to the variations of basin-wide circulation. The circulations are dominant in the central part of the South China Sea during summer and winter, an anticyclonic circulation during summer and a cyclonic circulation during winter. It is suggested that these circulations are controlled by the East Asian monsoon. Hence, there is an interannual variability of the basin-wide circulation associated with the variation of the East Asian monsoon. 相似文献
95.
The plankton food web structure and trophodynamics in the neritic area of Sagami Bay were investigated from January 2003 to
December 2005, based on abundance, biomass, production rate and nutritional requirements of pico- (0.2–2 μm), nano- (2–20
μm), micro- (20–200 μm) and mesoplankton (>200 μm: mainly copepods CI-CVI) at 0–10 m depth. The average carbon biomass of
the total plankton community was higher in spring and summer (1.452 and 1.466 g C m−2, respectively) than in winter and autumn (0.676 and 0.686 g C m−2, respectively). The average values of primary production and of production rate and food requirement of heterotrophic organisms
were higher in summer than in other seasons. During the study period the biomass, production rate and food requirement of
small heterotrophs (i.e. bacteria: BA; heterotrophic nanoflagellates: HNF; microzooplankton: MZ) were much higher than those
of copepod secondary (CSP) and tertiary producers (CTP), indicating that the microbial food web was the main route of carbon
flow from phytoplankton (PP) to CSP and CTP, rather than the grazing food chain. In particular, during summer and autumn the
biomass of pico- and nano-size PP plus BA was greater than that of micro-size PP, suggesting the high prevalence of the microbial
food web (pico-/nanophytoplankton/BA-HNF/MZ-copepods). During winter and spring, the biomass of micro-size PP was greater
than that of pico- and nano-size PP plus BA, suggesting that the indirect route (microphytoplankton-MZ-copepods) probably
prevailed, while the microbial food web might be important. 相似文献
96.
Takaaki Noguchi Akira Tsuchiyama Hirohide Demura Hideaki Miyamoto Tomoki Nakamura Sho Sasaki Takashi Kubota Michael E. Zolensky 《Icarus》2010,206(1):319-326
On the sub-kilometer S-type asteroid, 25143 Itokawa, some boulders on rough terrains seem to be exposed without any powdery material covering. Based on surface morphological features, there are two major types of boulders: one has rounded edges and corners (rounded boulders), while the other has angular edges and corners (angular boulders). The surface features of the rounded boulders suggest that they have hardness heterogeneity and that some may be breccias. The angular boulders appear to be more resistant to impact disruption than the rounded ones, which may be due to a difference in lithology. The major constituents of Itokawa may be LL chondrite-like brecciated lithology (rounded boulders) along with a remarkable number of boulders suggesting that lithology is atypical among LL chondrites (angular boulders). Some of both types of boulders contain intersecting and stepped planar foliations. Comparison with meteorite ALH76009 suggests that the planar foliations may be marks where rocks were torn apart. As lithified breccias cannot be formed on present-day sub-kilometer-sized Itokawa, it is reasonable that boulders with various lithologies on Itokawa were formed on its large ancestor(s). The rubble-pile structure of Itokawa suggested by its low density (∼1.9 g/cm3) indicates that boulders on Itokawa are reassembled fragments formed by catastrophic disruption of large ancestor(s). 相似文献
97.
Use of flood chronology for detailed environmental analysis: a case study of Lake Kizaki in the northern Japanese Alps,central Japan 总被引:1,自引:1,他引:0
Takuma Ito Haruka Iwamoto Koichi Kamiya Takehiko Fukushima Fujio Kumon 《Environmental Earth Sciences》2010,60(8):1607-1618
This paper presents a study of the usefulness of flood layers as a time marker in sediments and a report of a case study of
Lake Kizaki in central Japan. A flood layer can be identified as a layer having a higher density, coarser grain size, lower
TN content, and higher C/N ratio than those of the upper and lower horizons. It can also be characterized by a hyperpycnal
sequence composed of a basal coarsening-upward unit and a top fining-upward unit. When flood layers can be correlated with
heavy rains in meteorological records, detailed age markers are well established in the sediment. Five flood layers were identified
in the surface sediment of Lake Kizaki, and they could be attributed to the historical heavy rainfalls that took place on
July 12, 1995; September 28, 1983; August 25, 1974; September 26, 1959; and September 1, 1949 under the constraint of an age
model. A precise age model is essential to clarify the environmental changes such as the pollutant history in detail. 相似文献
98.
The Saga Plain is near Beppu–Shimabara graben, a region of potential active volcanism. In the graben, mantle He, which has a high 3He/4He ratio of 1.1 × 10−5, escapes easily from the underlying subduction zone. In groundwater of the Saga Plain, except in the Shiroishi district, this ratio gradually increased as the dissolved He content increased, to a maximum of 5 × 10−6. In central Shiroishi, however, the ratio reached a minimum of 8.7 × 10−7 with increasing dissolved He content, suggesting that groundwater in central Shiroishi has selectively accumulated radiogenic He, which has a very low ratio of 1 × 10−8, rather than reflecting the regional He, which is rich in mantle He. This can be explained if groundwater in Shiroishi has become mixed with fossil pore water drawn from impermeable marine clay aquitard layers. The withdrawal of pore water has also caused severe land subsidence in central Shiroishi. 相似文献
99.
A fundamental mechanism on the atomic level for self-diffusion in the proton layer of portlandite, Ca(OH)2, was investigated by conducting hydrogen–deuterium (H–D) exchange diffusion experiments and by deriving potential energy
curves of OH vibrations from optical absorption measurements. Synthetic single crystals of portlandite were used in H–D experiments
between 250 and 450°C at 150 MPa. Arrhenius parameters for proton diffusion perpendicular to the c-axis gave a frequency factor of 1.0 × 10−10 m2/s and activation energy of 0.61 eV (58.5 kJ/mol). The activation energy corresponds to the height of the potential barrier
between two oxygen atoms across an interlayer. The potential barrier height was also theoretically estimated using the OH
potential energy curve (OH-PEC) determined by optical absorption measurements. Experimental and theoretical results suggest
that the potential barrier height cannot be simply determined by overlapping two OH-PECs. The potential barrier derived theoretically
was 3.11 eV. This is too high for the activation energy of the proton diffusion. It implies that the interaction between a
diffusing proton and the vacancy of a proton site, and the shortening of interlayer oxygen distance by thermal vibration reduce
the potential barrier. 相似文献
100.
K. Ichimoto B. Lites D. Elmore Y. Suematsu S. Tsuneta Y. Katsukawa T. Shimizu R. Shine T. Tarbell A. Title J. Kiyohara K. Shinoda G. Card A. Lecinski K. Streander M. Nakagiri M. Miyashita M. Noguchi C. Hoffmann T. Cruz 《Solar physics》2008,249(2):233-261
The Solar Optical Telescope (SOT) onboard Hinode aims to obtain vector magnetic fields on the Sun through precise spectropolarimetry of solar spectral lines with a spatial
resolution of 0.2 – 0.3 arcsec. A photometric accuracy of 10−3 is achieved and, after the polarization calibration, any artificial polarization from crosstalk among Stokes parameters is
required to be suppressed below the level of the statistical noise over the SOT’s field of view. This goal was achieved by
the highly optimized design of the SOT as a polarimeter, extensive analyses and testing of optical elements, and an end-to-end
calibration test of the entire system. In this paper we review both the approach adopted to realize the high-precision polarimeter
of the SOT and its final polarization characteristics. 相似文献