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排序方式: 共有132条查询结果,搜索用时 31 毫秒
51.
Ki-Weon Seo Duane E. Waliser Baijun Tian Baek-Min Kim Seong-Chan Park Steve Cocke Byung-Ju Sohn Masayoshi Ishii 《Asia-Pacific Journal of Atmospheric Sciences》2012,48(2):153-158
Variations of global evapotranspiration (ET) and fresh water discharge from land to oceans (D) are important components of global climate change, but have not been well monitored. In this study, we present an estimate of twenty years (1989 to 2008) variations of global D and ET derived from satellite remote-sensed measurements and recent reanalysis products, ERA-Interim and CFSR, by using a novel application of the water balance equations separately over land and over oceans. Time series of annual mean global D and ET from both satellite observations and reanalyses show clear positive and negative trends, respectively, as a result of modest increase of oceanic evaporation (E o ). The inter-annual variations of D are similar to the in-situ-based observations, and the negative trend of ET supports the previous result that relative humidity has decreased while temperature has increased on land. The results suggest considerable sensitivity of the terrestrial hydrological cycles (e.g., D and ET) to small changes in precipitation and oceanic evaporation. 相似文献
52.
基于微粒变化对崇测冰帽浅层冰芯的定年结果 总被引:6,自引:1,他引:5
冰芯年代学的建立, 对于稳定同位素定年方法失效的钻点尤为困难. 依据粒径在0.66~1.33μm之间的不可溶尘埃微粒的浓度垂向分布, 并结合阳离子Ca2 的浓度剖面变化, 实现了对崇测冰帽冰芯浅层的断代. 该冰芯钻自海拔6 532 m的冰穹顶部, 解析的18.7 m冰芯长度占到钻点冰层深度约2/5, 辅助的定年参数包括钻点表层5 a的实测净积累率和大气核试验的地层标志. 综合各种技巧定年, 崇测冰帽该冰芯覆盖的记录年代为1902-1992年, 最底部累积误差在±2 a(约为2%). 相似文献
53.
54.
Tao Wang Jason McCormick Nobuya Yoshitake Peng Pan Yosuke Murata Masayoshi Nakashima 《地震工程与结构动力学》2008,37(6):955-974
The collapse of a one‐bay, four‐story steel moment frame is simulated in this study by the proposed peer‐to‐peer (P2P) Internet online hybrid test system. The typical beam hinging mechanism, which is ensured by a strong‐column, weak‐beam design, is reproduced. The plastic hinges at the column bases are taken as the experimental portions, while the superstructure is analyzed numerically by a general‐purpose finite element program. The implicit plastic rotations of the two column bases are treated as boundary displacements. In order to account for the complex behavior of the column bases, the P2P system is modified to use the secant stiffness during iterations, and the physical specimens are designed such that the plastic hinge behavior can be obtained. For this study, the three substructures are distributed to different locations. A large ground motion is repeatedly imposed until the column bases lose their capacity to sustain the gravity load. As a result, significant deterioration is observed at both column bases. The proposed P2P system is thus demonstrated to be able to accommodate multiple‐tested substructures involving unstable behavior. The results suggest that the P2P Internet online hybrid test system provides a reliable means of studying structures up to collapse. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
55.
Akira Masuda Tadao Kusaba Kenji Marubayashi Michiyoshi Ishibashi 《Journal of Oceanography》1999,55(2):289-305
The variability of the sea surface wind and wind waves in the coastal area of the Eastern Tsushima Strait was investigated
based on the hourly data from 1990 to 1997 obtained at a station 2 km off Tsuyazaki, Fukuoka. The annual mean wind speed was
4.84 m s−1, with strong northwesterly monsoon in winter and weak southwesterly wind in summer. Significant wave heights and wave periods
showed similar sinusoidal seasonal cycles around their annual means of 0.608 m and 4.77 s, respectively. The seasonal variability
relative to the annual mean is maximum for wave heights, medium for wind speeds, and minimum for wave periods. Significant
wave heights off Tsuyazaki turned out to be bounded by a criterion, which is proportional to the square of the significant
wave period corresponding to a constant steepness, irrespective of the season or the wind speed. For terms shorter than a
month, the significant wave height and the wave period were found to have the same spectral form as the inshore wind velocity:
white for frequencies less than 0.2 day−1 and proportional to the frequency to the −5/3 power for higher frequencies, where the latter corresponds to the inertial
subrange of turbulence. The spectral levels of wave heights and wave periods in that inertial range were also correlated with those of the inshore wind velocity, though the scatter was large.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
56.
Base shear capping buildings with graphite‐lubricated bases for collapse prevention in extreme earthquakes 下载免费PDF全文
Francesca Barbagallo Ikumi Hamashima Hongsong Hu Masahiro Kurata Masayoshi Nakashima 《地震工程与结构动力学》2017,46(6):1003-1021
Damage or collapse of buildings vulnerable to seismic forces may cause human casualties, and seismic upgrading of such structures is a practical solution to this deficiency. The study presented here proposes a simple approach to prevent structural collapse by separating the superstructure from its foundation to let the superstructure slide during extreme ground shaking. The sliding mechanism contributes to cap the horizontal force exerted on the superstructure. In such approach, the key is to maintain the friction force between the superstructure and the foundation sufficiently low and stable. This research proposes to realize a controlled sliding mechanism, which acts as a structural fuse, by means of carbon powder lubrication at the bases of the structure's columns. The fundamental behaviour of the proposed structural system, named the base shear capping building, is investigated by shaking table tests and numerical simulation. Both experimental and numerical results showed that graphite lubrication is an efficient and robust lubrication material, maintaining the friction coefficient between the steel column bases and mortar foundation at around 0.16. The sliding at the bases significantly reduced the acceleration transmitted to the superstructure, keeping the base shear coefficient not greater than about 0.40. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
57.
Stable isotope exchange processes between solid and liquid phases of a natural melting snowpack are investigated in detail by separating the liquid water from snow grains at different depths of the snowpack and collecting the bottom discharge using a lysimeter. In the melting–freezing mass exchange process between the two phases, the theoretical slope of the δD? δ18O line for newly refrozen ice is calculated to be nearly that of pore water. However, based on observations of the isotopic evolution and snow grain coarsening of the snowpack, it is demonstrated that the slope of the δD? δ18O line for newly refrozen ice is equal to that of the original ice. This is proved to be due to preferential water flow in the snowpack, which leads to relatively more deuterium and less oxygen‐18 in the mobile water than the immobile water because of the kinetic effect. Higher mass exchange rate in the mobile water region results in excess deuterium in the bulk refrozen ice, compared with the fractionation of uniform fractionation factors and exchange rate. This effect, which is termed the ‘preferential exchange rate effect of isotopic fractionation’, is shown to be larger in the lower part than the upper part of the snowpack. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
58.
Shoji?NishimotoEmail author Hidekazu?Yoshida Yoshihiro?Asahara Tadahiko?Tsuruta Masayuki?Ishibashi Nagayoshi?Katsuta 《Contributions to Mineralogy and Petrology》2014,167(1):960
Episyenite is a quartz-depleted vuggy rock resulting from hydrothermal alteration of granitic rocks. This is the first report of its existence in an island arc, which is identified in a deep drill core of the Toki Cretaceous granite distributed in central Japan. In order to understand the petrographical features of the episyenite, neutron porosity measurement, geochemical analysis, microscopic observation, and X-ray computed tomography scanning were carried out. The results show remarkably high porosity (35.4 %) due to interconnecting vugs and the removal of quartz, plagioclase, and biotite. The Rb–Sr isotopic results and the paragenetic sequence of secondary minerals in the vugs suggest that the hydrothermal alteration process can be divided into an episyenitization stage and a later hydrothermal stage. At the episyenitization stage (70.6 ± 3.1 Ma) ca. 6 million years after the emplacement of the unaltered granite (76.3 ± 1.5 Ma), dissolution of quartz, biotite, and plagioclase occurred and was followed by the precipitation of albite, vermicular chlorite, and platy calcite. The episyenitization is considered as a local alteration of the Toki granite in an isotopically closed system. At the later hydrothermal stage, illite and secondary quartz precipitated from circulating meteoric-derived water in the dissolution vugs. Superimposing alteration at the later hydrothermal stage is limited, which results in the preservation of the episyenite in an almost primitive condition. 相似文献
59.
T. Noguchi M. Kimura T. Hashimoto M. Konno T. Nakamura M. E. Zolensky A. Tsuchiyama T. Matsumoto J. Matsuno R. Okazaki M. Uesugi Y. Karouji T. Yada Y. Ishibashi K. Shirai M. Abe T. Okada 《Meteoritics & planetary science》2014,49(7):1305-1314
We observed cross sectional ultra‐thin sections near the surface of 12 particles recovered from the S‐type asteroid Itokawa by the Hayabusa spacecraft in 2010, using spherical aberration–corrected STEM and conventional TEM. Although their mineralogy is almost identical to the equilibrated LL chondrites and therefore basically anhydrous, micrometer‐to‐submicrometer‐sized sylvite was identified on the surface of Itokawa particle RA‐QD02‐0034. Separately, micrometer‐sized halite was also identified on the surface of Itokawa particle RA‐QD02‐0129. Detailed inspection of the sample processing procedures at the JAXA's Planetary Materials Sample Curation Facility and textural observation of the sylvite and halite indicate that they were clearly present on two Itokawa particles before they were removed from Clean Chamber #2 at JAXA. However, there is no direct evidence for their extraterrestrial origin at present. If the sylvite and halite are extraterrestrial, their presence suggests that they may be more abundant on the surface of S‐type asteroids than previously thought. 相似文献
60.
Masaya Masayoshi Saito Kiyotaka Tanikawa 《Celestial Mechanics and Dynamical Astronomy》2007,98(2):95-120
The dynamical structure of phase space of gravitational Newtonian three bodies which lie on a line (rectilinear three-body
system) is studied. We take an initial value plane and classify the points on the plane according to the fate of the orbits
starting from the points, using symbol sequences. The structure appearing on the initial value plane with this classification
was well studied for the equal-mass case (Tanikawa and Mikkola 2000, Chaos 10, 649–657). In this paper, we follow and clarify the changes of this structure with the mass ratio of three particles. 相似文献