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991.
Zhuo Liu Yinglong J. Zhang Harry V. Wang Hai Huang Zhengui Wang Fei Ye Mac Sisson 《Ocean Dynamics》2018,68(4-5):509-533
We present a novel and challenging application of a 3D estuary-shelf model to the study of the collective impact of many small-scale structures (bridge pilings of 1 m × 2 m in size) on larger-scale circulation in a tributary (James River) of Chesapeake Bay. We first demonstrate that the model is capable of effectively transitioning grid resolution from ~?400 m down to ~?1 m near the pilings without introducing undue numerical artifact. We then show that despite their small sizes and collectively small area as compared to the total channel cross-sectional area, the pilings exert a noticeable impact on the large-scale circulation, and also create a rich structure of vortices and wakes around the pilings. As a result, the water quality and local sedimentation patterns near the bridge piling area are likely to be affected as well. However, when evaluating over the entire waterbody of the project area, the near field effects are weighed with the areal percentage which is small compared to that for the larger unaffected area, and therefore the impact on the lower James River as a whole becomes relatively insignificant. The study highlights the importance of the use of high resolution in assessing the near-field impact of structures. 相似文献
992.
Geochemical research on C—O and Sr—Nd isotopes of mantle-derived rocks from Shandong Province,China 总被引:1,自引:0,他引:1
This paper presents systematic studies on the C—O and Sr—Nd isotopic compositions for Cretaceous Badou carbonatites, Fangcheng
basalts, and Jiaodong lamprophyres and Paleozoic Mengyin kimberlites in Shandong Province, China. Paleozoic kimberlites have
normal and uniform C—O isotopic compositions with δ13C and δ18O in the range of −4.8‰—−7.6‰ and +9.9‰—+13.2‰, respectively. However, Cretaceous three different types of mantlederived rocks
have quite different C—O isotopic compositions, indicating that the mantle sources are probably partially contaminated with
organic carbon-bearing crustal materials. These Cretaceous rocks show uniform and EMII-like Sr—Nd isotopic compositions and
also indicate that the mantle sources were affected by recycled crustal materials. Comparative studies of C—O and Sr—Nd isotopes
reveal that the lithospheric mantle beneath the eastern North China Craton had different isotope characteristics in the Paleozoic,
the early Cretaceous, and the Tertiary time. This demonstrates that the lithospheric mantle beneath the region underwent at
least twice reconstructions since the Paleozoic. Available data imply that the first reconstruction mainly happened during
the Triassic-Jurassic time with gradual changes and the second in the Cretaceous with abrupt changes. Results also show that
the early Cretaceous (especially at 120-130 Ma) was perhaps the key period leading to the dramatic change of the Mesozoic
geodynamics on the eastern North China Craton. 相似文献
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996.
G. S. Ivanov-Kholodny E. I. Mogilevsky V. Ye. Chertoprud 《Geomagnetism and Aeronomy》2006,46(2):139-145
Using the data of 1960–1999 on solar magnetic fields on the source surface and the Higuchi method, the fractal dimension of changes in the solar magnetic field energy at various heliolatitudes and in different time intervals is analyzed. The fractal dimension obtained on a moving 1-year interval displays substantial time variations. The 11-year cycle, which dominates at high latitudes, and quasi-biennial variations (QBVs), which dominate at low latitudes and are similar to QBVs of solar activity indices, are traced in these variations. Thus, solar QBVs that appear in all heliomagnetic activity indices are also present in the fractal structure of the solar magnetic field variations. 相似文献
997.
Any pair ofm L gz ,m L g b,mmxz andmm x h in the eastern six provinces of China show good linear relation this makes it easy to convert from one scale to another.mm x h may replaceM L (ECH) as the local earthquake magnitude scale for the eastern six provinces, yet retaining the level ofM L (ECH). The scalemm x h is 0.36 magnitude units higher thanM L (SC) for southern California. By comparingRm a x (Δ) withR 3 (Δ) of Yunnan, it is found that the γ-value ofMAX phase of about 1 section in Yunnan region is half as large as that in the eastern six provinces of China. Observation indicates thatmm x h≈mb for magnitude 4–5. It follows therefore thatmb (ECH)≈mb (WUS). This is supported by the result that the attenuation coefficient, the γ-value in eastern China is the same as in western United States. 相似文献
998.
中国城市人力资本水平与人口集聚对创新产出的影响 总被引:2,自引:1,他引:1
基于中国2007—2012年287个地级及以上城市的创新投入要素和专利申请量的面板数据(未含港澳台地区数据),采用面板固定效应模型和面板分位数回归模型,揭示人力资本水平提升对区域创新产出的影响机制及其区域异质性,以及人口空间集聚对人才创新驱动作用的调节机制。结果表明:① 平均而言,人力资本水平越高的城市,创新产出水平越高,但人口集聚程度与创新产出水平并不存在显著的关联;② 人力资本水平提升对创新的驱动作用存在区域差异,在创新等级越低的城市中其作用效果越强;③ 人口空间集聚强化了人力资本水平对创新的驱动作用,城市规模扩大促进了知识的溢出;④ 人口空间集聚调节作用的显现需要达到一定的创新基础门槛,城市创新等级越高,调节作用越强。因此,各地方政府应当结合当地发展的实际情况,制定适宜的人才培育和人才引进策略,合理引导人才流动。 相似文献
999.
甲烷(CH4)对全球温室效应有着较大的贡献。三峡水库自2003年蓄水以来,其CH4排放问题已受到广泛关注。但三峡水库反季节的运行方式,使支流库湾CH4的产生和传输过程受到多方面的影响,进而导致其CH4排放效应尚不十分明确。本文综述了三峡水库支流CH4排放的研究进展,典型支流的CH4排放通量普遍高于干流,位于三峡水库库尾的部分支流CH4排放通量高于三峡水库库首及库中支流。大多数典型支流的CH4通量在夏季均达到全年峰值,而在冬季高水位运行期均处于相对较低的水平。同时本文主要从水环境条件、水动力条件、人类活动及气象条件4个方面阐述了三峡水库支流CH4排放的影响因素。1)水环境条件:支流水华后藻类衰亡分解过程会驱动CH4释放,且藻类的演替过程会加剧CH4的产生;温度可以直接影响CH4的生成速率和消耗速率,也能通过促进藻的生长间接影响CH4排放;支流相对较低的甲烷氧化菌丰度是其CH4通量较高的原因之一。2)水动力条件:蓄水期CH4主要以扩散的方式进行释放,支流较低的流速促进了悬浮物的沉积,上游沉积物中的CH4含量高于下游;泄水期CH4主要以冒泡的方式进行释放,下游沉积物中TOC急剧增加,但干流的入侵会削弱支流的温度分层,破坏藻类生长环境,间接影响CH4通量。3)人类活动:农业耕作使支流水体中的营养物浓度增加,甲烷氧化菌的丰富度降低,细菌群落的营养相关代谢增强;建设用地扩大、支流筑坝增加抑制了有机物的传输,增加了水体中的产CH4底物,促进了CH4的产生。4)气象条件:降雨会携带更多营养物质进入支流,同时会增加水体浊度、破坏水体的温度分层,从而对CH4的产生和传输过程造成影响。最后对未来的研究热点进行了展望,以期为三峡水库CH4排放的控制和管理提供参考。 相似文献
1000.
According to Ambartsumyan, one of the forms of galactic activity is the outflow of gaseous material in the form of jets or
clouds from the region of the nucleus at velocities up to hundreds or thousands of km/s, which sometimes leads to the breakup
of the nucleus and the ejection of large bursts of material from it. Quite a lot is known about the results of these ejections,
especially for quasars and active galaxies. They have been detected and studied in detail with regard to changes in their
outer appearance. However, the exact time of the ejections is not known, although statistically they occur frequently and
irregularly. The detection of changes in the spectra of galaxies is of special interest, but these are much harder to detect
over short times. Nevertheless, the probability of detecting the time of an ejection within a short time is nonzero. Additional
new emission components of the hydrogen Hα, Hβ, and Hγ lines over a year in the spectrum of the Sy2 galaxy Mark 6 were first
discovered by Khachikian and Weedman in 1969. This paper describes the origin and subsequent interesting fate of this new
hydrogen formation (cloud). 相似文献