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431.
Food safety and its related influencing factors in China are the hot research topics currently, and cultivated land conversion
is one of the significant factors influencing food safety in China. Taking the North China Plain as the study area, this paper
examines the changes of cultivated land area using satellite images, estimates land productivity from 1985 to 2005 using the
model of Estimation System for Land Productivity (ESLP), and analyzes the impact of cultivated land conversion on the land
production. Compared with the grain yield data from statistical yearbooks, the results indicate that ESLP model is an effective
tool for estimating land productivity. Land productivity in the North China Plain showed a slight decreasing trend from 1985
to 2005, spatially, increased from the north to the south gradually, and the net changes varied in different areas. Cultivated
land area recorded a marginal decrease of 8.0 × 105 ha, mainly converted to other land uses. Cultivated land conversion had more significant negative impacts on land production
than land productivity did. Land production decreased by about 6.48 × 106 t caused by cultivated land conversion between 1985 and 2005, accounting for 91.9% of the total land production reduction.
Although the land productivity increased in Anhui and Jiangsu provinces, it can not offset the overall adverse effects caused
by cultivated land conversion. Therefore, there are significant meanings to control the cultivated land conversion and improve
the land productivity for ensuring the land production in the North China Plain. 相似文献
432.
433.
Stokes polarization profiles of the Mg?b2 5172.68 Å spectral line on two simple sunspots are obtained with the Multi-Channel Solar Telescope (MCST) at the Huairou Solar Observing Station (HSOS). This is done by means of scanning this line over the wavelength interval from 200 mÅ redward of the line center to 200 mÅ blueward, in steps of 10 mÅ. A generalized analytic solution to the transfer equation for polarized radiation is presented. With a nonlinear least-square fitting technique, the linear calibration coefficients for the low-chromospheric longitudinal magnetic field is obtained in the weak-field case. We also discuss the problems in calibrating the transverse field with this line. It is shown that the weak-field approximation is not applicable to the chromospheric Mg?b2 line for the transverse component of the magnetic field. 相似文献
434.
Jun-Liang Yuan Jin-Gen Deng Qiang Tan Bao-Hua Yu Xiao-Chun Jin 《Rock Mechanics and Rock Engineering》2013,46(5):1157-1164
Serious wellbore instability occurs frequently during horizontal drilling in shale gas reservoirs. The conventional forecast model of in situ stresses is not suitable for wellbore stability analysis in laminated shale gas formations because of the inhomogeneous mechanical properties of shale. In this study, a new prediction method is developed to calculate the in situ stresses in shale formations. The pore pressure near the borehole is heterogeneous along both the radial and tangential directions due to the inhomogeneity in the mechanical properties and permeability. Therefore, the stress state around the wellbore will vary with time after the formation is drained. Besides, based on the experimental results, a failure criterion is verified and applied to determine the strength of Silurian shale in the Sichuan Basin, including the long-term strength of gas shale. Based on this work, horizontal well borehole stability is analyzed by the new in situ stress prediction model. Finally, the results show that the collapse pressure will be underestimated if the conventional model is used in shale gas reservoirs improperly. The collapse pressure of a horizontal well is maximum at dip angle of 45°. The critical mud weight should be increased constantly to prevent borehole collapse if the borehole is exposed for some time. 相似文献
435.
Tsunami-induced scour at coastal roadways: a laboratory study 总被引:1,自引:1,他引:0
Coastal roads are lifelines for bringing emergency personnel and equipment into affected areas after tsunamis, thus careful thought should be given to how to make roadways safer from tsunamis. Scouring at roadways is the primary damage caused by tsunamis; however, tsunami-induced scouring and beach erosion are less understood compared to tsunami runup and tsunami inundation. A set of laboratory experiments are reported in this study on tsunami-induced scour at a road model situated on a sandy beach. Our experiments showed that the distance between the shoreline and a roadway, which varies with tides, was a key factor affecting the scour depth at the road. Having the coastal road at about half of the inundation distance is not the most ideal location. The depth of road embedment did not affect the scour depth in our experiments. It was also found that for typical tsunamis, the scour depth is unlikely to reach its equilibrium stage. The information reported in this study is useful for local authorities to assess potential tsunami damage of roads and to have a better plan for tsunami disaster relief. 相似文献
436.
The vertical-vertical noise cross-correlation functions (NCFs) between two seismic arrays, the Japan F-net and ChinArray phase II, are calculated using continuo... 相似文献
437.
对于已进入开发中后期的碳酸盐岩缝洞型油气藏,进行缝洞单元精细研究非常重要。盲目部署加密井,很容易导致因为所在单元的储量已被动用而失利。本文采用的碳酸盐岩缝洞单元多学科综合划分方法是:在有井控制的地区,首先分析井间连通性,然后结合生产动态、常规解析试井、流体性质、数值试井等多学科资料确定缝洞单元边界;在无井控制的地区,影响连通性最重要的主控因素是储层本身的相互连通性,其次才是断裂和裂缝,这时可在连通性约束下进行储层和裂缝预测,并以此为主要依据确定缝洞单元边界。对塔里木盆地轮古油气田轮古11井区划分出80个缝洞单元,其中有55个为储量未动用单元(潜力单元),并部署了一些加密井,已钻的XW1井获得了成功,投产初期日产油95t,不含水。 相似文献
438.
对冬瓜营古地震剖面研究的结果表明:阳宗海附近西支小江活断层上,近两千五百年以来至少发生过五次七级以上强震,它们的碳14年代分别为距今118±95年(b.p.)距今445±95年(b.p.);距今1347±213年(b.p.);距今1930±135年(b.p.);>距今2359±213年(b.p.)。其中,剖面记录的最晚两次古地震事件与历史记载的嵩明、宜良间1833年八级大地震和宜良1500年七级强震还能够相对应,说明该剖面记录的古地震事件可信度较高,具有一定的参考使用价值。 相似文献
439.
Journal of Geographical Sciences - Since the Three Gorges Dam (TGD) was put into operation, the flood water level at an identical discharge rate has not displayed a decreasing trend along the... 相似文献
440.
Huang Jixian Mao Xiancheng Deng Hao Liu Zhankun Chen Jin Xiao Keyan 《Natural Resources Research》2022,31(4):2181-2196
Natural Resources Research - Spatial non-stationarity is a common geological phenomenon, and the formation of orebodies is a typical non-stationary process. Therefore, a quantitative study of the... 相似文献