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981.
Lead,Sulfur, and Oxygen Isotope Systematics in Hydrothermal Precipitates from the 14°S Hydrothermal Field,South Mid‐Atlantic Ridge
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At the inside corner between the South Mid‐Atlantic Ridge (SMAR) and the Cardno fracture zone, the 14°S hydrothermal field, with its abundant silica‐rich sulfides, was identified as a volcanic massif, which provided the first opportunity to study inside corner‐related hydrothermal mineralization. S, Pb, and O isotopes were measured in hydrothermal sulfide samples from the two sites (volcanic top and slope sites) in the 14°S field. The homogeneous Pb isotope values (207Pb/204Pb = 15.466 ? 15.472; 206Pb/204Pb = 18.242 ? 18.252) and the δ34S values (top site, +6.3 to +6.85‰; slope site, +2.37 to +3.36‰) suggest that the source of metals and most of the sulfur is the upper crust, whereas some sulfur is sourced from downward‐penetrating seawater, especially in the top site. The calculated oxygen isotope equilibration temperatures from quartz and seawater are between 94 and 144°C for the top site and between 179 and 196°C for the slope site. These isotopic proxies, together with geological background survey data, have an important implication: Discrepancies between the sites may result from variations in crust permeability, which also affect the mixing level between downward‐penetrating seawater and upward hydrothermal end‐member fluids and determine the various mineralization types. 相似文献
982.
Land subsidence was first observed in Shanghai nearly a century ago, in 1921. Land subsidence attributed to groundwater extraction has been severe in China and is still occurring. Recent subsidence and associated earth fissures occurring since 2000 in three principal regions—the North China Plain, Fenwei Basin and Yangtze Delta—are introduced, and historical subsidence in these areas is briefly summarized. The subsidence-affected area in these regions with cumulative subsidence greater than or equal to 200 mm is more than 90,000 km2 and covers 22 provinces (cities), which include intensively developed and densely populated areas. Earth fissures accompanying the subsidence create significant geohazards; more than 1,000 earth fissures have been identified in the North China Plain, Fenwei Basin and Yangtze Delta. Effective land-subsidence-monitoring networks, that include continuous global positioning system (GPS) stations, repeat GPS and leveling surveys of geodetic benchmarks, InSAR, borehole extensometers, and groundwater observation wells, have been established in these three subsidence-affected areas. Mitigation measures and administrative means have been implemented in some areas, with good results in the Yangtze Delta area. 相似文献
983.
Land-subsidence prediction depends on an appropriate subsidence model and the calibration of its parameter values. A modified inverse procedure is developed and applied to calibrate five parameters in a compacting confined aquifer system using records of field data from vertical extensometers and corresponding hydrographs. The inverse procedure of COMPAC (InvCOMPAC) has been used in the past for calibrating vertical hydraulic conductivity of the aquitards, nonrecoverable and recoverable skeletal specific storages of the aquitards, skeletal specific storage of the aquifers, and initial preconsolidation stress within the aquitards. InvCOMPAC is modified to increase robustness in this study. There are two main differences in the modified InvCOMPAC model (MInvCOMPAC). One is that field data are smoothed before diagram analysis to reduce local oscillation of data and remove abnormal data points. A robust locally weighted regression method is applied to smooth the field data. The other difference is that the Newton-Raphson method, with a variable scale factor, is used to conduct the computer-based inverse adjustment procedure. MInvCOMPAC is then applied to calibrate parameters in a land subsidence model of Shanghai, China. Five parameters of aquifers and aquitards at 15 multiple-extensometer sites are calibrated. Vertical deformation of sedimentary layers can be predicted by the one-dimensional COMPAC model with these calibrated parameters at extensometer sites. These calibrated parameters could also serve as good initial values for parameters of three-dimensional regional land subsidence models of Shanghai. 相似文献
984.
Tian Xia Wenbin Wu Qingbo Zhou Peter H. Verburg Qiangyi Yu Peng Yang Liming Ye 《地理学报(英文版)》2016,26(2):171-187
985.
针对CINRAD/CD无机内测试信号的疑难故障案例,介绍如何借助大型电子设备规范化维修的理念和方法,结合雷达系统原理和信号流程,综合运用原理分析法、越级法、测量法、代替法等故障诊断方法进行分析与判断,逐步缩小故障排查范围,从而达到快速定位及排除故障的目的。最终确定该故障是由于接收与监控分机间的信号线断开,造成控制码没有送至微波组件内单刀双掷微波开关所导致的。文中提供了该类型故障的规范化维修流程,其诊断方法和思路可广泛应用于CINRAD技术保障工作中。 相似文献
986.
987.
988.
M.Ya. Marov V.S. Avduevsky N.F. Borodin A.P. Ekonomov V.V. Kerzhanovich V.P. Lysov B.Ye. Moshkin M.K. Rozhdestvensky O.L. Ryabov 《Icarus》1973,20(4):407-421
The Venera 8 descent module measured pressure, temperature, winds and illumination as a function of altitude in its landing on July 22, 1972, just beyond the terminator in the illuminated hemisphere of Venus. The surface temperature and pressure is 741 ± 7°K and 93 ± 1.5kgcm?2, consistent with early Venera observations and showing either no diurnal variation or insignificant diurnal variation in temperature and pressure in the vicinity of the morning terminator. The atmosphere is adiabatic down to the surface. The horizontal wind speed is low near the surface, about 35m/sec between 20 and 40km altitude, and increasing rapidly above 48km altitude to 100–140m/sec, consistent with the 4-day retrograde rotation of the ultraviolet clouds. The illumination at the center of the day hemisphere of Venus is calculated to be about 1% of the solar flux at the top of the atmosphere, consistent with greenhouse models and high enough to permit photography of the Venus surface by future missions. The attenuation below 35km altitude is explained by Rayleigh scattering with no atmospheric aerosols; above 35km there must be substantial extinction of incident light. 相似文献
989.
厦门及其邻近地区的地震活动 总被引:1,自引:1,他引:1
本文通过对厦门及其邻近地区历史地震和现今小震活动的研究,讨论了厦门可能遭受地震的危险性和厦门周围4个地震潜在震源区。文中用地震复发周期的方法求得今后100a内泉州-汕头地震带可能发生的重大地震震级为6.4,7级震的复发周期约360a。 相似文献
990.
稀释技术^14C测年可靠性的研究 总被引:1,自引:0,他引:1
稀释技术~(14)C测年的关键在于本底气的稳定,稀释技术测定的最大年限取决于样品的含碳量。同一样品无机碳部分和有机碳部分的对比实验和不同测年方法的对比实验,都证明稀释技术测定的~(14)C年龄不但复现性好而且可靠。 相似文献