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31.
This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
32.
科技进步是测绘事业发展的动力 ,讨论运用科技进步的评价指标 ,对测绘单位的科技进步速度和对经济增长的贡献等进行测算和分析 ,可以为测绘规划管理及决策提供参考。 相似文献
33.
The sand–loess transition zone in north China is sensitive to climate change, and is an ideal place to investigate past environmental changes. However, past climate change at millennial–centennial timescales in this region has not been well reconstructed because of limited numerical dating. Alternations of sandy loam soils with aeolian sand layers in the Mu Us and Otindag sand fields, which lie along the sand–loess transition zone, indicate multiple intervals of dune activity and stability. This change is probably a response to variations of the East Asian monsoon climate during the late Quaternary. The single aliquot regeneration (SAR) optically stimulated luminescence (OSL) dating protocol, which has been successfully applied to aeolian deposits worldwide, is applied to these two sand fields in this study. The OSL ages provide reliable constraints for reconstruction of past climate changes at suborbital timescale. Sections in both sand fields contain aeolian sand beds recording millennial‐scale episodes of dry climate and widespread dune activation, including episodes at about the same time as Heinrich Event 5 and the Younger Dryas in the North Atlantic region. These results demonstrate the potential of aeolian sediments in semi‐arid north China to record millennial‐scale climatic events, and also suggest that dry–wet climate variation at the desert margin in China may be linked to climatic change elsewhere in the Northern Hemisphere, through atmospheric circulation. This article was published online on 27 November 2008. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected (16 December 2008). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
34.
Afforestation has been suggested as a means of improving soil and water conservation in north‐western China, especially on the Loess Plateau. Understanding of the hydrological responses to afforestation will help us develop sustainable watershed management strategies. A study was conducted during the period of 1956 to 1980 to evaluate runoff responses to afforestation in a watershed on the Loess Plateau with an area of 1·15 km2, using a paired watershed approach. Deciduous trees, including locust (locusta L.), apricot (praecox L.) and elm (ulmus L.), were planted on about 80% of a treated watershed, while a natural grassland watershed remained unchanged. It was estimated that cumulative runoff yield in the treated watershed was reduced by 32% as a result of afforestation. A significant trend was also observed that shows annual runoff reduction increases with the age of the trees planted. Reduction in monthly runoff occurred mainly from June to September, which was ascribed to greater rainfall and utilization by trees during this period. Afforestation also resulted in reduction in the volume and peak flow of storm runoff events in the treated watershed with greater reduction in peak flow. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
35.
自1988年11月至1989年3月,对南极乔治王岛的长城湾沿岸水域中的海洋生物和环境因子进行了调查,1988年11月20日在2号站采得的冰芯中部有一层约5cm的棕色层,而1988年11月17日、20日和26日在5号站采得的冰芯样中有二层棕色层。固定冰中叶绿素a浓度范围在2.55~56.8mg/m~3之间,而且大部分含量集中在海冰的中间层中,而不象其它海区如昭和、戴维斯、凯西和麦克默多等站,大部分叶绿素a集中在海冰的底部,造成这种差别的原因、可能是由于海冰的结构和形成过程不同所致。 相似文献
36.
Based on the Germany Koldwey Station's 1994-2003 conventional observation hourly data, this paper conducts a statistical analysis on the short-term climate characteristics for an arctic tundra region (Ny-(A)lesund island) where our first arctic expedition station (Huanghe Station) was located. Affected by the North Atlantic warming current, this area has a humid temperate climate, and the air temperature at Ny-(A)lesund rose above 0 ℃ even during deep winter season during our research period. The wind speed in this area was low and appeared most at southeast direction. We find that the temperature at Ny-(A)lesund rose in the faster rate (0.68 ℃/10 a) than those at the whole Arctic area. Compared with the floating ices where our expedition conducted in the Arctic, Ny-(A)lesund was warmer and more humid and had lower wind speed. Comparison of the near surface air temperature derived by NCEP/NCAR reanalysis to the conventional measurements conducted at the Koldwey site in Ny-(A)lesund area shows a good agreement for winter season and a significant difference for summer season. 相似文献
37.
38.
利用 2 0 2个太阳附近疏散星团的视向速度和自行观测资料 ,对太阳的运动和银河系的运动学参数进行了研究。其中 ,距离在 0 .5kpc到 2kpc之间的 12 8个疏散星团对平均太阳运动分量的解算结果是 (u0 ,v0 ,w0 ) =(- 13.8± 1.4 ,- 5 .0± 1.6 ,- 11.6± 2 .9)km/s ;Oort常数和银河系径向运动参数的解算结果分别为 (A ,B) =(16 .9± 1.1,- 11.6± 2 .6 )km·s- 1·kpc- 1及 (C ,D) =(2 .5± 1.1,- 2 .1± 0 .9)km·s- 1·kpc- 1。 相似文献
39.
CygX—1硬态高能光子的时延 总被引:1,自引:1,他引:0
硬X射线和软射线光子的时延时研究主能辐射的一个重要方面,傅里叶交叉谱常常被用于教育处硬软光子之间的时延,但是交叉说示能在高于30Hz的傅里叶频率上从CygX-1测量到有统计意义的快速光变,由李惕培在时域上发展的交叉相关函方法能有效测量不同时间尺度上的时延,利用此交叉相关分析方法,讨论了不同观测时期CygX-1硬态高能光子时延 的性质,分析结果表明,CygX-1硬态在短的尺度(<0.1秒)上存存在有意义的时间延迟,并将短时间尺度上的观测结果和各种CygX-1硬态模型进行了比较讨论。 相似文献
40.
利用上海天文台的照相底片资料,确定了疏散星团NGC6530天区364颗恒星的自行和成员概率,并对有关自行测定的方法、结果和精度等问题作了较为详细的介绍和讨论。使用的底片历元差为87年,全部恒星自行中误差的均方根值为1.09mas/a。 相似文献