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151.
In this paper, the response of a visco-elastic half-space subjected to moving loads with static and dynamic components is investigated. Four types of vehicle loads are considered, including the moving point load, uniformly distributed wheel load, elastically distributed wheel load, and a train load simulated as a sequence of elastically distributed wheel loads. In each case, the influence of the moving loads traveling in the subsonic, transonic and supersonic ranges on the dynamic responses of the half-space is studied. The parametric study conducted herein enables us to grasp insight into the mechanism of wave propagation for a visco-elastic half-space under moving loads. 相似文献
152.
VARIABILITY OF AEROSOL OPTICAL PROPERTIES OVER HEFEI DURING SEPTEMBER 1993 TO SEPTEMBER 1994 总被引:7,自引:0,他引:7 下载免费PDF全文
An 8-wavelength sun-photometer has been operated at Hefei (31.31°N, 117.17°E) to monitoroptical properties of atmospheric aerosols. Altogether 133 solar spectral extinction data were ob-tained on clear days during the period from September 1993 through September 1994, In this pa-per, the feature of the sun-photometer is briefly described. A relative aureole method is intro-duced. which can be used to monitor temporal evolution of aerosol loading during the sun-pho-tometer calibration period. Temporal variabilities of spectral aerosol optical depths and Angstromturbidity parameters are presented. Relation of these variabilities with synoptic and local meteoro-logical conditions are analyzed and discussed, From measured spectral aerosol optical depths undersome representative atmospheric conditions, columnar aerosol size distributions have been retrievedby a linearly constrained inversion method. These typical columnar aerosol size distributions are al-so presented and discussed. 相似文献
153.
考虑湿度影响的城市气溶胶夜晚温度效应 总被引:10,自引:0,他引:10
本文利用一维非定常模式,研究了城市上空干、湿气溶胶粒子对夜间边界层温度的影响。结果表明,湿气溶胶粒子对低层大气有明显的升温作用,而对中上层大气则起降温作用,同时改变了贴地逆温层结构和边界层稳定度。 相似文献
154.
大气臭氧与气溶胶垂直分布的高空气球探测 总被引:17,自引:2,他引:17
本文给出了1993年9月12日利用高空科学气球在河北省香河地区探测到的大气臭氧和气溶胶的垂直分布。结果发现:(1) 大气臭氧的数密度在整个对流层较低(~10[12]mol/cm3),并从地面到对流层顶略有下降;对流层顶以上开始快速增加,极值层高度在~24 km,其值为4.78×10[12]mol/cm3;臭氧分压有类似的分布特征,极值146×10[-4]Pa,位于同一高度;(2) 在平流层低层,臭氧分压有一个次极值62×10[-4]Pa,位于15~16 km;(3) 0~30 km大气气溶胶数密度呈现出三个峰值:143,8和1.1 个/cm[3],分别位于近地面、5 km和21 km;(4)气溶胶的数密度谱在对流层为双模态;在平流层,次峰消失。同时,我们还与其他观测结果作了比较分析。 相似文献
155.
云南普洱地区6级以上地震前的Y值异常特征 总被引:1,自引:0,他引:1
本利用加卸载响应比方法研究了云南省普洱地区ML6.0级以上地震前的加卸载响应比随时间的变化,计算了这个地区近期的加卸载响应比,结果显示,普洱地区6级以上地震前Y值出现明显异常,近期的Y值显异常,表明该地区或在以其为中心方圆100-200公里的区域内在1995年或稍长时间内发生6.0级以上的地震的可能性很大。 相似文献
156.
In this paper the researches made in 1981-1990 have identified that the annual soil loss in the Three Gorges region is 157 million t. and the annual incoming sediment load of the Three Gorges reservoir is 40 million t. Soil erosion increases with the destruction of vegetative cover and its subsequent evolution. The annual amounts of sediment erosion for forest land, shrub land, grassland and farmland make up respectively 6.19%, 10.76%, 23.05% and 60% of the total erosion of the Three Gorges region; the quantities of incoming sediment load to the Yangtze River from the above four types of land account for 5.95%, 12.42%, 35.46% and 46.1 % of the total amount of sediment transported to the reservoir. The farmland of offers the main source of sediment. Gravitational erosion produces more bed loads, which will present serious threat to the Three Gorges Project if entering the reservoir. Resettlement of people to the upper parts of the mountainous areas for agricultural production will increase the sediment yield of the Three Gorges region by 10-20 million t and increase the incoming sediment of the Yangtze River by 50-60 million t. Consequently, it is necessary to make a realistic assessment of the soil erosion in the Three Gorges region. 相似文献
157.
火山气溶胶的辐射影响 总被引:2,自引:1,他引:2
本文应用辐射传输计算研究了火山气溶胶,特别是大的火山爆发后短时期及火山周围地区内的火山气溶胶,对到达地面的向下的总的太阳辐射通量、行星反照率及大气加热率的可能影响. 相似文献
158.
Roger A. Kuhnle 《地球表面变化过程与地形》1992,17(2):191-197
Bed load transport rates were measured with continuously recording pit samplers on two small gravel-bed streams in the Goodwin Creek Research Watershed, northern Mississippi, U.S.A. When transport samples were grouped according to whether the stage was rising or falling, significant differences in mean bed load transport rates were found at nearly all flow strengths. At higher flow strengths, mean bed load transport rates were greater during rising stages than during falling stages. The greater transport rates measured during rising stages may be caused by a lag in the formation and destruction of bed roughness elements. One of the streams also showed evidence for greater transport rates for low flows as the stage declined. This may be caused by differences in the stability of the bed material at the beginning and at the end of a transport event. 相似文献
159.
160.
ABSTRACTTo assess seasonal patterns of suspended sediment load and its erosion–transport interactions, 17 years of river monitoring data from the Isser River Basin (northwest Algeria) were studied, considering continuous and event-scale approaches. The results show significant differences in sediment yield and transport processes between dry and wet periods. A rate of 8 t ha?1 year?1 was estimated from continuous analysis, with values of 4.3 and 13 t ha?1 year?1 for wet and dry periods, respectively. Estimates of soil delivery ratio pointed to higher values during dry periods and the dominance of hillslope erosion processes. At the event scale, the hysteresis loops confirmed these seasonal patterns in transport dynamics. The calibration of the MUSLE model highlighted the severity of rainfall during the dry period. These results emphasize the importance of seasonality in erosion and transport processes with special relevance in terms of climate change predictions. 相似文献