Estimation of wind erosion rates by using 137Cs tracing technique: A case study in Tariat-Xilin Gol transect, Mongolian Plateau

Wind erosion is one of the major environmental problems in semi-arid and arid regions. Here we established the Tariat-Xilin Gol transect from northwest to southeast across the Mongolian Plateau, and selected seven sampling sites along the transect. We then estimated the soil wind erosion rates by using the 137Cs tracing technique and examined their spatial dynamics. Our results showed that the 137Cs inventories of sampling sites ranged from 265.63=44.91 to 1279.54=166.53 Bq. m-2, and the wind erosion rates varied from 64.58 to 419.63 t. km-2. a-~ accordingly. In the Mongolia section of the transect （from Tariat to Sainshand）, the wind erosion rate increased gradually with vegetation type and climatic regimes; the wind erosion process was controlled by physical factors such as annual precipitation and vegetation coverage, etc., and the impact of human activities was negligible. While in the China section of the transect （Inner Mongolia）, the wind erosion rates of Xilin Hot and Zhengxiangbai Banner were thrice as much as those of Bayannur of Mongolia, although these three sites were all dominated by typical steppe. Besides the physical factors, higher population density and livestock carrying level should be responsible for the higher wind erosion rates in these two regions of Inner Mongolia.     

Using 137Cs tracing technique to estimate wind erosion rates in the typical steppe region,northern Mongolian Plateau

Wind erosion is one of the major factors of land degradation in the typical steppe region, northern Mongolian Plateau. Using ^137Cs tracing technique, we estimated the wind erosion rates of different pastures and abandoned farmland at Bayannur and Karakorum in Mongolia. The pastures and cutting grassland at Bayannur were slightly eroded by wind, with the rates of 64.58-169.07 t·km^-2.a^-1. The abandoned farmland in Karakorum, however, was strongly eroded by wind, with annual surface soil loss of 4.05 mm. a^-1, and wind erosion rates up to 6723.06 t· km^-2. a^-1. The total loss of surface soil due to wind erosion has been 17.4 cm since the cultivation of the steppe land in the 1960s. The wind ero- sion rate at the abandoned farmland was much higher than that at the typical steppe sites, showing that the cultivation led to serious wind erosion in the typical steppe region, northern Mongolian Plateau. By contrast, traditional livestock grazing resulted in less disturbance to the surface soil, and did not induce to devastating wind erosion, which plays an important role in maintaining the stability of the steppe ecosystem in the northern Mongolian Plateau.     

基于泄流响应的高拱坝振源时域识别

高坝泄流诱发坝体振动的振源识别一直是水利界所关注的课题之一．在小波理论、结构动力学及随机振动理论的基础上,提出了基于小坡正交算子变换的多振源反分析方法,并结合水工结构的特点,探讨了进行振源识别时所需注意的关键技术问题．以拉西瓦拱坝水弹性模型为研究对象,通过少量测点的动位移实测值,反分析各等效激励荷载时程,进而对拉西瓦拱坝的流激振动进行全面评估,为拱坝结构的动态监测和损伤诊断提供了基础．     

黄河的综合治理方略

黄河是我国第二长河,为西北和华北地区提供了丰富的水资源、黄河灾害频繁,是世界上最难治理的河流．经过几千年的治理,黄河已经成了一条人工控制的河流．然而,黄河仍然面临侵蚀严重、河床不稳定、水体污染以及生态脆弱等诸多问题．笔者依据河流综合治理的原则,为达到“维持黄河健康生命”的目标,提出了控制沟道下切、增阻降速、建设通河湖泊湿地和控制点源污染等综合治理方略、     

三次混合Bézier类曲线

提出由多项式基底和有理函数基底构造出混合Bézier函数类的思想,由此定义了混合Bézier类曲线.并研究了一种实用的三次混合Bézier类曲线,同时给出由三次混合Bézier类曲线表示圆弧的实例.与Bézier曲线和有理Bézier分别相比较,三次混合Bézier曲线可以表示圆弧且计算较为简单.     

分断电弧燃弧时间研究

电弧是造成高、低压开关电器触头故障的主要因素,本文主要从电弧的产生过程和产生原因出发,分析总结了热效应、电流、电压、分断速度等因素对金属相电弧和气相电弧燃弧时间的影响规律。     

Dynamic study on water stability of soil structure and soil characteristics of several types of soils in southwest China

Three suborder soils in southwest China were adopted, namely Ustic Vertisol, Stagnic Anthrosol and Ustic Ferrosol, so as to carry out the basic physical and chemical analysis respectively, to design a dynamic measuring method for water stability of soil structure and conduct the comparative study on the quality of the soil structure. The results indicated that （1） The water stability dynamic characteristic of the soil structure could well reflect the maintaining capability of the soil structure as time goes on. （2） The quality of several soil structures in southwest China was sequenced as follows： Stagnic Anthrosols 〉 Ustic Vertisols 〉 Ustic Ferrosols. （3） The water stability of soil structure is very positively correlated with the capillary porosity and the clay particle （D 〈 0.002 mm） content （Co）, but is very negatively correlated with the silt （D is 0.05-0.002 ram） content （Csc）, and （4） The dynamic functional equation of the water stability of soil structure in southwest China was established, so that the water stability characteristics of various soil structures could be quantitatively expressed and the quality of different soil structures can be quantitatively compared from each other.     

西藏高原当前生态环境问题的初步研究

文章从西藏高原的各种侵蚀类型分别阐述其所带来的相应的生态问题以及形成的原因。西藏高原由于地理条件的特殊性,它的生态问题也拥有自己的特点：脆弱性、难恢复性。在制定保护措施、恢复方法方面还要具有针对性,同时,要考虑到人们的行为在此过程中所扮演的角色。     

基于磁控电弧传感的焊缝偏差信息检测与实时跟踪系统

将磁场控制电弧技术应用于焊缝跟踪,利用磁场作用电弧使电弧摆动来扫描焊缝,通过检测焊接电流的变化规律来检测焊缝的偏差信息,设计了一套焊缝跟踪系统,该焊接系统即为跟踪系统,大大提高了跟踪的实时性.在信号处理方面,采用硬件滤波和软件处理相结合的方式,取得了较好的效果.在跟踪策略上,分别分析了横向和高低偏差的处理方法.通过实际的焊缝跟踪试验,验证了磁控电弧传感具有良好的工作特性和整个跟踪系统的有效性.     

一种弧焊机器人熔池图像的快速标定方法

为了获得弧焊机器人焊接过程中熔池的几何尺寸,须在焊接过程中采用摄像机采集熔池图像,并完成系统的标定.将摄像机模型考虑为理想针孔透视模型,采用固定角度和高度对熔池图像进行采集,使标定模型参数缩减至8个,和传统标定方法相比,大大降低了计算量.采用同一平面4个目标点进行了系统标定和实验,理论和实际熔宽平均误差为0.031 mm,因此应用该方法对弧焊机器人熔池图像进行标定是可行的.