Differences Between Mode I and Mode II Crack Propagation

Although mode I and mode II crack propagation show many similarities, in particular when analysed by linear elastic fracture mechanics, they differ significantly in the micro-structural behaviour. These differences, which are clearly noticeable in the fracture surface morphology, lead to fundamental differences in the macroscopic behaviour. Thus, mode II crack expansion under remote loading, appears to obey micro-structural scaling laws, implying that the dimensions of the process region stay essentially constant during crack expansion, rather than increasing with crack length. Therefore, expanding mode II cracks can almost reach the Rayleigh velocity, and actually also intersonic velocities. An expanding mode I crack, on the other hand, seems to obey continuum scaling laws, implying that the dimensions of the process region increase in proportion to crack length, leading to self-similar crack expansion at a velocity significantly below the Rayleigh speed and dependent on the remote load.     

Spectral scaling in Mars topography: effect of craters

Extensive computer simulations aimed at testing a hypothesis that impact craters may explain the scaling behaviour of surface spectra are presented. The simulations show that indeed crater effects alone may explain the spectral scaling of Mars’ topography revealed from MOLA data. The range of the scaling exponents obtained for a wide range of simulation parameters does not exceed the limits observed for Mars. The simulations suggest that the shape of large craters is the key factor leading to the two scaling ranges in the surface spectra. Particular values of the scaling exponents may additionally depend on the depth-diameter relationship and the crater size distribution.     

玛纳斯河流域雷暴气候特征及防雷应用

选取玛纳斯河流域中上游和中下游4个气象站1970—2005年的雷暴气候资料进行统计分析,总结出玛纳斯河流域雷暴活动的气候特征,并根据其活动规律提出防御雷电灾害的几项事宜。     

环境污染及保护对策

环境保护中一个非常重要的工作,是广泛深入地开展环境地质工作。在赣南、江西乃至全国,环境地质工作的主要内容是防治水土流失,严禁废渣、废水随意排放,控制人口激增,保护有限耕地;为保护生态平衡,必须加强环境立法与执法,提高环境保护的重要性和必要性的认识,大规模切实地保护耕地,因地制宜植树造林。     

Observed winds,turbulence, and dispersion in built-up downtown areas of Oklahoma City and Manhattan

Wind and tracer data from the Oklahoma City Joint Urban 2003 (JU2003) and the Manhattan Madison Square Garden 2005 (MSG05) urban field experiments are being analyzed to aid in understanding air flow and dispersion near street-level in built-up downtown areas. The mean winds are separately calculated for groups of anemometers having similar exposures such as “near street level” and “on building top”. Several general results are found, such as the scalar wind speed at street level is about 1/3 of that at building top. Turbulent standard deviations of wind speed components and temperature, and vertical fluxes of momentum and sensible heat, are calculated from sonic anemometers near street level at 20 locations in JU2003 and five locations in MSG05, and from two rooftop locations in MSG05. The turbulence observations are consistent with observations in the literature at other cities, although the JU2003 and MSG05 data are unique in that many data are available near street level. For example, it is found that the local (i.e., at the measuring height) averages about 1.5 and the local averages about 0.25 in the two cities, where is the standard deviation of vertical velocity fluctuations, is the friction velocity, and u is the wind speed. The ratio of temperature fluctuations to temperature scale, , averages about −3 in both cities, consistent with similarity theory for slightly unstable conditions, where is the standard deviation of temperature fluctuations, and is the temperature scale. The calculated Obukhov length, L, is also consistent with slightly unstable conditions near street level, even at night during JU2003. The SF₆ tracer concentration observations from JU2003 are analyzed. Values of for the continuous releases are calculated for each release and arc distance, where is the 30-min average arc maximum concentration, Q is the continuous source emission rate, and u is the spatial-averaged wind speed in the downtown area. The basic characteristics of the JU2003 plot of averaged agree reasonably well with similar plots for other urban experiments in Salt Lake City and London (i.e., at . A is found to be about 3 during the day and about 10 during the night.     

A Numerical Verification of Self-Similar Multiplicative Theory for Small-Scale Atmospheric Turbulent Convection

The self-similar multiplicative theory（SSM theory）, aims to interpret the scaling behavior of the temperature structure function. In the present paper, the author report results from a numerical simulation of atmospheric turbulent convection in order to verify this theory. The simulation was based on a shell model which was deduced from simplified atmospheric convection equations. The numerical results agreed well with the theory prediction of scaling law from the first order to the eighth order. They also showed that the prediction of this theory was better than that given by the Kolmogorov＇s theory in 1941, log-normal, and β model theories.     

山西吕梁山北段中生代构造特征及对成矿的制约

为进一步研究山西吕梁山北段中生代构造特征及对成矿的制约,利用数字化填图方法,在偏关县一带开展1:25万区域地质调查。发现几条中生代大型构造带,查明了这些大型构造带的空间展布、性质、断裂组合及运动学特征; 证实了中生代为该区重要的多金属成矿期,成矿作用尽管与中生代岩浆活动关系密切,但在空间上分布受NE向隐伏构造的制约; 大型挠褶构造是地壳强烈隆升的标志,区内大型构造带多数是在挠褶构造的基础上叠加断层而形成的。该研究对于探讨山西中—新生代构造的演化发展具有重要意义。     

连续小波变换识别位场场源法的噪声影响分析与尺度因子的选择

为提高连续小波变换识别位场场源准确度,研究噪声对场源识别结果的影响和尺度因子优选方法问题。根据连续小波变换识别位场场源的基本原理,用该方法对不同噪声水平的合成数据进行场源识别,分析噪声对于场源识别结果的影响,研究小波变换的尺度因子对噪声压制的效果,讨论连续小波变换进行场源识别时尺度因子的选取方法。理论模型和实测资料场源识别结果表明,噪声会降低连续小波变换场源识别结果的准确度,笔者提出的尺度因子优选方法能有效压制噪声干扰,提高场源识别结果的准确度。     

辽宁水泉金矿成矿规律及矿山远景评价

用综合信息矿产资源定量预测的理论和方法，系统研究了辽宁水泉金矿成矿规律及控矿因素，特别是对控矿构造特征作了深入的研究，并建立了研究区的综合信息找矿模型。对水泉金矿的区域成矿远景和深部成矿远景进行了综合预测。