弹性波CT技术在大足石刻岩体破碎带探测中的应用

大足石刻是中国现存的重要石质文物之一,具有重要的历史和文化价值,其中有的石刻造像曾被列为国家石质文物保护“一号工程”;最近,文物保护部门又启动了对危岩体的加固和防渗工程。为确定大足石刻宝顶山大佛湾岩体中破碎带发育情况,应用跨孔弹性波CT技术对指定位置的工程岩体进行了探测。CT探测得到的岩体弹性波速成像清楚地揭示了两个钻孔之间岩体中破碎带的规模和产状,与岩体所在的区域地质构造应力场作用协调一致,证明了探测成像结果的可靠性,为大佛湾岩体的渗流和稳定性评估提供了依据。     

Probabilistic approach for active control of structures: experimental verification

In our previous study (Earthquake Engineering and Structural Dynamics 2003; 32 :2301), we have developed a probabilistic algorithm for active control of structures. In the probabilistic control algorithm, the control force is determined by the probability that the structural energy exceeds a specified target critical energy, and the direction of a control force is determined by the Lyapunov controller design method. In this paper, an experimental verification of the proposed probabilistic control algorithm is presented. A three‐story test structure equipped with an active mass driver (AMD) has been used. The effectiveness of the control algorithm has been examined by exciting the test structure using a sinusoidal signal, a scaled El Centro earthquake and a broadband Gaussian white noise; and, especially, experiments on control have been performed under different conditions to that of system identification in order to prove the stability and robustness of the proposed control algorithm. The experimental results indicate that the probabilistic control algorithm can achieve a significant response reduction under various types of ground excitations even when the modeling error exists. Copyright © 2004 John Wiley & Sons, Ltd.     

2010年民勤沙地近地面沙尘气溶胶浓度特征

为了更好地研究沙尘气溶胶起沙和输送特征,2010年4—5月,在民勤周边沙地利用EZ LIDAR ALS300&ALS450型激光雷达和 GRIMM 180型颗粒物采样器进行了大气气溶胶的外场连续观测,取得了晴天、浮尘、扬沙和沙尘暴天气条件下沙尘气溶胶总后向散射垂直剖面图和PM₁₀、PM_2.5、PM_1.0质量浓度采样资料,其中包含“0424”特强沙尘暴过程资料。结果表明：春季民勤近地层大气中沙尘气溶胶浓度较高,且随气象要素的变化很大;在整个观测期内,PM₁₀、PM_2.5、PM_1.0的平均质量浓度分别为202.3、57.4 μg/m³、16.7 μg/m³。在不同天气条件下,PM₁₀、PM_2.5、PM_1.0质量浓度的变化有很好的相关性,但变化趋势有所不同。在沙尘暴天气条件下,PM₁₀的日平均质量浓度高达2469.1μg/m³,是背景天气条件下PM10日平均质量浓度的100多倍,是浮尘天气条件下PM10日平均质量浓度的8倍,是扬沙天气条件下PM₁₀日平均质量浓度的2倍。PM_2.5在沙尘暴天气下日平均质量浓度为460.3 μg/m³,是背景天气条件下PM_2.5日平均质量浓度的45倍,是浮尘天气条件下PM_2.5日平均质量浓度的6倍,是扬沙天气条件下PM_2.5日平均质量浓度的1.4倍。PM_1.0在沙尘暴天气条件下的日平均浓度为92.7 μg/m³,是背景天气条件下PM_1.0日平均浓度的13倍,是浮尘天气条件下PM_1.0日平均浓度的7倍,是扬沙天气条件下PM_1.0日平均浓度的1.3倍。可见,风速增大时沙尘粒子浓度的增加对粒子粒径是有选择的,小粒子比重随沙尘浓度增加而相对减小,大粒子比重随沙尘浓度增加而相对增多;通过对“0424”特强沙尘暴过程的研究表明,一次沙尘暴过程往往包括沙尘暴、扬沙和浮尘天气中的两种类型;通过对激光雷达数据分析发现,在强沙尘暴发生过程当中,民勤沙地发生了非常严重的风蚀起沙现象。     

Estimation of PM_(2.5) Mass Concentration from Visibility

Aerosols in the atmosphere not only degrade visibility, but are also detrimental to human health and transportation. In order to develop a method to estimate PM_2.5 mass concentration from the widely measured visibility, a field campaign was conducted in Southwest China in January 2019. Visibility, ambient relative humidity(RH), PM_2.5 mass concentrations and scattering coefficients of dry particles were measured. During the campaign, two pollution episodes, i.e., from 4-9 Ja...     

关于结构振型参与系数和振型贡献的分析

采用振型分解反应谱法求解多自由度弹性体系的地震反应时,为了在满足所需计算精度的前提下减少工作量,需要对振型数量进行合理的选择,而振型数的确定主要取决于结构各阶振型对总体反应的贡献。通过数学推导,对振型贡献及振型数量的选择问题进行了研究。首先,讨论了振型参与系数的性质,在此基础上给出了能够反映结构振型贡献参数的数学表达式,对这些参数的力学含义进行了解释,并给出了相关证明;其次,对有效质量法、振型位移控制法等基于不同振型贡献标准的确定振型数的方法进行了分析比较,指出了其合理性和不足。本文研究对进一步理解结构振型贡献和振型数的选择问题具有一定的理论意义。     

岩体变形模量的尺寸效应

岩土工程中,现场岩体的承压板试验和变形试验可看作是不同尺寸岩体的变形试验。在某工程的现场岩石力学试验中,对同一组试点的岩体先后进行了承压板变形试验和承载力试验,研究了岩体变形模量的尺寸效应,结果表明,岩体变形模量主要受岩体中的裂隙发育状况控制,当岩体质量较好时,可以由承载力试验曲线来确定岩体的变形特性,这一做法具有一举两得的效果。     

测定堆石体密度的附加质量法理论分析研究

附加质量法是一种新兴的堆石体密度检测方法,它具有方便、无损等优点,近年来有较为广泛的应用,但该方法的应用效果会受到震源、雨水、双峰频谱等因素的影响.本文则考虑堆石体系统振动的阻尼因素,以及附加质量块与堆石体之间的非刚性连接,分别基于质弹阻模型以及双自由度-质弹阻模型对这些因素的影响进行了理论分析.结果表明,质弹阻模型可以解释主频随震源频率和雨水而变化的现象;而双自由度-质弹阻模型则可以解释主频随质量块偏移距和触地面积而变化的现象.在此基础上,本文对附加质量法的测试过程提出了几点改进建议.     

松动岩体工程特性研究——以雅砻江楞古水电站松动岩体为例

为了对松动岩体的工程特性进行系统研究,以楞古水电站厂址区边坡为例,对该边坡岩体进行了详细的地质编录和物理勘探试验,重点对节理裂隙的空间发育规律、镶嵌结构和碎裂结构岩体的发育深度及空间分布、软弱结构面发育分布规律以及边坡已有变形破坏特征这四个方面进行了系统的统计和分析,认为松动岩体是区域断裂活动和浅表生改造的结果,岩体工程效应差、变形模量低;同时结合应力测试、声波测速、高密度电磁勘探等试验成果进行分析,结果显示松动岩体具低波速（波速大部分小于3 000 m/s）、低应力（最大主应力不超过20 MPa）、强透水性（透水性系数大于10 L/（min·m·m））。认为岩体破碎主要受断层及节理裂隙影响,分析了岩体破裂松动的演化过程及特征。     

Analysis of Difference Between Direct and Geodetic Mass Balance Measurements at South Cascade Glacier, Washington

Net mass balance has been measured since 1958 at South Cascade Glacier using the 'direct method,' e.g. area averages of snow gain and firn and ice loss at stakes. Analysis of cartographic vertical photography has allowed measurement of mass balance using the 'geodetic method' in 1970, 1975, 1977, 1979–80, and 1985–97. Water equivalent change as measured by these nearly independent methods should give similar results. During 1970–97, the direct method shows a cumulative balance of about −15 m, and the geodetic method shows a cumulative balance of about −22 m. The deviation between the two methods is fairly consistent, suggesting no gross errors in either, but rather a cumulative systematic error. It is suspected that the cumulative error is in the direct method because the geodetic method is based on a non-changing reference, the bedrock control, whereas the direct method is measured with reference to only the previous year's summer surface. Possible sources of mass loss that are missing from the direct method are basal melt, internal melt, and ablation on crevasse walls. Possible systematic measurement errors include under-estimation of the density of lost material, sinking stakes, or poorly represented areas.     

Observations of hydrogen deficient binary Upsilon sagittarii

The absolute magnitudeM _v of the hydrogen deficient binary υ Sgr has been estimated as -4.8 ± 1.0 from the distribution of the interstellar reddening, polarization and interstellar lines of the surrounding stars. From the ANS observations obtained at the time of the secondary eclipse, it appears that the hotter secondary is surrounded by a disc with colours of a B8-B9 star. The λ 1550 CIv absorption line arising in the stellar wind does not show any change in strength during the secondary minimum. The upper limit to the mass-loss rate from the high temperature wind is estimated as ≤ 5 × 10^-7 M⊙ yr^-1 from the 2 cm and 6 cm radio observations. Based on observations obtained with the Astronomical Netherlands Satellite and VLA. The National Radio Astronomy Observatory’s Very Large Array at Socorro, New Mexico is operated by Associated Universities Inc. under contract with the National Science Foundation.