屏障隔振系统失效机理的探讨          下载免费PDF全文

邱畅  高广运  岳中琦  谭国焕 《地震工程学报》2003,25(3):198-203

屏障隔振是一种用来阻碍或改变外围振波向受保护区(屏蔽区)传播的工程方法，由于其机理的探讨尚不深入，工程实践中常出现隔振系统失效的现象．本假设屏障是埋入土介质的中厚弹性板，采用薄层法分析了该弹性板在振波作用下的振动响应和屏蔽区内位移变化规律；研究了影响屏障隔振效果的主要参量；发现了使屏障隔振效率降低甚至失效的入射波全透射现象．结果表明柔性屏障易发生波的全透射，并指出了避免屏障失效的措施．  相似文献   

鄱阳湖组(第四系)的修订及特征   总被引：3，自引：0，他引：3  

马振兴  蒋玉珍  魏源  李均辉  李长安 《地层学杂志》2003,27(3):212-215

根据对鄱阳湖地区 Zk0 1钻孔柱状剖面的研究 ,对鄱阳湖组的定义进行修订、补充 ,认为鄱阳湖组为一套以青灰色淤泥质粘土、黄褐色粘土、粉质粉土为主夹少量粉砂或细砂的湖泊—河口三角洲相沉积。年代地层为第四系全新统 ,底界年龄约 6 2 10± 12 5 a B.P.,开阔湖泊沉积始于 32 4 0± 180 a B.P.,且由北向南时代渐新 ,具有明显的穿时性  相似文献   

An Efficient Numerical Method for Computing Synthetic Seismograms for a Layered Half-space with Sources and Receivers at Close or Same Depths   总被引：1，自引：0，他引：1  

H.-m. Zhang  X.-f. Chen  S. Chang 《Pure and Applied Geophysics》2003,160(3-4):467-486

— It is difficult to compute synthetic seismograms for a layered half-space with sources and receivers at close to or the same depths using the generalized R/T coefficient method (Kennett, 1983; Luco and Apsel, 1983; Yao and Harkrider, 1983; Chen, 1993), because the wavenumber integration converges very slowly. A semi-analytic method for accelerating the convergence, in which part of the integration is implemented analytically, was adopted by some authors (Apsel and Luco, 1983; Hisada, 1994, 1995). In this study, based on the principle of the Repeated Averaging Method (Dahlquist and Björck, 1974; Chang, 1988), we propose an alternative, efficient, numerical method, the peak-trough averaging method (PTAM), to overcome the difficulty mentioned above. Compared with the semi-analytic method, PTAM is not only much simpler mathematically and easier to implement in practice, but also more efficient. Using numerical examples, we illustrate the validity, accuracy and efficiency of the new method.  相似文献   

黄河岸边开采地下水对大堤稳定性影响的探讨     

张畅 《岩土力学》2003,(Z2)

随着郑州市城市化进程的飞速发展和规模的不断扩大,尤其是郑东新区的建设,需水量急剧增加。为缓解郑州市供水紧张状况,调整引黄水量与地下水开采量的比例,确保郑州供水安全,需在黄河岸边开采地下水,水源地开采后,地下水流场范围内水位将下降,地下水流场的改变对黄河堤防稳定性是否产生影响,对此进行了初步研究和探讨。研究结果表明,开采浅层地下水,不会对黄河大堤造成危害。  相似文献   

Structural, chemical, and isotopic microanalytical investigations of graphite from supernovae     

T.Kevin Croat  Thomas Bernatowicz  Scott Messenger 《Geochimica et cosmochimica acta》2003,67(24):4705-4725

We report the results of coordinated ion microprobe and transmission electron microscope (TEM) studies of presolar graphites from the KE3 separate (1.65-1.72 g/cm³) of the Murchison CM2 meteorite. Isotopic analysis of individual graphites (1-12 μm) with the ion microprobe shows many to have large ¹⁸O excesses combined with large silicon isotopic anomalies, indicative of a supernova (SN) origin. Transmission electron microscopy (TEM) of ultramicrotome slices of these SN graphites revealed a high abundance (25-2400 ppm) of internal titanium carbides (TiCs), with a single graphite in some cases containing hundreds of TiCs. Isotopic compositions of individual TiCs by nanoscale resolution secondary ion mass spectrometry (NanoSIMS) confirmed their presolar origin. In addition to TiCs, composite TiC/Fe grains (TiCs with attached iron-nickel subgrains) and solitary kamacite internal grains were found. In the composite grains, the attached iron phase (kamacite [0-24 at. % Ni] or taenite [up to 60 at. % Ni]) was epitaxially grown onto one or more TiC faces. In contrast to the denser Murchison KFC1 graphites, no Zr-Ti-Mo carbides were observed. The average TiC diameters were quite variable among the SN graphites, from 30 to 232 nm, and were generally independent of the host graphite size. TiC grain morphologies ranged from euhedral to anhedral, with the grain surfaces exhibiting variable degrees of corrosion, and sometimes partially amorphous rims (3 to 15 nm thick). Partially amorphous rims of similar thickness were also observed on some solitary kamacite grains. We speculate that the rims on the internal grains are most plausibly the result of atom bombardment caused by drift of grains with respect to the ambient gas, requiring relative outflow speeds ∼100 km/s (i.e., a few percent of the SN mass outflow speed).Energy dispersive X-ray spectrometry (EDXS) of TiCs revealed significant V in solid solution, with an average V/Ti ratio over all TiCs of ∼83% of the solar value of 0.122. Significant variations about the mean V/Ti ratio were also seen among TiCs in the same graphite, likely indicating chemical equilibration with the surrounding gas over a range of temperatures. In general, the diversity in internal TiC properties suggests that TiCs formed first and had substantially diverse histories before incorporation into the graphite, implying some degree of turbulent mixing in the SN outflows.In most graphites, there is a decrease in the number density of TiCs as a function of increasing radial dis- tance, caused by either preferential depletion of TiCs from the gas or an acceleration of graphite growth with decreasing ambient temperature. In several graphites, TiCs showed a trend of larger V/Ti ratios with increasing distance from the graphite center, an indication of progressive equilibration with the surrounding gas before they were sequestered in the graphites. In all but one graphite, no trend was seen in the TiC size vs. distance from the graphite center, implying that appreciable TiC growth had effectively stopped before the graphites formed, or else that graphite growth was rapid compared to TiC growth. Taken together, the chemical variations among internal grains as well as the presence of partially amorphous rims and epitaxial Fe phases on some TiCs clearly indicate that the phase condensation sequence was TiC, followed by the iron phases (only found in some graphites) and finally graphite. Since graphite typically condenses at a higher temperature than iron at low pressures (<10⁻³ bars) in a gas with C > O and otherwise solar composition, the observed condensation sequence implies a relative iron enrichment in the gas or greater supersaturation of graphite relative to iron.The TEM observations allow inferences to be made about the physical conditions in the gas from which the grains condensed. Given the TiC sizes and abundances, the gas was evidently quite dusty. From the observed TiC size range of ∼20 nm to ∼500 nm (assuming ∼1 yr growth time and T ∼ 1800°K), we infer minimum Ti number densities in the gas to be ∼7 × 10⁴ to ∼2 × 10⁶ atoms/cc, respectively. Although the gas composition is clearly not solar, for scale, these number densities would correspond to a pressure range of ∼0.2 μbar to ∼5.0 μbar in a gas of solar composition. They also correspond to minimum TiC grain number densities of ∼3 × 10⁻⁴ to ∼0.2 grains/cc, assuming complete condensation of Ti in TiC. We estimate the maximum ratio of mean TiC grain separation distance in the gas to grain diameter from the Ti number densities as ∼3 × 10⁵ to ∼1 × 10⁶.  相似文献   

由卫星和航空磁测成果推断中国岩石圈的磁性特征   总被引：11，自引：2，他引：11  

张昌达 《地球物理学进展》2003,18(1):103-110

根据前人所得卫星和航磁异常解释结果，作者的综合研究表明：(1)在塔里木、四川和松辽盒地，地壳呈强磁性，至少可分为两层，上层磁化强度为1A／m，下层为2A／m或更强一些。在上述盆地中央，地幔顶部约10km厚，也是强磁性的，此外，在南中国海，地壳和地幔顶部也是强磁性的，卫星磁异常的源位于上述部位。(2)西藏高原，中国东南沿海一带以及其他一些褶皱带之下，地壳是弱磁性的，磁性层在地表以下30km以内，磁化强度约0.66A/m。特别要指出的是，在东南沿海一带，磁性层底面和莫霍面重合，而居里等温面恰在莫霍面之下，因此这个带可能是Wasilewsky PJ等提出的“莫霍面是一个磁性界面”的一例。  相似文献   

顾及地块时空特点的地籍数据组织及查询   总被引：2，自引：0，他引：2  

常征  陈军  杜道生 《武汉大学学报(信息科学版)》1997,(3)

通过分析地块变更的时空变化过程，总结出具有父子关系的时态地块的空间相交性和时间相接性特点，归纳出查询这种关系的约束条件。利用扩展时空复合模型和元组时区标记，借助于变更地块的约束条件，设计出查询变更地块的时态链算法。  相似文献   

South　China　Sea　Warm　Pool　in　Boreal　Spring   总被引：36，自引：1，他引：36  

Peter C. Chu  C.-P. Chang 《大气科学进展》1997,14(2):195-206

During the boreal spring of 1966, a warm-core eddy is identified in the upper South China Sea (SCS) west of the Philippines through an analysis of the U.S. Navy’s Master Oceanographic Observation Data Set. This eddy occurred before the development of the northern summer monsoon and disappeared afterward. We propose that this eddy is a result of the radiative warming during spring and the downwelling due to the anticyclonic forcing at the surface. Our hypothesis suggests an air-sea feedback scenario that may explain the development and withdrawal of the summer monsoon over the SCS. The development phase of the warm-core eddy in this hypothesis is tested by using the Princeton Ocean model  相似文献   

青海省湟水盆地历史地震调查及研究     

涂德龙  王赞军  夏玉胜  常振广 《高原地震》1997,(3)

通过对青海省湟水盆地影响较大的5次破坏性历史地震的重新考证，确定了每次地震的宏观震中、震级大小、发震断层以及地震等震线，从而得出盆地东部一平安至民和块体及其周边地区，基底介质强度较弱，为中强地震活动水平较高的危险地区。  相似文献   

水库地震主震发生时间的预测   总被引：1，自引：2，他引：1  

常宝琦  沈立英 《华南地震》1997,17(2):76-82

水利工程对水库地震的抗震设防要求事先对水为地震进行预测。预测内容包括蓄水后诱发地震的危险性（可能性、）最大震级、最大震的地占紧及不库地震对场址地震动参数的影响。除主震时间的预测外，本文第一作者都曾提出过初步的预测方法。本文认为，水库地震前震波速比异常、非线性灰色模型以及前震系列回归等方法，是预测主震时间的有前途的方法。  相似文献