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121.
????????????????? 总被引:2,自引:0,他引:2
根据实际工程中风载作用下导线传给输电塔的荷载特征,利用随机参数结构受随机激励响应的模型,计算了输电塔脉动位移的统计值. 相似文献
122.
A nonparametric structural damage detection methodology based on neural networks method is presented for health monitoring
of structure-unknown systems. In this approach appropriate neural networks are trained by use of the modal test data from
a ‘healthy’ structure. The trained networks which are subsequently fed with vibration measurements from the same structure
in different stages have the capability of recognizing the location and the content of structural damage and thereby can monitor
the health of the structure. A modified back-propagation neural network is proposed to solve the two practical problems encountered
by the traditional back-propagation method, i.e., slow learning progress and convergence to a false local minimum. Various
training algorithms, types of the input layer and numbers of the nodes in the input layer are considered. Numerical example
results from a 5-degree-of-freedom spring-mass structure and analyses on the experimental data of an actual 5-storey-steel-frame
demonstrate that neural-networks-based method is a robust procedure and a practical tool for the detection of structural damage,
and that the modified back-propagation algorithm could improve the computational efficiency as well as the accuracy of detection
Project supported by the National Natural Science Foundation of China (No. 59908003) and the Natural Science Foundation of
Hubei Province (No. 99J035). 相似文献
123.
在介绍双臂式电场仪探测原理的基础上,给出了子午工程探空火箭搭载的双臂式电场仪的具体设计.为了降低探针的不对称和不一致性,采用了铝制球形探针设计,使用石墨涂层以减少表面不均匀性,并采用独特的外形设计来消除支撑臂阴影影响|在信号处理部分,为了能提高系统动态范围,采用了分频段处理的方法.最后,结合整体系统设计的需要提出了几点误差考虑,并给出了系统性能测试结果.所设计的电场仪带宽0~5 MHz,直流探测范围为0.1 mV/m~±1 V/m,交流探测范围为10 μV/m~50 mV/m,可以实现对电场强度为0~±1 V/m的空间电场进行二维测量. 相似文献
124.
为了研究准分子激光刻蚀聚甲基丙烯酸甲酯(PMMA)的内在机理,将波长为248nm的KrF准分子激光垂直照射到PMMA材料表面,改变激光能量和脉冲数目,在大气背景下进行实验,照射后样品的表面形貌及化学结构用扫描电子显微镜(SEM)、3维形貌分析仪、X射线光电子能谱(XPS)等手段进行分析。SEM测试表明,在刻蚀区域出现孔状结构,说明刻蚀过程中有气体成分产生。XPS测试表明,激光照射后C1s峰的强度减弱而O1 s峰增强,据此推测PMMA侧链上的甲基被刻蚀掉且空气中的O2参与了反应。另外还研究了激光能量和脉冲数目对刻蚀率和表面粗糙度的影响。结果表明,随着激光能量和脉冲数目增加,刻蚀率和粗糙度并不是一直呈现递增的趋势。 相似文献
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128.
The lifetime Ts of a long-lived nuclear spin state (LLS) could be much longer than the longitudinal order T1. Many spin systems were used to produce long-lived states, including two or more homonuclear spins that couple to each other. For multiple homonuclear spins with rather small chemical shift difference, normally it is difficult to selectively control the spins and then to prepare a LLS. Herein, we present a scheme that prepares different spin orders in a multi-spin system by using optimal control and numerical calculation. By experimentally measuring the lifetime of the states, we find that for a three-spin physical system, although there are many forms of state combinations with different spin orders, each component has its own lifetime. 相似文献
129.
固相萃取-超高效液相色谱法测定烟用水基胶中丙烯酰胺 总被引:1,自引:0,他引:1
建立了采用固相萃取-超高液相色谱/紫外检测测定烟用水基胶中丙烯酰胺的分析方法。样品经超纯水进行超声提取,固相萃取柱进行富集净化后,经HSS T3色谱柱分离,以甲醇和水为流动相等度洗脱,紫外检测,外标法定量。结果显示,丙烯酰胺在浓度0.01~20.0μg·mL-1范围内有良好的线性关系,相关系数为0.9999。丙烯酰胺三个不同浓度的加标回收率为91.7%~105.1%;相对标准偏差为1.3%~4.7%(n=6);检出限为3.5μg·L-1。该方法分析时间短、结果准确可靠,满足烟用水基胶中丙烯酰胺的测定。 相似文献
130.
An efficient and practical method for the synthesis of indole as a key starting material for many useful chemicals is described. Using 2-nitrotoluene as starting material, hydroxymethylation with formaldehyde under alkaline conditions gave 2-(2-nitrophenyl)ethanol on a large scale. Raney Ni catalyst was used for both reduction of the nitro group as well as for the indole formation. The overall yield was 78% from 2-nitrotoluene. 相似文献