Applicability of a Backprojection Algorithm to Reconstruct Images of Subsurface Horizontal Planes for Laboratory Experiments in Electrical Resistance Tomography

This paper describes the use of a backprojection algorithm to reconstruct subsurface images of the electrical resistivity in horizontal planes parallel to the surface. The algorithm can be applied to detect buried objects such as tanks or pipes and possible leakages from them. Two imaging strategies are compared: juxtaposition of vertical planes, and 3D reconstruction from the sensitivity matrix corresponding to the entire volume whose surface is explored. The electrode arrays used for voltage measurement are the dipole–dipole array and a modified Schlumberger array. A personal computer controls current injection, electrode switching, and voltage detection. The system injects 1 kHz, 20 V peak-to-peak square waveforms, thus avoiding electrode polarization effects. Experimental laboratory measurements show that the algorithm detects localized objects such as an insulating sphere and a conductive cylinder immersed in water. Furthermore, covering half of the cylinder by a rubber sleeve to simulate a nonconductive leak, yields a distinct image for the leak. The backprojection algorithm does not need any regularization parameter and it is very fast in inverting the sensitivity matrix because it approximates the inverse matrix by its transposed. The dipole–dipole array usually yields a lower overall pixel error than the modified Schlumberger array but both allow the detection of simulated underground leaks.     

用L-曲线法确定半参数模型中的平滑因子

提出了一种新的方法——L-曲线法确定平滑因子。通过确定合适的平滑因子，更好地控制了残差部分V^TPV与光滑度部分S^TRS之间的平衡，得到了更准确的参数估值。通过算例，将基于L-曲线法确定平滑因子的半参数模型解算方法和其他方法进行了比较。结果表明，用L-曲线法确定平滑因子后，提高了半参数模型计算结果的精度，可以更好地将观测值中的系统误差分离出来。     

高分辨率遥感影像的精纠正

论述了对高分辨率遥感影像进行精纠正获得正射影像的关键技术。若干实际不同分辨率的高分辨率遥感影像被用于相应的实验，实例证明了本文算法的正确性。     

利用现有重力场模型求定CHAMP卫星加速度计修正参数

CHAMP卫星加速度计数据的标定是通过确定其尺度因子和偏差参数来完成的.本文基于能量守恒方程,给出利用现有重力场模型标定CHAMP卫星加速度数据的基本原理和数学模型;提出相邻历元间差分算法,大大简化了观测方程,同时避免积分常量的计算.该算法既能同时解算尺度因子和偏差参数,也可任意求解其中之一.基于实测的CHAMP卫星加速度数据,利用EGM96模型和最新公布的EIGEN-2模型进行计算与比较,验证该方法的有效性.     

用L-曲线法确定岭估计中的岭参数

运用L 曲线法来确定岭估计中的岭参数 ,推导了用L 曲线法确定岭参数的基本公式 ,在此基础上实现了其算法 ,并用两个算例 ,比较了新方法和以往方法。结果表明 ,L 曲线法不仅容易收敛 ,而且其计算结果的精度较高     

Identification of structural parameters of multistorey shear buildings from modal data

A procedure has been presented in this paper to identify the structural parameters, viz. mass and stiffness matrices, from modal test data for multistorey shear buildings. The first two orders of modal data have been used by other researchers to estimate the global matrices where they depend only on measurable points which are less than the total number of structural degrees of freedom. The above method has been refined here by using Holzer criteria along with other numerical methods to estimate the global mass and stiffness matrices of the structure. This shows the methodology to be more efficient and accurate. The reliability of the procedure has been shown by examples of multistorey buildings. Copyright © 2004 John Wiley & Sons, Ltd.     

Research on anisotropic parameters by syn-thetic seismogram

Introduction The anisotropy of the Earth crust medium is a common phenomenon(Crampin,1984).More and more observation materials and study results have proved that on most of the Earth′s upper crust is spread fluid-filled cracks and microcracks,which are aligned according to the contempo-rary stress-field.Such distributions of aligned cracks show effectively anisotropy to seismic wave and the phenomenon is called extensive-dilatancy anisotropy(EDA)(Crampin et al,1984).At the same time,it is …     

A study on the focal parameters of Shidian M =5.9 earthquake sequences in 2001

On the basis of about 300 earthquake wave forms observed in the Shidian M _S=5.9 sequences on April 12, 2001 recorded in Kunming Digital Seismic Network, the spectra of shear wave have been used to estimate the focal parameters of these earthquake sequences. The results show that within the magnitude range of 1.5–5.3, the seismic moments are 10¹⁰–10¹⁶ N·m, the corner frequencies are 0.2–0.8 Hz, radii of the focal rupture are 200–2 500 m and the stress drops are 0.1×10⁵–20×10⁵Pa. Through the statistical analyses of variation of corner frequency f _c and stress drop Δσ with time, it is discovered that the average corner frequency of the foreshock sequences is obviously lower than that of the aftershock sequences. Contrarily, the average stress drops Δσ of the foreshock sequences are clearly higher than that of the aftershocks. It is considered that these variation characteristics of average corner frequency and stress drops before and after the main shock have index significance to the precursory information before a strong earthquake. The higher stress drops for the foreshock sequences show that the higher shear stresses have been stored in the area of main shock. After the main shock, most of the stresses have been released, so the aftershock sequences show a rupture process of lower stresses. Foundation item: Scientific and Technological Key Project of Yunnan Province (2001NG46)     

Economic valuation of policies for managing acidity in remote mountain lakes: Examining validity through scope sensitivity testing

No Abstract. .The following two amendments concern the above mentioned article that appeared electronically Online First on June13, 2005 (this issue, pp. 274–291).1. the first name of the author Cooper is Philip (and not Phillip).2. the correct grant reference number is EVK1-CT-1999-00032 (instead of: EVK1-CT-2002-00121).     

Study on the Source Parameters of Earthquakes in the Middle Eastern Area of North Tianshan in Xinjiang

INTRODUCTIONThe study of source parameters is usually based oninversionfromobservational seismic waveformdata.Seismic wave affected bygeometric spreading,inelastic attenuation,scatteringandsite effects ofthe mediumontheir way fromsource to station.Therefo…