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When working in the areas with strong interference and limited sites, such as cities, dams, and mountainous areas, using the conventional transient electromagnetic (TEM) devices is difficult to lay out large transmitter loops for conventional surveys. The small-loop transient electromagnetic method, which has the advantages of lightweight and high efficiency, is a new technology of current researches. First of all, A one-dimensional (1-D) layered model and a three-dimensional (3-D) homogeneous half-space model were established by using numerical simulation method. The research results show that the small-loop TEM devices can not only accurately reflect the anomaly information of deep targets, but also be more sensitive to the detection of shallow targets. By using high-current technology, the signal intensity and detection depth of multi-turn small-loop TEM devices and that of large loop device are the same. Finally, the accuracy and effectiveness of small-loop devices were verified through analysing the results of dam karst investigation. The research work provides a reference for the qualitative analysis of response characteristics and data interpretation of small-loop TEM.

The small loop transient electromagnetic method (TEM) in shallow water has strong adaptability and high resolution and is one of the current research hotspots. In this paper, a shallow-water model of a typical low resistance anomaly is established, which can be obtained through numerical simulation analysis. In the early time, the shallow water layer has large response and the low resistivity abnormal body has small response; In the late time, the shallow water layer has small response induction response and the low resistivity anomaly has larger response, and the response curve shows “double peak” attenuation law; The effects of different thicknesses of shallow water layers on the response of low resistivity abnormal bodies show “single peak”, “double peak”, and “peak wave trough” attenuation laws; However, the effect of different resistivity in shallow water layer on the response of the low resistivity abnormal body only shows the attenuation pattern of “single peak” and “peak wave trough”. Finally, the article takes the highway site selection survey as an example, combined with the high density resistivity method comparison analysis, and verifies the reliability and accuracy of the detection results of the small loop TEM in shallow water. The research work provides a theoretical reference for the qualitative analysis of the response characteristics and data processing interpretation of the small loop TEM in shallow waters.

Corrosion testing of buried metal pipelines is an important measure to ensure the safe operation of pipelines. In order to investigate the transient electromagnetic field named response of buried metal pipelines, a three-dimensional simulation model was established by using multiphysics simulation software named ANSYS Multiphysics to calculate and analyze buried metal pipelines with different corrosion degrees, ie different wall thicknesses, on the receiving coil after the excitation signal is turned off[1]. The induced electromotive force changes, the results show that the larger the wall thickness, that is, the smaller the corrosion degree, the slower the attenuation of the induced electromotive force curve of the receiving coil, the smaller the wall thickness, the faster the attenuation; and the verification was experimented: the transient electromagnetic method can effectively detect the degree of corrosion of metal pipes buried under the ground.

Purpose – The purpose of this paper is to solve the interface discontinuities in radial basis function (RBF) method for multi-medium boundary value problems (BVPs). The discontinuity of the solution derivatives is not easily handled with RBF method because of infinitely smoothness. Design/methodology/approach – The essence of solving BVP is to construct the continuous potential function surfaces. Hence, from constructing surface aspect, this paper proposed and compared the global and subzone schemes for RBF method. Their implementation schemes and mathematic models can then be derived. Numerical experiments and comparison are carried out for electric and magnetic field calculation. Findings – In the numerical experiments, the subzone scheme has shown its significant advantageous, it can approximate not only the potential function but also its derivative on interface boundary with high accuracy. So the physical characteristics of discontinuities on the interface can be revealed clearly. The overall precision is significantly improved. Originality/value – This paper proposed an effective subzone scheme for RBF method in multi-medium BVP. It is an improvement for RBF method based on its domain decomposition idea. And it is also a candidate for solving complex BVP.

On the basis of Discrete Control Modeling for Three-phase Voltage Source SVPWM Rectifier, the mathematical model of VSR and feed forward decoupling control technique were analyzed, the proposed SVPWM algorithm of matrix format can reduce amount of calculation. Basic SVPWM real-time controlling model was composed of four models including space sector determination model, acting time judgment model of correlation vector, calculation model of switch transit time and PWM model, which were constructed on the basis of high-speed signal processing system VHS-ADC of Lyrtech company in Canada. Focus on the research of system model simulation when change the load. This research demonstrate the validity, high-speed, stability. And this research made a foundation for ht further development of laboratory equipment.

City is a kind of social-economic-natural complex ecosystem dominated by human activities. With the accelerating of urbanization,the land use is being transformed from natural landscape to impervious surface in urban areas, such as buildings,roads,roof,squares and so on. Urban imperious surface changes the environment factors,hinders energy exchange between air and soil,and influences urban plant growth. In this research we studied the effects of urban imperious surface on habitat of Ginkgo biloba and its ecophysiology response to the imperious surface. We designed two different types of imperious surface in urban areas. One is totally impervious cover ( TIC) which is a marble square,and the coefficient of permeability is zero. The other is partially impervious cover ( PIC) which is covered by bricks,and the coefficient of permeability is 33% . A turf cover ( NC) was chosen as the contrast,and the coefficient of permeability is 88% . The Ginkgo bilobas growing on the three kinds of land covers were planted in the same time and received the same maintenance. Soil temperature ( Ts ) and water content of soil ( WCS ) were measured by ECH2O. Gas exchange characteristics such as photosynthesis ( Pn ) ,transpiration ( Tr ) ,stomata conductance ( Gs ) ,saturation vapor pressure deficit of leaf ( VPDL ) were measured by Portable photosynthesis measuring system Li-6400. chlorophyll fluorescence