of the Ministry of Agriculture for help with field investigations, data analysis and translation. They also gratefully acknowledge the support of the Food and Agricultural Organisation for commissioning this study. 1. The three macro-studies were conducted by the Research Team on Rural Population Mobility of the China Population Information and Research Centre and Chen Jiyuan, Hu Biliang and Yu Dechang of the Rural Development Institute of the Chinese Academy of Social Sciences. On the basis of numerous nationwide surveys and studies these papers concluded that the number of rural migrants has reached some 120 million or so persons, which suggests that more than 15% of the total rural labour force in China have left their villages of origin for either short or long-term relocation and that the numbers of migrants are increasing and staying for longer periods away from their villages. Migration largely involves the relocation of village populations from rural to urban locations although a small proportion (10-20% or so) are estimated to move from rural to rural locations. Some 90% of movement has been from agricultural to non-agricultural occupations with the non-agricultural population reported to have increased by 108.38 million between 1979 to 1993. Some 80-90% of the movement has been from rural to urban destinations, roughly divided between large cities (30%), medium sized and small cities (40%) and townships (20%). A high proportion of the movement has been from the underdeveloped northwest , southwest and central provinces to the more economically developed south and eastern coastal regions. The surveys suggest that most of

Accurate differentiation of whether the defect position is located on the inside or outside surface is necessary in the low-frequency electromagnetic detection technique (LFET) on oil and gas pipelines. We design a set of composite probe arrays that consisted of inductive magnetic coils (LFET coils) and eddy current testing (ECT) coils to accomplish comprehensive inspection, meanwhile, the theoretical calculation and analysis of the mutual interference mechanism between LFET and ECT coils were mainly implemented. Experimental result demonstrates that the ECT coils can effectively minimize the low-frequency magnetic field interference and allow low-frequency excitation coil setting parameters to be adjusted in a wide range (760 V Hz of voltage–frequency product in this experiment) to identify the inside defects above 1 mm depth while nothing found to detect outside defects. This circumstance enables the identification of the inside defect of 4 mm wide and 1 mm deep (10% wall thickness) at a lift-off value of 14 mm.

Local stress concentrations pose a significant hazard to the safe operation of pipelines. However, the classical analytical model of the magnetic flux leakage (MFL) signal is still unable to effectively quantitatively analyze and accurately evaluate the local stress concentration zone of a pipeline. In this paper, based on the Jiles–Atherton model of the magnetomechanical effect, the mathematical relationship between stress and the magnetization of ferromagnetic material under hysteresis conditions is introduced, and an improved analytical model of the MFL signal based on the magnetomechanical model is established. The influence law of stress intensity on the MFL signal in the local stress concentration zone of the pipeline is calculated and analyzed, and the theoretical calculation results are verified through experiments. Simulation and experimental results show that, considering the hysteresis condition, the stress causes a change in the hysteresis loop of the ferromagnetic material, and the magnetization strength of the material decreases with increasing stress; the effect of stress on the magnetization strength of ferromagnetic materials is most obvious when the external magnetic field is approximately 5 KA/m. The MFL signal on the surface of the local stress concentration zone of the pipe changes abruptly, and the amount of change in the axial amplitude and radial peak-to-peak value of the leakage signal of the pipe tends to increase with the increase in the stress intensity of the local stress concentration zone. A comparison of the analysis with the classical analytical model of the MFL signal shows that the improved analytical model of the MFL signal is more suitable for the quantification study of the local stress concentration zone of the pipeline.

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