The high-intensity focused ultrasound (HIFU) in the clinical trials is prone to nonlinear effects, especially near the acoustic focal region, which has a great impact on the therapy effect of HIFU thermal ablation. In this paper, the Westervelt equation was introduced in theory.The HIFU transducer model was established to simulate the nonlinear ultrasonic propagation by the finite element simulation (FEM).The distortion waveform near the acoustic focal region are extracted separately, the spectrum analysis is performed and the distortion waveform is filtered. The simulations show that the nonlinear effect is most obvious in the focal area and the higher harmonics energy at the focus is very large, so the harmonics energy can’t be ignored. The study of the nonlinear effects of HIFU ultrasound field contributes to the accurate measurement of HIFU and lays a foundation for clinical trials of the HIFU systems.
Straw burning has great influence on ambient air quality. In this paper, we study the advantages of satellite remote sensing monitoring technology, extract the straw burning and aerosol remote sensing monitoring results from the MODIS data during Sep-Oct-Nov 2013 in Northeast China. We analyze the temporal and spatial distribution characteristics of straw burning and aerosol in autumn, and study through the statistics and relevant analysis method for the quantitative straw burning in northeast China's impact on local air quality. The results show that the monthly change of straw burning and AOD in the autumn of 2013 has a high consistency, from which in October the straw burning is the most frequent, aerosol pollution is also the most serious. And the straw burning point distribution density area and the AOD high value area are basically consistent with the space position. Furthermore, every increase of a straw burning point can make the monthly average AOD of the three provinces of northeast China increases by 0.0006.