Nanjing Li

Evolution of directional solidification microstructure of Pb-80wt%Sn alloy under medium-density direct current

The effect of a medium-density DC-current and its direction on the directional solidification microstructure and cooling behavior of Pb-80wt%Sn alloy were studied. Experimental results indicated that the microstructure was refined with DC compared to the one without. With the increase of DC density, the primary (λ1) and secondary (λ2) dendrite arm spacing of the primary phase decrease clearly. It is also found that not only the intensity of the DC current but also its direction affects the microstructure. The size of λ1 and λ2, in samples treated with positive DC, decreases more clearly than in those with negative DC. The interface morphology in samples processed without and with DC is different when the current direction is changed. Finally, the mechanism of microstructure evolution is discussed.

Influence of amplitude and phase errors on near-field to far-field transformation

Due to the influence of environment and multipath effect, the calibration data of spherical near-field antenna measurement are not accurate, which will result in amplitude and phase errors in the near-field to far-field transformation. In order to obtain more accurate antenna radiation pattern, the influence of amplitude and phase errors on the near-field to far-field transformation results are simulated. According to the analysis results, the amplitude and phase errors can be controlled within the tolerable range when the system is designed.

The polarized differential extinction coefficient with frequency determined by morphological characteristics of forest vegetation

The accurate multi-polarization 3-10 GHz frequency-domain data of some small trees are obtained by indoor wideband polarimetric scattering measurement system. The relationship between differential extinction coefficient and returned power is quantitatively derived, and the fluctuating of differential extinction coefficient changed with frequency is analyzed by combining the morphological characteristics of vegetation. The results show that when frequency is low, the plants with structural features present oriented distribution. As frequency increases, the plants show random distribution for the echoes mainly come from canopy.