利用快速热压烧结法制备了Bi2Te2.5Se0.5热电合金。通过XRD、SEM、四点探针法以及热电材料测试仪等分析了合金试片的微观结构与热电性能。结果表明:二次热压烧结后合金内部的晶粒具有特殊的排列方向,这可增强其热电性能。经二次热压烧结后,合金的室温电导率增至700 S/cm,塞贝克系数维持在-200μV/K左右,故其室温功率因子可增至2.9 m W/(m·K^2)。通过计算得出二次烧结后其热电优值在325~425 K时皆大于1。
[Objective] To study the digital image compression technology in rice monitoring system. [Method] A digital image compression technology program based on the discrete Fourier transform was proposed, and simulation experiments were carried out to compress the image at different compression ratios. [Result] When com- pression ratios were less than 30, the compression ratio, image entropy, average codeword length, coding efficiency and redundancy which reflected the quality of the coding, and the parameter PSNR which estimated the fidelity of the compressed im- age were all achieved good results that human eye could barely percept the differ- ence between the original image and decompressed image; and when the compres- sion ratios were more than 30, there was a certain distortion in the decompressed image. And when the compression ratio was 91.516 3, although the image had some distortion, the PSNR was still achieved to 21.528 2, and human eye could accept the decompressed image intuitively within the acceptable error range. [Conclusion] The results show that the proposed image compression program is a viable, effective, and better image compression technology which can satisfy the requirements of the crop monitoring system on image storage, transforming and transporting.
