A mechanistic analysis of the correlation between overall strength and indentation hardness in discontinuously reinforced aluminum

It is well established that the indentation hardness of metallic alloys shows a reasonable correlation with their yield strength or ultimate strength. Experiments illustrate that such a unique correlation is nonexistent for discontinuously reinforced metal matrix composites, even when the indentation size is much greater than the reinforcement size. For aluminum alloys reinforced with silicon carbide particles, the same composite yield strength and tensile strength with different reinforcement fractions do not lead to similar hardness, or vice versa. Finite element analyses are carried out to rationalize the experimental findings. The modeling utilizes a two-dimensional plane-strain formulation. Discrete particles are included in the material model, and the overall stress-strain response and the indentation response are numerically simulated. The results confirm the lack of unique correspondence between the composite hardness and strength. The alteration of local heterogeneity in the composite is found to affect the indentation response. Effects of the geometrical arrangement of particles and thermal residual stresses on the indentation response are also investigated numerically.     

^60Coγ射线对刚地弓形虫缓殖子感染性的影响

应用不同剂量的~(60)Coγ射线照射含NT株弓形虫包囊的鼠脑匀浆后,以0.4％胰蛋白酶液消化,使弓形虫缓殖子从包囊中释放出来,并用生理盐水作连续10倍稀释,使成为含不同数量缓殖子的悬液,将此悬液接种小鼠,用生物检测方法确定其感染性。另设未经照射处理的缓殖子悬液感染小鼠的对照组。结果表明,γ射线0.55kGy剂量为控制鼠脑中NT株弓形虫感染性的最小有效剂量。γ射线0.1kGy剂量对弓形虫缓殖子感染性无明显影响,而0.45kGy照射后,其感染性较前者下降了10~4倍。     

壳聚糖醇水分离膜的研究

本文制备了一系列不同脱乙酰度壳聚糖，研究了不同脱乙酰度聚糖膜的醇水分离性能，结果表明，随着脱乙酰度的增大，分离因子升高，渗透通量减小。当脱乙酰度大于９０％时，有较高的分离因子，符合单级分离要求。同时考察了料液浓度，料液温度等条件对壳聚糖膜醇水分离性能的影响，求得水和乙醇透过壳聚糖的表观活化能分别为：△Ｅｗ＝３２．６ｋＪ／ｍｏｌ，△Ｅｅ＝５７．２ｋＪ／ｍｏｌ。     

Measurement and analysis of the step response of pyranometers requiring second-order correction

We have measured the time response of Kipp and Zonen CM-5 pyranometers to a step function of radiation and observed that the pyranometer output varied significantly from a single exponential function of time. Using a multi-exponential function to fit the experimental data, we extracted the two dominant exponential components of the signal to obtain the analytic function describing the pyranometer response. A thermal model of the pyranometer has been developed, whose response displays the observed time behaviour. The model was applied to correct the time response error of the pyranometers subject to a step function of incident radiation, and compared with a single exponential correction scheme.     

窄带中频数字接收机高速信号处理技术

窄带中频数字接收机在雷达对抗侦察中得到了广泛应用，其高速信号处理技术是目前研究的重点。本文详细介绍了数字雷达告警接收机高速信号处理技术的发展现状和关键技术，最后通过对该技术的全面分析指出了值得深入研究的领域。