Numerical Simulation on Thermal Stresses and Solidification Microstructure for Making Fiber-Reinforced Aluminum Matrix Composites

The fabrication of fiber-reinforced metal matrix composites (MMCs) mainly consists of two stages: infiltration and solidification, which have a significant influence on the properties of MMCs. The present study is primarily focused on the simulation of the solidification process and the effect of the active cooling of fibers with and without nickel coating for making the continuous carbon fiber-reinforced aluminum matrix composites. The thermomechanical finite element model was established to investigate the effects of different cooling conditions on the temperature profile and thermal stress distributions based on the simplified physical model. The predicted results of the temperature distribution agree well with the results of the references. Additionally, a three-dimensional cellular automata (CA) finite element (FE) model is used to simulate the microstructure evolution of the solidification process by using ProCAST software. The results show that adding a nickel coating can make the heat flux smaller in the melt, which is favorable for preventing debonding at the coating/fiber and alloy interface and obtaining a finer microstructure. In the presence of the nickel coating, the number of grains increases significantly, and the average grain size decreases, which can improve the properties of the resultant composite materials. Meanwhile, the predicting results also show that the interfaces of fiber–coating, fiber–melt, and coating–melt experience higher temperature gradients and thermal stresses. These results will lead to the phenomenon of stress concentration and interface failure. Thus, it was demonstrated that these simulation methods could be helpful for studying the solidification of fiber-reinforced MMCs and reducing the number of trial-and-error experiments.     

公平理论在军队医院聘用制人员管理中的应用

组织公平对员工工作效率、组织绩效和组织目标有重要影响.本文对公平理论的概念与意义进行阐述,分析军队医院聘用制人员组织公平感的影响因素,提出提高军队医院聘用制人员组织公平感的措施.     

Effects of In-Process Ultrasonic Vibration on Weld Formation and Grain Size of Wire and Arc Additive Manufactured Parts

Wire and arc additive manufacturing (WAAM) is a competitive technique, which enables the fabrication of medium and large metallic components. However, due to the presence of coarse columnar grains in the additively manufactured parts, the resultant mechanical properties will be reduced, which limits the application of WAAM processes in the engineering fields. Grain refinement and improved mechanical properties can be achieved by introducing ultrasonic vibration. Herein, we applied ultrasonic vibration to the WAAM process and investigated the effects of wire feed speed, welding speed, and ultrasonic amplitude on the weld formation and grain size during ultrasonic vibration. Finally, a regression model between the average grain size and wire feed speed, welding speed, and ultrasonic amplitude was established. The results showed that due to the difference in heat input and cladding amount, wire feed speed, welding speed, and ultrasonic amplitude have a significant influence on the weld width and reinforcement. Excessive ultrasonic amplitude could cause the weld to crack during spreading. The average grain size increased with increasing wire feed speed and decreasing welding speed. With increasing ultrasonic amplitude, the average grain size exhibited a trend of decreasing first and then increasing. This would be helpful to manufacture parts of the required grain size in ultrasonic vibration-assisted WAAM fields.     

大承气汤对全身性炎症反应干预作用的实验研究

[目的]探讨大承气汤对全身炎症反应综合征(SIRS)的干预作用的机理。[方法]选用酵母多糖A诱导的小鼠SIRS模型，给予大承气汤后，分别在6h，12h和24h等时点用鲎试剂微量法测定小鼠血清内毒素含量，用放射免疫法测定血清肿瘤坏死因子—α(TNF—α)和白细胞介素—6(IL—6)含量。[结果]SIRS状态下模型小鼠血清内毒素、TNF—α、IL—6均升高；与同时点模型组比较，大承气汤6h、12h时点可以明显抑制血清内毒素的升高(P＜0．05或P＜0．01)；大承气汤6h组TNF—α水平降低(与造模后6h组比，P＜0.05)；血清IL—6水平方面，大承气汤各组比正常组升高的幅度均较模型各组低，在24h时点大承气汤组比模型组显著降低(P＜0．05)。[结论]大承气汤在SIRS过程中可以有效地抑制内毒素的转移和TNF—α、IL—6等炎症反应性细胞因子的产生。     

抗Stat3多克隆抗体的制备和其在乳腺癌诊断中的应用

目的:制备兔抗信号转导与转录激活因子3(Stat3)抗体,分析其在乳腺癌诊断中的价值.方法:应用人工重组小鼠Stat3蛋白,免疫雄性家兔制备抗Stat3抗体;用免疫印迹法分析检测抗Stat3抗体的纯度和特异性;应用免疫组化染色法检测65例乳腺癌和30例正常乳腺组织中Stat3蛋白的表达.结果:用Stat3蛋白免疫家兔被免疫6 wk后,其血清中抗Stat3抗体效价＞1∶ 256,000(A450 nm=0.40);SDS-PAGE和免疫印迹分析均在分子质量(Mr)92 000处有明显的带;65例乳腺癌组织的细胞浆和细胞核中,Stat3蛋白表达量在不同的组织学分级之间有统计学差异(P＜0.05).结论:高效价和特异性强的抗Stat3抗体被成功制备. 该抗体可用于乳腺癌组织细胞Stat3蛋白表达的检测.     

大鼠胚胎小脑的发育学研究

用Ｎｉｓｌ染色法对大鼠胚胎１４、１６、１８及２０ｄ小脑进行形态学观察。结果表明：胚胎１６ｄ以前小脑由室管膜层、外套层及边缘层构成。胚胎１８ｄ开始出现典型的皮层结构。外颗粒层由较密集的深染细胞组成，数目随着胎龄的增加而增多。蒲氏层由较大淡染细胞组成，数目随着胎龄的增加而逐渐减少。颗粒层内细胞成份较复杂，细胞密度随胎龄增加呈下降趋势。