Influence of cooling rate on the microstructure and ageing behavior of as-cast Al–Sc–Zr alloy

Al–0.3Sc–0.15Zr alloy was cast using copper die, insulated alumina mould, and conventional investment shell mould to obtain a wide range of cooling rates. A novel method of quenching the investment shell mould along with the liquid metal in oil was also used which resulted in a significant increase in the cooling rate. The order in increasing average cooling rate is 0.16, 0.78, 1.28, 5.93, 7.69 °C/s. The as-cast samples were aged isothermally at 300 °C and various temperatures for 2 h. Slow cooled samples (in alumina-insulated mould) showed the presence of as-cast primary precipitates as well as rod shaped discontinuous precipitates with high density of interfacial dislocation. The amount of as-cast precipitates decreased with increase in the cooling rate. These as-cast precipitates grew at the expense of Sc in solid solution reducing the number of precipitates formed during ageing process. This results in lower increment in hardness on ageing.     

基于多传感器的智能车系统设计

主要介绍电磁、光电、CMOS摄像头和测速传感器在智能车控制系统中的应用.以MC9S12XS128单片机作为系统的控制核心,设计了能够自主循迹的智能车,着重叙述信号检测模块.信号检测包括路径和反馈速度检测,分别使用了电磁、光电、CMOS摄像头和编码器等传感器,并运用PID算法计算PWM对电机和舵机的控制.实际测试表明,智...     

基于小波的信号分析

简介小波概念之后,对一组模拟信号进行分析,采用小波变换,选出合适的小波函数,处理后再重构。对采用Mexican hat小波、Shannon小波、Meyer小波这三种不同小波得到的去噪结果进行比较,验证信号的滤波效果与选取的小波类型有较大的关系。     

Synthesis and electrochemical characteristics of LiCrxNi0.5−xMn1.5O4 spinel as 5 V cathode materials for lithium secondary batteries

A series of electrochemical spinel compounds, LiCr_xNi_0.5−xMn_1.5O₄ (x=0, 0.1, 0.3), are synthesized by a sol–gel method and their electrochemical properties are characterized in the voltage range of 3.5–5.2 V. Electrochemical data for LiCr_xNi_0.5−xMn_1.5O₄ electrodes show two reversible plateaus at 4.9 and 4.7 V. The 4.9 V plateau is related to the oxidation of chromium while the 4.7 V plateau is ascribed to the oxidation of nickel. The LiCr_0.1Ni_0.4Mn_1.5O₄ electrode delivers a high initial capacity of 152 mAh g⁻¹ with excellent cycleability. The excellent capacity retention of the LiCr_0.1Ni_0.4Mn_1.5O₄ electrode is largely attributed to structural stabilization which results from co-doping (chromium and nickel) and increased theoretical capacity due to substitution of chromium.     

姜渣-玉米淀粉膜的制备及研究

目的 制备一种纯天然的、具有抑菌性的可食用淀粉膜。方法 以玉米淀粉为原料,通过添加适量的姜渣、甘油、羧甲基纤维素钠,采用流延法制备姜渣-玉米淀粉膜。结果 当淀粉的质量分数为3%,甘油的质量分数为1%,姜渣的质量分数为0.4%时,膜的透光性、透油性、水蒸气透过性、溶解度、溶胀度等各项指标的综合测定结果较好。生姜中含有姜辣素、姜油等活性成分,添加姜渣可作为天然的抑菌剂,微生物试验结果证实,姜渣-玉米淀粉膜对霉菌和酵母菌具有一定抑菌作用,且抑菌效果与姜渣的含量成正比关系。结论 所制备姜渣-玉米淀粉的结构紧密、光滑平整,并具有一定的抑菌性。     

图形渐变过程中图形重构关键技术研究

介绍了平面多边形渐变的基本原理,提出了基于三角形分解与重构中在计算机编程中碰到的重构图形中出现部分点偏离或方向相反的问题及其解决方案,实现了较好的多边形渐变效果,为程序人员实际实现图形渐变开发提供理论依据及实际编程方法。     

采用DSP控制并基于半桥逆变器UPS驱动电路的研究

文中设计了一种采用HCPL-316J芯片来驱动用TMS320F2812控制的基于三相半桥逆变器的UPS,分析了半桥逆变器的原理。实验结果表明,采用该驱动方案设计的UPS系统具有低成本、安全性高,并且具有带三相不对称负载能力强,输出电压波形总谐波失真度（THD）小,工作效率高等优点。     

超声辅助提取黑松松针多糖的工艺优化及其抑菌性研究

采用超声辅助水提法提取黑松松针多糖,苯酚-硫酸法测定提取的多糖含量。在单因素试验基础上,通过正交试验对黑松松针多糖的提取工艺进行优化。采用抑菌圈法考察了提取的松针多糖对大肠杆菌、枯草芽孢杆菌的抑菌效果。结果表明:松针多糖的最佳提取工艺条件为浸提时间2 h、液料比80∶1(m L/g)、浸提温度90℃、超声功率为130 W,在此条件下,黑松松针多糖得率为2.47%。提取的黑松松针多糖对大肠杆菌、枯草芽孢杆菌具有一定的抑制作用。     

Strengthening effect of unshearable particles of finite size: a computer experimental study

Equilibrium configurations of a dislocation interacting with randomly distributed unshearable obstacles of finite size under an applied stress are analyzed. Ashby's critical dipole spacing Q′ argument for the self-stress effect of dislocations is utilized but analysis suggests that the spacing Q′ varies with the local obstacle distribution as well as with the obstacle shape. Computer simulations of a dislocation slip process through circular or linear obstacles, that are extensions of earlier work by Forman et al., were conducted. The dependence of the strengthening stress on the obstacle size was found to be less than that predicted by equations currently in use, particularly for linear obstacles. New, modified Orowan equations are suggested for the strengthening effects due to spherical, rod-like, and plate-like obstacles. The effect of the orientation distribution of the linear obstacles demonstrated in the simulation is in agreement with recent experimental observations.