Hydrogen sorption properties of Mg-20wt.%Fe 23 Y8 composite prepared by reactive mechanical alloying

Mg-20wt.% Fe23Y8 composite was successfully prepared by reactive mechanical alloying (RMA). X-ray diffraction (XRD) measurement shows that the main phases of composite are MgH2 and Mg2FeH6. The composite exhibits excellent hydrogen abs/desorption properties and can absorb 4.36wt.% and 5.72wt.% hydrogen at 473 and 573 K in 10 min under 3.0 Mpa hydrogen pressure, respectively. The composite can desorb 5.27wt.% hydrogen at 573 K in 30 min under 0.02 Mpa hydrogen pressure. Compared with the pure MgH2, the hydrogen desorption temperature of Mg-20wt.% Fe23Y8 composite is decreased about 40 ℃. It is supposed that both the catalyst effect of Fe-Y distributed in Mg substrate and the crystal defects play the main role in improving hydrogen sorption properties of Mg-20wt.% Fe23Y8 composite.     

A study on the self-sealing process of anodic films on aluminum by EIS

The electrochemical behaviors of anodized aluminum in neutral NaCl and Na₂SO₄ solutions were studied using electrochemical impedance spectroscopy (EIS). The results reveal that there is a self-sealing process for unsealed anodic film in neutral NaCl and Na₂SO₄ solutions. The resistance of the porous layer (R_p) and the capacitance of the barrier layer (CPE_b) increase and the capacitance of the porous layer (CPE_p) decreases with immersion time in the initial stage. Corrosion resistance provided by the anodic film is improved by the self-sealing process of the porous layer. However, chloride ions have an opposite effect. The improving effect of the self-sealing process on film resistance is decreased with the increase of chloride concentration of the solution.     

不同流量下环翼型防冲板结构优化试验

为了研究不同流量条件下桥墩局部冲刷问题,在单片挡板基础上,增加防冲板数量形成了多级防冲结构。利用多元统计方法对防冲效果进行了主成分分析,认为最大冲坑深度最能体现试验效果,并以最大冲坑深度为指标进行试验分析。试验结果表明:在流量为75 m3/h时,增加防冲板数量并不能有效提升防冲效果;当流量增加到115 m3/h时,通过增加防冲板数量可在一定程度上提高桥墩的防冲能力,并且防冲效果随着防冲板间距的减小而增强,同时随着防冲板外径的增大而增强。但三级防冲板与二级防冲板防冲效果非常相近,第三级挡板对试验的结果影响甚微。因此,试验分析认为,在考虑不同流量条件下,环翼型防冲板最优防冲结构为两片防冲板,且防冲板外径为180 mm,间距取值为15 mm。     

基于纳米材料的电化学生物传感器研究进展

该文主要从纳米尺寸材料电极的构建以及纳米材料作为生物分子指示剂两部分展开讨论,描述了依赖于阵列纳米管排列的生物分子与电极间的直接电子传递,纳米管、纳米颗粒为基质的纳米电极的构建,以及以金纳米颗粒、DNA量子点和蛋白为基础的多路分析技术与负载于CNT的新的纳米生物标记,特别讨论了纳米电化学方法在检测DNA和免疫传感器领域取得的研究进展.     

二次拟合：一种提高软件可靠性模型精度的新方法

针对软件可靠性模型精度不高的问题,提出了"一次建模 + 二次拟合"的方法,通过误差补偿机制来提高模型精度,并将该方法应用于航天软件失效数据集.实践结果表明,提出的方法对于提高软件可靠性模型精度是有效的.     

一种基于数据连续性的聚类方法

为了解决数据遗漏问题,根据类内样品点均匀分布的性质提出了一种新的聚类方法,即：先从样品集中获得蕴含式类,然后通过支持度获得标准类,最后通过隶属度标识类内成员的强弱程度。该方法仅对类内样品点均匀分布性敏感,不需要预先设置包括类核坐标、类间距离阈值等先验参数,对非凸性类也能有效分类。同时,实验表明该方法是一个具有较高性能的聚类方法。     

一级直线倒立摆匀速行走的模糊控制研究与实现

当前针对倒立摆的研究一般是把角度控制或者位置控制作为控制目标,很少着眼于速度控制,有鉴于此,设计了一种简单的模糊控制器,应用于一级直线倒立摆的匀速行走控制中;仿真实验和实物实时控制实验均验证了该控制器的有效性,对于设定的速度整定值,通过调整几个比例环节的系数,系统具有很好的动态性能指标,而且控制器在有外界扰动时体现了很好的抗扰性;考虑到实际物理系统中倒立摆行程的限制,设计的自动换向开关实现了倒立摆在一段给定的行程上匀速来回行走的控制目标,通过手动切换开关也能实现倒立摆的位置控制。     

基于间歇控制的不确定主从Lur’e系统的指数同步

研究了不确定主从Lur’e系统的问歇控制同步问题．运用Lyapunov稳定性理论和S-过程,首先推导出保证标称主从Lur’e系统指数同步的一个充分条件．在此基础上进一步得到了具有范数有界不确定性主从Lur’e系统鲁棒指数同步的结果．这些同步判据以矩阵不等式的形式给出．另外我们还提出了一种最小化性能指标的优化策略．最后,通过两个数值例子验证了结果的有效性．     

Composition analysis of semiconductor quantum wells by energy filtered convergent-beam electron diffraction

We show how energy-filtered convergent-beam electron diffraction (EFCBED) patterns can be used to determine the chemical composition of buried semiconductor strained quantum wells. Our method is based on a quantitative analysis of the intensities of high-order Bragg lines in the transmitted disc of EFCBED patterns taken from plan-view samples. This analysis makes it possible to determine the displacement vector R introduced between the top and bottom parts of the matrix by the deformation of the quantum well and consequently to determine its composition. This is illustrated in the case of an In(x)Ga(1-)(x)As quantum well buried in a GaAs matrix. A detailed analysis of the effect of experimental parameters on Bragg lines intensity is performed. In particular, the importance of the choice of the diffraction vector is pointed out. The relative uncertainty on the measurement of the indium content x is found to be lower than 5% and a possible occurrence of slight compositional fluctuations in the (001) growth plane is pointed out.     

Fishtail magnetization in single crystal Tl2Ba2CuO6

We report extensive magnetization measurements on single crystals of Tl₂Ba₂CuO₆ superconductors. The fishtail magnetization is found to disappear above a characteristic temperature (60 K), which corresponds to a crossover temperature in the temperature dependence of the irreversibility line. Since the low temperature irreversibility field can be modeled by a Josephson coupled layered system, we propose that the fishtail magnetization in the Tl₂Ba₂CuO₆ system is due to dimensional crossover.