转子-轴承系统混沌运动的神经网络反馈控制方法

用神经网络技术对刚性Jeffcott转子-轴承系统进行混沌滞延反馈控制研究。研究结果表明,当转子-轴承系统进入混沌状态后,引入时间滞延反馈控制信号,可以消除转子-轴承系统的混沌振动,使嵌入在混沌吸引子中的不稳定周期轨道回到稳定周期轨道上。采用间接误差计算的BP神经网络学习方法和自适应学习率BP算法结合而形成的改进型BP神经网络方法,可以快速搜寻到次优化的滞延反馈控制强度,从而即时有效地消除转子-轴承系统的混沌振动。一旦混沌振动回归稳态周期振动,则反馈控制信号自动消失。该方法为控制转子-轴承系统的振动状态提供了理论依据,特别是对工程实际转子系统有实用价值。     

Characterization of functionally gradient epoxy/carbon fibre composite prepared under centrifugal force

Centrifugal force was employed in order to induce a spatial gradient of fibre distribution in the epoxy/carbon fibre system. The gradient structure of the epoxy/carbon fibre composite can be controlled by varying the rotation time and the material parameters, such as fibre length, fibre content and matrix viscosity. The spatial gradient distribution of carbon fibres in an epoxy matrix was achieved by the combined mechanism of packing and settling. The mechanical properties of the functionally gradient epoxy/carbon fibre composite were also investigated. At the same content of carbon fibre, the flexural strength of the functionally gradient composite was higher than that of conventional isotropic composite. This revised version was published online in November 2006 with corrections to the Cover Date.     

基于子结构法的升船机主传动系统的动力学建模

用动态子结构法对三峡升船机的主传动系统建立动力学模型。把整个系统分为8个一级子系统,每个一级子系统又分为4个二级子系统,建立每个二级子系统的动力学模型,利用边界条件,层层组装,最后组合成完整的动力学方程。     

64位Linux并行计算大气模型效率优化研究*

研究了CMAQ大气模型在64位Linux操作系统上不同CPU核心数目并行计算模拟耗时以及结果的差异情况。研究结果表明,并行计算能大幅缩短CMAQ模拟耗时,以16个CPU核心并行处理为性价比最佳值;此时连续模拟中国区域37天空气质量状况（分辨率36 km、167行×97列、垂直14层）平均耗时小于16 min/d,而相同情况下单核模拟耗时大于2 h/d;多于16个核心并行处理时,随核心数量的增加模型性能提升的趋势减缓;操作系统和参与运算的核心数目对CMAQ模型模拟结果没有影响。     

放电等离子体烧结技术制备过共晶Al-Si-Fe粉末冶金合金的显微组织和压缩变形行为

Al-Si-Fe基铝合金材料由于具有高耐磨性、低密度以及低热膨胀性能,因而主要用于汽车发动机部件。利用气体雾化粉末,采用放电等离子体烧结技术制备Al-17Si-5Fe-2Cu-1Mg-1Ni-1Zr合金。所制备材料的晶粒尺寸为530nm,并且观察到细等轴晶粒和均匀分布的析出物。研究了放电等离子体烧结技术制备的材料在不同温度和应变速率下的压缩变形行为。结果表明,所有的真应力一真应变曲线在达到峰值应力后呈稳态流动趋势,随着测试温度的升高和应变速率的降低,峰值应力呈下降趋势。在变形样品中,观察到了等轴晶粒和等轴晶粒中的位错结构。这些现象说明,合金在高温变形过程中发生了动态再结晶。     

RAPID SOLIDIFICATION OF SUBCOOLED SMALL METALLIC DROPS

Accurate rapidly and slowly varying analytical solutions are obtained for the problem of the rapid solidification by convection of subcooled small metallic drops. These solutions, which were suggested by the approximate results obtained by using a quasi-moving-boundary approach, are useful in estimating metallurgical parameters in rapid rate solidification technology.

The rapidly varying regular perturbation solution describes recalescence during which the liquid core increases very quickly from the nucleation temperature to the melting point. Enormous internal heat transfer rates dominate the process, and the solid-liquid interface is morphologically unstable, during recalescence. External convective heat transfer dominates after recalescence, and the slowly varying solution shows that this period begins when the dimensionless thickness of the solidified region is approximately equal to 1 ? (1 ? S)^1/3. The position of the interface after recalescense is given by (1 ? S ? 3Hθ)^1/3

Complete freezing of the droplets occurs at time t = (R²/α₁)(1 ? S)/3H. The time required for recalescence is on the order of microseconds and is usually only a small fraction of the total freezing time.     

微波辅助离子液体液-液微萃取分析水溶性化妆品中防腐剂的含量

采用微波辅助离子液体分散液-液微萃取对水溶性化妆品中的对羟基苯甲酸酯类防腐剂进行预处理,并结合高效液相色谱-紫外检测对其分析。考察了离子液体用量、分散剂种类及用量、微波时间、萃取时间、离心时间和盐效应对离子液体微萃取效果的影响。在最佳实验条件下,3种酯的富集因数为68.3～124.5,标准曲线在0.1～50 mg/L呈线性相关,线性相关系数r>0.9989,相对标准偏差(RSD,n=3)为4.9%～5.1%。3种物质的检测限为0.6～1.2μg/L。     

2,4-二甲基-3-氨基噻吩的合成

[方法]2,4-二甲基-3-氨基噻吩主要用于有机合成,是合成除草剂的重要中间体。以巯基乙酸和乙酰丙酮为起始原料,经过亲核加成、酯化、关环、水解、脱羧、还原等7步反应得到2,4-二甲基-3-氨基噻吩,并优化了关键的硝化反应。[结果]正交试验显示硝化反应的最优条件:反应温度15℃,3,5-二甲基噻吩-2-甲酸与乙酰硝酸酯的摩尔比1∶7,反应时间55 min。[结论]该路线简单经济,条件温和,收率高于其他路线,适合生产。     

相转移催化法合成糖苷类化合物的研究进展

相转移催化法具有操作简便,反应速度快,反应条件温和,后处理简单和立体选择性强等优点。近年来相转移催化法广泛应用于糖苷类化合物的合成。综述了相转移催化法所用的各类相转移催化剂(季铵盐类、叔胺类等)在糖苷类化合物合成中的应用,指出季铵盐类催化剂应用最为广泛。