Effect of sample radius on stabilityof electromagnetic levitation melting

Based on the power dissipating model of spherical sample in free convection gas medium and the expression of input power, the model of temperature calculation for electromagnetic levitation melting sample was established. Considering the limitation of levitation force and levitation sample temperature, the principle of stability levitation zone computation was determined. A spherical sample (ThDy)Fe2 under the protection of argon gas was examined, and the effect of radius of levitation sample and perturbation on the stable levitation zone was investigated.The results show that longitudinal perturbation and transverse perturbation can shorten the length of stable levitation zone and the range of levitation sample radius. By increasing the sample radius and weakening the perturbation the electromagnetic levitation melting stability of sample can be improved.     

我国加入WTO后先进制造技术发展的形势和应对策略

对先进制造技术(AMT)的概念和重要性进行了介绍和讨论。针对加入世界贸易组织(WTO)后我国先进制造技术所面临的机遇和挑战，提出了应对策略。     

基于神经网络和遗传算法的实验参数确定

将 BP神经网络用于实验数据结果的“预处理”,剔除奇异样本数据 ,并利用实数直接操作的遗传算法 (FGA) ,发挥 FGA概率搜索和群体优势 ,将处理后的数据分别代入给定的含参数的方程 ,在总体误差最小的情况下 ,寻求符合实验数据的参数的优化解 ;将优化结果与常规数理统计方法进行了比较 ,证实了该方法的有效性 ;而且对其它实验数据的处理及实验参数的确定 ,有一定的参考价值。     

基于虚拟现实的扫描探针显微镜仿真培训系统

阐述了虚拟现技术的概念和相关知识，提出了基于虚拟现实的发描探针显微镜仿真培训系统的总体设计思想和功能模块划分．在系统开发时，由于Java 3D三维造型功能类中仅包含标准几何形体的问题，提出了解决复杂曲面造型的方法．经试验，该系统效果较好．     

企业实施信息化的捷径

近几年兴起的ASP模式采用网络租赁的方式为企业提供信息化服务,无疑为中小企业实现信息化提供了一条捷径。介绍了ASP模式的概念和目前在我国的发展情况;分析并探讨了其在发展中小企业信息化方面的优势以及目前存在的一些问题;最后对中小企业选择ASP模式进行信息化时应考虑的问题提出了几点看法。     

基于Matlab无刷电动机模型参考自适应控制的研究与实现

本文在分析无刷电动机数学模型的基础上,建立了控制系统的仿真模型,提出了直流无刷电机调速系统模型参考自适应控制的新方法.在双闭环调速系统中,电流环采用电流滞环控制,转速环采用间接参考模型自适应控制,控制器参数估算采用最小二乘算法.仿真结果表明:这种新型的间接模型参考自适应控制方法响应快、无超调、鲁棒性强、抗干扰能力好,较传统PI控制具有更好的动、静态特性.     

地区电网应对各种事故的策略

本文研究各种电网事故发生的原因,提出综合性的应对策略,从地区电网的角度加强继电保护和安全稳定自动装置的优化配置;采用先进可靠的调度自动化系统对电网进行密切监控;保证正常情况下系统的安全稳定运行和事故时能够及时正确地切除故障,防止事故扩大。     

Estimation of break location and size for loss of coolant accidents using neural networks

In this work, a probabilistic neural network (PNN) that has been applied well to the classification problems is used in order to identify the break locations of loss of coolant accidents (LOCA) such as hot-leg, cold-leg and steam generator tubes. Also, a fuzzy neural network (FNN) is designed to estimate the break size. The inputs to PNN and FNN are time-integrated values obtained by integrating measurement signals during a short time interval after reactor scram. An automatic structure constructor for the fuzzy neural network automatically selects the input variables from the time-integrated values of many measured signals, and optimizes the number of rules and its related parameters. It is verified that the proposed algorithm identifies very well the break locations of LOCAs and also, estimate their break size accurately.     

Spark Plasma Sintering Bulk Sm2 Fe17NxMagnets

High performance Sm2Fe17Nx magnetic powders were fabricated by ball-milling method and were compacted using spark plasma sintering(SPS) technique.Effects of processing conditions on the magnetic properties and decomposition dynamic of the magnets were investigated.It is found that higher sintering temperature improves the densification of the magnets, while deteriorates their magnetic properties simultaneously due to the decomposition of the Sm2Fe17Nx.Sintering at lower temperature can preserve the crystal structure of Sm2Fe17Nx compound, while the powders cannot be consolidated into a fully dense compact.An increased compressive pressure leads to better magnetic properties and higher density for the magnet at the same sintering temperature.     

Preparation of AZ91D Slurries for Semi-Solid Forming Using Al8 ( Mn, Fe) 5 Precipitates

During the solidification of the AZ91D-alloys, the Al8(Mn, Fe)5 phase is generally precipitated in the melt in advance of the precipitation of the primary α-Mg. The basic principle for manufacturing AZ91D-alloy slurries for semi solid forming is to use the Al8(Mn, Fe)5 precipitates as the heterogeneous nucleation sites for primary α-Mg phases. Microscopic analysis for the location of the Al8(Mn, Fe)5 precipitate explains that the Al8(Mn, Fe)5 precipitate is the effective heterogeneous nucleation site for the primary α-Mg phase. It was also observed that increase of the Mn content in the melt and the cooling rate below to the solid/liquid two-phase region resulted in smaller and more globular primary α-Mg due to the increase of heterogeneous nucleation sites. It was found that the average α-Mg diameter grew as a function of t0.278, where t is the holding time at the solid/liquid two-phase region. This would be attributed to the Ostwald type ripening and coalescence between primary α-Mg phases. The cooling rate below to the solid/liquid two-phase region, Mn content in AZ91D alloy, and the holding time and temperature affected on the quality of slurry.