Controlled growth and photoluminescence of highly oriented arrays of ZnO nanocones with different diameters

Large-scale oriented ZnO nanocone arrays were directly grown on zinc substrate through a hydro-thermal reaction of Zn foil with aqueous butylamine solution(3 mol/L) at 100—180 ℃ for 12 h.The syn-thesized products were characterized with X-ray diffraction,Raman spectrum,scanning electron mi-croscopy and transmission electron microscopy.The results showed that the ZnO nanocones were single crystalline with the wurtzite structure and grown along the [0001] direction.The diameter of nanocones is decreased with ...     

Requirement of ultra-high voltage GIS arrester to voltage gradient of metal-oxide varistor

The surge arrester with excellent protection characteristics would decrease the overvoltage level ap- plied on the power apparatus to reduce their insulation levels and manufacturing bottleneck. The arrester for the 1000-kV ultra-high voltage ac power transmission system is designed as tank-type structure. The field-circuit combination numerical method combining the three-dimensional finite element method with circuit is proposed to analyze the potential distribution of GIS arrester. By comparing several design schemes, the most effective method to improve the potential distribution along the varistor column is to increase the voltage gradient of the ZnO varistor. Synthesizing several influential factors, the suitable voltage gradient of ZnO varistor should be controlled to 435 V/mm, and the resulted nonuniform degree of the potential distribution along the varistor column inside the GIS arrester would be controlled smaller than 10%. The result in this paper provides the fundamental technical index for the study of the high voltage gradient ZnO varistors.     

p-moment stability of stochastic impulsive differential equations and its application in impulsive control

The exponential p-moment stability of stochastic impulsive differential equations is addressed. A new theorem to ensure the p-moment stability is established for the trivial solution of the stochastic impulsive differential system. As an application of the theorem proposed, the problem of controlling chaos of Lorenz system which is excited by parameter white-noise excitation is considered using impulsive control method. Finally, numerical simulation results are given to verify the feasibility of our approach. Supported by the National Natural Science Foundation of China (Grant No. 10772046)     

Effect of acetic acid on electrochemical deposition of carbon-nitride thin film

Electrochemical deposition method was employed to prepare CNx thin film from methanol-urea solution,and it was shown that adding a little acetic acid in the solution significantly affected the deposition process.After optimizing the experiment conditions,we obtained polycrystalline grains with sizes of about 3―7μm on the faces of single crystal silicon.X-ray diffraction spectrua indicate that the grains are mainly composed of cubic phase mixed with a small amount of β and α phases.     

Fractal model of lightning channel for simulating lightning strikes to transmission lines

How to accurately evaluate the direct-strike lightning protection is one of the key issues in the design of transmission lines. In this paper, three important issues in applying the fractal simulation to the lightning protection of transmission lines were discussed, including the criteria and implementation of upward leader inception, the connection with the magnitude of lightning current, and the calculation and control of fractal dimensions. Then we conducted the simulation iterately, leading to statistical results, which indicate that even if the transmission line satisfies the perfect shielding condition, shielding failure fault remains possible. Furthermore, we calculated the shielding failure fault rates of an EHV line with different ground obliquities and distribution of strike points over the interval between two neighboring towers along a UHV-DC line to find out the weak point of transmission-line lightning protection. This work provides a promising approach for improving the lightning protection property of transmission lines by optimizing the configuration of shielding wires and phase or pole conductors.     

Precision forming machine with rolling plate cross wedge rolling

Roller cross wedge rolling (CWR) machines have high rigidity, but sector dies are difficult to process. Plate CWR machines have low rigidity and need large floor space, but plate dies are easy to process. Neither roller CWR machine nor plate CWR machine can produce larger workpieces. Based on the above conclusions, this paper presents the mechanical principle of the precision forming machine with rolling plate CWR. Then, its design principle and machine construction are presented. There are a top press roller above the upper sliding plate and a bottom press roller under the lower sliding plate. The press rollers make rolling contact with the sliding plates. The plate dies are mounted on the upper and lower sliding plates, respectively. Furthermore, the axes of both press rollers and centerline of workpiece always keep in the identical vertical plane during forming process. These make the machine retain advantages of high rigidity for roller CWR machine and simpleness of manufacturing dies for plate CWR machine, and abandon defects of poor rigidity for plate CWR machine and difficulty of manufacturing dies for roller CWR machine. Moreover, the machine can produce larger workpieces.     

武汉都市工业园区的比较研究及路径选择

以武汉市为例,从发展类型、推进模式、集群形态、产业结构和产业效益5个方面对武汉都市工业园区的发展进行了比较研究.在此基础上,提出了武汉都市工业园区产业发展的3种路径选择,并初步探讨了产业发展的政策取向.     

混沌伪随机序列发生器的实现

针对广泛应用于密码学、扩频通信、数字系统测试等领域的伪随机序列信号实现的疑难问题,应用DSPBuilder模块将Matlab中S函数产生的Kent混沌二进制序列算法转换成VHDL语言,在现场可编程阵列FPGA上实现混沌伪随机序列.通过分析可以看出Kent混沌二进制序列具有优良的伪随机性能.     

Fabrication of a gradient refractive index preform using laminar shear mixing

A gradient refractive index rod was successfully prepared by a new fabrication method using laminar shear mixing, and a graded index polymer optical fiber that satisfied IEEE1394b was obtained from the method. To fabricate the gradient refractive index rod, a liquid monomer mixture with a relatively low refractive index was placed in a prepared cylindrical glass reactor and a transparent polymer rod with a higher refractive index was introduced at the center of the reactor. The reactor and the polymer rod were then rotated concurrently with a small rotating speed difference to generate a Couette flow in the liquid phase. The centrifugal force generated by rotation and the polymer diffusion into the liquid monomer mixture developed a graded concentration profile in a radial direction. The Couette flow could reduce the concentration fluctuation in a tangential direction. In addition, the graded index profile could be controlled by the copolymer composition of the rod and its diameter. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1100–1104, 2005     

基于有色Petri网的1553B总线建模及分析

针对1553B总线的实时性评估问题,提出一种基于有色Petri网(Colored Petri Net,CPN)的1553B总线模型;该模型基于分层建模的思想,分别建立了1553B总线的拓扑模型、总线控制器模型、远程终端模型和总线信道模型,有效刻画了1553B总线的拓扑结构和动态行为;仿真实验验证了所建模型的正确性和有效性,该模型可为构建满足特定实时性要求的1553B总线系统提供理论依据。