High-pressure dc sputtering of High-Tc BPSCCO thin films withTc(0) above 100 K

High-T _c Bi(Pb)-Sr-Ca-Cu-O thin films have been made on single-crystal MgO substrates using high-pressure dc sputtering technique. X-ray studies confirm the crystallinity and highly oriented structure withc-axis perpendicular to the substrate. By optimizing the annealing schedule the formation of the high-T _c phase is stabilized. The best film exhibited superconducting transition temperature with zero-resistance temperature,T _c(0), as high as 101 K. Temperature dependence ofJ _c indicates the presence of Josephson-type weak links.     

Gel chromatographic investigation of p-benzoquinone and styrene products copolymerized in the presence of BF3·OEt2

The molecular weight distribution of copolymers of p-benzoquinone and styrene was studied by g.p.c.. It was shown that the products synthesized have low molecular weights and narrow MWD. p-Benzoquinone was found to be a copolymer macromolecule regulator.     

Adaptive prescribed time control for quadrotor formation with stochastic links failure

The formation control for multiple quadrotors subject to maintaining the formation configuration and collision avoidance in the situation of stochastic links failure is investigated in this paper. First, the distributed formation controller is designed, the position controller is developed to manage the desired formation of position, and the attitude controller is developed to control the translation and rotation movements of the quadrotor. Then, in order to avoid the collisions between multiple quadrotors and the obstacles, a potential energy function method is introduced into the quadrotor formation control combined with the nest adaptive control. Inspired by the design of event trigger controller, a communication compensation controller is designed to ensure the stability of quadrotor formation under the condition of random communication interruption and recovery. Moreover, a prescribed time function is designed, which means the convergence time of the formation system can be set in advance. The prescribed time stability of the formation control system is proved by Lyapunov theory. Finally, the simulation results verify the effectiveness and superiority of this method.     

以参考集为基础的排序指标之间的关系

目的　研究以参考集为基础的模糊量排序指标 ,即第二类排序指标所导出的序关系之间的联系 .方法　给出联系的定义 ,讨论两两联系 .结果与结论　指出了第二类所有排序指标中的相同性、有联系及独立性     

兼顾稳定性与经济性的交直流系统直流落点选择方法

直流电系统落入受端交流电网的落点选择需要考虑交直流系统的相互作用,主要包括有效短路比、静态电压稳定指标和受端系统的有功功率损耗。文中提出一种兼顾稳定性与经济性的直流落点选择方法。基于数学上解决多目标决策问题的线性加权和法,首先设置各指标的门槛值,然后对其进行归一化处理,采用组合赋权法合理确定权系数,建立目标函数,选出最...     

一种考虑无线链路突发差错的TCP流量新解析模型

该文提出新的TCP流量理论分析模型,研究无线链路突发差错引起的分组丢失对TCP流量性能的影响。理论分析及数值仿真结果表明,该解析模型是合理的,既有较准确的分析结果,又降低了复杂度。同时,还表明在慢衰落信道中相关性越强,TCP流量越大,独立同分布信道的TCP流量是下界,即物理信道相关性对TCP流量是有利的。     

本地网光缆线路物理双路由的互保问题

针对本地网光缆线路受市政建设的影响，迁、改割接比较频繁且常会受到外力的作用而阻断的情况，讨论了用户引入光缆和中继光缆物理双路由互保的问题。     

软切换FSO/RF链路混合编码调制算法性能分析

将自由空间光(FSO)通信链路的高速率优势与射频(RF)链路的可靠性优势互补结合,针对FSO/RF混合通信链路组网的物理层数据可靠传输问题,研究软切换机制下采用LDPC混合编码与2-PPM和16QAM调制的系统方案性能。混合系统FSO链路在Gamma-Gamma信道不同湍流强度与RF链路在Rician信道不同信噪比条件下的仿真结果表明,所述方案在软切换下达到1×10~(-6)误比特率时,不同条件下可获得1.3~8.0 dB不等的性能增益改善,显著提高在不同链路条件下FSO/RF混合通信系统的数据传输可靠性。     

Analysis of a satellite antenna tracking loop driven by BPSK modulated signals

The subject of this paper is an antenna tracking system used to maintain an antenna on board a geosynchronous (GEO) satellite, pointed towards a low earth orbit (LEO) satellite. The tracking system uses the BPSK modulated signals transmitted from the LEO satellite. The signal is received by an electronically switched antenna beam. A suitable processing of the received signal level then generates an error voltage which drives a tracking loop. The measurement of the received signal level is implemented by a power detector. Analysis of the antenna tracking algorithm is carried out and the performance is given in terms of linearized mean-square tracking error. The mean-square tracking error is related to the antenna beam parameters, to the closed loop bandwidth and to the statistics of the power measurement process. In particular, it is shown that a key parameter for the tracking loop performance is the signal-to-noise ratio (SNR) at the power detector output, which is inversely proportional to the variance of the pointing error, and a theory has been developed to find an accurate expression for the SNR. © 1997 John Wiley & Sons, Ltd.