IMPACT OF BUSY LINES AND MOBILITY ON CALL BLOCKING IN A PCS NETWORK

Several analytical models have been proposed to study the blocking probability for personal communications service networks or mobile phone networks. These models cannot accurately predict the blocking probability because they do not capture two important features. First, they do not capture the busy-line effect. Even if a cell has free channels, incoming and outgoing calls must be dropped when the destination portable is already in a conversation. Second, they do not capture the mobility of individual portables. In these models, mobility is addressed by net hand-off traffic to a cell, which results in traffic with a smaller variance to a cell compared with the true situation. We propose a new analytic model which addresses both the busy-line effect and individual portable mobility. Furthermore, our model can be used to derive the portable population distribution in a cell. The model is validated against the simulation experiments. We indicate that the previously proposed models approximate a special case of our model where the number of portables in a cell is 40 times larger than the number of channels.     

Microwave-assisted oxygenation of melt-processed bulk YBa2Cu3O7-δ ceramics

The properties (superconducting and non-superconducting) of YBa₂Cu₃O_7-δ bulk ceramics (YBCO) are strongly dependent on the oxygen deficiency, δ. Unfortunately, whether sintering or melt-processing is used to form the material, the final oxygen content is usually far from that which gives the optimum superconducting properties (δ≲0.1). Because of this, an additional oxygenation stage has to be carried out in which the material is heated and held at some elevated temperature (∼400–500 °C) for a significant time (often > 100 h) to allow oxygen to diffuse into the sample. Other diffusion-based processes (e.g. sintering) are known to be substantially enhanced in the presence of a microwave field, and it is reasonable to expect that the diffusion of oxygen into YBCO may also benefit from the application of such technology. The oxygenation of melt-processed YBCO using conventional and microwave-assisted heating has been compared. The diffusion coefficient at 400 and at 450 °C is shown to be enhanced by about 30% through the application of a high-frequency microwave field. Because the oxygenation time is inversely proportional to the diffusion coefficient, this represents a significant reduction in process time. The equilibrium value of the oxygen content is not affected by the application of a microwave field, and therefore the sample temperature must be the same for both microwave-assisted and conventional processing. Consequently, the observed enhancement is an example of a genuine non-thermal microwave effect. This revised version was published online in November 2006 with corrections to the Cover Date.     

基于MATLAB的行星轮系优化设计

针对行星轮系的常规设计流程常规设计的不足,以行星轮系体积最小为设计目标,确定目标函数与约束函数,建立最优设计的数学模型。根据所建立的数学模型,采用MATLAB优化工具箱中的fmincon优化函数编制相应的M文件并运行得到优化的设计参数,减小了行星轮系的体积,提升了设计的质量。     

一种用于GIS超高频检测的滤波器

为提高使用外置天线的GIS超高频检测系统的信噪比,设计了一种工作频带300~1000MHz的微带线带通滤波器。根据微带线滤波器设计原理,确定滤波器类型、结构和级数,利用先进的EDA仿真工具进行结构仿真和优化并提出了一种减小滤波器尺寸的方法。特性曲线和实测性能表明,该滤波放大器能抑制低频干扰信号,放大局放信号,提高信噪比,从而满足了UHF微弱信号滤波预处理要求。     

含冰蓄冷空调的冷热电联供型微网多时间尺度优化调度

冷热电联供型微网(CCHP-MG)对实现能源可持续发展和构建绿色低碳社会具有重要的应用价值,而内部复杂的能源结构与设备耦合关系、可再生能源的消纳和负荷波动的平抑给其优化运行带来了挑战。文中提出含冰蓄冷空调的CCHP-MG多时间尺度优化调度模型,研究冰蓄冷空调的不同运行方式对优化调度的影响。日前计划中通过多场景描述可再生能源的不确定性,侧重于一个运行优化周期内CCHP-MG的经济运行;日内调度基于日前计划方案,根据冷热电在不同时间尺度上的相关性和互补性,提出考虑冷热负荷变化的双层滚动优化平抑模型,求解各联供设备的调整出力。仿真结果表明:冰蓄冷空调的运行方式关系到CCHP-MG的综合效益的提高;多时间尺度优化调度模型不仅可以满足用户的冷、热、电能的需求,还能有效平抑日内阶段供需侧随机性波动,实现CCHP-MG经济及稳定运行。行带来了挑战。文中提出含冰蓄冷空调的CCHP-MG多时间尺度优化调度模型,研究冰蓄冷空调的不同运行方式对优化调度的影响。日前计划中通过多场景描述可再生能源的不确定性,侧重于一个运行优化周期内CCHP-MG的经济运行;日内调度基于日前计划方案,根据冷热电在不同时间尺度上的相关性和互补性,提出考虑冷热负荷变化的双层滚动优化平抑模型,求解各联供设备的调整出力。仿真结果表明:冰蓄冷空调的运行方式关系到CCHP-MG的综合效益的提高;多时间尺度优化调度模型不仅可以满足用户的冷、热、电能的需求,还能有效平抑日内阶段供需侧随机性波动,实现CCHP-MG经济及稳定运行。     

Optimal placement of distributed generation units in distribution systems via an enhanced multi-objective particle swarm optimization algorithm

This paper deals with the optimal placement of distributed generation （DG） units in distribution systems via an enhanced multi-objective particle swarm optimization （EMOPSO） algorithm. To pursue a better simulation of the reality and provide the designer with diverse alternative options, a multi-objective optimization model with technical and operational con- straints is constructed to minimize the total power loss and the voltage fluctuation of the power system simultaneously. To enhance the convergence of MOPSO, special techniques including a dynamic inertia weight and acceleration coefficients have been inte- grated as well as a mutation operator. Besides, to promote the diversity of Pareto-optimal solutions, an improved non-dominated crowding distance sorting technique has been introduced and applied to the selection of particles for the next iteration. After verifying its effectiveness and competitiveness with a set of well-known benchmark functions, the EMOPSO algorithm is em- ployed to achieve the optimal placement of DG units in the IEEE 33-bus system. Simulation results indicate that the EMOPSO algorithm enables the identification of a set of Pareto-optimal solutions with good tradeoff between power loss and voltage sta- bility. Compared with other representative methods, the present results reveal the advantages of optimizing capacities and loca- tions of DG units simultaneously, and exemplify the validity of the EMOPSO algorithm applied for optimally placing DG units.     

Adaptive PID control of systems with unknown time delay

A new algorithm for the adaptive control of systems with unknown time delay is presented in which the underlying control law has the familiar PID structure. The design is based on a continuous-time approach. This algorithm can be applied to a class of high-order systems which can be modelled by either a second-order system with time delay or a first-order system with time delay. The parameters of the system including time delay are estimated recursively by a derivative-free least-squares algorithm. The controller settings are selected according to a set of analytical formulae derived from mean-square error criteria. The algorithm is tested on simulated examples as well as a laboratory-scale coupled-tank apparatus.     

非金属矿物胶体优化建筑涂料性能的研究

由长径比为100左右的纤维状纳米矿物、微纳米结晶体矿物和片状纳米矿物为主构成的非金属矿物胶体,能对建筑涂料的开罐效果、触变性、贮存稳定性、对比率、耐洗刷性、耐沾污性等起到优化作],与钛白粉有协同的增效效应.能在涂料质量不变或略有提高的情况下减少乳液和钛白粉的用量,即降低涂料的生产成本.