正则表达式匹配引擎性能分析

正则表达式具有强大的描述能力,在计算机领域,正则表达式匹配技术应用十分广泛。目前,已经有多个正则表达式匹配引擎,在实际应用中,对于不同的匹配规则集和正则语法,不同的匹配引擎会有不同的性能表现。本文通过对PCRE、Greta、Boost、RE2四种常用正则表达式匹配引擎的性能测试,给出在不用的正则语法情况下的匹配速度,并深入分析不同坏境下适用的正则表达式匹配引擎。对实际系统设计中正则表达式库的选择有指导意义。     

快速高精度除法算法的FPGA实现

为在现场可编程门阵列(FPGA)中实现快速高精度除法,在传统的倒数除法的基础上,提出一种改进算法.对倒数求解采用泰勒级数展开结合优化搜索逼近,求出各个分区间内的拟合一次两项式,再通过一次牛顿迭代提高精度.时序仿真结果表明,以该算法构建的除法器易于在FPGA上实现,时延仅为6个时钟周期,能达到2(-34)的有效精度和86...     

EXPERIMENTAL ESTIMATION OF A SCALING EXPONENT FOR TIP VORTEX CAVITATION VIA ITS INCEPTION TEST IN FULL- ANDMODEL-SHIP

Tip vortex cavitation noise of marine propeller became primary concerns to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the tip vortex and its induced noise are normally conducted through the model test in a water cavitation tunnel. However the Reynolds number of model-test is much smaller than that of the full-scale, which subsequently results in the difference of tip vortex cavitation inception. Hence, the scaling law between model-and full-scales needs to be identified prior to the prediction and assessment of propeller noise in full scale. From previous researches, it is generally known that the incipient caivtation number of tip vortex can be represented as a power of the Reynolds number. However, the power exponent for scaling, which is the main focus of this research, has not been clearly studied yet. This paper deals with the estimation of scaling exponent based on tip vortex cavitation inception test in both full-and model-scale ships. Acoustical measurements as well as several kind of signal processing technique for an inception criterion suggest the scaling exponent as 0.30. The scaling value proposed in this study shows slight difference to the one of most recent research. Besides, extrapolation of model-ship noise measurement using the proposed one predicts the full-scale noise measurement with an acceptable discrepancy.     

Effective parameters on diameter of carbon nanotubes by plasma enhanced chemical vapor deposition

The effective parameters on the diameter of carbon nanotubes (CNTs) by plasma enhanced chemical vapor deposition (PECVD) were presented.Among lots of influential parameters,the effects of the catalytic film thickness and the pretreatment plasma power on the growth of CNTs were investigated.The results show that the size of catalytic islands increases by increasing the thickness of catalytic layer,but the density of CNTs decreases.The pretreatment duration time of 30 s is the optimal condition for growing CNTs with about 50 nm in diameter.By increasing the pretreatment plasma power,the diameter of CNTs decreases gradually.However,the diameter of CNTs does not change drastically from 80 to 120 W.The uniformly grown CNTs with the diameter of 50 nm are obtained at the pretreatment plasma power of 100 W.     

1 100 kV GIS用断路器的设计

介绍了所研制的1 100 kV、50 kA GIS用断路器的技术规范、基本结构及合闸电阻的合理布置;利用商用Maxwell2D,3D软件及专用的程序,对断路器灭弧室的电场分布情况进行了分析,对合闸电阻的热容量进行了计算,并做了相关的试验验证,证明该型断路器的开断性能良好,其所配用的合闸电阻的热容量满足使用要求。     

Optical fiber microwires and nanowires manufactured by modified flame brushing technique: properties and applications

The modified "flame brushing" technique has been used to manufacture microwires and nanowires from both silica and compound glasses. In this paper, the properties of the wires manufactured by this technique are presented. Applications fabricated from microwires are also discussed.