Detection time analysis for the multiple-user cooperative spectrum sensing scheme in cognitive radio networks

In this paper, a novel multiple-user cooperative spectrum sensing (MCSS) scheme is proposed to achieve the spatial diversity gains for cognitive radio (CR) networks, where only the best relay, selected among all the candidate relays in accordance with the quality of channel conditions, is utilized to cooperatively detect the primary user. Closed-form expressions of detection time for the traditional non-cooperative and the proposed MCSS schemes are derived over Rayleigh fading channels. In addition, numeric...     

MEMS材料力学性能的测试方法

介绍国内外MEMS(micro-electro-mechanical system)材料力学性能的测试方法,包括纳米压痕法、薄膜打压法、梁弯曲试验、微拉曼光谱法、单轴拉伸法等.分析各种测试方法的优缺点、基本原理和最新进展.详细介绍单轴拉伸试验方法的试验原理、特点及发展现状, 在此基础上介绍作者们在MEMS材料单轴拉伸试验方面的阶段性研究成果,包括单轴拉伸试样设计、夹具设计、加载方法及应变测量技术等.试样和夹具的设计采用有限元方法模拟不同形状参数试样的拉伸试验过程,确定试样的外形和尺寸.应变测量采用的是激光干涉应变计法(interference strain /displacement gauge, ISDG),并用所研制的微小试样拉伸试验机,成功测得多晶铜薄膜材料的应力-应变曲线.     

有效控制聚乙烯装置落地料的产生

介绍聚乙烯装置落地料的情况，指出淘析器的分离能力与风送量不匹配，振动筛Y-5012X／5012设计不合理以及相关仪表、联锁故障是该装置落地粒料与粉料产生的原因。采取风送系统技措及优化操作、改造Y-5012X／5012、调整仪表参数及联锁改造这三项措施后，有效控制和预防落地料的产生。     

异形高层建筑物施工测量技术

根据成都市温江海科大厦办公楼建筑物设计形式与施工特点(主楼、副楼位于同一圆心不同半径的两段圆弧放射线上,两楼的连接段则为方形建筑),介绍控制网加密的布设原则和数据处理的方法;对比目前常用的各种施工测量放样方法及其适用条件,分析了极坐标放样法在异形高层建筑物施工测量中的应用及优点.     

Optimal design of one-sided exponential cumulative sum charts with known and estimated parameters based on the median run length

As a useful tool in statistical process control (SPC), the exponential control chart is more and more popular for monitoring high-quality processes. Considering both known and estimated parameter cases, the one-sided exponential cumulative sum (CUSUM) charts are studied in this paper through a Markov chain approach. Because the shape of the run length (RL ) distribution of the one-sided exponential CUSUM charts is skewed and it also changes with the mean shift size and the number of Phase I samples used to estimate the process parameter, the median run length (MRL ) is employed as a good alternative performance measure for the charts. The optimal design procedures based on MRL of the one-sided exponential CUSUM charts with known and estimated parameters are discussed. By comparing the MRL performance of the chart with known parameters with the one of the chart with estimated parameters, we investigate the effect of estimated process parameters on the properties of the chart. Finally, an application is illustrated to show the implementation of the chart.     

罗茨泵/风机基于脉动品质的高形轻量化通用方法

为定量分析高形转子在脉动品质和轻量化程度方面的优势。依序推导出包含基础形状系数和高形基础形状系数两变量下的流量脉动系数与单位排量体积的计算公式,并由高形点恰好避让对偶共轭轮廓的几何位置,推导出高形形状系数关于基础形状系数的计算公式,及构建最简洁的轻量化模型。结果表明:基础形状系数、叶顶半角和转子叶数是影响流量品质和轻量化的三大独立参数;高形泵较基础泵均有很大改善等。得出基于脉动品质的高形轻量化可归结为采用最小的许可叶顶半角、最大的许可脉动系数下的单位排量体积最小化的结论。     

Experimental investigation on the yield behavior of metal foam under shear-compression combined loading

Metal foams are typically subjected to quasi-static or dynamic shear-compression combined loading in applications such as energy absorbers and structure protectors. The yield behavior of a metal foam under dynamic and quasi-static shear-compression combined loadings is investigated in this study. First, quasi-static and dynamic compression-shear combined tests at different loading angles are conducted using a universal testing machine and a rotatable Hopkinson bar system, respectively. Shear deformation reduces the plateau stress as the loading angle increases. Subsequently, the yield modes of the metal foam under combined loadings are investigated. Only one yield band occurs under a combined loading with large loading angles(mode I),whereas several yield bands occur under a combined loading with small loading angles(mode II). Finally, the yield surface plot of metal foam indicates significant enhancement in terms of normal stress and shear stress under dynamic loading. Quasi-static and dynamic phenomenological yield criteria for a shear-normal stress space are established to provide a brief and precise prediction of the behavior of metal foam under quasi-static and dynamic combined loadings.     

基于Radius协议的网络计费系统设计与实现

介绍了Radius协议的原理以及网络计费的原理和各种类型,并在此基础上给出了一个基于Radius协议的局域网计费系统的实现方案.     

飞机对中和偏心拦阻钩索动力学分析

研究装有尾钩飞机对中或偏心拦阻着陆后,计及弯折波在索中的传播情况下拦阻索的动力响应.计算作用在拦阻钩上的冲击载荷和飞机的减速过程.文中以美国BAK-13和E-28拦阻机为例进行计算分析,并用BAK-13拦阻机和各种机型,比较模拟计算和实测值的拦阻最大钩载.结果表明, 文中建立的模型和分析结果具有良好的精度,可为飞机-拦阻机相容性及舰载机的拦阻提供参考.