碳/环氧复合材料的冲击拉伸

该文研究了T300碳纤维单向增强的环氧复合材料,在应变率从10~(-3)/s到10~3/s范围内的冲击拉伸行为.通过对实验数据进行拟合,得出该范围内材料对应变率具有弱的敏感性,表现在破坏强度及破坏应变随应变率增加不显著变化,平均模量几乎不受应变率的影响.分析了试件的几何尺寸效应,讨论了应力波作用对破坏形态的影响以及实验中观察到的拔出现象.从应变率在10~2～10~3/s附近材料行为某些非确定性,指出在更宽范围内了解其性能的必要性.     

基于移动锚节点的无线传感器网络圆心定位

文章提出了一种利用无线传感器网络无线信号接收强度（RSSI）和移动锚节点轨迹来获得待定节点位置的算法。该算法在有多个可移动锚节点的情况下,定位将会更加高效。在定位阶段,通过RSSI测得锚节点到待定节点的距离,并利用三个以上移动锚节点的坐标（包括三个）来求解圆的方程,计算出待定节点的位置。     

基于RTLinux和AD2S80A的角位置测量系统设计与实现

基于RTlinux和AD2S80A的角位置测量系统,选用旋转变压器和感应同步器作为测量系统的传感器,利用AD2S80A轴角变换器将两种测量传感器输出的模拟信号转换为相应的数字信号。根据双通道测角系统粗精耦合的原理,在RTLinux嵌入式系统中对两种数字信号进行耦合处理,并对耦合后信号的进行补偿处理,实现角位置的高精度测量。检测数据表明,这种测量系统可以实现以内的测量精度。     

基于虚拟锚节点的序列定位算法研究

为解决无线传感器网络中现有序列定位算法存在的定位精度差、复杂度较高等问题,本文提出一种基于虚拟锚节点的序列定位算法。该算法根据未知节点与已有锚节点、虚拟锚节点(锚节点间连线的中点)间的RSSI值建立定位序列来获取未知节点的位置。仿真结果表明,基于虚拟锚节点的序列定位算法比原有算法在定位精度上有较大提高,且降低了算法的硬件代价和时间代价。     

浅析大尺寸测量的意义及发展趋势

以当今涉及大尺寸测量的生产单位所面临的实际问题为依据,分析了研究大尺寸测量的重要意义,阐述了国内外近年来大尺寸测量的发展概况及下一步的发展趋势,为设计符合生产实际需求的大尺寸测量机指明了方向。     

气动锚杆钻机冲击频率测量仪的设计

针对气动锚杆钻机冲击频率不易测量的问题,提出了一种新型气动锚杆钻机冲击频率测量仪的设计方案。该测量仪采用压力传感器采集钻机冲击信号,采用电压比较器和单稳态触发器处理冲击信号并输入到单片机,由单片机计算出钻机冲击频率。实际应用表明,该测量仪可准确、方便地测量出钻机冲击频率。     

一种测量工业环境感应传导干扰的方法

针对采用干扰测量仪或频谱分析仪只能测量工业环境中干扰源的辐射干扰强度的问题,提出了一种测量工业环境感应传导干扰的方法。该方法采用HBYV非双绞2芯线作为干扰接收体,采用数字示波器记录干扰波形的最大幅值和单个脉冲的最大强度,通过与标准干扰发生器感应到HBYV非双绞2芯线上的干扰信号大小进行比较,确定干扰强度。以瞬变脉冲群干扰强度和浪涌干扰强度的测量为例,详细介绍了该方法的具体实现。     

Finite-size effects in surface tension: Thermodynamics and the Gaussian interface model

It has been suggested by Kayser that finite-size effects associated with capillary waves might play a significant role in some surface tension measurements; for capillary rise between plates a distance D apart, an effect varying as 1/D and apparently observable in measurements, was proposed. In reconsidering this problem, one must analyze the thermodynamics of finite-size corrections to surface tension. In particular, one sees that capillary rise between plates does not measure the interfacial free energy density but, rather, a derivative of the interfacial free energy with respect to a system dimension. The quantity needed to draw definite conclusions, the finite-size residual free energy, can be calculated within the harmonic or Gaussian capillary wave model in d spatial dimensions with the aid of Poisson summation techniques and should yield the correct leading asymptotic behavior. For d=3 and experimentally relevant parameter values, the results are independent of the short-wavelength cutoff needed in the model and can be checked against the theory of conformai covariance at two-dimensional critical points. It is found that the finite-size effects in capillary-rise measurements of surface tension vary as 1/D ² (with a universal coefficient) but are too small to be seen in current experiments.Invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

A generalized equation for surface tension from the triple point to the critical point

A three-parameter generalized equation is proposed for surface tension from the triple point to the critical point. This equation not only fits the data well but also is good for interpolation between the normal boiling point and the critical point. This equation is also good for extrapolation to the triple point. This equation has been tested using the surface tension of water from the triple point to the critical point. The constants of this equation obtained using orthobaric surface tensions are given for a number of compounds. The isobaric surface tensions determined at a pressure of 1 atm do not differ significantly from the orthobaric surface tensions. Such data also have been used in obtaining equations from the triple to the critical point.Nomenclature T _c Critical temperature, K - T _t Triple point, K - T _m Melting point, K - T _r Reduced temperature, K - X (T _c-T)/T _c - Surface tension, dyne · cm^–1;10^–3N · m^–1 - _m Surface tension at the melting point - _f Surface tension at T _r=0.9 - _t Surface tension at the triple point - Relative deviation 100[ _obsd– _calcd]/ _obsd - Standard deviation [( _obsd– _calcd)²/(No. points—No. parameters)]^0.5     

A relation between interfacial and bulk properties along the saturation curve

A liquid-vapor interface in thermal equilibrium was considered, where the pressure tensor depends upon the density (z) and the position z. The surface tension coefficient results are parametrized with the bulk compressibility, liquid-vapor density difference, and interfacial width along the saturation curve. Previous results at the triple and critical points reported by other investigators are verified. Also included is a plot of the computed results using the parametric equation and experimental data for different substances.