调制度测量轮廓术在复杂面形测量中的应用

调制度测量轮廓术(MMP)是将物体的高度信息编码在投影到待测物面上的正弦条纹的调制度信息中,可以实现对物体的垂直测量,特别适合测量表面有高度剧烈变化或不连续区域的物体。探讨了基于傅里叶变换的调制度测量轮廓术在复杂面形测量中的应用,提出了调制度焦深的概念并详细分析了调制度焦深对测量的影响,以调制度焦深为基础从测量系统设计的角度提出了提高测量精度的具体措施,给出了实验系统设计方案,讨论了影响测量精度的几个实际问题及解决方案。对复杂面形和深孔物体的实测结果表明,基于傅里叶变换的调制度测量轮廓术测量复杂面形物体可以达到较高的测量精度。     

游程长度受限码RLL(4,18)的研究

介绍了一种新的用于高密度光盘存储的游程长度受限码。给出RLL(4,18)码的构造方法和编解码步骤。对RLL(4,18)码的编码器和解码器进行了CPLD实现。对不同游程长度受限码的主要性能参数进行了比较。     

脉宽调制亮度调节方式下冷阴极荧光灯性能的实验研究

从电学的角度看,由于冷阴极荧光灯(Cold cathode fluorescent lamp,CCFL)具有十分复杂的阻抗特性,例如,灯管的阻抗几乎随工作电流的增加而减小,因此对其亮度进行调节也十分困难,尤其是大亮度调节比的场合。在对逆变电路进行优良设计并进行同步调光的前提下,脉宽调制(Pulse width modulating,PWM)可以实现高达2000:1的亮度调节比。这种大范围亮度调节特性,可以满足机载显示器的亮度调节性能要求。另一方面,CCFL的亮度输出与PWM的占空比之间具有良好的线性关系。此外,还不会对CCFL的寿命造成任何的影响,从而保证了军用显示器件的可靠性。实验结果表明,PWM方式可以很好地调节多管并列式背光灯组的亮度,这是其他调节方式无法做到的。     

Self-calibration wavelength modulation spectroscopy for acetylene detection based on tunable diode laser absorption spectroscopy

The expressions of the second harmonic(2f) signal are derived on the basis of absorption spectral and lock-in theories.A parametric study indicates that the phase shift between the intensity and wavelength modulation makes a great contribution to the 2f signal.A self-calibration wavelength modulation spectroscopy(WMS) method based on tunable diode laser absorption spectroscopy(TOLAS) is applied,combining the advantages of ambient pressure,temperature suppression,and phase-shift influences elimination.Species concentration is retrieved simultaneously from selected 2f signal pairs of measured and reference WMS-2f spectra.The absorption line of acetylene(C_2H_2) at 1530.36 nm near-infrared is selected to detect C_2H_2 concentrations in the range of 0-400 ppmv.System sensitivity,detection precision and limit are markedly improved,demonstrating that the self-calibration method has better detecting performance than the conventional WMS.     

An experimental study of circular sand–water wall jets

Laboratory experiments were carried out to study the effects of sand particles on circular sand–water wall jets. Mean and turbulence characteristics of sand particles in the sand–water wall jets were measured for different sand concentrations c_o ranging from 0.5% to 2.5%. Effects of sand particle size on the centerline sand velocity of the jets were evaluated for sand size ranging from 0.21 mm to 0.54 mm. Interesting results with the range of measurements are presented in this paper. It was found that the centerline sand velocity of the wall jets with larger particle size were 15% higher than the jets with smaller particle size. Concentration profiles in the vertical direction showed a peak value at x/d = 5 (where x is the longitudinal distance from the nozzle and d is the nozzle diameter) and the sand concentration decreased linearly for x/d > 5. Experimental results showed that the turbulence level enhanced from the nozzle to x/d = 10. For sand–water wall jets with a higher concentration (c_o = 1.5–2.5%), the turbulence intensity became smaller than the corresponding single-phase wall jets by 34% due to turbulent modulation. A modified logarithmic formulation was introduced to model the longitudinal turbulent intensity at the centerline and along the axis of the jet.     

内分液结构调控竖直管间歇流型建模研究

内分液流型调控管依靠微尺度网孔阻气通液的毛细力学特性,调控气液两相间歇流型以实现传热强化.基于Lockhart-Martinelli 分相模型以及Zuber-Findlay 漂移流动模型,建立描述内分液竖直管内流体动力特性的一维数学模型. 采用模型求解实验工况,计算结果与实验结果误差均在20% 以内. 计算发现,液速对流动现象起决定作用,而气速影响通过丝网的渗透程度. 在定性分析基础上,采用三角立方插值与最小二乘B 样条拟合获得了流动特性与气速、液速的定量函数关系. 据此得出结论,当Re_l < 693 7 时,一定出现第1 类工况;当Re_l > 693 7,且Re_g < 67 时,可能会出现第2 类工况,此时较低的气速会促进第2 类工况的出现. 根据建立的模型与拟合关系式可实现内分液调控管的优化设计.      

利用波长调制光谱技术测量高温环境中的气体压强、温度和H_2O组分浓度

利用基于可调谐半导体激光器的扫描波长调制光谱技术,实现了高温燃烧场内气体参数的测量。提出了基于迭代算法实现气体压强、温度和组分浓度同时测量的方法,迭代算法具有收敛速度快以及对初始值不敏感等优点。采用频分复用技术,利用两条H_2O吸收谱线(7 454.45和6 806.03cm-1)的谐波信号,对高温燃烧场进行了实验研究,并将气体压强、温度和H_2O组分浓度测量结果与压力传感器、热电偶和直接吸收光谱法的测量结果进行比较,结果表明,基于波长调制光谱技术测得的气体压强、温度和H_2O浓度与预测值基本符合,最大偏差分别在7.6%,8.1%和7.5%以内。此方法具有多参数同时测量、免标定等显著优势,但由于依赖的参数较多,容易对测量精度造成影响。     

偏振双向衰减对光学成像系统像质影响的矢量平面波谱理论分析

偏振双向衰减(diattenuation)是指偏振元件引入的光场传播过程中表征电矢量的两个正交偏振态的振幅变化特性.在大部分有关偏振像差的讨论中,聚焦光场偏振态的振幅变化对其分布的影响较小而不被重视.但在一些大相对孔径光学系统中,对于分束器、光调制器等有复杂平面介质结构的低透过率光学元件而言,引入的偏振相关的振幅调制相对大得多.本文依据矢量平面波谱理论,建立了笛卡尔坐标系下的理想光学成像系统的矢量光学模型,验证了与德拜矢量衍射积分的一致性.在线偏振光入射的条件下,对在汇聚光路中使用的光学元件的偏振双向衰减特性对成像质量的影响进行理论研究.结果表明,在调制传递函数的低频率处(v0.2NA/λ),这种影响是可以忽略的;随着空间频率的增加,光学元件的偏振双向衰减特性对成像系统调制传递函数的影响逐渐变大.若要求调制传递函数的数值不低于衍射极限的90%,中频处(0.2NA/λv0.8NA/λ),s光和p光的透射/反射系数之比至少需要控制在[0.63,1.6]的范围内;而当v0.8NA/λ时,则需要控制在[0.9,1.11]的范围内.随着光学系统光轴与光学分界面法向的倾角增加,容差范围有所放宽.     

基于可调谐半导体激光器吸收光谱的高灵敏度甲烷浓度遥测技术

讨论了一种新的高灵敏度甲烷遥测方法,利用可调谐激光二极管的调制光谱技术扫描甲烷的吸收峰,通过在测量光路中插入参考气池,增强低浓度情况下的吸收峰辨识能力,以提高甲烷浓度遥测信号的信噪比.此外,可以将激光器的中心波长锁定至气体吸收峰的峰值位置从而使仪器工作于吸收峰锁定模式,进行甲烷浓度的连续监测.实验结果表明,在测量距离分别为10 m和20 m时,周围环境中的甲烷积分浓度探测极限可以分别达到5 ppm·m和16 ppm·m.在吸收峰锁定工作模式下,系统在37 m距离处具有22 ppm·m的检出限,并可以监测甲烷浓度的快速变化.     

Velocity modulation of electron transport through a ferromagnetic silicene junction

We address velocity-modulation control of electron wave propagation in a normal/ferromagnetic/normal silicene junc tion with local variation of Fermi velocity, where the properties of charge, valley, and spin transport through the junction ar investigated. By matching the wavefunctions at the normal-ferromagnetic interfaces, it is demonstrated that the variation of Fermi velocity in a small range can largely enhance the total conductance while keeping the current nearly fully valley and spin-polarized. Further, the variation of Fermi velocity in ferromagnetic silicene has significant influence on the valley and spin polarization, especially in the low-energy regime. It may drastically reduce the high polarizations, which can b realized by adjusting the local application of a gate voltage and exchange field on the junction.