Measurement of deviations from cylindricity

Conclusions It is suggested to measure spearately the diameter and the shape in the longitudinal and cross sections and to carry out a combined processing of the measurement result in order to obtain the radii of the surface points with respect to a given axis.The availability of the required instruments, the simple processing of results, and the small errors in determining the radii make it possible to recommend this technique for measuring high-precision components with lengths up to 1000 mm and diameters up to 200–300 mm. For components of a samller size it is advantageous to use instruments with two precise movements, consisting of a rotational and a longitudinal movement.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 64–65, October, 1969.     

从测量值计算非球面参数

为解决按测量值计算非球面光学系统成像质量的问题,提出了一种从三维坐标测量值提取标准非球面方程的参数的方法．首先在两个相互垂直的近似的中心剖面附近取值,并分别投影到这两个平面上;然后拟合曲线;再用这两条曲线在各自的平面内截取一组平行直线成一组线段,改变直线的斜率,使各线段中点共线,确定非球面的对称轴和顶点坐标;最后,平移、旋转坐标系后,将三维坐标降维,用多项式拟合成二维曲线,同时将标准形式方程中的无理项展为泰勒级数,对比二者的系数并推广,得到任意偶数阶标准非球面方程的参数．大量随机取值计算的统计结果表明,算法的误差是测量误差的1／2．     

基于光学测角与信号时差的同步卫星无源测轨

精确测量和确定同步卫星轨道是实现高精度导航、定位等应用的基础,光学测角定轨和卫星通信信号测时差定轨是两种最重要的无源测轨方法,各有优缺点。本文提出将光学测角与无线电通信信号测时差相结合,可实现对卫星的单次测量定位,多次测量提高定轨精度。推导得到卫星到光学站的距离表达式,实现对卫星位置的解析求解。通过GDOP方法,分析了光学站与无线电站的不同布站方式对定位精度的影响,据此提出了优化布站方式。通过计算机Monte-Carlo仿真,比较分析了联合测轨方法与单一光学测轨方法的测轨精度。仿真结果表明:若无系统误差时,24小时观测数据统计定轨位置误差为25m,预报1周位置误差为200m,约为单一光学方法的2/3;当存在系统误差时,需采用自校准方法估计系统误差,基于24小时观测数据的单一光学方法未能实现自校准定轨,而联合测轨方法定轨精度可达到约6m,归一化系统误差估计精度优于0.1,预报1周的位置误差约为140m。     

Measurement of diffusive flux of ammonia from water

An instrument was developed for the measurement of gaseous ammonia concentration, NH(3(sw,eq)), in equilibrium with surface waters, notably ocean water. The instrument measures the ammonia flux from a flowing water surface under defined conditions and allows the calculation of NH(3(sw,eq)) from the principles of Fickian diffusion. The flux collector resembles a wetted parallel plate denuder previously developed for air sampling. The sample under study runs on one plate of the device; the ammonia released from the sample is collected by a slow flow of a receptor liquid on the other plate. The NH(3) + NH(4)(+) (hereinafter called N(T)) in the effluent receptor liquid is preconcentrated on a silica gel column and subsequently measured by a fluorometric flow injection analysis (FIA) system. With a 6-min cycle (4-min load, 2-min inject), the analytical system can measure down to 0.3 nM N(T) in the receptor liquid. Coupled with the flux collector, it is sufficiently sensitive to measure the ammonia flux from seawater. The instrument design is such that it is little affected by ambient ammonia. In both laboratory (N(T) 0.2-50 μM), and field investigations (N(T) 0.18-1.7 μM) good linearity between the ammonia flux and the N(T) concentration in seawater (spiked, synthetic, natural) was observed, although aged seawater, with depleted N(T) content, behaves in an unusual fashion upon N(T) addition, showing the existence of an "ammonia demand". NH(3(sw,eq)) levels from ocean water measured in the Coconut Island Laboratory, HI, ranged from 6.6 to 33 nmol/m(3) with an average of 17.4 ± 6.9 nmol/m(3), in comparison to 2.8-21 nmol/m(3) (average 10 ± 7 nmol/m(3)) NH(3(sw,eq)) values previously reported for the Central Pacific Ocean (Quinn, P. K.; et al. J. Geophys. Res. 1990, 95, 16405-16416).     

Measurement of emissions from offshore combustion: user'srequirements

Over the last few years there has been marked change in culture towards offshore emissions from combustion equipment. Traditionally, offshore there has been a `fuel is free' mentality and emissions have rarely been measured. UK offshore legislation has now accelerated the need for accurate monitoring of pollutants, especially from gas turbines. In particular, the introduction of emissions trading requires accurate measurements so that any reductions are attributed correctly. The remote location of offshore platforms means that unique solutions are required, especially regarding any changes in the plant that are necessary to install instrumentation. This paper reviews the background to the user's requirements     

Measurement of low interfacial tensions from diffuse reflection

We describe a light-scattering method to measure interfacial tensions in the millidyne per centimetre range. This method allows in situ measurements and does not perturb the interfaces. Thus it appears to be complementary to the spinning drop techniques for systems which are destroyed by mechanical measurements.     

非接触式激光测量点云数据预处理

作为逆向工程中形状表面数字化应用最广泛的方式，非接触式激光测量具有接触式测量无可比拟的优势。然而激光测量所得的数据点云存在明显缺陷无法直接应用于三维模型重建。本文重点讨论了激光测量所得点云数据的特点，并针对其缺陷提出一些处理方法进行改善，使之可以直接应用于三维模型的重建。     

ARJ客机过顶飞行过程噪声的实验研究

对ARJ客机过顶的噪声源进行了现场实验分析。为了将飞机不同噪声源分开,利用了阵列信号处理技术,设计了多臂螺旋阵。实验发现:ARJ飞机的噪声源主要分布在发动机、起落架、襟翼、尾翼后部等位置,不同频率下,主要噪声源的组成不同,为飞机降噪工作提供了支持。     

Surface Current Determination from Electric-Fields Distribution Measurement

Determination of induced surface current on cylindrical reflectors in a parallel-plate region from measurements of electricfields distribution is described. The probe-reflector interaction in the measurement of electric-fields distribution is examined and the requirement of probe reflector spacing which ensure the small interaction is also investigated.     

Accuracy Evaluation of Algorithms for Processing a Posteriori Measurement Results Obtained from Tripled Measurement Channels

Measurement Techniques - The paper considers a problem associated with the evaluation of conditional (refined) confidence limits set for measurement errors using a posteriori information on...     

光纤出射光强分布研究

对多模光纤出射光束的光强分布用横向位移法进行了理论分析和实验研究,并用数值计算的方法分析实验测量数据.结果表明,高斯光束可以很好地描述光纤出射光强的分布,光纤出射光束光强分布参数主要与光纤芯径和出纤光功率等有关,为强度调制型光纤传感器的优化研制提供了必要的实验依据.     

Measurement of large,discontinuous displacement from digital images

One main limitation of conventional digital image correlation (DIC) methods is their incapacity to treat with large, discontinuous displacements. This paper seeks to resolve this issue using a variational method. Specifically, the objective function is written in a form of L¹-norm instead of L²-norm for discontinuity preservation. This convex, non-differentiable objective function is resolved by a proximal gradient method. Then, the entire correlation process is embedded into a multi-level image pyramid, enabling large displacements to be measured accurately. The proposed method is first validated on images with prescribed small displacements; its performance to treat with discontinuous, large displacements is then examined. The results show that the proposed method exhibits an acceptable performance when measuring some extreme displacements up to 16.5 pixels in a 500 × 500 pixels resolution image. Concerning subpixel accuracy, the errors can be lessened to a very low level with optimised parameters even for a dense correlation at each pixel. Good performance is also demonstrated in forms of noise proof and illumination fluctuation tolerance. Finally, an application is conducted on an experiment concerned with cracking in desiccated soils, in which the proposed method succeeds in tracking the nucleation and propagation processes of multiple cracks.     

Measurement uncertainties arising from unpowered shipment of dcvoltage references

We have measured the hysteresis in output voltage arising from loss of power for three Fluke 732B dc voltage references. Continuously powering the internal temperature-controlled oven provides the best accuracy with such Zener-diode-based dc voltage references. Batteries are used to provide power continuity when shipping between laboratories. We have shown that for these particular instruments, an apparent hysteresis induced by humidity is likely to dominate any hysteresis arising from loss of battery power when transit between laboratories takes three days or more. Our conclusion is that as much, if not more, care needs to be taken when dealing with humidity than with loss of battery power when shipping between laboratories. When the highest accuracy of dc voltage comparison is required, it becomes necessary to apply voltage corrections using the measured values of humidity coefficients and the relative humidity occurring during transit     

Measurement of radio emission from extensive air showers with LOPES

A new method is explored to detect extensive air showers: the measurement of radio waves emitted during the propagation of the electromagnetic shower component in the magnetic field of the Earth. Recent results of the pioneering experiment LOPES are discussed. It registers radio signals in the frequency range between 40 and 80 MHz. The intensity of the measured radio emission is investigated as a function of different shower parameters, such as shower energy, angle of incidence, and distance to shower axis. In addition, new antenna types are developed in the framework of LOPES^star and new methods are explored to realize a radio self-trigger algorithm in real time.     

道路交通噪声中单车辐射噪声测量及分析

以道路通行的单个车辆为研究对象,导出半自由场单车点声源的噪声辐射模型,应用噪声测量分析手段,结合相应的声学评价量,对实际道路条件下单车辐射噪声的声级大小、时域信号、频谱、声学品质等特性进行探讨和研究。结果表明,随车辆与测点距离的变化,单车辐射声的声级呈现先增大后减小的非线性变化规律;其高频声压级随距离增加而衰减;与小车相比,中车和重车辐射噪声中的低频成份比例大,声级值高;小车辐射声响度在低频125Hz和高频1kHz频段的贡献量较大,重车则体现为低频段（250~500 Hz）贡献量大,而高频段的贡献量不明显。     

Thermal Radiative Properties and Temperature Measurement from Turbine Coatings

Recent studies have displayed the spectral radiative properties of ceramic thermal barrier coatings which are finding applications in high performance turbine engines. As a function of temperature, a region in the long wavelength infrared spectrum exhibits properties which will minimize the classical errors associated with temperature measurement by radiometric detection. Hollow sapphire waveguides transmit the portion of the long wavelength infrared spectrum which is optimum for radiometric temperature measurement from these materials, while the physical properties of the sapphire can withstand the combustion conditions within the engine. A prototype long wavelength infrared radiation thermometer was constructed to obtain surface temperature measurements from coated turbine blades subjected to high temperature combustion conditions.     

Measurement of nanomovements of an object from the optical phase image

We examine a method for measuring small movements of an object, based on calculation of the displacement of the image obtained using an optical interferometer. We estimate the effect of phase noise in reconstruction of the coherent structure of the field on the accuracy in measuring the movements. We have made practical estimates of the displacements of the real object from phase image data. We compare the estimates with the results of direct measurements of the displacements. We show that it is possible to detect movements of less than 10 nm using a commercial microscope.