Elastoplastic crack analysis by boundary integral method and surface spectrum measurement

The paper describes a hybrid experimental-numerical technique for elastoplastic crack analysis. It consists of the experimental surface spectrum measurement of plastic strains ahead the crack tip and the boundary element method (BEM). The light scattering method is used to measure the power density spectrum from which the values of plastic strains are obtained by comparison with a calibration experiment on the same material. Plastic strains obtained experimentally are conveniently used for the calculation of unknown boundary displacement or traction vectors by the boundary element method. Instead of an iterative solution of the boundary integral equations in pure numerical solution, the boundary unknowns are computed once for a required loading level. Also asymptotic distribution of strains or stresses is not needed in the evaluation of the domain integral for the BEM formulation in the vicinity of the crack tip. Significant CPU time saving is achieved in comparison with the pure BEM solution. The method presented is illustrated by the example for a three point bending specimen with an edge crack.     

海底沉积物声学测量中频谱分析方法应用研究

海底沉积物声学测量数据中包含着的频谱特征和信息,是区分和判别沉积物类型的重要依据。应用频谱分析方法,研究海底沉积物声学测量的频谱特征,分析声波探测仪器的性能,判断沉积物测量异常数据,研究温度变化下频漂现象,探寻到沉积物内在特征的一些规律性现象。并通过对两类沉积物的频谱分析结果比较,进一步论证区分沉积物的可行性。实测结果表明,频谱分析能够为声波探测仪器的性能测试及海底沉积物声学物理性质研究提供技术手段和分析方法。     

An extensible complex fast Fourier transform processor chip forreal-time spectrum analysis and measurement

This paper describes in detail the design of a CMOS custom fast Fourier transform (FFT) processor for computing a 256-point complex FFT. The FFT is well-suited for real-time spectrum analysis in instrumentation and measurement applications. The FFT butterfly processor reported here consists of one parallel-parallel multiplier and two adders. It is capable of computing one butterfly computation every 100 ns thus it can compute a 256-point complex FFT in 102.4 μs excluding data input and output processes     

Temperature and heat spectrum measurement using mathematical statistic apparatus

A nonconventional method of temperature measurement is observed, where no information about heated surface emissivity is required. Main principles of simultaneous spectrum and temperature measurement via ratio pyrometry are described. Measurement device optical scheme and results of blackbody and colored body simulators’ radiation temperature measurements are given. Comparison of emissivity of colored body simulators and optical transmission coefficient of glasses used for simulation is conducted.     

全承载大客车底架动态载荷谱分析

针对全承载式大客车底架设计的需要,在底架后悬和发动机附近选择3个测点。分别在阻隔带路况和小鹅卵石路面进行行走测试,提取大客车底架动态应变的时间历程数据,并利用雨流计数法对实测数据作载荷谱的应变频次分析,得到3个测点两种路面的载荷谱的应变大小和变化规律。发现行驶状态的变换引起应变载荷波动,基本不改变载荷幅值频次分布规律,这表明不同的路面等级将引起底架不同程度的疲劳损伤。测试结果为全承载式大客车底架的设计、仿真与试验提供技术基础。     

Evaluation of spectrum measurement devices for operational use

Several neutron spectrometers manufactured by Bubble Technology Industries (BTI) were tested and evaluated in a variety of neutron fields. Findings and conclusions are presented for the following BTI instruments: a modification of the Rotational Spectrometer (ROSPEC) that includes a thermal and epithermal capability, the Simple Scintillation Spectrometer that is used in conjunction with the ROSPEC to extend its high-energy range, and the MICROSPEC N-Probe which is capable of providing a crude spectrum over the energy range from thermal to 18 MeV. The main objective of these measurements was to determine the accuracy of both the energy spectrum and dose equivalent information generated by these devices. In addition, the dose response of the Wide-Energy Neutron Detection Instrument (WENDI-II) was measured in all neutron fields relative to a bare ²⁵²Cf calibration. The performance of the WENDI-II rem meter was compared to the dose information generated by the neutron spectrometers. The instruments were irradiated to bare ²⁵²Cf and ²⁴¹AmBe sources, and in a series of moderated ²⁵²Cf fields using a standard D₂O sphere and a set of polyethylene spheres. The measured spectra were benchmarked with a set of detailed Monte Carlo calculations with the same energy bin structure as that of the instruments under test. These calculations allowed an absolute comparison to be made with the measurements on a bin by bin basis. The simulations included the effects of room return and source anisotropy.     

Measurement and analysis of hydroluminescence spectrum

The spectrum of hydrodynamic luminescence (HL)—that is, of light emitted from a liquid flow under strong mechanical action—has been studied. It is shown that the light-emitting gas has low rotational and high vibrational temperatures, which is evidence in favor of an electrical, rather than thermal, nature of HL excitation.     

Modified channeled spectrum for fast measurement of thin films

A simple and effective technique for the simultaneous measurement of the refractive index and the thickness of thin films is proposed. The method is based on the spectral dependence of the visibility of interference fringes that result from thin-film interference when the film is illuminated with a white light. The film is on the special substrate, and an optical contact is provided between them. The measurement consists of finding the local change of the fringes' visibility in the observed channeled spectrum expressed as the seaming change of the fringes' periodicity. The method can be applied for real time optical inspection during the manufacturing of thin polymer films.     

Real time spectrum analysis

Spectrum analysis in a real time environment is achieved in a recently developed instrument. All incoming pulses are digitized and digital windows set to define up to 50 regions of interest (ROIs). Up to 20 outputs (analog, relay, digital), defined by combining the count rates of ROIs and standard mathematical functions, are recalculated as frequently as once per second. User defined time response and wide range of smoothing functions allow the outputs to be selected according to the measurement requirements. The characteristics of a number of smoothing functions are analyzed and compared. Examples are given of high precision radioactivity measurements in dynamic environments.     

Method for improving terahertz band absorption spectrum measurement accuracy using noncontact sample thickness measurement

The terahertz absorption spectrum has a complex nonlinear relationship with sample thickness, which is normally measured mechanically with limited accuracy. As a result, the terahertz absorption spectrum is usually determined incorrectly. In this paper, an iterative algorithm is proposed to accurately determine sample thickness. This algorithm is independent of the initial value used and results in convergent calculations. Precision in sample thickness can be improved up to 0.1 μm. A more precise absorption spectrum can then be extracted. By comparing the proposed method with the traditional method based on mechanical thickness measurements, quantitative analysis experiments on a three-component amino acid mixture shows that the global error decreased from 0.0338 to 0.0301.     

Synthesis and fluorescence spectrum analysis of CdS nanocrystals

An optimized synthesis route was applied for control the preparation of CdS nanocrystals (NCs) in an aqueous solution. Some key factors which influencing the characters of CdS NCs, such as stabilizers, ratio of reactant etc, were investigated. It was found that the fluorescence (FL) intensity of CdS NCs could be dramatically enhanced by refluxing. The size, shape, crystal structure and the optical properties of CdS NCs were also characterized by TEM, XRD, UV–Vis and FL spectra. The result showed that the well-disperse spheres CdS NCs with 6 nm in diameter were obtained.     

Mechanical fatigue and spectrum analysis of small-satellite structure

Mechanical fatigue due to environmental loads and spectrum analysis due to launch loads of the primary structure of a low cost, low-earth orbit small satellite intended for earth observation missions are presented. The payload of the satellite under consideration is a precise optical unit to image the earth’s surface having a mass of 45 kg. 3-D Finite Element Model for the satellite structure is generated by applying substructure method. Modal analysis is required to determine natural frequencies of the satellite and define its mode shape. Then, ranking of mode shapes according to specific constraint is performed. Harmonic analysis at resonance frequencies with the highest ranking is done and cumulative fatigue damage analysis is performed. Spectrum analysis is performed for Small Sat structure to verify the satellite structure reliability under all dynamic random vibration loads applied during transportation and launch cases.     

Accuracy of measurement of bremsstrahlung spectrum limit with absolute scale calibration

Translated from Izmeritel'naya Tekhnika, No. 9, pp. 54–55, September, 1992.     

Comparative analysis of errors of two methods for measurement of multipole components of a heart electric generator

Translated from Izmeritel'naya Tekhnika No. 6, pp. 55–58, June, 1992.     

测量不确定度原理及在理化检验中的应用 第六讲 试验机载荷示值及等离子光谱法测量结果不确定度的评定

1　万能材料试验机负荷示值误差测量结果的不确定度评定1.1　概述 (第一步 )1.1.1　测量方法依据JJG 139- 1999拉力、压力和万能试验机检定规程。1.1.2　环境条件温度 10～ 35℃ ,温度波动≯ 2℃ /h ,相对湿度≯ 80 % (本报告测量温度为 2 6℃ )。1.1.3　测量标准0 .3级标准测力仪相对扩展不确定度U95=0 15 %年稳定度为± 0 .3%。1.1.4　被测对象WEW 30 0C型微机液压万能试验机 (以下简称试验机 ) ,测量范围为 6～ 30 0kN ,示值相对最大允许误差为± 1.0 %。1.1.5　测量过程在规定环境条件下 ,使用试验机对标准测力仪施加载荷至相应的…     

矢量水听器性能参数测试及分析

随着声呐探测系统性能和稳定性的不断提高,矢量水听器因能同时共点测量声波的声压和振速信息,已开始应用于声呐探测系统。为保障海上实验,设计制作了胶囊形三维压电同振式矢量水听器。依据比较法测量原理,分别在驻波声管和消声水池中,对矢量水听器的x、y、z和p通道的低频段和高频段进行了灵敏度和指向性测试。测试结果表明,该型矢量水听器灵敏度较高、指向性较好,能够满足海上实验的需求。     

Correction of spectrum of turbulence in the measurement by a conduction anenometer

The equivalent spectral characteristic of the sensor of a conduction anenometer with external magnetic field is determined. Its use is demonstrated for the correction of the spectrum of turbulent velocity fluctuations.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 2, pp. 243–247, August, 1976.     

Broad spectrum measurement of the birefringence of an isothiocyanate based liquid crystal

Tunable materials with high anisotropy of refractive index and low loss are of particular interest in the microwave and terahertz range. Nematic liquid crystals are highly sensitive to electric and magnetic fields and may be designed to have particularly high birefringence. In this paper we investigate birefringence and absorption losses in an isothiocyanate based liquid crystal (designed for high anisotropy) in a broad range of the electromagnetic spectrum, namely 0.1-4 GHz, 30 GHz, 0.5-1.8 THz, and in the visible and near-infrared region (400 nm-1600 nm). We report high birefringence (Δn = 0.19-0.395) and low loss in this material. This is attractive for tunable microwave and terahertz device applications.