Iterative least-squares fit procedures for the identification of organic vapor mixtures by Fourier transform infrared spectrophotometry

Least-squares fitting (LSF) was applied to the qualitative analysis of IR spectra based on comparing standard reference spectra with the sample mixture spectrum. Identification of compounds in the sample was made by judging the fit level of the spectrum of each compound with the sample spectrum. An iterative procedure was developed to eliminate compounds with the worst fit levels in order to approach an optimal fit for the sample spectrum. The qualitative analysis results obtained from the optimal fit were further used for quantitative analysis.     

基于小波包分析的拉索损伤声发射信号特征提取

结合显式有限元和小波包分析技术开展了拉索损伤声发射信号特征提取的仿真分析。采用ANSYS/LS-DYNA模拟得到拉索损伤声发射信号的仿真信号,基于小波包能量谱对拉索声发射的有限元仿真信号进行了特征提取,从小波包分解层次、特征频带数量的选择及特征参数的噪声鲁棒性三个方面开展了讨论分析。结果表明:(1)通过选择适当的小波包分解层次,小波包能量谱可以精细地反映信号的特征;(2)选取少数特征频带就能使得小波包能量谱反映声发射信号的特征信息;(3)基于小波包能量谱的特征参数具有良好的损伤敏感性及噪声鲁棒性,能在强噪声影响下实现对拉索不同损伤类型的判别。     

Analysis of the First Spectrum of Ruthenium (Ru I)

The analysis of the first spectrum of ruthenium has been extended with the aid of digital computers. A total of 105 even and 206 odd levels are listed with observed Landé g-factors for 54 even and 148 odd levels. A complete list of approximately 3,400 classified lines in the range 2013 to 11484 A is presented. The ionization limit calculated from a two member series is 59410 cm⁻¹ or 7.364 v.     

地铁对周边建筑物振动影响分析

建立了土层系统-建筑物二维共同作用有限元模型，采用Newmark隐式逐步数值积分法，从地铁列车荷载频谱特征和场地土层类型角度，分析了由地铁运行所诱发的周边建筑物振动响应规律。分析表明，在同一频率地铁振动荷载影响下，同一建筑物各楼层振动响应水平基本相同，上部楼层的振动仅比下部楼层振动有小幅上升；地铁低频段荷载对建筑物振动的影响大于高频段荷载的影响，但该低频段宽度要比建筑抗震分析中所考虑的地震荷载频段要宽；不同类型土层上建筑物的振动响应规律基本相同，表现为随建筑物距离地铁线路距离的增大，由地铁运行所诱发的建筑物的振动响应波动减小，但随土层硬度增加，建筑物的振动响应水平和衰减幅度也随之减小。     

Dual nonlinear correlator based on computer controlled joint transform processor: Digital analysis and optical results

Abstract

The hybrid optoelectronic processor, presented in this paper, realizes the dual nonlinear correlation (DNC) in a set-up based on a two-step nonlinear joint transform correlator architecture. In the first step three power spectrum distributions (input scene power spectrum, reference target power spectrum, and the joint power spectrum) necessary for the nonlinear processing are captured with a CCD camera. Nonlinear modification of the joint power spectrum, which does not have to be symmetrical in the input and reference channels, is introduced digitally. In the second step, the modified joint power spectrum is Fourier transformed optically. Numerical analysis of this processor shows a crucial influence of the dynamic range and the limited number of grey levels of the CCD camera during image acquisition in the first step, on the output signal parameters and the discrimination capability of the set-up. Optical results of recognition obtained for noise-free segmented input scenes show that the set-up enables the realization of various correlation operations as CMF, POF, IF, PPC, etc. without any filters and that the discrimination capability is easy to control by a proper selection of the type of nonlinear processing.     

A model for fitting peaks induced by fast neutrons in an HPGe detector

Inelastic neutron scattering in the HPGe detector produces wide, triangular-shaped peaks in the spectrum. We develop an accurate model for the peak shape and show that the inclusion of the model in the gamma spectrum analysis makes it possible to quantify fast neutron scattering in the Ge crystal and improves the estimation of the baseline. This in turn facilitates the detection of fission products present at trace levels in environmental samples. The model, together with simulations, is used to deduce some properties of the underlying neutron energy distribution. The neutron evaporation temperature of 1.1 MeV is obtained from the analysis of environmental monitoring gamma spectra.     

Analytical study of fatigue crack growth in AA7050 notched specimens under spectrum loading

An analytical study of fatigue crack growth in aluminium alloy 7050-T7451 notched specimens under a fighter aircraft wing root bending moment spectrum was conducted. The crack growth data were measured by quantitative fractography for three groups of specimens with different stress concentration geometrical features. Under spectrum loading and for each spectrum peak stress level, a minimum of five specimens were tested. Based on the analysis of the measured spectrum crack growth data using linear elastic fracture mechanics, it was found that the concept of geometry factors formulated in the stress intensity factor could not collapse the crack growth rate data derived from each stress concentration feature, particularly near the small crack growth region. In order to investigate the possible reasons for this, three-dimensional elastic-plastic finite element analysis was used to determine notch plastic zone sizes for each stress concentration geometry. As a consequence, an alternative crack growth driving force by considering both notch elastic-plastic stress field and gross net-section stress field was proposed and used to interpret the fatigue crack growth data under spectrum loading. It was found that the predictions of crack growth under spectrum loading for different stress concentration factors at different peak load levels agree reasonably well with the experimental results.     

结构抗震性态谱的确定方法

为了克服反应谱无法反映性能目标对地震的需求,提出了性态谱的新概念。以地震地面运动数字记录为输入,计算单自由度体系最大地震加速度的统计平均值。在三维坐标中,根据性能目标,建立地震需求和结构周期、弹塑性状态的函数关系。获取具有统计意义的、按照地震波分类的弹性和弹塑性性态谱,研究了性态谱特征和谱曲线规律,拟合了弹性和弹塑性性态谱的设计公式,并对拟合公式进行了验证。性态谱为多目标抗震性能设计提供了新途径。     

平稳和非平稳振动信号的若干处理方法及发展

回顾了稳态或准稳态振动信号处理方法中的离散频谱分析与校正，细化选带频谱分析，解调分析和高阶谱分析，非平稳振动信号处理方法中的转速跟踪分析，短时傅立叶分析，Wigner-Ville分布，小波分析和Hibert-Huang变换的发展历史，论述了各类方法的原理，分析其特点和在工程中的应用，探讨了发展前景。     

A simple facility to measure the scalar neutron spectrum in an assembly

An inexpensive, simple and safe facility was constructed to measure the neutron spectrum in an assembly, by setting a neutron source outside the assembly. A normalization technique for the neutron spectrum and error analyses are mentioned. The error of the calculated spectrometer efficiency is cancelled at the final spectrum normalization. The error caused by the present method is within acceptable levels.     

A Comparative Study of the Effect of Noise and Background Clutter on Optical Image Recognition Methods

Abstract

A study by digital simulation of the behaviour of correlation when scenes are degraded by noise or background has been carried out. Our analysis includes a comparison between the most common correlation filters used to improve discrimination and a non-linear joint transformer correlator in which the power spectrum has been binarized considering different threshold levels. Signal-to-noise ratio, peak sharpness and discrimination capability have been taken into account in order to assess correlation quality.     

Emission spectrum of a Λ-type three-level atom driven by the squeezed coherent field and grey-body radiation field

Abstract

By means of quantum electrodynamics, an analytical expression of emission spectrum for a Λ-type three-level atom with the two non-degenerate lower levels in the cavity is given. The character of the emission spectrum for the input in pure number state, a squeezed coherent state and grey-body state are exhibited. The effects of the atomic initial state, the field property, the cavity absorptivity and the system temperature on the time-dependent physical spectrum are analysed.     

Spectrum etiquettes for terrestrial and high-altitude platform-based cognitive radio systems

Two spectrum etiquettes are developed for the use on the downlink of coexisting high-altitude platform (HAP) and terrestrial fixed broadband systems that are intended for future application with cognitive radio-based user terminals with directional antennas. The spectrum etiquettes are based on the interference to noise ratio and carrier to interference plus noise ratio levels at the receiver of an incumbent user. Antenna beamwidths and multiple modulation scheme levels determine the parameter settings for coexistence performance. It is shown that coexistence performance can be improved by exploiting the surplus transmitter power of the terrestrial system, thereby enabling the incumbent terrestrial system to accommodate additional interference arising from a newly activated HAP system.     

机械振动信号的听觉谱表达及其特性研究

人类听觉系统具有非凡的信号分析、处理和识别能力,因此,建立人类听觉系统的数学模型并将其应用于各种动态信号分析场合具有一定的可行性。引入听觉模型ZCPA(模型输出为听觉谱),通过对各种实测信号的分析,检验了听觉谱对平稳、非平稳和带有瞬时突变成分的振动信号的描述效果,揭示了听觉谱表达振动信号时的基本特性,并阐述了其内在机理。各种分析检验结果表明,听觉谱可以用很少的点数大体描述信号的频率结构,尤其是对于中高频区间的微弱信号具有很好的描述效果,并且在表征信号中的瞬时突变方面具有明显优势。     

青岛近海航船相关海洋环境噪声谱级特性分析

为了了解航船以及禁渔政策对我国近海海域低频环境噪声特性的影响,文章分析了青岛近海航道区域和非航道区域的海洋环境噪声在25～500 Hz频段实测数据的1/3倍频程功率谱密度。结果表明,在30～100 Hz频段,航道附近海域海洋环境噪声谱级比非航道海域高大约5～10 dB;非禁渔期在150～400 Hz频段的海洋环境噪声谱级比禁渔期高大约4～5.5 dB。文章获取的近海低频环境噪声谱级特性,对了解和利用我国以及世界范围内近海环境噪声低频特性具有较重要借鉴意义。     

台风中的降雨对水下环境噪声的影响

利用数值模型和实验数据分析了台风过境前后雨成噪声对水下环境噪声的影响。该数值模型是基于简正波理论和雨成噪声的统计分析方法。在没有航船噪声和生物噪声的影响下,环境噪声主要是风成噪声和雨成噪声的总和。通过对海上实验数据的分析,深海水下噪声将会在台风眼壁到达前和离开后的两小时时刻受到雨成噪声的影响。在1～3 kHz的频段处,台风中的雨成噪声要比风成噪声大5～6 dB,并且雨成噪声谱的强度随频率的变化比风成噪声谱的变化平缓。理论和实验对比结果显示,数值模型可以较好地预测实验数据。     

隔震结构弹塑性反应谱分析研究

根据弹塑性反应谱理论,按照非线性恢复力模型的等效阻尼比和位移延性的关系,以单质点弹塑性反应分析结果为依据,建立基于等效阻尼比的隔震结构弹塑性反应谱。进一步比较弹塑性反应谱和我国规范得到的反应谱,结果显示规范的加速度反应谱在长周期段谱值过大,阻尼衰减系数也较大。基于单质点弹塑性地震分析的结果,在我国规范反应谱公式的基础上提出的隔震结构弹塑性反应谱公式。最后通过对5层钢框架隔震结构模型进行振动台试验、数值时程分析、规范反应谱计算、以及用弹塑性反应谱进行计算。结果表明,时程分析法的分析结果和振动台试验的结果比较接近,而按照规范反应谱的等效线形化方法计算出的结果与振动台试验的结果有一些偏差,弹塑性反应谱的地震反应更加接近试验实测的结果,表明了新提出的弹塑性反应谱进行隔震结构的地震反应分析时具有良好的计算精度。     

人工模拟爆破震动信号及其频谱特性检验

对人工模拟爆破震动信号的合成进行了研究 ,并采用了功率谱和反应谱分析方法对合成信号的模拟程度进行相关性检验。在合成模拟信号时 ,首先采用某一已知爆破振动加速度信号的反应谱来初步计算出将要模拟的爆破震动信号的功率谱并将其作为目标谱 ,然后在所需研究的谱率范围内产生一定数量的均匀分布随机数来作为模拟爆破震动信号的频率。在假设爆破震动信号由不同频率的谐波函数组成的基础上 ,通过将不同频率的谐波函数叠加来初步合成模拟爆破震动波 ,同时用振幅窗函数对它进行振幅校正 ,然后对合成信号与原信号进行功率谱值与反应谱值的相关性检验。编程计算证明 ,由本文提出的合成信号方法及检验方式来模拟爆破震动信号是可行的。     

A regression model of fatigue crack propagation under flight simulation loading

A multi-variable regression analysis is made of crack propagation data under flight simulation loading for the 2024-T3 and 7075-T6 alloys. The study is made using an effective stress range concept based on cracl closure considerations. A two-variable regression model of the equivalent stress range is suggested. The model is used to calculate fatigue crack propagation lives. Predictions using the proposed model are compared with empirical results. It is shown that the model accounts for the influence of maximum, minimum and mean stress levels of the load spectrum.     

基于多采样率的频域倍频程研究

传统倍频程分析采用带通滤波器组算法实现,带通滤波器组算法仅能满足国家标准要求,并且用于分析分数阶倍频程时,滤波器组的数量及计算量成倍增长。提出了一种基于多采样率在频域分析倍频程及分数阶倍频程的算法。该算法首先对信号按通道重采样,并利用FFT转换到频域计算信号的倍频程及分数阶倍频程谱。仿真验证了算法的正确性,并与带通滤波器组算法做了比较。仿真及对比结果表明,相比于带通滤波器组算法,该算法能提供更好的谱分辨率,并且对于分数阶倍频程,该算法计算量明显少于滤波器组算法计算量。