原子钟钟差预测不确定度的建模与分析

钟差预测是原子钟时标产生和原子钟驾驭的关键环节。原子钟作为精准的信号源,其信号由确定信号部分和固有噪声即随机部分组成。氢钟和铯钟主要包含两种噪声,即调频白噪声和调频随机游走噪声,这两种噪声是产生预测不确定度的主要因素。根据原子钟数学模型补充推导出原子钟时差数据预测不确定度的数学表达式,并得出了钟组的最小预测不确定度,分析了钟组的台数对预测不确定度的影响。最后通过数据仿真验证了理论的正确性。     

Clock Error with a Wiener Predictor and by Numerical Calculation

This paper gives a closed-form solution for the minimum error one can expect from a linear prediction filter applied to a clock for which the fractional frequency power spectrum consists of white noise and the integral of white noise. Measurement error is also included. Expressing the problem as a Wiener filter rather than a Kalman filter simplifies the solution. The Kalman matrices in the Wiener representation are diagonal. This permits one to derive the optimum linear filter directly from the spectrum. Since the spectrum of flicker noise is not rational, no closed-form Wiener solution is possible. It is demonstrated, however, that all error terms including flicker can be taken into account by a technique of numerical integration in the frequency domain. The technique is valid for any filter for which the integrals, and consequently the error, do not diverge. It is shown that every first-order prediction filter with two poles must have the form of the Wiener filter, except for the position of the poles. A special case of this filter is shown to be the first-order exponential predictive filter. The error can be expressed in powers of the prediction time, with four coefficients, one for each spectral term. The values of these coefficients were calculated and plotted for the first-order exponential filter. These coefficients were used to calculate the error for three clocks. The results are plotted for prediction times of two hours and one day.     

三维空间有源消声的一种通用优化方法

本文根据声源辐射理论、声场叠加原理以及测得的声功率大小与所选取的测量面无关这一特点,提出了一种通过最小化初级声源和次级声源总的声功率对三维空间噪声的主动控制进行优化的数值方法。文中采用边界元近似,将总的声功率表示成次级声源复强度的二次型正实函数。本优化方法是Bullmore 等人提出的解析方法的推广,具有广泛的适用性,可用于设计初级声源在各面元上的声压可知、次级声源到各面元上的声传播可确定的任何场合下控制器优化传递函数。计算过程中仅用了几次复矩阵乘法和一组复系数线性方程组的求解,因此计算简便、速度较快。文中采用这种方法对圆柱壳和无幕活塞辐射器这两种具有典型指向特性的分布初级声源辐射噪声的优化控制问题进行了研究,说明了方法的有效性。文中还给出了实验验证结果。     

A wavelet-based multiscale ensemble time-scale algorithm

The wide-spread availability of ensembles of high-performance clocks has motivated interest in time-scale algorithms. There are many such algorithms in use today in applications ranging from scientific to commercial. Although these algorithms differ in key aspects and are sometimes tailored for specific applications and mixtures of clocks, they all share the goal of combining measured time differences between clocks to form a reference time scale that is more stable than any of the clocks in the ensemble. A new approach to forming time scales is presented here, the multiscale ensemble timescale (METS) algorithm. This approach is based on a multiresolution analysis afforded by the discrete wavelet transform. The algorithm does not assume a specific parametric model for the clocks involved and hence is well-suited for an ensemble of highly disparate clocks. The approach is based on an appealing optimality criterion which yields a reference time scale that is more stable than the constituent clocks over all averaging intervals (scales). The METS algorithm is presented here in detail and is shown in a simulation study to compare favorably with a time-scale algorithm based on Kalman filtering.     

Visualisation and analysis of noise sources of a gear unit

In technical acoustics, noise source visualization is an important tool. There are many different techniques of noise source visualization, most of which have been developed, bearing a specific noise source in specific type of acoustic environment in mind. Consequently, an individual visualization method is restricted to certain types of noise sources in a specific acoustic environment and in a limited frequency area. This article presents a new visualization method of complex noise sources using an acoustic camera. In this respect, a new algorithm is used, enabling visualization of all types of different complex noise sources. Monopole, dipole or quadruple noise sources can be observed simultaneously. A moving noise source can be tracked by means of an acoustic camera. In addition to that, various transient acoustical phenomena can be noted. On the basis of this, advanced determination of the condition of mechanical systems by means of noise is possible.     

Study of the excess noise associated with demodulation of ultra-short infrared pulses

The demodulation of ultra-short light pulses with photodetectors is accompanied by excess phase noise at the pulse repetition rate and harmonics in the spectrum of the photocurrent. The major contribution to this noise is power fluctuations of the detected pulse train that, if not compensated for, can seriously limit the stability of frequency transfer from optical to microwave domain. By making use of an infrared femtosecond laser, we measured the spectral density of the excess phase noise, as well as power-to-phase conversion for different types of InGaAs photodetectors. Noise measurements were performed with a novel type of dual-channel readout system using a fiber coupled beam splitter. Strong suppression of the excess phase noise was observed in both channels of the measurement system when the average power of the femtosecond pulse train was stabilized. The results of this study are important for the development of low-noise microwave sources derived from optical "clocks" and optical frequency synthesis.     

In-plane effects on segmented-mirror control

Extremely large optical telescopes are being designed with primary mirrors composed of hundreds of segments. The "out-of-plane" piston, tip, and tilt degrees of freedom of each segment are actively controlled using feedback from relative height measurements between neighboring segments. The "in-plane" segment translations and clocking (rotation) are not actively controlled; however, in-plane motions affect the active control problem in several important ways, and thus need to be considered. We extend earlier analyses by constructing the "full" interaction matrix that relates the height, gap, and shear motion at sensor locations to all six degrees of freedom of segment motion, and use this to consider three effects. First, in-plane segment clocking results in height discontinuities between neighboring segments that can lead to a global control system response. Second, knowledge of the in-plane motion is required both to compensate for this effect and to compensate for sensor installation errors, and thus, we next consider the estimation of in-plane motion and the associated noise propagation characteristics. In-plane motion can be accurately estimated using measurements of the gap between segments, but with one unobservable mode in which every segment clocks by an equal amount. Finally, we examine whether in-plane measurements (gap and/or shear) can be used to estimate out-of-plane segment motion; these measurements can improve the noise multiplier for the "focus-mode" of the segmented-mirror array, which involves pure dihedral angle changes between segments and is not observable with only height measurements.     

Partial least squares based decomposition of five spectrally overlapping factors

The development of a multi-sensory fiber-optic based fluence rate probe (MSP) for light monitoring and dosimetry during photodynamic therapy (PDT) created the need for a robust multivariate signal analysis algorithm capable of quantifying the intensity of five component spectra, representing the sensors, which display a large degree of spectral overlap. Partial least squares (PLS) analysis, as an option for such an analysis algorithm, was evaluated through simulations in the presence of three types of noise, which experimentally may limit the accuracy of PLS quantification of component spectra contributions. Random, or white noise, background was varied over a range of 0-15% relative intensity. A non-random (Gaussian) background vector was simulated, as an experimentally relevant spectral interferent, over a range of 0-7% relative intensity. Spectral variation was modeled by a spectral shift of +/-1-5 nm. Procedures for selecting preferred combinations of fluorophores, with minimum possible spectral overlap, were developed. To illustrate the importance of this selection process, PLS performance results were compared for two possible combinations of five fluorophores, as well as for the combination of three fluorophores currently in experimental use with MSPs. Experimentally anticipated worst-case quantifications were identified for all three types of simulated noise (5% random background, 0.5% Gaussian background, and +/-2 nm spectral shift). The effects of single and combined types of noise were evaluated by independently varying each type of simulated noise over the experimentally relevant range. The mean percentage error in determining the fluorophore contributions and hence quantification of the fluence rate were compared with the required performance standard of better than 10% error for optical power meters in medical use. The PLS algorithm provided an accuracy of 7 +/- 2% for five fluorophores and 3.3 +/- 0.8% for three fluorophores, indicating that PLS is an appropriate choice for this application.     

Noise reduction using mean shift algorithm for estimating 3D shape

Abstract

The technique to estimate the three-dimensional (3D) geometry of an object from a sequence of images obtained at different focus settings is called shape from focus (SFF). In SFF, the measure of focus — sharpness — is the crucial part for final 3D shape estimation. However, it is difficult to compute accurate and precise focus value because of the noise presence during the image acquisition by imaging system. Various noise filters can be employed to tackle this problem, but they also remove the sharpness information in addition to the noise. In this paper, we propose a method based on mean shift algorithm to remove noise introduced by the imaging process while minimising loss of edges. We test the algorithm in the presence of Gaussian noise and impulse noise. Experimental results show that the proposed algorithm based on the mean shift algorithm provides better results than the traditional focus measures in the presence of the above mentioned two types of noise.     

Data fusion algorithm for pulsed eddy current detection

A weighted data fusion algorithm based on matching pursuit (MP)-wavelet packet (WP) atomic decomposition and its applications in pulsed eddy current (PEC) non-destructive testing systems for estimation of feature parameters is presented. MP-WP atomic decomposition is used to estimate each noise-free pulse response from its noisy observation of a single-sensor PEC probe and obtain the peak value parameter from each estimated response. A weighted data fusion algorithm, on the basis of minimum mean square error (MMSE), is applied to fuse each obtained peak value together to get final optimum parameter estimation. Based on the difference of each noisy pulse response and its estimation, the variance of noise in each pulse response can be computed, respectively. Accordingly, the weight of each pulse response for data fusion is calculated by the variance of its noise. Finally, the peak value parameter is estimated by the utilised data fusion algorithm. In terms of MMSE, this weighted fusion presents an optimum estimation of the feature parameter of multi-pulse responses of PEC sensor, compared with normal averaging process.     

高速铁路减振CRTS-Ⅲ型无砟轨道桥梁振动噪声研究

以减振CRTS-Ⅲ型轨道系统为研究对象,基于车辆、轨道、桥梁系统二维模型,利用动柔度法分别计算车辆和轨道系统的动柔度,建立频率域的车辆-轨道耦合模型,计算桥梁振动加速度并与常规CRTS-Ⅲ型轨道系统相比较。采用有限元法计算桥梁结构近场点和远场点噪声,探讨桥梁各子结构板对近场点和远场点噪声的声贡献率。计算结果表明：与常规CRTS-Ⅲ型轨道系统相比,减振CRTS-Ⅲ型轨道系统下,桥梁的振动峰值加速度减小69.9%,加速度平均值降低60.4%;近场和远场噪声计算点声压级分别降低8.4、8.5dB;桥梁顶板声贡献率分别达65.28%,68.30%。采用减振CRTS-Ⅲ型轨道系统能够有效的降桥梁结构噪声。声贡献率计算表明顶板振动是导致桥梁噪声的主要噪声源。     

Robust design optimisation via surrogate network model and soft outer array design

Robust design searches for a performance optimum with least sensitivity to variable and parameter variations. Taguchi method applies an inner array for control factors and an outer array for noise factors to estimate the Signal-to-Noise ratio (S/N). However, the cross product arrays impose serious cost concerns for expensive samplings. Also, rigorous control of noise factors to pre-set levels is impractical in industrial applications. This study presents a soft computing-based robust optimisation that merges control and noise factors into a combined experimental design to establish a surrogate using artificial neural network. Genetic algorithm is applied to search in the sub-space of control factors in the surrogate with a soft outer array to estimate the S/N served as the evolution fitness. Performance variations due to the tolerances of control and uncontrollable factors can then be estimated without conducting actual experiments. The verifications of the predicted optima become additional learning samples to refine the surrogate, and the iteration continues until convergence. The robust optimisation of a micro-accelerometer with maximised gain is used as an illustrative example. The proposed algorithm provides a superior robust optimum using a much smaller sample and less controlling cost compared with Taguchi method and a conventional response surface method.     

一种低信噪比环境下的语音端点检测算法

端点检测技术是语音信号处理的关键技术之一，为提高低信噪比环境下端点检测的准确率和稳健性，提出了一种非平稳噪声抑制和调制域谱减结合功率归一化倒谱距离的端点检测算法。该算法首先通过抑制非平稳噪声再采用调制域谱减消除残余噪声来提升信噪比，减少语音失真。然后再提取每帧信号的功率归一化倒谱系数，计算每帧信号与背景噪声的功率归一化倒谱距离。最后将该倒谱距离作为检测参数，采用双门限判决方法进行端点检测。实验结果表明，该端点检测算法对语音帧和噪声帧具有较好的区分性。此外，在低信噪比环境下，所提出的算法对于不同类型的噪声都具有较好的稳健性。     

一种估计吊放声呐工作深度的简易方法

反潜战中,吊放声呐的工作深度对探测效果影响较大,研究如何根据不同声速剖面确定最佳工作深度使探测距离达到最远,可有效提高探测效率。先将声速剖面划分为典型的几类,然后设计了一种使计算机能够自动识别其类型的方法,再在此基础上利用Bellhop模型找出不同声速剖面下的最佳工作深度规律。仿真结果证明快速算法在一定条件下可替代逐深度计算声呐作用距离,再通过比较选出最佳工作深度的传统算法的。     

GPS在轨卫星原子钟性能评估

卫星钟在轨性能评估对于卫星钟差预报与系统完好性监测具有重要作用。利用国际GNSS服务组织发布的事后GPS精密卫星钟差数据,基于频率准确度、漂移率、万秒稳定度及天稳定度对GPS Block IIR、IIR-M、IIF与IIIA 4类卫星的星载钟性能进行评估。结果表明:1) GPS卫星钟的频率准确度与天漂移率分别在10^-13～10^-12量级与10^-15～10^-14量级;2) 星载铷钟的万秒稳定度与天稳定度分别可达10^-14与10^-15量级,比星载铯钟的同类指标高近一个数量级;3) 新型Block IIIA卫星的星载钟的天稳定度比另外3种类型卫星的星载钟的天稳定度更高,达到(3～5)×10^-15的水平;4) 无论对于不同系列卫星还是同一系列卫星,各星载钟之间均存在一定的性能差异,这种差异与卫星钟在轨运行时间长短无显著关系。     

一种原子钟频率稳定度的估计方法

为了更合理地评估处于相同实验条件下原子钟的绝对频率稳定度,以理论视角分析了算法模型及求解过程,研究了噪声相关条件下绝对频率稳定度的估计方法。用3台原子钟仿真数据对该方法进行了评定,假设噪声独立条件下随着噪声相关性的增强测试结果不断偏离频率稳定度真值;考虑噪声相关条件下测试结果与频率稳定度真值相对误差不超过1.7%。该方法被进一步应用到中国计量科学研究院实验室4台铯原子钟,360天实际测量数据验证了其有效性。     

DNA microarray stochastic model

A stochastic model of the DNA microarray image pixels is presented. The model includes spot pixel intensity distribution, interpixel correlations and the intensity distribution of background noise. The data is indicative of a small exponential additive noise process and a larger Gaussian fluctuation that scales with spot intensity. Correlations are observed among pixels in the spot and between test and control images. The correlated fluctuations may be attributed to variations across each spot in the amount of DNA placed on the spot during the array fabrication process. The model may be used in gene expression estimation algorithm development, both to test new algorithms through simulation and to develop optimum algorithms. The model should also be easily adapted to new array based technologies in proteomics.     

Time-domain equalisation for discrete multi-tone transceivers: new results and performance analysis

The time-domain equaliser (TEQ) is a commonly used device to shorten the channel impulse response in a discrete multitone (DMT) receiver. Many methods have been proposed to design the TEQ with a capacity maximisation criterion. An implicit assumption used by existing methods is that circular convolution can be conducted for the noise signal and the TEQ. This assumption is not valid because the noise vector, observed in a DMT symbol, does not have a cyclic prefix. A similar assumption is also made for the residual inter-symbol interference (ISI) signal. Because of these invalid assumptions, the TEQ-filtered noise and residual ISI powers in each subcarrier were not properly evaluated. As a result, optimum solutions derived are not actually optimal. This paper attempts to resolve this problem. We first analyse the statistical properties of the TEQ-filtered noise signal and the residual ISI signal in detail, and derive precise formulae for the calculation of the TEQ-filtered noise and residual ISI powers. Then, we re-formulate the capacity maximisation criterion to design the true optimum TEQ. Simulations show that the proposed method outperforms the existing ones, and its performance closely approaches the theoretical upper bound.     

A biogeography-based optimization for optimum discrete design of skeletal structures

This article presents a modified biogeography-based optimization (MBBO) algorithm for optimum design of skeletal structures with discrete variables. The main idea of the biogeography-based optimization (BBO) algorithm is based on the science of biogeography, in which each habitat is a possible solution for the optimization problem in the search space. This algorithm consists of two main operators: migration and mutation. The migration operator helps the habitats to exploit the search space, while the mutation operator guides habitats to escape from the local optimum. To enhance the performance of the standard algorithm, some modifications are made and an MBBO algorithm is presented. The performance of the MBBO algorithm is evaluated by optimizing five benchmark design examples, and the obtained results are compared with other methods in the literature. The numerical results demonstrate that the MBBO algorithm is able to show very competitive results and has merits in finding optimum designs.     

超磁致伸缩驱动器自适应精密驱动控制研究

超磁致伸缩驱动器(GMA)虽然具有很多优点,但是超磁致伸缩材料(GMM)在磁化过程中存在磁滞非线性,磁滞误差可达20 %,要解决这一问题,必须对GMA采用精确有效的方法实现建模,并用于GMA驱动位移精密控制。研究中采用LMS算法对研制的GMA进行自适应系统模型辨识,用不同频率的正弦信号和方波信号作为输入,辨识模型都能精确逼近GMA输出信号,辨识精度高达0.069 μm;最后采用Fx-LMS算法对GMA进行驱动位移控制实验,通过在线辨识有效减小磁滞误差,提高控制精度。