Velocity spectrum for non-Markovian Brownian motion in a periodic potential

Non-Markovian Brownian motion in a periodic potential is studied by means of an electronic analogue simulator. Velocity spectra, the Fourier transforms of velocity autocorrelation functions, are obtained for three types of random force, that is, a white noise, an Ornstein—Uhlenbeck process, and a quasimonochromatic noise. The analogue results are in good agreement both with theoretical ones calculated with the use of a matrix-continued-fraction method, and with the results of digital simulations. An unexpected extra peak in the velocity spectrum is observed for Ornstein-Uhlenbeck noise with large correlation time. The peak is attributed to a slow oscillatory motion of the Brownian particle as it moves back and forth over several lattice spaces. Its relationship to an approximate Langevin equation is discussed.     

Information entropy of a dynamical system driven by quasimonochromatic noise

This paper shows the Fokker-Planck equation of a dynamical system driven by quasimonochromatic noise. Based on the Fokker-Planck equation and the definition of Shannon's information entropy, the exact time dependence of entropy flux and entropy production for the system is calculated. The relationship between the properties of quasimonochromatic noise and dissipative parameter and their effects on entropy flux and entropy production are discussed.     

Symmetry breaking of fluctuation dynamics by noise color

Activated escape is investigated for systems that are driven by noise whose power spectrum peaks at a finite frequency. Analytic theory and analog and digital experiments show that the system dynamics during escape exhibit a symmetry-breaking transition as the width of the fluctuational spectral peak is varied. For double-well potentials, even a small asymmetry may result in a parametrically large difference of the activation energies for escape from different wells.     

Time evolution of information entropy for a stochastic system with double singularities driven by quasimonochromatic noise

<正>This paper deals with the time evolution of information entropy for a stochastic system with double singularities driven by quasimonochromatic noise.The dimension of the Fokker-Planck equation is reduced by the linear transformation. The exact expression of the time dependence of information entropy is obtained based on the definition of Shannon’s information entropy.The relationships between the properties of dissipative parameters,system singularity strength parameter,quasimonochromatic noise,and their effects on information entropy are discussed.     

Spatial localization of temporal noise in digital channels

The feasibility of temporal noise spatial localization in a communication channel intended for digital signal transmission is studied. As in the case of temporal noise localization for analog signals, we use the Hadamard integral transformation with specially ordered basis functions. When the noise intensity is estimated through the probability of error in determining the output signal with different lengths of digital words, the localization of noise for digital signals is shown to be identical to that of analog signals.     

Nonlinear dynamic filtering of logarithmically amplified fringe signals in optical coherence tomography applied to paper measurements

Application of the nonlinear Kalman filtering method to logarithmically amplified low-coherence fringe signals measured from paper samples is considered. Experimental results of dynamic fringe envelope recovery in optical coherence tomography (OCT) systems are presented. The analog fringe envelope and digital dynamic fringe envelope recoveries from noisy signals are compared. The results show that the nonlinear discrete Kalman filtering method can be applied to estimate envelopes of logarithmically transformed low-coherence fringe signals with high noise immunity. Logarithmic amplification reduces quantization error in dealing with small signal values. The experimental results obtained demonstrate the possibility of purely digital signal processing in OCT. The text was submitted by the authors in English.     

The acoustic telescope

A system has been developed for real-time sound source location on full-size jet engines. It consists of an array of microphones connected to a small digital computer, via a sequence of preamplifiers, analog filters and analog to digital converters and multiplexer. Microphone signals can be processed on-line to give displays of time varying source distributions or statistical averages with respect to position and frequency, by using a colour television as well as a display screen and printer/plotter. The whole system can be transported in a small estate car and can be used on both model scale and full size engine test rigs.A theoretical analysis of system performance is in terms of a line source of generally correlated omni-directional sound radiators, which shares the measurable far-field properties of a jet engine noise source. The general properties of the system are described, including its use to correlate spatially separated sound sources, application in the presence of ground reflections and use in a moving airstream. The statistical properties of apparent source distributions are also discussed.A series of experiments on a Rolls-Royce/SNECMA Olympus engine is described, in order to illustrate application of the system.     

天文观测相机低噪声CCD视频处理电路的分析与设计

在讨论天文观测相机低噪声视频处理电路的基础上,对前置放大、差分放大、可编程增益放大、相关双采样及16bit模数转换等关键组成部分进行了分析,给出各组成部分的设计方法。对所设计的低噪声视频处理电路进行了PSPICE仿真和实验测试,仿真和实验结果表明,该视频处理电路在本身引入噪声较小的同时,有效地抑制了CCD的复位噪声和1/f等低频噪声,使天文观测相机的整机噪声<15e-,达到了指标要求。     

自适应中值-加权均值混合滤波器

为了去除图像中混入的脉冲噪声和高斯噪声,提出了一种基于自适应中值滤波和自适应加权均值滤波的混合滤波方法。该方法先将图像分为若干区域,并对每个区域进行噪声检测以实现两类噪声的分离,然后再分别采用自适应中值滤波和自适应加权均值滤波将分离出的脉冲噪声和高斯噪声去除。对这种新方法进行了计算机模拟实验。结果表明:新方法较前人提及的三种混合滤波方法具有更优的滤波性能,在有效抑制混合噪声的同时能很好地保护图像中的细节,为消除图像中的混合噪声提供了一种有效的途径。     

Fiberoptic receiver performance: A tutorial review

A tutorial review of fiberoptic receivers is presented, and their performance analyzed in terms of two quantities: quantum noise, a fundamental limit, and Noise Equivalent Power, or NEP, an engineering parameter. The NEP, a quantity specified by manufacturers as constant, is shown to vary with bandwith (data rate). The exact dependence of NEP on bandwidth is derived for two types of receivers: transimpedance and integrating, in both analog and digital modes. The results are applied to the calculation of the minimum required power for digital and analog receivers operation, and universal curves ofpower vs. bandwidth are presented. It is shown that the NEP specified by manufacturerscan be fitted to these universal curves, from which receiver performance can be predicted.

For tutorial purposes, the treatment is self-contained and many well-known classical results such as signal-to-noise ratio of PCM signals and noise-equivalent circuits are re-derived from fundamental principles.     

反馈有源噪声控制系统水床效应的分析与改善

本文依据反馈有源噪声控制原理分析了水床效应存在机理,以一模拟反馈有源噪声控制系统作为实例介绍了水床效应的分析方法,提出了通过展宽噪声放大频段和均匀噪声放大频段内的噪声放大量来优化反馈控制器,改善水床效应的方法。采用数字反馈控制器实现了水床效应的改善,给出了具体设计过程,并且考虑了数字时延对系统性能影响。仿真和实验表明了所提出方法的有效性。     

Digital detection and processing of multiple quadrature harmonics for EPR spectroscopy

A quadrature digital receiver and associated signal estimation procedure are reported for L-band electron paramagnetic resonance (EPR) spectroscopy. The approach provides simultaneous acquisition and joint processing of multiple harmonics in both in-phase and out-of-phase channels. The digital receiver, based on a high-speed dual-channel analog-to-digital converter, allows direct digital down-conversion with heterodyne processing using digital capture of the microwave reference signal. Thus, the receiver avoids noise and nonlinearity associated with analog mixers. Also, the architecture allows for low-Q anti-alias filtering and does not require the sampling frequency to be time-locked to the microwave reference. A noise model applicable for arbitrary contributions of oscillator phase noise is presented, and a corresponding maximum-likelihood estimator of unknown parameters is also reported. The signal processing is applicable for Lorentzian lineshape under nonsaturating conditions. The estimation is carried out using a convergent iterative algorithm capable of jointly processing the in-phase and out-of-phase data in the presence of phase noise and unknown microwave phase. Cramér-Rao bound analysis and simulation results demonstrate a significant reduction in linewidth estimation error using quadrature detection, for both low and high values of phase noise. EPR spectroscopic data are also reported for illustration.     

Spectra of discontinuous noise waves

The article considers the problem of the transformation of the energy spectrum of an intense random wave in a nonlinear, nondisperse medium. It is assumed that at the inlet to the nonlinear medium there is given a random quasimonochromatic wave, and an investigation is made of the spectrum of a nonlinear wave at distances where the original continuous wave goes over into a sequence of sawtooth pulses with a random position of the discontinuity and with random amplitudes. In the work, an investigation was made of the dependence of the spectral characteristics of discontinuous noise waves on the statistics of the amplitude and phase of the input quasimonochromatic wave. The form of the spectrum of the wave is found at low frequencies, which appear due to the effect of the autodetection of the quasimonochromatic wave in a nonlinear medium. The effect of the viscosity of the medium on the form of the energy spectrum is also discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 21, No. 11, pp. 1627–1636, November, 1978.The authors are indebted to A. N. Malakhov and A. I. Saichev for their valuable evaluations.     

准单色噪声驱动的耗散动力系统的信息熵演化

准单色噪声是一类所谓真正有色的噪声.本文对准单色噪声驱动的耗散动力系统的信息熵演化进行研究,文中首先运用线性变换的方法给出了所研究系统的Fokker-Planck方程,然后结合Shannon信息熵定义推导了该系统随时间演化信息熵的精确表达式,最后分析了系统耗散参数和准单色噪声对系统信息熵的显著影响.     

A modified phase generation carrier technique for fiber-optic distributed disturbance sensor

A modified phase generation carrier technique used in fiber-optic distributed disturbance sensor (FDDS) is proposed and investigated. The FDDS locates the disturbance by dual Mach–Zehnder (MZ) interferometers, however, the initializing phase error of the two MZ interferometer causes the location errors. For the modified PGC technique, a narrow band analog low pass filter is designed, which solves the problem of facilitating the digital narrow band low pass filter in high speed A/D acquisition. In addition, a special demodulation signal is proposed to demodulate higher-order harmonic, compensate the time delay of the long optical fiber and enhance the signal to noise ratio. It is found that the location errors caused by phase drift can be eliminated in our experiments.     

Wavelet filtering applied to time-average digital speckle pattern interferometry fringes

In this paper we are presenting a filtering scheme using Symlet wavelet to remove the speckle noise from the time-averaged digital speckle pattern interferometry fringes. To demonstrate the potential of Symlet wavelet filtering, experiments are conducted to remove the speckle noise from the fringes recorded for the surface of computer hard disk. Experimental results demonstrate that this filtering removes the speckle noise to the large extent.     

Activated escape of periodically driven systems

We discuss activated escape from a metastable state of a system driven by a time-periodic force. We show that the escape probabilities can be changed very strongly even by a comparatively weak force. In a broad parameter range, the activation energy of escape depends linearly on the force amplitude. This dependence is described by the logarithmic susceptibility, which is analyzed theoretically and through analog and digital simulations. A closed-form explicit expression for the escape rate of an overdamped Brownian particle is presented and shown to be in quantitative agreement with the simulations. We also describe experiments on a Brownian particle optically trapped in a double-well potential. A suitable periodic modulation of the optical intensity breaks the spatio-temporal symmetry of an otherwise spatially symmetric system. This has allowed us to localize a particle in one of the symmetric wells. (c) 2001 American Institute of Physics.     

Intra-vehicle digital communications: characterization and simulation of the electromagnetic environment

Most of the studies on electromagnetic noise and the potential sources of interference were conducted to protect analog communications and have now appeared to be insufficient given the widespread development of digital communications. New approaches appropriate for digital communications are currently under development. We have chosen to illustrate these recent approaches by focusing on the particular application of intra-vehicle transmission. In this article, we consider two examples of data transmission: wire transmissions over a power line network, better known as power line communication, and wireless links inside the vehicle's passenger cell. We focus on characterizing the electromagnetic environment but we also highlight the potential of reverberation chambers for reproducibly simulating multi-path environments. To cite this article: F. Rouissi et al., C. R. Physique 10 (2009).     

一种数字有源降噪耳机控制器设计方法

为了得到一种作用于低频宽带噪声的有源降噪耳机,采用固定系数的数字控制器实施降噪,并提出了一种前反馈混合的控制器设计方法。比较了前馈及混合两种控制模式下对低频宽带噪声的控制效果;进一步提出了一种综合优化方法,改善噪声不同角度入射下的降噪性能。仿真和基于DSP平台的实验表明,提出的方法对多方向入射的20～1500 Hz低频宽带噪声均具有较好控制效果。     

PID数字控制器多指标优化模拟设计方法研究

建立PID数字控制器多指标统一优化模拟设计方法;用SIMULINK仿真研究数字PID控制对模拟PID控制的复现能力和PID计算机控制系统的阶跃响应,用MATLAB仿真筛选PID参数的优化组合值;提出并建立了一种新的PID数字控制器多指标优化模拟设计方法,包括:PID初值确定方法、模拟PID优化参数MATLAB筛选方案和软件流程图、模拟PID参数转换数字PID参数的方法、SIMULINK仿真验证设计结果的有效性的方法等;研究表明,该方法可用于1～5ms采样周期的PID数字控制器多指标优化模拟设计,且能独立使用、无需PID经验数据和其它设计/整定方法;提供了4个代表性的实例设计,验证了该方法的有效性。