STUDY OF ALGORITHMS FOR ESTIMATING SIGNALS WITH A PULSED-DISTURBANCE FLOW

Using the methods of the Markov theory of optimal nonlinear filtering, we derive equations of the algorithm for estimating random signals described by linear difference equations in discrete time in the case of a pulsed-disturbance flow. Optimal estimates of signals are represented as the sum of auxiliary estimates allowing for the influence of pulsed disturbances spaced apart by a multiple number of pulses. The results of mathematical simulation are given and the algorithm structure is discussed.     

Algorithm for Optimal Estimation of Appearance Times of Pulsed Signals in Discrete Time

Using the methods of optimal nonlinear Markov filtering, we obtain an algorithm for optimal mean-square estimation of appearance times of random pulsed variations in signal parameters against the background of white Gaussian noise in discrete time. Linear difference equations are used to describe signals, noise, and the observed processes. Equations of the algorithm permitting real-time calculations of the a posteriori variances and optimal estimations of pulse-appearance times are obtained in the approximation of Gaussian conditional probability densities. We present simulation results for algorithm operation in the particular problem of estimating the appearance times of two pulsed signals having the known shapes and observed against noise background.     

Pulsed ultrasonic spectroscopy of gas bubbles

Transient processes associated with gas bubble excitation by ultrasonic pulses are investigated based on the numerical solution to the Rayleigh-Plesset equation. The results are used to consider ultrasonic methods of gas bubble detection and sizing in liquids and biological tissues on the basis of linear and nonlinear bubble properties. The possibility of frequency separation of signals received from bubbles with different sizes in the case of their pulsed excitation is experimentally demonstrated.     

Estimation of Markov Sequences with Jump-Like Variation of Parameters by the Interpolation Method

Using the methods of the theory of optimal nonlinear filtering, we develop an algorithm for obtaining optimal estimates of the sequence of hidden states of discrete-valued Markov processes with abruptly changing parameters at unknown time. Optimal estimates of the states of Markov processes and of the time of appearance of an abrupt change in parameters are obtained as a result of interpolation by processing the entire observation sequence. The results of simulation of the algorithm work are presented. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 7, pp. 628–639, July 2005.     

Optimal filtering in multipulse sequences for nuclear quadrupole resonance detection

The application of the multipulse sequences in nuclear quadrupole resonance (NQR) detection of explosive and narcotic substances has been studied. Various approaches to increase the signal to noise ratio (SNR) of signal detection are considered. We discussed two modifications of the phase-alternated multiple-pulse sequence (PAMS): the 180° pulse sequence with a preparatory pulse and the 90° pulse sequence. The advantages of optimal filtering to detect NQR in the case of the coherent steady-state precession have been analyzed. It has been shown that this technique is effective in filtering high-frequency and low-frequency noise and increasing the reliability of NQR detection. Our analysis also shows the PAMS with 180° pulses is more effective than PSL sequence from point of view of the application of optimal filtering procedure to the steady-state NQR signal.     

Internal tissue displacement measurement based on ultrasonic wave Doppler signal digital detection and its application to fetal movement monitoring

We have developed a fetal movement monitoring system based on small displacement measurement of internal tissues. When ultrasonic pulses are transmitted to the fetus, the reflected ultrasonic waves which have a Doppler frequency shift due to the fetal movements are detected by using an ultrasonic pulsed Doppler technique. In this paper, we propose a displacement measurement method for internal tissues which is based on the Doppler signal digital detection technique. In the method, the received ultrasonic RF signals are sampled with a sampling frequency of four times higher than the centre frequency of the ultrasonic waves; the Doppler frequency shift signals are derived using digital signal processing. From the detected signals, the internal displacements are estimated using the arc-tangent method. The basic algorithm of the detection method has already been used in the area of blood flow sensing, however, we apply the algorithm to the displacement measurement of internal tissues. The comparison between the proposed method and the conventional method is presented. The fetal movement quantitative monitoring system based on the method which has been constructed is shown.     

The Viterbi Algorithm for Models of Hidden Markov Processes with the Unknown Moment of Appearance of Parameter Jump

The methods of the theory of optimal nonlinear filtering of the Markov processes is used to develop the Viterbi algorithm for obtaining optimal estimates of a sequence of hidden states in the model of discrete-value Markov processes generalized to the case of jump-like changing parameters with an unknown time of the jump appearance. The results of numerical simulation of the algorithm performance are given. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 4, pp. 358–366, April 2005.     

Nonlinear chirp compensation by scan filtering in SAIL

The nonlinear chirp of a tunable laser generates the phase errors and damages the range resolution in synthetic aperture imaging ladar (SAIL). In the compensation algorithms establishing matched and nonmatched reference paths, the phase errors were compensated in a whole echo pulse. In this paper a compensation algorithm of nonlinear chirp by scan filtering is proposed.The heterodyne signals of different echoes from all target points in a footprint are scan filtered from one whole heterodyne signal of one whole echo pulse in the spectrum. The phase errors of these heterodyne signals are measured by phase-shifting algorithm in reference path and compensated separately. Then all the compensated signals are combined back into a whole heterodyne pulse and compressed in range. After all heterodyne pulses are compressed in range, the azimuth compensation is followed.The mathematical flow of this compensation algorithm is established. The simulation of the airborne SAIL model validates the feasibility, and the bandwidth of range compression decreases obviously. The effects of nonlinear chirp and the pass bandwidth of the scan filter are analyzed and discussed finally.     

Adaptive joint filtering of parameters of the pulsed signals

Based on representing parameters of the pulsed signals by discrete and continuous Markov processes, we synthesize adaptive algorithms and devices for joint nonlinear filtering of parameters of the pulsed correlated signals, whose operation does not require knowledge of a priori statistical data about the filtered process during reception. The obtained results confirm the possibility of developing the receiving devices which efficiently use the statistical redundancy of signals for improving reliability of the data transmission. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 4, pp. 364–370, April 2007.     

提高飞秒超强激光脉冲对比度的新方法

文章在简要描述飞秒超强激光脉冲对比度有关概念及其测量方法的基础上,介绍了空间滤波和时间滤波,以及提高注入脉冲种子对比度和强度的技术,环形腔放大技术,光参量啁啾脉冲放大技术（OPCPA）,双啁啾脉冲放大技术（DCPA）,采用高阶非线性晶体滤波等几种提高对比度的新方法和新技术.采用这些方法和技术,在最近一两年的时间里,人们成功地将多年来徘徊在106量级的飞秒超强激光脉冲对比度,提高到了1011的新水平,从而为强场物理的研究提供了更为理想的光源.     

Parameter estimation for the piecewice-polynomial mean value trend of a stochastic time series

We consider the problem of mean value trend estimation for a stochastic time series in a mixture with noise. The trend is simulated as a polynomial function of time with parameters changing discontinuously at a random instant. The proposed solution of this problem is based on the optimal nonlinear filtering theory for pulsed Markovian processes. An algorithm for approximate estimation of piesewise-linear trend parameters is devised as an example. The results of numerical simulation of a synthesized algorithm are presented. Lobachevsky State University, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 11, pp. 1405–1415, November, 1997.     

Measuring protein self-diffusion in protein-protein mixtures using a pulsed gradient spin-echo technique with WATERGATE and isotope filtering

Here we report a modified pulsed gradient spin-echo (PGSTE) pulse sequence to measure diffusion coefficients. This approach incorporates WATERGATE combined with isotopic filtering into a standard PGSTE experiment. Doing this eliminates much of the disadvantages from the combination of diffusion encoding and heteronuclear selection intervals and allows for facile modification of the diffusion pulse sequence with flexibility of the time period between RF pulses. The new diffusion pulse sequence is demonstrated using an 15N-labeled peptide and an 15N-labeled protein in a mixture with a protein of similar size.     

Stimulated spin echo upon excitation with pseudorandom pulses

Different regimes of excitation of a stimulated spin echo by pseudorandom pulses and short coherent delta-shaped pulses are considered. Radio pulses phase-shifted by a 127-element M sequence are used as pseudorandom signals. The shape of the complex envelope of the stimulated echo is simulated in linear and nonlinear regimes with respect to the phase-shifted pulses. It is demonstrated that the excitation pulses can be described by correlation functions. Appropriate conditions are determined under which the amplitude of the stimulated echo can be greater than the amplitude corresponding to the classical algorithm used for exciting a stimulated echo by three delta-shaped pulses. The results obtained can be used for analyzing the formation of a stimulated photon echo.     

Use of the Frank sequence in pulsed EPR

The Frank polyphase sequence has been applied to pulsed EPR of triarylmethyl radicals at 25 6 MHz (9.1 mT magnetic field), using 256 phase pulses. In EPR, as in NMR, use of a Frank sequence of phase steps permits pulsed FID signal acquisition with very low power microwave/RF pulses (ca. 1.5 mW in the application reported here) relative to standard pulsed EPR. A 0.2 mM aqueous solution of a triarylmethyl radical was studied using a 16 mm diameter cross-loop resonator to isolate the EPR signal detection system from the incident pulses.     

Spectral shaping of femtosecond pulses in aperiodic quasi-phase-matched gratings

We analyze the use of cascading second harmonic interactions in quadratic nonlinear crystals to mould the spectral characteristics of broadband near-infrared femtosecond pulses. Using a genetic algorithm, we optimize the design of the aperiodically poled ferroelectric crystal capable of generating the desired femtosecond infrared pulsed radiation.     

混沌信号自适应协同滤波去噪

混沌信号协同滤波去噪算法充分利用了混沌信号的自相似结构特征,具有良好的信噪比提升性能.针对该算法的滤波参数优化问题,考虑到最优滤波参数的选取受到信号特征、采样频率和噪声水平的影响,为提高该算法的自适应性使其更符合实际应用需求,基于排列熵提出一种滤波参数自动优化准则.依据不同噪声水平的混沌信号排列熵的不同,首先选取不同滤波参数对含噪混沌信号进行去噪,然后计算各滤波参数对应重构信号的排列熵,最后通过比较各重构信号的排列熵,选取排列熵最小的重构信号对应的滤波参数为最优滤波参数,实现滤波参数的优化.分析了不同信号特征、采样频率和噪声水平情况下滤波参数的选取规律.仿真结果表明,该参数优化准则能在不同条件下对滤波参数进行有效的自动最优化,提高了混沌信号协同滤波去噪算法的自适应性.     

Holography of wave packets

We describe the principles of holographic storage and reconstruction of ultrashort light pulses using spectrally nonselective media. This can be achieved by the application of a 3-D recording medium and by the holography of waves produced by spatial spectral decomposition of light pulses. We also describe various transformations of optical temporal signals based on holographic spectral filtering and nonlinear interaction of spectral decomposition waves.     

Methods for Attenuation of the Cross-Modulation Effects in the Wigner–Ville Distribution

We consider the characteristics of typical nonlinear distortions in the dynamical spectra of signals, obtained using the Wigner–Ville method, and discuss the existing techniques for attenuating these distortions. Certain methods are proposed to clean Wigner–Ville distributions of products of the nonlinear interaction between the signal component under study and its more powerful harmonic or pulsed components. The proposed techniques are mainly based on a preliminary linear processing (e.g., using the fast Fourier transform) and/or frequency filtering of the signal. A software package for calculating the Wigner–Ville distribution on a PC is developed. Using this package, we approved successfully the proposed algorithms for test and actual signals.     

Nonlinear identification of NMR spin systems by adaptive filtering

In this paper, we present two new methods for identifying NMR spin systems. These methods are based on nonlinear adaptive filtering. The spin system is assumed to be time-invariant with memory. The first method uses a truncated discrete Volterra series to describe the nonlinear relationship between excitation (input) and system response (output). First-, second-, and third-order kernels of this series are estimated employing the least mean square (LMS) algorithm. Three parallel filters can then model the NMR spin system so that its output is no more than simple sum of three convolution products between combinations of the input signal and filters coefficients. It is also shown that the contribution of the Volterra second-order term to the total system response is neglected compared with the contributions of the first- and the third-order terms. In the second identification method, the output signal is related to the input signal through a recursive nonlinear difference equation with constant coefficients. The LMS algorithm is used again to estimate the equation coefficients. The two methods are validated with a simulated NMR system model based on Bloch equations. The results and the performances of these methods are analyzed and compared. It is shown that our methods permit a simple identification of NMR spin systems. The field of applications of this study is promising in the optimization of NMR signal detection, especially in the cases of low signal-to-noise ratios where optimum signal filtering and analysis must be performed.     

用脉冲光声法测量固体介质中声速

提出了一种利用脉冲光声技术测量固体介质中声速的方法,建立了由YAG激光器和超声探测器组成的实验系统,脉冲激光在固体表面产生脉冲超声波,通过测量脉冲声波在固体内多次反射后的出射信号及固体的厚度,即可算出固体介质中的声速.对黄铜及铝的测量结果表明,这是一种准确性较高的固体介质中声速测量方法.该测量方法可作为综合设计性物理实...