Time-domain wavefield reconstruction inversion

Wave field reconstruction inversion （WRI） is an improved full waveform inversion theory that has been proposed in recent years. WRI method expands the searching space by introducing the wave equation into the objective function and reconstructing the wavefield to update model parameters, thereby improving the computing efficiency and mitigating the influence of the local minimum. However, frequency-domain WRI is difficult to apply to real seismic data because of the high computational memory demand and requirement of time-frequency transformation with additional computational costs. In this paper, wavefield reconstruction inversion theory is extended into the time domain, the augmented wave equation of WRI is derived in the time domain, and the model gradient is modified according to the numerical test with anomalies. The examples of synthetic data illustrate the accuracy of time-domain WRI and the low dependency of WRI on low-frequency information.

FM interference suppression for PRC-CW radar based on adaptive STFT and time-varying filtering

The influence of frequency modulation （FM） interfer- ence on correlation detection performance of the pseudo random code continuous wave （PRC-CW） radar is analyzed. It is found that the correlation output deteriorates greatly when the FM inter- ference power exceeds the anti-jamming limit of the radar. Accord- ing to the fact that the PRC-CW radar echo is a wideband pseudo random signal occupying the whole TF plane, while the FM in- terference only concentrates in a small portion, a new method is proposed based on adaptive short-time Fourier transform （STFT） and time-varying filtering for FM interference suppression. This method filters the received signal by using a binary mask to excise only the portion of the TF plane corrupted by the interference. Two types of interference, linear FM （LFM） and sinusoidal FM （SFM）, under different signal-to-jamming ratio （S JR） are studied. It is shown that the proposed method can effectively suppress the FM interference and improve the performance of target detection.

An application of matching pursuit time-frequency decomposition method using multi-wavelet dictionaries

In the time-frequency analysis of seismic signals, the matching pursuit algorithm is an effective tool for non-stationary signals, and has high time-frequency resolution and a transient structure with local self-adaption. We expand the time-frequency dictionary library with Ricker, Morlet, and mixed phase seismic wavelets, to make the method more suitable for seismic signal time-frequency decomposition. In this paper, we demonstrated the algorithm theory using synthetic seismic data, and tested the method using synthetic data with 25% noise. We compared the matching pursuit results of the time-frequency dictionaries. The results indicated that the dictionary which matched the signal characteristics better would obtain better results, and can reflect the information of seismic data effectively.

Application of a time-magnitude prediction model for earthquakes

In this paper we discuss the physical meaning of the magnitude-time model parameters for earthquake prediction. The gestation process for strong earthquake in all eleven seismic zones in China can be described by the magnitude-time prediction model using the computations of the parameters of the model. The average model parameter values for China are： b = 0.383, c=0.154, d = 0.035, B = 0.844, C = -0.209, and D = 0.188. The robustness of the model parameters is estimated from the variation in the minimum magnitude of the transformed data, the spatial extent, and the temporal period. Analysis of the spatial and temporal suitability of the model indicates that the computation unit size should be at least 4°× 4°for seismic zones in North China, at least 3° × 3° in Southwest and Northwest China, and the time period should be as long as possible.

Form-Preserving Transformations of Time-Dependent Schrodinger Equation withTime- and Position-Dependent Mass

We study space-time transformations of the time-dependent Schrodingerequation (TDSE) with time- and position-dependent (effective) mass. We obtain the most generalspace-time transformation that maps such a TDSE onto another one of its kind. The transformedpotential is given in explicit form.

Directed transport of coupled Brownian ratchets with time-delayed feedback

A time-delayed feedback ratchet consisting of two Brownian particles interacting through the elastic spring is consid ered. The model describes the directed transport of coupled Brownian particles in an asymmetric two-well ratchet potential which can be calculated theoretically and implemented experimentally. We explore how the centre-of-mass velocity is af fected by the time delay, natural length of the spring, amplitude strength, angular frequency, external force, and the structure of the potential. It is found that the enhancement of the current can be obtained by varying the coupling strength of the delayed feedback system. When the thermal fluctuation and the harmonic potential match appropriately, directed current evolves periodically with the natural length of the spring and can achieve a higher transport coherence. Moreover, the external force and the amplitude strength can enhance the directed transport of coupled Brownian particles under certain conditions. It is expected that the polymer of large biological molecules may demonstrate a variety of novel cooperative effects in real propelling devices.

High-precision frequency attenuation analysis and its application

Based on seismic attenuation theory in a fluid-filled porous medium, we improve conventional methods of low-frequency shadow analysis （LFSA） and energy absorption analysis （EAA） and propose a high-precision frequency attenuation analysis technology. First, we introduce the method of three-parameter wavelet transform and the time-frequency focused criterion and develop a high-precision time-frequency analysis method based on an adaptive three-parameter wavelet transform, which has high time-frequency resolution with benefit to LFSA and can obtain a single-peaked spectrum with narrow side-lobes with benefit to EAA. Second, we correctly compute absorption coefficient by curve fitting based on the nonlinear Nelder-Mead algorithm and effectively improve EAA precision. Practical application results show that the proposed frequency attenuation analysis technology integrated with LFSA and EAA can effectively predict favorable zones of carbonate oolitic reservoir. Furthermore, reservoir prediction results based on LFSA correspond with EAA. The new technology can effectively improve reservoir prediction reliability and reduce exploration risk.

大功率机车牵引四象限变流器解耦控制方案

在机车牵引等兆瓦级大功率四象限变流器(four-quadrant converter,4QC)应用场合,功率器件的开关频率低至数百赫兹,直接电流控制的优势难以发挥,通常采用间接电流控制。传统的间接电流控制又难以对变流器网侧的有功功率和无功功率进行独立控制。针对这类情况,在静止直角坐标系建模,采用功率解耦的电流控制方法,实现了单相四象限变流器有功功率与无功功率的独立解耦控制;通过引入有功电流和无功电流的有效值闭环控制,使得电流的稳态精度提高,降低了系统对输入电感参数和电网电压幅值的敏感度;采用两重化载波移相调制,使得网侧电流的谐波成分大为减少;分析了变流器两重化并联运行时环流的产生机理,并进行了有功和无功的均流控制。基于上述控制方案,实现了大功率机车牵引四象限变流器控制系统,实验证明了该控制方案的有效性。

Improved absorbing boundary condition based on linear interpolation for ADI-FDTD method

With the linear interpolation method, an improved absorbing boundary condition（ABC）is introduced and derived, which is suitable for the alternating-direction-implicit finite- difference time-domain （ADI-FDTD） method. The reflection of the ABC caused by both the truncated error and the phase velocity error is analyzed. Based on the phase velocity estimation and the nonuniform cell, two methods are studied and then adopted to improve the performance of the ABC. A calculation case of a rectangular waveguide which is a typical dispersive transmission line is carried out using the ADI-FDTD method with the improved ABC for evaluation. According to the calculated case, the comparison is given between the reflection coefficients of the ABC with and without the velocity estimation and also the comparison between the reflection coefficients of the ABC with and without the nonuniform processing. The reflection variation of the ABC under different time steps is also analyzed and the acceptable worsening will not obscure the improvement on the absorption. Numerical results obviously show that efficient improvement on the absorbing performance of the ABC is achieved based on these methods for the ADI-FDTD.

基于航空电源的九开关变换器控制方法研究

对基于航空电源的九开关变换器控制方法进行了研究,该系统由永磁同步发电机、九开关变换器以及控制器组成。介绍了九开关变换器的分时控制原理,将变换器的控制分为机侧整流控制模型和网侧逆变控制模型来分别进行研究,机侧与网侧模型都采用了双闭环控制的方法,通过Matlab/Simulink仿真得出:所采用的控制方法达到了变速恒频发电的要求,并有效地减少了网侧输出电流的谐波含量。

Data Acquisition System for Electron Energy Loss Coincident Spectrometers

A Data Acquisition System （DAQ） for electron energy loss coincident spectrometers （EELCS） has been developed. The system is composed of a Multiplex Time-Digital Converter （TDC） that measures the flying time of positive and negative ions and a one-dimension positionsensitive detector that records the energy loss of scattering electrons. The experimental data are buffered in a first-in-first-out（FIFO） memory module, then transferred from the FIFO memory to PC by the USB interface. The DAQ system can record the flying time of several ions in one collision, and allows of different data collection modes. The system has been demonstrated at the Electron Energy Loss Coincident Spectrometers at the Laboratory of Atomic and Molecular Physics, USTC. A detail description of the whole system is given and experimental results shown.

一种逆变器均流控制方法

在逆变器均流控制方法中,下垂控制和平均功率控制都需要精确计算逆变器输出有功功率和无功功率以控制输出电压的幅值和相角(频率)。在轻载和空载情况下,由于输出电流很小,电流采样和功率计算存在很大误差,有功功率环流会造成直流母线过压故障甚至损坏逆变器。本文采用电感电流代替输出电流计算逆变器输出有功功率和无功功率,并通过改变电感电流采样时刻提高了功率计算的精度。利用两台三相四线逆变器并联系统验证了理论分析的正确性,实验证明运用该功率计算方法取得了良好的并联均流效果。

IDENTIFICATION OF TIME-VARIANT CONTINUOUS SYSTEM BY A QUASI-NEWTON METHOD

A quasi-Newton method (QNM) for solving an unconstrained optimization problem in infinite dimensional spaces is presented in this paper. We apply the QNM algorithm to an identification problem for a nonlinear system of differential equations, that is, to identify the parameter vector q = q(t) appearing in the following system of differential equations, based on the measurement of the state , where is a measurement operator. We give two examples to show the algorithm.

Performance Analysis of STFT Based Timing Approach to OFDM Systems

This paper mainly focuses on performance analysis of the previously proposedSTFT based 2-D timing approach to OFDM systems and presents simulations results of its performancein AWGN and multipath fading environment and its robustness against the duration of Channel ImpulseResponse (CIR) and frequency offset. Simulation results suggest that a revised version of Short-TimeFourier Transform (STFT) can be used to greatly reduce computational complexity, especially athigher SNR.

Experimental Study of Short-Wavelength Li-like Soft X-ray Lasers

In this paper,the results of the X-ray laser-gain experiments of Li-like K and Ca ions conducted recently at LF12 Laser Facility of SIOFM with KC1 and CaFi slab targets,will be presented.Also presented will be the space-resolved time history of ASE emission in the Li-like X-ray lasers and the in-situ calibration for the X-ray film used in the experiments.