基于小波分析频差性的电力电缆故障测距

为了提高电力电缆在线单端故障测距方法运用到放射状中压配电系统的准确性,研究了电压行波在配电系统不同地点的反射和透射频差特性,运用小波变换结果模极大值确定电压行波到来时刻的同时,利用所选小波滤波器相频特性提炼电压行波信号携带的原有频差特性信息,有效地判断出到达母线的第2个行波是故障点反射波还是对端母线反射波。基于某变电站出线构建EMTP仿真模型,仿真结果表明这种利用小波分析频差性的电力电缆在线单端故障测距方法能够较精确地寻找到故障点。

Frequency Response Computation and Error Analyses

Aim To derive the error formulae for the algorithm of frequency response computation. Methods This algorithm was introduced theoretically, the error sources of the algorithm were analyzed and the formulae of the main error were derived. Results The repeatability and stability of the processing results of the algorithm are better than those measured by 1250 Frequency Analysor. Conclusion The error formulae derived are theoretically right and practically valid.

Finite-difference modeling of surface waves in poroelastic media and stress mirror conditions

During seismic wave propagation on a free surface, a strong material contrast boundary develops in response to interference by P- and S- waves to create a surface-wave phenomenon. To accurately determine the effects of this interface on surface-wave propagation, the boundary conditions must be accurately modeled. In this paper, we present a numerical approach based on the dynamic poroelasticity for a space–time-domain staggered-grid finite-difference simulation in porous media that contain a free-surface boundary. We propose a generalized stess mirror formulation of the free-surface boundary for solids and fluids in porous media for the grid mesh on which lays the free-surface plane. Its analog is that used for elastic media, which is suitable for precise and stable Rayleigh-type surface-wave modeling. The results of our analysis of first kind of Rayleigh （R1） waves obtained by this model demonstrate that the discretization of the mesh in a similar way to that for elastic media can realize stable numerical solutions with acceptable precision. We present numerical examples demonstrating the efficiency and accuracy of our proposed method.

Wideband dipole logging based on segmen linear frequency modulation excitation

A wideband dipole signal is required for dipole dispersion correction and nearborehole imaging. To obtain the broadband flexural wave dispersion, we use a nonlinear frequency modulation （NLFM） signal and propose a segment linear frequency modulation （SLFM） signal as the dipole excitation signal to compensate for the excitation intensity. The signal-to-noise ratio （SNR） of the signal over the entire frequency band is increased. The finite-difference method is used to simulate the responses from a Ricker wavelet, a linear frequency modulation （LFM） signal, an NLFM signal, and an SLFM signal in two borehole models of a homogeneously hard formation and a radially stratified formation. The dispersion and radial tomography results at low SNR of the sound source signals are compared. Numerical modeling suggests that the energy of the flexural waves excited by the Ricker wavelet source is concentrated near the Airy phase. In this case, the dispersion is incomplete and information regarding the formation near or far from the borehole cannot be obtained. The LFM signal yields dispersion information near the Airy phase and the high-frequency range but not in the low-frequency range. Moreover, the information regarding the formation far from the borehole is not accurate. The NLFM signal extends the frequency range of the flexural waves by compensating for the excitation intensity and yields information regarding the formation information, but it is not easy to obtain. The SLFM signal yields the same results as the NLFM signal and is easier to implement. Consequently, the dipole detection range expands and the S-wave velocity calculation accuracy improves.

Anti-Jamming Performance of Fountain Coded Differential Frequency Hopping Systems in AWGN

Based on the anti-jamming performance of differential frequency hopping （DFH） systems in Additive White Gaussian Noise （AWGN） channel, Fountain code is introduced to the DFH systems as the outer error correcting code in this paper to investigate the improvements against partial-band jamming over AWGN channel. The performance of Fountain coded DFH is theoretically analyzed and numerically simulated. The total frequency of hopping in the simulation is 16, and results show that, on one hand, when exact jamming state information （JSI） is available, and the number of jamming frequency is n= 16, the bit error rate （BER） of 10~3 is achieved with the signal to interference ratio （SIR） approximately 7.5 dB over AWGN channel, and the performance improves about 1-1.5dB compared with the no-coded system. When the number of jamming frequency is n=2, the performance increases 15-17dB. On the other hand, when JSI is unavailable, a joint JSI estimation and decoding algorithm is proposed. The BER of 10 3 is achieved with jamming-frequency n 16, SIR=8dB and signal noise ratio （SNR） 10dB over AWGN channel. It＇s proved that this algorithm provides robust anti-jamming pertbrmance even without JSI. The anti-jamming performance of Fountain coded DFH systems is obviously superior to no-coded DFH systems.

Analysis and Design of a High-Stability,High-Accuracy,Low-Dropout Voltage Regulator

A high-accuracy,low-dropout （LDO） voltage regulator is presented. Using the slow-rolloff frequency compensation scheme, the LDO effectively overcomes the stability problem, facilitates the use of a ceramic capacitor, and improves the output voltage accuracy, which is critical for powering high-performance analog circuitry. The slow-rolloff compensation scheme is realized by introducing three pole-zero pairs, including the proposed polezero pair and sense zero. The post-layout simulation results demonstrate that this LDO has robust system stability, a high open-loop gain, and a high unit-gain frequency,which lead to excellent regulation and transient response performance. The line and load regulation are 27μV/V and 3.78μV/mA, and the overshoots of the output voltage are less than 30mV,while the dropout voltage is 120mV for a 150mA load current.

MDL-based root-mean-squared delay spread estimation for MIMO OFDM systems

This paper studied the application of minimum description length (MDL) criterion for estimating root-mean-squared (RMS) delay spread (RDS) for MIMO OFDM systems. The analytic relationship between the powers and the correlation matrix of multipath components established the feasibility of the application of the MDL criterion to RDS estimation. The estimator presented both the estimate of instantaneous RDS and the estimates of noise variance, channel power and SNR of current channel with low computational complexity. Given the powers of the estimated multipath components, the MDL criterion was adopted to acquire the number of paths and the time delays of each path of current channel without making eigendecomposition of the correlation matrix normally required by MDL criterion, following which the noise variance and the power of each path can be estimated. The power delay profile (PDP) and RDS of the current channel were achieved. Simulation results showed that the proposed estimator was insensitive to variance of SNR and robust against frequency-selectivity.

ESSENTIAL INFORMATION AGGREGATION OF INTRA CODED VIDEO FRAME FOR WIRELESS TRANSMISSON

A novel error resilient method based on Essential Information Aggregation (EIA) technique is proposed for robust wireless transmission of intra coded video frames. This method modifies the original video stream structure so as to mitigate the effect of decoding loss of synchronization within a video frame, for which Macro Block Aligned (MBA) error detection method is accompanied to be developed. Experiments on an Additive White Gaussian Noise (AWGN) wireless simulation platform and H.263+ baseline video codec show that it can obtain better subjective and objective image quality than existing error resilience approaches.

Correction of Dynamic Error Result from Measurement System Limitations

The main cause of dynamic errors is due to frequency response limitation of measurement system. One way of solving this problem is designing an effective inverse filter. Since the problem is ill-conditioned, a small uncertainty in the measurement will came large deviation in reconstncted signals. The amplified noise has to be suppressed at the sacrifice of biasing in estimation. The paper presents a kind of designing method of inverse filter in frequency domain based on stabilized solutions of Fredholm integral equations of the fast kind in order to reduce dynamic errors. Compared with previous several work, the method has advantage of generalization. Simulations with different Signal-to-Noise ratio （SNR） are investigated. Flexibility of the method is verified. Application of correcting dynamic error is given.

Sensibility to Changes of Vibrational Modes of Excited Electron： Sum Frequency Signals Versus Difference Frequency Signals

In this paper, we investigate a two electronic level system with vibrational modes coupled to a Brownian oscillator bath. The difference frequency generation （DFG） signals and sum frequency generation （SFG） signals are calculated. It is shown that, for the same model, the SFG signals are more sensitive than the DFG signals to the changes of the vibrational modes of the electronic two-level system. Because the SFG conversion efficiency can be improved by using the time-delay method, the findings in this paper predict that the SFG spectrum may probe the changes of the microstructure more effectively.

Cyclic beamforming using fractional Fourier transform domain cyclostationarity

A minimum mean-squared error （MSE） beamforming algorithm employing the optimum fractional Fourier transform （Opt-FrFT） domain second-order cyclostationarity is proposed. This method can efficiently filter out the compact desired chirp signal, with a consequence that the cyclically uncorrelated interferences and stationary （colored） Gaussian noise are greatly suppressed in the Opt- FrFT domain. This improves the MSE minimization cyclic beamformer by reducing effectively the Opt-FrFY domain signal-noise cross terms in the presence of finite data length de-correlation operation. Simulation results show that the new method works well under a wide range of signal-to-noise ratio （SNR） and signal-to-interference ratio （SIR）.

A Novel Two-step Frequency Offset Estimator for OFDM

Based on an orthogonal frequency division multiplexing(OFDM) training symbol with L identical parts, a novel carrier frequency offset (CFO) estimator is proposed for OFDM systems. The CFO is estimated in two steps, fine estimate and coarse estimate. In the first step, the fine estimation is performed based on the principle of minimum variance. However, the fine estimation has ambiguity since its estimate range is limited. In the second step, the coarse estimation is obtained, which results in a larger estimate range but less precision. Using the coarse estimation, the ambiguity of fine estimation is resolved. To fully use the correlation among L identical parts, the fine estimation resolved the ambiguity and the coarse estimation are optimally combined to obtain the final estimation. Furthermore, the estimation variance of the proposed method is derived. Simulation results demonstrate that the novel two-step estimator outperforms the conventional two-step estimator in terms of estimate performance and computational complexity.

Joint Transceiver Design for OFDM Systems

Orthogonal Frequency Division Multiplexing(OFDM) is an effective technique to deal with a frequency selective channel since it can convert the channel into some flat fading subchannels.However,very different output SNR values of the subchannels will lead to poor bit error performance when a linear equalizer and Equal Bit Allocation(EBA) are adopted in OFDM systems.So,we proposed three novel nonlinear Joint Transceiver(JT) schemes based on Zero-Forcing(ZF) criterion and Minimum Mean Square Error(MMSE) criterion respectively,which can transform all subchannels of an OFDM system into subchannels with identical channel gain.Thus,EBA is equivalent to the Optimum Bit Allocation(OBA) for these subchannels.Numerical analysis helps us to obtain the theoretical approximate BER values of the JT scheme.Simulation results verify the numerical analysis and confirm that the performance of our proposed JT scheme greatly outperforms the traditional linear equalizer with EBA at moderate and high SNR values.

GENERALIZED CONFIDENCE REGIONS OF FIXED EFFECTS IN THE TWO-WAY ANOVA

The authors discuss the unbalanced two-way ANOVA model under heteroscedasticity. By taking the generalized approach, the authors derive the generalized p-values for testing the equality of fixed effects and the generalized confidence regions for these effects. The authors also provide their frequentist properties in large-sample cases. Simulation studies show that the generalized confidence regions have good coverage probabilities.

Comparison of the effect of low-frequency electroacupuncture on serum leptin and NPY contents of male and female patients with simple obesity

Objective To explore the difference of low-frequency electroacupuncture in regulating serum leptin and neuropeptide Y（NPY） of male and female patients with simple obesity due to spleen deficiency and damp exuberance. Methods Eighty patients with simple obesity, including 37 males and 43 females, were included in this study. In both groups（male group and female group）, Yīnlíngquán（阴陵泉 SP 9）, Sānyīnjiāo（三阴交 SP 6）, Zúsānlǐ（足三里 ST 36）, Fēnglóng（丰隆 ST 40）, Qūchí（曲池 LI 11）, Tiānshū（天枢 ST 25）, Zhōngwǎn（中脘 CV 12）, Shuǐfēn（水分 CV 9）, Qìhǎi（气海 CV 6）, and Guānyuán（关元 CV 4）. were selected, and low-frequency electroacupuncture treatment was applied. Needles were retained for 30 min. The treatment was conducted once a day, and 10 times were considered as one course of treatment. Two courses were needed. The changes of weight, BMI（body mass index）, F%（fat percentage） and serum leptin and NPY contents of patients in the two groups before and after treatment were observed and analyzed comparatively. Results After treatment, in male group, the weight lost（9.24±2.55） kg, BMI reduced by 4.19±2.30, F% reduced by 3.98±2.13, serum leptin level reduced by（0.66±0.23） ng/m L, and serum NPY level reduced by（18.56±2.89） pg/m L; in female group, the weight lost（6.77±2.31） kg, BMI reduced by 2.65±0.93, F% reduced by 4.98±2.30, serum leptin level reduced by（3.49±1.09） ng/m L, and serum NPY level reduced by（11.21±1.97） pg/m L. The results reduced significantly when compared with the level before treatment（P〈0.05, P〈0.01）. The loss of weight, BMI and serum NPY content in male group was more obvious than that in female group（all P〈0.01）, and the loss of F% and serum leptin content in female group was more obvious than that in male group（both P〈0.01）. Conclusion Low-frequency electroacupuncture can significantly regulate the weight, BMI, F% and serum leptin and NPY contents of male and female patients with simple obesity, and there are gender differences. In terms of reducing weight, BMI and serum NPY content, the efficacy of low-frequency electroacupuncture in males is superior to that in females, while in terms of reducing F% and serum leptin content, the efficacy in females is superior to that in males.