采用C语言FPGA技术实现LDPC码译码算法

针对LDPC码(Low Density Parity Check Codes)译码算法的特点和最新一代Impulse C语言的并行编程技术,提出一种对LDPC码译码器进行FPGA(Field Programmable Gate Array)设计与实现的便捷新方案,以获得译码速率和硬件资源消耗的平衡.在XC2V2000芯片上实现了一种码率1/2,码长2500的(3,6)LDPC码译码器.实验表明当最大迭代次数为10次,主频50MHz时,译码速率可达10Mbps.     

脉冲—应答技术测定传递与吸附系数的最优化计算

本文采用单纯形搜索法,借助于电子计算机对脉冲-应答实验得到的50℃条件下,糠醛在固定床反应器中多孔催化剂 BHK-1上的传递与吸附系数做了最优化计算。结果表明,该方法在模拟工业操作条件下表征固定床中多孔催化剂的传递与吸附特性是行之有效的。     

Estimates of the Wigner Distribution in Gaussian Noise Environment

The influence of Gaussian noise to the Wigner distribution is considered.Due to the quadratic nature of the Wigner distribution, the resulting noise exhibits impulse nature even in the case of Gaussian input noise. Estimators of the Wigner distribution which take into account this fact are considered.They can outperform the standard and the robust Wignerdistribution.     

Low-order parametric force model for a salient-pole synchronous machine with eccentric rotor

In this paper, a low-order parametric force model to represent the electromagnetic force on an eccentric rotor of a salient-pole synchronous machine was developed and verified. The force model with parameters estimated from the results of impulse method showed excellent performance. The proposed model allowed quick and accurate calculation of the electromagnetic force at the desired whirling frequency values and provided an opportunity to effectively combine the electromagnetic and mechanical analyses of electrical machines. Besides, results presented in this paper also verified the suitability of computationally efficient impulse method for the analysis of a synchronous machine.     

Absorption of shocks in nonlinear autoregressive models

It generally is difficult, if not impossible, to fully understand and interpret nonlinear time series models by considering the estimated values of the model parameters only. To shed light on the characteristics and implications of a nonlinear model it can then be useful to consider the effects of shocks on the future patterns of the time series variable. Most interest in such impulse response analysis has concentrated on measuring the persistence of shocks, or the magnitude of their (ultimate) effect. A framework is developed and implemented that is useful for measuring the rate at which this final effect is attained, or the rate of absorption of shocks. It is shown that the absorption rate can be used to examine whether the propagation of different types of shocks, such as positive and negative shocks or large and small shocks follows different patterns. The nonlinear floor-and-ceiling model for US output growth is used to illustrate the various concepts. The presence of substantial asymmetries in both persistence and absorption of shocks is documented, with interesting differences arising across magnitudes of shocks and across regimes in the model. Furthermore, it appears that asymmetry became much less pronounced due to a large decline in output volatility in the 1980s.     

The influence of laser welding parameters on the microstructure and mechanical property of the as-jointed NiTi alloy wires

The Nd:YAG laser welding was used to join the binary NiTi alloy wires with different compositions(Ti-50.0 at.%Ni and Ti-50.9 at.%Ni) which had the same diameter of 1 mm. The wires were welded with different parameters, including impulse width and welding current. The aim was to assess the influence of the laser-welding process on the microstructure and mechanical properties of the welded joint of binary NiTi wires. The optical microscopy (OM) and the metallographic microscopy (MM) were used to analyze the microstructure of the welded joints. The tensile test and the differential scanning calorimetry (DSC) were carried out to examine the ultimate tensile strength and the reverse martensitic transformation temperatures of the welded joints. It was found that the welding current and the impulse width had great influence on the quality of the welded joints, an optimal parameter combination would remove the pores and micro-cracks appeared in the fusion zone, and result in good mechanical properties such as higher fracture strength and elongation. The laser welding had a few effect on the reverse martensitic transformation temperatures of the welded joints.     

Restoration of signals degraded by impulse noise by means of a low-distortion non-linear filter

A simple low-distortion non-linear filter for the restoration of signals degraded by random impulsive noise is proposed. It performs considerably better than a median filter, lowering the reproducing error both in mean-square and maximum-error sense, although being comparable in computing time and in terms of storage.     

Impulse Density Measurements after the Held Method

The introduction shows the importance of the impulse on damage, if the high explosive amount is smaller than 1000 kg.     

超宽带无线通信技术

本文首先介绍了超宽带(UWB)技术的定义及其频谱规划情况,分析了UWB的调制与多址技术,然后介绍了目前IEEE 802.15.3 SG3a建议使用的UWB路径损耗模型及多径信道模型,最后展望了其应用前景及目前发展状况与需进一步研究的问题.     

An impulse-response extracting method from the modulated signal in a roller bearing

In this paper, a signal processing method is proposed to derive the impulse responses of the defect impacts for a roller bearing, and is carried out in two steps. First, the envelope detection for the vibration signal with amplitude modulation is implemented through the linear least square analysis under the assumption of a stepwise function for the envelope signal. Secondly, the signal processing of impulse-response enhancement is applied to eliminate the sidebands around the defect frequencies. The impulse responses of the defect impacts could be derived and the sidebands in the impulse-response spectrum could be theoretically eliminated. Accordingly, the spectrum would be helpful to apply in the bearing defect diagnosis, especially under the condition of non-uniform loading. From the theoretical analysis and the experimental studies, it is shown that the proposed signal processing method could effectively derive the impact responses of the defects impacts for a roller bearing system and the sidebands in the impulse-response spectrum could be reduced or even eliminated.