Time–frequency higher‐order spectra with adjustment to the instantaneous frequency variation

Novel time–frequency techniques are proposed: the short time instantaneous higher‐order spectra (HOS) with adjustment to measured or known a priori time variation of the instantaneous frequency of transient signals. It is shown that the proposed transforms are more effective than the non‐instantaneous HOS (i.e. without adjustment to time variation of the instantaneous frequency) in recognizing a non‐stationary nonlinearity. Copyright © 2008 John Wiley & Sons, Ltd.     

行波测距在电力系统中应用

简要分析电力系统现状,阐述行波理论,在此基础上将行波理论用于实际情况来验证可行性并举出算例进行说明,最后分析并展望行波理论。     

基于经验模式分解三相流型信号去噪方法研究

经验模式分解(EMD)作为一种信号处理技术,它是基于数据本身的,且能在空间域中将信号进行分解,从而可以区分噪声和有用信号。应用经验模式分解(EMD)对模拟信号及实测油气水三相流压差波动信号进行滤波去噪处理,分别与db8小波及Haar小波的滤波去噪效果进行定量比较。结果表明:EMD方法与小波方法一样能有效地处理短时瞬态及含宽带噪声的信号,但EMD方法更直接,更方便,且不受小波基函数选择的影响,因此EMD方法更具有通用性和稳定性,从而为三相流流型信号的预处理提供了又一种有效的方法。     

HTPB推进剂危险性实验研究

依据联合国危险品分级方法,探讨了热刺激、机械刺激和冲击波刺激对低燃速HTPB推进剂、高燃速HTPB推进剂和四组元HTPB推进剂危险性的影响。结果表明,3种HTPB推进剂的热安定性良好,但对火焰热刺激均十分敏感,具有爆燃性;高燃速HTPB推进剂对机械刺激也极其敏感,摩擦感度(p)为96%,撞击感度特性(H50)为37.2 cm。在无约束条件下,3种HTPB推进剂裸药柱对雷管爆轰作用不敏感,而在钢管的强约束条件下,四组元HTPB推进剂对爆轰冲击波作用敏感,隔板值大于18mm。     

High frequency complex permeability of flake-shaped Fe_(74)Cr_2Mo_2Sn_2P_(10)Si_4B_4C_2 particle composite material

A composite consisting of flake-shaped Fe74Cr2Mo2Sn2P10Si4B4C2 particles was prepared.The flake-shaped particles included in the composite were prepared by planetary ball milling.The complex permeability of the composite material was measured at frequency range from 10 MHz to 8.5 GHz.The permeability of the composite containing flake-shaped particles was much higher than that of the spherical particles.The permeability of particles was improved by means of heat-treatment.In contrast to the random-spatial-di...     

Optimization of exit-plane waves restored from HRTEM through-focal series

Atomic-resolution transmission electron microscopy has largely benefited from the implementation of aberration correctors in the imaging part of the microscope. Though the dominant geometrical axial aberrations can in principle be corrected or suitably adjusted, the impact of higher-order aberrations, which are mainly due to the implementation of non-round electron optical elements, on the imaging process remains unclear. Based on a semi-empirical criterion, we analyze the impact of residual aperture aberrations on the quality of exit-plane waves that are retrieved from through-focal series recorded using an aberration-corrected and monochromated instrument which was operated at 300 kV and enabled for an information transfer of ∼0.05 nm. We show that the impact of some of the higher-order aberrations in retrieved exit-plane waves can be balanced by a suitable adjustment of symmetry equivalent lower-order aberrations. We find that proper compensation and correction of 1st and 2nd order aberrations is critical, and that the required accuracy is difficult to achieve. This results in an apparent insensitivity towards residual higher-order aberrations. We also investigate the influence of the detector characteristics on the image contrast. We find that correction for the modulation transfer function results in a contrast gain of up to 40%.     

超声振动辅助等离子沉积成形的研究

介绍了等离子沉积成形的原理、应用及其存在的优缺点,从超声原理出发介绍了超声振动对等离子沉积过程中晶粒及组织的影响,并设计了超声振动辅助等离子沉积成形的实验装置,对实验过程中以及该实验可能涉及的问题进行了探讨.     

小波神经网络在液压装置压力测试中的应用

压力是反映液压系统正常工作的重要参数之一,对压力进行检测是液压装置故障诊断的重要内容。传统的压力检测多采用介入式方法,但这些方法需要插入液压管道中才能实施检测,存在必须预留接口、安装困难、影响系统动态性能等诸多缺陷。对液压装置的超声非介入式测压方法进行了研究,通过对声速和液压装置压力之间关系的研究,基于小波神经网络建立了液压装置的超声测压模型,并对影响液压装置超声测压精度的主要因素进行了分析。     

Comparative evaluation of sliding mode fuzzy controller and PID controller for a boost converter

Nonlinear controllers such as fuzzy controllers and sliding mode controllers have been applied to boost converters because of their nonlinear properties. Although both fuzzy and sliding mode controllers have desirable characteristics, they have disadvantages in practice when applied individually. A sliding mode fuzzy controller is proposed to control boost converters. The sliding mode fuzzy controller combines the advantages of both fuzzy controllers and sliding mode controllers. It also has advantages of its own that are well suited for digital control design and implementation. A sliding mode fuzzy controller is designed and verified with experimental results using a prototype boost converter with a DSP-based digital controller. Experimental results of the boost converter using sliding mode fuzzy control are evaluated in comparison with experimental results using a linear PID and PI controller. The comparison indicates that the sliding mode fuzzy controller is able to obtain the desired transient response under varying operating points without chattering. The startup response using sliding mode fuzzy control is superior to the response using PID and PI control, while the load transient response shows no obvious advantage.     

风暴潮过程中波浪对地形演变影响的数值研究

建立了一个波流耦合作用下泥沙输移的平面二维数值模型，以研究风暴潮过程中地形冲淤变化的规律及波浪的影响。水流和泥沙输运的模拟采用水沙耦合数值模型，以考虑强冲淤条件下地形变化与水流运动之间的相互作用。波浪场模拟采用SWAN模型，计算得到的波浪辐射应力输入水沙耦合数值模型实现波流耦合。采用建立的模型对风暴潮过程中近岸地形变化进行了分析，结果表明，波浪对地形演变的影响程度随着风暴潮潮位的增加而减小。当风暴潮潮位较小时，近潮汐通道处形成不对称的三角洲、入口处形成冲刷坑；当风暴潮潮位较高时，形成的三角洲不对称性较小。当风暴潮潮位升高，近岸水深与波长之比大于0.15时，波流耦合模型与不考虑波浪作用模型计算所得的地形变化的绝对误差为整体地形变化的5%，但前者计算时间增加了一倍，因此，波流耦合计算对于风暴潮潮位较低，近岸水深与波长之比小于0.15时具有重要意义。