Circumferential and longitudinal defect detection using T(0,1) mode excited by thickness shear mode piezoelectric elements

Different kinds of defects, such as corrosions, notches and cracks etc, exist in pipes. Mode choice is important since unfortunately not all ultrasonic guided wave modes are suitable for these kinds of defect detection. T(0,1) mode which is non-dispersive is the lowest and fastest torsional mode and most suitable for defect detection in pipes. Two completely different artificial defects including longitudinal and circumferential defects are processed successively in a 4-m-long, 60-mm-OD, 3.5-mm-wall steel pipe. T(0,1) mode at 45 kHz is excited to detect these defects using thickness shear mode piezoelectric elements. Experimental results show that two kinds of defects are detectable using T(0,1) mode. Comparing with longitudinal modes, torsional modes are dominant in pipe inspection for their sensitivities to different kinds of defects.     

Collision-induced dissociation of hydrated adenosine monophosphate nucleotide ions: protection of the ion in water nanoclusters

Fragmentation of singly charged anions of adenosine 5'-monophosphate (AMP-) induced by collisions with neutral atoms (Ne, Na) has been studied at a collision energy of 50 keV. The experiments were performed with isolated AMP- as well as with AMP- anions nanosolvated in a cluster with a given number m of water molecules. In the first case, the dominant fragmentation channels concern the loss of adenine, PO3- and H2PO4-. In the latter, loss of water molecules becomes the dominating process, and the AMP- ion is fully protected when m is larger than approximately 13. The observed fragment distributions are well described with the model of an evaporative ensemble.     

Control of an ultrasonic transducer to realize low speed driven

This paper deals with the control of a transducer to realize low speed. A new PWM control is proposed to fit the transducer. By this control method, the transducer is directly excited by pulses whose width can be modulated. The noise induced by conventional PWM control is eliminated and the motor works more steadily and more quietly. Instead of the general method of decreasing vibrating amplitude of ultrasonic motor to realize low speed, in this paper, two fast contrary elliptical vibrations of the transducer's two Langevin vibrators are excited to restrain skip-slip influence on ultrasonic motor's low speed performance and the driven is realized by the difference of the two vibrators' vibrating amplitudes. Experiments had been carried out by driving an aerostatic guide and fuzzy control is applied. The controlled speed reached 0.1 mm/s.     

The evolution of the cavitation bubble driven by different sound pressure

In this paper, the relation between the ambient radius R(0) of the acoustic cavitation bubble and its driving pressure was investigated by an improved method. The evolution of the bubble was gained with a long-distance microscope and a bundle of 532 nm laser switched by an acousto-optic modulator. The ambient radius R(0) was determined by fitting the numerical calculation based on Rayleigh-Plesset equation to the experimental data. The results showed that as the sound pressure increased R(0) decreased at beginning and increased after the pressure reached to about 1.2 atm. Although the same rule was gotten from the relation between the maximum radius R(m) and the sound pressure, the ratio R(m)/R(0) varied monotonously with the sound pressure. It indicates that enhancing the sound pressure can increase the compression ratio of the bubble even if the mass inside the bubble is also increased.     

Magnetic,electrical transport and electron spin resonance studies of ferromagnetic insulating manganites Nd0.85Na0.15MnO3

We have investigated the magnetic, electrical transport and electron spin resonance (ESR) properties of polycrystalline Nd_0.85Na_0.15MnO₃ prepared by sol–gel method. A ferromagnetic–paramagnetic (FM–PM) transition is observed around 110 K, which is not accompanied by a metal–insulator transition. The sample displays the complete PM state associated with the ESR spectra fitted by single Lorentzian line shape above 130 K. Below 130 K, ESR spectra become distorted and then linewidth increases rapidly, where short-range magnetic order develops and coexists with PM phase due to the inhomogeneous magnetic state. In addition, the large difference between the activation energies obtained from the resistivity and ESR parameters (peak-to-peak linewidth and line intensity) at the frame of adiabatic small polaron hopping model is pointed out for Nd_0.85Na_0.15MnO₃.     

基于观测器的液压系统健康状态评估方法研究

为了实时评估液压系统的健康状态,提出了基于观测器的健康状态评估原理,利用解析模型、仿真模型和数据模型及其配合等方法进行液压系统标准模型的建立,联合实际液压系统的监测数据,构建液压系统的状态观测器。将实际系统的相关参数作为输入,实际监测点的输出与标准模型的输出进行特征分析与对比,在数据处理的基础上形成残差及其向量,运用数据分析方法计算系统健康度,并解析各元素及其耦合所映射的故障类型与故障程度,实现液压系统的故障定位与评估。最后,利用某型装备的起竖液压系统进行了应用举例,介绍了模型构建、故障模式与参数选择、残差构成及健康度计算的方法。所研究的状态评估方法对实时评估液压系统,及开展液压系统视情维修具有参考价值。     

混沌参数调制下RSA数据加密算法研究

随着网络信息通讯技术的发展,信息数据的通讯安全成为信息化网络信息数据通讯过程中的重要问题。面对大量侵入程序与数据漏洞的威胁,一套强有效的数据加密算法成为数据研究领域的研究方向。RSA数据加密算法作为如今常用的安全性最高的算法,在大数据动态数据节点混沌排列的条件下,无法有效保证数据的加密安全。混沌参数下,出现加密逻辑断裂、溢出、数列逆排等严重的算法漏洞。对此,提出混沌参数调制下RSA数据加密算法研究,采用混沌参数特征处理单元、特征序列逻辑控制单元与混沌FIE-RSA算法,对传统RSA加密算法存在的问题进行针对性解决。通过仿真实验证明,提出的混沌参数调制下RSA数据加密算法研究中,采用的一系列方法具有加密处理响应速度快、处理运算时间短、加密安全度高、反破解性能强等特点。     

1KeV电子入射单电离氦原子三重微分散射截面的理论研究

用3C模型、DS3C模型对1KeV电子入射氦原子(e,2e)反应中的三重微分散射截面进行了计算,并将理论计算结果与实验数据进行了比较,研究了各种屏蔽效应对散射平面内以及垂直平面内三重微分散射截面的影响,并对三重微分散射截面变化规律进行了探讨.结果表明:各种屏蔽效应对散射平面内三重微分散射截面的贡献可以忽略;而在垂直平面内,这些效应对三重微分散射截面结构存在较强影响;另外,末态出射电子与靶核的相互作用直接影响散射平面内和垂直平面内截面的结构及其变化规律.     

基于VxWorks新型映像的三模冗余启动机制研究

针对VxWorks启动映像依赖于ROM地址,不能适应航天型号中三模存储要求的缺点,利用VxWorks自带的压缩算法,按照航天型号软件任务要求设计了一种基于VxWorks内存型映像的新型压缩映像,实现了软件映像与ROM区地址无关。并且实现了新型压缩映像的三模冗余引导启动,启动时每一个bit数据都从三份映像获取,并进行三取二判断,将最后结果拷贝到内存作为目的映像的bit数据,目的映像启动后能够回写正确数据自动纠正空间环境下可能发生的单粒子翻转错误,为软件的可靠启动建立了基础。