A Correlation Coefficient Approach for Evaluation of Stiffness Degradation of Beams Under Moving Load

This paper presents a new approach using correlation and cross-correlation coefficients to evaluate the stiffness degradation of beams under moving load.The theoretical study of identifying defects by vibration methods showed that the traditional methods derived from the vibration measurement data have not met the needs of the actual issues.We show that the correlation coefficients allow us to evaluate the degree and the effectiveness of the defects on beams.At the same time,the cross-correlation model is the basis for determining the relative position of defects.The results of this study are experimentally conducted to confirm the relationship between the correlation coefficients and the existence of the defects.In particular,the manuscript shows that the sensitivity of the correlation coefficients and cross-correlation is much higher than the parameters such as changes in stiffness(EJ)and natural frequency values(Δf).This study suggests using the above parameters to evaluate the stiffness degradation of beams by vibration measurement data in practice.

Effects of signal modulation and coloured cross-correlation of coloured noises on the diffusion of a harmonic oscillator

The diffusion in a harmonic oscillator driven by coloured noises ξ（t） and η（t） with coloured cross-correlation in which one of the noises is modulated by a biased periodic signal is investigated. The exact expression of diffusion coefficient d as a function of noise parameter, signal parameter, and oscillator frequency is derived. The findings in this paper are as follows. 1） The curves of d versus noise intensity D and d versus noises cross-correlation time z3 exist as two different phases. The transition between the two phases arises from the change of the cross-correlation coefficient A of the two Ornstein-Uhlenbeck （O-U） noises. 2） Changing the value of T3, the curves of d versus Q, the intensity of colored noise that is modulated by the signal, can transform from a phase having a minimum to a monotonic phase. 3） Changing the value of signal amplitude A, d versus Q curves can transform from a phase having a minimum to a monotonic phase. The above-mentioned results demonstrate that a like noise-induced transition appears in the model.

Research on Leak Location Method of Water Supply Pipeline Based on MVMD

At present,the leakage rate of the water distribution network in China is still high,and the waste of water resources caused by water distribution network leakage is quite serious every year.Therefore,the location of pipeline leakage is of great significance for saving water resources and reducing economic losses.Acoustic emission technology is the most widely used pipeline leak location technology.The traditional non-stationary random signal de-noising method mainly relies on the estimation of noise parameters,ignoring periodic noise and components unrelated to pipeline leakage.Aiming at the above problems,this paper proposes a leak location method for water supply pipelines based on a multivariate variational mode decomposition algorithm.This method combines the two parameters of the energy loss coefficient and the correlation coefficient between adjacent modes,and adaptively determines the decomposition mode number K according to the characteristics of the signal itself.According to the correlation coefficient,the effective component is selected to reconstruct the signal and the cross-correlation time delay is estimated to determine the location of the pipeline leakage point.The experimental results show that this method has higher accuracy than the cross-correlation method based on VMD and the cross-correlation method based on EMD,and the average relative positioning error is less than 2.2%.

基于响度级、耳间互相关系数和中心频率的主观声场宽度预测模型

耳机回放音频时,大脑感知到的音频的主观声场宽度受其响度级、耳间互相关系数和频率成分的影响显著.采用虚拟声学指针作为参考信号,针对响度级在60~80方,耳间互相关系数在0~1的倍频程信号进行了主观声场宽度听音实验.实验结果表明:随着响度级的提高主观声场宽度在不同频段有不同的增幅,增幅最大值在200Hz附近,最小值在1600Hz附近,每增加10方,平均声场宽度增幅为5.4°;随着耳间互相关系数的降低,主观声场宽度的增幅在400~800Hz最大,耳间互相关系数每降低0.2,主观声场宽度增加约4.8°.根据实验结果建立了一个基于响度级、耳间互相关系数和中心频率的三因素主观声场宽度预测模型.验证实验表明,该模型的预测结果和听音者的实验结果误差在5.4°,符合实验的精度要求,能够对给定信号的声场宽度进行有效的预测.

基于循环神经网络的双耳助听器语音增强算法

基于神经网络的语音增强算法相比于传统方法具有更好的语音增强效果,但因网络规模大导致其难以实时实施于助听器中。对此,本文提出了一种具有低复杂度的循环神经网络用于增强双耳语音。该算法结合双耳语音提取梅尔频率倒谱系数和耳间相位差作为网络的输入特征,在使用双耳语音振幅信息的基础上结合语音空间线索更好的映射目标语音和带噪语音之间的关系。实验结果表明,与助听器常用算法相比,本文算法的双耳平均信噪比和短时语音可懂度平均提高了4.68 dB和4.5%;与基于神经网络的算法相比,本文算法的双耳平均信噪比和短时语音可懂度分别提高了1.63 dB和4.8%。当时钟频率为10 MHz时,本文网络的硬件设计需要4.2 ms左右的处理时间,可以满足助听器的实时需求。

Study on S wave splitting in Dayao earth-quake sequence with M=6.2 and M=6.1 in Yunnan in 2003

The polarization direction of fast wave and the delay time between fast and slow wave were measured for two earthquake sequences occurred continuously on 21 July （M=6.2） and 16 October （M=6.1） in Dayao, Yunnan in 2003 using cross-correlation coefficient method, after determining the high-resolution hypocentral locations of the earthquake sequences using the double-difference earthquake location algorithm. The results indicated that ① The phenomena of S wave splitting are obvious in the two earthquake sequences, and the average polarization directions of fast wave in most stations are almost consistent with regional maximum horizontal compressive stress direction except the station Santai. There are bimodal fast directions in the polarization directions at station Santai and the mean polarization direction is N80°E, indicating an inconsistent phenomenon referred to regional maximum horizontal compressive stress direction. ② There is no apparent relation between delay time and focal depth in the sequences, but the polarization direction show different character in different delay time range. ③ The comparison of S wave splitting results in the two earthquake sequences show that the polarization direction in M=6.2 earthquake sequence is more scattered and its average fast direction is 20° larger than that of M=6.1 sequence, and the delay times between two sequences show a little difference. ④ The spatial variation in S wave splitting polarization direction may be due to the stress disturbance imposed by the M=6.2 and the M=6.1 mainshocks on regional background stress field.

利用声场双耳互相关函数和声源自相关函数计算音乐信号与脉冲响应卷积信号的IACC(英文)

双耳脉冲响应(BIRs)是用以表征音乐厅和歌剧院声场特征的参量.由于BIRs是表征声场的转移函数,因此,在消声室中录制的声源信号与BIRs卷积,就代表在实际声场中听到的信号.为了探究原信号的声学特征,一种有效的方法是计算其自相关函数(ACF),因为从ACF中导出的参量能与听者的主观优选良好相关.因此可以说,卷积与相关是室内声学中最重要的计算方法.文中通过将BIRs导出的双耳互相关函数(IACF)和将干信号与BIRs卷积后的IACF作比较,探讨了声源信号与声场之间的关系.在特定条件下,卷积与相关是等同的,此时,干信号与BIRs卷积后的IACC可直接由BIRs导出的IACC与干信号的ACF的有效时间τ_e来表示.

DIRECT MEASUREMENT OF MULTIPLE QUANTUM RELAXATION TIME

A multiple quantum coherence (MQC) with a given order subjected to its own relaxa-tion decay in the evolution period can be transferred into observable single quantum (SQ)coherences in the detection period, the MQ relaxation time in a spin system, therefore, canbe directly measured by the 1-dimensional (1-D) Hahn echo method since the amplitudes ofSQC’s are modulated by the decayed MQC. This 1-D approach is an alternation to the 2-Dmeasurement for MQ relaxation time, the latter being somewhat time-consuming. The 1-Dapproaches can readily get rid of the inhomogeneous broadening of MQ lines. A method forselective measurement of various MQ relaxation times in AX_n systems (n=1,2, and 3) witha given MQ order is presented. Consequently, the cross correlation coefficients of the sys-tems, which are not accessible in the SQ relaxation study, can be determined.