Envelope Correlation Parameter Measurements in a MIMO Antenna Array Configuration

In a 2 × 2 MIMO antenna array system envelope correlation coefficient “ρ” shows the influence of different propagation paths of the RF signals that reach the antenna elements. The approximated value of this coefficient is based on a simple closed-form equation and also varies from 0 to 1. Quite perfect performance for MIMO applications is achieved when this parameter approximates to zero. In this paper, we evaluate an antenna diversity MIMO system by measuring the envelope correlation coefficient. The corresponding results in our antenna array configurations show that the measured “ρ” has very small values and approximates to zero. This observation indicates quite perfect behavior and performance of our MIMO antenna array system.

AN EFFICIENT SIMULATION OF MULTIPLE CORRELATED RAYLEIGH FADING ENVELOPES

In order to better assess the performance of wireless communication systems,it is desirable to produce multiple Rayleigh fading envelopes with specified correlations.In this paper,we analyze theoretically a procedure which generates correlated Gaussian random variables from independent Gaussian random variables and give a physical explanation for the limitation of this procedure.Then,based on some uncorrelated Rayleigh fading envelopes,a simple but efficient procedure for generating an arbitrary number of cross-correlated Rayleigh fading envelopes is proposed.Simulation results and computational complexity analysis are presented,which show that the proposed method has some advantages,such as high accuracy,low computational complexity and easy implementation,over the conventional simulation method.

The Correlation of Hospital Operational Efficiency and Average Length of Stay in China: A Study Based on Provincial Level Data

Objective: To measure the hospital operation efficiency, study the correlation between average length of stay and hospital operation efficiency, analyze the importance of shortening average length of stay to the improvement of the hospital operation efficiency and put forward relevant policy suggestion. Methods: Based on China provincial panel data from 2003 to 2012, the hospital operation efficiencies are calculated using Super Efficiency Data Envelopment Analysis model, and the correlation between average length of stay and hospital operation efficiency is tested using Spearman rank correlation coefficient test. Results: From 2003 to 2012, the average of national hospital operation efficiency was increasing slowly and the hospital operations were inefficient in most of the areas. The national hospital operation efficiency is negatively correlated to the average length of stay. Conclusion: Measures should be taken to set average length of stay in a scientific and reasonable way, improve social and economic benefits based on the improvement of efficiency.

A Method for Incipient Fault Diagnosis of Roller Bearings Based on the Wavelet Transform Correlation Filter and Hilbert Transform

Noise is the biggest obstacle that makes the incipient fault diagnosis results of roller bearings uncorrected; a new method for diagnosing incipient fault of roller bearings based on the Wavelet Transform Correlation Filter and Hilbert Transform was proposed. First, the weak fault information features are picked up from the roller bearings fault vibration signals by use of a de-noising characteristic of the Wavelet Transform Correlation Filter as the preprocessing of the Hilbert Envelope Analysis. Then, in order to get fault features frequency, de-noised wavelet coefficients of high scales which represent high frequency signal were analyzed by Hilbert Envelope Spectrum Analysis. The simulation signals and diagnosing examples analysis results reveal that the proposed method is more effective than the method of direct wavelet coefficients-Hilbert Transform in de-noising and clarifying roller bearing incipient fault.

Temporal sequential correlation analysis on compoundaction potentials of the auditory nerve versus the stimulating AM-sound envelope

Compound action potentials of the auditory nerve in response to amplitude modulating tones were recorded in guinea pigs with electrode implanted to the exit of the internal auditory meatus and temporal sequential correlation between the responses and the modulators was studied in a paradigm of systematically changing acoustic parameters. Three kinds of modulators were used. continuous or burst sinusoids of fixed frequency (in the range of 40 Hz-5 kHz), short bursts of sinusoids with changing frequency and short segments of speech signal. Ranges of parametric variation were 500 Hz-20 kHz for carrier frequency, 5%-95% for modulation depth and 20 dB-90 dB SPL for intensity. For continuous or burst sinusoidal modulators of fixed frequencies, the correlation coefficient (r) remained quite high in most parametric conditions, ranging from 0.80 to 0.95. It became smaller mainly in instances of decreased response amplitude on account of unfavourable parameters. For burst modulators of changing frequency, r varied around 0.66-0.86. When segments of speech signal served as the modulators, significant correlation (r around 0.50 ) also existed, indicating the validity of the timing mode of information encoding for speech sound at the cochlear nerve level. Some theoretical and technical points in studying the timing mechanism of audition is discussed.

Three-Dimensional Sound Source Location Algorithm for Subsea Leakage Using Hydrophone

Leakages from subsea oil and gas equipment cause substantial economic losses and damage to marine ecosystem,so it is essential to locate the source of the leak.However,due to the complexity and variability of the marine environment,the signals collected by hydrophone contain a variety of noises,which makes it challenging to extract useful signals for localization.To solve this problem,a hydrophone denoising algorithm is proposed based on variational modal decomposition(VMD)with grey wolf optimization.First,the average envelope entropy is used as the fitness function of the grey wolf optimizer to find the optimal solution for the parameters K andα.Afterward,the VMD algorithm decomposes the original signal parameters to obtain the intrinsic mode functions(IMFs).Subsequently,the number of interrelationships between each IMF and the original signal was calculated,the threshold value was set,and the noise signal was removed to calculate the time difference using the valid signal obtained by reconstruction.Finally,the arrival time difference is used to locate the origin of the leak.The localization accuracy of the method in finding leaks is investigated experimentally by constructing a simulated leak test rig,and the effectiveness and feasibility of the method are verified.

VMD引导的轮对与轴承复合故障诊断方法

针对列车轮对轴承系统复合故障难以辨识与诊断问题,提出一种变分模态分解(variational mode decomposition,VMD)引导的多故障特征提取匹配方法.首先,为避免预定义模式数在运行过程中对先验知识依赖从而对诊断结果造成影响,对原始轴箱振动数据进行逐阶VMD分解,模式数为2~N;其次,对VMD分解获取的本征模态函数(VMD intrinsic mode functions,VIMF)进行相关峭度计算,提取相关峭度最大的VIMF;然后,将相关峭度最大的VIMF进行平方包络分析,提取故障特征频率;最后,将所提方法与快速峭度谱、相关峭度谱方法进行对比.仿真信号和试验数据分析表明:所提方法完全规避了VMD模型中关键参数K的选择问题,可以准确、有效地分别提取出轮对和轴承的故障特征;与快速谱峭度与相关谱峭度方法相比,获取的故障特征谐波分量在数量和信噪比上均具有明显优势.

超声穿透式测温传感器设计与系统实验研究

针对目前国内缺乏1200℃以上长时间超高温气体环境下有效的温度测试手段,基于超声脉冲穿透测温原理,通过设计均匀分布的平面八元圆环温度传感器阵列,成功研制出一种高效的温度场检测系统。依据波速V与气体温度T之间的经验函数,利用高温实验获得了各传感器性能数据。实验结果表明:该系统在1200℃高温环境下测量精度达到了97.98%,重复性95.52%以上,响应时间毫秒(ms)级别,符合设计要求。

基于FPGA的AES和ECC算法图像加密

随着数字图像的使用次数日益增多,保护机密图像数据免受未经授权的访问较为重要。针对数字图像在通信、存储和传输等领域存在的安全问题,文中基于对称算法模型和非对称算法模型的优点提出一种具有高安全性和高速度性的数字信封技术密码方案。该方案以AES(Advanced Encryption Standard)和ECC(Elliptic Curve Cryptography)为基础,经优化后用于对称密钥共享的ECC硬件架构来提高密钥的安全性。通过加入伪随机数、使用列移位替代列混淆运算以及三维S-box等方式对传统AES进行优化,在保持香农扩散和混淆原理的同时降低了时间复杂性。基于FPGA(Field Programmable Gate Array)实现AES算法的数字图像加密仿真以及性能测试。测试结果表明,所提密码方案具有快速性、高安全性和有效性等优点,能够有效地实现图像加密。

基于MCKD的海上风机齿轮箱轴承故障诊断方法

海上风机齿轮箱结构复杂、故障多发,同时受海上风机运行的强噪声干扰,轴承故障的特征信号提取较为困难。针对以上问题,提出了一种基于最大相关峭度解卷积(MCKD)的故障诊断方法,通过MCKD算法对振动信号进行降噪处理和特征增强,并利用增强包络谱对轴承的故障特征频率进行提取,从而实现对轴承的故障诊断。将该方法应用到海上风机齿轮箱轴承的模拟信号和实测信号中,研究结果表明:该方法对海上强噪声环境下齿轮箱轴承故障的特征提取和诊断具有良好的效果。

基于MOBWO-MCKD的风机滚动轴承故障特征提取方法

针对风力发电机轴承振动信号受强背景噪声及其他设备激励源影响,导致早期微弱故障特征不易提取这一问题,提出了一种基于多目标白鲸优化算法(MOBWO)优化的最大相关峰度反卷积(MCKD)风力发电机轴承故障特征提取方法。首先,采用MOBWO强大的全局及局部搜索能力优化了MCKD关键参数,获取了最佳参数组合;其次,利用优化后的MCKD对原始信号进行了解卷积运算,消除了背景噪声及其他设备激励源的影响,突出了轴承周期性脉冲信号;然后对解卷积信号进行了包络谱分析,提取了轴承故障特征频率,并将其与理论计算故障特征频率值进行了诊断结果对比;最后,采用实际工程中采集到的风力发电机轴承内圈和外圈的故障数据,对MOBWO-MCKD方法的有效性进行了试验验证。研究结果表明:基于MOBWO-MCKD的故障特征提取方法能够有效地消除背景噪声及其他设备激励源的干扰;由内圈信号包络谱可得到的内圈故障频率为f IR=125.87 Hz、2f IR=251.74 Hz;由外圈信号包络谱可得到的外圈故障频率为f OR=84.47 Hz、2f OR=168.94 Hz、3f OR=253.41 Hz。该特征提取方法可以为实际工程风力发电机轴承早期微弱故障特征提取研究提供一定的参考。

运载火箭测试数据分析与故障诊断方法

针对如何从运载火箭大量历史测试发射数据中发掘有用信息的问题,提出了一种基于数据挖掘的运载火箭数据分析与故障诊断方法,为火箭的故障诊断、产品设计、状态检测提供服务;针对火箭数据的特性和实际业务分析的需求,使用基于皮尔逊系数的相关性分析方法、基于希尔伯特变换的包络分析方法、基于窗口滑动函数的故障诊断方法组建火箭数据分析平台,对运载火箭的数据进行了深层次的挖掘和诊断;采用某型号火箭测试数据对火箭数据分析平台进行了验证,结果表明:以数据驱动的火箭数据分析平台相关性分析准确、参数包络线绘制精准、可有效识别异常数据,分析结果与理论知识相符,具有较高的实用价值,相比于传统数据分析方法更为精准、全面。

基于SVMD-SES的滚动轴承故障诊断

针对在进行复杂工业设备滚动轴承故障诊断时,由于强噪声影响使故障微弱瞬态冲击特征难以识别的问题,提出一种基于平方包络谱逐次变分模态分解的机械故障诊断方法。首先在变分模态分解的基础上进行逐次变分模态分解推导,降低模态混叠现象和计算复杂度。其次利用峭度指数和互相关系数的加权值构造相关峭度,通过筛选所得分量得到真实的故障模态成分。通过平方包络谱凸显信号瞬态冲击信息并进行特征提取。最后通过实验室平台采集轴承振动数据进行验证分析,实验结果表明:采用所提方法能准确识别周期性瞬态冲击,有效提取微弱特征,提高对复杂机器进行故障诊断的准确性和效率。

生猪养殖上市企业绩效评价——基于灰色关联度与数据包络分析

生猪养殖是畜牧行业重要的组成部分。本文以10家生猪养殖上市企业为实证对象,收集2023年相关数据。首先,利用灰色关联分析方法(GRA)对投入产出指标加以筛选,在此基础上结合数据包络法(DEA)对生猪养殖上市企业绩效情况进行评价。研究结果显示,10家企业综合效率与规模效率平均值分别为66%和67%,共有4家企业达到DEA有效,表明生猪养殖上市企业绩效综合效率和规模效率有待提高。据此结合行业实际情况提出强调优化资源配置、加强技术创新与合理扩大规模等参考建议。

基于小波相关滤波-包络分析的早期故障特征提取方法

噪声是影响齿轮、滚动轴承等机械设备早期故障诊断正确性的主要因素,利用小波相关滤波法的降噪特性,将小波相关滤波降噪方法和Hilbert包络谱分析相结合,提出了小波相关滤波-包络分析的早期故障特征提取新方法,即首先利用小波相关滤波方法作为包络分析的前置处理手段提取振动信号的微弱故障信息特征,以求得信噪比较高的小波系数;然后对高频段尺度域的小波系数进行Hilbert包络细化谱分析,得到早期故障的特征频率。仿真信号和诊断实例分析结果表明,该方法比直接小波系数包络分析法更能有效抑制噪声,凸现早期故障频率。

基于DEA的加权灰色关联分析方法

提出了一种基于数据包络分析(DataEnvelopmentAnalysis,简记DEA)的新的加权灰色关联分析方法。该方法综合了DEA和灰色关联分析两种方法的优势,以灰色关联分析为中心模型,以DEA模型为辅助模型,通过DEA模型来确定每一个子因素各点关联系数的权重向量,从而计算出相对最优的关联度,实现对各因素客观的优先排序。基于DEA方法的加权灰色关联分析方法既克服了确定权重时的主观性,又通过"非均一"赋权达到了优先序评价的"最优性",从而实现了分析结果的"公正性"。最后通过绿色产品的评价实例说明了方法的有效性。

超声回波信号解调及其包络相关时延估计算法

互相关函数法是脉冲法超声测距中最常用的时延估计算法,但窄带超声回波信号的振荡特性导致它们的相关函数在峰值位置近似作等幅振荡,从而为精确搜索相关函数的峰值带来困难,所以有必要对相关函数包络的峰值进行搜索.首先分析了超声回波信号解调的常规算法,然后提出了基于FFT的直接提取相关函数包络的快速算法.仿真与实验研究表明,该方法能精确提取相关函数的包络,在不增加计算量的情况下精确搜索到相关函数的峰值位置.

基于优化包络相关法的罗兰C天波延迟估计算法

针对低信噪比条件下,罗兰C天波信号延迟时间估计的准确性和有效性问题,提出基于优化包络的相关系数时域法。通过分析标准罗兰C信号包络的特征,分别采用微分和二次微分方法对罗兰C信号包络进行优化,形成陡峭的包络信号上升沿;利用相关系数法对接收信号包络和参考信号包络进行匹配,形成的匹配峰值分别对应地波和天波信号到达的时刻,由此可获得天波信号的延迟时间;通过仿真分析和实测信号试验验证,证明该方法能满足数字化接收机的实际要求,并具有更高的抗干扰能力、估计准确性和自动识别功能的特点。估计的结果还可以作为判别相位跟踪和周期识别正确率的辅助依据。

基于小波相关滤波法的滚动轴承早期故障诊断方法研究

目前基于小波分析的滚动轴承故障诊断方法研究已经很多,但是这些方法对于强噪声背景下的早期故障微弱信号特征提取效果并不理想。为此,提出了适用于强噪声背景的小波相关滤波滚动轴承早期故障诊断方法。该方法将小波相关滤波降噪方法和Hilbert包络细化谱分析相结合:对被测信号进行小波相关滤波降噪处理,对降噪处理后的高频段尺度域的小波系数进行Hilbert包络细化谱分析。该方法在滚动轴承的早期故障诊断中的试验结果表明,该方法与直接小波系数包络谱诊断方法相比,较大地增强了对滚动轴承早期故障诊断的能力,在强噪声背景下有效地提取出滚动轴承的早期故障频率。

大作用距离超声波传感技术研究

研制了谐振频率为24.5kHz的新型气介超声测距传感器,其作用距离超过了32m。该传感器是由径向-厚度耦合谐振模式的超声波换能器、推挽变换器和具有高信噪比的时间-增益可变接收器所组成的。其中,作为超声波发送器的推挽变换器能够为阻抗为475Ω的换能器负载提供峰-峰值超过400V的交变电压。建立了基于NI6024E数据采集控制卡和PC机的超声波测距平台,采用超声波发送信号与回波信号的包络相关来估计声波的射程时间,提高了超声波测距系统的鲁棒性。