An Active Anti-Jamming Approach for Frequency Diverse Array Radar with Adaptive Weights

Due to the rapid development of electronic countermeasures(ECMs),the corresponding means of electronic counter countermeasures(ECCMs)are urgently needed.In this paper,an act-ive anti-jamming method based on frequency diverse array radar is proposed.By deriving the closed form of the phase center in a uniform line array FDA,we establish a model of the FDA signal based on adaptive weights and derive the effect of active anti-jamming in this regime.The pro-posed active anti-jamming method makes it difficult for jammers to detect or locate our radar.Fur-thermore,the effectiveness of the two frequency increment schemes in terms of anti-jamming is ana-lyzed by comparing the deviation of phase center.Finally,the simulation results verify the effective-ness and superiority of the proposed method.

Frequency Weighting Filter Design for Automotive Ride Comfort Evaluation

Few study gives guidance to design weighting filters according to the frequency weighting factors,and the additional evaluation method of automotive ride comfort is not made good use of in some countries.Based on the regularities of the weighting factors,a method is proposed and the vertical and horizontal weighting filters are developed.The whole frequency range is divided several times into two parts with respective regularity.For each division,a parallel filter constituted by a low-and a high-pass filter with the same cutoff frequency and the quality factor is utilized to achieve section factors.The cascading of these parallel filters obtains entire factors.These filters own a high order.But,low order filters are preferred in some applications.The bilinear transformation method and the least P-norm optimal infinite impulse response（IIR） filter design method are employed to develop low order filters to approximate the weightings in the standard.In addition,with the window method,the linear phase finite impulse response（FIR） filter is designed to keep the signal from distorting and to obtain the staircase weighting.For the same case,the traditional method produces 0.330 7 m · s^–2 weighted root mean square（r.m.s.） acceleration and the filtering method gives 0.311 9 m · s^–2 r.m.s.The fourth order filter for approximation of vertical weighting obtains 0.313 9 m · s^–2 r.m.s.Crest factors of the acceleration signal weighted by the weighting filter and the fourth order filter are 3.002 7 and 3.011 1,respectively.This paper proposes several methods to design frequency weighting filters for automotive ride comfort evaluation,and these developed weighting filters are effective.

A WEIGHTED GENERAL DISCRETE FOURIER TRANSFORM FOR THE FREQUENCY-DOMAIN BLIND SOURCE SEPARATION OF CONVOLUTIVE MIXTURES

This letter deals with the frequency domain Blind Source Separation of Convolutive Mixtures (CMBSS). From the frequency representation of the "overlap and save", a Weighted General Discrete Fourier Transform (WGDFT) is derived to replace the traditional Discrete Fourier Transform (DFT). The mixing matrix on each frequency bin could be estimated more precisely from WGDFT coefficients than from DFT coefficients, which improves separation performance. Simulation results verify the validity of WGDFT for frequency domain blind source separation of convolutive mixtures.

STUDY ON FREQUENCY ESTIMATION BASED ON WEIGHTED LEAST SQUARE METHOD WITH THREE FOURIER COEFFICIENTS

In this paper,a sinusoidal signal frequency estimation algorithm is proposed by weighted least square method.Based on the idea of Provencher,three biggest Fourier coefficients in the maximum periodogram are considered,the Fourier coefficients can be written as three equations about the amplitude,phase,and frequency,and the frequency is estimated by solving equations.Because of the error of measurement,weighted least square method is used to solve the frequency equation and get the signal frequency.It is shown that the proposed estimator can approach the Cramer-Rao Bound(CRB)with a low Signal-to-Noise Ratio(SNR)threshold and has a higher accuracy.

Deletion of Gpr128 results in weight loss and increased intestinal contraction frequency

AIM: To generate a Gpr128 gene knockout mouse model and to investigate its phenotypes and the biological function of the Gpr128 gene.

Frequency-dependent friction in pipelines

A comprehensive study of modeling the frequency-dependent friction in a pipeline during pressure transients following a sudden cut-off of the flow is presented. A new method using genetic algorithms（GAs） for parameter identification of the weighting function coefficients of the frequency-dependent friction model is described. The number of weighting terms required in the friction model is obtained. Comparisons between simulation results and experimental data of transient pressure pulsations close to the valve in horizontal upstream and downstream pipelines are carried out respectively.The validity of the parameter identification method for weighting function coefficients and the calculation method for the number of weighting terms in the friction model is confirmed.

l_(1)-norm Based GWLP for Robust Frequency Estimation

In this work,we address the frequency estimation problem of a complex single-tone embedded in the heavy-tailed noise.With the use of the linear prediction(LP)property and l_(1)-norm minimization,a robust frequency estimator is developed.Since the proposed method employs the weighted l_(1)-norm on the LP errors,it can be regarded as an extension of the l_(1)-generalized weighted linear predictor.Computer simulations are conducted in the environment of α-stable noise,indicating the superiority of the proposed algorithm,in terms of its robust to outliers and nearly optimal estimation performance.

Analysis of the COVID-19, Outbreak in Brazil Using Topological Weighted Centroid: An Intelligent Geographic Information System Approach

This study used Topological Weighted Centroid (TWC) to analyze the Coronavirus outbreak in Brazil. This analysis only uses latitude and longitude in formation of the capitals with the confirmed cases on May 24, 2020 to illustrate the usefulness of TWC though any date could have been used. There are three types of TWC analyses, each type having five associated algorithms that produce fifteen maps, TWC-Original, TWC-Frequency and TWC-Windowing. We focus on TWC-Original to illustrate our approach. The TWC method without using the transportation information predicts the network for COVID-19 outbreak that matches very well with the main radial transportation routes network in Brazil.

对医用电气设备漏电流试验的探讨

针对医用电气设备的漏电流和患者辅助电流试验,本文以电气安全标准GB 9706.1—2020为基础,简要阐述了医用电气设备的产生原因并分析漏电流的危害,浅析医用电气设备漏电流的分类、测试网络的要求、单一故障状态,并从理论和实际操作上进行分析,介绍试验过程中需要注意的事项以及符合性判定,为有源医疗器械制造商和第三方检验检测机构的研发、测试人员正确理解该试验提供一定参考。

Loudness Summation and Weightings for Loudness and Environmental Noise Assessment

A stationary loudness model has been built up on the basis of the former ISO 226: 1987 concerning equal-loudness-level contours. The loudness and loudness level expressions derived in the study include the same parameters as used when determining the equal-loudness-level contours of the former ISO standard. However, as an additional main idea, a loudness summation rule has been proposed in the study. Moreover, the loudness expressions have been normalised to give the same values for people who have a similar sense of hearing. It has also been found that the loudness expressions include basically two different weightings. The first weighting is a conservative frequency weighting in the domain of sound pressure level, and the second weighting consists of coefficients applied to the weighted sound pressure levels. The latter have the greatest effect on the very low-frequency range. Finally, the paper includes a new way to use the A-weighting which takes into account the compressed character of the equal-loudness-level contours at the low frequency range. This method remarkably transforms the character of the A-weighting as a measure for low-frequency environmental noise.

Research on Horizontal Vibration of Heavy-Weight Drill Pipes in Directional Drilling

The mode of load and deformation of directional drilling string and the expression of trigonometric series of deflection equation are established by means of elastic deformation energy and of the vertical and horizontal bending. A calculation formula for natural frequency of horizontal resonance and rotational speed is derived based on the calculation method by Ritz, with which analysis is made for the cause and affecting factors of the excessive abrasion of heavy-weight drill pipe in high-angle holes so as to provide reference and basis for rational selection of drilling parameters and drilling tools in the future high-angle directional drilling.

APPLICATION OF WEIGHTED NONOSCILLATORY AND NON-FREE-PARAMETER DISSIPATION DIFFERENCE SCHEME IN CALCULATING THE FLOW OF VIBRATING FLAT CASCADE

A dual-time method is introduced to calculate the unsteady flow in a certain vibrating flat cascade. An implicit lower-upper symmetric-gauss-seidel scheme（LU-SGS） is applied for time stepping in pseudo time domains, and the convection items are discretized with the spatial three-order weighted non-oscillatory and non-free-parameter dissipation difference （WNND） scheme. The turbulence model adopts q-co low-Reynolds-number model. The frequency specmuns of lift coefficients and the unsteady pressure-difference coefficients at different spanwise heights as well as the entropy contours at blade tips on different vibrating instants, are obtained. By the analysis of frequency specmuns of lift coefficients at three spanwise heights, it is considered that there exist obvious non-linear perturbations in the flow induced by the vibrating, and the perturbation frequencies are higher than the basic frequency. The entropy contours at blade tips at different times display an intensively unsteady attribute of the flow under large amplitudes.

基于集合经验模态分解和多目标遗传算法的火-多储系统调频功率双层优化

针对分布于区域电网不同网络节点的多座储能电站参与电网调频功率调度问题,该文提出一种基于集合经验模态分解(EEMD)和多目标遗传算法(MOGA)的火-多储系统调频功率双层优化策略。该策略包含火-储调频功率优化层和多储能电站调频功率优化层:上层计及火-储调配资源各自优势及剩余调频能力,构建火-储调频功率优化分配模型,完成火-储调频功率的分配;下层引入关于调频成本和荷电状态(SOC)的自适应权重系数,以调频成本最低和SOC均衡为优化目标,完成调频功率在多储能电站之间的分配。仿真结果表明,所提策略可以提升区域电网调频效果并降低调频成本,均衡控制多个储能电站的调频成本和SOC,可以防止经济性较好的储能电站长期处于SOC越限边缘状态,提升储能电站参与调频的积极性和可持续性。

基于电导率加权平均法的频率域航空电磁三维谱元正演模拟研究

三维电磁正演算法的精确性和有效性对于实测电磁数据的反演和解释至关重要。近年来,谱元法逐渐被应用于三维电磁正演中,其中基于规则/形变六面体网格的谱元法在航空电磁正演模拟中的效果已得到了验证。然而,常规谱元法在处理每个离散单元时,通常赋予其单一的物理属性,导致在模拟复杂模型时仍需采用精细网格以满足模型离散需求,对复杂模型的适用性存在不足。鉴于谱元法基函数的高阶性,提出了一种基于电导率体积加权平均的谱元法。该方法将物理模型离散化与数值网格离散化相分离,实现了对单元内物理属性变化的精细描述,同时避免了正演方程未知数数量的增加。以频率域航空电磁三维正演为例,对改进的谱元法的精度与效率进行了分析。数值算例结果表明,改进的谱元正演算法能够在保证不低于常规正演算法精度的前提下,减少所需的自由度,从而提高计算效率。

基于联合加权谱密度的结构振型频域识别方法

针对传统加权谱密度(weighted spectral density,WSD)法中加权函数指数因子选取不当导致模态振型识别精度降低的问题,建立基于联合WSD的结构振型频域识别方法,提升了WSD方法的识别精度及适用范围。根据盲源分离与振型叠加法的相似性,采用WSD方法对结构振动信号进行解耦与分离;利用预设的多个加权密度矩阵构建三维张量加权谱,并采用平行因子2模型自适应选取加权函数指数因子;在此基础之上,引入最小谱方差评判准则进行评价,从而实现模态振型分离矩阵的精确估计。三自由度系统理论模型的模态振型识别结果表明:所提方法能准确获取各阶模态振型所对应的最优加权函数指数因子,针对结构模态振型的识别精度均优于传统频域分解法和二阶盲辨识方法,即使在数据较短、频谱毛刺严重时仍具有较高的识别精度,为建筑结构模态振型识别提供了一种新的识别算法。

高频超声联合磁共振扩散加权成像对乳腺癌预后的预测价值

目的 探讨高频超声联合磁共振扩散加权成像对乳腺癌预后的预测价值。方法 选取本院2020年7月到2022年12月收治的95例乳腺癌患者作为研究对象,均行根治性手术治疗,患者术前行高频超声及磁共振扩散加权成像检查。术后随访2年,根据预后分为预后良好组(70例)和预后不良组(25例)。比较组间表观弥散系数(ADC)、收缩期峰值血流速度(PSV)、阻力指数(RI)等参数变化。单因素及多因素Logistic回归分析高频超声及磁共振扩散加权成像对乳腺癌预后的预测风险价值,绘制受试者工作特征(ROC)曲线评估其对乳腺癌预后的预测价值。结果 相较于预后良好组,预后不良组ADC降低,PSV、RI升高(P<0.05);多因素Logistic回归分析显示,ADC、PSV、RI为预测乳腺癌预后的影响因素(P<0.05);ROC曲线显示,ADC、PSV、RI联合检测时对乳腺癌预后不良的预测价值较高。结论 高频超声与磁共振扩散加权成像联合检测对乳腺癌预后有一定的预测价值。

基于新权重函数的MIX-GARCH-L模型及其应用

文章引入一种新的权重函数,并构建新的波动率模型——MIX-GARCH-L模型,新模型能够充分利用高低频数据提炼出更有价值的信息。针对新模型参数估计问题,提出MIX-GARCH-L模型的参数估计方法来分析估计量的理论性质,证明了对应的中心极限定理以及用Service-Boostrap方法模拟检验估计量的数据表现。所提模型具有以下优势:新权重函数能够更好地根据交易特征的变动来自动调整不同交易日的权重,从而使每个高频交易日所分配到的权重与未来波动率产生的冲击效果一致;能够利用同一交易过程中多种高频交易数据,信息利用更加充分,使得MIX-GARCH-L模型具有更好的预测精度和预测优势。实证结果显示:MIX-GARCH-L模型的MSPE值明显小于GARCH-RV模型和GARCH-M模型的MSPE值,说明MIX-GARCH-L模型不仅在模型预测上有更高的预测精度,而且在稳健性上的表现也更好。

试验环境水下声信号的特征提取方法

水下试验环境参数的反演是水声学研究领域的重要内容。而当前研究的关键是通过对水下声信号做特征提取从而获取参数信息。针对特征提取较难、模型很难拟合等问题。本文提出了一种试验环境水下声信号的特征提取方法。将水下声信号同时用梅尔频谱倒谱系数及线性预测系数处理,两者运用特征加权组合方法得到新的特征矩阵;再应用映射插值算法对特征矩阵进行处理,获得适应神经网络输入的三通道矩阵。本文选取的网络模型为残差神经网络。利用实验室所录制的对河口水库数据集测试表明,本文提出的特征提取方法普遍优于仅利用梅尔频谱倒谱系数或线性预测系数的特征处理方法。利用单频矩形脉冲信号对环境进行深度5分类,准确率平均提升2%。利用线性调频信号对环境进行深度5分类,准确率平均提升2.03%。本文提出的特征提取方法对线性调频信号在深度分类任务下处理的结果要优于单频矩形脉冲信号处理的结果。

融合多特征信息与GWO-SVM的机械关键设备故障诊断

为了提高机械关键设备故障诊断的精度,建立机械关键设备故障诊断模型。文章提出一种融合机械关键设备故障信号多特征信息与灰狼优化算法(Grey Wolf Optimization Algorithm,GWO)改进支持向量机(Support Vector Machine,SVM)(GWO-SVM)的机械关键设备故障诊断模型。首先,提取机械关键设备故障信号的时域特征、频域特征和多尺度加权排列熵特征,分别对比不同特征的机械关键设备故障诊断结果。其次,为提高SVM模型性能,运用GWO算法对SVM模型的惩罚参数P和核函数参数g进行优化选择,提出一种融合多特征信息与GWO-SVM的机械设备故障诊断模型。与GA-SVM、PSO-SVM和SVM相比,基于GWO-SVM的机械设备故障诊断模型的诊断精度最高。这里算法可以有效提高机械关键设备故障诊断正确率,为机械关键设备故障诊断提供了新的方法。

基于WRLS-ARMAX系统辨识的新能源电力系统惯量评估

随着高比例新能源机组并入电网,电力系统低惯量特性愈加显著,严重影响了系统运行稳定性。为了准确估计新能源电网实际运行状态下的惯量大小,提出了一种基于加权递推最小二乘(WRLS)-受控自回归滑动平均(ARMAX)系统辨识的新能源电力系统等效惯量评估方法。首先,以发电机为对象,建立不同扰动情况下发电机功频响应特性的通用惯量解析模型;其次,以发电机并网母线有功功率和频率扰动作为输入和输出,建立ARMAX模型,考虑到实际电网运行过程中受大、小扰动共同影响,实际测量数据具有异方差性,采用WRLS求解模型中的待辨识参数;然后,提取辨识模型中包含惯量响应的传递函数模型,利用阶跃响应计算惯量源的惯性时间常数,进而计算得到系统等效惯量大小;最后,通过Matlab/Simulink仿真算例验证了所提方法的准确性和实用性。