Noise cancellation of a multi-reference full-wave magnetic resonance sounding signal based on a modified sigmoid variable step size least mean square algorithm

Nano-volt magnetic resonance sounding(MRS) signals are sufficiently weak so that during the actual measurement, they are affected by environmental electromagnetic noise, leading to inaccuracy of the extracted characteristic parameters and hindering effective inverse interpretation. Considering the complexity and non-homogeneous spatial distribution of environmental noise and based on the theory of adaptive noise cancellation, a model system for noise cancellation using multi-reference coils was constructed to receive MRS signals. The feasibility of this system with theoretical calculation and experiments was analyzed and a modified sigmoid variable step size least mean square(SVSLMS) algorithm for noise cancellation was presented. The simulation results show that, the multi-reference coil method performs better than the single one on both signal-to-noise ratio(SNR) improvement and signal waveform optimization after filtering, under the condition of different noise correlations in the reference coils and primary detecting coils and different SNRs. In particular, when the noise correlation is poor and the SNR<0, the SNR can be improved by more than 8 dB after filtering with multi-reference coils. And the average fitting errors for initial amplitude and relaxation time are within 5%. Compared with the normalized least mean square(NLMS) algorithm and multichannel Wiener filter and processing field test data, the effectiveness of the proposed method is verified.

Size selectivity of combined square and diamond mesh codends of shrimp beam trawl for banded scad Caranx(Atule)kalla in the northern South China Sea

The shrimp beam trawl fishery in the northern South China Sea is characterized by high by-catch and poor selectivity problems.Among by-catch species,banded scad(Caranx(Atule)kalla)is economically the most important one.The aim of this study is to improve the selective properties of codends for banded scad.Size selectivity of 2 traditional diamond mesh codends,with mesh size 25 and 30 mm(defined as D25 and D30,respectively),and 4 new combined square and diamond mesh codends,with25 mm square-mesh and 25 mm diamond-mesh(S25+D25),30 mm square-mesh and 25 mm diamondmesh(S30+D25),35 mm square-mesh and 25 mm diamond-mesh(S35+D25),and 35 mm square-mesh and18 mm diamond-mesh(S35+D18),were tested for banded scad in shrimp beam trawl fishery of the South China Sea.A total of 54 valid hauls were finished using the covered codend method,and 5750 banded scad were caught.Selective parameters were obtained using the logistic equation with the maximum likelihood method,by incorporating the between-haul variation.The results show that the present minimum mesh size for shrimp beam trawl in the South China Sea,25-mm diamond mesh size,is insufficient to release immature banded scad.The S35+D25 codend is proved to be the most eff ective codend to release immature banded scad,and its 50%retention length(L _(50))is larger than the minimum landing size(MLS=63.5 mm)of banded scad.However,the 95%confidence intervals of L _(50) overlap among the three combined mesh codends,the S25+D25,S30+D25 and S35+D25 codend.For a sustainable exploitation of banded scad,larger mesh sizes are suggested to be investigated for the combined mesh codends.

A novel dynamic step size LMS optimization scheme for interference reducing in FBMC-QAM

Filter bank multicarrier quadrature amplitude modulation(FBMC-QAM)will encounter inter-ference and noise during the process of channel transmission.In order to suppress the interference in the communication system,channel equalization is carried out at the receiver.Given that the con-ventional least mean square(LMS)equilibrium algorithm usually suffer from drawbacks such as the inability to converge quickly in large step sizes and poor stability in small step sizes when searching for optimal weights,in this paper,a design scheme for adaptive equalization with dynamic step size LMS optimization is proposed,which can further improve the convergence and error stability of the algorithm by calling the Sigmoid function and introducing three new parameters to control the range of step size values,adjust the steepness of step size,and reduce steady-state errors in small step sta-ges.Theoretical analysis and simulation results demonstrate that compared with the conventional LMS algorithm and the neural network-based residual deep neural network(Res-DNN)algorithm,the adopted dynamic step size LMS optimization scheme can not only obtain faster convergence speed,but also get smaller error values in the signal recovery process,thereby achieving better bit error rate(BER)performance.

Magnetization of Nano-Size Subsystem in a Two-Dimensional Ising Square Lattice

A two-dimensional Ising square lattice is modeled as a nano-size block array to study by Monte Carlo simulation the magnetic thermal stability of nano-structure magnetic media for data storage, thereon in the blocks J1 > 0 is assigned for the interaction of a pair of nearest-neighbor spins, while 0 J0 J1 for that in regions between the blocks and (J0 + J1)/2 for the nearest-neighbor pairs with one in the block and the other one out of but near-most the block. We show that the magnetic thermal stability of the block accrues with the increase of J1 and with the decrease of J1 - J0 for a given J1, but contrarily, the anchoring ability for the initial magnetic orientation in nano-size block trails off as J1 - J0 diminish. This phenomena and size dependence of such anchoring ability are discussed in detail.

Lattice structure adaptive IIR notch filter based on least square kurtosis

A new variable step-size algorithm for a second-order lattice form structure adaptive infinite impulse response （IIR） notch filter to detection and estimation frequency of sinusoids in Gaussian noises is proposed. Utilizing least square kurtosis of output signals as a cost function, the new gradient-based algorithm to update frequency of the adaptive IIR notch filter and the new variable step-size algorithm are given. The computer simulation results show that the proposed algorithm has better ability in suppressing colored Gaussian noises and better accuracy in estimating parameters at low SNR than previous algorithms.

基于sigmoid-sinh分段函数的变步长FxLMS算法

为改善滤波-x最小均方(filtered-x least mean square,FxLMS)算法在噪声主动控制时无法兼顾收敛速度和稳态误差的问题,提出了基于sigmoid-sinh分段函数的FxLMS(SSFxLMS)算法,并引入蚁狮算法对SFxLMS(sigmoid filtered-x least mean square)、ShFxLMS(sinh filtered-x least mean square)、SSFxLMS算法的参数进行优化。分别采用高斯白噪声和实测簇绒地毯织机噪声为输入信号,采用FxLMS、SFxLMS、ShFxLMS、SSFxLMS算法进行噪声主动控制仿真,对比分析这4种算法的性能。结果表明:与其他3种算法相比,采用SSFxLMS算法对高斯白噪声和簇绒地毯织机噪声进行控制时,误差信号的平均绝对值更小,平均降噪量与收敛速度也有大幅度提升。由此可知,SSFxLMS算法有效改善了FxLMS算法无法兼顾收敛速度和稳态误差的问题,研究结果为噪声主动控制算法设计提供了一定的参考。

基于最小二乘回归的定量指标一致性评价的样本量公式研制

目的构建并验证基于最小二乘回归法的定量资料一致性评价的样本量计算公式。方法根据最小二乘回归法定量一致性评价的原理,结合统计推断和公式推导,获得基于回归常数和回归系数的样本量计算公式。同时,使用3个实例数据验证公式的准确性,并与Bland-Altman(BA)法样本量计算公式结果进行对比。结果通过公式推导得到回归法定量一致性评价的样本量计算公式,并用实例验证了本公式的准确性。此外,本公式与BA法样本量公式所得结果具有一定差异,在回归法样本量公式计算结果下,回归分析与BA法分析均能得到一致性结论;而在BA法公式结果下,回归分析与BA法分析一致性结论有时不成立。结论本研究首次提出用于回归法定量一致性评价的样本量公式,为该领域研究提供了方法学支持。

基于机器视觉的电子线束产品尺寸检测方法

针对电子线束产品尺寸的传统人工检测方式效率低、主观测量误差较大等问题,提出一种基于机器视觉的非接触式检测方法。设计和搭建了视觉检测系统,使用张正友标定法对相机进行标定并采集产品图像信息,采用改进的Canny算法对图像进行边缘检测,提取产品轮廓并对图像进行水平倾斜校正;将校正后的产品轮廓进行区域划分并用最小二乘法对轮廓边缘采样点进行直线拟合;根据轮廓边缘上测量点的图像坐标和相机标定结果计算得到世界坐标系下的产品尺寸;对产品分别进行传统游标卡尺测量和视觉测量试验,结果表明,该方法重复测量误差和绝对测量误差均不超过0.1 mm,平均检测耗时在1 s以内,能够实现电子线束产品尺寸的快速准确检测。

圆锥体全局角度尺寸评定方法

提出了基于圆周轮廓提取方案的圆锥全局角度尺寸的评定方法,建立了圆锥最小二乘全局角度尺寸和最大最小全局角度尺寸的评定模型。基于所建立的评定模型,给出了圆锥全局角度尺寸评定的飞蛾扑火优化算法(MFO)的流程图,并编制了圆锥全局角度尺寸评定及最小二乘圆锥面、最大最小圆锥面可视化程序。采用所编制的程序,对4个圆锥仿真试样进行了最小二乘全局角度尺寸和最大最小全局角度尺寸评定,对其不同评定方法、不同优化初始参数和不同优化方法得到的全局评定结果进行了比较。用乌鸦搜索算法、人工生态优化算法、平衡优化器算法和粒子群优化算法对1个试样的最大最小全局角度尺寸进行了评定,并与MFO的评定结果进行了比较。除了优化初始值对评定结果有影响外,搜索区间、种群数和最大迭代次数对评定结果均有影响,但其规律性不强。总体上讲,MFO的评定结果优于其他4种优化方法的评定结果。

足尺拼接式方形高强钢管混凝土柱轴压承载力数值分析

对两种不同的新型拼接式方形高强钢管混凝土足尺柱的轴压承载性能进行了数值模拟,分析了混凝土强度、钢材强度、缀材间距和宽厚比对该类组合柱轴压承载力及荷载–位移曲线的影响规律,研究表明:同种参数影响下两种形式的组合柱荷载–位移曲线及承载力变化规律相似;材料强度和宽厚比对承载力影较为显著,如钢材屈服强度从345 MPa提升至460 MPa时,两种组合柱承载力分别提高了9.13%和9.42%,宽厚比从83.3增大至100时,两类柱子承载力分别降低了5.08%和5.00%;可初步采用GB 50936—2014《钢管混凝土结构技术规范》计算该类新型柱的轴压承载力。

双曲正切函数的新型变步长LMS算法

针对自适应最小均方误差(Least Mean Square,LMS)滤波算法迭代步长在算法收敛速度、稳态误差间的折中问题,设计了一种基于双曲正切函数的新型变步长算法,算法以双曲正切函数为基础,建立步长因子μ(n)与误差信号e(n)的非线性函数关系,并引入参数α、β和m,设计了一种新的步长调整公式,使得在算法迭代初始阶段采用较大步长因子,达到更快的收敛速度,在接近收敛时采用较小的步长因子,获得更小的稳态误差。通过仿真分析了不同参数对算法性能的影响,与已有典型变步长算法相比,论文算法具有更快的收敛速度、更小的稳态误差和更优的追踪能力。

变步长CMA和DD-LMS双模式切换盲均衡算法

针对经典盲均衡算法收敛速度较慢和稳态误差较大的问题,提出了一种基于变步长恒模算法(Constant Modulus Algorithm, CMA)和判决引导的最小均方(Decision Directed Least Mean Square, DD-LMS)算法的双模式切换盲均衡算法。在算法收敛初期采用CMA算法,以确保算法可以较快收敛。在收敛之后切换至DD-LMS算法,以进一步降低稳态误差。通过设定阈值来切换算法,取相邻多次迭代误差的平均值作为算法的切换值,以确保算法切换时机的合理性。另外,引入Softsign变步长函数并加入3个参数对该函数进行改进,使得Softsign变步长函数可以依据不同信道环境设定最佳参数,同时提高算法的收敛速度。仿真结果表明,在卫星通用信道条件下,所提算法的收敛迭代次数约为1 000次,稳态误差为-12 dB,在信噪比为15 dB时,误码率为1×10~(-6)。与相关算法对比,所提算法的收敛速度较高,误码率和稳态误差较低。

Square mesh codend improves size selectivity and catch pattern for Trichiurus lepturus in bottom trawl used along Northwest coast of India

The size selectivity and catch pattern of Trichiurus lepturus in 40 mm diamond and square mesh codends were investigated in this study.A 34 m high opening trawl was used,which is a common design used by fishermen operating along the northwest coast of India,and the cover codend method was employed to determine codend selectivity.Along with the changes in the length at 50%retention rate for Trichiurus lepturus with the usage of the square and diamond mesh codends,indicators to understand the exploitation pattern of this species in the fishery were assessed based on the total number of individuals and on total weight of the catch.The mean selection length increased and discard fraction is reduced when 40 mm square mesh codends are used in place of diamond meshes,however,it is observed that individuals at commercial length are also lost.The results demonstrate that mandatory use of legal mesh sizes alone will be insufficient to aid in the sustainable harvest of this species,given its estimated length at first sexual maturity of 61.2 cm.This is the first study to compare the size selection of this species in 40 mm diamond and square mesh codends along Northwest coast of India.Results of the study will help as a baseline for gear-based regulations in the region.

山地果树微锥四方形覆膜技术

水资源的缺乏和降雨量的不均匀严重制约着农业生产的可持续发展,采用山地果树微锥四方形覆膜技术有助于解决山地果树干旱和降雨量不均匀等引起的果树干旱胁迫和花芽分化少等一系列问题。采用山地果树微锥四方形覆膜技术起垄能够节水保墒,提高水分利用率;选择覆盖黑色地膜可以在春季提温保墒,提高水分利用率,防止杂草生长;利用四面横竖双沟既能在干旱少雨的春季起到集雨的作用,又能在秋季多雨的季节分流雨水,有效控制果树的营养生长,从而促进果树花芽分化。

基于激光粒度仪的悬移质泥沙颗粒级配试验研究

为探究国产激光粒度仪应用于悬移质泥沙颗粒级配分析时的准确性及适用性,以赣江外洲水文站为例,利用国产YRCC.NEG-2800型激光粒度仪和马尔文激光粒度仪对河流泥沙开展了准确性、重复性、平行性试验,并采用最小二乘法分析了两者试验结果的相关关系。结果表明:国产激光粒度仪的准确性、重复性、平行性误差小于3%,达到SL 42-2010《河流泥沙颗粒分析规程》要求,可应用于江西省河流悬移质泥沙颗粒级配分析。国产激光粒度仪与马尔文激光粒度仪的比测误差小,测试样本中最大误差仅为1.12%,分析的成果精度高。

Novel LMS adaptive filtering algorithm with variable step size

By analyzing algorithms available for variable step size least mean square(LMS)adaptive filter,a new modified LMS adaptive filtering algorithm with variable step size is proposed,along with performance analysis based on different parameters.Compared with the existing algorithms through the simulation,the proposed algorithm has faster convergence speed and smaller steady state error.

Active micro-vibration control based on improved variable step size LMS algorithm

The contradiction of variable step size least mean square(LMS)algorithm between fast convergence speed and small steady-state error has always existed.So,a new algorithm based on the combination of logarithmic and symbolic function and step size factor is proposed.It establishes a new updating method of step factor that is related to step factor and error signal.This work makes an analysis from 3 aspects:theoretical analysis,theoretical verification and specific experiments.The experimental results show that the proposed algorithm is superior to other variable step size algorithms in convergence speed and steady-state error.

结构尺寸对方钢管混凝土短柱抗震性能影响的试验研究

为了研究在低周往复荷载作用下结构尺寸对方钢管混凝土短柱抗震性能的影响,对6根方钢管混凝土短柱开展了水平往复加载试验,分析了截面尺寸对柱破坏形态、滞回曲线、骨架曲线以及不同抗震性能指标(如刚度退化、耗能能力、延性等)的影响,阐明了不同截面尺寸对柱名义抗剪强度的影响规律和机制,研究结果表明:不同截面尺寸的试件破坏形态基本相同,表现为柱底部钢管鼓曲、核心混凝土被压碎的破坏形态;当截面尺寸由200 mm增至600 mm时,在不同加载方向上,方钢管混凝土短柱名义抗剪强度分别下降了63.1%(59.8%),表现出显著的尺寸效应;随着截面尺寸增大,相对名义刚度与平均耗能系数呈降低趋势;JIN等提出的考虑尺寸效应的抗剪强度公式计算值与试验值吻合良好,说明考虑尺寸效应的方钢管混凝土柱抗剪承载力计算公式能够较为准确的预测其抗剪承载力。

不同雾化方式喷雾场的数值分析与试验验证

为了研究植保雾化喷头的雾化效果,基于CFD中拉格朗日粒子跟踪气液两相流模型,分别结合压力雾化和空气雾化模型对不同风速下的雾滴粒径、运动速度、质量浓度分布规律进行了对比计算.计算结果表明:压力雾化模型中,雾滴粒径小于100μm的占比小于2%,粒径175μm的细雾滴占比约为25%,近喷雾口处雾滴速度更高,约是空气雾化模型的5倍;雾滴质量浓度分布更均匀;当风速达到4 m/s时,细雾滴分布比例增加,雾滴会出现二次破碎.空气雾化模型,中等雾滴粒径分布在400~600μm,占比约为20%,雾滴速度衰减慢,喷雾口附近雾滴不易逆风运动;雾滴沉积范围小,喷幅较窄,大部分雾滴沉降在以喷头为中心的1.5 m范围内.此外,完成了低速风洞试验,收集雾滴沉积并进行卡方检验,结果表明2个雾化模型对于喷雾场中液滴沉积值均可信,但压力雾化模型计算值与试验值偏离度较小.

基于圆/柱度仪的回转体两点尺寸测量方法研究

提出了一种基于圆/柱度仪的回转体两点尺寸测量的方法。建立了基于标准圆柱直径的圆/柱度仪径向尺寸测量系统误差模型;以最小二乘圆圆心为坐标原点和最小二乘圆圆心与第一个采样点的连线为x轴向,建立新的坐标系。通过坐标平移和旋转,将原坐标系中各采样点的坐标转换到新的坐标系中的坐标,并将其转换成相应的极坐标值;基于这些极坐标值,建立其三次样条插值方程,并由其确定圆柱体的两点尺寸。给出了回转体两点尺寸测量与评定的流程,用所编制的程序对在圆柱度仪上提取的圆柱体要素的轮廓进行了两点尺寸评定与统计分析。该研究将为符合GB/T 24637.3定义的回转体两点尺寸提供一种可行的测量方法。