NOISE AMPLIFICATION ANALYSIS AND COMPARISON OF TWO PERIODIC NONUNIFORM SAMPLING RECONSTRUCTION METHODS USED IN DPCA SAR

General Sampling Expansion Reconstruction Method (GSERM) and Digital Spectrum Reconstruction Method (DSRM), which prove effective to reconstruct azimuth signal of Displaced Phase Center Apertures (DPCA) Synthetic Aperture Radar (SAR) system from its Periodic Non-Uniform Sampling (PNUS) data sequences, would amplify the noise and sidelobe clutter simultaneously in the reconstruction. This paper formulates the relation of the system transfer matrixes of the above two methods, gives the properties, such as periodicity, symmetry, and time-shift property, of their Noise and Sidelobe Clutter Amplification Factor (NSCAF), and discovers that DSRM is more sensitive than GSERM in the white noise environment. In addition, criteria based on initial sampling point analysis for the robust PRF selection are suggested. Computer simulation results support these con-clusions.

Stability analysis of networked control systems with time-varying sampling periods

In this paper, we present an interval model of networked control systems with time-varying sampling periods and time-varying network-induced delays and discuss the problem of stability of networked control systems using Lyapunov stability theory. A sufficient stability condition is obtained by solving a set of linear matrix inequalities. In the end, the illustrative example demonstrates the correctness and effectiveness of the proposed approach.

Iterative Learning Fault Diagnosis Algorithm for Non-uniform Sampling Hybrid System

For a class of non-uniform output sampling hybrid system with actuator faults and bounded disturbances,an iterative learning fault diagnosis algorithm is proposed.Firstly,in order to measure the impact of fault on system between every consecutive output sampling instants,the actual fault function is transformed to obtain an equivalent fault model by using the integral mean value theorem,then the non-uniform sampling hybrid system is converted to continuous systems with timevarying delay based on the output delay method.Afterwards,an observer-based fault diagnosis filter with virtual fault is designed to estimate the equivalent fault,and the iterative learning regulation algorithm is chosen to update the virtual fault repeatedly to make it approximate the actual equivalent fault after some iterative learning trials,so the algorithm can detect and estimate the system faults adaptively.Simulation results of an electro-mechanical control system model with different types of faults illustrate the feasibility and effectiveness of this algorithm.

H_∞ Controller Design for Networked Control Systems via Active-varying Sampling Period Method

这份报纸学习由使用一个活跃变化的采样时期方法与两导致网络的时间延期和包退学学生为联网的控制系统(NCS ) 设计 H 控制器的问题，在采样时期在一个有限集合切换的地方。一个新奇线性基于评价的方法被建议补偿包退学学生，和 H 控制器设计被使用多客观的优化方法论也介绍。模拟结果说明活跃变化的采样时期方法和线性基于评价的包退学学生赔偿的有效性。

A Method to Reconstruct Nth-Order Periodically Nonuniform Sampled Signals

It is well known that nonuniform sampling is usually needed in special signals processing. In this paper, a general method to reconstruct Nth-order periodically nonuniform sampled signals is presented which is also developed to digital domain, and the designs of the digital filters and the synthesis system are given. This paper extends the studies of Kohlenberg, whose work concentrate on the periodically nonuniform sampling of second order, as well as the studies of A.J.Coulson, J.L.Brown, whose work deal with the problems of two-band signals’ Nth-order sampling and reconstruction.

Digital Spectral Representation of Nonuniformly Sampled Periodic Signals

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Life prediction and test period optimization research based on small sample reliability test of hydraulic pumps

Hydraulic pumps belong to reliable long-life hydraulic components. The reliability evaluation includes characters such as long test period,high cost,and high power loss and so on. Based on the principle of energy-saving and power recovery,a small sample hydraulic pump reliability test rig is built,and the service life of hydraulic pump is predicted,and then the sampling period of reliability test is optimized. On the basis of considering the performance degradation mechanism of hydraulic pump,the feature information of degradation distribution of hydraulic pump volumetric efficiency during the test is collected,so an optimal degradation path model of feature information is selected from the aspect of fitting accuracy,and pseudo life data are obtained. Then a small sample reliability test of period constrained optimization search strategy for hydraulic pump is constructed to solve the optimization problem of the test sampling period and tightening end threshold,and it is verified that the accuracy of the minimum sampling period by the non-parametric hypothes is tested. Simulation result shows it could possess instructional significance and referenced value for hydraulic pump reliability life evaluation and the test's research and design.

Performance of Optical Sampling Based on SHG in CPPLN Waveguide

Sampling efficiency and bandwidth of the optical sampling system based on second harmonic generation （SHG） in chirped periodically poled LiNbO3 （CPPLN） are numerically researched. A broad sampling bandwidth can be obtained by adjusting chirp coefficient and waveguide length of CPPLN, and sampling efficiency can be improved by using higher pump power, increasing waveguide length and choosing appropriate chirp coefficient. Results show that both sampling bandwidth and efficiency in CPPLN waveguides are controllable and that CPPLN waveguides are more suitable for multiwavelength optical sampling systems.

Fast SSED-MoM /FEM Analysis for Electromagnetic Scattering of Large-Scale Periodic Dielectric Structures

A hybrid method combining simplified sub-entire domain basis function method of moment with finite element method( SSED-MoM /FEM) is accelerated for electromagnetic( EM) scattering analysis of large-scale periodic structures.The unknowns are reduced sharply with non-uniform mesh in FEM. The computational complexity of the hybrid method is dramatically declined by applying conjugate gradient-fast Fourier transform( CG-FFT) to the integral equations of both electric field and magnetic field. The efficiency is further improved by using OpenMP technique. Numerical results demonstrate that the SSED-MoM /FEM method can be accelerated for more than three thousand times with large-scale periodic structures.

FAST ALGORITHM FOR NON-UNIFORMLY SAMPLED SIGNAL SPECTRUM RECONSTRUCTION

In this paper, a fast algorithm to reconstruct the spectrum of non-uniformly sampled signals is proposed. Compared with the original algorithm, the fast algorithm has a higher computational efficiency, especially when sampling sequence is long. Particularly, a transformation matrix is built, and the reconstructed spectrum is perfectly synthesized from the spectrum of every sampling channel. The fast algorithm has solved efficiency issues of spectrum reconstruction algorithm, and making it possible for the actual application of spectrum reconstruction algorithm in multi-channel Synthetic Aperture Radar (SAR).

入侵意图分析下的软件定义网络DDoS攻击检测方法

为在数据样本回溯期内解决因本地信息熵值增大而造成的服务攻击问题,维护软件定义网络的运行安全性,提出入侵意图分析下的软件定义网络分布式拒绝服务(DDoS)攻击检测方法。按照软件定义网络场景重构原则,确定因果网转换标准,实现对识别参数的更新处理,完成攻击性行为的入侵意图分析,再定义DDoS数据集,根据攻击行为的时空特性,求解模型参数的取值范围,完成入侵意图分析下软件定义网络DDoS攻击检测方法的设计。实验结果表明,在该算法控制下数据样本回溯期为10 min,低于传统算法,能够较好维护软件定义网络的运行安全性。

塔里木河“四源”洪水演变规律及成因分析

基于1981—2020年塔里木河流域“四源”5个水文站的日径流数据及格网温度、降水和雪深等数据,采用最大值及POT采样法,分析洪水发生量级、频率和峰现时间等特征,同时采用相关性分析揭示不同洪水指标与影响因素之间的关系并识别关键影响因子。结果表明:(1)1981—2020年塔里木河“四源”各站点洪峰流量大小依次为:卡群>协和拉>同古孜洛克>沙里桂兰克>大山口,年及季节尺度洪峰流量普遍呈增加趋势,冬季洪峰发生时间均呈提前状态,其中沙里桂兰克年均提前最多为2.61 d,卡群站提前仅0.67 d。(2)研究时段内塔里木河流域共有2个洪水高发期,为1994—2002年和2006—2011年,流域内大量级洪水集中发生在1990年之后。(3)洪水发生前不同时间内最小温度、降水和雪深以增加趋势为主;而最大温度以减少趋势为主。春季洪水指标与最大3 d降水的相关性最高,而秋季洪水指标与最大7 d降水的相关性最高。相比于单日降水,多日降水与洪水指标的相关性更高。在雪深相关因子中,最大15 d雪深与各站点的春季洪水指标相关性最高。研究结果对区域水资源管理以及洪水灾害预测提供理论依据。

平均降采样多周期微分均值的旋转部件故障特征增强方法

为解决编码器的瞬时角速度(Instantaneous Angular Speed,IAS)信号中旋转部件故障特征微弱的难题,本文提出一种平均降采样多周期微分均值(Average Down⁃Sampling Multi⁃period Differential Means,ADSMPDM)的故障特征增强方法。基于IAS信号的估计特性,开展了IAS信号的平均降采样研究,验证了平均降采样具有抑制随机噪声的特性;基于平均降采样抑制随机噪声特性、降低计算成本和减小存储空间的优势,结合多周期微分均值的累积特性,提出一种ADSMPDM算法对原始IAS信号中的旋转部件故障分量进行增强处理;通过阶次谱分析揭示故障特征。采用仿真数据和实验数据进行验证分析,并与快速谱峭度、可调整多点优化最小熵反卷积、离散随机分离和谱幅值调制算法进行对比,验证了ADSMPDM算法增强旋转部件故障特征的有效性和优势。

考虑传输时滞的电力负荷频率采样控制系统稳定性分析

研究了一类考虑传输时滞的电力负荷频率采样控制系统相关稳定性问题。首先,采用PI型的LFC系统方案,并建立考虑采样和传输时滞的LFC闭环系统模型;其次,根据建立的模型,采用基于双边闭环泛函判据计算系统的时滞稳定裕度,研究系统采样周期与时滞稳定裕度之间的关系,并通过单区域LFC系统对结果进行仿真验证。计算结果表明,与现有文献结果相比,在相同的系统参数条件下,使用提出方法得到的结果保守性降低,且采样周期越大,系统时滞稳定裕度越小,而一定大小的时滞可以增大系统采样周期上界;仿真结果进一步验证了所提出方法的有效性和优势。

交交变频调速系统中变周期均值采样的研究应用

针对交交变频调速系统中电压、电流纹波含量较大且纹波周期时变,无法直接反馈于调速控制系统的问题,提出一种变周期均值采样算法。首先,该算法以实时交交变频功率器件触发脉冲的间隔时间作为均值周期,对电压、电流实际值进行均值计算。其次,根据电压、电流实时频率及均值周期计算该均值周期所带来的相位滞后角度。最后,按照相位滞后角度进行滞后补偿及插补运算,得到更理想的电压、电流反馈值,用于调速控制系统。相较于一般的均值采样,该算法更适合交交变频纹波周期时变的情况,并能消除采样滞后,提升调速系统控制性能及稳定性。

甘精胰岛素注射液质量状况评价与研究

目的评价甘精胰岛素注射液的质量现状及存在问题,对现行质量标准的科学性及合理性进行评估,为其安全评价及安全监管提供参考。方法对甘精胰岛素注射液进行国家评价性抽检,采用法定标准方法对抽检样品的有关物质及含量测定项目进行检验,并对不同企业的样品进行了稳定性研究及样品使用期有关物质增长情况研究,采用LC-MS方法对含量较高的有关物质进行了结构确认,根据研究结果对企业标准及《中华人民共和国药典》(2020年版)各论中有关物质的限度规定进行了科学性及合理性评估。结果按照法定标准检验,48批次的甘精胰岛素注射液样品有关物质及含量测定结果均合格,合格率100%。稳定性研究发现,部分企业样品有关物质的数量及含量结果偏高;样品使用期有关物质增长情况研究发现,部分企业样品中最大有关物质的含量有超出企业质量标准限度规定的风险。结论甘精胰岛素注射液总体质量较好。建议企业考察产品在货架期及使用期(尤其是近效期产品)的有关物质的增长情况,并参考《中华人民共和国药典》(2020年版)甘精胰岛素注射液各论,科学合理地制定标准限度规定。

采煤机截割轨迹自动跟踪系统的设计

为解决采煤机依靠人工控制存在的效率低、安全性差的问题,在对采煤机轨迹跟踪自动调高原理分析的基础上,确定了截割轨迹自动跟踪系统的采样周期和进刀方式,提出了基于多传感器对采煤机的截割状态监测的方案,并为其配套设计了自动跟踪控制模块,验证了基于速度前馈模糊PID控制策略的控制效果.

Optical sampling system using periodically-poled lithium niobate waveguide and nonlinear polarization rotation mode-locked fiber laser

A novel design of optical sampling system has been developed by using sum-frequency generation （SFG） in a periodically-poled lithium niobate （PPLN） waveguide and using passive mode-locked fiber laser pulses as optical sampling pulses. The system achieved high temporal resolution and high sensitivity using a 30 mm length PPLN with quasi phase match period of 19.3 μm and 151 fs sampling pulses which were generated by passive modelock fiber laser based on nonlinear polarization rotation （NPR）. Clear eye-diagram of 10 Gbit/s non-return-to-zeros （NRZ） pseudorandom binary sequence （PRBS） optical signal were successfully reconstructed by this system.

寒潮天气小样本条件下的短期风电功率组合预测

寒潮作为一种典型气象灾害,其对风电以及以风电主体的新型电力系统的安全运行带来了极大挑战,而针对性的提供准确的风电功率预测将是有效的应对措施。为此,该文提出一种寒潮天气小样本条件下的短期风电功率组合预测方法。首先定义寒潮天气事件并分析风电出力特点。针对寒潮天气下样本数据稀缺而难以建模的问题,采用TimeGAN算法来丰富气象和功率样本。然后,分别基于XGBoost和Transformer算法建立风电功率基准值和损失值预测模型,以量化表征寒潮天气下的理论出力和功率缺额。另外,结合风机保护控制参数,提出一种基于注意力机制的Seq2Seq二分类模型来预判功率损失是否发生,通过提取风电功率损失时段进行针对性组合预测。最后,分别通过以大风、强降雨、大风与强降雨相结合为代表气象的寒潮天气事件进行测试,相比于常规预测模式,该文方法在寒潮天气下表现出良好的预测性能。

基于等距拆分和随机森林算法的皖北小麦始花期气象预报

为探讨基于等距拆分和随机森林算法用于皖北小麦始花期气象预报的可行性,利用1980-2019年皖北地区7个农业气象观测站的冬小麦始花期原位观测物候数据和平行观测的气象数据,采用相关系数法,筛选影响始花期早迟的特征变量,采用有序等距离抽样法,拆分出训练集和测试集。基于随机森林算法(RF),从4月10日到4月15日,每日训练1个预报模型,实现小麦始花期逐日滚动气象预报,并与基于类神经网络(ANN)、线性支撑向量机(LSVM)、多元回归(RG)和支持向量机(SVM)4种算法训练的预报模型进行比较。结果表明,由平均气温、最高气温、日照时数3类气象要素构成的40个关键气象因子与小麦始花期早迟密切相关;训练出的6个始花期逐日气象预报模型中,4月10-14日5个模型入选特征变量均为40个,4月15日模型入选特征变量为39个;6个气象预报模型训练集与测试集的平均正确率分别为93.3%和80.4%,平均均方根误差(RMSE)分别为1.860~1.960和2.510~2.709,平均决定系数分别为0.944和0.841;基于RF算法训练的预报模型3项检验指标均优于ANN、LSVM、RG和SVM算法训练的预报模型;利用RF算法模型在2020年和2021年进行预报,提前7~9 d准确预报出当年始花期。由此可见,采用有序等距离抽样拆分出训练集,再基于RF算法构建的皖北地区小麦花期气象预报模型,能够以较高精度对小麦始花期进行预报。