Underdetermined direction of arrival estimation with nonuniform linear motion sampling based on a small unmanned aerial vehicle platform

Uniform linear array(ULA)radars are widely used in the collision-avoidance radar systems of small unmanned aerial vehicles(UAVs).In practice,a ULA's multi-target direction of arrival(DOA)estimation performance suffers from significant performance degradation owing to the limited number of physical elements.To improve the underdetermined DOA estimation performance of a ULA radar mounted on a small UAV platform,we propose a nonuniform linear motion sampling underdetermined DOA estimation method.Using the motion of the UAV platform,the echo signal is sampled at different positions.Then,according to the concept of difference co-array,a virtual ULA with multiple array elements and a large aperture is synthesized to increase the degrees of freedom(DOFs).Through position analysis of the original and motion arrays,we propose a nonuniform linear motion sampling method based on ULA for determining the optimal DOFs.Under the condition of no increase in the aperture of the physical array,the proposed method obtains a high DOF with fewer sampling runs and greatly improves the underdetermined DOA estimation performance of ULA.The results of numerical simulations conducted herein verify the superior performance of the proposed method.

Comparison of uniform resampling and nonuniform sampling direct-reconstruction methods in k-space for FD-OCT

The nonuniform distribution of interference spectrum in wavenumber k-space is a key issue to limit the imaging quality of Fourier-domain optical coherence tomography(FD-OCT).At present,the reconstruction quality at different depths among a variety of processing methods in k-space is still uncertain.Using simulated and experimental interference spectra at different depths,the effects of common six processing methods including uniform resampling(linear interpolation(LI),cubic spline interpolation(CSI),time-domain interpolation(TDI),and K-B window convolution)and nonuniform sampling direct-reconstruction(Lomb periodogram(LP)and nonuniform discrete Fourier transform(NDFT))on the reconstruction quality of FD-OCT were quantitatively analyzed and compared in this work.The results obtained by using simulated and experimental data were coincident.From the experimental results,the averaged peak intensity,axial resolution,and signal-to-noise ratio(SNR)of NDFT at depth from 0.5 to 3.0mm were improved by about 1.9 dB,1.4 times,and 11.8 dB,respectively,compared to the averaged indices of all the uniform resampling methods at all depths.Similarly,the improvements of the above three indices of LP were 2.0 dB,1.4 times,and 11.7 dB,respectively.The analysis method and the results obtained in this work are helpful to select an appropriate processing method in k-space,so as to improve the imaging quality of FD-OCT.

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.

Optimizational production of phenyllactic acid by a Lactobacillus buchneri strain via uniform design with overlay sampling methodology

A Lactobacillus buchneri GBS3 strain isolated from the traditional Chinese pickles was used for the production of 3-phenyllactic acid(PLA), an important compound with antimicrobial activities against a wide species of grampositive and gram-negative bacteria and some fungi. The growth performance of this strain in the de Man, Rogosa and Sharpe(MRS) medium, the production of metabolites of valuable organic acids, and the biosynthesis of PLA using this strain as the whole-cell biocatalyst and phenylpyruvic acid(PPA) as the precursor, were investigated experimentally. The uniform design method with overlay sampling was developed for the optimization of the biotransformation conditions. The results showed that although it produced naturally lactic acid with the maximum concentration of 1.84 g·L^(-1) and PLA with the concentration of 0.015 g·L^(-1) after 66 to 72 h cultivation in MRS broth by fermentation, the present strain displayed an effective utilization ability by transforming PPA to PLA. By the uniform design method with overlay sampling for the design and optimization of transformation conditions, a maximum yield of 10.93 g·L^(-1) PLA with the mole conversion ratio of 83.07% from PPA to PLA was achieved under the optimized condition, i.e., 20 g·L^(-1) glucose, 270 g·L^(-1) cells, 13 g·L^(-1) PPA, pH 8.0 and the reaction time of 15 h, indicating that Lactobacillus buchneri GBS3 was an interesting strain for the biosynthesis of PLA via the microbial transformation. The prediction of PLA yield under different conditions was achieved successfully based on the limited information of only a small number of experiments by the uniform design with overlay sampling. Therefore, the present methodology is effective and helpful for the optimization of the biosynthesis processes of PLA.

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).

Research Progress of the Sampling Theorem Associated with the Fractional Fourier Transform

Sampling is a bridge between continuous-time and discrete-time signals,which is import-ant to digital signal processing.The fractional Fourier transform(FrFT)that serves as a generaliz-ation of the FT can characterize signals in multiple fractional Fourier domains,and therefore can provide new perspectives for signal sampling and reconstruction.In this paper,we review recent de-velopments of the sampling theorem associated with the FrFT,including signal reconstruction and fractional spectral analysis of uniform sampling,nonuniform samplings due to various factors,and sub-Nyquist sampling,where bandlimited signals in the fractional Fourier domain are mainly taken into consideration.Moreover,we provide several future research topics of the sampling theorem as-sociated with the FrFT.

基于均匀相位采样提高阻抗谱测量精度的研究

周期性信号采样中,等效采样利用较低采样频率的A/D转换实现高频周期信号的采集,一定程度上弥补欠采样测量精度低的缺陷。为了有效地提高高频测量中阻抗谱测量精度与稳定性,提出一种基于等效采样思想的均匀相位采样的阻抗谱测量方法。利用单片机共时钟基准的模/数转换器(digital to analog convertor,DAC)与数/模转换器(analog to digital convertor,ADC)模块,在完成激励信号产生、输入输出信号同步采集的基础上,合理设计激励信号频率、采集频率与信号重构方法,实现高频信号单周期内均匀相位分布的等效高频采样,同时为克服常规A/D转换速度条件下难以准确实现高频阻抗谱测量的问题提供了新思路。从误差假设与拟合算法的角度,理论上分析证明了该方法降低误差的原因。并通过两种等效电路模型的阻抗谱测量对比实验,表明该方法在所设计的20~100 kHz高频段上,阻抗测量精度与稳定性得到了显著的提高。

吸入气雾剂递送剂量均一性考察抽样方案对比分析

目的比较吸入气雾剂递送剂量均一性考察中不同抽样方案的差异。方法汇总2020年版《中国药典(四部)》(简称ChP)、《European Pharmacopoeia 11.0(VolumeⅠ)》(简称EP)/《British Pharmacopoeia 2023(VolumeⅢ)》(简称BP)、《USP-NF online 2024》(简称USP)及我国进口药品注册标准(简称JX)中吸入气雾剂递送剂量均一性考察的抽样方案和判定标准。以硫酸沙丁胺醇吸入气雾剂为例,按ChP及USP抽样方案分别测定4家企业(企业A,B,C,D)6批样品的递送剂量均一性。采用蒙特卡洛模拟法进行数据模拟,并绘制工作特性曲线。结果按ChP抽样方案,样品的递送剂量均一性均符合规定;按USP抽样方案,仅企业C有1批样品的平均递送剂量不符合规定(低于70μg),且与企业D样品比较差异显著(P<0.05)。ChP的工作特性曲线较其他3种判定标准更宽,接受区域更广;EP/BP与JX抽样方案第一阶段接受概率和总接受概率均较接近;USP与JX抽样方案在标准差较小(≤6)时几乎相同,随着标准差的增大,前者的第一阶段接受概率和总接受概率下降程度更显著,在标准差≥10的情况下,其总接受概率<90%。结论不同抽样方案对吸入气雾剂递送剂量均一性的接受概率存在一定差异,USP较ChP,EP/BP,JX对变异较大的产品容忍度更低。

基于非均匀间隔采样的光幕过靶信号波形获取

为确保光幕阵列的测量精度,提出一种基于非均匀采样的过靶信号波形获取方法。首先分析光幕过靶弹丸信号特性,得出该信号具有瞬态性、非周期性、大频带宽等特性;其次,对非均匀分数采样原理进行阐述;再次,设计相应信号采集系统并介绍系统组成及其工作原理;最后,通过试验验证与传统方法相比,系统测量精度满足要求,同时可降低测量成本。

塑料脆化温度的测定能力验证设计研究

为了满足实验室对塑料脆化温度检测能力评估和提高的需求,对塑料脆化温度的测定能力验证中的设备和试验类型选择、试样加工方法、试样材料选择和破坏判定四个关键问题进行研究。实现能力验证方案设备方法涵盖面广、测试样品均匀性好、温度范围应用广泛和破坏情况全面且易判定,为更多具备该项目检测能力的实验室找到检测中存在的问题,提高检测能力,也为实验室认证认可管理部门对该领域获证实验室的监管提供依据。

四烯菌素B标准样品的研制

目的:依据GB/T 15000.3—2008《标准样品工作导则(3)标准样品定值的一般原则和统计方法》,研制四烯菌素B标准样品。方法:以淀粉酶产色链霉菌(Streptomyces diastatochramogenes)1628发酵液为原料,通过萃取、AB-8和SephardexLH-20柱层析分离纯化得四烯菌素B纯品。利用紫外(UV)、红外(IR)、质谱(MS)和核磁图谱(NMR)分析,查阅文献数据,进行结构确认。样品分装成100瓶(10 mg/瓶),结合液相色谱法对该样品展开均匀性、稳定性检验以及联合定值分析。结果:该样品经F检验在95%的置信区间范围内均匀性良好;在-20~-18℃条件下保存12个月稳定性良好;经国内8家具有分析资质的实验室协同定值,四烯菌素B纯度为99.37%,扩展不确定度为0.22%。结论:四烯菌素B达到国家标准样品的技术要求,可用于有关四烯菌素B的检测方法校准和相关产品的质量控制。

考虑负荷特性的光伏消纳能力的模拟与评估

针对目前在配电网光伏消纳能力评估过程中不能全面考虑电力系统中负荷特性多样化对光伏消纳能力影响的不足,提出一种考虑负荷运行中的实际情况,光伏消纳模拟与概率评估的方法。首先采用支持向量机-随机森林算法对负荷数据进行清洗,再采用改进谱聚类算法对不同类型的负荷特性进行聚类分析,然后基于场景分析法选取不同负荷的类型曲线作为节点处负荷数据,最后基于蒙特卡洛模拟法和均匀抽样法进行光伏消纳方案随机模拟与消纳能力近似评估。基于IEEE 33节点系统算例分析,对有无考虑负荷特性的抽样结果进行对比,有效验证了所述方法的适用性。

基于等角多段探测器的非均匀采样CT直接FBP重建算法研究

本文提出了一种基于等角多段探测器的非均匀采样计算机断层成像(Computed Tomography,CT)系统,并针对该系统推导了直接滤波反投影重建算法,分析了算法在处理非均匀采样CT数据时的局限性,特别是算法中权重函数的非光滑性对重建图像的影响。本文的理论推导和仿真实验结果显示:尽管直接滤波反投影(Filtered Back Projection,FBP)重建算法可能导致环状伪影,但通过适当的系统设计,这些伪影的影响可以被控制在可接受的范围内,并能保持图像的分辨率,使得基于等角多段探测器的非均匀采样CT的FBP算法具有一定的实用价值。本文研究成果为新型CT系统的设计和优化提供了理论依据和实践指导。

多采样率地震勘探技术(MrSET)探讨

时间采样以及空间采样问题是地震勘探基本问题,空间采样方式包括规则采样、非均匀(非规则)采样、随机采样等.从地震波场的带限性、空间域非均匀性、地下构造多样性出发,提出多采样率地震勘探技术(MrSET),尝试组合不同空间采样方式.多采样率地震勘探观测系统设计一般应满足5项准则,探讨了多采样率数据处理基本方法,并以合成数据和实际数据的处理效果为基础,总结了多采样率地震勘探技术的7个方面优势.在相同道密度前提下,与规则采样相比,多采样率地震勘探技术更能满足复杂地震波场、弱能量绕射波与散射波充分采样的需要,是一项能提高反射地震数据成像精度的地震勘探技术,经过进一步研究将有巨大潜力成为(陆上、海洋)节点地震勘探时代常规技术.

基于频移调制的间歇非均匀采样干扰研究

针对传统间歇采样干扰存在的缺点:脉压结果呈现规律性,易于被多体制雷达识别剔除;生成的干扰落后真实目标。本文研究了一种基于频移调制的非均匀间歇采样干扰,其可以对采样信号施加多普勒频移以及非均匀转发,其干扰后的脉压结果分布于真实目标两侧,并且破坏原有均匀采样的规律性。仿真实验表明,基于频移调制的间歇非均匀采样干扰和传统方法相比产生了较好的干扰效果和抗识别特性。

基于扩散概率模型的非均一地震数据插值方法

【目的】能源勘探领域长期面临非均一地震数据插值的难题。由于检波器无法精确放置在理论网格点,现有均一插值技术常导致结果存在偏差和细节失真。【方法】为解决此问题,提出一种基于扩散概率模型的非均一插值新方法。扩散概率模型是一种新兴的生成式深度学习模型,分为扩散和生成两个过程。在扩散过程中,对完整地震数据迭代施加噪声,训练神经网络的去噪能力;在生成过程中,使用神经网络对噪声数据迭代去噪,得到重构数据。利用插值算子计算迭代数据与采集数据的偏差,作为神经网络的额外输入,提高扩散概率模型的非均一插值能力。在数值实验部分,使用二维合成数据集与实际数据集对非均一采样进行了测试,并使用均一插值模型与所提模型进行比较。【结果和结论】结果表明:该方法显著提升了扩散概率模型对非均一采样的处理能力,在合成数据与实际数据测试中,信噪比大约提高了7 dB,有效提高了深度学习方法对非均一插值的精度,为非均一地震数据插值算法提供了新的思路。

基于Uniform LBP和DMMA的单样本人脸识别

在单样本人脸识别系统中,为了获得更好的人脸面部特征,提出了一种融合Uniform LBP特征和多流形判别分析(Discriminative Multi-Manifold Analysis,DMMA)的特征提取方法。对每幅人脸图像进行分块构成一个子集。使用统一局部二值模式(Uniform LBP)算子提取每个子集中图像的直方图,每个子集中的直方图形成一个统计流形,应用DMMA算法获得人脸图像的低维特征。采用基于重建的流形-流形间的距离识别未知的人脸图像。在AR数据库和ORL数据库上实验结果表明,该算法的识别性能优于一般的DMMA算法。

脉内步进频信号非均匀间歇转发干扰特性研究

随着数字射频存储技术的快速发展,间歇采样转发干扰凭借其突出的欺骗和压制效果,在实际的干扰场景中有广泛的运用,对雷达的识别和探测造成了严重的威胁。区别于常规的均匀间歇干扰,采样信号非均匀的样式进一步拓展了干扰的灵活性和欺骗性,对雷达有更明显的干扰压制效果。通过研究雷达发射脉内步进频信号和非均匀间歇采样转发干扰类型的产生机理,对其脉压后的时频特性进行分析,最后通过仿真实验对脉内捷变步进频受到非均匀间歇采样干扰的效果进行验证。

负反馈和状态空间重构的UPWM失真问题校正方法

针对数字D类音频功率放大器中的均匀采样脉冲宽度调制(Uniform-Sampling Pulse Width Modulation,UPWM)失真,提出了一种负反馈和状态空间重构的全数字UPWM失真问题校正方法。该方法利用数字Σ-Δ(Sigma-Delta)调制器的高开环增益特性,通过构造包含数字Σ-Δ调制器和UPWM发生器的闭环负反馈环路,使得环路的输入与输出近似呈线性关系,从而校正UPWM产生的失真。在构造闭环时,通过对数字Σ-Δ调制器的状态空间表达式进行重构,并添加插零值模块和抽取模块使该环路在保持稳定性的同时,拥有与原数字Σ-Δ调制器相同的噪声整形效果。实验结果表明,该方法相比其他的UPWM失真校正方法,不仅能降低谐波失真,还能大幅降低数字UPWM调制器输出信号的本底噪声,从而可使数字UPWM调制器在频率6 kHz和幅度为满量程的-5 dB的正弦数字信号输入情况下,输出信噪失真比达到95.26 dB,同时所提方法可全数字电路实现、硬件实现简单且易于移植。

基于部分均匀采样的蒙特卡洛仿真模型

针对海面紫外光散射传输中存在的衰减问题,提出了一种基于部分均匀采样的蒙特卡洛仿真模型。该模型考虑到海平面上空气中的粒子浓度较高导致能见度较低的情况,对距离参数采用重要性采样方法,而对方向参数中的天顶角则采用均匀采样方法。仿真结果表明:与传统的蒙特卡洛仿真模型相比,在保证相同性能的前提下,所提出的模型能够显著提高计算效率,计算效率提升了约5个数量级,非常适合应用于海上千米量级的实际传输场景。