SINGULAR CROSS SPECTRUM APPLIED ON DIAGNOSTIC ANALYSIS OF AIR-SEA INTERACTION

The Singular Cross Spectrum Analysis (SCSA) method was employed to investigate the coupledperiods of air-sea/mid-low circulation interaction using 1951-1993 500-hpa geopotential heights and the seasurface temperature (SST) in the Northern Hemisphere. Results show that air-sea correlation is noticeable on the3-7 year scale which is similar to ENSO circle. In this sense, ENSO is a Strong signal. Quasi-ten/quasi-four yearperiods are prominent in the mid-low interaction, and quasi-if our year oscillation is uniform with the ENSO circle.Studies indicate that the mid-low interaction possess quasi-ten year oscillation beside being affected by ENSO.

Cross-Band Spectrum Prediction Based on Deep Transfer Learning

Spectrum prediction is a promising technology to infer future spectrum state by exploiting inherent patterns of historical spectrum data.In practice,for a given spectrum band of interest,when facing relatively scarce historical data,spectrum prediction based on traditional learning methods does not work well.Thus,this paper proposes a cross-band spectrum prediction model based on transfer learning.Firstly,by analysing service activities and computing the distances between various frequency points based on Dynamic Time Warping,the similarity between spectrum bands has been verified.Next,the features,which mainly affect the performance of transfer learning in the crossband spectrum prediction,are explored by leveraging transfer component analysis.Then,the effectiveness of transfer learning for the cross-band spectrum prediction has been demonstrated.Further,experimental results with real-world spectrum data demonstrate that the performance of the proposed model is better than the state-of-theart models when the historical spectrum data is limited.

基于互相关谱滑动平均的OFDR应变传感精度提升研究

OFDR在长距离大应变传感时易出现相位噪声,使得应变传感精度较差或无法还原真实应变变化。文章采用互相关谱滑动平均方法对OFDR原始互相关谱进行处理以提升应变传感精度。阐述了应变解调干扰噪声产生机理,分析了基于互相关谱滑动平均的OFDR应变传感精度提升原理,搭建了OFDR应变传感系统,在103.8m传感光纤上进行了实验验证,并讨论了不同大小的滑动平均块对结果的影响。实验结果表明,在扫频范围60nm,滑动平均块大小为1×10时,可在103.8m待测光纤实现空间分辨率为1.33cm,最大值为4000με的应变传感,应变区波长偏移量标准差显著降低。研究证明,互相关谱滑动平均方法可以有效提升OFDR系统应变解调精度。

Angular Distribution and Cross Section Measurements of ^(64)Zn(n,α)^(61)Ni Reaction for Neutron Energy 5 MeV

A twin gridded ionization chamber with dual parameter data acquisition sys-tem is used to study neutron induced charged particle emission reaction.The angulardistribution and cross section of n-particles from the 64Zn（n,α）61Ni reaction are meas-ured at neutron energy 5 MeV.

声波法在输油管道上的可检测泄漏率分析

为了确保输油管道出现泄漏时能够及时检测到泄漏,对声波法在输油管道上的可检测泄漏率进行了分析。首先,建立了声波产生和传播衰减模型,根据模型分析了声波在管道内的衰减性,得到管道两端声波衰减幅值的计算方法;其次,采用基于互信息优化的自适应噪声完备集合经验模态分解(complete ensemble empirical mode decomposition with adaptive noise,简称CEEMDAN)和互谱分析相结合的去噪算法对采集的信号进行去噪,并实验验证了衰减模型可准确估计声波的衰减幅值,去噪算法可以有效消除信号中的噪声;最后,分析了管道特性与声波法在输油管道上的可检测泄漏率之间的关系。研究表明,管道特性在一定程度上决定了声波法的可检测泄漏率,声波法在输油管道上的最小可检测泄漏率可达0.45%。

Using activation method to measure neutron spectrum in an irradiation chamber of a research reactor

Neutron spectrum should be measured before test samples are irradiated.Neutron spectrum in an irradiation chamber of a research reactor was measured by using activation method when the reactor is in normal operation under 2 MW.Sixteen kinds of non-fission foils(19 reaction channels) were selected,of which 10 were sensitive to thermal and intermediate energy regions,while the others were of different threshold energy and sensitive to fast energy regions.By measuring the foil radioactivity,the neutron spectrum was unfolded with the iterative methods SAND-Ⅱ and MSIT.Finally,shielding corrections of group cross-section and main factors affecting the calculation accuracy were studied and the uncertainty of solution was analyzed using the Monte Carlo method in the process of SAND-Ⅱ.

Application of the Double-difference Relocation Method Combined with Waveform Cross-correlation on the Three Gorges Reservoir Seismicity

In this paper,we use the double difference location method based on waveform crosscorrelation algorithm for precise positioning of the Three Gorges Reservoir( TGR)earthquakes and analysis of seismic activity. First,we use the bi-spectrum cross-correlation method to analyze the seismic waveform data of TGR encrypted networks from March,2009 to December,2010,and evaluate the quality of waveform cross-correlation analysis.Combined with the waveform cross-correlation of data obtained, we use the double difference method to relocate the earthquake position. The results show that location precision using bi-spectrum verified waveform cross-correlation data is higher than that by using other types of data,and the mean 2 sig-error in EW,NS and UD are 3.2 m,3.9 m and 6.2 m,respectively. For the relocation of the Three Gorges Reservoir earthquakes,the results show that the micro-earthquakes along the Shenlongxi river in the Badong reservoir area obviously show the characteristics of three linear zones with nearly east-west direction,which is in accordance with the small faults and carbonate strata line of the neotectonic period,revealing the reservoir water main along the underground rivers or caves permeated and induced seismic activity. The stronger earthquakes may have resulted from small earthquakes through the active layers.

双台振动试验相干系数的选择

针对目前飞行器双台振动试验中没有互谱条件而导致难以选择和设置与互谱相关的相干系数的问题,进行了理论分析和试验研究:分析飞行器在飞行中和地面振动试验中的激励源的相关性,明确了试验中相干系数的确定原则;通过统计分析得出了试验中相干系数超差在频率分布上的规律以及异常超差的原因;同时通过细长体飞行器双台振动试验验证了不同相干系数设置在测点响应量级、均衡速度和驱动量级方面的试验效果差别。根据分析与试验结果提出了分频段选择不同相干系数以及有限放大容差的设置方法。试验证实了该设置方法的可行性。研究结果对于多台振动试验互谱设置有指导意义。

基于波数-频率谱分析的线阵列后向台阶流速测量

后向台阶湍流介质流速测量存在重复性较低、鲁棒性较差的问题,为了解决这些问题,提出了一种基于波数-频率谱分析的线阵列传感器流速测量方法。首先,分析了后向台阶数据的湍流度和“泰勒冻结”信号特征;其次,使用频域波束形成算法和多信号分类算法将传感器数据从域转换至域,呈现出与后向台阶流速相关的特征“脊线”;然后,探究不同波束形成滤波算法和功率谱分块长度对流速“脊线”的影响;最后,应用波数-频率谱分析“脊线”斜率求解流速。结果表明波数-频率谱方法能够有效地实现后向台阶流速测量,与传统的互相关法比较,相对误差为2.83%,重复性为0.32%,具有较好的重复性和鲁棒性。

Optical Path Length,Temperature,and Wavelength Effects Simulation on Ozone Gas Absorption Cross Sections towards Green Communications

Ozone is a green house gas. Ozone absorption cross sections have been reported with discrepancies and inconsistencies. In this paper, simultaneous effects of the optical path length and temperature variations on ozone gas absorption cross sections are investigated at different wavelengths. HITRAN 2012, the latest available line list on spectralcalc.com simulator, is used in this study to simulate ozone gas absorption cross sections in relation to the simultaneous effects of the optical path length and temperature at the wavelengths of 603 nm and 575 nm. Results obtained for gas cells with the optical path length from 10 cm to 120 cm show that the decrease in temperatures from 313 K to 103 K results in the increase in ozone gas absorption cross sections. At wavelengths of 603 nm and 575 nm, the percentage increase of ozone gas absorption cross sections is 1.22% and 0.71%, respectively. Results obtained in this study show that in the visible spectrum, at constant pressure, ozone gas absorption cross sections are dependent on the temperature and wavelength but do not depend on the optical path length. Analysis in this work addresses discrepancies in ozone gas absorption cross sections in relation to the temperature in the visible spectrum; thus, the results can be applied to get optimal configuration of high accuracy ozone gas sensors.

GPR信号去噪的变分模态分解

为了进一步提高探地雷达(ground penetrating radar,GPR)数据的信噪比,压制由随机扰动引起的随机绕射能量,将二维变分模态分解(two-dimensional variational mode decomposition,2D-VMD)引入二维GPR数据的噪声压制处理中。首先,对GPR数据进行2D-VMD处理,并分析各阶本征模态函数(intrinsic mode function,IMF)分量及其对应的频率-波数域谱来确定雷达剖面中的各回波类型。然后,计算IMF分量与原始数据的互相关系数来确定信号模态和噪声模态,并对信号模态进行重构得到降噪后的数据。理论数据和实测数据测试表明,相比于传统的1D-VMD法,2D-VMD滤波后的含噪正演记录峰值信噪比由6.44 dB增加到7.72 dB;经2D-VMD降噪处理后的雷达剖面在保留有效信号的基础上,可以有效压制随机扰动带来的噪声,并且得到的雷达剖面同相轴连续性更好。

Frequency Domain Fatigue Evaluation on SCR Girth-Weld Based on Structural Stress

The Steel Catenary Riser(SCR)is a vital component for transporting oil and gas from the seabed to the floating platform.The harsh environmental conditions and complex platform motion make the SCR’s girth-weld prone to fatigue failure.The structural stress fatigue theory and Master S-N curve method provide accurate predictions for the fatigue damage on the welded joints,which demonstrate significant potential and compatibility in multi-axial and random fatigue evaluation.Here,we propose a new frequency fatigue model subjected to welded joints of SCR under multiaxial stress,which fully integrates the mesh-insensitive structural stress and frequency domain random process and transforms the conventional welding fatigue technique of SCR into a spectrum analysis technique utilizing structural stress.Besides,a full-scale FE model of SCR with welds is established to obtain the modal structural stress of the girth weld and the frequency response function(FRF)of modal coordinate,and a biaxial fatigue evaluation about the girth weld of the SCR can be achieved by taking the effects of multi-load correlation and pipe-soil interaction into account.The research results indicate that the frequency-domain fatigue results are aligned with the time-domain results,meeting the fatigue evaluation requirements of the SCR.

陕西省2021年极端秋雨成因分析

利用NCEP/NCAR 2.5°×2.5°的逐月再分析资料和NOAA提供的逐月海温资料等从海温异常、大尺度环流异常、水汽输送异常等角度分析2021年秋季陕西降水异常偏多的原因,结果表明:(1)小波交叉谱分析显示Ni?o3.4区海温距平与陕西秋季降水存在2~4 a的共振周期,前期冬季海温与次年秋季降水关系呈正相关的共振周期。(2)受双峰型La Nina事件影响,2021年9-11月西太平洋副热带高压(简称“副高”)控制的范围明显偏大,副高脊线位置较气候态偏北1°,西伸脊点较气候态偏西23°,造成主雨带偏西偏北。(3)中低层西北太平洋到我国华北北部的异常反气旋,与孟加拉湾北侧异常的气旋中心,造成气流在我国西北地区东部异常辐合。(4)从水汽收支来看,陕西2021年秋季水汽净流入较气候态偏多66.7%,尤其是东边界的异常水汽输送,还增强了低层冷垫,利于暖湿气流在冷垫上爬升导致陕西降水较常年异常偏多。

面向小型载荷的宽带通信信号随机共振检测方法

随着人工智能等领域的飞速发展,无人机在各个领域,尤其是现代战争中发挥着越来越重要的作用。无人机凭借其强大的灵活性和高隐蔽性优势,对现代作战具有颠覆性影响。在无人机执行战场侦察、监视、通信、电子干扰、雷达诱骗、激光制导等任务的过程中,及时探测敌方辐射信号尤为重要。随机共振方法利用特定非线性系统可以使输入其中的信号与噪声在一定条件下产生协同作用的特点,将噪声的能量转移到信号中来放大信号,是常用的微弱信号检测方法之一。窄带信号的随机共振检测技术已趋于成熟。而对小型载荷无人机监视、通信等场景下的微弱宽带通信信号,现有随机共振检测方法直接采用窄带信号的时域能量检测方法,并未基于宽带信号特点设计专门的检测方法,低信噪比条件下检测性能受限。为了满足对微弱宽带通信信号的检测要求,本文以常用的宽带通信信号为研究对象,对于单通道接收场景,提出基于宽带信号局部频谱的随机共振信号检测方法,该方法与传统的随机共振信号检测方法相比性能提升约6 dB。其次,对于更低信噪比的情况,提出一种随机共振与互相关检测相结合的双通道协同检测方法,并提出基于随机共振后两路互相关系数最大化的系统参数优化准则。典型场景下的仿真分析表明,对于单通道接收的低信噪比微弱宽带通信信号,局部频谱法可以有效提升检测性能;对于更低信噪比宽带通信信号,采用随机共振处理后的双通道互相关检测可以进一步提升检测性能。

基于拉曼光谱鉴定书写/打印文件的朱墨时序

朱墨时序鉴定是司法鉴定文件检验研究与实践领域中的热点和难点问题。朱墨时序的鉴定可证明文件真伪,推断文件物证是否与案件事实相符,从而为司法机关的侦查破案和案件判定提供法律依据。常见的检验方法有显微镜法、荧光法、文检仪法、计算机软件辅助法等,其鉴定结论易受检验人员主观意识的影响,因不够客观而备受质疑。研究在制备3类签字笔和9种印油组合54个书写样本、激光打印和9种印油组合18个打印样本的基础上,运用共焦显微拉曼光谱仪对其进行检验。以10#百乐签字笔和1#印之秀印油为样本测试得到最佳实验条件,将制备的72个样本放入储存箱内避光保存1年,依次测定样本中先字后印、先印后字、印油和字迹4个位点的拉曼光谱,每个样本测试3次。实验结果基本不受储存环境、纸张本底等因素的干扰,无论是书写样本还是打印样本,先字后印交叉点显示出了印油的部分特征,先印后字交叉点显示出了字迹的部分特征,交叉位点的拉曼光谱图显示大部分为上层相应的字迹或印油的拉曼位移,这与20倍物镜观察的μView图显示结果相互印证。通过比对印文交叉部位的拉曼位移,进而鉴定出样本的朱墨时序。结果表明:相比常规检验方法,此新颖方法简便快捷、无损、灵敏度和准确率高,对文件的朱墨时序鉴定具有指导意义。

基于星载合成孔径雷达图像交叉谱的全球海浪特征研究

星载合成孔径雷达(Synthetic Aperture Radar, SAR)因其全天时、全天候的观测能力,为全球海洋动力环境要素研究提供了重要数据支撑。然而,SAR海浪成像是非线性过程,现有理论中的近似求解会导致海浪谱反演的信息缺失。SAR图像交叉谱技术的提出一定程度上突破了这一限制,能够很好地量化海浪谱特性及海浪传播方向。本研究延续前人系列成果,利用最新提出的面向径向海浪的图像谱强度,开展不同尺度海浪随局地风速的变化趋势分析,并基于雷达视向图像谱强度提取了谱峰波数,进而结合欧洲空间局环境遥感卫星先进合成孔径雷达波模式在开阔大洋获取的近400万景SAR图像,分析了谱峰波数的全球分布特征,为量化全球风浪耦合过程提供新视角,揭示了海浪与风速耦合关系的空间分布与季节变化规律。

海南省东方市社区居民疾病谱分析

目的探讨2021年海南省东方市社区居民的疾病构成及流行病学特征。方法采用横断面研究设计,分析了2021年1月1日—12月31日海南省东方市疾病监测数据库196761例社区居民的病历资料。对该人群进行了年龄标准化后,分析和描述了前十位疾病构成。结果196761例社区居民中,男性91621例(占46.56%),女性105140例(占53.43%),男女比为0.87;以≥45岁居民居多,占46.13%(90763/196761)。疾病谱前3位依次是呼吸系统疾病[32.69%(64327/196761)]、循环系统疾病[7.86%(15470/196761)]和消化系统疾病[7.21%(14191/196761)];前10位系统疾病中,男性损伤、中毒和外因的某些其他后果的年龄标准化患病率高于女性(3.11%vs 2.30%),女性泌尿生殖系统疾病的年龄标准化患病率高于男性(3.01%vs 1.20%)。呼吸系统疾病以急性上呼吸道感染(5.17%)、急性支气管炎(1.84%)和慢性支气管炎(1.44%)为主,其在<5岁组的患病率(38.59%)和伤残损失寿命年率(656.01/10万)最高;循环系统疾病以高血压病(1.72%)、脑梗死(0.71%)和慢性缺血性心脏病(0.49%)为主,其在≥60岁组的患病率(17.13%)和伤残损失寿命年率(2175.49/10万)最高;消化系统疾病以胃炎和十二指肠炎(1.10%)、其他非感染性胃肠炎和结肠炎(0.43%)以及龈炎和牙周疾病(0.38%)为主,其在≥60岁组的患病率(6.98%)和伤残损失寿命年率(1710.75/10万)最高。结论2021年海南省东方市社区居民以呼吸系统疾病、循环系统疾病和消化系统疾病为主,且疾病负担主要归因于需要长期管理的疾病。东方市应针对疾病谱特征优化和调配医疗资源,加强高危人群的健康促进和防治工作。

应用屏栅电离室测量^(16)O(n,α)^(13)C反应的模拟研究

基于Geant4建立了一套利用屏栅电离室测量^(16)O(n,α)^(13)C反应的模拟方法,能预测不同入射中子能量、不同屏栅电离室结构、不同工作气体和样品参数等实验条件下屏栅电离室测量到的阴极-阳极幅度2维谱。为了验证该模拟方法的可靠性,在北京大学4.5 MV静电加速器上开展了实验,实验所用的中子能量为5.06 MeV,工作气体为0.3 MPa的Ar与体积分数为3.45%CO 2组成的混合气体(其中的氧作为待测样品)。实验测得了屏栅电离室的阴极阳极幅度2维谱,且模拟与实验结果吻合较好。基于此模拟方法提出了一套实验条件的优化方案,可为下一步在宽能区精确测量^(16)O(n,α)^(13)C反应截面提供参考。

强干扰下基于三阶互累积量的FMCW雷达信号DOA估计算法

针对车载调频连续波雷达存在相互干扰的实际情况,本文提出了一种基于三阶互累积量的多目标波达方向超分辨估计方法.该方法利用同步采集的阵列信号并根据回波信号和干扰信号的非相关特性,构造三阶互累积量矩阵,随后根据子空间方法获得二维空间谱,实现距离和方位的联合估计.计算机仿真结果表明,本文所提方法能够在抑制强干扰影响的同时实现3°以内多目标识别,与现有超分辨法和重构法相比,具有更高的角度分辨率和估计精度.

基于遥感数据的大汶河流域济南段水体面积变化分析及生态流量评价

气候变化与人类活动对大汶河生态健康影响日益显著,为维持河流生态健康的稳定性,开展生态流量评价至关重要。以大汶河流域济南段为研究范围,采用多源遥感资料提取水体面积信息,由水体面积与实测流量构建拟合方程,推求基本生态流量对应的生态水体面积,开展基于遥感数据的生态流量评价。研究结果显示:1985-2021年大汶河流域济南段水体面积41.84 km^(2),水体面积呈增加趋势,其中季节性水体占32%,永久性水体占68%。6种水体指数中EWI、NDWI适用于大汶河流域济南段,精度达到90%。由线性拟合方程推求,陈北、马小庄流域生态水体面积分别为13.98 km^(2)、18.49 km^(2)。1985-2021生态流量保障率分别为65%、42%。受自然因素与人为因素影响,2004年前后生态流量保障率变化明显,分别由43%、7%提高到83%、73%,至2020年均达到100%。交叉小波与小波相干谱分析表明,水体面积与气候因素中降水、平均湿度呈正相关,与平均风速呈负相关,与平均温度的相干性不显著,降水与平均湿度是影响水体面积变化的主要因素。土地利用因素中,水体面积变化主要受耕地、草地面积影响,呈负相关。由不同水体面积比例,确定流域内雪野水库生态水体面积10.82 km^(2),生态水位228.97 m,生态库容1.02亿m^(3)。研究成果可为大汶河流域生态流量评价、监管与调度提供技术支撑。