High-sensitivity methane monitoring based on quasi-fundamental mode matched continuous-wave cavity ring-down spectroscopy

Continuous-wave cavity ring-down spectroscopy(CW-CRDS)is an important technical means to monitor greenhouse gases in atmospheric environment.In this paper,a CW-CRDS system is built to meet the needs of atmospheric methane monitoring.The problem of mode matching is explained from the perspective of transverse mode and longitudinal mode,and the influence of laser injection efficiency on measurement precision is further analyzed.The results of cavity ring-down time measurement show that the measurement precision is higher when the laser is coupled with the fundamental mode.In the experiment,DFB laser is used to calibrate the system with standard methane concentration,and the measurement residual is less than±4×10^(-4)μs^(-1).The methane concentration in the air is monitored in real time for two days.The results show the consistency of the concentration changes over the two days,which further demonstrates the reliability of the system for the measurement of trace methane.By analyzing the influence of mode matching,it not only assists the adjustment of the optical path,but also further improves the sensitivity of the system measurement.

ANALYSIS OF MONOPOLE ANTENNA ON CIRCULAR DISC BY MODE MATCHING

Mode matching is used for the analysis of monopole antenna on circular disc, which is achieved by developing a novel model consisting of two artificial ground planes above and bellow the monopole antenna. Using this model, the input impedance is computed and compared with measured data reported in literatures, and excellent agreement is observed.

MATCH-MODE METHOD AND ITS NUMERICAL SIMULATION FOR ROTOR-STATOR INTERACTION SOURCE MODES AND PROPAGATION MODES IN AN ANNULAR DUCT WITH MULTI-TREATMENTS

The suppressing design of the engine nacelle in an aircraft can benefit from the development of the prediction system for the sound fields in engine ducts which includes the prediction of the source generation and that of sound propagation in ducts. First, the acoustic match mode principle between the source modes of rotor stator interaction noise and the propagation modes is presented in this paper. Second, by utilizing this principle, the theoretical prediction method for rotor stator interaction noise generation and its propagation and attenuation in an annular duct with multi treatments is developed. That means that the prediction of sound propagation and attenuation in the segmented ducts might no longer completely depend on the in duct mode measurements, and the investigation on the sound propagation and attenuation in ducts can be accomplished not only by acoustic mode measurement, but also by making use of the source prediction to determine the source modes excited by rotor stator interaction. The effects of fan speed, blade/vane numbers, axial spacing between rotor and stator on the in duct sound attenuation and generated sound power level before and after ducts (also including the sound power level of blade passing frequency and its harmonics at the inlet of ducts) have been numerically calculated by using this prediction method. The reliability of this prediction method is verified by reasonable agreement between the predicted results with measured results in references. By analyzing the results of calculating cases, some reference criteria are provided for the engineering design of the suppressing engine nacelle.

Guided Waves Mode Discrimination in Pipes NDT Based on the Matching Pursuit Method

Ultrasonic guided wave have the multi-modes and dispersive characteristics, and its modes are easy to be converted at boundary or when running into defects in pipes, which makes the discrimination of different guided waves modes of the reflection signals in pipes NDT very hard. In this work, firstly, the experiments are carried out to test two kinds of stainless steel pipes by applying guided waves NDT, one is integrated pipe and another is non-integrated pipe with a small hole defect, and the detected guided waves echo signals are respectively obtained. Secondly, the measured signals are processed by matching pursuit method and the Chirplet matching atom parameters are calculated. By calculating the time-frequency distributions spectrum of detected guided waves echo signals, torsional, flexural and longitudinal guided waves modes are identified from the intact pipe, and the two wave-packets with torsional and flexural guided waves modes are also identified from the pipe with hole defect. The results showed that the matching pursuit method has a tremendous advantage to identify different guided waves modes in pipes nondestructive testing.

IMPROVED MODE-MATCHING AND NETWORK ANALYSIS OF E-PLANE WAVEGUIDE BRANCH DIRECTIONAL COUPLERS

The E-plane waveguide branch directional couplers are analyzed by a method which combines the multimode network theory with rigorous mode-matching approach. The electromagnetic field components are expanded by the superposition of LSEx modes rather than TE and TM modes in the mode-matching procedure. Meanwhile, the electromagnetic problem is transferred into the network problem through the mode-matching treatment. It is shown that the present method has the advantages of simplicity and less computation without affecting the accuracy of the calculation.

Fast inter-mode decision method based on best matching block for H.264 encoding

In H.264 encoder, all possible coding modes should be checked to choose the most appropriate mode for every macroblock, which adds a heavy computation burden to the encoder. In this paper, a fast inter-mode decision method is presented to reduce computation complexity of an H.264 encoder. By detecting the best matching block （BMB） before transform and quantization, some coding modes can be skipped and the corresponding encoding steps can be omitted for these BMBs. Meanwhile this method can also be used to detect all-zero blocks. The experimental results show that this method achieves consistently significant reduction of encoding time while keeping almost the same rate-distortion performance.

改进的k-modes聚类算法在协同过滤就业推荐算法中的应用

为了给高校毕业生提供精准的个性化就业推荐服务,将基于动态权重相互依存距离的改进k-modes聚类算法应用于协同过滤推荐算法中。定义不同样本点属性之间的距离等于属性值内部距离和属性间外部距离的加权和,选择初始簇质心时,动态调整样本点与簇质心的距离以及簇密度的组合权重,动态设置簇密度计算公式的半径,根据样本点的概率值选出初始簇质心;迭代计算和优化得到满足精度的学生簇和职位簇;构建学生-职位矩阵,计算应届生和往届生的相似度、往届生和入职岗位的相似度,选择二者的相似度超过阈值的应届生簇和职位簇组合为匹配对进行匹配,并将匹配信息降序排列形成匹配列表,依据匹配列表进行双向推荐和信息推送,为高校的就业推荐和指导提供信息导向和技术支持。

MULTI-MODE NETWORK ANALYSIS FOR DISCONTINUITIES IN PARALLEL-PLATE WAVEGUIDES PARTIALLY FILLED WITH MULTI CHIRAL RODS

The reflection and transmission characteristics of the guided modes in parallel-plate waveguides partially filled with one or multi chiral rods have been investigated by a method, which combines the multi- mode network theory with a rigorous mode matching procedure. The formulas of the reflection and transmis- sion coefficient matrix are derived. The numerical results for different cases are presented and have indicated that the chirality parameters and the geometrical dimensions of the chiral rods have significant influence on the reflection and transmission characteristics of the guided modes.

Signal prediction based on empirical mode decomposition and artificial neural networks

In view of the usefulness of Empirical Mode Decomposition （EMD）, Artificial Neural Networks （ ANN）, and Most Relevant Matching Extension （MRME） methods in dealing with nonlinear signals, we pro- pose a new way of combining these methods to deal with signal prediction. We found the results of combining EMD with either ANN or MRME to have higher prediction precision for a time series than the result of using EMD alone.

On the Modal and Non-Modal Model Reduction of Metallic Structures with Variable Boundary Conditions

Vibration mode based model reduction methods like Component Mode Synthesis (CMS) will be compared to methods coming from control engineering, namely moment matching (MM) and balanced truncation (BT). Conclusions based on the theory together with a numerical demonstration will be presented. The key issues on which the paper is focused are the reduction of metallic structures, the sensitivity of the reduced model to varying boundary conditions, full system response, accurate statics and the possibility to determine “a priori” the number of needed modes (trial vectors). These are important topics for the use of reduction methods in general and in particular for the implementation of FE models in multi body system dynamics where model reduction is widely used. The intention of this paper is to give insight into the methods nature and to clarify the strengths and limitations of the three methods. It turns out, that in the considered framework CMS delivers the best results together with a clear strategy for an “a priori” selection of the modes (trial vectors).

电磁损耗介质对谐振腔TM_(0)模谐振频率和品质因数的影响研究

微波谐振腔作为现代工业微波器件的基本组成部分,在决定器件性能方面起着重要作用。在实际应用中,通常在谐振腔壁涂敷电磁损耗介质以满足设计需求,因此分析这类谐振腔的电磁特性具有一定的理论意义和应用价值。本文基于一个加载电磁损耗介质谐振腔的基本模型,依据模式匹配方法在介质不连续处建立起的匹配关系,得到了计算TM_(0)模谐振频率和品质因数的一般表达式,通过计算第一个谐振模式TM_(01)模分析了损耗介质厚度、种类对其电磁特性的影响规律。计算结果与电磁场仿真软件微波工作室(Computer Simulation Technology Microwave Studio,CST-MWS)仿真结果吻合良好,证明了该算法对于电磁损耗介质加载的谐振腔特性计算与分析是有效的。

基于历史数据驱动的厂站接线图自动生成

在分析电网变电站主接线方式及特征的基础上,结合电网历史图形数据,研究实现无拓扑信息场景下的电网厂站接线图自动生成。利用设备双重命名规范构建拓扑关系;通过解析历史图形间隔的组成结构,自动构建厂站特征库,为绘制目标厂站间隔提供数据基础。基于特征向量及子图匹配算法进行特征模板匹配,进而研究基于图形模板和间隔模板的布局算法,完成基于历史数据驱动的图形自动生成,达到电网厂站接线图图模数一体化构建的目的,为自动化人员的日常运维工作提供支撑。经过实际项目应用,自动生成的图形满足要求。

重大突发疫情中的对口支援关系匹配优化研究

重大突发事件中的对口支援是典型的具有中国特色的应急救援措施,也是我国社会制度优越性的重要体现。现有相关研究大多为定性研讨,鲜有从管理科学视角探讨供需双方如何实现匹配优化。研究应急响应阶段中的对口支援关系优化问题,并以全国支援湖北抗击疫情为例:首先从“人”“机”“物”等角度界定支援地供应能力,同时创新定义了受灾地的需求紧迫度和供需匹配函数,然后借鉴指派优化问题的建模思想,以加权的需求满足率最大化为目标函数,构建了应急响应阶段的对口支援结对关系匹配优化模型。计算实验表明:所提出的模型兼顾了应急资源分配的公平性,能最大限度地覆盖灾区需求情况;在资源紧缺和资源充裕两个极端情况下,“物”和“人”分别是提升灾区需求满足率的关键。

时间匹配程度对学龄儿童通学出行方式的影响

改善学生与家长的通勤时间约束、优化或转变儿童通学出行方式是缓解拥堵、提升安全的有益选择。基于时间地理学理论,提出儿童通学时间与家长通勤时间的匹配程度测度方法,划分时间制度约束型、出行时间宽裕型和出行时间约束型三种时间匹配值类型。采用多项Logit模型分析父母不同时间匹配值类型对儿童通学出行方式的影响。结果表明,家长与儿童的时间匹配程度会影响儿童通学出行方式选择。在不同时间匹配值类型条件下,儿童通学出行方式与家长性别高度关联。上学出行中,母亲与儿童在时间制度约束下小汽车出行比例增加;放学出行中父亲受到时间制度约束反而会增加儿童步行通学出行的概率。因此,制定鼓励学生步行通学出行的政策时要重视时间制度与上下学时间情境的影响。

基于ABS+ESC混合动力商用车制动系统的开发应用

基于传统底盘的混合动力商用车整车开发流程是在传统防抱死制动系统(ABS)+电子稳定控制(ESC)系统商用车开发流程的基础上,将传统的燃油发动机制动系统与传统商用车二类底盘做匹配的过程。文章详细阐述了混合动力制动系统在传统燃油制动系统增加纯电模式,匹配电控空压机、电控空气干燥器、ABS+ESC的设计、储气筒容积、电控脚制动阀及管线的匹配设计。通过匹配计算选型,搭载整车通过各种道路试验对制动性能做全方位的试验验证过程及应用。通过对混合动力牵引车的制动系统制动效能的验证及制动时方向稳定性等制动性能方面的试验,发现制动响应时间、制动减速度、制动距离、驻车制动性能及应急制动性能等满足国家法规要求。

矩量法的一般波端口电磁建模方法

针对矩量法中非规则截面波端口的电磁建模问题,提出了一种基于高阶基函数矩量法的一般波端口建模方法。基于等效原理和模式匹配法建立了波端口表面积分方程,并利用二维有限元法对非规则波端口的模式进行高精度数值分析,将矩量法的规则波端口模型拓展为可用于规则及非规则波端口建模的一般波端口模型。在此基础上,使用定义于双线性曲面四边形单元的高阶基函数取代传统低阶基函数,减少了矩量法矩阵的未知量,显著降低了算法的内存需求和计算时间。通过数值算例对方法进行测试,与有限元法的数值结果进行对比,验证了方法的正确性;与低阶矩量法的数值结果对比,验证了方法的高效性。结果表明,该方法进行一般波端口模型建模仿真具有高效率和高数值精度的特点。

一种基于逐次变分模态分解的谐波检测方法

传统谐波检测算法受噪声影响导致检测精度低,并且边界处容易出现畸变。对此,本文基于逐次变分模态分解,提出一种结合小波降噪和特征波形匹配延拓的谐波检测方法。首先,通过构造的自适应小波阈值函数对信号进行平滑降噪,剔除不良数据对分解结果的干扰;其次,利用特征波形匹配延拓法对信号边缘进行延拓后再裁剪,遏制边界效应带来的波形端点处畸变;最后,使用逐次变分模态分解对谐波信号进行检测,提取稳态谐波的幅频信息以及定位暂态谐波的起止时刻。仿真实验表明,本文提出的方法有效降低了噪声的干扰,并减轻边界效应造成的波形畸变。在电弧炉实例信号仿真中,幅值平均误差和频率平均误差分别为0.545%和0.146%。

环状气囊水消声器声学性能的预测与分析

水消声器作为一种有效的噪声控制装置被广泛应用于水管路系统。分别使用模态匹配法和有限元法对环状气囊水消声器的声学性能进行仿真计算,分析气囊水消声器声学特性的原理,并研究气囊水消声器不同媒介间的特性声阻抗大小关系对消声性能的影响规律。计算结果表明:由于阻抗失配关系,在气囊水消声器中气体对声波的传递起主要反射作用。随着橡胶的特性阻抗增大,橡胶会对从水中传递过来的声波起到一定的阻碍作用。当气体体积被压缩时,气体对声波的反射衰减效果会逐渐减弱,从而使得气囊水消声器的传递损失曲线整体幅值下降,消声性能减弱。

基于手机信令数据的交通方式识别模型

为解决现有研究在区分居民交通方式方面存在的问题,提出一个基于手机信令数据的居民交通方式分类模型。模型数据清洗部分采用滑动窗口方式提取3类特征训练模型,成功检测出80%以上的噪声数据;交通识别部分划分为3个二分类问题,即机动车与非机动车、步行和骑行、公交车和私家车。模型利用自主采集的信令数据,结合路网、导航数据和站点匹配算法,设计出居民交通方式分类模型。实验结果表明,与其它方法相比,公交车和私家车的分类准确率达到94%,4种分类结果的整体准确率达到了86.76%,验证了该设计的准确性和可行性。

根瘤菌和丛枝菌根真菌单双接种对不同品系大豆生长的影响

为探索丛枝菌根真菌(abuscular mycorrhiza fungi,AMF)和大豆根瘤菌单双接种效果及其与不同品系大豆的匹配性,采用蛭石混土作为基质在光照培养室(26℃,16 h光照/8 h暗期,相对湿度75%)进行盆栽试验,探究根瘤菌与AMF单接种和双接种对我国大部分区域种植的10种不同品系大豆生长的影响。结果显示,根瘤菌Bradyrhizobium japonicum USDA110和菌根真菌Rhizophagus irregularis均能侵染10种品系大豆植株,形成共生结构。单接种根瘤菌和菌根真菌均能显著提高大豆地上部鲜质量,其中单接种根瘤菌能使品系大豆119、851、921植株地上部鲜质量增加102%~429%,单接种菌根真菌也能使大部分品系大豆地上部鲜质量增加39%~255%。根瘤菌和菌根真菌双接种条件下,菌根真菌的侵染共生表现出共生定殖延迟的现象;菌根真菌存在时,品系大豆985、851、115根系的单个根瘤体积增大,固氮酶活性增强。因此,相同接种方式对不同品系大豆影响不同,相同品系大豆经过不同接种方式处理,长势存在差异;985、115品系大豆采用双接种方式最佳,167、509、921、187品系大豆采用单接种根瘤菌方式效果最佳,119、909、045则可采用单接种根瘤菌或菌根真菌来提升产量。