Irregular and regular LDPC codes with high spectrum efficiency modulation in image transmission over fading channel

If the degree distribution is chosen carefully, the irregular low-density parity-check (LDPC) codes can outperform the regular ones. An image transmission system is proposed by combining regular and irregular LDPC codes with 16QAM/64QAM modulation to improve both efficiency and reliability. Simulaton results show that LDPC codes are good coding schemes over fading channel in image communication with lower system complexity. More over, irregular codes can obtain a code gain of about 0.7 dB compared with regular ones when BER is 10 -4. So the irregular LDPC codes are more suitable for image transmission than the regular codes.

SAR tomography imaging via higher-order spectrum analysis

To deal with the non-Caussian noise in standard 2-D SAR images, the deramped signal in imaging plane, and the possible symmetric distribution of complex noise, the fourth-order cumulant of complex process is introduced into SAR tomography. With the estimated AR parameters of ARMA model of noise through Yule-Walker equation, the signal series of height is pre-filtered. Then, through ESPRIT, the spectrum is obtained and the aperture in height direction is synthesized. Finally, the SAR tomography imaging of scene is achieved. The results of processing on signal with non-Gaussian noise demonstrate the robustness of the proposed method. The tomography imaging of the scenes shows that the higher-order spectrum analysis is feasible in the application.

Speciflc Heat-Phonon Spectrum Inversion Problem of High T_c Superconductor

The phonon density of states of YBa2Cu3O6.92 is obtained with the method of Fourier decon-volution and Tikhonov-s regularization technique from the experimental specific heat data. The result is compared with that of neutron inelastic scattering.

Influence of the initial electronic state on minima of high-order harmonic spectrum radiated from hydrogen molecular ion

We theoretically investigate the high-order harmonic generation of the one-dimensional hydrogen molecular ion at fixed intermediate internuclear distance, driven by a multicycle laser field. Our results show that the initial electronic state of the hydrogen molecular ion affects the modulation of the high-order harmonic spectrum, especially the positions of the minima. Based on the two-state model, the underlying physical mechanism of the minimum is analyzed and discussed. Further analysis shows that the different positions of the minima in the different initial electronic states can be understood via the different interferences of the two phase-adiabatic states at the ionization times.

High efficiency spreading spectrum modulation using double orthogonal complex sequences

This paper presents a novel scheme of high efficiency spreading spectrum modulation using double orthogonal complex sequences(DoCS).In this scheme,input data bit-stream is split into many groups with length M.Each group is then mapped into a word of width M and then utilized to select one sequence from 2M-2 DoCS sequences each with length L.After that,the selected sequence is modulated on carrier in quadrature phase shift keying(QPSK) mode.In addition,a new method named forward phase correction(FPC) is put forward for carrier recovery.Theoretical analysis and bit-error-ratio(BER) experiment results indicate that the proposed scheme has better performance than the conventional direct sequence spread spectrum(DSSS) scheme both in bandwidth efficiency and processing gain of the receiver.

Analysis of external noise spectrum of high-speed railway

A schematic to make the spectra of the exterior noise of high speed railway was put forward. The exterior noise spectrum was defined based on the characteristics of the high-speed train exterior noise. Its characteristics considered here include identifying the exterior main sources and their locations, their frequency components including the Doppler effect due to the noise sources moving at high speed, the sound field intensity around the train in high-speed operation, the sound radiation path out of the train, and the pressure level and frequency components of the noise at the measuring points specified by the International Organization for Standardization(ISO). The characteristics of the high-speed train exterior noise of the high speed railways in operation were introduced. The advanced measuring systems and their principles for clearly indentifying the exterior noise sources were discussed in detail. Based on the concerned noise results measured at sites, a prediction model was developed to calculate the sound level and the characteristics of the exterior noise at any point where it is difficult to measure and to help to make the exterior noise spectrums. This model was also verified with the test results. The verification shows that there is a good agreement between the theoretical and experimental results.

On The Hardening of The Spectrum of High-Energy Particles Formed in Heavy-Ion Collisions Considered within The Framework of The Hydrodynamic Approach

The emission of high-energy particles in 16O + 197Au collisions at energy 20 MeV / nucleon is considered within the framework of the time evolution of a hot spot taking into account the hydrodynamic compression and expansion stages. In addition, the evaporation of the particles that are formed in the early (hot) stage of the evolution of the hot spot is included in the calculation of the spectrum. This leads to a hardening of the particle spectrum in its high-energy part, which is in agreement with experimental data.

宽带无线通信系统环境的电磁处理体系与方法

围绕系统性电磁处理,分析了近年来相关研究工作和进展,提出了基于辐射端点连接面为基准的电磁处理网络架构和基站终端多维辐射体等效辐射模型,以及面向正向电磁利用、反向电磁抑制的电磁互作用分析技术和面向空中电磁特性控制的测试技术等。仿真和测试表明,所提出的多频组网电磁频谱规划突破了多频带及大带宽难题,提高了频谱利用率和复杂环境的主动电磁调控能力;所提出的基本模型及计算方法,突破了受限空间中高效电磁计算预测以及电路天线一体化难点;室外场景重构测试建模提升了精准重现及多场景辐射一致性评估水平。16双极化探头均匀分布、支持4×4的多探头方法被3GPP 5G标准TR 38.827正式采纳。

轴承转子系统快变过程振动响应的高精度频谱分析

针对高速轴承转子系统的启停过程,研究平稳和非平稳信号的高精度频谱分析方法,利用比例校正法对平稳信号频谱分析后的频率、幅值、相位进行了校正,建立一种将t时空域非平稳信号转变为t~2时空域平稳信号的方法,并基于平稳信号的比例校正法对其进行频谱分析,最后返回到t时空域获得某时刻的频域参数。仿真分析结果表明:该方法可以准确提取平稳信号的谱特征,也能较精确地提取非平稳信号特定时刻的频率、幅值和相位,提取结果精度较好,有效解决轴承转子系统快变过程的谱分析特征提取问题,为动力学特性分析提供了新思路。

深空探测超宽光谱定标黑体源研制

针对深空探测超宽光谱定标黑体源的关键技术问题,构建了一种基于优化微结构和纳米超黑涂层的深空探测星上黑体定标源。基于有限元方法仿真,验证了微锥结构不同宽高比与黑体发射率间的对应关系,确定了周期性线阵V槽结构相对于平面结构在黑体发射率方面的提升作用。优化星上黑体源高发射率微结构,优选空间超黑高发射涂层,设计星上黑体源高精度测温系统,进而完成黑体源工程设计。最后,通过星上黑体源发射率计量及实验室辐射定标稳定性测试进行验证。检测结果表明,深空探测超宽光谱定标黑体源具有超宽光谱范围、高发射率、高温度稳定性等特点,其光谱范围为5~50μm,法向平均发射率为0.986,温度稳定性达到0.16 K。该定标黑体源可大幅提升高发射率辐射定标源的光谱范围,为深空探测载荷的在轨高精度星上辐射定标提供支撑。

基于深度张量投影网络的机械故障诊断方法研究

针对现有的、基于深度卷积神经网络的故障诊断方法利用池化层对高阶输入张量降维时容易破坏张量数据,造成数据信息丢失,以及网络结构相对复杂的不足,构造了一种深度张量投影网络。该网络利用张量投影层代替传统卷积神经网络中的池化层,在对输入的高阶张量数据进行降维时,不会对张量数据造成破坏,避免了特征信息的丢失,提高了模型对故障的识别准确率;并且张量投影层是一种维度可变的降维层,可以简化网络结构。在此基础上,结合高阶谱和深度张量投影网络各自的优点,提出了基于深度张量投影网络的机械故障诊断方法。在提出的方法中,利用高阶谱提取故障信号特征,将得到的高阶张量谱图输入到构建的深度张量投影网络模型中进行高阶张量降维和识别。提出的方法成功应用到齿轮箱故障诊断中。实验结果表明,所提方法能够更好地保留原始故障信息,有效识别不同类型的故障,准确率优于传统深度卷积神经网络故障诊断方法。

高频率分辨的金刚石氮-空位色心宽频谱成像技术

高分辨率宽频谱测量技术在天文学、无线通信、医学成像等领域具有重要应用价值.金刚石氮-空位(nitrogen-vacancy,NV)色心因其高稳定性、高灵敏度、实时监测、单点探测以及适用于长时间测量等特性已成为频谱分析仪备受关注的选择.目前,基于NV色心作为探测器的宽频谱分析仪能够在几十GHz频带内进行实时频谱分析,然而其频率分辨率仅达到MHz水平.本文通过搭建结合连续外差技术的量子金刚石微波频谱成像系统,利用磁场梯度对NV色心谐振频率进行空间编码,成功获取了900 MHz—6.0 GHz范围内完整的频谱数据.在可测频谱范围内,系统进一步采用连续外差的方法,同时施加谐振微波和轻微失谐的辅助微波对NV色心进行有效激发,增强了NV磁强计对微弱微波信号的响应.该方法使系统在可测频谱范围内实现了1 Hz的频率分辨率,并能够对间隔为1 MHz扫频步进的多个频点的频率分辨率进行单独测量.以上研究结果表明基于NV色心的宽频谱测量可实现Hz级频率分辨,为未来的频谱分析和应用提供了有力的技术支持.

基于近红外光谱技术的水稻节间主要碳氮代谢组分分析

近年来,近红外光谱技术在作物样品组分检测和育种材料快速筛选等方面得到广泛应用,而关于水稻源库器官,尤其是水稻节间主要碳氮代谢组分高通量检测的研究鲜见报道。本研究以试验获得的576份代表性节间样本为材料,在获得样本化学实测值的基础上,采集样本的近红外光谱信息,并利用偏最小二乘(partial least square,PLS)法构建水稻节间主要碳氮代谢组分蔗糖、淀粉、总氮模型。模型验证结果显示:水稻节间蔗糖、淀粉、总氮含量PLS模型验证集决定系数分别为0.988、0.977和0.957,相对分析误差均大于3,模型的性能指数分别为85.20、85.80和86.50,表明所建模型预测结果准确可靠。此外,水稻叶片和叶鞘的淀粉、总氮含量和碳氮比的PLS模型也具有较高的精度。本研究构建了水稻节间主要碳氮代谢组分的近红外光谱模型,为水稻栽培生理和高产栽培理论研究提供了技术支撑。

燃煤锅炉温度场与高温腐蚀气氛场同步在线检测装置开发及应用

燃煤锅炉主燃区燃烧场的经济性、安全性和环保性对于智慧电厂建设具有重要意义。其中,水冷壁近壁面高温腐蚀H_(2)S和CO气体浓度的实时在线监测尤为重要。为实现燃煤锅炉主燃区温度场和高温腐蚀气氛场的同步测量,基于红外热成像原理,采用Optris-PI1M小型红外热成像仪,基于LabVIEW温度实时采集应用软件,在炉膛的观察口对主燃区温度场进行连续监测。以低成本1.5μm附近的通信波段激光器作为测量高温腐蚀气体H_(2)S和CO的激光光源,并结合波长调制光谱技术和频分复用技术,以实现H_(2)S和CO气体浓度的同步检测。线性度实验表明,其线性拟合相关系数为0.9995。将研制的同步检测仪器对某300 MW四角切圆燃煤锅炉的主燃区的温度场和气氛场进行了现场应用试验。现场测试结果表明,锅炉主燃区温度主要分布范围在1300~1400℃,最高温度达到了1500℃;同时得到了锅炉主燃区的H_(2)S和CO浓度分布,H_(2)S浓度在12~125 mg/m^(3)的范围内波动,而CO浓度主要分布在10%~20%之间,最高可达22%;炉内H_(2)S和CO的浓度呈正相关,氧气浓度保持在1%以下,由于厌氧燃烧会导致两种气体的含量增加,从而造成对水冷壁近壁面的高温腐蚀。

1μm/1.5μm基于非互易性相移器的高重频飞秒光纤激光器

高重频的飞秒脉冲激光器在工业加工、医疗、精密测量等各个领域都有着重要应用。为了分析“9”字腔锁模激光器的自启动性能,利用琼斯矩阵建立了非线性放大环形镜的传输函数,分析了环形镜中不同波片角度对腔内往返传输函数的影响。搭建了基于非线性放大环形镜的光纤激光器,分别使用了掺镱光纤、掺铒光纤作为增益介质,在1μm和1.5μm波段分别实现了重复频率为600 MHz和280 MHz的基频锁模。所设计的激光器具有脉宽窄、光谱宽、稳定性好、自启动成功率高的特点,激光器完成了集成化封装,能够满足微纳加工、激光医疗、光频率梳等领域对飞秒激光的应用需求。

不同轨道不平顺激励下线形关键点处列车走行性分析

为探究不同轨道不平顺激励下,列车以更高速度经过缓圆点(HY)、曲中点(QZ)和圆缓点(YH)时,曲线超高、平面圆曲线半径及缓和曲线长度与列车速度之间的匹配关系,以中国某高速动车组为原型,建立了具有50个自由度的车-线动力学分析模型.研究结果表明,中国无砟轨道谱和德国低干扰谱对于列车在道路线形关键点处的动力响应随列车行驶速度和平面线形参数变化的趋势大致相同,但各关键点之间的响应程度不同;超高和圆曲线半径的变化对于列车动力响应的影响程度较缓和曲线长度大.研究结果可为高铁列车更高速度运行时的线路设计及线路平面参数之间的匹配关系提供一定的理论参考.

高铁地震波场的高精度密集观测及应用前景:基于通讯光缆的观测和处理结果

利用高清分布式光纤声波传感(HD-DAS)系统,进行高铁地震波场的高精度分布式采集。传感单元采用结构简单、成本低廉的通信光缆即可实现很好的监测效果,可以方便地根据实际环境进行布设,大大提高了野外观测的效率。采用多光缆并行布放,信号叠加后可有效地抑制噪声,提高高铁地震信号的信噪比。对HD-DAS系统采集到的高铁地震信号进行数据分析,发现高铁地震信号呈现分立谱特性。通过分析地震波信号的衰减规律,并通过频率-波数谱得到地震波在近地表的传输速度,表明光纤采集的高铁地震波信号可用于探测地下结构,并进一步实现对介质状态变化的监测,从而保障高铁的运行安全。

基于轨道阱高分辨质谱联用技术建立食品中罂粟壳生物碱的快速筛查方法

本文采用超高效液相色谱-四极杆/轨道阱高分辨质谱法,建立食品中5种罂粟壳生物碱的快速筛查方法,同时建立质谱数据库,摆脱标准品依赖,实现高通量筛查。食品中5种罂粟壳生物碱采用优化后的前处理方法进行提取,HILIC色谱柱实现分离,采用全扫描自动触发二级扫描模式(Full MS/dd MS^(2))对吗啡、可待因、罂粟碱、那可丁和蒂巴因进行检测。方法线性范围1~100 ng/mL,相关系数大于0.99,检出限0.1~0.5μg/kg,回收率69.9%~118.7%,相对标准偏差3.2%~15.4%。方法前处理简便、检测灵敏度高、重现性好,可用于食品中罂粟壳生物碱的快速筛查。

基于微纳光纤谐振环的温度传感器研究

该项工作制作并验证了基于微纳光纤结型谐振环的高灵敏度且扩大测量范围的温度传感器。在微纳光纤谐振环中产生多个模式并参与谐振,多个模式谐振的光谱相互叠加,形成带包络的游标光谱。通过提取游标光谱的包络线,实现高灵敏度的温度测量,灵敏度高达-10 nm/℃。但计算得到利用游标光谱时的温度测量范围仅约为4℃。为解决测量范围过小的问题,将包络光谱与单一频率组分对应的谐振光谱相结合,使测量范围扩大至约20℃。相比于单一频率组分对应的谐振光谱,利用游标包络光谱实现了灵敏度约1600倍的放大。该方案利用游标效应提高温度测量灵敏度的同时,利用单一频率组分对应的谐振光谱扩大了游标光谱的温度测量范围,提高了传感器的性能和实用性。

无轴泵喷叶片流激共振产生机理及其抑制

针对无轴泵喷异常高频梳状线谱噪声,本文研究了梳状线谱的产生原因及其噪声抑制特点。基于推进器实测噪声谱、振动谱梳状特征,初步定位梳状线谱与泵喷叶轮密切相关;进一步采用单向流固耦合分析方法,验证了无轴泵喷高频线谱来源于流激引起的叶轮面内2弯模态共振,并提出了一种在叶轮过流通道增设环筋以提高叶片支撑刚度的方案。流固耦合仿真及实测结果表明:带有环筋加强的泵喷叶轮对流激振动与噪声有明显抑制作用,梳状线谱噪声降幅达25.2~30.2 dB,且未向其他频段转移。