Extraction of mode attenuation coefficient from low frequency reverberation signal

A method of extracting normal mode attenuation coefficient from low frequency reverberation signal has been proposed.Pseudo-inverse normal mode filtering method is implemented to get single mode reverberation field firstly.Based on the assumption of separability of modal back-scattering matrix,effective back-scattering matrix element can be calculated using single mode average reverberation intensity.Finally,mode attenuation coefficient is extracted by comparing effective back-scattering matrix elements at different ranges.The extracted mode attenuation coefficients are used to predict sound transmission loss at the same experiment area. Results show that the predicted transmission loss agrees well with the measured data.This method avoids the difficult of treating the coupling between bottom scattering attenuation and normal mode propagation attenuation.Research on extraction of mode attenuation coefficient from low frequency reverberation signal is useful for both geoacoustic inversion and rapid underwater environment assessment.     

Auditory filter based broadband MUSIC algorithm for sound source localization

Based on the analysis of the shortcomings of broadband MUSIC algorithm with short-time Fourier transform （SF-MUSIC） for sound source localization, a broadband MUSIC algorithm with auditory filter （AF-MUSIC） was proposed. The proposed algorithm first em- ploys auditory filter bank to decompose the signals received on the microphone array, and then locates the sound source with MUSIC algorithm over every frequency channel. At last, by combining with the subinterval frequency estimation, the final localization result is gained. Evaluations on the proposed algorithm prove that comparing with the SF-MUSIC algorithm, the AF-MUSIC algorithm decreases the average error of the estimation results with 2.5479 de- gree in different source conditions. The accuracy of sound source DOA estimation is enhanced effectively.     

非线性囚禁离子模型中振幅平方压缩效应

本文从非线性Jaynes-Cummings模型出发,研究了受驻波场驱动的离子的质心运动振幅平方压缩效应.结果表明,非线性参数η对压缩效应有明显的影响.随着参数η的增大,离子处于压缩态的时间增长,压缩程度加深,但当η越过某一临界值时,离子最大压缩量减小,压缩时间相对变短;另外,驻波场的相位也对压缩效应有明显的影响.     

基于动平台多源数据的运动目标测量方法研究

根据运动目标性能试验需求及试验平台的特点,建立一个影像数据测量系统,实现目标的运动视频记录和外部参数测量。采用基于OpenCV的棋盘格内参数标定结合基于平台上固定标识点、线为基准的外场标定的摄像机标定方法,采用高速影像数据、中线视频数据和GPS数据相结合的方法实现目标运动的轨迹、姿态等参数的测量。通过测量精度分析及多次试验结果证明,测量精度达到水平方向优于10 cm,高程方向优于5 cm,姿态精度优于05。     

直视型微光夜视系统最小可分辨对比度模型

从信号检测和人眼视觉角度出发,研究了直视微光夜视系统综合性能评估理论,推导出直视型微光成像系统的MRC（最小可分辨对比度）模型。该模型将光学传递特性与系统信噪比结合,建立了系统直视微光夜视MRC与目标特性、直视微光夜视仪以及人眼各部分参数之间的数学关系。验证结果表明,由该模型得到的系统极限分辨率相较于系统实际测出的分辨率相对误差为3.08%。     

中波红外3 μm～5 μm宽带通滤光片的研制

 中波红外宽带通滤光膜通常膜系层数多,膜层总厚度非常大（厚度达到10 μm左右）,膜层的镀制工艺难度较大。通过分析红外带通滤光片几种设计方法的特点,并结合实际镀制工艺技术,采用了长波通与短波通及非规整薄膜设计技术相结合的方法,设计了以锗材料为基底的中波3 μm～５ μm宽带通滤光膜。该设计大幅度降低了膜层的总厚度（约为8.65 μm）,缩短了膜层的镀制周期,提高了膜层的牢固度;在膜层的镀制工艺过程中,通过改变薄膜材料的蒸发速率、修正蒸发硫化锌材料时电子枪的扫描方式、调整蒸发材料在坩埚中的装载方法,使膜层获得了优异的光谱性能,其通带平均透过率大于96%,截止区域的平均透过率小于1%。     

利用低相干光纤动态光散射法测量浓悬浮液中多分散颗粒粒径分布

本文针对高浓度散射介质,用低相干光纤动态光散射技术测量浓悬浮液中多分散颗粒系的粒径及其粒径分布。利用迭代CONTIN算法对实验数据进行反演运算,得到多分散颗粒系的粒径分布结果。结果表明,浓悬浮液中多分散颗粒系的峰值粒径测量值与给定的两种标准粒径值相吻合,其误差在4%之内,粒径分布曲线中各散射颗粒所反映的散射体光强分布与根据Mie散射计算得到的理论值相吻合。实验结果证明低相干光纤动态光散射实验系统能准确测量浓悬浮液中多分散颗粒粒径及粒径分布。     

Imprints of molecular orbitals using photoelectron angular distribution by strong laser pulses of circular polarization

We theoretically investigate the strong-field ionization of H+2 molecules in four different electronic states by calculating photoelectron angular distributions in circularly polarized fields. We find that the structure of photoelectron angular distribution depends on the molecular orbital as well as the energy of the photoelectron. The location of main lobes changes with the symmetric property of the molecular orbital. Generally, for molecules with bonding electronic states, the photoelectron's angular distribution shows a rotation of π/2 with respect to the molecular axis, while for molecules with antibonding electronic states, no rotation occurs. We use an interference scenario to interpret these phenomena. We also find that, due to the interference effect, a new pair of jets appears in the waist of the main lobes, and the main lobes or jets of the photoelectron's angular distribution are split into two parts if the photoelectron energy is sufficiently high.     

6H-SiC衬底上AlGaN基垂直结构紫外LED的制备

利用金属有机物化学气相沉积方法,在n型6H-SiC衬底上制备了15对Si掺杂Al_(0.19)Ga_(0.81)N/Al_(0.37)Ga_(0.63)N DBR,并采用低温AlN缓冲层有效抑制了DBR结构中裂纹的产生,得到了表面均方根粗糙度仅为0.4 nm且导电性能良好的n型DBR,其在369 nm处峰值反射率为68%,阻带宽度为10 nm。在获得导电DBR的基础上,进一步在n型6H-SiC衬底上构建了有、无DBR的垂直结构紫外LED。对比两者电致发光光谱,发现DBR结构的引入有效增强了LED紫外发光强度。     

GaN基HEMT器件的缺陷研究综述

GaN基高电子迁移率晶体管(HEMT)因具有高输出功率密度、高工作频率、高工作温度等优良特性,在高频大功率等领域具有广泛应用前景。目前,HEMT器件在材料生长和工艺制备方面都取得了巨大的进步。但是,由缺陷产生的陷阱效应一直是限制其发展的重要原因。本文首先论述了HEMT器件中的表面态、界面缺陷和体缺陷所在位置及其产生的原因。然后,阐述了由陷阱效应引起的器件电流崩塌、栅延迟、漏延迟、Kink效应等现象,从器件结构设计和工艺设计角度,总结提出了改善缺陷相关问题的主要措施,其中着重总结了器件盖帽层、表面处理、钝化层和场板结构4个方面的最新研究进展。最后,探索了GaN基HEMT器件在缺陷相关问题上的未来优化方向。