一种基于序贯估计的直达声区水面舰船 被动测距方法 *

该文利用基于射线的盲解卷积方法，从直达声区的水面舰船噪声中提取出船和锚系于海底的垂直接收阵之间的时域信道响应，并利用直达波在不同阵元相对于参考阵元的到达时间差，通过序贯方法，利用射线模型和声速剖面信息，对水面舰船距接收阵的距离进行了估计。通过处理海深约为580 m的2016年美国圣巴巴拉海峡的实验数据，对1.6~3.5 km直达声区范围内Anna Maersk商船与垂直阵之间的距离进行了估计，验证了测距方法的有效性，并将结果与系统测量值和几何方法的估计值进行了比较。由于该方法不需要对海底参数进行估计，所以在海底参数未知时要优于传统匹配场方法；在声速剖面存在跃层且海底为多层分布的复杂信道条件下，该方法仍能对距离进行有效估计，且与测量值的相对误差在6%以内，小于几何方法的估计误差，测距结果精度较高。     

Three-level all-fiber laser at 915 nm based on polarization-maintaining Nd^3+-doped silica fiber

Nd3+-doped fiber lasers at around 900 nm based on the 4F3/2→4I9/2 transition have obtained much research attention since they can be used as the laser sources for generating pure blue fiber lasers through the frequency doubling.Here,an all-fiber laser at 915 nm was realized by polarization-maintaining Nd3+-doped silica fiber.A net gain per unit length of up to 1.0 dB/cm at 915 nm was obtained from a 4.5 cm fiber,which to our best knowledge is the highest gain coefficient reported in this kind of silica fiber.The optical-to-optical conversion efficiency varies with the active fiber length and the reflectivity of the output fiber Bragg grating(FBG),presenting an optimal value of 5.3%at 5.1 cm fiber length and 70%reflectivity of the low reflection FBG.Additionally,the linear distributed Bragg reflector short cavity was constructed to explore its potential in realizing single-frequency 915 nm fiber laser.The measurement result of longitudinal-mode properties shows it is still multi-longitudinal mode laser operation with 40 mm laser cavity.These results indicate that the Nd3+-doped silica fiber could be used to realize all-fiber laser at 915 nm,which presents potential to be the seed source of high-power fiber laser.     

In-situ SiN combined with etch-stop barrier structure for high-frequency AlGaN/GaN HEMT

The etch-stop structure including the in-situ SiN and AlGaN/GaN barrier is proposed for high frequency applications.The etch-stop process is realized by placing an in-situ SiN layer on the top of the thin AlGaN barrier.F-based etching can be self-terminated after removing SiN,leaving the AlGaN barrier in the gate region.With this in-situ SiN and thin barrier etch-stop structure,the short channel effect can be suppressed,meanwhile achieving highly precisely controlled and low damage etching process.The device shows a maximum drain current of 1022 mA/mm,a peak transconductance of 459 mS/mm,and a maximum oscillation frequency(fmax)of 248 GHz.     

QEPAS系统中石英音叉模态仿真计算与研究

对石英音叉增强型光声光谱(QEPAS)系统中常用的石英音叉进行了有限元模态计算，获得石英音叉前6阶振型与模态频率，认知了第4阶对称摆动振型为有效振动，利用单因素法分析了石英音叉的音臂长度l₁、音臂宽度w₁、音臂厚度t、音臂切角θ、音臂圆孔直径d及音臂圆孔高度h对低阶有效共振频率(Fre)的影响，敏感度依次为： l₁> w₁>d>θ>t>h，考虑实际设计情形，筛选出了l₁，w₁，d与h四个石英音叉设计变量，采用Box-Behnken实验设计方案与RSM(response surface methodology)方法，以Fre为函数目标，建立l₁，w₁，d与h的二次回归响应面模型，得到了参数之间的交互作用，利用Design-Expert软件对响应面模型进行设计参数反求，结果表明，在15 000 Hz≤Fre≤25 000 Hz计算区域内误差较小，基本满足QEPAS系统的计算需求，所提出的研究与设计方法具有一定通用性，可为QEPAS系统中石英音叉结构参数设计提供参考。     

纯奇点范畴中的Buchweitz定理

我们定义纯奇点范畴D_(psg)~b(R)为有界纯导出范畴D_(pur)~b(R)与纯投射模构成的有界同伦范畴K~b(■)的Verdier商,得到了纯奇点范畴D_(psg)~b(R)三角等价于相对纯投射模的Gorenstein范畴的稳定范畴■的一个充分必要条件.同时,还给出三角等价D_(psg)~b(R)≌D_(psg)~b(S)的充分条件,这里R和S都是环.     

蓖麻油交联改性对室温自愈合聚氨酯性能的影响

以蓖麻油(CTO)或三羟甲基丙烷(TMP)作为交联剂,合成了一系列自愈合聚氨酯弹性体(PU)。借助核磁共振仪和红外光谱仪分析了产物结构,通过电子拉力试验机研究了交联剂添加量对PU的力学性能以及自愈合性能的影响。结果表明:CTO和TMP均能提高PU的拉伸强度,但是断裂伸长率会降低。随着交联剂用量的增加,PU内部交联度提升,自愈合性能下降。当PPG与TMP的物质的量之比为6∶4时,自愈合能力消失。在交联剂用量相同的情况下,CTO交联PU的自愈合性能保留效果比TMP交联PU更好。随着CTO用量的增加,断裂后愈合PU的拉伸强度先增加后减小。当聚丙二醇(PPG)与CTO的物质的量之比为7∶3时,总体性能最佳,在提高样品拉伸强度的同时,其自愈合后的拉伸强度恢复率为80.95%。     

解析Sobolev型空间上的算子与算子代数

介绍Hardy-Sobolev空间和Fock空间及其算子与算子代数研究方面所做的工作,包括对这两类空间上几类特殊算子有界性、紧性、Fredholm性、指标理论、谱和本性谱、范数和本性范数、Schatten-p类的讨论,以及由它们所生成的C~*-代数的研究.