基于感知域测量值的自适应压缩采样方法

现有的自适应采样方法需要在采集端获得原始信号,这在实际的蒸发波导相关气象要素压缩感知过程中不易实现。针对这一问题,提出了一种以测量值数据特征为依据的采样率自适应设定方法。该方法以能量表征各信号块的重要性,以观测值能量近似估计原信号块能量,根据感知域中测量值的能量变化自适应地为各块设定采样数目。理论分析和实验表明,该方法的重构性能优于传统自适应方法,相同采样率下可获得更高的重构信噪比。     

六种木材的微波处理实验研究*

微波处理可以破坏木材的微观结构,有效提高木材的流体渗透性。为探究微波处理木材流体渗透性改善机理,同时为人工林木材的功能化改性研究提供理论依据,文章对杉木、落叶松、樟子松、毛白杨、泡桐及尾巨桉六种木材进行微波处理实验。从扫描电镜图片中可以看出,微波处理后,微波处理材会产生射线薄壁细胞之间或与轴向组织的胞间层处产生破坏、闭塞纹孔的打开、纹孔膜破坏、细胞壁破坏及内含物重新分布等变化。微观结构的破坏导致处理材力学性能下降。其中,微波处理后樟子松、杉木、落叶松、尾巨桉、毛白杨及泡桐的抗弯弹性模量(MOE)较处理前分别下降了31.1%、35.4%、45.6%、5.5%、24.4%和23.2%;抗弯强度(MOR)分别下降了38.4%、29.4%、67.2%、9.1%、34.0%和29.1%。同时,不同树种木材中不同的微观结构破坏形式造成处理材不同的吸水性测试结果。而根据微波处理材的吸水性及力学性能测试结果,可以选择适合用于微波处理后进行功能化改性处理的树种。     

Three-dimensional scan-based algorithm for directional neighbor discovery in ad hoc networks

In recent years, neighbor discovery techniques using directional antennas have attracted widespread attention. Most currently available directional neighbor discovery techniques are designed based on two-dimensional (2D) space. Although these algorithms can accomplish the discovery between nodes, the algorithm portability is poor for three-dimensional (3D) platforms, and the application scenarios are limited since new communication scenarios such as unmanned aerial vehicle (UAV) groups and maritime fleets emerge where information needs to be delivered in real time and nodes are located in 3D space. This paper proposes a new deterministic directional neighbor discovery algorithm in 3D space named 3D scan-based algorithm (3D-SBA) to meet the needs of the line-of-sight (LOS) scenes. Four existing neighbor discovery algorithms, namely, SBA-based random mode selection (SBA-R), quorum, complete random algorithm (CRA), and SBA-based leader election algorithm (LE), have been extended to our proposed 3D algorithm model for simulation and comparative analysis with 3D-SBA. The simulation results show that the 3D-SBA algorithm consumes 51.15%, 180.20%, 9.48%, and 17.49% of the time slots compared with the four existing algorithms mentioned above. However, the quorum algorithm has a very high node collision rate, up to 92.11%. Ultimately, the 3D-SBA algorithm has the best performance considering the conflicts and the density of network nodes.     

晶圆探针测试系统校准

阐述了消除探针测试系统误差的方法,通过分析校准原理和计算校准模型,提出了把已知的校准位放在校准基片上,通过修改网络分析仪(VNA)的校准位和信号接收端口,利用探针台的移动和探针与校准位的接触提取和反馈信号,修正系统误差。     

飞秒激光脉冲在大气中的色散及补偿

卫星飞秒激光测距理论上可达到亚微米量级的测距精度,但飞秒激光脉冲在大气中传输时由色散导致的脉冲展宽显著,会使测距精度下降。为补偿飞秒激光脉冲在大气中的色散需对其色散量进行定量计算。推导了飞秒激光脉冲在大气中的群速度色散和脉冲展宽公式,表明脉冲展宽程度和群速度色散及传输距离有关;中心波长相同的飞秒激光脉冲脉宽越窄色散越严重,而当脉宽相同时,中心波长越短色散越严重。计算比较了大气和BK7玻璃的群延时、群速度色散和三阶色散。卫星激光测距系统应采用中心波长较长的1 550 nm的飞秒激光脉冲,脉宽应适当选取。由于飞秒激光色散严重,提出了采用单模光纤序列进行粗补偿和采用光栅对进行精密补偿的两种补偿相结合的方式对其色散进行补偿。     

钨粉化学镀铜对压制性能的影响

通过钨粉表面化学镀铜,使其表面包覆一层均匀的诱导铜膜,以此制备W-15Cu电子封装材料。采用扫描电镜和双对数压制方程理论分析,研究钨粉表面化学镀铜含量对钨粉压制性能的影响,结果表明钨粉表面化学镀铜可改善其压制性能,且随化学镀铜含量的增加,压制同等生坯密度的制品压力增大。     

Structural and optical properties of (Al,K)-co-doped ZnO thin films deposited by a sol–gel technique

Thin films of Al-doped ZnO (AZO) and (Al, K)-co-doped ZnO (AKZO) were synthesized by sol–gel spin coating and their structural and optical properties were investigated. All the films had a preferential orientation in which the c-axis was perpendicular to the substrate. The optical bandgap increased after Al doping, but decreased after K doping at a given Al doping concentration. UV emission and a broad visible emission band were observed in photoluminescence (PL) spectra. The intensity of both emission bands decreased after Al and K co-doping. PL excitation (PLE) spectra of the blue emission band indicate that the initial state is possibly the same for all the samples and a similar case occurs for the orange–red emission band. The green emission can be attributed to electronic transitions involving oxygen vacancies. A possible process for the orange–red emission of the thin films is radiative recombination of an electron trapped in a zinc interstitial defect with a hole deeply trapped in interstitial oxygen.     

基于TSB-HMM模型的雷达高分辨距离像目标识别方法

针对雷达高分辨距离像(HRRP)的识别问题,该文提出了一种基于时域特征的截断Stick-Breaking过程隐马尔可夫模型(TSB-HMM),并建立了基于TSB-HMM模型的分层识别算法,利用TSB-HMM模型结合时域特征和功率谱特征对HRRP进行分层识别。实测数据的实验结果表明,该方法是一种有效的雷达HRRP识别方法,分层识别的算法可极大提高目标的平均识别率。特别是在训练样本数极少的情况下,TSB-HMM模型仍能获得较好的识别性能。     

双基地雷达测量定位精度分析

文中对双基地雷达的目标测量定位方法及其定位精度进行了研究，选取收发站方位同步的工作模式，在极坐标下推导出了双基地雷达目标定位时误差传递的解析解，使双基地雷达目标测量定位的误差特性有了一个准确的数学描述，并给出一组反映双(多)基地雷达定位误差特征的等误差曲线。     

非均匀微结构光纤中超连续光的产生和传输

报道了利用自行拉制的具有大空气比、小纤芯的非均匀微结构光纤同纳焦耳量级的飞秒激光脉冲相互作用的试验研究。大空气比所带来的大折射率差能将传输的光场强烈地局域在纤芯中，大大增强了非线性效应，所以在1～2cm的传输距离内，便有白光产生，传输60cm后，输入的24nm，35fs飞秒脉冲就展宽成超过一个倍频程(Octave)(390～1050nm)的超连续光谱，并且由于其包层具有非均匀分布的大小不等的空气孔，从而在传输过程中观察到由这种结构形成的非完全光子带隙影响下，侧向光泄露呈现颜色变化的新现象。