正弦振动对航空相机成像影响的分析与验证

航空相机拍照时,由于受到振动影响成像分辨率会降低。采用动态调制传递函数研究正弦振动对成像的影响,通过基于空间域的计算方法对高频和低频振动的调制传递函数(MTF)进行了分析,指出了曝光时间不等于振动周期整数倍的一般情况时,高频振动对成像质量的影响也具有随机性,但没有低频振动的随机性明显。采用快速反射镜作为振动源进行成像实验,对获得的振动图像使用小波变换提取图像的高频信息。实验中将曝光时间设定为20ms,振动频率为50Hz时,高频信息波动范围仅为0.0582×104,可以认为基本没有波动。当振动频率为15Hz时,波动范围为0.6233×104,随机性很明显,而振动频率为65Hz时,波动范围为0.1245×104,随机性不明显。通过高频信息与MTF的对应关系,实验证明了理论分析的正确性。在理论分析和实验的基础上,总结了正弦振动对成像影响的普遍性结论。该结论可用于分析成像系统光机结构设计,也可应用于图像去模糊,具有一定的意义。     

树型结构半导体光放大器光交换矩阵的可靠性(英文)

针对光交换系统的可靠性研究已卓有成效,但作为光交换系统的核心元件——光交换矩阵的可靠性却始终没有得到足够的重视.本文利用可靠性框图对基于半导体光放大器的树型结构光交换矩阵进行了可用性分析.分析结果表明该型光交换矩阵在可靠性上存在的不足,需要设计保护结构.通过对已有的光交换系统可靠性研究工作的分析总结,提出了两种针对树型结构光交换矩阵的保护结构,并利用可靠性框图和概率统计方法对其进行比较分析了两种结构的特点.研究表明,交换矩阵对于SOA的可靠性最为敏感.交换矩阵保护结构的设计过程,实际上是系统可靠性、成本、体积及性能的折衷.因其对成本和可靠性的影响,能否提供有效的检测和维护也应在保护结构的设计过程中予以考虑.     

Effects of Annealing on Schottky Characteristics in A1GaN/GaN HEMT with Transparent Gate Electrode

A1GaN/GaN heterostructure transistors are promising for power and switching applications. In addition, the transparent wide band-gap A1GaN/GaN heterostructure systems have received considerable attention to transparent electronics. Nowdays, Al-doped ZnO （AZO） thin film plays an increas- ingly important role in various fields of transparent electronics.The AZO-gated A1GaN/GaN HEMT with good dc characteristics and frequency character- istics has been reported. Annealing is widely used to improve the electri- cal characteristics of A1GaN/GaN HEMTs. It is re- ported that the Schottky leakage current can be re- duced by over four orders of magnitude by annealing in an A1GaN/GaN heterostructure with ITO/Ni/Au electrode. Pei et al. reported that the transparency of Ni/ITO gates of A1GaN/GaN HEMTs has been sig- nificantly improved after annealing. However, the evaluation of Schottky C V characteristics was ab- sent. Up to now, few results are reported on the Schot- tky annealing characteristics of AZO in A1GaN/GaN HEMT. Thus the effects of annealing on the leakage current, transparency and interface states character- istics need further study.     

非常温溶液除湿自主再生空调系统性能分析

提出一种新型的将溶液除湿与热泵相结合的温湿度独立处理空调系统,该系统使用低温、低浓度的除湿溶液,在任何工况下冷凝热都能满足溶液再生的需求。建立了整个系统的数学模型,研究系统自身参数变化(溶液温度、浓度)和环境参数变化(空气温度、湿度)对系统性能的影响;并对系统应对高温、高湿度环境的调整方法进行了分析。结果表明,在夏季典型工况下,除湿溶液的理想温度为17~19℃、相应的质量浓度为25.39%~26.88%;系统具有较高的能效,并且能够在高温潮湿地区发挥其节能潜力。     

Positron-Lithium Atom and Electron-Lithium Atom Scattering Systems at Intermediate and High Energies

The coupled-channel optical method is used to study positron scattering by atomic lithium at energies ranging from the ionization threshold to 60eV, The present method simultaneously treats the target channels and the positronium （Ps） channels in the coupled-channel method together with the continuum effects via an ab-initio optical potential. Ionization, elastic and inelastic cross sections in target channels, and the total cross section are also reported and compared with other theoretical and experimental data. A comparative study with the corresponding electron-lithium data is also reported.     

Neural Signal Tuned by Random Long-range Connections in Coupled FitzHugh-Nagumo Neurons Systems

We investigate the effect of random long-range connections on signal propagation in an array of coupled FitzHugh- Nagumo （FHN） neurons. The neural network can be obtained by randomly adding a small fraction of shortcuts in an originally locally coupled one-dimensional chain. It is shown that when the first neuron is subjected to external stimuli, it fires and excites its connected neighbours, such that the neural signal may propagate along the chain favoured by the shortcuts. Moreover, there exists an optimal number of shortcuts which can lead to the most synchronous behaviour. In addition, how the region of the fraction of shortcuts varies with the coupling strength is also discussed. These results suggest that topological disorder in the neural network may play a vital role in helping information processing in living systems.     

Optimization of a Cryogenic System at Temperature 2 K for the PKU-FEL Facility

The conceptual design of a cryogenic system at temperature 2 K for the Peking University Free Electron Laser （PKU-FEL） facility is carried out. In order to minimize the scale of the cryogenic system and the running cost, the superconducting accelerator and the superconducting injector will mainly run at a long-pulsed mode. Optimization of the 2-K cryogenic system is carried out based on the heat load estimation and running parameters. Total cooling power of 52.5 W for the long-pulsed mode is necessary for the PKU cryogenic system. The PKU cryogenic system will be the first 2-K system for accelerators in China and will provide experience for similar facilities.     

On the linearization of the coupled Harry－Dym soliton hierarchy

This paper is devoted to the study of the underlying linearities of the coupled Harry--Dym (cHD) soliton hierarchy, including the well-known cHD equation. Resorting to the nonlinearization of Lax pairs, a family of finite-dimensional Hamiltonian systems associated with soliton equations are presented, constituting the decomposition of the cHD soliton hierarchy. After suitably introducing the Abel--Jacobi coordinates on a Riemann surface, the cHD soliton hierarchy can be ultimately reduced to linear superpositions, expressed by the Abel--Jacobi variables.     

空地激光通信系统中捕获子系统仿真

针对空地激光通信系统,推导了复合光栅螺旋扫描捕获方法所需的最大捕获时间、平均捕获时间和捕获概率的计算公式,建立了捕获性能仿真模型,分析了捕获时间和捕获概率的关系,以及空中平台的相对速度对捕获系统的影响和抑制方法.仿真结果表明,当通信终端的捕获不确定区域为50mrad,扫描重叠因子为0.12时,捕获探测器的信噪比大于6时,空地激光通信系统总的捕获概率优于95%,最大捕获时间约为36s,平均捕获时间约为12s.