遥感相机自动检焦技术研究

将基于图像处理的自动检焦技术应用于线阵CCD推扫成像的空间遥感相机中。图像法检焦的关键在于对焦评价函数的选取。通常对焦评价函数是在摄影目标不变的情况下得出的,而推扫成像的线阵CCD相机在任意时刻所拍摄的景物都是不同的,这就给对焦评价函数的选取增加了难度。用功率谱的方法对任意景物在空间频域进行分析表明,功率谱对于自然景物具有一定的不变性。由此建立了基于功率谱的对焦评价函数,采用小波去噪与亮度归一化相结合的图像预处理技术有效地去除了图像噪声和亮度变化对对焦精度的影响。通过对功率谱评价函数进行加权处理,提高了对焦评价函数曲线的灵敏度。仿真实验表明了所构造的对焦评价函数是可行的。     

可调谐相对论磁控管的实验研究

实验研究了高有载品质因数下有无阳极端帽时调谐性能的差异,以及低有载品质因数下,没有阳极端帽时的可调谐相对论磁控管性能。研究结果表明：没有阳极端帽时,可调谐相对论磁控管具有更宽的调谐范围;在高有载品质因数下,可以达到2.52～3.31 GHz的调谐范围,输出功率范围为44～790 MW;低有载品质因数下,调谐范围为2.55～3.05 GHZ,调谐范围内输出功率1～1.7 GW。     

Dual-band frequency selective surface with quasi-elliptic bandpass response

Based on the substrate integrated waveguide technology,we present a dual-band frequency selective surface(FSS) with a quasi-elliptic bandpass response.The characteristics of the quasi-elliptic bandpass response are realized by shunting two substrate integrated waveguide cavities of different sizes,with the same slots on both sides of the metal surfaces.Four cavities of different sizes and two slots of different sizes are used to design the novel FSS.Every bandpass response with sharp sidebands is induced by two transmission nulls that are generated by the coupling between the slot aperture resonance and the cavity resonance.The simulation results show that such dual-band FSS has the advantages of high selectivity and stable performance at different oblique incident angles.Moreover,it is easy to fabricate.     

高压换流站交流滤波器组相干噪声源声功率反演

针对高压换流站内交流滤波器组相干噪声源的声功率难以确定的问题,该文提出了一种基于几何声学理论的声功率反演方法。该方法采用可同时考虑噪声源强度和相位的几何声学理论建立相干声场模型,在此基础上构建声功率反演模型,通过寻找使声学模型输出和实测数据差异最小的声源参数(强度和相位),实现了对相干噪声源声功率的反演。数值仿真和实验数据验证了该方法的有效性。     

非对称结构大功率940 nm量子阱激光器

为改善940 nm大功率InGaAs/GaAs半导体激光器输出特性,通过模拟计算了非对称波导层及限制层结构的光场分布,并参照模拟制作了非对称结构半导体激光器器件。采用低压金属有机物气相沉积（LP-MOCVD）生长技术,获得了低内吸收系数的高质量外延材料,通过实验数据计算得到激光器材料内吸收系数仅为0.44 mm-1。进而通过管芯工艺制作了条宽100 m、腔长2000 m的940 nm半导体激光器器件。25 ℃室温10 A直流连续（CW）测试镀膜后器件阈值电流251 mA,斜率效率1.22 W/A,最大输出功率达到9.6 W,最大光电转化效率超过70%。     

Investigation and optimization of the covering power and coloristic properties of paint coatings of complex composition

A method for finding the optimum sizes of pigment particles, their volume concentration, and the paint coating thickness that provide the covering power and the required coloristic characteristics of reflected light for the minimum flow rate of pigments is based on using a four-flow approximation of the solution to the equation of radiation transfer in dispersion media and is extended to coatings of complex composition. The capabilities of the method are demonstrated by examples of coatings of mixtures of hematite and rutile particles in a binder with n=1.5 for variations of the modal size and the half-width of the size distribution of the pigment particles. B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 90–96, January–February, 1997.     

带开口磁环的周期永磁聚焦系统的2维模拟

 由于目前常用的磁聚焦系统设计方法不能直接计算带有非轴对称开口磁环的磁系统,因此在行波管磁系统实验测试基础上,提出了双面带极靴的开口磁环体积等效概念：将开口磁环等效为相等体积磁性材料的2维轴对称磁环,两者都双面带极靴时轴上的磁场值相等。使用2维电磁计算软件FEMM计算了采用该等效模型后的周期磁聚焦系统的轴上磁场值,计算结果与带有开口磁环的实际系统测试值符合良好,两者相差仅3×10^-3 T。该2维等效模型能代替开口磁环进行计算。     

Meshless acoustic analysis using a weakly singular Burton-Miller boundary integral formulation

The Burton-Miller boundary integral formulation is solved by a complex variable boundary element-free method (CVBEFM) for the boundary-only meshless analysis of acoustic problems with arbitrary wavenumbers. To regularize both strongly singular and hypersingular integrals and to avoid the computation of the solid angle and its normal derivative, a weakly singular Burton-Miller formulation is derived by considering the normal derivative of the solid angle and adopting the singularity subtraction procedures. To facilitate the implementation of the CVBEFM and the approximation of gradients of the boundary variables, a stabilized complex variable moving least-square approximation is selected in the meshless discretization procedure. The results show the accuracy and efficiency of the present CVBEFM and reveal that the method can produce satisfactory results for all wavenumbers, even for extremely large wavenumbers such as k = 10 000.     

二维色谱/光谱重叠峰的定性定量方法研究(I)——水中多种酚二维色谱/光谱重叠峰的分辨与定性定量

探讨了HELP法在水中酚类色谱重叠峰的分辨与定性定量分析中的应用.实验结果表明,各组分浓度比为1:50的范围内分辨光谱与真实光谱十分吻合.在10^-4～10^-6g/mL的浓度范围内分辨色谱的定量结果线性关系良好.分辨下限3.0×10^-7g/mL,相对标准偏差为5.0%.     

Frequency doubling of a fibre-amplified 1083 nm DBR laser

A good frequency standard is required at 1083 nm for measurements on the fine structure of helium and of the fine structure constant. Several milliwatts of CW frequency-doubled light offers the prospect of stabilisation to a Doppler-free hyperfine transition in molecular iodine. The 1083 nm emission of an extended-cavity DBR diode laser has been amplified using an ytterbium-doped fibre amplifier, and applied to a type-I phase matched Mg:LiNbO₃ crystal in a high-Q fundamental-resonant cavity for frequency doubling. The amplifier gain at 1083 nm under typical operating conditions was 13.8 dB, with a coherent output power up to 63 mW, limited by the maximum signal input power. The doubling cavity Q was , and about 70% of the incident power was coupled in. The maximum 2nd-harmonic conversion efficiency exceeded 20% and provided an output power of 3.7 mW for making continuous frequency scans of up to 600 MHz in the green. An optical spectrum analyser at 541.5 nm showed fringes of 4.6 MHz full width half maximum, close to the instrumental width. Received: 25 February 1998 / Revised and Accepted: 28 May 1998