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关于康托集类光栅的实验探究 总被引:1,自引:1,他引:0
设计制作了康托集分形衍射光栅,通过对康托集分形光栅3个阶段的夫琅禾费衍射现象的观察,根据惠更斯-菲涅耳原理,得到了一维康托集分形光栅的夫琅禾费衍射光强分布特性. 相似文献
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利用菲涅耳 基尔霍夫光栅衍射原理和傅里叶分析方法,对具有分形结构互补Sierpinski地毯光栅的夫琅和费衍射现象进行了探讨。导出了观察平面上的频谱函数、振幅函数以及光强函数。运用MATLAB软件对该光栅的衍射现象进行了仿真,并绘制出其幅 频特性曲线。结果表明,在各阶光栅的衍射图样中,幅度较大的部分主要集中在接收屏的中心区域,而在偏离中心的区域内,幅度值较小,在较远区域幅度值趋近于零,这说明获得的衍射图样不仅具有衍射光的基本特性,而且都呈现出明显的分形特征。 相似文献
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分形介质的传热与传质分析(综述) 总被引:9,自引:0,他引:9
本文论述了分形介质的分形理论和数学基础,并简要综述了用分形理论和方法研究分形介质的传热与传质特性(如多孔介质的渗透率、热导率以及池核态沸腾换热)方面目前所取得的研究进展,最后扼要展望了用分形理论和方法进一步研究分形介质的传热与传质的可能的若干课题和方向。 相似文献
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超微粒聚集体的分形特征 总被引:2,自引:0,他引:2
超微粒及其聚集体在制备过程中由于其远过程的相似迭代,最容易呈现分形结构,因而具有明显的分形特征,文章对超微粒聚集体几何特征、特性以及生长演化诸方面呈现的分形特征进行讨论。 相似文献
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针对海杂波背景下小目标检测对海情依赖性强的问题, 本文采用分数布朗运动模型对实测海杂波建模, 结合多重分形去势波动分析法确定分形参数, 分析了海杂波的单尺度、多重分形特性. 在单尺度分形的基础上, 利用表征海杂波分形特征的分数维和Hurst指数构建了分形差量, 提出了基于分形差量的小目标检测方法;在多重分形基础上, 比较了两种海杂波的高尺度多重分形特性. 结果表明, 当尺度q > 10时, 纯海杂波的多重分形参数H(q) < 0, 而存在小目标的H(q) > 0, 此差异性为高尺度分形参数的海杂波背景小目标检测提供了判定依据. 所研究的两种方法均能实现不同海情下的小目标检测. 相似文献
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分形结构对随机取向烟尘团簇粒子光散射特性的影响 总被引:1,自引:0,他引:1
利用蒙特卡罗方法对不同分形维数和分形前向因子的随机取向烟尘团簇粒子的分形结构进行了仿真,采用离散偶极子近似(DDA)方法对随机取向烟尘团簇粒子的缪勒矩阵元进行了数值计算,并与球形粒子模型进行了比较,深入探讨了烟尘团簇粒子的分形维数和分形前因子对其散射特性的影响。研究表明,等效球形粒子的光散射特性与随机取向烟尘团簇粒子的光散射特性存在很大差别,并且此差别随着团簇粒子的分形维数以及分形前向因子的增大而减小;分形维数对表征团簇粒子散射特性的缪勒矩阵元的影响在一定散射角范围内均比较明显,分形前向因子对团簇粒子的缪勒矩阵元角分布的影响与分形维数的影响类似,不过其影响相对分形维数较弱。 相似文献
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用衍射屏平移相因子计算夫琅禾费衍射场强分布 总被引:3,自引:0,他引:3
用Fresnel-Kirchhoff衍射积分求解夫琅禾费衍射场分布时引入衍射屏平移相因子,可简化对较复杂衍射屏夫琅禾费衍射的讨论,加深对衍射、干涉现象的理解. 相似文献
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Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide 总被引:1,自引:0,他引:1
Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs. 相似文献
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S. G. Nedel’ko M. A. Krysyuk A. L. Apanasenko L. N. Lymarenko Z. T. Moroz 《Journal of Applied Spectroscopy》1997,64(1):55-61
Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped
with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly
described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation
(5.5·104 Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum
cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics
of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure
crystals is analyzed (preliminarily).
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997. 相似文献
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A multi-conjugate adaptive optics (MCAO) can offer a possibility of widening field of view (FOV) characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle's expressions of two deformable mirrors (DMs) MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance. 相似文献
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Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use. 相似文献
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40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm. 相似文献
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A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands. 相似文献
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References: 《声学学报:英文版》2008,27(1):85-96
Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation. 相似文献
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Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser. 相似文献
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Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored. 相似文献