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281.
282.
基于Drude模型,采用解析法与数值模拟法研究了具有电与磁非线性效应超常介质中光束的聚焦特性。结果表明超常材料中光束聚焦现象不但可以发生在自聚焦非线性介质中(正折射区)而且可以发生在自散焦非线性介质中(负折射区),且光束中心频率离介质的等离子频率越近,其聚焦效应越明显。特别是当电与磁非线性极化率为异号时,超常介质的非线性符号可以通过调控电与磁等离子频率的相对大小控制,这为主动操控光束的传输提供一种新的自由度。 相似文献
283.
Subluminal to superluminal light propagation in a V-type three-level atomic system interacting with squeezed vacuum 下载免费PDF全文
We study the light propagation properties in a V-type three-level atomic system interacting with two independent broadband squeezed baths. Using the graphic method, the dependences of the absorption and the dispersion of the system on the coupling field strength, the incoherent pumping field strength and the intensity of the squeezed vacuum are analysed. The result shows that the probe pulse propagation can be changed from subluminal to superluminal speed. 相似文献
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Zhenjun Yang 《Acta Mechanica Sinica》2006,22(3):243-256
The scaled boundary finite element method (SBFEM) is a recently developed numerical method combining advantages of both finite element methods (FEM) and boundary element methods (BEM) and with its own special features as well. One of the most prominent advantages is its capability of calculating stress intensity factors (SIFs) directly from the stress solutions whose singularities at crack tips are analytically represented. This advantage is taken in this study to model static and dynamic fracture problems. For static problems, a remeshing algorithm as simple as used in the BEM is developed while retaining the generality and flexibility of the FEM. Fully-automatic modelling of the mixed-mode crack propagation is then realised by combining the remeshing algorithm with a propagation criterion. For dynamic fracture problems, a newly developed series-increasing solution to the SBFEM governing equations in the frequency domain is applied to calculate dynamic SIFs. Three plane problems are modelled.
The numerical results show that the SBFEM can accurately predict static and dynamic SIFs, cracking paths and load-displacement curves, using only a fraction of degrees of freedom generally needed by the traditional finite element methods.The project supported by the National Natural Science Foundation of China (50579081) and the Australian Research Council (DP0452681)The English text was polished by Keren Wang. 相似文献
286.
破前漏(简称LBB)是压力容器、核电站设备结构设计与评价中的一个重要准则.表面裂纹准静态扩展的几何形貌变化规律的预测是破前漏(LBB)评判十分重要的课题之一.本文对特定焊接残余应力场加载作用下,含三维表面裂纹的压力容器模型,用有限元软件(ABAQUS)进行了表面裂纹准静态扩展模拟计算,得到在此残余应力场作用下应力强度因子沿裂纹前缘的分布规律.结合外载引起的应力强度因子,就可以判别裂纹的扩展形貌,从而判断结构是否满足LBB要求. 相似文献
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基于广义惠更斯-菲涅尔原理以及大气湍流理论,推导出部分相干光束在大气湍流中传输的光束传输M 2因子的解析表达式.定量分析了表征大气湍流参数的折射率结构常数 C2n和涡旋内尺度 l 0对 M 2因子的影响,并由此提出了一种通过实验测量大气湍流中光束的 M 2因子,进而确定出大气湍流参数的新方法.研究结果表明,由于大气湍流对相干性好的光束影响更为明显,在测量中可采用具有高相干性的基模高斯光束作为测量光源,而测量装
关键词:
2因子')" href="#">光束传输 M 2因子
大气湍流参数
湍流折射率结构常数
湍流涡旋内尺度 相似文献
289.
We theoretically investigate the propagation of few-cycle laser pulses in resonant two-level dense media with a sub- wavelength structure, which is described by the full Maxwell-Bloch equations without the frame of slowly varying envelope and rotating wave approximations. The input pulses can be shaped into shorter ones with a single or less than one optical cycle. The effect of the parameters of the subwavelength structure and laser pulses is studied. Our study shows that the media with a subwavelength structure can significantly shape the few-cycle pulses into a subcycle pulse, even for the case of chirp pulses as input fields. This suggests that such subwavelength structures have potential application in the shaping of few-cycle laser pulses. 相似文献
290.
Hiroyuki Nakamura Makiko Seno Tsuneyuki Sato 《Journal of polymer science. Part A, Polymer chemistry》1997,35(1):153-162
The effect of LiClO4 on the polymerization of di-2-[2-(2-methoxyethoxy)ethoxy]ethyl itaconate (DMEI) with dimethyl 2,2′-azobisisobutyrate (MAIB) was investigated in methyl ethyl ketone (MEK) kinetically and by ESR. The polymerization rate (Rp) at 50°C, where the concentrations of DMEI and MAIB were 1.00 and 5.00 × 10−2 mol/L, increased with increasing [LiClO4]. Marked acceleration was observed at higher [LiClO4]s than 1.0 mol/L. The molecular weight of resulting polymer (ca. 10,000) was relatively insensitive to [LiClO4], indicating occurrence of chain transfer. IR analysis of mixtures of LiClO4/DMEI and LiClO4/poly(DMEI) indicated complexation of LiClO4 with DMEI and its polymer. The rate constants of propagation (kp) and termination (kt) were determined by ESR. kp (1.7–10.5 L/mol s at 50°C) increased with [LiClO4]. kt (5.2–1.0 × 104 L/mol s at 50°C) showed remarkable decrease at higher [LiClO4]s than 1.0 mol/L. Rp of polymerization of equimolar complex of LiClO4/DMEI with MAIB at 50°C in MEK was expressed by Rp = k[MAIB]0.5[DMEI]2.4. kp increased and kt decreased with [DMEI]. The activation energies of overall polymerization, propagation and termination were estimated to be 34.5, 8.0, and 59.4 kJ/mol. Copolymerization of DMEI with styrene was also profoundly affected by the presence of LiClO4. Such large effects of LiClO4 on the homo- and copolymerization of DMEI are explicable in term of association of LiClO4-complexed DMEI monomers. © 1997 John Wiley & Sons, Inc. 相似文献