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181.
The paper essentially deals with the analysis of photonic band-gap fibers in analogy with the electron wave motion in periodic crystal lattice. As such, the analyses are based on Bloch formulation. The dispersion characteristics of such fibers are presented by considering some illustrative values of design parameters. The effect of design parameters on the dispersion characteristics is also presented in terms of the variation of widths of allowed and forbidden bands of band-gap fibers. It is found that the number of allowed bands increases with the increase in difference between refractive indices of different layers. Further, widths of the allowed and forbidden bands increase with the increase in layer thickness. 相似文献
182.
掺铒聚合物光波导放大器的数值分析 总被引:1,自引:1,他引:0
针对掺铒聚合物光波导放大器(EDWA),提出了一种基于Douglas离散格式改进的有限差光束传播法(FD-BPM)的数值计算方法。对每一传输步长结合多能级速率方程计算出EDWA中光场传输强度分布,及掺铒光波导放大器的增益传输特性。设计并研究了掺铒聚合物通道波导和Y形分束器的放大增益特性。在掺铒聚合物直波导中,Er3 浓度为9.0×1025ions·m-3,输入信号和泵浦光功率分别为1μW和2mW,其增益为1.6dB/cm;在掺铒聚合物Y形分束器中,输出信号光分束比相等,并能实现无损耗分束。 相似文献
183.
R. Fedele H. Schamel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):313-320
An investigation to deepen the connection between the family of nonlinear Schr?dinger equations and the one of Korteweg-de
Vries equations is carried out within the context of the Madelung's fluid picture. In particular, under suitable hypothesis
for the current velocity, it is proven that the cubic nonlinear Schr?dinger equation, whose solution is a complex wave function,
can be put in correspondence with the standard Korteweg-de Vries equation, is such a way that the soliton solutions of the
latter are the squared modulus of the envelope soliton solution of the former. Under suitable physical hypothesis for the
current velocity, this correspondence allows us to find envelope soliton solutions of the cubic nonlinear Schr?dinger equation,
starting from the soliton solutions of the associated Korteweg-de Vries equation. In particular, in the case of constant current
velocities, the solitary waves have the amplitude independent of the envelope velocity (which coincides with the constant
current velocity). They are bright or dark envelope solitons and have a phase linearly depending both on space and on time coordinates. In the case of an arbitrarily
large stationary-profile perturbation of the current velocity, envelope solitons are grey or dark and they relate the velocity u0 with the amplitude; in fact, they exist for a limited range of velocities and have a phase nonlinearly depending on the combined
variable x-u0 s (s being a time-like variable). This novel method in solving the nonlinear Schr?dinger equation starting from the Korteweg-de
Vries equation give new insights and represents an alternative key of reading of the dark/grey envelope solitons based on the fluid language. Moreover, a comparison between the solutions found in the
present paper and the ones already known in literature is also presented.
Received 20 February 2002 and Received in final form 22 April 2002 Published online 6 June 2002 相似文献
184.
185.
186.
提出了一种基于大气声传播通道的爆炸声源能量估计方法,通过将计算大气声学的传播能量分布结果与大气中传播的声压幅度衰减模型相结合,使用平流层通道与热层通道传播损失能量比例作为修正量,提高了对爆炸声源能量的估计精度。在多次地面爆炸实验得到的数据中,使用观测距离800 km以上且同时存在平流层通道与热层通道的次声接收信号,对比了平流层顶风速修正的能量估计方法与该文提出的基于大气声传播通道的能量估计方法。实验结果验证了相对于传统风速修正的能量估计方法,该方法可显著降低估计误差。 相似文献
187.
建立了一种数值算法,从光波在湍流大气中传播的闪烁时间频谱的高频特征反演大气光学湍流谱.此算法具有两点优越性:(1)反演出的湍流谱直接表征大气折射率的起伏而非大气温度场的起伏;(2)可以获得高空间波数、大部分位于耗散区的湍流谱,而用其它方法不易获得此区域的湍流谱.对Hill湍流谱以及一种复杂的湍流谱进行了大量数值模拟来检验此种算法,结果表明:如果知道大气风速与湍流内尺度就可以相当有效地获得湍流谱. 相似文献
188.
A. Montanaro 《Journal of Elasticity》1999,57(1):25-53
By extending the procedure of linearization for constrained elastic materials in the papers by Marlow and Chadwick et al., we set up a linearized theory of constrained materials with initial stress (not necessarily based on a nonlinear theory).
The conditions of propagation are characterized for small-displacement waves that may be either of discontinuity type of any
given order or, in the homogeneous case, plane progressive. We see that, just as in the unconstrained case, the laws of propagation
of discontinuity waves are the same as those of progressive waves. Waves are classified as mixed, kinematic, or ghost. Then we prove that the analogues of Truesdell"s two equivalence theorems on wave propagation in finite elasticity hold for
each type of wave.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
189.
190.
疲劳裂纹扩展门槛值的研究进展 总被引:6,自引:0,他引:6
Ⅰ.引言 大量的研究和疲劳裂纹扩展的试验表明,对于存在一定尺寸裂纹及缺陷的材料或构件,只有当裂纹尖端的应力强度因子达到或超过某一值时,裂纹才会在交变应力的作用下扩展。当裂纹尖端的应力强度因子小于这一值时,裂纹在交变应力作用下不发生扩展。这个应力强度因子值,就是界限应力强度因予幅值△K_(th),在疲劳研究中称为裂纹扩展的门槛值。 门槛值△K_(th)和疲劳裂纹扩展速率da/dN一样,是反映带裂纹或缺陷构件抗疲劳性能的 相似文献