Electromagnetically induced transparency in a non-uniform plasma

Electromagnetically induced transparency in a non-uniform plasma is investigated. We discuss the possible frequency ranges in which a weak beam below cutoff can propagate transparently in this plasma with the presence of a strong high frequency field. We also analyze the effect of driving intensity on the frequency range of the probe. Received 3 March 2000 and Received in final form 21 April 2000     

How parabolic free boundaries approximate hyperbolic fronts

A rather complete study of the existence and qualitative behaviour of the boundaries of the support of solutions of the Cauchy problem for nonlinear first-order and second-order scalar conservation laws is presented. Among other properties, it is shown that, under appropriate assumptions, parabolic interfaces converge to hyperbolic ones in the vanishing viscosity limit.

     

Nonlinear Comparison of High-order and Optimized Finite-difference Schemes

The effect of reducing the formal order of accuracy of a finite-difference scheme in order to optimize its high-wavenumber performance, is investigated using the 1-D nonlinear unsteady inviscid Burgers' equation. Both explicit and compact schemes are compared to schemes wilh various levels of optimization. Results are given for the absolute and L2 errors as a function of time. It is found that the benefits of optimization do carry over into nonlinear applications.     

离轴椭圆矢量光场传输中的光斑演变

对离轴椭圆矢量光场的传输特性进行了研究. 推导出离轴椭圆矢量光场在自由空间传输电场和光强的解析表达式. 数值分析结果表明, 离轴高阶圆柱矢量光场具有非对称的光强分布, 传输后的光强分布由传输距离、错位位移、椭圆率决定. 在传输过程中除了光斑会展宽外, 光场中的暗斑会逐渐消失, 最终趋于一种稳态光强分布; 相对于初入射平面的椭圆光斑, 稳态椭圆光斑长短轴互换了. 研究结果有助于深入理解离轴情况下椭圆矢量光场的动态传输特性, 同时可以指导实际椭圆矢量光场的校准.     

高功率微波土壤击穿的数值验证研究

高功率微波在土壤中传播时, 会引起土壤击穿电离而导致土壤电阻率的非线性变化, 土壤电阻率的变化又将反作用于传播过程, 加剧高功率微波衰减, 影响其能量传输效率. 通过对土壤动态电离过程的分析, 结合Maxwell方程组构建了高功率微波土壤传播模型, 采用时域有限差分法对该模型进行数值验证. 数值结果显示了高功率微波在土壤中传播、衰减等物理图像, 以及土壤电阻率的非线性变化过程. 理论分析验证了这些数值结果.     

基于PT对称高斯势的孤子单向散射的操控

本文运用数值模拟的方法讨论在PT对称高斯势中孤子的散射问题,包括演化动力学,孤子振幅和质心位置的传输动力学以及PT对称高斯势对孤子单向散射特性的影响.结果表明在一定的参数范围内,单个孤子或孤子串的散射都能展现出单向流的特性,并且可以通过适当地调节PT对称高斯势的参数来实现孤子单向散射的操控.     

Problème spectral pour la propagation conique des ondes élastiques dans un réseau de galeriesA spectral problem for conically propagating elastic waves through an array of cylindrical channels

This Note is devoted to the analysis of elastic waves conically propagating through a doubly periodic array of cylindrical channels. A new method, based on a multiple scattering approach, has been proposed to reduce the problem to an algebraic system of the Rayleigh type. We obtain an eigenvalue problem formulation that enables us to construct the high-order dispersion curves and to study phononic band gap structures in oblique propagation. We note an effect of singular perturbation associated with a small angle of conical propagation. To cite this article: S. Guenneau et al., C. R. Mecanique 330 (2002) 491–497.