双色线偏振激光场驱动H2+分子产生椭圆偏振阿秒脉冲

理论研究了双色线偏振激光场驱动H2+分子产生椭圆偏振谐波及阿秒脉冲的特点。计算结果表明：随着不同偏振角的引入,谐波光谱呈现不规则的椭圆率。但是,随着空间非均匀效应的引入,不仅谐波谱的椭圆率可以稳定在ɛ = 0.1和ɛ = 0.3之间,而且谐波发射的截止能量明显增强。形成4个具有较小干涉结构带宽在406 eV,299 eV,381 eV和582 eV的超长平台区。最后,通过傅里叶变换,可获得5个脉宽及椭圆率为24 as (ε = 0.1),22 as (ε = 0.3),24 as (ε = 0.3),19 as (ε = 0.3),19 as (ε = 0.3)的阿秒X射线脉冲。     

利用三束中红外空间非均匀激光场产生超长平台区

数值研究了氦离子在三束中红外激光场下发射高次谐波以及阿秒脉冲的特点. 计算结果表明, 通过适当调节三束激光场的延迟时间和相位角, 不仅谐波发射的截止能量得到了延伸, 而且单一的量子路径也被选择出来对谐波发射起作用, 随后通过适当的引入空间非均匀参数,谐波截止能量得到了进一步扩展,形成了一个超长的1773eV的平台区. 并且我们发现当选择氦离子的基态和第一激发态为叠加初始态时,谐波的强度被增强了4-6个数量级. 最后, 通过叠加谐波谱上的谐波, 可获得一系列脉宽为32as左右的阿秒X射线光源. 并且这些光源的强度比氦离子基态作为初始态时增强了4-6个数量级.     

双色线偏振激光场驱动H_2~+分子产生椭圆偏振阿秒脉冲

理论研究了双色线偏振激光场驱动H_2~+分子产生椭圆偏振谐波及阿秒脉冲的特点.计算结果表明:随着不同偏振角的引入,谐波光谱呈现不规则的椭圆率.但是,随着空间非均匀效应的引入,不仅谐波谱的椭圆率可以稳定在ε=0.1和ε=0.3之间,而且谐波发射的截止能量明显增强.形成4个具有较小干涉结构带宽在406 e V,299 e V,381 e V和582 e V的超长平台区.最后,通过傅里叶变换,可获得5个脉宽及椭圆率为24 as(ε=0.1),22 as(ε=0.3),24 as(ε=0.3),19 as(ε=0.3),19 as(ε=0.3)的阿秒X射线脉冲.     

HeH2+分子多通道谐波发射的理论研究

利用非波恩奥本海默近似模型,理论研究了强激光场下HeH2+分子发射高次谐波的特点。计算结果表明,HeH2+分子的谐波截止能量要大于经典预言值。理论分析表明,延伸的谐波截止能量是由于激发态激光诱导电子跃迁所产生的多通道电子电离-回碰过程所导致的。随后利用双色空间非均匀激光场机制,谐波截止能量进一步延伸,形成了1个由单一量子路径贡献而成的482eV的超长平台区。该辐射能量相当于单色激光场场强被增强了3倍的结果。并且高振动激发态会产生强度更高的谐波光谱。最后,通过适当的叠加谐波平台上的谐波, 可获得一系列脉宽在30as的超短X射线光源。     

New frontiers in metamaterials research: Novel electronic materials and inhomogeneous metasurfaces

In reviewing some recent work in metamaterials, we highlight two exciting new frontiers just emerging in this field — metamaterials made by new electronic materials (particularly graphene) and inhomogeneous metasurfaces to control light wave-fronts.     

位势流动和非均匀介质中声波方程的36种形式

声波方程是对大多数声学问题进行数学描述的出发点. 那些得到 广泛应用的经典波动方程及对流波动方程都存在苛刻的适用条件, 即仅适用于描述处于静态或匀速运动状态的定常 均匀介质中的线性无耗散声波. 然而, 很多实际场合并不满足这些严格的适用条件. 本文对经典声波方程和对流声波 方程进行推广, 导出了编号为W1$\sim$W36的36种不同形式的声波方程, 涵盖了处于静止、势流或旋涡流状态下的非均匀 和/或非定常介质中的声波传播问题. 所考虑的声波传播情形包括: (1) 线性波, 即具有小梯度(小振幅)性质; (2)非线性波, 即具有陡峭梯度性质, 包括``波纹'(小振幅大梯度)或者大振幅波. 本文仅考虑非耗散声波, 即排除了由剪切、体积黏度及热传导所引起的耗散. 对具有匀熵或等熵(熵沿流线守恒)性质的均匀介质和非均匀介质中的声传播进行了研究但非等熵(即耗散)情况除外; 另外, 对非定常介质中的 声波问题也进行了分析. 所涉及的介质可以处于静止、匀速运动状态, 或者是非匀速的和/或非定常的平均流动, 包括: (1)低Mach数的势平均流(即不可压缩的平均态), 或高速势平均流(即非均匀可压缩的平均流); ② 变截面管 道中的准一维传播, 包括无平均流的号管和具有低或高Mach数平均流的喷管; 或③平面的、空间的、或轴对称的单 向剪切平均流. 本文没有探讨其他类型的旋涡平均流(将与耗散及其他情形一起留待下一步研究), 例如, 可能与剪切效应相结合的轴对称旋转平均流. 通过对流体力学的一般方程进行消元处理或根据声学变分原理, 导出了36种波动方程, 对一些波动方程还采用这两种方法进行相互校验. 尽管声波方程的36种形式没有涵盖非线性、非均匀与非定常及非匀速运动介质 这3个效应的所有可能的组合情形, 但它们的确包括了孤立状态下的各种效应, 并包括了多种多重效应组合的 情形. 虽然经典波动方程和对流波动方程仅适用于处于静止(或匀速运动)的均匀定常介质中的线性无耗散声波, 但它们在 相关文献中已被广泛采用; 本文给出的36种声波方程提供了它们多种有用的推广形式. 在许多实际应用中, 经典波动方 程和对流波动方程仅是粗略的近似, 声波方程的更一般形式可提供更令人满意的理论模型. 本文每节末尾给出了这些应用 的众多范例. 在这篇评论文章中引用了240篇参考文献.     

Analytical Solitary Wave Solutions to a (3+1)-Dimensional Gross-Pitaevskii Equation with Variable Coefficients

A (3+1)-dimensional Gross-Pitaevskii (GP) equation with time variable coefficients is considered, and is transformed into a standard nonlinear Schrödinger (NLS) equation. Exact solutions of the (3+1)D GP equation are constructed via those of the NLS equation. By applying specific time-modulated nonlinearities, dispersions, and potentials, the dynamics of the solutions can be controlled. Solitary and periodic wave solutions with snaking and breathing behavior are reported.     

Propagation of nonlinear waves in an inhomogeneous gas-liquid medium. Derivation of wave equations in the Korteweg-de Vries approximation

Equations describing the propagation of waves of small but finite amplitude in a liquid with gas bubbles are derived. The bubble distribution density is a continuous function of bubble size and spatial coordinates. It is found that, for a uniform bubble distribution, the obtained equations become the Korteweg-de Vries, Kadomtsev-Petviashvili and Khokhlov-Zabolotskaya equations. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 2, pp. 188–197, March–April, 2009.     

Inhomogeneous Bulk Viscous Fluid Universe with Electromagnetic Field and Variable ∧-Term

Cylindrically symmetric inhomogeneous cosmological model for bulk viscous fluid distribution with electro- magnetic field is obtained. The source of the magnetic field is due to an electric current produced along the z-axis. F12 is the non-vanishing component of electromagnetic field tensor. To get the deterministic solution, it has been assumed that the expansion 0 in the model is proportional to the shear σ. The values of cosmological constant for these models are found to be small and positive at late time, which are consistent with the results from recent supernovae Ia observations. Physical and geometric aspects of the models are also discussed in presence and absence of magnetic field.     

A new model analysis of the third harmonic voltage in inductive measurement for critical current density of superconducting films

The critical current density J c is one of the most important parameters of high temperature superconducting films in superconducting applications,such as superconducting filter and superconducting Josephson devices.This paper presents a new model to describe inhomogeneous current distribution throughout the thickness of superconducting films applying magnetic field by solving the differential equation derived from Maxwell equation and the second London equation.Using this model,it accurately calculates the inductive third-harmonic voltage when the film applying magnetic field with the inductive measurement for J c.The theoretic curve is consistent with the experimental results about measuring superconducting film,especially when the third-harmonic voltage just exceeds zero.The J c value of superconducting films determined by the inductive method is also compared with results measured by four-probe transport method.The agreements between inductive method and transport method are very good.