纳米三明治结构光子超材料中电磁场振荡行为研究

对金属-介质-金属的三层纳米三明治结构中的磁性等离子体模式特性进行了时域有限差分数值计算分析,并给出该类谐振器的品质因数变化规律.基于纳米三明治结构中的磁性等离子体模式对该种结构进行设计,研究几何构型参数以及介质材料折射率对磁性等离子体模式的调控规律.以电感电容等效电路近似理论对纳米三明治结构磁性等离子体模式谐振频率的变化规律进行理论解释,理论解释与数值计算结果符合很好.同时还研究了纳米三明治振荡器对电磁能量的限制,并从热和辐射两方面分析了该类结构的品质因数变化情况,可为基于磁性等离子体模式的新型波导及激光器结构的设计提供指导.     

非线性对大气介质中阵列聚焦声场分布影响的研究

基于时域有限差分算法将大气中近似到二阶微小项的非线性声波波动方程进行离散化,得到了模拟采用的差分波动方程.在此基础上,数值模拟了初始声压强弱不同的5个点声源组成的线阵列垂直或斜向辐射的连续正弦波在大气中传播时二维声场的分布情况.将线性条件下的模拟结果与非线性条件下的模拟结果进行比较后发现:弱非线性会对声场的分布和阵列聚焦增益产生一定的影响,使声场分布波形比线性条件下的声场分布波形更加靠近阵列,聚焦效果变差;强非线性会使波形发生更严重畸变,这是由于产生了基频以外的其他频率声波引起的;非线性对斜向传播时声场分布的影响与垂直传播时的影响效果基本相同,但由于斜向辐射时的声波几何扩展造成的轴向声压衰减要大于垂直辐射时的轴向声压衰减,因此聚焦增益和强非线性的影响都将小于垂直辐射时的情况.     

基于时分复用技术的甚多束光脉冲产生系统

提出了一种基于时分复用技术的全光纤、全固化的用于惯性约束聚变驱动器的甚多路光脉冲产生系统.系统中采用单纵模振荡器输出连续激光信号,利用时分复用技术结合高速电光调制技术实现序列脉冲的产生和甚多束脉冲的独立整形.采用偏振无关的声光调制技术实现甚多束脉冲的独立输出.每个序列脉冲包含8个子脉冲,子脉冲间隔设置为120ns,对子脉冲独立整形和选单后将其传输放大至微焦耳量级输出.实验成功验证了采用时分复用技术完全可以实现序列脉冲输出,各子脉冲可以独立任意整形且最后的单束输出能量为1.275μJ.     

Lagrange equations of nonholonomic systems with fractional derivatives

This paper obtains Lagrange equations of nonholonomic systems with fractional derivatives. First, the exchanging relationships between the isochronous variation and the fractional derivatives are derived. Secondly, based on these exchanging relationships, the Hamilton's principle is presented for non-conservative systems with fractional derivatives. Thirdly, Lagrange equations of the systems are obtained. Furthermore, the d'Alembert–Lagrange principle with fractional derivatives is presented,and the Lagrange equations of nonholonomic systems with fractional derivatives are studied. An example is designed to illustrate these results.     

Triggering and guiding of high voltage discharge by using femtosecond laser filaments with different parameters

This paper demonstrates the triggering and guiding of the stationary high voltage (HV) discharges at 5--40 kV by using plasma filaments generated by femtosecond laser pulses in air. A significant reduction of the breakdown voltage threshold due to the pre-ionization of the air gap by laser filamentation is observed. The discharge experiments are performed by using laser pulses with different energy from 15--60 mJ. The electron density of filaments is detected by sonography method. The influence of the electron density of laser filaments on the triggering and guiding HV discharge is experimentally investigated. The results have shown that the behaviour of plasma filaments can strongly affect the efficiency of triggering and guiding HV discharge.     

Xe（4d10）（e, 2e）反应三重微分截面的理论研究

采用修正后的扭曲波玻恩近似理论,计算了共面不对称几何条件下Xe（4d10）（e, 2e）反应的三重微分截面。散射电子能量为1000eV,敲出电子能量为20eV,散射电子角度分别固定在2o,4o和7.5o。理论计算与Avaldi等人的实验结果和扭曲波玻恩近似理论计算进行了比较,发现出射电子之间的后碰撞相互作用较弱,极化效应在反应过程中起着重要作用。     

Characterization of a velocity-tunable 87Rb cold atomic source with a high-speed imaging technology

This paper has developed and characterized a method to produce a velocity-tunable 87 Rb cold atomic source for atomic interferometry application.Using a high speed fluorescence imaging technology,it reports that the dynamic process of the atomic source formation is observed and the source performances including the flux and the initial velocity are characterized.A tunable atomic source with the initial velocity of 1.4～2.6 m/s and the atomic source flux of 2 × 10 8 ～ 6 × 10 9 atoms/s has been obtained with the built experimental setup.     

Dielectronic recombination of Co-like tantalum

Ab initio calculation of the total dielectronic recombination (DR) rate coefficient from the ground state of Co-like tantalum is performed using the relativistic distorted-wave approximation with configuration interaction. The contributions to the total DR rate coefficients are explicitly calculated from the complexes of Ni-like tantalum: 3s²3p⁶3d_3/2³ 3d_5/2⁶ n'l', 3s²3p⁵3d¹⁰n'l', 3s3p⁶3d¹⁰n'l', 3s²3p⁶3d⁸4ln'l', 3s²3p⁵3d⁹4ln'l' and 3s3p⁶3d⁹4ln'l' with n' ≤ 25, and 3s²3p⁶3d⁸5ln'l' with n' ≤ 9. The l' and n' dependences of partial DR rate coefficients are investigated. The contributions from higher n'complexes are evaluated by a level-by-level extrapolation method. The total DR rate coefficients mainly come from the complex series 3s²3p⁶3d⁸4ln'l', 3s²3p⁵3d⁹4ln'l' and are fitted to an empirical formula with high accuracy. Comparison of the present results with those of other works shows that the previously published data underestimate significantly the DR rates of Co-like tantalum.     

Density and impurity profile behaviours in HL-2A tokamak with different gas fuelling methods

The electron density profile peaking and the impurity accumulation in the HL-2A tokamak plasma are observed when three kinds of fuelling methods are separately used at different fuelling particle locations. The density profile becomes more peaked when the line-averaged electron density approaches the Greenwald density limit n_G and, consequently, impurity accumulation is often observed. A linear increase regime in the density range n_e< 0.6n_G and a saturation regime in n_e > 0.6n_G are obtained. There is no significant difference in achieved density peaking factor f_ne between the supersonic molecular beam injection (SMBI) and gas puffing into the plasma main chamber. However, the achieved f_ne is relatively low, in particular, in the case of density below 0.7n_G, when the working gas is puffed into the divertor chamber. A discharge with a density as high as 1.2n_G, i.e. n_e = 1.2n_G, can be achieved by SMBI just after siliconization as a wall conditioning. The metallic impurities, such as iron and chromium, also increase remarkably when the impurity accumulation happens. The mechanism behind the density peaking and impurity accumulation is studied by investigating both the density peaking factor versus the effective collisionality and the radiation peaking versus density peaking.     

Thermally activated magnetization reversal in magnetic tunnel junctions

In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlO_x/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants.