Systematic study on visible light collimation nanostructured slits in the metal surface

We present a systematic experimental investigation on visible light collimation by a nanostructured slit flanked with a pair of periodic array of grooves in gold thin film. A wide variety of aspects are considered, such as the polarization state, the transport path of incident light, the groove-groove spacing, the groove width and depth. Our results clearly show that the relationship between the collimation wavelength and the periodicity of the slit-groove structure accords well with the surface plasmon dispersion model proposed by previous researchers. Furthermore, the surface plasmon wave phase retardation effect induced by the surface structure is also verified via the measurement for samples with different groove widths and depths. These results indicate that the detailed geometry of the groove structure has obvious impacts on the collimation effect and the angular distribution of the diffraction light in the subwavelength plasmonic system.     

Above-threshold detachment of negative ions by circularly polarized few-cycle laser fields

In accordance with nonperturbative quantum scattering theory,we investigate photoelectron angular distributions(PADs) from above-threshold detachment(ATD) of negative ions irradiated by circularly polarized few-cycle laser fields.Electrons ejected on the polarization plane demonstrate distinct anisotropies in angular distributions which distinctly vary with the carrier-envelope(CE) phase.The anisotropy is caused by interference between transition channels;it also depends strongly on laser frequency,pulse duration,and kinetic energy of photoelectrons.Optimal emission of photoelectrons,which varies with CE phase,makes it possible to control photoelectron motion.     

Studies on the mechanisms of powerful terahertz radiations from laser plasmas

A survey on the mechanisms of powerful terahertz (THz) radiation from laser plasmas is presented.Firstly,an analytical model is described,showing that a transverse net current formed in a plasma can be converted into THz radiations at the plasma oscillation frequency.This theory is applied to explain THz generation in a gas driven by two-color laser pulses.It is also applied to THz generation in a tenuous plasma driven by a chirped laser pulse,a few-cycle laser pulse,a DC/AC bias electric field.These are well verified by particle-in-cell simulations,demonstrating that THz radiations produced in these approaches are nearly single-cycles and linear polarized.In the chirped laser scheme and the few-cycle laser scheme,THz radiations with the peak field strength of tens of MV/cm and the peak power of gigawatt can be achieved with the incident laser intensity less than 10 17 W/cm 2.     

Radially polarized and passively Q-switched Nd:YAG laser with composite structure of gain medium

We report on a radially polarized and passively Q-switched Nd:YAG/Cr4+:YAG laser.The bulk Nd:YAG crystal is bonded with two undoped YAG crystal end caps to weaken the thermal lens e?ect and thus,enhance the extraction of stored energy in the bulk gain material.In the absence of active water cooling,the average laser power reaches 383 mW with 33% slope efficiency,and the laser pulse achieves 1.457-W peak power,18.9-ns duration,and 13.9-kHz repetition rate with 97.6% polarization purity.     

主惯导旋转调制对传递对准性能的影响

旋转调制技术在调制惯性器件常值误差,有效提高惯导系统长航时导航精度的同时,也引入了由系统旋转而造成的速度误差以旋转周期和旋转周期二倍频波动,这种波动对以速度为匹配量的传递对准有一定的影响。从旋转调制系统的误差特性出发,分析了旋转调制对以速度为匹配量传递对准的有利和不利影响,并针对不同的旋转调制周期进行了仿真验证,仿真结果表明当旋转周期远大于舒勒周期时,旋转调制引起的不利和有利影响都很小,可忽略不计;当旋转周期远小于舒勒周期时,旋转调制可提高子惯导的方位对准精度,但延长了系统的传递对准时间。例如,当旋转周期为3(°)/s时,水平对准时间由3 min延长到4 min,而对准精度由1.2′提高到0.2′;方位对准时间由10 min延长到16 min,而对准精度由2.2′提高到0.4′。     

2010年高考数学北京卷第14题的背景研究

2010年高考数学北京卷文理科第(14)题,都是以沿轴滚动的正方形的一个顶点所形成的图形为着眼点,考查函数的性质以及平面图形的面积问题,视角独特,设计新颖,不失为一道优秀的试题:1试题的简解及分析题目(2010年北京卷理第14题)如图1放置     

基于广义动态因子模型的中国出口周期分析与预测

研究出口周期的景气循环对于进一步扩大出口及推动整个国民经济的发展具有重要的意义.基于传统的先行指标体系和SW景气指数方法能够为出口周期的监测和预警提供参考,而近年来逐渐完善的广义动态因子模型基于频域分析方法,在处理高维数据方面比前两种方法更具有优势,同时该方法在拐点的探测方面也具有重要的作用.作者首先对三种指数构建方法进行了理论上的介绍;其次,分别运用三种方法构建了中国出口增长循环的一致及先行指数;最后,对三种方法在中国出口周期分析上的表现进行了比较与评价,得出了一些重要的结论.     

多周期多目标条件风险值模型

在商业、工业、电力和房地产等行业中存在许多复杂的多周期风险决策问题,它的数学模型研究对于解决这些问题具有重要的作用.作者建立了一种新的多周期多目标条件风险值(CVaR)数学模型理论和方法.先定义了一种带时间段的多周期多目标损失函数下的α-VaR和α-CVaR值,给出了一类多周期多目标CVaR最优化模型.然后,证明了多目标意义下的对应模型的等价定理,给出了多周期多目标CVaR模型的近似求解等价模型.最后,建立了一种生产企业在供过于求和供不应求两种情形下产生的多周期双目标CVaR模型,针对一个电力生产企业进行的数值实验,表明了模型可以得到在最小供给的用电损失分布下的各周期下的相匹配供电策略,可以帮助供电部门各个时期供电不平衡状况下的风险控制.     

一类具有偏差变元的高阶中立型Lienard方程周期解的存在性

利用重合度理论和不等式分析技巧,获得了一类具有偏差变元的高阶中立型Lienard方程(x(t)-cx(t-δ))~((m))+f(x(t))x′(t)+β(t)g(x(t-T(t)))=p(t)周期解存在性的新充分条件,推广和改进了已有文献的相关结论.     

一类超线性Duffing方程的Aubry-Mather集

本文通过引进适当的作用-角变量变换并结合新的估计方法,对超线性Duffing方程的Poincaré映射应用推广的Aubry-Mather定理,获得了一类超线性Duffing方程的Aubry-Mather集存在的充分性条件.