单纵模Nd∶YAG激光抽运CH_4中强后向受激拉曼散射

用单纵模Nd∶YAG二倍频激光[波长532 nm,线宽Δνp<100 MHz,脉宽(半峰全宽)6.5 ns]抽运CH4气体,观察到很强的后向一级斯托克斯(BS1)受激拉曼散射,这与前人采用脉宽30 ns的单纵模抽运激光得到的绝大部分为后向受激布里渊散射(SBS)完全不同,其原因是脉宽6.5 ns与本实验条件下CH4的受激布里渊散射声子寿命接近,受激布里渊散射处于瞬态。理论计算表明,这时的受激布里渊散射瞬态增益系数已略小于后向一级斯托克斯的增益系数,而被其竞争抑制。当脉冲重复频率为2 Hz,抽运能量为95 mJ时,在1.1 MPa CH4中,后向一级斯托克斯的量子转换效率高达73%,其时间波形出现张弛振荡,脉宽被压窄到1.2 ns,从而使后向一级斯托克斯峰值功率达到了抽运激光功率的2.7倍,而且其光束质量要大大优于抽运激光的光束质量。用编制的准二维计算机模型程序相当好地再现了实验中后向一级斯托克斯的时间波形张弛振荡。     

600 kJ供能系统及其在轨道炮中的应用

 本文介绍了一种适合于电磁轨道炮使用的600 kJ供能系统。初级能源是电容器组。经过短路开关和电感储能线圈组成的转换电路，把能量输送给轨道炮。系统的主控开关和短路开关是金属接触型固体介质爆炸开关。本文推荐了一种爆炸开关闭合电阻随时间变化的经验模型。这套供能系统经过实验证明，它运行可靠、性能稳定。     

A new method and instrument for accurately measuring interval between ultrashort pulses

Using second-order autocorrelation conception, a novel method and instrument for accurately measuring interval between two linearly polarized ultrashort pulses with real time were presented. The experiment demonstrated that the measuring method and instrument were simple and accurate (the measurement error ＜ 5 fs). During measuring, there was no moving element resulting in dynamic measurement error.     

An automated system for the determination of fluoride

A procedure is reported for the automated determination of fluoride by the method of standard addition. Additions of standard are made via a peristaltic pump and the amounts of standard added are computed from the change in weight of the standard in its container on a digital electronic balance.     

Few-cycle pulse compression through cascade of bulk media and hollow-core fiber

We experimentally demonstrated a new few-cycle pulse compression technique through the cascade of bulk media and hollow-core fiber (HCF) and this compression system has been intensively studied. The pulses with the duration of ∼5 fs and the energy of 0.33 mJ near 800 nm have been generated by compressing the ∼40 fs input pulse from a commercial laser system. In principle, this technique allows compression of pulses with duration of picoseconds to a few cycles (sub-7 fs) and the output can be above 1 mJ.     

Convergence and quasi-optimality of an adaptive finite element method for optimal control problems with integral control constraint

In this paper we study the convergence of an adaptive finite element method for optimal control problems with integral control constraint. For discretization, we use piecewise constant discretization for the control and continuous piecewise linear discretization for the state and the co-state. The contraction, between two consecutive loops, is proved. Additionally, we find the adaptive finite element method has the optimal convergence rate. In the end, we give some examples to support our theoretical analysis.     

级联双稳Duffing系统的随机共振研究

研究了级联双稳Duffing系统的随机共振特性, 证明级联双稳Duffing系统变尺度系数、阻尼比和级数等参数的适当调节, 不仅可实现大参数信号的级联随机共振, 而且可优化单级双稳Duffing系统的随机共振特征, 即参数调节的级联双稳Duffing系统能实现比单级双稳Duffing系统更好的随机共振输出. 此外, 级联双稳Duffing系统对方波信号具有良好的滤波整形作用, 可用于实现含噪方波信号的波形恢复. 关键词： 级联双稳Duffing系统 随机共振 变尺度 参数调节     

Online retailers’ promotional pricing,free-shipping threshold,and inventory decisions: A simulation-based analysis

We consider a two-stage decision problem, in which an online retailer first makes optimal decisions on his profit margin and free-shipping threshold, and then determines his inventory level. We start by developing the retailer’s expected profit function. Then, we use publicly-available statistics to find the best-fitting distribution for consumers’ purchase amounts and the best-fitting function for conversion rate (i.e., probability that an arriving visitor places an online order with the retailer). We show that: (i) a reduction of the profit margin does not significantly affect the standard deviation of consumers’ order sizes (purchase amounts) but increases the average order size; whereas, (ii) variations in a positive finite free-shipping threshold affect both the average value and the standard deviation of the order sizes. We then use Arena to simulate the online retailing system and OptQuest to find the retailer’s optimal decisions and maximum profit. Next, we perform a sensitivity analysis to examine the impact of the ratio of the unit holding and salvage cost to the unit shipping cost on the retailer’s optimal decisions. We also draw some important managerial insights.