Hopf Bifurcations for the Recently Proposed Smooth-and-Discontinuous Oscillator

We investigate the Hopf bifurcations of the recently proposed smooth-and-discontinuous （SD） oscillator which exhibits both smooth and discontinuous dynamics depending on the value of a parameter a. The nonlinearity presented in this system characterizes irrationality and piecewise linearity for smooth and discontinuous cases, respectively, which could not meet the requirements of the conventional methods due to the barrier of Taylor expansion. Introducing a series of new kinds of elliptic integrals of the first and second kind to the perturbed oscillator, we obtain the Poincare-Birchoff normal forms of Hopf bifurcations for both smooth and discontinuous regimes. We also demonstrate the criteria for the occurrence of Hopf bifurcations, the stability of periodic solutions bifurcating from the equilibria and the excellent agreement between the theoretical and numerical results.     

Excitation Transfer for K2 in High-Lying States by N2

A K-N2 mixture is irradiated in a glass fluorescence cell with pulses of 710hm radiation from an OPO laser, populated K2 （^1∧g） state by two-photon absorption. The cross section for ^1∧g →^3∧g transfer in K2 is determined using molecular fluorescence spectrometry. The cell temperature is kept constant at 553K. The N2 pressure is varied between 40 Pa and 400 Pa. The effects of K2-K collisions could not be neglected. These effects are subtracted out by using the results of the pure K experiment. The cross sections are （3.8 ± 1.5） ×10^-15 cm^2 for K2 （^1∧g） ＋ N2 → K2（^3∧g） ＋N2 and （8.9 ± 3.5） × 10^-15 cm^2 for K2 （^3∧g） collisions with N2.     

过模结构表面波振荡器模式选择

过模结构能提高器件的功率容量和工作频率, 能使器件工作在低磁场状态, 越来越多的器件采用过模结构.但是过模结构允许多个模式同时存在, 这可能会引起模式竞争问题.本文通过理论分析和数值计算, 研究了过模结构模式选择问题.计算结果表明, 通过选择合适的结构参数和电参数, 使得器件工作在行波状态, 可以实现不同横向模式的选择.在此基础上, 通过选择合适的电子束和结构参数, 能实现不同纵向模式的选择.对计算结果进行了粒子模拟验证, 与理论分析符合较好, 达到了模式选择的目的. 关键词： 过模结构 模式选择 色散关系 表面波振荡器     

改进的三维电磁PIC系统模拟并行算法

为了更好地实现对大尺度器件的模拟,以及更系统地验证和解决高功率微波系统在设计和实验中负载变化等影响,在进一步深入研究电磁PIC并行算法的基础上,运用MPI消息传递函数做出了改进。提出了一种整体建模、分段解析的并行算法,并从并行时序算法入手,通过减少一次同步提高了计算的效率。最后经过一个磁绝缘线振荡器进行验证,改进的算法正确,并且当计算进程数4个增加到16个时,计算速度能提高2.5倍左右。     

宽波段连续调谐全固态CW PPMgLN光学参量振荡器

利用半导体激光泵浦输出1064 nm波长的全固态连续Nd:YVO4激光器作为泵浦源,采用周期调谐和温度调谐组合调谐技术,对基于掺氧化镁周期性极化铌酸锂晶体（MgO:LiNbO3, PPMgLN）准相位匹配（QPM）的全固态连续波（CW）光学参量振荡器（OPO）宽波段无分立连续调谐输出特性进行研究。实验采用连续工作模式和外腔结构,基于多周期PPMgLN晶体的30.2,30.4和30.6 m周期,在改变晶体的极化周期的基础上,同时在30～100 ℃范围内调节晶体工作温度。实验结果表明:CW PPMgLN OPO的泵浦阈值仅为0.22 W;不同极化周期需要的温度调谐范围不同;信号光在1 559.8～1 597.2 nm近红外波段和闲频光在3 187.3~3 347.3 nm中红外波段连续调谐输出。实现了外腔式全固态CW OPO在信号光和闲频光波段的无分立连续调谐输出。     

1 053-nm all-fiber pulse multi-pass stretcher using a linear chirped fiber Bragg grating

An all-fiber optical laser pulse multi-pass stretcher using a chirped fiber Bragg grating (CFBG) is demonstrated. Pulses from a 1 053-nm mode-locked fiber seed oscillator are stretched by multiple passing through a chirped fiber grating set in a fiber regenerative amplifier structure. We stretch the pulse from 16 ps to 1.855 ns after it transmits seven loops in the stretcher. The main factors that affect the stretching results are discussed.     

Enhanced Synchronization of Intercellular Calcium Oscillations by Noise Contaminated Signals

We consider the dynamics of locally coupled calcium oscillation systems, each cell is subjected to extracellular contaminated signal, which contains common sub-threshold signal and independent Gaussian noise. It is found that intermediate noise can enhance synchronized oscillations of calcium ions, where the frequency of noise-induced oscillations is matched with the one of sub-threshold external signal. We show that synchronization is enhanced as a result of the entrainment of external signal. Furthermore, the effect of coupling strength is considered. We find above-mentioned phenomenon exists only when coupling strength is very small. Our findings may exhibit that noise can enhance the detection of feeble external signal through the mechanism of synchronization of intercellular calcium ions.     

Solution of the Fermi--Ulam Model in the Case of Periodic Perturbation

We discuss the evolution of the state and the average energy of the Fermi Ulam model in the case of periodic perturbation. By a perturbation technique, the time-dependent Sehr6dinger equation is solved and it is found that the particle will continuously absorb or radiate energy Jf the frequency of the oscillating wall meets the resonance condition. Usually, these two states cannot exist together at a certain frequency. However, there is an exception if the frequency is at some special values. We find these values and reveal that the energy for transmission has the minimum equivalent unit, which is in the form of a harmonic oscillator.     

Synchronization in Coupled Oscillators with Two Coexisting Attractors

Dynamics in coupled Dufling oscillators with two coexisting symmetrical attractors is investigated. For a pair of Dufl~ng oscillators coupled linearly, the transition to the synchronization generally consists of two steps： Firstly, the two oscillators have to jump onto a same attractor, then they reach synchronization similarly to coupled monostable oscillators. The transition scenarios to the synchronization observed are strongly dependent on initial conditions.     

S波段相对论速调管振荡器研究

介绍利用20 GW加速器二极管产生的电子束源,开展S波段相对论速调管振荡器(RKO)的理论设计、粒子模拟和实验研究的情况.该RKO采用3个紧密耦合的圆柱腔作为振荡腔,束流经过一段漂移管的群聚后采用三轴输出腔提取微波.该振荡器具有起振时间快、结构紧凑、束波转换效率较高等优点.采用无箔空心阴极和0.9 T的恒流源磁场引出的电压1 MV、束流13kA、脉宽40 ns的环形电子束驱动RKO,单次运行输出了3.5 GW的辐射微波功率,效率27％,频率2.86 GHz,瞬时带宽2%;脉冲重复频率20 Hz运行时,输出 关键词： 相对论速调管 振荡器 三轴提取腔 高功率微波