两个二能级原子与真空辐射场相互作用中的偶极平方压缩

研究了两个二能级原子与真空辐射场相互作用中原子的偶极平方压缩效应。通过数值计算,讨论了原子与辐射场之间耦合常数相对大小值以及原子的初始相干性对偶极平方压缩效应的影响     

稠环芳烃有机物的三阶非线性光学性能研究

采用Ｎｄ：ＹＡＧ皮秒锁模脉冲激光λ＝５３２．０ｎｍ,运用３Ｄ前向简并四波混频（ＤＦＷＭ）的方法,测量了稠环芳烃中的１．２．５．６二苯并蒽（Ｃ２２Ｈ１４）,１．２．８．９．二苯并五苯（Ｃ３０Ｈ１８）的三阶非线性极化率Ｘ＾（３）,非线性折射系数ｎ２以及三阶非线性的时间响应。发现该类材料具有较大的非线性效应,文中分析了非线性形成机制以及相关的影响因素。     

级联三能级系统中五阶极化拍频的理论研究

本文从理论上系统地研究了由于五阶极化强度间的干涉所导致的级联三能级系统相位共轭超快调制光谱学。 它对激光绝对频率的测量可达到与激光线宽同一量级的精度。 无论泵浦光束为窄带线宽或宽带线宽,它对能级差测量的总体精度仅仅取决于光学跃迁的均匀增宽,而与激光线宽和多普勒增宽无关。     

双光子非共振作用系统中纯度和密度算符间距的演化

研究了双光子非共振作用系统中纯度和密度算符间距的特性.讨论了相干光场与激发态二能级原子作用时失谐量对纯度和密度算符间距演化的影响.数值计算表明:失谐量对末态与初态的间距和原子与光场的缠结有调制作用.     

双模相干态和压缩真空态光场-非等同两原子体系的腔场谱

研究了两个非等同二能级原子与双模腔场相互作用过程的腔场谱.导出了双模初始光场处于任意量子态时腔场谱的计算公式,给出了光场处于相干态和压缩真空态时的数值结果,讨论了相对耦合常数R=g2/g1和初始场强对腔场谱的影响.发现相干态光场的腔场谱在R很小时为双峰,在R接近于1时为3峰.压缩真空态的腔场谱在弱场条件下表现为复杂的多峰结构,在强场条件下则只有单一经典共振峰或裂距很小的双峰.     

Secondary instabilities of the in-phase synchronized wakes past two circular cylinders in side-by-side arrangement

In the present study we investigate the secondary instability of the in-phase synchronized vortex shedding from two side-by-side circular cylinders at low Reynolds numbers. Two distinct Floquet modes become unstable for different values of the Reynolds number and of the non-dimensional gap spacing, leading to the onset of the well-known flip-flop instability of the two cylinder wakes. In both cases the two-dimensional Floquet analysis reveals that at very low Reynolds numbers, a pair of complex-conjugate multipliers crosses the unit circle, showing the same frequency as the biased gap-flow flip-over. In the past literature this behaviour has been often ascribed to a bistability of the flow. On the contrary, the present DNS and stability results provide evidence that at low Reynolds numbers, the flip-flopping behaviour originates from a Neimark–Sacker bifurcation of the in-phase shedding cycle.     

Response and wake patterns of two side-by-side elastically supported circular cylinders in uniform laminar cross-flow

Vortex-induced vibrations (VIV) of two side-by-side elastically supported circular cylinders in a uniform flow with the Reynolds number of 100 are numerically investigated by using the immersed boundary method. The cylinders are constrained to oscillate in the cross-flow direction with a center-to-center spacing ratio $T/D$ ranging from 2 to 5. The structural damping is set to zero to enable large vibration amplitudes in the range of reduced velocity $U_r=3-10$. It is found that the proximity of the cylinders does not have a significant impact to the lock-in region and cylinder responses, except at a small spacing ratio of $T/D=2$. The critical spacing ratio is determined as $T/D=4$ and beyond that the interaction between the cylinders is negligible. The following six near-wake patterns are observed; the irregular pattern, in-phase flip-flopping pattern, out-of-phase flip-flopping pattern, in-phase-synchronized pattern, antiphase-synchronized pattern and the biased antiphase-synchronized pattern. These patterns are plotted in a plane of $U_r$ and $T/D$, together with approximate borderlines to distinguish one region from the others. The time histories, spectral features and wavelet transform contours of drag and lift forces are presented to elucidate the mechanisms of the in-phase and out-of-phase flip-flopping phenomena. It is established that the in-phase flip-flopping stems from the long-short near-wake pattern and its low-frequency flip-over, whereas the out-of-phase pattern originates from the large vortex shedding from the fictitious bluff-body with an augmented characteristic length.     

两模光场与原子相互作用中光场周期性和频效应-理想Kerr介质腔中非关联双模相干态光场与V型三能级原子相互作用系统中光场的不等阶和压缩效应

利用多模压缩态理论,通过数值计算研究了高Q Kerr介质腔中非关联双模相干态光场与V型三能级原子相互作用系统中双模光场的不等幂次高次和压缩效应,分别绘出了两模光场第一模i次方第二模j次方不等幂次和压缩度的第一正交分量(Sh1_ij),第二正交分量(Sh2_ij)的时间演化曲线.结果表明:1)Kerr介质的存在和嵌放在介质中的V型三能级原子是产生双模光场不等阶和压缩效应的物质条件,二者缺一不可.2)腔中光场和原子发生光子交换是导致双模光场不等幂次和压缩效应的微观机制.3)在不考虑坐标度的情况下,不同条件下的时间演化曲线呈现非常相似的"崩坍-复原-凹谷"式结构,且复原区的波型振荡次数及凹谷区的振荡下降和振荡上升型式一样.4)在χ以及,不变的条件下,不等幂次高次和压缩度时间演化曲线的崩坍-复原-凹谷式结构的持续时间随压缩阶次的升高而缩短,压缩度随压缩阶数的升高而迅速下降.5)在平均光子不变(即,恒定),但Kerr介质不同(即χ变化)的条件下,不等幂次高次和压缩度曲线的周期随Kerr介质的三阶非线性极化系数χ的增加而缩短,幅度则不受Kerr介质的三阶非线性极化系数变化的影响.6)不等幂次高次和压缩效应的持续时间等强烈地依赖于Kerr介质的非线性程度,χ越大不等阶和压缩效应持续时间就越短.在相同压缩幂次的情况下,不等幂次高次和压缩度演化曲线正向幅度随平均光子数的增大而增大.     

Decay rate for a PH/M/2 queue with shortest queue discipline

In this paper, we consider a PH/M/2 queue in which each server has its own queue and arriving customers join the shortest queue. For this model, it has been conjectured that the decay rate of the tail probabilities for the shortest queue length in the steady state is equal to the square of the decay rate for the queue length in the corresponding PH/M/2 model with a single queue. We prove this fact in the sense that the tail probabilities are asymptotically geometric when the difference of the queue sizes and the arrival phase are fixed. Our proof is based on the matrix analytic approach pioneered by Neuts and recent results on the decay rates. AMS subject classifications: 60K25 · 60K20 · 60F10 · 90B22     

双频全息光栅的空间衍射特性及其应用

本文详细讨论了双频全息光栅的空间衍射特性,指出利用双频全息光栅的空间衍射特性可以方便地获得等强度双光束干涉场,该干涉场既可有效地用于制作高质量全息光栅,亦可以作为产生叠栅条纹的空间虚光栅,用于微小位移、转角、变形及三维面形的高灵敏度和非接触测量。文中还给出了相应的实验结果。