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481.
482.
ZHANG Xiao-Qiang WANG Guang-Rui CHEN Shi-Gang 《理论物理通讯》2008,49(4):1033-1038
A shell-model version of passive scalar problem is introduced, which is inspired by the model of K. Ohkitani and M. Yakhot [K. Ohkitani and M. Yakhot, Phys. Rev. Lett. 60 (1988) 983; K. Ohkitani and M. Yakhot, Prog. Theor. Phys. 81 (1988) 329]. As in the original problem, the prescribed random velocity field is Gaussian and δ correlated in time. Deterministic differential equations are regarded as nonlinear Langevin equation. Then, the Fokker-Planck equations of PDF for passive scalars are obtained and solved numerically. In energy input range (n<5, n is the shell number.), the probability distribution function (PDF) of passive scalars is near the Gaussian distribution. In inertial range (5≤n≤16) and dissipation range (n≥17), the probability distribution function (PDF) of passive scalars has obvious intermittence. And the scaling power of passive scalar is anomalous. The results of numerical simulations are compared with experimental measurements. 相似文献
483.
V. G. Shcherbitskii V. É. Kisel' A. V. Podlipenskii M. I. Demchuk N. V. Kuleshov V. I. Levchenko V. N. Yakimovich M. Mond S. Kück G. Huber B. I. Denker S. E. Sverchkov 《Journal of Applied Spectroscopy》2002,69(2):254-259
The spectroscopic properties of Cr2+ ions in Cr:Cd1–x
Mn
x
Te (CMT) crystals are studied, and the possibility of using these impurity crystals as active media and saturable absorbers of solidstate lasers of medium IR range is demonstrated. The bands of absorption with a maximum at 1.9 m and of luminescence with a maximum at 2.6 m correspond to the transitions between the levels 5
T
2 and 5
E of the tetracoordinated Cr2+ ions with more than 1·10–18cm2 cross sections. The pulsed and continuous lasing modes of a Cr:CMT laser are realized in the 2.6m region. The Cr:CMT crystals are characterized by effective saturation of impurity absorption. The cross sections of absorption from the ground and excited states of the Cr2+ ions at = 2.09 m are determined: gsa = 1.1·10–18 cm2; esa/gsa < 0.1. With the use of the Cr:CMT crystals as a passive gate the regime of Qswitching of the Cr,Tm,Ho:YAG laser emitting at = 2.09 m is obtained. 相似文献
484.
WANG Songtao ZHAO Shengzhi ZHANG Xingyu WANG Qingpu SUN Lianke ZHANG Shaojun 《Chinese Journal of Lasers》1998,7(4):293-297
The Cr4+-doped saturable absorber Cr4+:YAG is used as the passive Q-switch for a conventional pulsed Nd:Sr5(VO5)3F(Nd:S-VAP) oscillator, and the short high-peak-power pulses of laser have been obtained. The laser output characteristics are investigated under the conditions of different small-signal transmittance of Cr4+:YAG and different reflectivity of the output coupler. The rate equtions of Q-switched coupling wave are given, and the numerical solutions of equations are in agreement with the experimental results. 相似文献
485.
We present a functional integration method for the averaging of continuous productsP
t
ofN×N random matrices. As an application, we compute exactly the statistics of the Lyapunov spectrum ofP
t
. This problem is relevant to the study of the statistical properties of various disordered physical systems, and specifically to the computation of the multipoint correlators of a passive scalar advected by a random velocity field. Apart from these applications, our method provides a general setting for computing statistical properties of linear evolutionary systems subjected to a white-noise force field. 相似文献
486.
研制了一台水介质布鲁姆林线驱动被动紫外预电离放电泵浦KrF准分子激光器,研究了其振荡和放大输出特性。在充电电压25kV,工作气压0.2MPa,以振荡器工作方式输出激光能量近200mJ。以放大器方式工作时,注入激光脉宽25ns,能量70mJ,放大输出达330mJ。 相似文献
487.
488.
阐述了基于四元平面十字阵的声音目标被动定位的原理.利用目标与基阵平台分布在不同平面的特点,采用简单的平面阵实现目标的三维定位,简化了布阵的复杂性.针对基于四元平面十字阵的声音目标被动定位算法,分析了野值产生的原因,并研究了水平方位角、垂直俯仰角、时延估计误差度、目标距离、基阵尺寸等因素对野值产生的影响. 相似文献
489.
490.
对激光二极管(LD)抽运的自拉曼Nd∶GdVO4被动调Q激光器进行了详细的理论和实验研究。实验中采用Nd∶GdVO4晶体同时作为激光介质和拉曼晶体,分别用了两块不同初始透射率的Cr4 ∶YAG晶体,得到并比较了采用不同初始透射率的Cr4 ∶YAG晶体时被动调Q自拉曼激光器的性能。测量了平均输出功率、脉冲宽度和脉冲重复率随抽运功率的变化关系。当Cr4 ∶YAG的初始透射率为0.91,输入功率是5.7 W时,得到的拉曼光的最高功率为244.6 mW,相应的转换效率为4.3%。通过数值求解基频光和拉曼光空间分布的速率方程并应用到被动调Q自拉曼Nd∶GdVO4激光器。获得的理论结果与实验结果大致相符。 相似文献