A Geometry Model for Tortuosity of Streamtubes in Porous Media with Spherical Particles

A geometry model for tortuosity of tortuous streamtubes in porous media with spherical particles is proposed based on the assumption that some particles in a porous medium are unrestrictedly overlapped and hence of different configurations. The proposed model is a function of porosity with no empirical constant imposed on it.The model predictions are found to be in good agreement with the available experimental data.     

脉冲激光烧蚀块状靶材的双动态界面研究

给出脉冲激光作用块状靶材的烧蚀模型.根据能量平衡原理,导出烧蚀面的位置随时间的变化关系.利用绝热近似、温度连续性条件和能量平衡原理来获得烧蚀面与固液相界面边界条件.结合热传导方程,利用精确解与积分近似法相结合的方案,给出固液两相的温度分布与时间和位置的变化关系,以及固液相界面的位置随时间的变化规律,并与已有的理论和实验结果进行比较.最后以铝靶为例计算模拟了激光烧蚀的全过程计算. 关键词： 脉冲激光 等离子体 固液相界面 烧蚀面     

Effects of Continuous Size Distributions on Pressures of Granular Gases

Direct Monte Carlo simulations are employed to investigate the granular pressures in granular materials with a power-law particle size distribution. Specifically, smooth circular discs of uniform material density are engaged in a two-dimensional rectangular box, colliding inelastically with each other and driven by a homogeneous heat bath at zero gravity. The resulting pressures are found to decrease as the widths of particle size distribution are increased. Moreover, the granular pressures in power-law systems are found to be unequally distributed among the various sizes of particles, with large particles possessing more pressure than their smaller counterparts. The width-dependent nature of the total pressures is induced by the more dispersion of smaller particles in the system as the particle size distribution is widened.     

脉冲激光制备薄膜材料的机理

给出脉冲激光作用块状靶材的烧蚀模型.根据能量平衡原理,导出烧蚀面的位置随时间的变化关系.利用绝热近似、温度连续性条件和能量平衡原理来获得烧蚀面与固液相界面边界条件.结合热传导方程,利用精确解与积分近似法相结合的方案,给出固液两相的温度分布与时间和位置的变化关系,以及固液相界面的位置随时间的变化规律,并将理论结果与实验数据进行比较.由流体动力学理论,得出了脉冲激光产生的等离子体的空间输运方程,将此方程与靶材烧蚀率公式结合起来,根据实验数据研究了不同激光功率密度和波长对KTN(KTa_0.65Nb_0.35O₃)薄膜沉积特性的影响,得到了一些有价值的结果,并对结果进行了详细的讨论.     

KTN薄膜脉冲激光沉积过程的机理研究

根据能量平衡原理,导出了脉冲激光作用靶材的烧蚀率公式,并根据流体动力学理论,得出了脉冲激光产生的等离子体的空间运动特性方程,将靶材烧蚀率公式与等离子体空间动力学方程结合起来,根据实验研究了不同激光功率密度和波长对Kta_0.65Nb_0.35O₃(KTN)薄膜沉积特性的影响,得到了一些有价值的结果,并对结果进行了详细的讨论,理论计算结果与实验大体符合. 关键词： PLD技术 烧蚀率 等离子体 KTN薄膜     

Dynamic simulation on the preparation process of thin films by pulsed laser

An ablation model of targets irradiated by pulsed laser is established. By using the simple energy balance conditions, the relationship between ablation surface location and time is derived. By an adiabatic approximation, the continuous-temperature condition, energy conservation and all boundary conditions can be established. By applying the analytical method and integral-approximation method, the solid and liquid phase temperature distributions are obtained and found to be a function of time and location. The interface of solid and liquid phase is also derived. The results are compared with the other published data. In addition, the dynamics process of pulsed laser deposition of KTN (Kta_0.65Nb_0.35O₃) thin film is simulated in detail by using fluid dynamics theory. By combining the expression of the target ablation ratio and the dynamic equation and by using the experimental data, the effects of laser action parameters on the thickness distribution of thin film and on the thin film component characteristics are discussed. The results are in good agreement with the experimental data.