一维氢原子团簇模型下的兆电子伏离子与库仑爆炸： 简化的数值模拟

本文使用一维双列氢原子团簇模型对强激光场中的团簇动力学过程进行了数值模拟。计算所得的质子最大动能和能谱均与他人的计算或实验结果符合较好,但计算大为简化。表明本文所述模型适用于氢原子团簇模拟。本文亦根据逸出质子数量随入射激光强度变化的规律总结出一个描述团簇库仑爆炸的光强阈值公式。     

随机取向烟尘团簇粒子的光学截面的数值计算

采用蒙特卡罗方法根据团簇—团簇凝聚（CCA）模型对由球形原始微粒凝聚而成的烟尘团簇粒子进行了模拟,利用离散偶极子近似（DDA）方法数值计算了不同原始微粒粒径和数目组成的随机取向的烟尘团簇粒子的总消光截面、吸收截面及散射截面等光学特性参数,研究了原始微粒粒径及数目对随机取向烟尘团簇粒子光学特性的影响。结果表明：当入射波长一定时,随机取向烟尘団簇粒子的光学特性主要取决于原始微粒的粒径和数目;烟尘团簇粒子对不同波段激光的吸收和散射存在差别,这种差别随原始微粒粒径及数目变化而变化。这一工作为研究电磁波在烟尘中的传输特性提供重要参考数据。     

随机取向烟尘团簇粒子激光散射特性研究

利用蒙特卡罗方法根据团簇-团簇凝聚(CCA)模型对由球形原始粒子凝聚而成的烟尘团簇粒子进行了模拟,用离散偶极子近似(DDA)方法研究了烟尘团簇粒子随机取向时的激光散射特性,并与等效球形粒子的激光散射特性进行了比较。结果表明,等效球形粒子的激光散射特性与随机取向烟尘团簇粒子的激光散射特性存在着明显差别,不能用等效球形粒子来代替随机取向的团簇粒子;随机取向的烟尘团簇粒子的激光散射特性受基本粒子数量和粒径的影响比较大。该结果将为进一步研究随机取向团簇粒子的形成机理、形态特性以及激光在其中的传输特性提供了一种理论方法。     

激光在随机分布烟尘团簇粒子中的衰减特性

基于分形理论,采用团簇—团簇凝聚模型对随机分布烟尘团簇粒子的分形结构进行了模拟.利用离散偶极子近似方法研究了不同类型的随机分布烟尘团簇粒子的单次散射特性.利用蒙特卡罗方法研究了激光信号在随机分布烟尘团簇粒子中的传输衰减特性.讨论了入射角、激光波长、烟尘粒子数密度以及组成单个烟尘团簇粒子的原始微粒粒径和数目等参量对激光衰减特性的影响.研究结果对激光在复杂随机介质中的传输衰减特性分析提供了理论依据.     

激光在随机分布烟尘团簇粒子中的衰减特性

基于分形理论,采用团簇—团簇凝聚模型对随机分布烟尘团簇粒子的分形结构进行了模拟.利用离散偶极子近似方法研究了不同类型的随机分布烟尘团簇粒子的单次散射特性.利用蒙特卡罗方法研究了激光信号在随机分布烟尘团簇粒子中的传输衰减特性.讨论了入射角、激光波长、烟尘粒子数密度以及组成单个烟尘团簇粒子的原始微粒粒径和数目等参量对激光衰减特性的影响.研究结果对激光在复杂随机介质中的传输衰减特性分析提供了理论依据.     

分形结构对随机取向烟尘团簇粒子光散射特性的影响

利用蒙特卡罗方法对不同分形维数和分形前向因子的随机取向烟尘团簇粒子的分形结构进行了仿真,采用离散偶极子近似（DDA）方法对随机取向烟尘团簇粒子的缪勒矩阵元进行了数值计算,并与球形粒子模型进行了比较,深入探讨了烟尘团簇粒子的分形维数和分形前因子对其散射特性的影响。研究表明,等效球形粒子的光散射特性与随机取向烟尘团簇粒子的光散射特性存在很大差别,并且此差别随着团簇粒子的分形维数以及分形前向因子的增大而减小;分形维数对表征团簇粒子散射特性的缪勒矩阵元的影响在一定散射角范围内均比较明显,分形前向因子对团簇粒子的缪勒矩阵元角分布的影响与分形维数的影响类似,不过其影响相对分形维数较弱。     

用类O原子波函数对H+9团簇的体心立方结构与能量的研究

在单中心球模型近似下,选用类O原子解析函数,用变分法计算了H+9团簇体心立方结构与能量。结果表明当中心氢原子核到顶角氢原子核之间的距离R=1.97a0时,体系能量有一极小值E=-4.376h0(a0=0.529177×10-10m,h0=27.2eV)。这表明H+9团簇的体心立方结构是稳定的结构,H+9团簇是存在的。     

随机分布烟尘簇团粒子缪勒矩阵的数值计算

利用蒙特卡罗方法根据团簇-团簇凝聚（CCA）模型对由球形原始粒子凝聚而成的烟尘簇团粒子进行了模拟,用离散偶极子近似（DDA）方法对随机分布的烟尘簇团粒子的缪勒矩阵元素进行了数值计算,给出了不同入射波长情况下随机分布烟尘簇团粒子的缪勒矩阵元素与组成簇团粒子的基本粒子的粒径和数目的数值关系,为进一步研究随机分布簇团粒子的形成机理、形态特性、散射特性提供了一种理论方法. 关键词： 烟尘簇团粒子 缪勒矩阵 离散偶极子近似方法     

有限步扩散反应置限分形聚集

综合考虑扩散粒子浓度n、粒子扩散限制范围Δ、扩散粒子与种粒子或团簇相遇时，反应概率P及粒子扩散步数W的影响，提出了有限步扩散反应置限聚集的分形生长模型，模拟得到一系列典型的聚集生长图形，计算了相应的分形维数.结果表明，在粒子浓度n较小时，呈离散团簇状生长；而在粒子浓度较大时，则随反应概率P或粒子扩散步数W的增大，从离散团簇状生长转变为连续枝叉状生长. 关键词：     

石墨烯形核初期Cu(111)面上CxHy团簇生成的理论研究

采用基于密度泛函理论的第一原理计算方法,我们研究了Cu(111)表面上石墨烯成核生长过程中CxHy小团簇的吸附和生成行为. 计算结果表明：随着氢原子饱和度、氢原子个数的增大,CxHy团簇的形成能减小,碳原子与铜表面的平均距离增加,C-C键的平均键长呈增大趋势. 然而,当生成的CxHy团簇具有空间对称结构时,在一定程度上打破了上述规律性. 令人惊奇的是,形成的C3H4和C3H5对称团簇具有类似石墨烯的空间结构,这类结构可能在石墨烯的形成过程中起着重要的作用.     

Solvent effects on model telechelic polymers

A theory to predict the competition between intermolecular and intramolecular hydrogen bonding is extended to mixtures and applied to a model telechelic mixture. The theory is tested by comparing with simulation results for a mixture of fully flexible linear chains that can associate in a hydrogen bonding solvent. The simulation model for the telechelic is a flexible linear tetramer hard sphere chain with two hydrogen bonding sites, one on each terminal segment. The solvent is modelled as a hard sphere with four tetrahedrally arranged hydrogen bonding sites. The solvent is seen to affect the ability of the solute to bond intermolecularly and intramolecularly. The extent of hydrogen bonding and thermodynamic properties of the system were studied using Monte Carlo simulation and compared with predictions from a new statistical mechanics based theory for mixtures. Agreement of simulation and theory is good over the range of densities, temperatures and compositions studied.     

并联型光电设备稳定平台稳定解算研究

并联型光电设备稳定平台是针对光电跟踪系统需要而设计的一种新型并联机构,具有两个相互独立的转动自由度。以并联稳定平台为研究对象,介绍了动载体下并联稳定平台的工作原理,进行了并联稳定平台的运动学分析。采用齐次坐标变换方法,推导了从大地坐标系到平台定坐标系的转移矩阵,建立了并联稳定平台的稳定解算模型,进行了并联稳定平台的数值仿真研究。结果表明：随着旋转角增大,并联稳定平台的姿态角偏差和方位角偏差越来越大;在实际控制系统中若不考虑旋转角作用,这将严重影响并联型光电设备稳定平台的稳定精度。该研究为并联型稳定平台控制系统设计提供了一定的理论依据。     

基于JASMIN框架的区域大气模式并行程序开发及试验

以自主研制的区域中尺度暴雨大气模式为研究对象,基于JASMIN并行编程框架,建立构件化、层次化的区域大气模式大规模高效并行程序,并针对典型天气实例,对模式并行计算程序的正确性、并行性能及高分辨率模拟效果进行验证.结果证明,基于JASMIN框架的新模式程序与原串行模式具有很好的计算一致性,其不仅能保持原有模式良好的预报效果,且能显著提升模式大规模并行计算性能和可扩展性,在进一步提高模式分辨率后能得到更好的预报结果.     

抛物方程的多重非均匀网格模型及其应用

提出了抛物方程的多重非均匀网格模型,以准确求解三维空间存在多辐射源的电波传播问题。通过对不同辐射源建立不同的坐标系,并对其仿真空间采用不同的非均匀网格划分,构建了抛物方程的多重非均匀网格模型。在此基础上,实现了三维多辐射源问题的并行计算。实例仿真了空间存在四个辐射源的电波传播特性。结果表明,抛物方程的多重非均匀网格模型能够准确求解多源的空间电磁场分布特性,且在该算例中,并行技术使得抛物方程的计算速度提升了2.41倍,极大地提高了抛物方程对三维多源问题的求解效率。     

Effect of structural conduction and heat loss on combustion in micro-channels

This paper presents a simple analytical model for the effects of heat exchange within the structure of a micro-channel combustor, and heat loss from the structure to the environment. This is accomplished by extending reasoning similar to that employed by Mallard and Le Chatelier in their thermal theory for flame propagation. The model is used to identify some of the basic parameters that must be considered when designing an efficient micro-combustor and its predictions are compared with the results of a numerical simulation of stoichiometric premixed combustion of a hydrogen–air mixture stabilized between two parallel plates. The simulation incorporates a one-dimensional continuity/energy equation solver with full chemistry coupled with a model for thermal exchange in the structure. The results show that heat exchange through the structure of the micro-combustor can lead to a broadening of the reaction zone. Heat loss to the environment decreases the broadening effect and eventually results in flame quenching. This behaviour, which arises from the thermal coupling between the gas and the structure, influences the maximum achievable power density of microscale combustors.     

Diffusion of hydrogen in heterogeneous systems

The effective long-range long-time tracer diffusivity D_eff for interstitial diffusion of hydrogen through heterogeneous systems was studied theoretically for model systems consisting of isolated grains of material G embedded in a matrix of material M. Different solubilities of hydrogen in these two materials as well as different diffusivities are allowed for. Additionally, modified diffusion barriers at the phase boundaries were included in the diffusion model. The effect of different sizes, arrangements, and forms of the grains was also considered. D_eff was determined by Monte Carlo (MC) simulations on simple lattice models of the systems described above. An equilibrium distribution of hydrogen atoms among the two constituent materials was assumed. Our main interest was focused on whether and how D_eff may be related to mesoscopic or macroscopic quantities characterizing the heterogeneous system and its constituent materials, such as the volume fractions of the two materials, the fraction of lattice sites in the immediate vicinity of the phase boundary, the hydrogen concentrations c_G and c_M in the grains and in the matrix and the respective hydrogen diffusivities D_G(c_G) and D_M(c_M). In order to obtain good estimates for these relations in terms of analytic formulas, we attempted to model a heterogeneous system by a network of diffusion elements connected in series and in parallel, in analogy to an electric network. The properties of the basic connections, in parallel and in series, were studied on layered structures, for which analytic expressions for D_eff could be derived. The network formulas for different grain–matrix systems were tested by comparing with results of MC simulations. In general, the network formulas describe the corresponding MC results for D_eff fairly well. It was found that differences in the hydrogen solubilities in the two phases as well as modified energy barriers at the phase boundaries may have dramatic effects on D_eff. Received: 19 September 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001     

The kinetic process of non-smooth substrate thin film growth via parallel Monte Carlo method

A Monte Carlo simulation model of thin film growth based on parallel algorithm is presented. Non-smooth substrate with special defect mode is introduced in such a model. The method of regionalizing is used to divide the substrate into sub-regions. This method is supposed to be modulated according to the defect mode. The effects of surface defect mode and substrate temperature, such as the nucleation ratio and the average island size, are studied through parallel Monte Carlo method. The kinetic process of thin film growth in the defect mode is also discussed. Results show that surface defect mode contributes to crystal nucleation. Analyzing parallel simulation results we find that density defect points, substrate temperature and the number of processors contribute decisively to the parallel efficiency and speedup. According to defect mode we can obtain large grain size more feasibly and the parallel algorithm of this model can guide the non-smooth substrate simulation work.     

油资源运移聚集并行数值模拟和分析

多层油资源运移聚集并行数值模拟,其功能是重建油气盆地的运移聚集演化史,对于油资源的评价,确度油藏位置,估计油藏贮量均具有重要的价值.从生产实际出发,提出数学模型,构造大规模精细并行计算的耦合算子分裂隐式迭代格式,设计了并行计算程序和并行计算的信息传递和交替方向网格剖分方法.并对不同的网格步长进行了并行计算和分析.对滩海地区进行精细数值模拟,计算结果在油田位置等方面和实际情况相吻合.对模型问题(非线型性耦合问题)进行数值分析,得到最佳阶L²误差估计,解决了这一计算渗流力学和石油地质的困难问题.     

Recurrence spectra and dynamical simulation of Rydberg hydrogen atom near a metal surface

By using the closed-orbit theory including the effect of Coulomb scattering together with an electrical image potential approach, the recurrence spectra and the dynamical behaviours of the Rydberg hydrogen atom near a metal surface are presented. Theoretical analysis and numerical simulation reveal that the impacts of the image potential contributing to the recurrence spectrum are qualitatively analogous to that of the parallel electrical and magnetic fields on the Rydberg atom. The recurrence spectra are computed for a few selected scaled energies and the results demonstrate that the scaled energy dominates the dynamical properties of system. With the increase of the scaled energy e from small to large, the whole trend of spectral structure is from simple to complex,and then simple.     

Efficient solid state NMR powder simulations using SMP and MPP parallel computation

Methods for parallel simulation of solid state NMR powder spectra are presented for both shared and distributed memory parallel supercomputers. For shared memory architectures the performance of simulation programs implementing the OpenMP application programming interface is evaluated. It is demonstrated that the design of correct and efficient shared memory parallel programs is difficult as the performance depends on data locality and cache memory effects. The distributed memory parallel programming model is examined for simulation programs using the MPI message passing interface. The results reveal that both shared and distributed memory parallel computation are very efficient with an almost perfect application speedup and may be applied to the most advanced powder simulations.