Diffusion and Adsorption of Benzene and Propylene in MFI,MWW and BEA Zeolites:Molecular Dynamics and Grand Canonical Monte Carlo Simulations

The diffusion and adsorption behaviors of benzene and propylene in zeolites MFI, MWW and BEA have been studied by molecular dynamics（MD） and grand canonical Monte Carlo（GCMC） simulations. The diffusion coefficients of benzene and propylene in MFI, MWW and BEA zeolites were calculated by simulating the mean-square displacements（MSD） at 298 and 600 K. Benzene and propylene showed the different adsorption rules in the channels of the three zeolites. For propylene, the molecular loadings decreased in the order： BEA（linear channel）〉BEA （tortuous channel）〉MFI（linear channel）〉MWW（12-membered rings, 12MR channel）〉MFI（tortuous channel）〉MWW （10-membered rings, 10MR channel）; for benzene, the molecular loadings decreased in the order： BEA（linear chan-nel）〉BEA（tortuous channel）〉MWW（12MR channel）〉MFI（linear channel）〉MFI（tortuous channel）〉MWW（10MR channel）. Besides, the adsorption isotherms of benzene and propylene in the three zeolites at 298 and 443 K were simulated. The results show that the different factors influenced the molecular adsorption at various temperatures and pressures, leading to the different rules for the adsorption of benzene and propylene molecules in the zeolites. At a low pressure, the unfavorable energy would make the loadings of propylene lower than those of benzene. When pressure was higher than 0.25 kPa, the adsorption of benzene in MFI would nearly reach saturation.

Sorption and permeation of gaseous molecules in amorphous and crystalline PPX C membranes: molecular dynamics and grand canonical Monte Carlo simulation studies

Amorphous and crystalline poly （chloro-p-xytylene） （PPX C） membranes are constructed by using a novel com- putational technique, that is, a combined method of NVT＋NPT-molecular dynamics （MD） and gradually reducing the size （GRS） methods. The related free volumes are defined as homology clusters. Then the sorption and the permeation of gases in PPX C polymers are studied using grand canonical Monte Carlo （GCMC） and NVT-MD methods. The results show that the crystalline PPX C membranes provide smaller free volumes for absorbing or transferring gases relative to the amorphous PPX C area. The gas sorption in PPX C membranes mainly belongs to the physical one, and H bonds can appear obviously in the amorphous area. By cluster analyzing on the mean square displacement of gases, we find that gases walk along the x axis in the crystalline area and walk randomly in the amorphous area. The calculated permeability coefficients are close to the experimental data.

Monte Carlo Simulation of Laser-Ablated Particle Splitting Dynamic in a Low Pressure Inert Gas

A Monte Carlo simulation method with an instantaneous density dependent meanfree-path of the ablated particles and the Ar gas is developed for investigating the transport dynamics of the laser-ablated particles in a low pressure inert gas.The ablated-particle density and velocity distributions are analyzed.The force distributions acting on the ablated particles are investigated.The influence of the substrate on the ablated-particle velocity distribution and the force distribution acting on the ablated particles are discussed.The Monte Carlo simulation results approximately agree with the experimental data at the pressure of 8 Pa to 17 Pa.This is helpful to investigate the gas phase nucleation and growth mechanism of nanoparticles.

DYNAMIC MONTE CARLO STUDY ON THE CORRELATION BETWEEN SHAPE AND SIZE OF LINEAR POLYMER CHAINS

The correlation between shape and size of linear chains on the simple cubic lattice is investigated using a dynamicMonte Carlo technique. A positive correlation between the asphericity parameter A and the square of the end-to-end distanceR^2, as well as that between A and the square of the radius of gyration S^2, is found for both RW and SAW chains, indicatingthat a chain conformation of small size is usually more spherical than one of large size. The result can explain why the shapeof the SAW chain deviate much more from a sphere than that of the RW chain, and can also explain the similar dependenceof size and shape on chain stiffness and on the distance of the first bead of a chain from an infinitely large flat surface.

Noninvasive in vivo study of NADH fluorescence and its real-time intrinsic dynamical changes: Experiments and seven-layered skin model Monte Carlo simulations

Reduced nicotinamide adenine dinucleotide(NADH)plays a crucial role in many biochemical reactions in human metabolism.In this work,a flow-mediated skin fluorescence(FMSF)-postocclusion reactive hyperaemia(PORH)system was developed for noninvasive and in vivo measurement of NADH fluorescence and its real-time dynamical changes in human skin tissue.The real-time dynamical changes of NADH fluorescence were analyzed with the changes of skin blood flow measured by laser speckle contrast imaging(LSCI)experiments simultaneously with FMSFPORH measurements,which suggests that the dynamical changes of NADH fluorescence would be mainly correlated with the intrinsic changes of NADH level in the skin tissue.In addition,Monte Carlo simulations were applied to understand the impact of optical property changes on the dynamical changes of NADH fluorescence during the PORH process,which further supports that the dynamical changes of NADH fluorescence measured in our system would be intrinsic changes of NADH level in the skin tissue.

纯铜动态再结晶的Monte Carlo法模拟

本文建立了一种基于能量判据的确定动态再结晶各个阶段临界应变的方法,并基于此种方法利用Monte Carlo（MC）法进行了纯铜动态再结晶的二维模拟,定量计算了变形引起的存储能与变形之间的关系,计算出了发生动态再结晶的临界应变.模拟结果表明,采用MC法可以揭示动态再结晶的形核生长过程与应变历史之间的关系,结合本文所建立的基于能量判据的确定动态再结晶各个阶段临界应变的方法,可以预测开始发生动态再结晶的临界变形条件.

嵌段聚醚非离子表面活性剂在油水界面吸附的动态Monte Carlo模拟

发展了一种利用MonteCarlo方法模拟两嵌段共聚物型非离子表面活性剂在油水界面吸附的动态算法,可以同时获得吸附过程的一些静态性质(如平衡后油水界面上所吸附的共聚物分子数目、界面层的厚度、对称性以及油水界面张力)和动态性质(如系统达到平衡所需时间等);在模拟过程中可以观察到共聚物分子在油水界面形成的亲油基伸展在油相、亲水基伸展在水相的定向排列的稳定的单分子界面膜;在其他条件一致的情况下,本文所描述的方法与静态算法所得到的界面上吸附的共聚物分子数基本相同,但略有差异,文中给出了合理的解释;绘制了界面吸附的共聚物分子数随模拟进程的变化图,当作用能参数不同时得到不同的吸附曲线,随着模拟的进行,高作用能系统平稳达到吸附平衡值,而低作用能系统的吸附曲线则在达到最大值后逐渐降低,最终达到平稳值,与文献报道的实验结果十分吻合,利用物理化学的基本原理对这些不同进行了解释。图7表2参14。

力传感器惯性质量的改进Monte Carlo校准方法

惯性质量是力传感器模型的重要校准参数,也是影响动态力测量精度的关键因素之一。为了消除参数误差对惯性质量校准模型引起的病态,提出一种改进Monte Carlo校准(MMCC)方法。首先,建立力传感器惯性质量、配重质量与测量响应之间的模型;其次,利用伪随机数生成技术,分别对该模型中的配重质量、加速度和电压进行样本空间的全域模拟;然后,根据区间判断准则筛选出满足预设精度的有效样本;最后,结合有效样本的概率,估计出力传感器的惯性质量,并实现动态校准。为了验证本文方法的准确性,利用正弦激振台对Kistler 9331B型力传感器进行动态校准。实验结果表明,惯性质量的估计值为83.91 g,估计误差为0.67%,标准差为0.74 g;动态力的校准误差范围为[-7.88%,11.46%]。校准误差明显低于传统的二次及多次配重法。

高分子链动态行为的Monte Carlo模拟

运用Monte Carlo方法对线型高分子链格点模型进行模拟,研究了高分子链的动态行为随体系内组分间相互作用能的变化情况.讨论了随着溶剂分子与高分子链段间的相互作用能εPS与高分子链段间的相互作用能εPP的增大,链动力学物理量gcm(t),gm(t),ge(t)和gr(t)的变化情况.结果显示,εPP对高分子链的动态行为较εPS影响较小,但体系缠结的特征不完全取决于εPS和εPP的变化,主要受体系链长度的影响.

Monte Carlo模拟在建设用地需求预测中的应用

在建设用地需求预测中 ,以自变量的分布函数为基础 ,建立未来各年用地规模函数 ,通过MonteCarlo模型模拟 ,可以有效地预测未来年份的用地规模 。

高分子抑制蛋白质聚集的动态Monte Carlo模拟

抑制聚集是蛋白质产品下游加工特别是制剂过程中的重要问题。本文采用动态Monte Carlo方法和二维晶格HP蛋白质模型,通过建立高分子-蛋白质复合物微观结构和蛋白质构象概率分布来研究高分子对蛋白质聚集行为的影响。结果表明,高分子的疏水性、分子量及其浓度对于蛋白质的聚集行为有显著的影响。当其疏水性适宜时,高分子可富集在蛋白表面疏水位点,强化蛋白质分子在水溶液中的分散,从而抑制聚集。高分子还可缠绕在蛋白质分子表面形成限制性空间从而稳定蛋白质的天然结构。

高速精密冲床可靠性的Monte Carlo模拟与试验验证

下死点动态精度是评价压力机性能的重要指标之一,决定着冲压件的冲压质量。在瞬时可靠度理论的基础上建立了高速冲床运动精度可靠性的计算模型,并用瞬时状态矩阵对Monte Carlo模拟方法进行改进和简化。基于改进后的Monte Carlo模拟方法分析了JF75G-300高速冲床在不同速度下制造误差、弹性变形和运动副间隙对运动精度可靠性的影响。仿真结果表明:不同速度下的位移误差均服从正态分布,且随着速度的提高位移误差的波动量增大,运动精度的瞬时可靠性明显降低。通过测量JF75G-300高速冲床不同速度下的下死点动态精度,验证了速度变化对冲床运动精度可靠性影响的模拟结果。以上模拟方法可在设计阶段对冲床的下死点动态精度进行预测,为加工精度、杆件刚度及装配精度的选择和优化提供理论基础。

凝并和成核机理下颗粒尺度分布的Monte Carlo求解

颗粒的凝并和成核现象影响其尺度分布,现有的Monte Carlo方法描述颗粒尺度分布的时间演变过程存在若干困难.提出了一种新的多重Monte Carlo(MMC)算法,基于时间驱动,利用加权的虚拟颗粒的思想,在模拟过程中保持虚拟颗粒总数不变和计算区域体积不变.利用该算法对“常凝并核,一阶成核”的情况下颗粒尺度分布的时间演变过程进行了数值求解,所得结果与数值解相符,表明MMC算法具有高且稳定的计算精度.另外,MMC算法由于跟踪比实际颗粒数目少得多的虚拟颗粒而具有较低的计算代价.

自由基引发的凝胶化反应的Monte Carlo模拟

基于自由基凝胶化反应的基本原理，在一个具有周期性边界条件的二维网络上，利用动态ＭｏｎｔｅＣａｒｌｏ 方法模拟了聚合物凝胶的自由基凝胶化反应，得到了凝胶的具体结构，研究了总单体浓度（ 单体浓度和交联剂浓度之和） 对凝胶的分形结构和孔径分布的影响．模拟中首次考虑了聚合后单体的运动对凝胶结构的影响．结果表明：考虑聚合后单体的运动，可使所得凝胶网络的分形维数和凝胶化所需的最低浓度均显著小于动力学凝胶化模型和ＤＬＡ 模型的相应值．用移动气泡法得到了凝胶网络的孔径分布，发现凝胶网络中大孔所占百分率明显多于随机纤维网络模型．

气固两相流中颗粒碰撞的Monte-Carlo数值模拟

利用颗粒碰撞动力学模型和颗粒几何碰撞率模型,采用Monte-Carlo算法来模拟颗粒之间碰撞,把该算法与求解雷诺应力-概率密度函数模型的有限差分-MonteCarlo算法耦合起来,对轴对称突扩通道内的两相旋流场进行了数值模拟,模拟结果表明,由于颗粒碰撞使颗粒的动能和湍动能在三个坐标方向上进行了再分配,从而导致颗粒的动能和湍动能在三个坐标方向上趋于各向同性;另外,由于颗粒碰撞破坏了颗粒-颗粒、颗粒-流体微团之间的速度关联,从而造成颗粒湍动能及两相速度脉动关联的降低。

高分子动态Monte Carlo模拟的协同运动算法

A Monte Carlo simulation algorithm of polymer was proposed, which was similar to the cooperative motion algorithm in literatures. In this algorithm several segments of the polymer can move cooperatively, this may be interpreted as the effect of tensile force in the polymer chain. Its dynamic behavior is in agreement with the Rouse theory, so it can be used as a dynamic Monte Carlo simulation algorithm.

直圆管道中分子流态下“位置束流效应”的Monte Carlo法模拟

利用Monte Carlo模拟方法计算证明,气体在分子流态下通过直圆管道时有“位置束流效应”存在,即在直圆管道中心区域,分子通过的密度增大;而在靠近管壁的边缘区域,分子通过的密度减少。为了恰当地反映位置束流效应现象,专门定义了评价参数γ为通过某一圆环区域的分子数密度与通过整个截面的分子数密度之比。模拟计算得出,在直圆管道的中心区域,评价参数的平均值γ≈1.11;而在边缘区域,γ≈0.91。

1-丁烯在MCM-22分子筛中的吸附与扩散：Monte Carlo与动力学模拟研究

采用巨正则Monte Carlo方法和分子动力学方法研究了1-丁烯在MCM-22分子筛中的吸附现象和扩散行为,得到了1-丁烯吸附在该分子筛孔道中的相互作用能和在不同孔道中的扩散轨迹和扩散系数.结果表明1-丁烯在MCM-22分子筛中主要存在两个相互作用能区间,1-丁烯优先吸附在十元环孔道中;1-丁烯的扩散和移动主要发生在十二元环超笼的中部,十元环孔道中的1-丁烯扩散速度明显小于十二元环超笼系统中的扩散速度.

基于Monte-Carlo方法的耳垂动态光谱检测研究

选择耳垂作为测量部位,建立了多层耳垂组织仿真模型,利用Monte-Carlo方法研究了不同光源特性(光束半径,入射能量大小及分布等)及模型参数下耳垂组织模型的光透射能量及分布规律,由透射光能量分布、光电二极管光敏面积和探测灵敏度推出特定测量信噪比要求的入射光能量。研究结果表明,耳垂组织的实际入射光能量能够满足动态光谱检测的要求,获得了更高的动态光谱测量精度,可满足动态光谱法的血液成分检测的要求。

二维三角格子上高分子动态Monte Carlo模拟的协同运动算法

在动态MonteCarlo模拟的协同运动算法中 ,几个相邻的链节可以同时运动 ,这可以理解为高分子链中张力的作用引起的协同运动。将这一算法用于二维三角格子模型上RW链和SAW链的模拟。结果表明RW链的动力学行为符合Rouse理论 ,说明该算法可以用于高分子动力学研究 ,其优点是不需要使用键长涨落模型。