利用Monte Carlo (MC) 方法,研究了一氧化碳和氢气在不同密度正己烷中的等温吸附情况.模型考虑了正己烷密度对一氧化碳和氢气在催化剂表面吸附量与吸附速率的影响.结果表明,主要有三个因素会影响溶质的吸附量:当溶剂密度低于其临界密度时,体系压力是影响溶质吸附量的主要因素；当体系处于超临界区时,超临界溶剂的溶解能力以及溶质和溶剂之间的竞争吸附是影响溶质吸附量的主要因素.在一定范围内增加溶剂的密度（压力）可以提高溶质在催化剂表面的吸附速率. 相似文献
Stretching and relaxation of a single DNA molecule tethered in a specially designed thin slit were studied using Monte Carlo simulation combined with bond fluctuation method. It was found that the extension and relaxation of the single DNA molecule are greatly affected by the confined environment. If the extent of the confined environment is increased by decreasing the distance between the two planar surfaces of the slit, the extension of the single DNA molecule increases, due to the screening of the hydrodynamic interaction of DNA segments by the planar surfaces of the slit. The relaxation of the single DNA molecule in different confined environments verifies this assumption completely. The correlation between the end-to-end separation and flow velocity obtained by Monte Carlo simulation is in good agreement with either the experimental results or theoretical consideration reported previously. 相似文献
We present a computational approach, using quantum Monte Carlo, that provides some insight into the effect of electron correlation on chemical bonding between individual pairs of atoms. Our approach rests upon a recently suggested relation between the bond order and charge fluctuations with respect to atomic domains. Within the present implementation we have taken a compromise between conceptual rigour and computational simplicity. In a first step atomic domains were obtained from Hartree-Fock (HF) densities, using Bader’s definition of atoms in molecules. These domains were used in a second step in quantum Monte Carlo calculations to determine bond orders for pairs of atoms. Correlation effects have been studied by comparison of HF bond orders with those obtained from pure diffusion quantum Monte Carlo calculations. We illustrate this concept for C–O and C–S bonds in different molecular environments. Our results suggest an approximate linear relation between bond order and bond length for these kinds of bonds. 相似文献
Summary: Monte Carlo method was used to simulate the degradation of porous PLA scaffolds. The simulated volume was assumed to be divided homogeneously between the pore and solid PLA with the ratio equal to the bulk porosity of the scaffold. The volume was divided into surface and bulk elements where the surface elements were in direct contact with the aqueous degradation medium, while the bulk elements were surrounded by the pore and solid PLA. The effect of degradation time on PLA ester groups and carboxylic acid end‐groups for surface and bulk elements, pH, PLA degradation rate and mass loss, and PLA molecular weight distribution was simulated. For surface elements, pH remained constant at 7.4 over the entire time of degradation, while for bulk elements its value decreased significantly to as low as 5.8. The highest drop in pH within the scaffold was observed for the highest porosity of 90%. There was a lag time of at least 7 weeks in the mass loss for surface as well as bulk elements for porosities ranging from 70 to 90%. The mass loss for bulk elements was considerably faster than the surface elements. This difference in the rate of mass loss between the surface and bulk elements could affect the 3D morphology and dimensional stability of the scaffold in vivo as degradation proceeds. The simulation predicts that, due to differences in the rate of bulk and surface degradation, hollow structures could form inside the scaffold after 19, 17, and 15 weeks for initial porosities of 70, 80, and 90%, respectively.
A schematic diagram illustrating the degradation of an element on the outer surface of the scaffold (surface element) versus an element within the volume of the scaffold (bulk element). 相似文献
Summary: The properties of a single semiflexible mushroom chain at a plane surface with a long-ranged attracting potential are studied by means of lattice Monte Carlo computer simulation using the bond fluctuation model, configurational bias algorithm for chain re-growing and the Wang-Landau sampling technique. We present the diagram of states in variables temperature T vs. strength of the adsorption potential, εw, for a quite short semiflexible chain consisting of N = 64 monomer units. The diagram of states consists of the regions of a coil, liquid globule, solid isotropic globule, adsorbed coil and cylinder-like liquid-crystalline globule. At low values of the adsorption strength εw the coil–globule and the subsequent liquid–solid globule transitions are observed upon decreasing temperature below the adsorption transition point. At high values of εw these two transitions change into a single transition from an adsorbed coil to a cylinder-like liquid-crystalline solid globule. We conclude that for a semiflexible chain the presence of a plane attracting surface favors the formation of a globule with internal liquid-crystalline ordering of bonds. 相似文献
