土体大变形单剪试验的SPH数值模拟

针对目前常规数值计算方法的局限,该文采用一种纯拉格朗日、无网格方法-光滑粒子流体动力学法(简称SPH法)对土体的大变形力学行为进行数值模拟.首先,根据SPH法的基本理论,对弹塑性力学控制方程进行了离散,构造了应力-应变关系的SPH求解格式,并采用Jaumann应力率进行土体应力.应变与内部质点运动间的转换.然后,进行两...     

Self-diffusion Measurements of Liquid Sn Using the Shear Cell Technique and Stable Density Layering

Metallurgical and Materials Transactions B - By utilizing the shear cell technique and achieving stable density layering with the addition of an alloying element Bi, the self-diffusion coefficients...     

Porous biodegradable polyesters. I. Preparation of porous poly(L‐lactide) films by extraction of poly(ethylene oxide) from their blends

Porous poly(L ‐lactide) (PLLA) films were prepared by water extraction of poly(ethylene oxide) (PEO) from solution‐cast PLLA and PEO blend films. The dependence of blend ratio and molecular weight of PEO on the porosity and pore size of films was investigated by gravimetry and scanning electron microscopy. The film porosity and extracted weight ratio were in good agreement with the expected for porous films prepared using PEO of low molecular weight (M_w = 1 × 10³), but shifted to lower values than expected when high molecular weight PEO (M_w = 1 × 10⁵) was utilized. The maximum pore size was larger for porous films prepared from PEO having higher molecular weight, when compared at the same blending ratio of PLLA and PEO before water extraction. Differential scanning calorimetry of as‐cast PLLA and PEO blend films revealed that PLLA and PEO were phase‐separated at least after solvent evaporation. On the other hand, comparison of blend films before and after extraction suggested that a small amount of PEO was trapped in the amorphous region between PLLA crystallites even after water extraction and hindered PLLA crystallization during solvent evaporation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 629–637, 2000     

Kinetic studies of thermally induced phase separation in polymer–diluent system

Thermally induced phase separation was studied by the light scattering in polypropylene/methyl salicylate system. Data could be well fitted with the linear Cahn theory for spinodal decomposition (SD) in the early stage of phase separation. Characteristic properties of the early stage of SD, such as an apparent diffusion coefficient and an interphase periodic distance, were obtained. The periodic distance ranged from 3 μm to 4 μm. The growth of the phase‐separated structure obeyed power‐law scaling in the later stage, and the structure factor could be scaled into a universal time‐independent form. Domain sizes obtained from the light‐scattering measurements were consistent with the optical microscope measurements. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1028–1036, 2000     

Diffusive permeability of ionic solutes in charged chitosan membrane

The permeabilities of three kinds of solutes with similar sizes such as anionic benzenesulfonic acid, neutral styrene glycol, and cationic theophylline in the chitosan membrane were investigated. The chitosan membrane becomes cationic below its pKa value. Benzenesulfonic acid showed the highest permeability, whereas theophylline showed the lowest, although these solutes have almost the same size. This can be explained by the electrostatic attraction or repulsion between the solute and the membrane instead of the size exclusion effect. The permeabilities of benzenesulfonic acid and theophylline increased and decreased, respectively, with the decrease of pH from 7.4 to 4.0 because of the increase of the charge density of the membrane. Thus, the selectivity of benzenesulfonic acid to theophylline increased and reached about 30 at pH 4.0, in contrast to the selectivity of nearly unity in poly(vinyl alcohol) (PVA) membrane. The partition coefficients for three solutes showed the similar tendencies to those in the permeabilities. Contrary to the results of the permeabilities, the partition coefficients increased with the increase of the degree of the crosslinking in the membrane. This is probably due to the increase of the electrostatic interaction between the solute and the membrane brought about by the smaller mesh size and also due to the increase of the bound water fraction in the membrane. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 397–404, 1999     

The role of ion-membrane interactions in fast and selective mono/multivalent ion separation with hierarchical nanochannels

Precise control over the nanofluid behavior of polyelectrolyte-based membranes is a primary step toward understanding the structure-morphology-property relationships to ultimately determine the mass transfer characteristics. In this study, a high-performance multistacked polyelectrolyte-based cation exchange membrane (CEM) with a heterogeneous structure and versatile surface chemistry was developed to achieve selective ion conductance. The self-assembled CEM can facilitate ion permeation with fluxes of 2.9 mol m⁻² h⁻¹ for K⁺ and 0.22 mol m⁻² h⁻¹ for Mg²⁺, reaching a mono/multivalent ionic selectivity of up to 13, outperforming mono/divalent fractionation when compared with state-of-the-art membranes. Molecular dynamic (MD) simulations illustrated the ionic transport trajectory in hierarchical channels with angstrom-scale cavities using multilayered CEMs. Both the experimental measurements and theoretical simulations indicated that ionic fractionation was associated with a large disparity in the energy barrier between mono/multivalent cations, which was the primary origin of the differences in the ion dehydration-rehydration processes in the angstrom-confinement membrane ion channels.