电化学界面处离子分布、静电势和ξ势的研究

Density functional theory is applied to predicting the structures and electrostatic potentials of planar electrochemical surfaces within the framework of the restricted primitive model where small ions are represented by charged hard spheres of equal diameter and the solvent is assumed to be a continuous dielectric medium. The hard-sphere contribution to the excess Helmholtz energy functional is evaluated using the modified fundamentalmeasure theory and the electrostatic contribution is obtained from the quadratic functional Taylor expansion using the second-order direct correlation function from the mean-spherical approximation. Numerical results for the ionic density profiles and the mean electrostatic potentials near a planar surface of various charge densities are in excellent agreement with molecular simulations. In contrast to the modified Gouy-Chapman theory, the present density functional theory correctly predicts the second layer formation and charge inversion of charged surfaces as observed in simulations and in experiments. The theory has also been tested with the zeta potentials of positively charged polystyrene particles in aqueous solutions of KBr. Good agreement is achieved between the calculated and experimental results.     

聚合物纳米孔迁移的朗之万动力学研究:摩擦系数影响(英文)

The driven polymer translocation through a nanopore with unbiased initial configuration has been studied by using Langevin dynamics(LD) simulations.It is found that the scaling relationship between translocation time and the polymer chain length is strongly affected by the friction coefficient in LD and the driving force.However,there is no scaling relationship between the translocation time and the friction coefficient.The translocation time is almost inversely proportional to the driving force,which is in agreement with those obtained in biased translocation.The scaling relationship between gyration radius(R g) of subchain at the trans side with the subchain length(L) is R g ～L 0.33 that is in good agreement with the limiting value for molten globule state,while the curve of R g of subchain at the cis side has two distinct stages.During translocation,the subchain at the cis side is being stretched gradually,and the structure of the subchain transforms from sphere-like to rod-like.When the effect of stretching reaches the tail end,the subchain is at the most stretched state.Finally the subchain will rapidly restore to coil structure.According to the results of force analysis,the retarding force at the trans side is more crucial during the practical translocation.     

涡流桨搅拌槽内流动非稳定性的大涡模拟

The aim of this work is to investigate the flow instabilities in a baffled, stirred tank generated by a single Rushton turbine by means of large eddy simulation （LES）. The sliding mesh method was used for the coupling between the rotating and the stationary frame of references. The calculations were carried out on the ＂Shengcao-21C＂ supercomputer using a computational fluid dynamics （CFD） code CFX5. The flow fields predicted by the LES simulation and the simulation using standard κ-ε model were compared to the results from particle image velocimetry （PIV） measurements. It is shown that the CFD simulations using the LES approach and the standard κ-ε model agree well with the PIV measurements. Fluctuations of the radial and axial velocity are predicted at different frequencies by the LES simulation. Velocity fluctuations of high frequencies are seen in the impeller region, while low frequencies velocity fluctuations are observed in the bulk flow. A low frequency velocity fluctuation with a nondimensional frequency of 0.027Hz is predicted by the LES simulation, which agrees with experimental investigations in the literature. Flow circulation patterns predicted by the LES simulation are asymmetric, stochastic and complex, spanning a large portion of the tanks and varying with time, while circulation patterns calculated by the simulation using the standard κ-ε model are symmetric. The results of the present work give better understanding to the flow instabilities in the mechanically agitated tank. However, further analysis of the LES calculated velocity series by means of fast Fourier transform （FFT） and/or spectra analysis are recommended in future work in order to gain more knowledge of the complicated flow phenomena.     

Large Eddy Simulations of Mixing Time in a Stirred Tank

Large eddy simulations （LES） of mixing process in a stirred tank of 0.476m diameter with a 3-narrow blade hydrofoil CBY impeller were reported. The turbulent flow field and mixing time were calculated using LES with Smagorinsky-Lilly subgrid scale model. The impeller rotation was modeled using the sliding mesh technique. Better agreement of power demand and mixing time was obtained between the experimental and the LES prediction than that by the traditional Reynolds-averaged Navier-Stokes （RANS） approach. The curve of tracer response predicted by LES was in good agreement with the experimental. The results show that LES is a reliable tool to investigate the unsteady and quasi-periodic behavior of the turbulent flow in stirred tanks.     

反渗透过程的浓度极化及其传质系数测定

The relationship between osmotic pressure difference across the membrane and mass transfer coefficient is developed in this paper. On the basis of this relationship, a method for measuring mass transfer coefficient by using experimental data on reverse osmosis is established. Pitzer's equations are used to calculate osmotic pressure differences in order to assure accuracy of results. Under the conditions of constant operating pressure and bulk flow, mass transfer coefficient is scarcely affected by membrane structure, but decreases slightly with increasing feed concentration. The solute concentration in the polarization layer is calculated by using the measured values of mass transfer coefficient. Polarization layer concentration increases with augmentation in bulk concentration. However, their difference increases with increasing bulk concentration until a maximum difference is reached, and then decreases. Mass transfer coefficient increases with higher velocity of bulk flow. If mass transfer coefficient is so large that the ratio(PwΔπσ/k)becomes very small, polarization could be neglected.     

Influence of Ferrovanadium Slag on Bauxite Based Self-flow Castables

Bauxite based self-flow castables were prepared by using bauxite,ferrovanadium slag,microsilica,high efficient admixture as main starting materials,and calcium aluminate cement as binder. The cold modulus of rupture,cold crushing strength and permanent linear change were determined. The phase constituents of the specimens were analyzed by X-ray diffraction( XRD),and the microstructure was observed with scanning electron microscopy( SEM). The experimental results show that with increasing the addition of ferrovanadium slag,the strength of specimens dried at 110 ℃ decreases,while the strength of specimens fired at 1 350 ℃ first increases and then decreases,the bulk density of specimens slightly decreases,the crystalline phase content of the formed magnesium-aluminate spinel increases in the structure and the permanent linear change( PLC) of specimens transforms from contraction to expansion. The appropriate addition of ferrovanadium slag is beneficial to improve the sintering strength and volume stability of bauxite based castables and the optimal addition of ferrovanadium slag is 40 mass%.     

EQUATIONS OF STATE FOR HARD-SPHERE CHAIN FLUIDS AND SQUARE-WELL CHAIN FLUIDS

Based on the statistical theory for chemical association,equations of state for hard-spherechain fluids(HSCFs)and square-well chain fluids(SWCFs)can be derived through the n-particlecavity correlation function(CCF)of the corresponding reference system,where n is the chain lengthor the number of segments of a chain molecule.The reference system is a fluid composed of only cor-responding monomers.In this work,the n-particle CCF is approximated by a product of effectivetwo-particle CCFs which accounts for correlations in nearest-neighbour and next-to-nearest-neighboursegment pairs.The CCFs for SWCFs may be expressed by a product of the corresponding functionfor HSCFs and a perturbation term originated from the square-well attractive potential.All these ef-fective two-particle CCFs and perturbation terms are density dependent.The dependence is determinedmainly by using computer-simulation results.The obtained equations can excellently describecompressibility factors and second Virial coefficients for HSCFs     

Tao-Mason状态方程扩展用于重正烷烃(英文)

In our previous paper we extended the Tao and Mason equation of state (TM EOS) to refrigerant fluids, using the speed of sound data. This is a continuation for evaluating TM EOS in predicting PVT properties of heavy n-alkanes. Liquid density of long-chain n-alkane systems from C 9 to C 20 have been calculated using an analytical equation of state based on the statistical-mechanical perturbation theory. The second virial coefficients of these n-alkanes are scarce and there is no accurate potential energy function for their theoretical calculation. In this work the second virial coefficients are calculated using a corresponding state correlation based on surface tension and liquid density at the freezing point. The deviation of calculated densities of these alkanes is within 0.5% from experimental data. The densities of n-alkanes obtained from the TM EOS are compared with those calculated from Ihm-Song-Mason equation of state and the corresponding-states liquid densities (COSTALD). Our results are in favor of the preference of the TM EOS over other two equations of state.     

L-抗坏血酸在葡萄糖和蔗糖溶液中的黏度及其热力学性质的研究

Visosities and densities at ,several temperatures from 293.15 K to 313.15K are reported for L-ascorbic acid in aqueous glucose and sucrose solutions at different concentrations.The parameters of density,Viscosity coefficient B and partial molar volume are calculated by regression.The experimental results show that densities and viscositis decrease as temperature increases at the same solute and solvent (glucose and sucrose aueous solution)concentrations,and increase with concentration of glucose and sucrose at the same solute concentration and temperature,B increases with concentration of glucose and sucrose and temaperature,L-ascorbic acid is sturcture-breaker or structure-making for the glucose and sucrose aqueous solutions ,Furthermore,the solute-solvent interactions in ternary systems of water-glucose-electrolyte and water-sucrose-electrolyte are discussed.     

Molecular dynamics simulations of supercritical water at the iron hydroxide surface

The adsorption properties of supercritical water confined between electrostatically neutral but hydrophilic surfaces of iron (II) hydroxide were determined through molecular dynamics simulations. Simulations were conducted at temperatures of 715, 814 and 913 K, and at water densities typically found in the heat transport system of the supercritical water cooled nuclear reactor (SCWR). Surface water layer densities were obtained and compared to those of the bulk water. Adsorption coverage was calculated as a function of the number of waters per OH group on the surface. Images of the water molecules configurations are provided along with the density profile of the adsorption layer. The localized adsorption and surface clustering of supercritical water, as seen in this study, would likely produce more localized corrosion phenomena in the water bearing components of the SCWR.     

电化学界面处离子分布、静电势和ζ势的研究

Density functional theory is applied to predicting the structures and electrostatic potentials of planar electrochemical surfaces within the framework of the restricted primitive model where small ions are represented by charged hard spheres of equal diameter and the solvent is assumed to be a continuous dielectric medium. The hard-sphere contribution to the excess Helmholtz energy functional is evaluated using the modified fundamental-measure theory and the electrostatic contribution is obtained from the quadratic functional Taylor expansion using the second-order direct correlation function from the mean-spherical approximation. Numerical results for the ionic density profiles and the mean electrostatic potentials near a planar surface of various charge densities are in excellent     

Atomic and electronic structure of crystalline–amorphous carbon interfaces

Interfaces of diamond with amorphous carbon (a-C) are investigated using tight-binding molecular dynamics simulations. Such interfaces are found to be stable, with a-C atoms covalently bonded to the diamond surfaces. The atomic and electronic structure of the a-C region is consistent with previous results on pure a-C and does not depend critically on the diamond face exposed. However, surface properties influence the relative stability of interfaces with high density a-C. In this case, the interfacial region is small and very dense homogeneous a-C grows on diamond. At lower densities, carbon atoms nucleate on diamond surfaces and create an intermediate region between diamond and a-C. The shape of diamond crystals embedded in a-C is predicted using the Wulff construction with appropriately defined energies for surfaces with overlayer material. These predictions are verified by empirical potential simulations of nanodiamond inclusions in a-C matrix. The electronic density of states and the dielectric function, calculated for our samples containing a-C/diamond interfaces, show that optoelectronic properties of these composite materials are dominated by a-C.     

基于N4分子的高能量密度材料:第一性原理计算的合成路线

为了探索合成和稳定聚合氮形式的分子或晶体的途径,基于第一性原理计算提出了两种基于N₄分子合成高能量密度材料的方法:第一种方法是在单晶金属表面吸附N₄(T_d)分子;第二种方法是利用结构搜索获取稳定的N₄相关结构。提出了P-43m-N₄、P₄/m-LiN₄和Amm2-G/N₄三种含有N₄分子的晶体,并计算了它们的能量密度、热力学和动力学稳定性以及电子结构性质。结果表明,在超高真空和低温条件下,N₄(T_d)在金属表面可以通过失去T_d对称而稳定。AIMD模拟结果表明,它们在50GPa、50或300K下是稳定的。通过N₄与金属原子形成的配位键,聚合N₄可以在高压下合成,并在低温条件下稳定。     

BaO-Al2O3-SiO2微晶玻璃密度的计算

为了评估密度作为BaO-Al2O3-SiO2(BAS)微晶玻璃晶化热处理和质量监控手段的可行性和准确性,提出一种测定微晶玻璃密度的方法.利用x射线衍射和Rietveld结构精修法准确测定烧结制备的BAS微晶玻璃中各晶相的质量分数和密度,研究了加和法则应用于BAS系微晶玻璃的准确性.对比精修得到的晶相的晶胞参数和对应标准卡片上纯晶相的晶胞参数,得到样品中各晶相的密度.结果表明:BAS微晶玻璃中各晶相与对应纯晶相的密度差别极其微小.利用获得的各相的质量分数,根据玻璃工艺学的经验数据计算残余玻璃相的密度.最后,根据加和法则计算得到BAS微晶玻璃样品的密度,所得的密度值与利用Archimedes法测得的密度值的相对偏差小于1.4%.     

硬球链流体在平板和硬球表面分布的密度泛函理论

采用Yethiraj和Woodward的密度泛函理论方法,结合胡英和刘洪来等发展的硬球链流体状态方程,得到了自由连接硬球链流体在平板狭缝中和球形固体颗粒表面附近的密度分布表达式,并计算了在两平行壁所组成的狭缝中和直径大小不同的球形固体颗粒周围硬球链分子的链节密度分布.理论计算结果与作者采用Dickman 和Hall 的方法进行Monte Carlo计算机模拟结果非常吻合.颗粒直径对链状分子的密度分布有一定的影响,随着固体颗粒直径的增加,靠近颗粒表面附近的链节密度降低.     

水泥-粉煤灰的颗粒群匹配与其胶砂性能的关系研究

本文将某低钙灰试样经粉磨处理,以不同比例与一定细度的纯硅酸盐水泥进行匹配,制成一系列粉煤灰水泥试样。根据Dinger-Funk的数学模型可得出粉体最佳颗粒群分布(即堆积密度达最大时的分布),并通过水泥与粉煤灰激光粒度检测结果计算各粉煤灰水泥的实际颗粒群分布。运用灰色关联分析原理,考察各粉煤灰水泥试样的颗粒群分布与Dinger-Funk最紧密堆积颗粒群分布的相关性。同时,对各粉煤灰水泥进行标准稠度用水量以及胶砂强度测定。结果证明:当粉煤灰与水泥的匹配后的颗粒群分布与最紧密堆积的关联度较高时,相应的粉煤灰水泥标准稠度用水量较少,胶砂强度则较高。     

Determination of fracture toughness of epoxy using fractography

Fracture toughness of epoxy was determined by quantitative fractography, one of the techniques for brittle materials based on fracture mechanics. Two different epoxy systems, an anhydride‐cured and an amine‐cured epoxy based upon diglycidyl ether of bisphenol A (DGEBA) were studied. Epoxies with different average molar mass between crosslinks (M_c) or crosslink density were prepared by varying the cure profiles. The materials were characterized using differential scanning calorimetry (DSC), dynamic mechanical spectroscopy (DMS), and density measurements. Optical microscopy was used to measure the dimensions of the different regions on the fracture surfaces of unnotched samples that were tested to failure under tension. The fracture toughness values were calculated from the relationship between the measured sizes and fracture stress. Epoxies with lower M_c values or higher crosslink densities have lower fracture toughness values. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 257–268, 1999