Criteria for chemical equilibrium with application to methane steam reforming

A literature survey reveals significant inaccuracy of the prediction of equilibrium models. A thermodynamic analysis is presented to show that the equilibrium calculations rest on a critical assumption of reversible heat exchange between a reactive system and its surrounding. Indeed, a correct application of the energy conservation and entropy balance equation leads to a modified Gibbs function. Minimization of the modified Gibbs function happens to be identical to maximization of the total entropy generation. The actual chemical equilibrium is shown through a methane steam reforming, as an illustrative example, to be correctly predicted by kinetic modeling. The state of chemical equilibrium does not necessarily correspond to maximum entropy generation. Once a chemical equilibrium has been established, both the total entropy generation and the modified Gibbs function remain unaltered and independent of time.     

Mechanisms of ionic conductivity for zwitterionic polymers

In this work, ionic conductivity data of zwitterionic polymers are compared with predictions of the random free-energy barrier model for a.c. conduction in disordered solids. It is shown that conductivity follows a long range delocalized diffusion of charge carriers within an equally probable distribution of free-energy barriers. Accordingly, it follows time–temperature superposition, expressed as a master curve for the normalized conductivity as a function of the non-dimensional frequency. The dielectric behaviour is dominated by ionic conductivity, and results suggest a process of quasi-ideal conduction of the ion carriers, consistent with a large value of the dielectric relaxation time characteristic of delocalized conduction processes. It is further remarked that alternative interpretations to the conduction behaviour in these polymers can also be given by other theories and models.     

A Comparative Study to Decipher the Structural and Dynamics Determinants Underlying the Activity and Thermal Stability of GH-11 Xylanases

With the growing need for renewable sources of energy, the interest for enzymes capable of biomass degradation has been increasing. In this paper, we consider two different xylanases from the GH-11 family: the particularly active GH-11 xylanase from Neocallimastix patriciarum, NpXyn11A, and the hyper-thermostable mutant of the environmentally isolated GH-11 xylanase, EvXyn11^TS. Our aim is to identify the molecular determinants underlying the enhanced capacities of these two enzymes to ultimately graft the abilities of one on the other. Molecular dynamics simulations of the respective free-enzymes and enzyme–xylohexaose complexes were carried out at temperatures of 300, 340, and 500 K. An in-depth analysis of these MD simulations showed how differences in dynamics influence the activity and stability of these two enzymes and allowed us to study and understand in greater depth the molecular and structural basis of these two systems. In light of the results presented in this paper, the thumb region and the larger substrate binding cleft of NpXyn11A seem to play a major role on the activity of this enzyme. Its lower thermal stability may instead be caused by the higher flexibility of certain regions located further from the active site. Regions such as the N-ter, the loops located in the fingers region, the palm loop, and the helix loop seem to be less stable than in the hyper-thermostable EvXyn11^TS. By identifying molecular regions that are critical for the stability of these enzymes, this study allowed us to identify promising targets for engineering GH-11 xylanases. Eventually, we identify NpXyn11A as the ideal host for grafting the thermostabilizing traits of EvXyn11^TS.     

基于内弹道过程的膛内燃烧产物的计算

为提供弹丸出膛口后流场计算的初始数据,在内弹道计算的基础上引入了发射药燃烧产物组分的计算。内弹道计算采用经典内弹道计算模型,发射药燃烧产物组分的计算采用最小自由能法。在最小自由能法中,使用实际气体的范德瓦尔斯状态方程,采用剩余性质法计算实际气体的Gibbs自由能。通过计算,得到了膛内火药燃烧产物组分的变化情况。分析表明,该文的计算结果可以作为弹丸出膛口后流场计算的初始数据。     

气体吸附过程中煤比表面Gibbs函数变化规律

煤体瓦斯吸附为放热过程,解吸为吸热过程,其温度能量变化的幅度与煤的变质程度、瓦斯吸附平衡压力等有关。以往的研究都采用等温吸附实验得出气体相关吸附数据,并通过其孔隙结构、相互作用力等来分析煤吸附气体的影响因素,但是鲜有学者从比表面Gibbs函数变化角度来探讨煤吸附气体机理。为此,研究了气体吸附过程中煤比表面Gibbs函数变化的相关特征参数计算公式,利用凤凰山矿和裴沟矿两种煤样进行等温吸附实验,得到了在4个不同温度(20,30,40,50 ℃)以及6个压力(0.2,1.2,1.5,2.5,3.0,4.0 MPa)下的等温吸附实验数据,利用单层吸附和多层吸附模型分别计算出不同煤样吸附气体过程中的比表面Gibbs函数变化。研究表明:采用两种不同方式计算煤样吸附甲烷的比表面Gibbs函数,随着温度的升高比表面Gibbs函数变化量减少,随着压力的升高比表面Gibbs函数变化增加。而应用单层吸附和多层吸附计算的能量相差较大,对这种现象分析了原因;计算了气体吸附解吸过程的热量,对比分析可知采用多层BET吸附模型得出的比表面Gibbs函数变化更接近实际;探讨了气体吸附能量变化的机理,表明气体吸附能量变化影响着吸附量的变化,而能量变化又同样受到煤样微观结构以及内部化学结构的影响。因此,煤样吸附解吸是一个复杂多变的过程,可以从改变能量的角度去探讨如何影响瓦斯解吸,达到提高瓦斯抽采效果的目的。     

基于最小自由能原理设计黑火药组成

应用最小自由能原理计算了不同配比黑火药的燃烧平衡产物和热力学参数,对数值模拟结果进行定性分析。从反应动力学的角度探究燃烧机理,并以爆温、火药力、产物成分为取向,设计出低腐蚀、低污染的环保型黑火药配方。还就其燃烧产物、p-t曲线与传统黑火药进行了对比。     

电场作用下Al6CuMg4准晶相自由能的计算

基于Thomas—Fermi模型，系统定量地计算研究了在电场作用下Al6CuMg4准晶相对于Al-Cu-Mg固溶体及普通化合物的自由能和吉氏自由能的变化趋势。结果表明：Al6CuMg。准晶相、Al2CuMg及Al-Cu-Mg固溶体的自由能与吉氏自由能，均随着电场强度的增大而升高。正电场作用要高于负电场作用，但差距不大。Al6CuMg。准晶相的自由能与吉氏自由能相对于固溶体对电场的变化更为敏感，随着电场的升高，Al6CuMg4与固溶体间的自由能与吉氏自由能的差值迅速增加。电场作用使得准晶相的不稳定性增加，Al2CuMg的稳定性显著高于Al6CuMg4的电场稳定性。对于Al-Cu-Mg固溶体，随着Mg含量的增加，合金对电场的敏感性增强，但增大幅度要远远小于化合物与准晶相的增大幅度。     

二维Cu—O面中的铁磁极化子

本文讨论二维Ｃｕ－Ｏ面中ｈｏｌｏｎ引起铁磁极化子的强关联系统的自由能．根据自由能极小时系统稳定的特性,求得铁磁极化子在低温（ｋＢＴ＜＜Ｊｅｆｆ）下的稳定半径为γｆ＝ ａ．并指出铁磁极化子配对引起超导电性的可能性．     

醋酸水溶液汽液非接触相平衡的蒙特卡罗模拟研究

采用蒙特卡罗分子模拟法,在吉布斯系综中抽样,对纯组份水和醋酸,以及醋酸水溶液模拟计算汽液平衡共存线。纯组份水SPC/E模型的模拟结果与实验数据相当一致,纯组份醋酸OPLS-UA模型计算的饱和蒸汽压偏低、沸点偏高。对于双组份混合物,液相区的所有模拟点比较接近实验曲线,由于醋酸模型较简单,气相区只有在醋酸摩尔分数X_(HAc)处于中间值(0.5～0.7)时,模拟与实验数据才较为接近。     

NTO负一价离子的水合Gibbs自由能和水合熵变及体系[Mn+(g)+nNTO-(g)+mH2O(g)]水合过程的焓变

提出了一个估算NTO负一价离子标准水合Gibbs自由能ΔhGθm(NTO-,g)的简易公式.用所建立的估算式和热力学关系式,算得ΔhGθm(NTO-,g)＝-267.24kJ·mol-1,ΔhSθm(NTO-,g)＝380.71J·(K·mol)-1.用热化学循环,算得体系[Mn (g) nNTO-(g) mH2O(g)](M=La,Ce,Pr,Eu,Sm,Gd,n=3,m=7;M=Y,Yb,n=3,m=6;M=Dy,Tb,n=3,m=5;M=Nd,n=3,m=8)水合过程的焓变.