关于惯性力场的讨论

对惯性力场进行了讨论．     

离心力场作用下三维流动和传热的场协同理论探讨

通过对能量方程进行体积分得到了三维流场中场协同理论的表达式。该式不仅含速度矢量与温度梯度矢量的点积项,还含有速度矢量与压力梯度矢量的点积项。在此基础上讨论了速度场、压力场、温度场之间的协同关系,探讨了通过政变边界条件调节诸场形态,实现传热强化的方法。并通过三个盘腔算例,对此方法进行了验证。     

再结晶和外力场下第二相析出的相场法模拟

在讨论相场法模拟基本方程的基础上,提出了晶界范围宽度的新概念,解释了相场模拟模型中有序化参数梯度范围的物理意义,论证了晶界范围不是晶界原子错排的宽度,而是界面能和界面元素偏析存在范围的观点.建立了一个模拟合金再结晶的相场模型,提出了一系列法则来获得模型中各参数的物理真实值,以AZ31镁合金为例,实现了再结晶过程晶粒长大的真实时间和空间的模拟,通过与试验数据的对比证明了模型的有效性.此外,还列举了相场法模拟Ti-25Al-10Nb合金中O相在外力场作用下析出过程的一系列有趣的新结果,讨论了外力场对第二相析出的重要影响和机理以及模拟结果对合金开发潜在的重要指导意义. 关键词： 相场法 再结晶 析出 外力场     

多原子分子力场的量子化学研究

本文报道了一种由量子化学方法获得的笛卡尔力场F_x矩阵转换成内坐标力场F_r矩阵的方法。利用该方法获得的力场和Wilson-GF矩阵方法对多原子分子和离子的力场、振动模式和频率进行了研究,获得了十分满意的结果。     

外力场对冷凝过程影响的分子动力学模拟研究

固壁表面发生的冷凝过程在工程应用中广泛存在,本文采用非平衡分子动力学模拟方法对高温蒸气在低温壁面上发生的冷凝过程进行了模拟研究.着重对该过程中的密度和局部温度等热力学参数分布进行了研究.同时,考察了两种气固温差条件下,壁面内、外法线方向上,不同强度的外力场对冷凝过程的影响,得到了结论:外力场是壁面内法线方向时促进冷凝进行,反之则阻碍冷凝进行,力场强度越大则影响效果越显著;当外力场一定时,气固温差越小,则外力场的相对影响程度越大.     

脱氧核糖核酸柔性的分子动力学模拟:Amber bsc1和bsc0力场的对比研究

脱氧核糖核酸(DNA)的结构柔性对DNA生物功能的实现具有重要作用,全原子分子动力学模拟是一种研究DNA结构柔性的重要方法.DNA的分子动力学力场在Amber bsc0基础上有了进一步的发展,即Amber bsc1.本文采用基于最新bsc1力场和先前bsc0力场的分子动力学模拟对DNA的宏观柔性和微观柔性进行对比研究,发现力场的改进对DNA宏观柔性参量的预测有一定改善,即所预测的拉伸模量和扭转-伸缩耦合比与实验值更为接近,而弯曲持久长度和扭转持久长度两种力场结果皆与实验值一致.微观分析发现,除了滑移量稍变大,bsc1力场得到的微观结构参量如扭转角和倾斜角与实验值更为接近,且新力场下DNA宏观柔性的改善与DNA的微观结构参量及其涨落紧密相关.     

静电场对静止液体压强的影响

论述了由于静电场的存在,在大气压力场中,静止液体内任意两点间的压强差与重力和静电场力的关系.     

磁流变抛光入口区域剪切力场形成机制数值分析

平面光学元件的浸入深度、凸球面光学元件的浸入深度、凸球面光学元件的曲率半径不同会使磁流变抛光入口区域剪切力场发生变化.为了研究磁流变抛光入口区域剪切力场的形成机制,建立磁流变抛光过程中必要的流体模型,对入口区域的几何特征进行分析;通过数值计算平面光学元件不同浸入深度、凸球面光学元件不同浸入深度、凸球面光学元件不同曲率半...     

气相多组分反应流场的一种新算法

本文提出气相多组分方程组采用时间推进法,把混合气连续方程同状态方程相联系,把密度的调整量转化为压力的调整量,计算绝对压力场,对大温差下的有化学反应的多组分炉内流场进行计算,获得成功．     

噬菌体T4溶菌酶溶液构象模拟中分子力场和水模型的选择

蛋白质在溶液中可能以不同构象的集合形式存在,不能用单一的静态结构来表示. 分子动力学模拟已成为对溶液中蛋白质构象进行采样的有用工具,但分子力场和水模型的选择是关键问题. 这项工作介绍了噬菌体T4溶菌酶的个例研究. 本文发现,使用经典的AMBER99SB力场和TIP4P水模型,分子动力学模拟不能很好地描述野生型噬菌体T4溶菌酶在微秒时间尺度上的铰链弯曲结构域运动. 其它新型力场和水模型的组合,如被称为RSFF2+的残基特异性力场和离散校正的水模型TIP4P-D,能够对噬菌体T4溶菌酶溶液构象进行合理的采样,与实验数据有良好的一致性. 这项工作为进一步研究噬菌体T4溶菌酶的溶液构象转变提供了分子力场和水模型的参考.     

洛伦兹力对自由燃烧弧和壁稳非转移弧流场的影响

通过耦合迭代求解流体力学方程和电磁场方程,数值模拟了转移式自由燃烧电弧和具有细长中间段及突扩阳极结构的壁稳式非转移直流电弧的流场,分析了洛伦兹力对这两种典型直流电弧流场的影响。结果显示:在自由燃烧电弧情况下,电流自感磁场的洛伦兹力对流场特性有显著影响,自磁压缩是约束电弧的主要机制;而在壁稳式非转移直流电弧情况下,相对于强壁面约束和气动力作用而言,洛伦兹力对流场的影响有限。特别在中间段出口以后,洛伦兹力与气动力的比值小于0.010,因此,当主要考虑壁稳式非转移直流电弧发生器出口参数时,为了提高数值模拟效率,可忽略洛伦兹力的作用。     

Molecular dynamics simulation of HIV-protease with polarizable and non-polarizable force fields

The effect of polarization in biomolecular force field is investigated by performing Molecular Dynamics (MD) simulation of HIV-protease by using two AMBER force fields, namely ff99 (non-polarizable) and ff02 (polarizable). The results of simulation show that the overall structural fluctuation of HIV-protease is reduced in the polarizable simulation. Comparison with the NMR order parameters with the calculated values shows that although some residues are less flexible in the ff02 simulation, the dynamics of two β-hairpins (flaps), the most flexible part of the protein, is relatively insensitive to the effect of polarization. The flap-active site distance, a measure of flap opening, is distinctly more in the non-polarizable simulation. The water count and radial distribution functions are investigated near a representative residue of three types — charged, polar and hydrophobic. Both water count and radial distribution function differ significantly near the charged residue (catalytic Asp25) between the force fields. However, the water movement is similar near the polar (Ser37) and hydrophobic (Ile85) residues. The preliminary results of this investigation show that polarization is likely to influence both global and specific local motions of protein and solvent.      

Force-field dependence of the conformational properties of α,ω-dimethoxypolyethylene glycol

A molecular dynamics (MD) study of α,ω-dimethoxypolyethylene glycol has been carried out under various conditions with respect to solvent composition, ionic strength, chain length, force field and temperature. A previous MD study on a 15-mer of polyethyleneglycol (PEG) suggested a helical equilibrium structure that was stabilised by hydrogen bonding and bridging water molecules. Experiments show that PEG is highly soluble in water, and indicate that clustering is not favoured. In the present study using different force fields, the GROMOS force fields 45A3 and 53A6, a variation on the latter 53A6_OE, and a force field by Smith et al. produced different results. For the GROMOS force fields 45A3 and 53A6 no helical structure was found, but formation of more or less compact random coils in aqueous solution due to hydrophobic interactions was observed. For the other two force fields used, α,ω-dimethoxypolyethylene glycol stayed flexible and more or less elongated in aqueous solution, more in agreement with experimental observations and the previous MD study.     

确定SQM力场标度因子的新方法

建立了一种计算ＳＱＭ力场标度因子的新方法，它具有简捷、精确、且不依赖于实验信息的特点，改善了ＳＱＭ方法。将其在Ａｂｉｎｉｔｉｏ水平上计算的力常数用于振动分析，所得计算频率与观测频率十分吻合。     

Surface tension calculations of the cationic (CTAB) and the zwitterionic (SB3-12) surfactants using new force field models: a computational study

Actual CTAB and SB3-12 surfactant force field models fail to reproduce one of the most important thermodynamic property of those molecules, the surface tension. Molecular dynamics simulations were conducted to construct new force fields of the cationic surfactant, Cetyl Trimethyl Ammonium Bromide (CTAB), and the non-ionic, cocoamidopropyl betaine, surfactants using united atom models. By scaling the Lennard Jones parameters, the well depth potential (ε) and the intermolecular distance (σ), we constructed an united atom model of the cationic and the betaine surfactants. The new models were tested with actual experiments reported in the literature. With the correct parameters, surface tensions of both surfactants were calculated at different temperatures and different areas per molecule. Electrostatic properties and micelle structures were also calculated with the new set of parameters and radius of gyrations, i.e. micelle radius, were evaluated showing good affinity with experimental data. The new force fields were proved with two different water models, TIP4P/ε and SPC/E, having good agreement with actual experiments     

Equilibrium structure of methylcyanide

The quadratic and cubic force fields of methylcyanide have been calculated at the MP2 and CCSD(T) levels of theory employing a core-valence basis set of triple-zeta quality. Semi-experimental equilibrium structures have then been derived from the experimental ground-state rotational constants available for various isotopologues and the corresponding vibrational corrections calculated from the ab initio force fields. These structures have been found in excellent agreement with the pure ab initio structure calculated at the CCSD(T) level of theory using a basis set of sextuple-zeta quality and including core correlation corrections.     

New Mechanism for Mass Generation of Gauge Field

A new mechanism for mass generation of gauge field is discussed in this paper.By introducing two sets of gauge fields and making the variations of these two sets of gauge fields compensated each other under local gauge transformations,the mass term of gauge fields is introduced into the Lagrangian without violating the local gauge symmetry of the Lagrangian.This model is a renormalizable quantum model.