Tinker‐OpenMM: Absolute and relative alchemical free energies using AMOEBA on GPUs

The capabilities of the polarizable force fields for alchemical free energy calculations have been limited by the high computational cost and complexity of the underlying potential energy functions. In this work, we present a GPU‐based general alchemical free energy simulation platform for polarizable potential AMOEBA. Tinker‐OpenMM, the OpenMM implementation of the AMOEBA simulation engine has been modified to enable both absolute and relative alchemical simulations on GPUs, which leads to a ∼200‐fold improvement in simulation speed over a single CPU core. We show that free energy values calculated using this platform agree with the results of Tinker simulations for the hydration of organic compounds and binding of host–guest systems within the statistical errors. In addition to absolute binding, we designed a relative alchemical approach for computing relative binding affinities of ligands to the same host, where a special path was applied to avoid numerical instability due to polarization between the different ligands that bind to the same site. This scheme is general and does not require ligands to have similar scaffolds. We show that relative hydration and binding free energy calculated using this approach match those computed from the absolute free energy approach. © 2017 Wiley Periodicals, Inc.     

Role of emulsifier on the particle size and polymer particle size distribution using multiwavelength spectroscopy measurements

Latex emulsions depend strongly on the polymer composition, and particle size distribution, which in turn, is a function of the preparation of the latex and on the formulation and composition variables. This study reports measurements of particle size and particle size distribution of latex emulsions as function of the reaction time and the type and concentration of emulsifier by using the multiwavelength spectroscopy technique. Results show changes in the particle size of latex emulsions with the reaction time, obtaining larger particles and broader distributions with increasing of Tween 80 ratio. The steric stabilization provides the sole nonionic emulsifier is not enough to protect the polymer particle, causing the flocculation among the interactive particles, resulting in unstable latex. However, latex emulsions prepared with Tween 80 ratio <70 wt.% can stabilize efficiently the nucleated particles, probably due to the effects provided by both, the electrostatic and steric stabilization mechanisms. The same effect is shown in the curves of conversion (%) as a function of reaction time, resulting in slower polymerization rate for Tween 80 ratio >70 wt.%. On the other hand, smaller polymer particles, in all range of emulsifier mixture, have been obtained to higher emulsifier concentration.     

CO_2捕集炭膜的前驱体结构设计及性能

从分子结构设计出发,合成了一系列新型刚性、高自由体积的聚酰亚胺炭膜前驱体,并制备了炭膜.采用热重分析(TGA)、傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)和高分辨透射电子显微镜(HRTEM)研究了不同聚酰亚胺前驱体的热分解特性及在热解炭化过程中化学结构、微结构的变化规律;测试了所制备炭膜的气体分离性能.结果表明,前驱体的自由体积分数显著影响炭膜的气体分离性能;聚合物结构越具刚性,自由体积越大,所得炭膜结构越疏松,极微孔道尺寸越大,越有利于气体分子在炭膜极微孔道中的渗透、扩散与传输.其中,刚性大体积基团芴基、酚酞cardo基团和六氟异丙基的引入能有效破坏分子链间的堆积,提高聚合物的自由体积,所形成炭膜的结构较疏松,均表现出优异的气体渗透性和分离选择性,超越了Robeson上限,解决了传统炭膜气体渗透性能低的问题.特别是采用羟基官能化聚酰亚胺前驱体制备的炭膜在保持较高气体分离选择性的同时,CO_2气体的渗透性高达24770 Barrer(1 Barrer≈7.5×10-18m2·s-1·Pa-1),可实现对CO_2的有效分离和捕集,展现出良好的商业化应用前景.     

旋转压电纳米梁的振动分析

本文基于非局部弹性理论，对旋转压电纳米梁模型的振动进行了分析．首先由哈密顿原理导出旋转压电纳米梁的动力学控制方程及相应的边界条件；再通过微分求积法对控制方程和两类边界条件进行离散；最后通过数值计算分析振动特性．通过改变旋转角速度、轮毂半径、非局部参数以及外部电压分析它们对压电纳米梁振动频率的影响关系．数值结果表明这些参数对压电纳米梁固有频率有不可忽略的影响，本文进一步讨论了旋转角速度对结构模态的影响．     

VERIFICATION OF SMOM AND QMOM POPULATION BALANCE MODELING IN CFD CODE USING ANALYTICAL SOLUTIONS FOR BATCH PARTICULATE PROCESSES

For many processes of industrial significance, due to the strong coupling between particle interactions and fluid dynamics, the population balance must be solved as part of a computational fluid dynamics （CFD） simulation. In this work, a CFD based population balance model is tested using a batch crystallization reactor. In this CFD model, the population balance is solved by the standard method of moments （SMOM） and the quadrature method of moments （QMOM）. The results of these simulations are compared to analytical solutions for the population balance in a batch tank where 1） nucleation, 2） growth, 3） aggregation, and 4） breakage are taking place separately. The results of these comparisons show that the first 6 moments of the population balance are accurately predicted for nucleation, growth, aggregation and breakage at all times.     

Pulsatile flows in a lateral aneurysm anchored on a stented and curved parent vessel

We present particle tracking velocimetry measurements and flow visualization of pulsatile flow fields in a stented cerebrovascular lateral aneurysm model with a wide ostium anchored on a curved parent vessel. Among the stent parameters, the blocking ratioC _α ranging from 0% to 75% was selected to study its effect on the changes of intra-aneurysmal hemodynamics for the reference of minimally invasive endovascular aneurysm treatment. The Womersley number was 3.9 and the mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 850, and 300, respectively. The results are characterized in terms of velocity vector field, coded streak images, region averaged velocity, vorticity, and wall shear stress. A critical range ofC _α related to the inflow location as well as the shape and number of intra-aneurysmal vortices is identified. The intra-aneurysmal flow activity, vortex strength, and wall shear stress are found to decrease with increasingC _α. Among theC _α examined,C _α=75% is the most favorable in attenuating the risk of aneurysmal rupture and promoting intra-aneurysmal thrombus.     

颗粒材料破碎演化路径细观热力学机制

颗粒材料在高应力环境下会发生颗粒破碎现象,颗粒破碎不仅影响颗粒材料的力学特性,同时与大量工程问题密切相关.目前的相关研究主要集中在唯象地描述颗粒破碎的演化以及破碎对力学特性的影响层面,对颗粒破碎演化路径的物理机制研究较少.本文基于热力学框架,采用细观力学中细观-宏观的均匀化方法推导了颗粒体系弹性能和破碎能量耗散,并在最大能量耗散的假设下,在热力学框架内,建立了理想化的无摩擦球体颗粒等向压缩过程的弹性-破碎模型,阐述了颗粒材料破碎演化路径细观热力学机制.由于模型的推导不依赖任何唯象的经验公式,因此模型中包含的参数均有明确的物理意义.模型预测与前人试验结果对比表明,材料的初始级配对弹性压缩模量和破碎应力的影响并不相同:不同分形维数级配对应的弹性体变模量存在极大值,而破碎应力却随着分形维数的增大单调递增;颗粒破碎的演化符合最大能量耗散原理,且颗粒材料的压缩曲线可以分为弹性-破碎-拟弹性3个机制不同的阶段.      

SOLVING THE FREE BOUNDARY PROBLEM IN CONTINUOUS CASTING BY USING BOUNDARY ELEMENT METHOD

ＳＯＬＶＩＮＧＴＨＥＦＲＥＥＢＯＵＮＤＡＲＹＰＲＯＢＬＥＭＩＮＣＯＮＴＩＮＵＯＵＳＣＡＳＴＩＮＧＢＹＵＳＩＮＧＢＯＵＮＤＡＲＹＥＬＥＭＥＮＴＭＥＴＨＯＤＬｉＹａｏｙｏｎｇ（李耀勇）；ＺｈａｎｇＺｈｉｌｉ（张自立）（ＲｅｃｅｉｖｅｄＪｕｎｅ，１８，１９...     

在无单元法里直接准确施加位移边界条件和材料不连续条件

在无单元伽辽金法(EFG)里，由于其滑动最小二乘近似位移函数不满足Kronecker条件，使得它不能准确地施加本质边界条件和材料不连续条件，从而极大地限制了EFG法的发展和进一步应用。本文在位移边界和不同材料交界面的离散结点上采用实际的结点位移值，提出了一种准确施加位移边界和材料不连续条件的方法，该方法实施简单、稳定、求解精度高，而且其推导得出的整体刚度矩阵具有正定、对称和带状分布的特点，可以和有限单元法一样，直接利用各种成熟、高效的线性方程组解法求解系统平衡方程。数值算例结果表明了文中理论和方法的正确性和可靠性。     

SiCp尺寸对SiCp／Cu基复合材料抗磨性能的影响

以纳米级(30nm)、亚微米级(130nm)、微米级(14μm)3种粒径的SiCp和微米级(10μm)铜粉为原料，用冷压烧结和热挤压方法制备了纳米、亚微米和微米级SiCp／Cu复合材料，考察了SiCp尺寸对SiCp／Cu复合材料抗磨性能的影响．结果表明，不同尺寸的SiCp颗粒作为增强相均能显著改善铜基复合材料的抗磨性能；随着SiCp尺寸的增大，SiCp／Cu复合材料的抗磨性能提高幅度显著增大，但偶件磨损表面的犁削加剧；以微米级SiCp为原料制备的SiCp／Cu复合材料的抗磨性能最佳，但其导致偶件40Cr钢犁削作用显著加剧．从摩擦副整体的摩擦磨损性能角度而言，宜采用SiCp尺寸为130nm的SiCp／Cu复合材料同40Cr钢组成摩擦副．