无规共聚高分子溶液相平衡的Monte Carlo模拟

引　言近年来 ,随着计算机硬件能力的不断提高和新的模拟方法的不断涌现 ,对于高分子溶液的相平衡问题的计算机模拟研究取得了很大的进展 ,但大多将注意力放在如何改进模拟方法以获得更长的均聚高分子溶液的相平衡数据 ,以检验Ｆｌｏｒｙ -Ｈｕｇｇｉｎｓ理论、修正Ｆｒｅｅｄ理论等的有效性 .如Ｍａｄｄｅｎ等[1]曾利用蛇行法 (ｒｅｐｔａｔｉｏｎ)和伪动态模拟算法( ｐｓｅｕｄｏｋｉｎｅｔｉｃｓｉｍｕｌａｔｉｏｎａｌｇｏｒｉｔｈｍ)、Ｍａｃｋｉｅ等[2 ]在邻位数Ｚｎ=2 6的格子模型上用Ｇｉｂｂｓ系综法、Ｗｉｌｄｉｎｇ等[3]用键长涨…     

随机共聚高分子凝胶溶胀和体积相变行为的分子热力学模型

基于随机共聚高分子溶液的格子模型,建立了一个可以描述温度和pH双重响应的随机共聚高分子凝胶溶胀行为的分子热力学模型。该模型考虑了溶剂与不同高分子的混合、高分子网络的弹性以及包含小分子离子在凝胶内外分布的Donnan平衡和聚合物网络上的大分子离子及其反离子之间的静电相互作用的离子影响对化学势的贡献。与其他模型不同的是,该模型还考虑了高分子的组成f。该模型有两类可调的模型参数,一类是溶剂与不同高分子网络之间的相互作用能参数ε槇ij,另一类是高分子网络自身的尺寸参数Mc。研究结果表明,该分子热力学模型只需较少的模型参数就可较好地描述温度和pH双重敏感的随机共聚高分子凝胶的溶胀行为。     

共聚高分子体系的分子热力学模型

以共聚硬球链流体的分子热力学模型为基础，通过引入链节间方阱位能相互作用的贡献。建立了实际共聚高分子系统的分子热力学模型，对纯共聚高分子ＰＶＴ的关系结果，平均相对误差为０．２２％－０．８０％。     

NaCl在聚电解质溶液中活度系数的实验测定

引　言聚电解质是指在极性溶剂中能够电离形成聚离子和反离子的高分子[1] ,在生物体中广泛存在 ,如蛋白质、ＤＮＡ和ＲＮＡ等都是聚电解质 ,聚丙烯酸盐和聚苯乙烯磺酸盐则是典型的人工合成聚电解质 .在聚电解质的水溶液中 ,由于聚离子带有大量的电荷 ,对反离子具有很强的静电吸引作用 ,即使在极低的浓度下溶液仍具有很大的非理想性 ,这与普通电解质溶液显著不同[2 ,3 ] .建立聚电解质溶液热力学性质的计算方法一直是溶液理论研究的热点 ,现已取得长足进展 ,如Ｍａｎｎｉｎｇ的反离子凝聚理论[2 ,3 ] 、柱状胞腔模型基础上的ＰＢ方程理论[4 ,…     

密炼机转子棱尖与内壁之间隙对混炼的影响

本文探讨了关于转子凸棱棱尖和混炼室内壁间的间隙影响填充剂分散的各种不同的见解。1.间隙狭窄理论高分子材料的混炼理论早就由 Bernhord[1]Mckdvey[2]等人建立了体系。而在班伯里密炼机的混炼作业中,由于其转子设计复杂和温度难以控制,不少人认为要建立一个完全适用的理论是困难的。在承认这一点的基础上,Bernhar提出:转子凸棱棱尖(Tip)和混炼室内壁间的间隙等,即使混炼机的规格大小改变,它仍保     

固液界面高分子吸附研究(Ⅰ)──模型的建立和检验

从常用密堆积格子模型导出了高分子溶液中自由高分子链节的几率表达式,在此基础上,通过类比的方法,建立了固液界面层中自由高分子链节的几率表达式,与DiMarzio-Rubin的高分子统计矩阵方法相结合,从而建立了基于密堆积格子的固液界面吸附模型．模型预测的高分子在界面层中的浓度分布与MC计算机模拟结果进行了比较,表明基于RevisedFreed和Guggenheim模型的固液界面吸附模型的计算结果比基于Flory-Huggins理论的模型计算结果,更接近于MC模拟值．     

Flory-Huggins格子上的混合亥氏函数模型

在Florg-Huggins格子中,引入有效的链插入几率表达过量熵,以Wohl式表达过量内能,建立了多元系链状高分子溶液的分子热力学模型.二元系的计算结果表明:在r_1=1,r_2=1～10000条件下,该模型比Freed理论更接近于计算机模拟结果;在其它条件下,两者基本吻合.Flory-Huggins理论因引入平均场近似,结果与之相差甚远.本文模型不仅能够描述常见的三元系统液液平衡,而且能描述三元系环形液液平衡曲线.     

固液界面高分子吸附研究(Ⅰ)──模型的建立和检验

从常用密堆积格子模型导出了高分子溶液中自由高分子链节的几率表达式，在此基础上，通过类比的方法，建立了固液界面层中自由高分子链节的几率表达式，与DiMarzio-Rubin的高分子统计矩阵方法相结合，从而建立了基于密堆积格子的固液界面吸附模型．模型预测的高分子在界面层中的浓度分布与MC计算机模拟结果进行了比较，表明基于RevisedFreed和Guggenheim模型的固液界面吸附模型的计算结果比基于Flory-Huggins理论的模型计算结果，更接近于MC模拟值．     

复杂材料的微相分离和结构演变

共聚高分子和表面活性剂系统常常能够形成不同尺度的复杂结构,在材料和生物技术领域具有广泛的用途.这种结构及其形成过程与自然界中大量存在的斑图及其演化过程具有非常类似的机理,受到不同学科研究者的广泛关注.在高分子系统的分子热力学、微相分离及结构演变过程领域已经开展了大量的研究工作,已成为凝聚态物理、高分子物理、统计力学理论和计算机模拟的热点之一.在分子尺度上,基于格子和自由空间的分子热力学模型、计算机分子模拟方法可以用于描述高分子系统的相平衡和分子的聚集形态.在介观尺度上,时间相关的Ginzberg-Landau理论、元胞动力学方法等可以有效地研究微相分离结构的演变过程及其受外场的影响.而耗散粒子动力学模拟则可以将分子尺度和介观尺度的研究结合起来,是一种跨尺度的研究方法.多尺度研究方法的发展将成为今后研究的重点.本文总结了该领域的某些研究进展.     

三元高分子共混体系Spinodal方程的理论推导

将经过改进的Flory状态方程(EOS)理论，引入到三元均聚高分子共混体系，得到三元体系的Flory状态方程。通过对高聚物共混自由能(△G^m)的热力学判据的讨论，得出三元均聚高分子共混体系相容性的临界条件，从而推导出三元均聚高分子共混体系的Spinodal方程。     

Modeling of Diffusion in Ellipsoidal Solids: A Simplified Approach

A three-dimensional model was applied to rigorously interpret the diffusion phenomena in ellipsoidal solids. The numerical solution of the diffusion equation was obtained by the finite difference method for ellipsoids of various shape factors. Due to its complexity for practical use, the spheroidal model (two-dimensional model) was utilized as a better alternative. In comparison with the numerical results generated by the three-dimensional model, the spheroidal model still fails to give good predictions in some cases, although it was assumed to have the same volume and surface area (i.e., same shape factor) as that of the ellipsoidal model. Consequently, a simplified approach was developed with satisfactory predictions, that is to apply a one-dimensional model to solve the diffusion problem with equivalent diameter as well as equivalent liquid diffusivity, which is a function of the intrinsic diffusivity and geometry factor.     

Mathematical modelling of the MCFC cathode

Different models for the NiO cathode have been compared with respect to their abilities to predict polarization curves and the influence of the amount of electrolyte on the electrode performance. It has been shown that the agglomerate model for the MCFC cathode gives more reasonable results when the exterior agglomerate surface area is specifically taken into account. In the cathode only the outermost layer of nickel oxide particles in the agglomerate is utilized for the electrochemical reaction. The pseudohomogeneous approach is questionable for these agglomerates since the individual particles constituting the agglomerate are of the same size as the reaction zone thickness. A thin-film model with a roughness factor for the electrode surface appears to be as good a model as the agglomerate model. A model based on a chain of spherical agglomerates and the partially drowned agglomerate model are physically more realistic models than the homogeneous agglomerate model for the prediction of the influence of electrolyte fill on the electrochemical performance.     

新垂直筛板塔汽体不混合时的板效率数学模型

本文在新垂直筛板双池模型基础上,建立了汽体不混合时板效率数学模型,给出了逐板逐池数值计算方法,导出了液体并流塔板的板效率解析式,将液体并流及逆流塔板的板效率结果分别与假定汽体完全混合时的板效率值进行了比较。     

ON GENERALIZED FRACTIONAL PROCESSES

Abstract. A class of stationary long-memory processes is proposed which is an extension of the fractional autoregressive moving-average (FARMA) model. The FARMA model is limited by the fact that it does not allow data with persistent cyclic (or seasonal) behavior to be considered. Our extension, which includes the FARMA model as a special case, makes use of the properties of the generating function of the Gegenbauer polynomials, and we refer to these models as Gegenbauer autoregressive moving-average (GARMA) models. While the FARMA model has a peak in the spectrum at f = 0, the GARMA process can model long-term periodic behavior for any frequency 0 f 0.5. Properties of the GARMA process are examined and techniques for generation of realizations, model identification and parameter estimation are proposed. The use of the GARMA model is illustrated through simulated examples as well as with classical sunspot data.     

Process simulation of gas-to-particle-synthesis via population balances: Investigation of three models

The simulation of complex gas-phase reactors for the synthesis of fine particles requires the coupling of particle and fluid dynamics. A previously developed CFD-coupled simulation technique based on a monodisperse population balance model is an efficient tool but seriously restricted when the product's polydispersity is of interest. Therefore, two other sectional population balance models have been developed: an extended 1-dimensional model and a simplified 2-dimensional model. Comparing calculations were performed with all three models, and temperature, concentration and sintering time were chosen as varying parameters. Using the 2-dimensional model as a benchmark, the conformity with the 1-dimensional sectional model is excellent for all cases investigated. Hence, due to the enormous difference in computational effort and time, clear preference can be given to the simpler sectional model. With respect to the monodisperse model, quite satisfactory results are found deviating mainly because of the typical, slower coagulation behavior of monodisperse particle systems. As a CFD-coupled technique only the 1-dimensional model is considered as an alternative to the simple monodisperse model as the computational demand of the 2-dimensional model is extremely high. A simple test simulation proves that the 1-dimensional model coupled with a commercial CFD software is a generally feasible technique. However, the computational time required is tremendous and impedes the present application.     

Modeling and predictive control of nonlinear processes using transfer learning method

This work develops a transfer learning (TL) framework for modeling and predictive control of nonlinear systems using recurrent neural networks (RNNs) with the knowledge obtained in modeling one process transferred to another. Specifically, transfer learning uses a pretrained model developed based on a source domain as the starting point, and adapts the model to a target process with similar configurations. The generalization error for TL-based RNN (TL-RNN) is first derived to demonstrate the generalization capability on the target process. The theoretical error bound that depends on model capacity and the discrepancy between source and target domains is then utilized to guide the development of pretrained models for improved model transferability. Subsequently, the TL-RNN model is utilized as the prediction model in model predictive controller (MPC) for the target process. Finally, the simulation study of chemical reactors via Aspen Plus Dynamics is used to demonstrate the benefits of transfer learning.     

A two-dimensional hydrodynamic model of a slurry system with immersed filters

A model describing hydrodynamics of a filtering slurry system is presented, incorporating axial effects in the entire slurry volume as well as radial effects at the axial positions where a filter is present. It is demonstrated that the model is capable of handling all different types of hydrodynamic steady states that may occur.Model predictions with respect to build-up of filter cake are compared to previously reported results of experiments and calculations using a model neglecting axial variations at the positions where a filter is present. In the experimental range of interest quantitative results (especially for the surface renewal model) are slightly altered when taking axial variations in the filter zone into account. However, after fitting the unknown model constants to experiments, the relevant trends remain unchanged as compared to previous results.The physical meaning of dimensionless numbers derived from the model equations is discussed as well as the implications different values for these numbers (not limited to the experimental range) have on model results. It is also demonstrated that when applying the force balance model to describe radial hydrodynamics, a relatively uniform cake distribution is observed as compared to applying the surface renewal model. A physical explanation is offered for the existence of a maximum allowable filter length as mentioned in literature for systems free of filter cake. Implications of model results for design of filtering slurry systems are given.     

Phenomena and Modeling of Hydrophobic Interaction Chromatography

Comprehension of the mechanisms of hydrophobic interaction chromatography is not as deep as for other chromatographic steps. This article shows the combination of modeling and experimental model parameter determination. Original mammalian cell culture is applied for validation instead of often-used test systems with for example, three pure proteins. This approach can have a huge benefit for process development and optimization of production processes under project conditions. To simulate the separation by hydrophobic interaction chromatography, a distributed plug flow model with inner pore diffusion is applied. The needed model parameters are determined by small scale experiments on a 1 ml column to reduce feed amount consumption and experimental procedure. Effects caused by system setup are optimized in relation to the volume. Gradient experiments are performed for the determination of isotherm parameters. The model parameters determined are experimentally validated at different set-ups of operation parameters as well as scaled up to 10 ml columns. The practicability of the proposed stepwise procedure of physico-chemical modeling in combination with laboratory scale experiments for the prediction of separation performance of original mammalian cell culture is proved. A model parameter determination directly with fermentation mixture is as well feasible.     

Development of an ionic polymer–metal composite stepper motor using a novel actuator model

A novel ionic polymer–metal composite (IPMC) actuated stepper motor was developed in order to demonstrate an innovative design process for complete IPMC systems. The motor was developed by utilizing a novel model for IPMC actuators integrated with the complete mechanical model of the motor. The dynamic, nonlinear IPMC model can accurately predict the displacement and force actuation in air for a large range of input voltages as well as accounting for interactions with mechanical systems and external loads. By integrating this geometrically scalable IPMC model with a mechanical model of the motor mechanism an appropriate size IPMC strip has been chosen to achieve the required motor specifications. The entire integrated system has been simulated and its performance verified. The system has been built and the experimental results validated to show that the motor works as simulated and can indeed achieve continuous 360° rotation, similar to conventional motors. This has proven that the model is an indispensable design tool for integrated IPMC actuators into real systems. This newly developed system has demonstrated the complete design process for smart material actuator systems, representing a large step forward and aiding in the progression of IPMCs towards wide acceptance as replacements for traditional actuators.     

液固散式流态化CFD模拟中曳力模型的影响

基于无黏性双流体简化模型在商业化软件平台上,通过增加用户自定义子程序考察了Gidaspow、Syamlal-O’Brien、Di Felice、Gibilaro、Dallavalle和BVK曳力模型对液固散式流态化CFD模拟结果的影响行为,探讨了相应的影响机制。经与文献中不同颗粒Reynolds数的代表性实验数据对比后发现：BVK和Dallavalle曳力模型对床层膨胀高度和整体固含率的预测精度较高;BVK、Syamlal-O’Brien以及Dallavalle曳力模型给出的床内固含率径向分布较为准确;BVK曳力模型较为准确地再现了颗粒轴向速度的径向分布特征。BVK曳力模型的影响机制与液固散式流态化中颗粒动力学特性相符合,在所考察范围内其预测性能最优;Dallavalle曳力模型在其余5个传统模型中预测性能较优且形式简洁在程序中易于实现。