修正UNIFAC(Dortmond)模型预测二元溶液气液平衡活度系数的计算软件设计

基团贡献法是一种常用且有效估算气液平衡活度系数的方法,修正UNIFAC(Dortmond)模型预测精度最高,但计算过程相对复杂,手工计算效率较低,目前缺乏独立开放的应用软件。本文基于MATLAB设计了一套利用修正UNIFAC(Dortmund)模型计算二元溶液气液平衡活度系数的计算机应用程序。集成了Dortmund数据库(DDB)中常见化合物基团参数等计算数据,根据修正UNIFAC(Dortmund)拆分规则定义二元溶液体系组分的基团信息,输入温度及任一组分的摩尔分数,即可自动计算活度系数(γ)。程序计算结果与文献中用修正UNIFAC(Dortmond)模型的预测结果一致。与Bruce基于标准UNIFAC(Dortmond)模型设计的程序对比,本程序计算结果和实验值更为接近,误差值小于15%。     

间苯二甲酸在301.45～463.15 K水中的溶解度

在301.45 K至463.15 K温度范围内测定了间苯二甲酸在水中的溶解度。所采用的实验方法是在一台50升不锈钢高压釜中使过量的溶质与水溶液达到平衡后取样滴定分析饱和液体的组成。总结了三种同分异构体苯二甲酸在水中的溶解度数据，并基于固液平衡计算关联了UNIFAC活度系数模型中组合项的分子参数。结果表明，三种同分异构体溶解度的差别可以采用UNIFAC模型中组合项中的q／r作为可调参数进行定量地关联。     

含临界区流体混合物的统计缔合理论研究

含临界区流体混合物汽液平衡等热力学性质的研究是化工热力学的一个难题。本文用改进的统计缔合流体理论方程(SAFT-CP)^[1,2]结合范德华单流体混合规则(vdWl)计算了含临界点的二元混合物的汽液平衡。与原始的SAFT方程^[3/4]相比，SAFT-CP方程以非球形的硬体项作为参考流体，代替原来的硬球项，考虑了分子成链对色散作用的影响，对于极性流体，考虑了分子的偶极-偶极相互作用而忽略了缔合作用。本文计算的二元体系包括非极性-非极性体系：二氧化碳-丙烷、二氧化碳-丁烷和二氧化碳-戊烷，以及非极性～极性体系：硫化氢-戊烷、甲烷-丙酮和二氧化碳-甲醇。含临界点在内的计算结果与文献实验值符合很好，表明该方程适用于二元混合物含临界区的相平衡计算，具有广阔的应用前景。     

计算液液平衡的基团溶解度参数模型研究

为得到一种简便可靠的计算液液平衡的新方法,利用Delphi语言构建了液液平衡数据库,以此为基础对基团溶解度参数模型(GSP模型)进行了研究。采用的基团溶解度参数具有4维,分别表征基团间4种主要的相互作用。通过建立液液平衡算法,并采用非线性优化方法SIMPLEX作为优化方法,对548个三元体系液液平衡数据进行回归得到模型参数的具体数值。对于这些体系,GSP模型计算的平均R．M．S．为0．07446(mol),计算总体摩尔浓度分数的绝对误差为0．05305(mol)。采用改进的UNIFAC模型进行了同样的关联计算以进行比较。结果表明,对应所收集的平衡数据,GSP模型可以达到与改进的UNIFAC模型同样的关联计算精度,而所需要的参数更少,参数值也更容易得到。     

碳酸二甲酯—甲醇二元体系汽液平衡数据的推算与关联

利用共沸点数据,分别用Wilson,NRTL和UNIFAC方程模拟计算了碳酸二甲酯－甲醇二元体系在常压下的汽液平衡,3种不同模型的计算结果与实验值都较为吻合,其中以UNIFAC方程的拟合结果为最好。     

二甲苯在分子筛孔道中扩散特性的分子模拟研究

应用分子模拟技术研究了甲苯歧化反应中的产物二甲苯各同分异构体在MFI、MEL和CAN分子筛孔道中的扩散特性,得到二甲苯各同分异构体与不同分子筛之间的相互作用能,以及吸附位和扩散特性等相关信息。计算结果表明,吸附质分子扩散的难易程度受到孔径和孔道结构的共同影响。MFI分子筛对于p-xylene有很好的选择性,不论是直孔还是弯孔,均有此特性,但弯孔中的扩散能垒较直孔中高,因此吸附质分子更倾向于在MFI分子筛直孔中进行扩散;MEL分子筛的孔径略小于MFI分子筛,各吸附质的扩散能垒较在MFI分子筛孔道中高,二甲苯各同分异构体中p-xylene的扩散能垒远小于m-xylene和o-xylene,因此,MEL分子筛也表现出对于p-xylene的选择性;在CAN分子筛的孔道中,二甲苯各种同分异构体的扩散能垒按p-xylene＜m-xylene＜o-xylene的顺序依次升高,但由于数值整体偏低,所以CAN分子筛不能够表现出对于p-xylene的择形性。     

应用UNIFAC法计算非电解质溶液的活度系数

UNIFAC基团贡献法是目前流行的一种重要的推算汽液平衡的方法,可用以预测化工生产中遇到的许多非电解质液体混合物的活度系数。本文对一百三十三个体系应用UNIFAC 模型在微机上进行了计算,并对该模型的活度系数计算结果与文献实验值作了比较,从而对模型的实际应用作出了估计。     

Entropic-FV活度系数模型预测膜的溶胀性能

根据Vrentas-Duda自由体积理论，结合基于UNIFAC活度系数模型，在较宽的浓度范围内预测了聚合物膜在溶液中溶胀行为。用UNIQUAC方程计算液相中组分的活度，考虑了温度对模型方程中二元交互作用参数的影响。对水／乙二醇(EG)／聚乙烯醇(PVA)膜体系，三个不同温度60℃、70℃和80℃下计算结果和实验数据基本一致。模型方程中自由体积部分影响较大，考虑聚合物的粘弹性贡献对预测结果有一定改进。     

基于非线性最小二乘法的Van Laar常数计算

以汽液平衡实验数据或以基于UNIFAC模型计算获得的汽液平衡数据为基础,采用非线性最小二乘法与数值计算的方法相结合计算VanLaar常数,对计算的过程和方法进行了详细的分析,并利用计算得到的VanLaar常数对20余个二元混合物进行模拟计算,其中包含了恒温和恒压条件下的数据计算,也包含了不同温度和不同压力条件下的汽液平衡数据计算,并应用计算结果进行验算,与相应的实验结果或通过UNIFAC模型计算获得的结果进行对比,计算所获得数据与实验数据相比,平均误差小于3%。同时,对不同的物系进行误差分析,非理想物系和强极性物系的误差较大,一般物系的平均误差小于1%,并使用计算获得的VanLaar常数进行汽液平衡曲线模拟,与实际汽液平衡曲线对比,效果理想。结果表明,采用非线性最小二乘法结合数值计算方法获得的VanLaar常数误差较小,可用于相关汽液平衡的模拟和计算。     

UNIFAC-ZM活度系数模型预测聚合物溶液中溶剂扩散系数

根据Vrentas-Duds自由体积理论，结合基于UNIFAC活度系数模型，在较宽的浓度范围内预测了聚合物溶液中小分子的扩散行为。对某些聚合物体系，计算结果和实验数据基本一致。表明UNIFAC-ZM模型可代替Flory-Huggins方程用于预测聚合物溶液中小分子扩散系数。调节自由体积模型中的指前因子D0数值可改善预测结果。     

Soil loss predictions with three erosion simulation models

Quantification of soil loss is one of the greatest challenges in natural resources and environmental planning. Computer simulation models are becoming increasingly popular in predicting soil loss for various land use and management practices. In this study, three soil erosion prediction models — the Water Erosion Prediction Project (WEPP), the Erosion Productivity Impact Calculator (EPIC), and the Areal Nonpoint Source Watershed Environment Response Simulation (ANSWERS) were used for simulating soil loss and testing the capability of the models in predicting soil losses for three different tillage systems (ridge-till, chisel-plow, and no-till). For each model, the most sensitive model parameters were calibrated using measured soil erosion data. After calibration, models were run and predicted soil loss values were compared with the measured soil loss values. The measured soil erosion data were collected from an erosion experiment field of Kansas State University at Ottawa (Kansas), USA. Field experiments were conducted from 1995 to 1997 on small plots to measure runoff and soil losses under all three tillage systems. All three models were evaluated on the basis of individual event, total yearly, and mean event-based soil loss predictions. Results showed that all the three models performed reasonably well and the predicted soil looses were within the range of measured values. For ridge-till and chisel-plow systems, WEPP and ANSWERS gave better predictions than those by EPIC model. For no-till system, WEPP and EPIC predictions were better than those by ANSWERS. The overall results indicate that WEPP predictions were better than those by the other two models in most of the cases, and it can be used with reasonable degree of confidence for soil loss quantification for all the three tillage systems.     

基于答案及其上下文信息的问题生成模型

基于文本的问题生成是从给定的句子或段落中生成相关问题。目前,主要采用序列到序列的神经网络模型来研究包含答案的句子生成问题,然而这些方法存在以下问题: ①生成的疑问词与答案类型不匹配; ②问题与答案的相关性不强。该文提出一个基于答案及其上下文信息的问题生成模型。该模型首先根据答案与上下文信息的关系确定与答案类型匹配的疑问词;然后利用答案及其上下文信息确定问题相关词,使问题尽可能使用原文中的词;最后结合原句作为输入来生成问题。相关实验表明,该文提出的模型性能明显优于基线系统。     

A case for fractured mirrors

The decomposition storage model (DSM) vertically partitions all attributes of a table and has excellent I/O behavior when the number of attributes accessed by a query is small. It also has a better cache footprint than the standard storage model (NSM) used by most database systems. However, DSM incurs a high cost in reconstructing the original tuple from its partitions. We first revisit some of the performance problems associated with DSM and suggest a simple indexing strategy and compare different reconstruction algorithms. Then we propose a new mirroring scheme, termed fractured mirrors, using both NSM and DSM models. This scheme combines the best aspects of both models, along with the added benefit of mirroring to better serve an ad hoc query workload. A prototype system has been built using the Shore storage manager, and performance is evaluated using queries from the TPC-H workload.Received: 3 September 2002, Accepted: 15 February 2003, Published online: 10 July 2003Edited by P. Bernstein     

Enhanced Fuzzy System Models With Improved Fuzzy Clustering Algorithm

Although traditional fuzzy models have proven to have high capacity of approximating the real-world systems, they have some challenges, such as computational complexity, optimization problems, subjectivity, etc. In order to solve some of these problems, this paper proposes a new fuzzy system modeling approach based on improved fuzzy functions to model systems with continuous output variable. The new modeling approach introduces three features: i) an improved fuzzy clustering (IFC) algorithm, ii) a new structure identification algorithm, and iii) a nonparametric inference engine. The IFC algorithm yields simultaneous estimates of parameters of c-regression models, together with fuzzy c-partitioning of the data, to calculate improved membership values with a new membership function. The structure identification of the new approach utilizes IFC, instead of standard fuzzy c-means clustering algorithm, to fuzzy partition the data, and it uses improved membership values as additional input variables along with the original scalar input variables for two different choices of regression methods: least squares estimation or support vector regression, to determine ldquofuzzy functionsrdquo for each cluster. With novel IFC, one could learn the system behavior more accurately compared to other FSM models. The nonparametric inference engine is a new approach, which uses the alike -nearest neighbor method for reasoning. Empirical comparisons indicate that the proposed approach yields comparable or better accuracy than fuzzy or neuro-fuzzy models based on fuzzy rules bases, as well as other soft computing methods.     

基于晶格理论的聚合物溶液活度模型

根据Gibbs-Helmholtz热力学基本关系式,结合溶液晶格模型推导出适合聚合物体系的活度系数模型,该模型方程含有结合项、剩余项和自由体积项。将其与Entropic-FV(EFV)、UNIFAC-FV及UNIFAC模型,同时用于预测14个由PIB、PS和PPO等聚合物与苯、甲苯和丁烷等溶剂组成的聚合物-溶剂体系中溶剂的活度,并与实验数据进行比较,活度的平均偏差分别为3．98%、6．61%、4．92%、19．19%。计算结果显示该模型的预测精度高于其它3种常用的聚合物、溶剂体系的溶剂活度模型。     

对多氯代二苯并二噁的定量结构-气相色谱保留行为关系研究

采用分子电性距离矢量(MEDV)描述子表征多氯代二苯并二(口惡)(口英)(PCDDs),结合基于预测的变量选择和建模方法(VSMP),从MEDV中挑选出1-2个描述子,对不同固定相下PCDDs的气相色谱保留值建立定量线性模型。结果表明MEDV分子描述子对分子结构具有很好的分辨能力。利用VSMP方法挑选的MEDV描述子很好表达了描述子与气相色谱保留值之间的相关关系,所建立的模型相关系数(R)均大于0.98,留一法交互检验的相关系数(q)均大于0.97;并均匀挑选2/3有实验数据的异构体作为训练集,余下的1/3作为检验集,进行了变量挑选、建模,结果表明,挑选的变量与用全部已知样本建模时一致,最后对没有实验值的异构体进行了预测。