乙烯在醋酸中溶解度的Gibbs系综蒙特卡罗模拟

使用Gibbs系综蒙特卡罗方法,采用TraPPE-UA力场对乙烯-醋酸体系的溶解度和液相密度进行了模拟计算。对303.15K时,45KPa、105KPa和185KPa三个压力点的模拟值与实验值进行了对比,确认了模拟方法对低于常压时的适用性。由于醋酸的缔合特性,为了修正常压及高于常压时的计算结果,使用Dmol3计算了8种醋酸二聚体的能量,并选择其中2种拟合出Lennard-Jones曲线和参数,以此为初值修正了力场参数,进行计算后与实验数据再次比较,偏差缩小至约15%~17%。使用修正后的力场,根据实际工况,对101KPa时温度从285K到395K的溶解度和密度进行了预测计算。计算结果为精馏的设计提供了参考。     

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。     

从常温到超临界条件下水的分子动力学模拟

采用MD模拟方法研究了从常温到超临界条件下不同状态水的微观结构、氢键结构及氢键松弛的动态性质。模拟结果表明,随着温度的升高,成键分子中O…O间的平均距离基本保持不变,O…H间距离增加,水分子的氢键作用逐渐减弱,形成氢键的两水分子O…O一H取向角的分布呈线型分布的概率降低;同一温度下密度的变化对O-O、O-H径向分布函数和氢键的键角分布的影响不大。由于温度升高使氢原子热运动增强,水的四面体结构缺陷增加,氢键的平均寿命显著缩短,温度是影响氢键平均寿命的主要因素。     

不同温度下水的分子动力学模拟

采用分子动力学模拟的方法对不同温度下水的氢键结构及扩散性质进行了研究。模拟发现随温度的升高,水分子平均氢键配位数减小,氢键键角分布变宽,键角分布峰值减小,即水分子间氢键作用不断减弱。扩散系数随温度的增加而上升,液体水的扩散系数与温度之间的关系符合Ａｒｒｈｅｎｉｕｓ行为。     

稀醋酸共沸精馏脱水工艺的模拟

醋酸是一种重要的化工原料,其水溶液广泛存在于各类工业过程中。由于醋酸与水会缔合使得两者的相对挥发度不大,生产中用于分离醋酸/水的工艺能耗较高,因此研究者和工业界都在寻求更好的分离方法。本文以醋酸正丙酯做挟带剂,应用Aspen Plus流程模拟软件,汽相逸度采用Hayden-O’Connell方程,液相活度系数采用NRTL方程计算,实现了稀醋酸共沸精馏脱水工艺的模拟。本文详细讨论了全塔理论板数、进料位置、回流比等因素对脱水塔性能的影响。结果表明,在理论板数50块,回流比3.2,醋酸进30块板,挟带剂与进料比0.15条件下,塔釜得到醋酸浓度高于95%。模拟结果对醋酸脱水工艺的设计和改造具有重要的指导意义。     

不同路线合成乙醇的热力学分析(英文)

运用吉布斯自由能最小法对3种不同路线（合成气直接合成、甲醇同系化、醋酸加氢）合成乙醇热力学进行了分析,在温度373 K～873 K,压力0.1 MPa～10 MPa的范围内获得了各路线原料转化率与产物平衡组成随温度与压力变化的关系。对于合成气直接合成乙醇,低温对CO平衡转化率有利,在压力为2 MPa时,温度从373 K升高到873 K,CO平衡转化率从100%降到1.56%:在甲醇同系化合成乙醇工艺中,甲醇的转化率在所研究的温度压力范围内都几乎为100%,低温时（T<473 K）甲醇经同系化反应接近完全转化为乙醇,高温时（7>673 K）甲醇几乎全部分解为CO与H₂;醋酸加氢制乙醇工艺中醋酸的转化率均大于70.79%。对于这3种路线,乙醇的平衡组成在10MPa、373K时达到最大,分别为50%,50%与25%。     

水的汽液相平衡及径向分布的分子模拟研究

采用J．R．Errington等提出的固定点电荷水分子新模型,分别以Buckingham Exp-5势能结合哥伦布势能模型计算分子间的短程作用及Ewald Summation方法计算电荷间的长程作用,采用恒NVT吉布斯系综Monte Carlo模拟方法模拟了水在300K～600K下的汽液相平衡,并采用经典的恒NVT系综Monte Carlo模拟方法模拟了水在温度T=300K,ρ=1．0g／cm^3下的原子对径向分布函数。模拟结果与文献中的实验值吻合良好。本文工作为推广至更复杂水溶液体系的模拟打下了良好的基础。     

基于化学传递反应模拟甲烷和乙炔燃焰中碳沉积的条件

通过乙炔和甲烷与氧的化学平衡计算和化学传递反应的机理来模拟碳的气化和沉积的温度范围,结果表明,降低压力有利于降低碳沉积的温度范围。对于C-H体系,在常压下(1bar)发生碳沉积的化学传递反应的温度范围为2 800 K→1 600 K,而在低压下(0．01bar),温度范围为2 000 K→1 250 K,这个结果与文献中低压下化学气相沉积合成金刚石的实验数据相吻合。本文提出的模型和计算结果的意义在于,通过对一组化学传递反应器中温度的调节可以较为精确地控制碳沉积过程的过饱和度,从而适应于合成金刚石或碳纳米管的需要。本文所定义的模型和方法可以推广到C-O和C-H-O等体系碳的化学气相沉积的模拟计算。     

乙醇、异丙醇在超临界二氧化碳中的溶解度及其模型

采用固定体积可视观察法,测定温度313 K～393 K范围内,不同压力下乙醇和异丙醇在超临界CO2中的的溶解度,并应用Chrastil半经验溶解度模型关联这些溶解度.实验结果表明,在相同温度下,随着CO2密度的升高,溶质在气相中的溶解度也升高.且得到了相应于该系统的溶解度方程参数,与实验数据几乎一致.     

醋酸水溶液局域结构中氢键环的感知与统计-CPMD模拟结果分析

提出了用于分子动力学模拟后处理氢键网络图的感知算法。对从头算分子动力学(CPMD)模拟的轨迹文件进行统计分析,得到了水溶液中醋酸单分子水合体系的局域结构特征信息。由径向分布函数得到定义氢键的上限,运用图论方法分析了溶液结构中水合团簇大小和简单氢键环结构及头环分布,其中六元环的突出含量与从头算稳定性分析一致。     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.