The use of neural networks for fitting complex kinetic data

In this paper the use of neural networks for fitting complex kinetic data is discussed. To assess the validity of the approach two different neural network architectures are compared with the traditional kinetic identification methods for two cases: the homogeneous esterification reaction between propionic anhydride and 2-butanol, catalysed by sulphuric acid, and the heterogeneous liquid-liquid toluene mononitration by mixed acid. A large set of experimental data obtained by adiabatic and heat flux calorimetry and by gas chromatography is used for the training of the neural networks. The results indicate that the neural network approach can be used to deal with the fitting of complex kinetic data to obtain an approximate reaction rate function in a limited amount of time, which can be used for design improvement or optimisation when, owing to small production levels or time constraints, it is not possible to develop a detailed kinetic analysis.     

On the thermal stability of xanthan gum

The thermal stability of xanthan gum in dilute aqueous solutions at 90°C is considered. The relative viscosity as a function of ageing time is discussed, and it has been found to depend on the polymer concentration and conformation as well as on the salt content. The effectiveness of a quencher demonstrates the existence of a free-radical process in the degradation. During ageing, the molecular weight first decreases by rapid random hydrolysis of the main chain and loss of the pyruvate and acetate substituents. Later, oligomers are formed corresponding to a breakdown of both the side chain and the main chain. The identification of cellodextrins in the oligomer pool demonstrates the second effect.     

氢氧化物阻燃剂在聚乙烯中的应用技术和研究进展

综述了近年来国内外氢氧化物阻燃聚乙烯的研究现状及其应用技术进展，简要评价了阻燃技术的发展趋势。     

Composition and seasonal variation of fatty acids of <Emphasis Type="Italic">Diplodus vulgaris</Emphasis> L. from the Adriatic Sea

Muscle tissue from the common two-banded sea bream Diplodus vulgaris L. originating from the Adriatic Sea, Croatia, was analyzed. The FA composition of neutral (TAG) and polar (PE, PC, PI/PS) lipid classes was determined, as well as the lipid and water contents during winter and summer periods. Both the total lipid and water contents were higher in the winter period. We identified 16 different FA. The major constituents of the total FA in both seasons were saturates: palmitic (16∶0) and stearic acids (18∶0); monoenes: oleic (18∶1n−9) and palmitoleic acids (16∶1n−7); and polyunsaturates: arachidonic acid (20∶4n−6), EPA (20∶5n−3), and DHA (22∶6n−3), but their amounts and ratios differed significantly between the two seasons and between lipid fractions. The FA composition showed a noticeable pattern of seasonality that reflected fluctuations mainly in TAG. The diminution of the monounsaturated FA content in the summer was clearly followed by an increase in PUFA content. Diplodus vulgaris is a good source of natural n−3 PUFA and would therefore be suitable for inclusion in highly unsaturated low-fat diets.     

基于GPS实时数据的在线过滤与补遗研究*

为提高GPS数据的有效性与可靠性,使之为实现实时交通流量预测与交通诱导服务,首先基于GPS历史数据,以变异系数极小化为优化目标进行GPS数据过滤模型的优选,并对实时数据缺损提出两种补遗算法;然后给出基于动态GPS实时数据的在线数据过滤与补遗一体化算法;最后结合2008年杭州市GPS历史数据对模型进行应用。结果表明,基于简单算术平均的滤波模型即为GPS数据过滤的最佳模型;基于时间序列缺失数据的快速补遗算法能够很好地满足实时预报要求,实现快速补遗。     

银川市近49a来降雨变化特征分析

根据银川市4个气象站(银川站、永宁站、贺兰站、灵武站)近49 a(1960—2008年)的实测降雨资料,运用统计学理论、回归分析、Mann-Kendall非参数检验、克里金插值等方法进行研究,依据有关统计量的计算结果,分析了银川市近49 a来降雨量的时空变化特征.研究结果表明:银川市年内降雨量分配不均,夏季降雨量最大,占全年降雨量的56.83%~58.32%,冬季最小,仅占全年降雨量的1.93%~2.07%;年际以及年代际降雨量变化大,多年平均降雨量为186.7 mm,且以20世纪60年代降雨量最大,90年代降雨量最小.经Mann-Kendall非参数检验和一元线性回归分析,发现银川市降雨量呈现逐年减小的趋势,Mann-Kendall非参数检验趋势系数β为-0.18 mm/a,线性回归倾向率为-5.386 mm/(10 a).银川市降雨量还存在空间分布不均的特点,灵武市降雨量最大,减小的趋势最小;贺兰县降雨量最小,减小的趋势最大.     

Effect of variation in gas distribution on explosion propagation characteristics in coal mines

In order to investigate the effect of variation in the distribution of gas on explosion propagation characteristics in coal mines, experiments were carried out in two different channels with variation in gas concentration and geometry. Flame and pressure transducers were used to track the explosion front velocity. The flame speed (Sf) showed a slight downward trend while the methane concentration varied from 10% to 3% in the experimental channel. The peak overpressure (Pmax) dropped dramatically when com-pared with normal conditions. As well, the values of Pmax and Sf decreased when the methane concentration dropped from 8% to 6%. The flame speed in the channel, connected to a cylinder with a length varying from 0.5 to 2 m, was greater than that in the normal channel. The peak overpressure was also higher than that under normal conditions because of a higher flame speed and stronger pressure piling up. The values of Pmax and Sf increased with an increase in cylinder length. The research results indicate that damage caused by explosions can be reduced by decreasing the gas concentration, which should be immediately detected in roadways with large cross-sections because of the possibility of greater destruction caused by more serious explosions.     

一种基于全变分模型的图像修复改进算法

为了恢复图像中划痕、文字等小目标去除后丢失的相关信息,对全变分(TV)模型及其自适应算法进行了分析和改进。在Chan提出的图像修复原则的基础上给出了两个阈值参数,对原有算法中的权值系数进行了改进。仿真实验结果表明,本文算法在保证原有算法修复效果的同时能够有效地提高运算速度,取得了较好的实际效果。     

预张力悬索桥及其静力学性能分析

为从理论上获得预张力悬索桥的力学特性,利用大位移不完全广义势能变分原理,建立了预张力悬索桥的一般基础微分方程.在进一步引入假设条件下,导出了基于古典挠度理论的平衡微分方程.通过对微分方程的解析,讨论了预张力悬索桥的静力学特性及其与普通悬索桥的区别.结合算例悬索桥的数值分析表明,预张力悬索桥由于抗风索的存在,以及结构中建立的预张力,在提高结构刚度、减小加劲梁弯矩等方面具有一定的优越性.     

基于关联与回溯的产品变异设计过程重用方法

为实现在复杂度和数量上急剧增长的产品过程模型和关联知识的重用,提出一种产品变异设计过程的重用方法.对设计系统的模块进行精细化和抽象化,建立具有规范化数据接口的产品结构变异设计的信息模型,用状态空间的带权有序检索树存储变异设计过程;将变异设计语义添加至可移植结构,当发生分割、合并和变换的变异设计行为时,对其抛弃、保持或复制等处理,实现变异设计语义随变异设计行为的继承与变迁;再通过检索变异设计语义不断获得待变异结构,将离散的设计过程关联;深度优先搜索获得把初始状态变换为目标状态的操作序列,执行可行解集,回溯变异设计过程并实现重用.以ACIS为几何造型内核开发自主原型系统,实现涡轮风扇发动机的压气机的转子叶片变异设计过程的重用.结果表明,该方法将设计重用对象由静态的孤立设计结果拓展到动态的连续设计过程,对于准确、快速地实现产品的结构变异设计具有重要意义.