共查询到18条相似文献,搜索用时 171 毫秒
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本文应用Flory的链分子统计理论研究1,2-聚丁二烯的链构象,选择固定键长和键角的分子模型,计算构象能,构成势能面图,并由势能面的构型积分,得到了表征1,2-聚丁二烯链构象特征的统计权重矩阵. 相似文献
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本文应用Flory的链分子统计理论研究1,2-聚丁二烯的链构象,选择固定键长和键角的分子模型,计算构象能,构成势能面图,并由势能面的构型积分,得到了表征1,2-聚丁二烯链构象特征的统计权重矩阵. 相似文献
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本文以Cl+H_2的经典轨线计算为例,介绍了准经典轨线法的原理,即LEPS势能面的选取,运动方程的建立以及初始条件的选择.应用Monte Carlo方法大量随机选择变量的初始条件,所计算的轨线可分为非反应和反应的两大类.通过轨线计算可以得到反应截面积和分子反应的其他有关信息. 相似文献
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利用神经网络力法,基于47783个高精度从头算能量点构建了反应体系H+CH4←→H2+CH3的一个全域势能面.通过大最的准经典轨线以及量子散射计算测试了势能面的收敛性质.这个势能面对于拟合过程以及从头算点的数目都已经完全收敛,拟合误差很小县比Shepard插值的势能面计算速度更快,代表了此标志性多原子反应体系最好的势能面. 相似文献
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本文利用LIF方法,在单次碰撞条件下,首次研究了Ba与C_2H_5Br,n-C_3H_7Br,n-C_4H_9Br,n-C_5H_(11)Br的反应。通过计算机模拟实验光谱,得到了产物BaBr的振动布居,发现其振动激发和反应截面随碳链增长而增大。同时从实验结果反演出了Ba+CH_3Br的“准三原子”LEPS模型势能面,并利用基于模型势能面的经典轨线计算对以上体系进行了研究。这些研究表明,质量因子和C—Br键强度的不同是引起产物振动激发和反应截面随碳链增大而变化的最重要的因素,得到了描述所有Ba+C_mH_(2m+1)Br反应体系的势能面。而且进行了ab initio,证实了所构造势能面的可靠性。 相似文献
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The paper describes the application of SOMs (Self-Organizing Maps) and SVR (Support Vector Regression) to pattern recognition in GC-MS (gas chromatography-mass spectrometry). The data are applied to two groups of apples, one which is a control and one which has been inoculated with Penicillium expansum and which becomes spoiled over the 10-day period of the experiment. GC-MS of SPME (solid phase microextraction) samples of volatiles from these apples were recorded, on replicate samples, over time, to give 58 samples used for pattern recognition and a peak table obtained. A new approach for finding the optimum SVR parameters called differential evolution is described. SOMs are presented in the form of two-dimensional maps. This paper shows the potential of using machine learning methods for pattern recognition in analytical chemistry, particularly as applied to food chemistry and biology where trends are likely to be non-linear. 相似文献
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Quasiclassical, direct dynamics trajectories have been used to study the reaction of formaldehyde cation with molecular hydrogen, simulating the conditions in an experimental study of H2CO+ vibrational effects on this reaction. Effects of five different H2CO+ modes were probed, and we also examined different approaches to treating zero-point energy in quasiclassical trajectories. The calculated absolute cross-sections are in excellent agreement with experiments, and the results provide insight into the reaction mechanism, product scattering behavior, and energy disposal, and how they vary with impact parameter and reactant state. The reaction is sharply orientation-dependent, even at high collision energies, and both trajectories and experiment find that H2CO+ vibration inhibits reaction. On the other hand, the trajectories do not reproduce the anomalously strong effect of nu2(+) (the CO stretch). The origin of the discrepancy and approaches for minimizing such problems in quasiclassical trajectories are discussed. 相似文献
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The quantum distribution of initial conditions suggested recently by Careless and Hyatt as a means of “phase-averaging” classical trajectories is shown to lead to reaction probabilities which depend on the initial distance between the reagents even when this distance is sufficiently large for the corresponding interaction energy to vanish. We used that distribution to calculate reaction probabilities for the collinear H + H2 exchange reaction on a potential energy surface for which quasi-classical and exact quantum results had been previously obtained. The dependence of the resulting reaction probabilities on the arbitrarily chosen value of the initial atom-molecule separation was substantial. We conclude that the use of such quantum distributions for initial conditions is physically unacceptable. 相似文献
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建立由UV–化学模式识别法评价丹参质量的方法。分别用正己烷、乙酸乙酯、水、乙醇提取不同产地的丹参,并测绘其紫外光谱。取紫外光谱各波长的吸光度为特征数据,进行主成分分析、聚类分析,对不同产地丹参质量的差异进行了评价。不同溶剂提取液的光谱聚类结果有所差异,可将不同产地丹参聚为3类。UV–化学模式识别技术可以从整体上反应丹参所含成分的差异,可为丹参质量控制与评价提供依据。 相似文献
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A technique based on pattern recognition of data obtained by supersonic jet spectrometry is employed for the prediction of chemical structure. The degree of similarity is evaluated quantitatively by calculating a cross correlation factor between sample and reference molecules. A probability density function is determined by fitting the data to a specified equation. The functional group and its position are also predicted by a similar technique. The pattern recognition provides a method for prediction of the chemical structure and is applicable to samples that have not been examined by supersonic jet spectrometry. 相似文献
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Since the late sixties, pattern recognition techniques have been used by analytical chemists to facilitate the interpretation of multivariate analytical information. Most research within the field has focused on adapting pattern recognition methods to chemical data. This has been necessary since chemical data are often complicated by the fact that distributions are unknown. Through the first decade of chemical pattern recognition, promising results have been obtained even though the data sets studied have frequently been rather small for statistical analysis. The past few years have shown that an increasing number of analytical chemists are interested in the sheer utility of pattern recognition. This can be taken as a valid sign of a useful approach. The present communication surveys this development. Those methods which have proved most useful for analytical chemical data are described in some detail, and applications within the various fields of analytical chemistry are reviewed. 相似文献
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The possibilities of action-orientated pattern recognition with the supervised pattern recognition technique, ALLOC, are discussed. The emphasis is on the importance of the definition of overlapping regions between classes as a way for obtaining more information about the separation between classes. Action-orientated classification and feature selection with ALLOC are discussed using the results obtained for two data bases concerning the characterization of the functional state of the thyroid and the determination of the origin of milk samples. 相似文献
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葡萄酒分析中模式识别方法的研究:Ⅱ.原汁含量的多元判别分析 总被引:1,自引:0,他引:1
本实验采用常规分析方法,分析了18个不同含汁量酒样的乙醇,总酸,挥发酸,固定酸,干浸出物,pH值,灰份,灰份碱度,总酚,甘油,钾,钠,镁,干浸出物与甘油比,Q值,修正干浸出物共17个变量。采用计算机模式识别技术,利用逐步判别方法,得出了葡萄酒中原汁含量种逐步别方法的判别函数和回判结果。 相似文献