20～6000 K温度范围内二氧化碳配分函数的计算

在20～6000 K温度范围内,通过乘积近似计算了二氧化碳及其同位素的总的配分函数.其中振动配分函数用谐振子近似,转动配分函数考虑了离心扭曲修正.20～6000 K温度范围被划分为五个小区间.在每一个小区间,计算的总的配分函数被拟合到一个温度T的四阶或五阶多项式,从而获得五个或六个拟合系数.通过这些拟合系数可以快速准确的获得分子在所研究温度范围内任意温度下的总配分函数.     

基于归一化割的主题划分算法研究

为了保证抽取信息的全面性,主题划分成了不可或缺的工作。借助同义词词林,从词语的语义角度计算文本中各个段落间的相似度,建立段落文本关系图。基于文本关系图对归一化割分割准则中权值矩阵的构建做出调整,使之更能体现出段落间的相似程度,并使用该准则对文本进行主题划分。结果表明,该方法无论是对连续段落还是跨段落表达同一主题的主题划分均较为有效。     

图的k-单圈划分中的优化问题

图的划分问题曾引起图论界的广泛关注，在文献[4]中讨论了k-单圈划分，本文进一步研究基于k-单圈划分的优化问题，即在一个赋权图中求一个最小权可k-单圈划分的支撑子图，以及对一个不存在k-单圈划分支撑子图的图，如何添最少的边使得它有k-单圈划分的支撑子图。     

Dependence of the rate constants on the treatment of internal rotation modes: the reaction OH + CH3SH --> CH3S + H2O as an example

The title reaction has been used as an example to test the importance of using a hindered rotor treatment instead of a harmonic oscillator model for calculating vibrational partition functions corresponding to low-frequency internal rotation modes. First, a normal-mode analysis according to the Ayala and Schlegel's algorithm has been used to identify the internal rotation modes of methanethiol and the transition state structure. Then, after calculation of the energy barrier for each internal rotation, the corresponding hindered rotor partition functions have been calculated following the CW scheme of Chuang and Truhlar. The results show that the anharmonic treatment produces a rather modest improvement of the rate constants at room temperature or below.     

Aqueous solubilities and octanol-water partition coefficients of binary liquid mixtures of organic compounds at 25°C

From thermodynamics and certain assumptions it is shown that, under the usual experimental conditions, the octanol-water partition coefficient (K_o/w) of a given organic liquid should be the same whether the substance is partitioned neat or as part of a mixture. Measurements of several mixtures of n-propylbenzene (log K_o/w=3.71±0.04)+ethylbenzene (log K_o/w=3.16±0.01) clearly confirm this. It is also shown that the aqueous solubility (S_w) of a neat organic liquid can be related to its aqueous solubility (S _w ), when it is present at volume fraction in an organic liquid mixture, by S _w =S_w, where is its activity coefficient in the organic mixture. The measured S _w values for n-propylbenzene + ethylbenzene (1), n-hexane + nitrobenzene (>1) and di-isopropyl ether + chloroform (<1) are found to be in good agreement with the predicted values (average differences of, respectively, <2%, 8% and 6%). In general, the bounds on S _w are expected to be 0w w.     

Formation and stability of a charged jet in a strong electric field

The shape of a charged jet is determined in the approximation of a strong electric field. The stability of the jet with respect to both axisymmetric and nonaxisymmetric perturbations of the sinusoidal type is investigated in the linear approximation. The domains of predominance of the axisymmetric and bending modes and the longitudinal partition mode are determined. Experimental data on the longitudinal partition of a polymeric jet into several daughter jets are given.     

Volumetric path following algorithms for linear programming

We consider the construction of small step path following algorithms using volumetric, and mixed volumetric-logarithmic, barriers. We establish quadratic convergence of a volumetric centering measure using pure Newton steps, enabling us to use relatively standard proof techniques for several subsequently needed results. Using a mixed volumetric-logarithmic barrier we obtain an O(n ^1/4 m ^1/4 L) iteration algorithm for linear programs withn variables andm inequality constraints, providing an alternative derivation for results first obtained by Vaidya and Atkinson. In addition, we show that the same iteration complexity can be attained while holding the work per iteration to O(n ² m), as opposed to O(nm ²), operations, by avoiding use of the true Hessian of the volumetric barrier. Our analysis also provides a simplified proof of self-concordancy of the volumetric and mixed volumetric-logarithmic barriers, originally due to Nesterov and Nemirovskii. This paper was first presented at the 1994 Faculty Research Seminar “Optimization in Theory and Practice”, at the University of Iowa Center for Advanced Studies.     

QSAR-based toxicity classification and prediction for single and mixed aromatic compounds

Quantitative structure-activity relationships (QSARs) based on the octanol/water partition coefficient were employed to predict acute toxicities of 36 substituted aromatic compounds and their mixtures. In this study, the model developed by Verhaar et al. was modified and used to calculate octanol/water partition coefficients of chemical mixtures. To validate the model, acute toxicities of these chemicals were measured to Vibrio fischeri in terms of EC⁵⁰. The results indicated that the obtained QSAR models could be used to predict toxicities of samples consisting of these substituted aromatic compounds, individually or in combinations. The obtained equations were proved to be robust enough by using the leave-one-out test method. By classifying these chemicals into two groups, polar and non-polar, the toxicities of chemical mixtures within each group can be predicted accurately from their calculated partition coefficients.     

三嗪类化合物溶解度参数及毒性构—效关系

测定了１２种三嗪类化合物的水溶解度，辛醇水分配系数和对发光菌的毒性，并用分子连结性指数建立了预测三嗪类化合物的溶解度，辛醇水分配系数及对发光菌毒性的定量结构活性相关方程，其中１０种化合物献中未见报道。e