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Edward A. Dietz 《Journal of separation science》1996,19(9):485-491
Gas chromatrography (GC) with sulfur chemiluminescence detection (SCD) is an outstanding combination for selectively determining trace concentrations of sulfur compounds in hydrocarbon samples. GC peaks can be identified by retention times when reproducible, automated injection techniques are used. However, as described in this work, analysts should be on the look out for retention shifting due to solvent effects from sample components. Three examples of retention shifting are presented: (1) thiophene by benzene; (2) methylthiophenes by toluene; and (3) dibenzothiophene by gas oil. Depending on samples and analysis conditions, retention shifts from a few hundredths to 1.5 min have been observed. Such retention shifts are likely to cause errors in peak identifications. Therefore, when using SCD, simultaneous FID monitoring is recommended as an aid in evaluating chromatograms for possible retention shifting due to solvent effects. 相似文献
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Min-qiangYu Zhi-pingZhou De-yueYan 《高分子科学》2004,(2):155-167
This work deals with the kinetics of co-condensation polymerization of AB2 and AB monomers, giving expressions of the two-dimensional molecular weight distribution function and the number/weight average molecular weights of the resulting copolymers. The two-dimensional molecular weight distribution depends on two indices, n and l, which are the respective numbers of AB2 and AB units in a copolymer species. The evolution of the two-dimensional weight and z distributions during the co-condensation polymerization has been evaluated systematically. Finally, the two-dimensional distribution was transformed into a one-dimensional molecular weight distribution with only one variable (the molecular weight of the products instead of the degree of polymerization). The calculated results show that the highly branched copolymer has a very broad molecular weight distribution when the co-condensation polymerization approaches completion. 相似文献
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依据摩擦学定量构效关系理论(QSTR),采用比较分子力场分析(CoMFA)和比较分子相似性指数分析(CoMSIA)这两种方法研究了含氮杂环类润滑油添加剂的抗磨损性能的摩擦学三维定量构效关系(3D-QSTR),并建立了相应的3D-QSTR模型.结果表明:仅利用静电场构建CoMFA或CoMSIA模型时,模型预测能力最好,r~2,q~2均大于0.5.根据CoMFA或CoMSIA模型等高线图分析得出:分子静电场对含氮杂环类润滑油添加剂的抗磨损性能影响最大,在特定区域的引入带负电荷或带正电荷的基团将有助于抗磨性能的提高. 相似文献
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《Mathematische Nachrichten》2017,290(17-18):2977-2991
Essential and continuous spectrum of symmetric difference equations have been investigated. It has been shown that the deficiency indices and the existence of these components of the spectrum are determined by the growth conditions of the coefficients. In particular, the deficiency indices are superimposition of those clusters determined by the coefficient growth. Finally, we have proved the neccessary and sufficient conditions for the existence of essential spectrum of selfadjoint subspace extensions using subspace theory and asymtotic summation. 相似文献
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Infrared spectroscopic characteristics and gas chromatographic retention indices of tri- and tetramethylcyclohexenyl butenyl ketones were determined at different temperatures of analysis. Thermodynamic characteristics of sorption on the apolar stationary phase were calculated. The sorption characteristics of tri- and tetramethylcyclohexenyl butenyl ketones show that under conditions of capillary gas chromatography these compounds are retained due to the dispersive energy. It was shown by FTIR spectroscopy that the formation of conjugation systems of double bonds is responsible for the higher retention of the -isomers compared with that of the -isomers. The shortening of the distance between the carbonyl and trimethylcyclohexenyl groups was found to be accompanied by a decrease in the retention of the isomeric compounds. 相似文献
70.
The asymptotic properties of maximum likelihood estimates of a vector ARMAX system are considered under general conditions, relating to the nature of the exogenous variables and the innovation sequence and to the form of the parameterization of the rational transfer functions, from exogenous variables and innovations to the output vector. The exogenous variables are assumed to be such that the sample serial covariances converge to limits. The innovations are assumed to be martingale differences and to be nondeterministic in a fairly weak sense. Stronger conditions ensure that the asymptotic distribution of the estimates has the same covariance matrix as for Gaussian innovations but these stronger conditions are somewhat implausible. With each ARMAX structure may be associated an integer (the McMillan degree) and all structures for a given value of this integer may be topologised as an analytic manifold. Other parameterizations and topologisations of spaces of structures as analytic manifolds may also be considered and the presentation is sufficiently general to cover a wide range of these. Greater generality is also achieved by allowing for general forms of constraints. 相似文献