Ion chromatographic separation of car☐ylic acids prediction of retention data

The retention behavior of biologically relevant monovalent (formic, acetic, propionic, lactic and pyruvic) and divalent (oxalic, malonic, succinic, fumaric, maleic and tartaric acids) car☐ylic acids together with inorganic analytes (chloride and sulphate) has been studied. The separation was performed on a latex-based strong anion-exchange resin using carbonate buffer systems in suppressed IC. The retention behaviour of analytes was investigated at different pH values and [HCO₃⁻]+[CO₃²⁻] concentrations. A theoretical model, involving ion-exchange equilibria of sample and eluent anions, was derived and applied to the chromatographic data obtained. Chromatographic ion exchange selectivity values were determined and retention data were calculated for the anions using different carbonate eluent conditions. The average of errors between the predicted and the measured retention volumes of the analytes studied does not exceed 4.0%. The study effectively characteristics the behaviour of different analytes under elution conditions of practical importance.     

Molecular parameters and retention characteristics of unsubstituted polyaromatic hydrocarbons in HPLC

Summary The present research studies the possibility of using the correlation dependence between molecular parameters of unsubstituted polyaromatic hydrocarbons (PAH) and their retention in reversed-phase liquid chromatography to optimize the conditions for the separation and identification of unknown peaks on the chromatograms of multicomponent mixtures. A linear correlation equation, that takes the number and environment of the carbon atom in the PAH molecule into account as well as the differences in the specific interactions of isomeric molecules with polar eluent, has been proposed. The adequacy of the proposed PAH retention model was verified by comparing the calculated retention values with the experimental data. The possibility of identifying unsubstituted PAH according to the number of carbon atoms of various types and according to the values of the molecules lengths (calculated on the basis of the retention of these substances under different eluent compositions) was exemplified by various chromatographic systems (reversed phase-eluent-PAH molecules).     

高锰酸盐指数的灰色GM(1,1)预测

以中山市岐江河近7年的高锰酸盐指数监测数据为基础，采用灰色系统理论中的预测方法，建立了岐江河高锰酸盐指数的灰色预测模型。用该模型预测岐江河2006年、2007年、2008年高锰酸盐指数的值分别为5．3，5．4和5．4。     

Using new structurally related additive schemes in the precalculation of gas chromatographic retention indices of polychlorinated hydroxybiphenyls on HP-5 stationary phase

A new additive scheme is proposed for the precalculation of gas chromatographic retention indices of complex organic compounds. The principal feature of this approach is the absence of previously calculated I increments for any structural fragments or functional groups in the molecule. Instead, arithmetical operations involving I values of simpler structural analogues of target compounds are used directly. I precalculation for polychlorinated hydroxybiphenyls (839 congeners) on the HP-5 stationary phase was chosen as one of the most important applications of the method under discussion. Such a large number of congeners cannot be obtained as reference samples and their gas chromatographic (GC)-mass spectrometric (MS) identification should therefore be based currently on precalculated I values.     

Correlation of antioxidant depletion and mechanical performance during thermal degradation of an HTPB elastomer

Thermal degradation studies of a stabilized HTPB based elastomer were conducted at temperatures from 50 °C to 110 °C. The concentration of extractable antioxidant (AO2246) in the polymer was quantified via AO extraction and a gas chromatography-based method using internal standards. The decrease in extractable AO levels as a function of time and temperature was evaluated and correlated with mechanical property changes. Most importantly, AO depletion features were found to be temperature dependent. At elevated temperatures (>80 °C) extractable AO levels decreased rapidly and faster than the concurrent loss in mechanical properties. While extractable AO concentrations decrease quickly, the material is able to maintain some useful mechanical properties, perhaps via non-extractable or grafted AO species formed during degradation providing additional protection. At lower aging temperatures extractable or free AO levels decreased more slowly than the mechanical properties. Therefore, for condition monitoring purposes a universal correlation between AO levels and aging state or material condition could not be established. Most importantly, however, loss of mechanical properties and oxidative degradation is observed at lower temperatures despite significant levels of free antioxidant in the material. The antioxidant appears to be limited in its effectiveness to completely prevent degradation reactions, or only fractions of the total AO available are actually involved in the inhibition process.     

The W algorithm and the D transformation for the numerical evaluation of three‐center nuclear attraction integrals

Three‐center nuclear attraction integrals over exponential‐type functions are required for ab initio molecular structure calculations and density functional theory (DFT). These integrals occur in many millions of terms, even for small molecules, and they require rapid and accurate numerical evaluation. The use of a basis set of B functions to represent atomic orbitals, combined with the Fourier transform method, led to the development of analytic expressions for these molecular integrals. Unfortunately, the numerical evaluation of the analytic expressions obtained turned out to be extremely difficult due to the presence of two‐dimensional integral representations, involving spherical Bessel integral functions. % The present work concerns the development of an extremely accurate and rapid algorithm for the numerical evaluation of these spherical Bessel integrals. This algorithm, which is based on the nonlinear D transformation and the W algorithm of Sidi, can be computed recursively, allowing the control of the degree of accuracy. Numerical analysis tests were performed to further improve the efficiency of our algorithm. The numerical results section demonstrates the efficiency of this new algorithm for the numerical evaluation of three‐center nuclear attraction integrals. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Nonlocality as a feature of the physical world

Aprediction puzzle leads to a form ofnecessary realism which forces the rejection of a central tenet of the Copenhagen interpretation. This leads to reconsidering conceptual difficulties related to Bell's locality premise. It is shown that aparadox of elementary probability theory puts new light on Bell's assumption that causality and statistical independence are mutually incompatible. Nemo dat quod non habet : No one can offer more than he has ability to give; in that spirit, this paper is dedicated to the memory of J.S. Bell.     

Numerical solution of minimax problems of optimal control,part 1

This paper contains general transformation techniques useful to convert minimax problems of optimal control into the Mayer-Bolza problem of the calculus of variations [Problem (P)]. We consider two types of minimax problems: minimax problems of Type (Q), in which the minimax function depends on the state and does not depend on the control; and minimax problems of Type (R), in which the minimax function depends on both the state and the control. Both Problem (Q) and Problem (R) can be reduced to Problem (P).For Problem (Q), we exploit the analogy with a bounded-state problem in combination with a transformation of the Jacobson type. This requires the proper augmentation of the state vectorx(t), the control vectoru(t), and the parameter vector , as well as the proper augmentation of the constraining relations. As a result of the transformation, the unknown minimax value of the performance index becomes a component of the parameter vector being optimized.For Problem (R), we exploit the analogy with a bounded-control problem in combination with a transformation of the Valentine type. This requires the proper augmentation of the control vectoru(t) and the parameter vector , as well as the proper augmentation of the constraining relations. As a result of the transformation, the unknown minimax value of the performance index becomes a component of the parameter vector being optimized.In a subsequent paper (Part 2), the transformation techniques presented here are employed in conjunction with the sequential gradient-restoration algorithm for solving optimal control problems on a digital computer; both the single-subarc approach and the multiple-subarc approach are discussed.This research was supported by the National Science Foundation, Grant No. ENG-79-18667, and by Wright-Patterson Air Force Base, Contract No. F33615-80-C3000. This paper is a condensation of the investigations reported in Refs. 1–7. The authors are indebted to E. M. Coker and E. M. Sims for analytical and computational assistance.