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981.
To determine the rate constants for the second order consecutive reactions of the form U + V -(k1)--> W -(k2)--> P, a number of chemometrics and hard modeling-based methods are described. The absorption spectroscopic data from the reaction were utilized for performing the analysis. Concentrations and extinctions of components were comparable, and all of them were absorbing species. The number of steps in the reaction was less than the number of absorbing species, which resulted in a rank-deficient response matrix. This can cause difficulties for some of the methods described in the literature. The standard MATLAB functions were used for determining the solutions of the differential equations as well as for finding the optimal rate constants to describe the kinetic profiles. The available knowledge about the system determines the approaches described in this paper. The knowledge includes the spectra of reactants and products, the initial concentrations, and the exact kinetics. Some of this information is sometimes not available or is hard to estimate. Multiple linear regression for fitting the kinetic parameters to the obtained concentration profiles, rank augmentation using multiple batch runs, a mixed spectral approach which treats the reaction using a pseudo species concept, and principal components regression are the four groups of methods discussed in this study. In one of the simulated datasets the spectra are quite different, and in the other one the spectra of one reactant and of the product share a high degree of overlap. Instrumental noise, sampling error are the sources of error considered. Our aim was the investigation of the relative merits of each method. 相似文献
982.
Portfolio optimization with linear and fixed transaction costs 总被引:1,自引:0,他引:1
We consider the problem of portfolio selection, with transaction costs and constraints on exposure to risk. Linear transaction
costs, bounds on the variance of the return, and bounds on different shortfall probabilities are efficiently handled by convex
optimization methods. For such problems, the globally optimal portfolio can be computed very rapidly. Portfolio optimization
problems with transaction costs that include a fixed fee, or discount breakpoints, cannot be directly solved by convex optimization.
We describe a relaxation method which yields an easily computable upper bound via convex optimization. We also describe a
heuristic method for finding a suboptimal portfolio, which is based on solving a small number of convex optimization problems
(and hence can be done efficiently). Thus, we produce a suboptimal solution, and also an upper bound on the optimal solution.
Numerical experiments suggest that for practical problems the gap between the two is small, even for large problems involving
hundreds of assets. The same approach can be used for related problems, such as that of tracking an index with a portfolio
consisting of a small number of assets. 相似文献
983.
984.
985.
An efficient one-pot method has been developed for the synthesis of α-oxycarbanilinophosphonates via a one-pot reaction of an aldehyde with diethyl phosphite in the presence of magnesium oxide followed by reaction with an isocyanate under solvent-free conditions using ultrasonic irradiation. This method is simple, rapid and good yielding. 相似文献
986.
Maryam Mirza‐Aghayan Rabah Boukherroub Mahshid Rahimifard Mohammad Bolourtchian 《应用有机金属化学》2010,24(6):477-480
Reduction of a variety of nitroaromatic compounds with triethylsilane in the presence of catalytic amounts of palladium chloride in ethanol resulted in the formation of the corresponding anilines in excellent yields. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
987.
988.
989.
A new rarely reported ZnII mixed‐polypyridine coordination polymer with both rigid and flexible spacers, {[Zn(bpp)2(μ‐4,4′‐bipy)(H2O)2](ClO4)2 · H2O}n ( 1 ), has been synthesized and characterized by elemental analysis, IR‐, 1H NMR‐, 13C NMR spectroscopy and single‐crystal X‐ray diffraction. The thermal stability of compound 1 was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The single‐crystal X‐ray structure of 1 shows that the complex has been formed from a 1D polymer as a result of bridging by the 4,4′‐bipy ligands. Solution and solid‐state luminescent spectra of the compound 1 indicate intense fluorescent emissions at ca. 353.6 and 468.8 nm, respectively. Removal of the interstitial water guest molecules results in a loss of crystallinity, but exposure to water vapor reestablishes the original structure, thus constituting 1 as a third‐generation porous framework. 相似文献
990.
Maryam Shojaei Abdolreza Mirmohseni Yadollah Omidi Maryam Farbodi 《Applied biochemistry and biotechnology》2009,159(1):54-64
Homovanillic acid (HVA) and vanillylmandelic acid (VMA) were selectively determined by quartz crystal nanobalance sensor in
conjunction with net analyte signal (NAS)-based method called HLA/GO. An orthogonal design was applied for the formation of
calibration and prediction sets including HVA, VMA, and some common and structurally similar urine compounds. The selection
of the optimal time range involved the calculation of the NAS regression plot in any considered time window for each test
sample. The searching of a region with maximum linearity of NAS regression plot (minimum error indicator) and minimum of predicted
error sum of squares value was carried out by applying a moving window strategy. Based on the obtained results, the differences
on the adsorption profiles in the time range between 1 and 300 s were used to determine mixtures of compounds by HLA/GO method.
Several figures of merit like selectivity, sensitivity, analytical sensitivity, and limit of detection were calculated for
both compounds. The results showed that the method was successfully applied for the determination of VMA and HVA. 相似文献