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81.
Sanjeev K. Garg 《Tetrahedron letters》2005,46(10):1721-1724
Copper(II) tetrafluoroborate has been found to be a new and highly efficient catalyst for Michael addition of thiols to α,β-unsaturated carbonyl compounds under solvent-free conditions and in H2O at room temperature. The reactions are very fast and are completed in 2 min to 1 h affording high yields. The rate of thiol addition was dependent on the steric hindrance at the β-carbon of the α,β-unsaturated carbonyl substrate. In the case of chalcones, the reactions are best carried out in MeOH as solvent. 相似文献
82.
Ram Manohar & Rajen Kumar Sinha 《计算数学(英文版)》2022,40(2):147-176
This article studies a posteriori error analysis of fully discrete finite element approximations for semilinear parabolic optimal control problems. Based on elliptic reconstruction approach introduced earlier by Makridakis and Nochetto [25], a residual based a posteriori error estimators for the state, co-state and control variables are derived. The space discretization of the state and co-state variables is done by using the piecewise linear and continuous finite elements, whereas the piecewise constant functions are employed for the control variable. The temporal discretization is based on the backward Euler method. We derive a posteriori error estimates for the state, co-state and control variables in the $L^\infty(0,T;L^2(\Omega))$-norm. Finally, a numerical experiment is performed to illustrate the performance of the derived estimators. 相似文献
83.
In this paper we present and study a new algorithm for the Maximum Satisfiability (Max Sat) problem. The algorithm is based on the Method of Conditional Expectations (MOCE, also known as Johnson’s Algorithm) and applies a greedy variable ordering to MOCE. Thus, we name it Greedy Order MOCE (GO-MOCE). We also suggest a combination of GO-MOCE with CCLS, a state-of-the-art solver. We refer to this combined solver as GO-MOCE-CCLS.We conduct a comprehensive comparative evaluation of GO-MOCE versus MOCE on random instances and on public competition benchmark instances. We show that GO-MOCE reduces the number of unsatisfied clauses by tens of percents, while keeping the runtime almost the same. The worst case time complexity of GO-MOCE is linear. We also show that GO-MOCE-CCLS improves on CCLS consistently by up to about 80%.We study the asymptotic performance of GO-MOCE. To this end, we introduce three measures for evaluating the asymptotic performance of algorithms for Max Sat. We point out to further possible improvements of GO-MOCE, based on an empirical study of the main quantities managed by GO-MOCE during its execution. 相似文献
84.
Best possibility of the Furuta inequality 总被引:5,自引:0,他引:5
Let , and . Furuta (1987) proved that if bounded linear operators on a Hilbert space satisfy , then . In this paper, we prove that the range and is best possible with respect to the Furuta inequality, that is, if or , then there exist which satisfy but .
85.
Nikolai N. Brandt Andrey Yu. Chikishev Inna K. Sakodinskaya 《Journal of Molecular Structure》2003,648(3):177-182
Raman spectroscopy is employed to study tris-(hydroxymethyl)aminomethane and its complexes with 18-crown-6. The results obtained are used to interpret the known effect of α-chymotrypsin activation by crown ether in organic solvents. Raman spectra of the samples lyophilized from aqueous solutions at various pH values are measured in solid state, acetonitrile and cyclohexane. 相似文献
86.
The vertical ionization potentials of difluoramine are calculated by perturbation corrections to Koopmans' theorem. The calculation shows that difluoraimine has three overlapping bands between 15 and 16 eV. The calculated results compare well with the experimental values. The photoelectron spectrum of difluoramine is compared with that of OF2 and CH2F2. 相似文献
87.
The reactions of benzocyclic ketones and α-ketoacids as carbonyl components in the Biginelli reaction were investigated. These unusual Biginelli substrates furnished novel drug-like dihydropyrimidinone scaffolds suitable for further elaboration. 相似文献
88.
The reactions of α-trifluoromethylated α-arylacetates 1 with 3 equiv of hydrazine, methylhydrazine or benzylhydrazine in 1,4-dioxane at reflux for 24 h afforded the corresponding 5-fluoropyrazolin-3-one derivatives 3a-m in high yields. Similarly, treatment of 1 with 3 equiv of PhNLiNH2 in THF at −78 °C, followed by warming to room temperature, resulted in the formation of 3n-s in high yields. 相似文献
89.
Application of mono (6A-N-ethylenediamine-6A-deoxy) perphenylcarbamoylated β-cyclodextrin (β-CD) bonded stationary phase (CSP) in micro-high performance liquid chromatography (micro-HPLC) and pressurized capillary electrochromatography (p-CEC) was firstly presented. A series of racemic α-amidophosphonates were resolved in reversed- and normal-phase modes on this CSP. The investigated chromatographic parameters include retention factor (k′), separation factor (α) and resolution (Rs) of solutes. In addition, the structural variation of the solutes and the experimental factors affecting chiral separations have been examined, including the percentage of alcohol modifier, the linear velocity (u) of the mobile phase, electrical field strength, etc. Baseline separation was achieved for most of the entities. Hydrophobic interaction, steric effect and π-π interaction contribute to the possible mechanism. Comparative results indicate that higher Rs value up to 3.1 was found in micro-HPLC, higher efficiency up to 29,970 in p-CEC. 相似文献
90.