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91.
Coelho AC Almeida Paz FA Klinowski J Pillinger M Gonçalves IS 《Molecules (Basel, Switzerland)》2006,11(12):940-952
We report the one-step syntheses in good yields of the complexes cis-[M(CO)4(pzpy)] {M = Mo, W; pzpy = ethyl[3-(2-pyridyl)-1-pyrazolyl]acetate} directly from the corresponding M(CO)6 starting materials by using microwave-assisted heating and reaction times of either 30 s (M = Mo) or 15 min (M = W). The structure of the molybdenum tetracarbonyl complex was determined by single crystal X-ray diffraction. The compound is monomeric and the molybdenum atom has a highly distorted octahedral geometry. The close packing of the individual cis-[Mo(CO)4(pzpy)] species is essentially driven by the need to fill the space effectively, closely mediated by weak C-H-O and pi-pi interactions. 相似文献
92.
In this paper we show how, based on a decomposition of the likelihood ratio test for sphericity into two independent tests and a suitably developed decomposition of the characteristic function of the logarithm of the likelihood ratio test statistic to test independence in a set of variates, we may obtain extremely well-fitting near-exact distributions for both test statistics. Since both test statistics have the distribution of the product of independent Beta random variables, it is possible to obtain near-exact distributions for both statistics in the form of Generalized Near-Integer Gamma distributions or mixtures of these distributions. For the independence test statistic, numerical studies and comparisons with asymptotic distributions proposed by other authors show the extremely high accuracy of the near-exact distributions developed as approximations to the exact distribution. Concerning the sphericity test statistic, comparisons with formerly developed near-exact distributions show the advantages of these new near-exact distributions. 相似文献
93.
94.
Filipe M. Pedro 《Tetrahedron letters》2005,46(45):7777-7779
Methyltrioxorhenium (MTO) catalyses the olefination of ketones with ethyl diazoacetate in the presence of triphenylphosphane. Unactivated ketones require the addition of 0.5 equiv of benzoic acid to achieve good yields, while trifluoromethyl ketones require no co-catalyst. The optimised system allows the olefination of aromatic, aliphatic, unsaturated, cyclic and trifluoromethyl ketones. 相似文献
95.
Tiago de Oliveira F Bominaar EL Hirst J Fee JA Münck E 《Journal of the American Chemical Society》2004,126(17):5338-5339
[2Fe-2S] clusters found in the xanthine oxidase family of proteins exhibit an S = 1/2 EPR feature, called signal II, for which one g-value is significantly above g = 2.0. The g-values of signal II cannot be explained with the standard spin coupling model that has been so successful in describing the g = 1.94 signals of [2Fe-2S] ferredoxins. We have studied the EPR spectra of the Rieske protein from Thermus thermophilus at pH 14 and observed a signal II-type EPR spectrum, with g-values at 1.81, 1.94, and 2.14. It is shown that the g-values of signal II can be explained by including an antisymmetric exchange term, d.S1xS2, in the spin Hamiltonian. The presence of this term is sensed by EPR if the isotropic exchange coupling constant J is sufficiently small. For the Rieske protein we determined J = 43 cm-1 which is at least 4 times smaller than the J values reported for [2Fe-2S] clusters that yield standard g = 1.94 signals. 相似文献
96.
Rodrigues Filipe Agra Agostinho Hvattum Lars Magnus Requejo Cristina 《Journal of Heuristics》2022,28(3):329-350
Journal of Heuristics - Local search algorithms are frequently used to handle complex optimization problems involving binary decision variables. One way of implementing a local search procedure is... 相似文献
97.
J. C. Machado G. Goulart Silva L. S. Soares 《Journal of Polymer Science.Polymer Physics》2000,38(8):1045-1052
Positron annihilation lifetime spectroscopy (PALS) and differential scanning calorimetry (DSC) measurements were performed in atactic poly(methylmethacrylate) and low molecular weight poly(ethylene oxide) (PEO) polymer blends, prepared by codissolution in acetonitrile, covering the full range of composition. Results from the two techniques indicate that a “window of miscibility” is attained at around 20–30 wt % of the semicrystalline PEO. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1045–1052, 2000 相似文献
98.
99.
A. T. Goulart M. F. de Jesus Filho J. D. Fabris J. M. D. Coey 《Hyperfine Interactions》1994,83(1):451-455
Mixtures of synthetic maghemite and hematite have been studied by Mössbauer spectroscopy at room temperature with an applied magnetic field of 0.2 T. The results show that the relative area of each subspectrum reproduces very satisfactorily the weighted quantities, whereas the agreement is poor in absence of the external field, particularly for higher fractions of hematite. 相似文献
100.