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21.
22.
The methoxycarbonylation of styrene has been studied using Pd(OAc)2/L/acid catalytic systems with L being chiral ferrocene- and biphosphole-based ligands. Good activities are obtained in mild conditions. Chemoselectivities and regioselectivities (up to 98% in favour of the branched isomer) are excellent but enantioselectivities remain moderate (ee up to 17%). 相似文献
23.
In this paper we study a four-dimensional linear center. Based on the averaging theory, we investigate the existence of limit cycles of the system. 相似文献
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26.
F. M. Diab 《Ukrainian Mathematical Journal》1997,49(4):569-575
We introduce and investigate some new differential properties of functions by using geometrical properties of directional
monogeneity sets.1
University of Cairo, Giza, Egypt. Published in Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 4, pp. 517–522, April, 1997. 相似文献
27.
Salah-Eddine Chorfi Ghita El Guermai Lahcen Maniar Walid Zouhair 《Mathematical Methods in the Applied Sciences》2023,46(1):911-929
This paper studies an inverse hyperbolic problem for the wave equation with dynamic boundary conditions. It consists of determining some forcing terms from the final overdetermination of the displacement. First, the Fréchet differentiability of the Tikhonov functional is studied, and a gradient formula is obtained via the solution of an associated adjoint problem. Then, the Lipschitz continuity of the gradient is proved. Furthermore, the existence and the uniqueness for the minimization problem are discussed. Finally, some numerical experiments for the reconstruction of an internal wave force are implemented via a conjugate gradient algorithm. 相似文献
28.
Mohamed M. El-Galy Farage A. Issa Osman A. Desouky Hanan M. Diab Mahmoud R. Khattab 《Journal of Radioanalytical and Nuclear Chemistry》2011,288(3):805-811
The present study aims to use the ??-spectrometry, at NMA. A radiochemical technique [1, 2] for analysis of U-isotopes was carried out for some granite samples from Gabal Gattar and El Missikat localities and also for some reference soil samples of IAEA. Several steps of sample preparation, radiochemical separation, and source preparation were performed before analysis. The concerned sample was leached by HNO3, HF and H2O2 acids after ashing. The ashed sample was spiked with uranium tracer (232U) for chemical yield and activity calculation. Then uranium was extracted from the matrix elements with trioctylphosphine oxide (TOPO) and stripped with 1 M NH4F/0.1 M HCl solution. The uranium fraction was purified by co-precipitation with LaF3 to ensure complete removal of thorium and traces of resolution degrading elements. This was followed by a final clean-up step using an anion exchange. The pure uranium fraction was electrodeposited on a stainless steel disc from HCl/oxalate solution. The obtained results from the soil reference samples indicate general similarities between the techniques of ??-spectrometers of NMA, EAEA and IAEA for analysis of U-isotopes. The U-isotopes in the granite samples of high radioactivity levels need more attempts after dilution process to be in the limit detection of ??-spectrometry. 相似文献
29.
1,4 and 1,5-diols heated with 0.3 equivalent of HMPA undergo cyclodehydration leading to tetrahydrofurans and tetrahydropyrans. 相似文献
30.
P. Mison R. Chaabouni Y. Diab R. Martino A. Lopez A. Lattes F. W. Wehrli T. Wirthlin 《Magnetic resonance in chemistry : MRC》1976,8(2):79-89
13C chemical shifts for twenty-nine alkyl and phenyl substituted N-unsubstituted aziridines have been measured. Additivity parameters for methyl, phenyl and aziridyl carbons have been derived with the aim of testing the consistency of the assignments made on the basis of chemical shift considerations and off-resonance decoupling information. The observed chemical shifts are discussed in terms of steric and pseudoconjugation effects. 相似文献