排序方式: 共有13条查询结果,搜索用时 109 毫秒
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Synthèse et étude structurale de dérivés substitués en -2 du thiazolidine carboxylate d'éthyle-4 (R)
Abdesselam Hamri Marie-Hlne Pra Houda Fillion 《Journal of heterocyclic chemistry》1987,24(6):1629-1633
Pharmacological properties of thiazolidine derivatives are of great interest. For this purpose we prepared two series: 2-hydroxyalkyl-4-carbethoxythiazolidines and 2-carbalkoxyalkyl-4-carbethoxythiazolidines. Their syntheses involve a condensation reaction between L-carbethoxy-cystein and several α-hydroxyketones or β-ketoesters. Compounds 4 and 5 was obtained as an unequal mixture of diastereoisomers. Protons nmr spectra at 300 MHz in the presence of trifluoroacetic acid shows a modification of diastereoisomer percentages which indicate the existence of an equilibrium through an imminium ion intermediate. Therefore, the stereoselectivity observed reflects the relative stability of the different diastereoisomers. 相似文献
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W. Hamri O. O. Shyshkina T. M. Tarasiuk T. A. Volovnenko K. Mesbah S. Rhouati Y. M. Volovenko V. V. Medviediev O. V. Shishkin 《Journal of heterocyclic chemistry》2015,52(5):1373-1376
A one‐pot method for the synthesis of 3‐amino‐7‐nitro‐1,2‐dihydroisoquinoline‐4‐carbonitriles from 2‐chloro‐5‐nitrobenzylamines and malononitrile has been developed. 相似文献
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In this work, a new three-dimensional autonomous chaotic system has been introduced by modifying a hybrid optical system.
The single quadratic nonlinearity is replaced by a single cubic nonlinearity; the new system can display two 1-scroll chaotic
attractors simultaneously or one 2-scroll chaotic attractor. The bifurcation diagram is obtained and Lyapunov spectrum is
calculated for the proposed system. The results show that the new system exhibits rich complexity features such as stable,
periodic, and chaotic dynamics. 相似文献
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In this paper, a chaotic fractional-order modified hybrid optical system is presented. Some basic dynamical properties are further investigated by means of Poincaré mapping, parameter phase portraits, and the largest Lyapunov exponents. Fractional Hopf bifurcation conditions are proposed; it is found that Hopf bifurcation occurs on the proposed system when the fractional-order varies and passes a sequence of critical values. The chaotic motion is validated by the positive Lyapunov exponent. Finally, some numerical simulations are also carried out to illustrate our results. 相似文献
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Mohammed-Salah Abdelouahab Nasr-Eddine Hamri 《Mediterranean Journal of Mathematics》2016,13(2):557-572
Contrary to integer-order derivative, the fractional-order derivative of a non-constant periodic function is not a periodic function with the same period. As a consequence of this property, the time-invariant fractional-order systems do not have any non-constant periodic solution unless the lower terminal of the derivative is ±∞, which is not practical. This property limits the applicability of the fractional derivative and makes it unfavorable, for a wide range of periodic real phenomena. Therefore, enlarging the applicability of fractional systems to such periodic real phenomena is an important research topic. In this paper, we give a solution for the above problem by imposing a simple modification on the Grünwald–Letnikov definition of fractional derivative. This modification consists of fixing the memory length and varying the lower terminal of the derivative. It is shown that the new proposed definition of fractional derivative preserves the periodicity. 相似文献
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X-ray diffraction has shown that CrAs0.50Sb0.50 undergoes at the Néel temperature a crystallographic distortion (NiAs → MnP) accompanied by a discontinuous volume change. Neutron diffraction revealed in this compound a helimagnetic structure very similar to the ‘double spiral’ in CrAs discovered recently. The pressure dependence of the Néel temperature is estimated in the framework of the Bean Rodbell theory and compared with the CrAs value. 相似文献
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B. Briat M. T. Borowiec H. Bou Rjeily F. Ramaz A. Hamri H. Szymczak 《辐射效应与固体损伤》2013,168(6-12):989-993
Electron paramagnetic resonance is detected optically via the change of magnetic circular dichroism under microwaves at 35 v GHz. The technique is applied to Bi 12 GeO 20 samples co-doped with vanadium and a second transition metal (Cr, Mn, Co, Cu). The optical and magnetic properties of several paramagnetic defects (V Ge 4+ and Cr Ge 4+ ) are directly correlated. The basic photochromic processes occuring in samples doped with V, Mn, and Mn+V are explained. The V Ge 4+/5+ level is positioned roughly 2.2 v eV above the valence band. 相似文献
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Salha Hamri Jose Rodríguez Joan Basset Gérald Guillaumet M. Dolors Pujol 《Tetrahedron》2012,68(31):6269-6275
We report a direct iodination of indole and derivative compounds with iodine monochloride (ICl) in the presence of Celite®. This procedure has now been extended to the iodination of substituted indoles, azaindoles and pyrroles. The scope of this procedure is exemplified by the iodination of melatonin in 98% yield. 相似文献