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71.
Chiraz Youssef Hamed Ben Ammar Mohamed Belhouchet Kassem Beydoun Ridha Ben Salem Henri Doucet Pierre H. Dixneuf 《Journal of heterocyclic chemistry》2011,48(5):1126-1131
2‐(Arylidene)cyanomethylbenzoxazoles have been prepared in water from benzoxazole‐2‐ylacetonitriles. Using multi‐component reactions, a variety of heterocycles containing benzoxazole and nitrile functionality has been prepared. J. Heterocyclic Chem., (2011). 相似文献
72.
3-Amino-3-thioxopropanamide (1) reacted with ethyl acetoacetate to form 6-hydroxy-4-methyl-2-thioxo-2,3-dihydropyridine-3-carboxamide (2), which reacted with α-haloketones 3 to produce 2,3-disubstituted-8-hydroxy-6-methyl-2H,5H-pyrido[3,2-f]-[1,4]thiazepin-5-ones 4a-c. Benzoylation of 4c led to the formation of the dibenzoate derivative 9. Compounds 4a-c could be prepared stepwise through the formation of S-alkylated derivatives 10a-c. Compounds 2, 4a-c, 9 and 10a-c were prepared using microwave as a source of heat, and gave better yields in shorter times than those achieved by traditional methods. Coupling of 4a-c with arenediazonium chlorides proceeded unusually to give the 6-hydroxy-4-methyl-2-(arylazo)thieno[2,3-b]pyridin-3(2H)-one ring contraction products 14. Structures of the newly synthesized compounds were proven by spectral and chemical methods. 相似文献
73.
This paper deals with pairs of binary relations defined on the same finite basis and which the 3-element restrictions are isomorphic and those of 5-element restrictions are isomorphic or anti-isomorphic. To each of these pairs, we associate an equivalence relation which yields a decomposition of these relations into classes that we will characterize. As application, we get the treshold of half-reconstruction for tournaments. 相似文献
74.
75.
Marquina's approximate Riemann solver for the compressible Euler equations for gas dynamics is generalized to an arbitrary equilibrium equation of state. Applications of this solver to some test problems in one and two space dimensions show the desired accuracy and robustness. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
76.
Youssef A. Fakhreddine Paul Zoller 《Journal of Polymer Science.Polymer Physics》1994,32(15):2445-2459
This article reports on an experimental investigation of the equation of state and the transition behavior of main-chain thermotropic liquid crystalline polymers over a wide temperature range, and at pressures to 200 MPa. The materials studied were a series of azomethine ether polymers. A varying number n (= 4, 7, 8, 9, 10 and 11) of methylene spacer units in the backbone provided systematic variation of the structure. Experimental techniques used included high-pressure dilatometry (PVT measurements) to 200 MPa, high-pressure differential thermal analysis, also to 200 MPa, and conventional (atmospheric-pressure) differential scanning calorimetry (DSC). The equation of state of the materials can be well represented by the Tait equation in distinct regions, separated by a glass transition, Tg(P), a first-order transition to a nematic state, Tk-n(P), and a first-order transition to an isotropic melt state Tc(P). The atmospheric pressure values of Tk-n and Tc decreased with increasing number of spacer units and showed a clear odd-even effect. Tg and Tk-n both increased with pressure. The pressure dependence of Tc could not be observed due to the onset of degradation in the same temperature region. On isobaric cooling at 3°C/min, the crystallization from the nematic state occurred a few tens of degrees below Tk-n. This supercooling was independent of pressure for some materials, while for others it increased with increasing pressure. The values of the enthalpy and entropy associated with the first-order transition into the nematic state were lower than those of typical isotropic polymers at their melting transitions. The transition enthalpy did not have any systematic variation with increasing number of spacer units. Values of the transition enthalpy calculated from the Ciapeyron equation did not always agree with the values measured by DSC. This may be due to the two-phase nature of the low-temperature state. At the transition to the isotropic state, the transition enthalpy at P = 0 decreased with n and showed an odd-even effect. © 1994 John Wiley & Sons, Inc. 相似文献
77.
The elastic differential cross-section forē-Na scattering in the presence of non-resonant laser field is studied for the exchange ofℓ=0, 1, 2 photons. The undressed contribution is evaluated within the framework of the eikonal Born series approximation and
the effect of exchange is taken into account via the Ochkur approximation. The sodium atom has been treated in the frozen
core approximation with special attention to the effect of the dressing of the target by the laser field. The ‘dressing’ of
the target leads to quite an increase in the cross-section over the ‘undressed’ value near the forward direction for the exchange
of one or two photons. 相似文献
78.
M. S. Antonious M. N. Ramsis A. O. Youssef 《Monatshefte für Chemie / Chemical Monthly》1996,127(1):15-27
Summary The kinetics of the crystallization of barium chromate have been studied conductometrically at 298 K for both spontaneous and seeded growth systems. The rate of growth follows a quadratic dependence upon the relative supersaturation which suggests a surface-controlled growth mechanism. This rate equation holds fairly well for the various supersaturation and solid/solution ratios used. The presence of seeds in the solution appears to accelerate the growth rate. Analysis of the calculated induction times in unseeded systems corroborates the surface-controlled growth mechanism. The effect of some additives on the kinetics of growth has also been studied. The retarding effect of these inhibitors is interpreted in terms of adsorption of inhibitor ions at the active crystal growth sites.Dedicated to the memory of ProfessorE. N. Rizkalla who passed away on November 29, 1993 相似文献
79.
Youssef Haouat 《Archiv der Mathematik》1988,51(6):515-519
Sans résumé 相似文献
80.
T. A. El-Khalafawy A. M. Youssef V. V. Demchenko V. G. Diatlov 《Physics letters. A》1972,40(5):409-411
It has been demonstrated that a small-scale drift instability occurs in a theta-pinch with a superimposed azimuthal magnetic field, subsequently resulting in turbulization of oscillations andheating of the plasma. The data obtained agree well with the available theoretical models. 相似文献