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991.
M. S. Sakr A. A. El-Shazly M. M. Mostafa H. A. El-Sayed A. A. Mohamed 《Czechoslovak Journal of Physics》1990,40(11):1261-1266
Apparent steady-state creep of Cd-2 wt. % Zn and Cd-17·4 wt. %Zn alloys has been studied under different constant stresses ranging from 6·4 MPa to 12·7 MPa, near the transformation temperature of 483 K. The strain rate of the steady-state creep for both compositions has shown two temperature regions of deformation, the low-temperature region (below 483 K) and the high-temperature region above this temperature. The stress exponent m' was found to change from 4·7 to 2 for Cd-2 wt. % Zn and from 3·1 to 2·4 for Cd-17·4 wt. % Zn alloys. The activation energies in the temperature region below the transformation temperature have been found to be 84 kJ/mole for Cd-2 wt. % Zn and 70 kJ/mole for Cd-17·4 wt. % Zn alloys characterizing the mechanism of volume self-diffusion in Cd. 相似文献
992.
Basset JM Copéret C Lefort L Maunders BM Maury O Le Roux E Saggio G Soignier S Soulivong D Sunley GJ Taoufik M Thivolle-Cazat J 《Journal of the American Chemical Society》2005,127(24):8604-8605
Alkane metathesis, a reaction catalyzed by the silica-supported tantalum hydride [(SiO)2Ta-H], 1, which transforms acyclic alkanes into their higher and lower homologues, was reported in 1997. New studies conducted in a continuous flow reactor in the case of propane indicate that, by varying the contact time, hydrogen and olefins are primary products. This crucial observation, as well as the known properties of tantalum alkyls to perform alpha-H or beta-H eliminations, supports the proposition of a new mechanism involving metallacyclobutane intermediates just like in olefin metathesis. The observed selectivities for linear and branched Cn+1 and Cn+2 products as well as the linear/branched ratio can be well-explained on the basis of the minimization of steric interactions between 1,2- or 1,3-substituents in the various tantallacyclobutane intermediates or during their formation. Hydrogen plays a specific role in the cleavage of metal alkyls to complete the catalytic cycle. 相似文献
993.
We have investigated the behavior of single-walled carbon nanotubes and nanospheres (C(60)) under high hydrostatic pressure using Raman spectroscopy over the pressure range 0.2-10 GPa using a diamond anvil cell. Different liquid mixtures were used as pressure transmission fluids (PTF). Comparing the pressure dependence of the Raman peak positions for the nanotubes and the nanospheres in different PTF leads to the observation of a number of new phenomena. The observed shift in Raman peak position of both radial and tangential modes as a function of applied pressure and their dependence on the PTF chemical composition can be rationalized in terms of adsorption of molecular species from the of PTF on to the surface of the carbon nanotubes and/or nanospheres. The peak shifts are fully reversible and take place at a comparatively modest pressure (2-3 GPa) that is far below pressures that might be required to collapse the nanoparticles. Surface adsorption of molecular species on the nanotube or nanospheres provides a far more plausible rational for the observed phenomena than ideas based on the notion of tube collapse that have been put forward in the recent literature. 相似文献
994.
Jacob LA Matos B Mostafa C Rodriguez J Tillotson JK 《Molecules (Basel, Switzerland)》2004,9(8):622-626
Benzyl selenocyanates can be made from the corresponding benzylic bromides or chlorides in 30-60 minutes using acetonitrile as a solvent. The products may be obtained pure in satisfactory yields without recourse to chromatography. 相似文献
995.
Ibrahim El-Sayed El-Kholy Hassan Mostafa Fuid-Alla Marcos Michael Mishrikey 《Journal of heterocyclic chemistry》1980,17(3):541-544
While the reaction of the cyclopropane ester 1 with hydrazine hydrate or phenylhydrazine led to the formation of diazabicycloheptenones, its reaction with several para-substituted phenyl-hydrazines gave the corresponding hydrazones. With hydroxylamine, either oxime or 1,2-oxazinone is formed. 相似文献
996.
Maji TK Mostafa G Chang HC Kitagawa S 《Chemical communications (Cambridge, England)》2005,(19):2436-2438
Two novel isomorphous porous frameworks of Ln(III), {[Ln2(imidc)2(H2O)3](H2O)}n, [Ln = Gd(III) (1) and Er(III) (2)] have been synthesized hydrothermally using multifunctional 4,5-imidazoledicarboxylic acid (imidc) as a connector; they have a zeolite-like network topology which can provide another form upon dehydration, and exhibit selective adsorption properties for H2O over N2, CO2 and MeOH. 相似文献
997.
This paper deals with the problem of heating a finite slab using laser radiation in relation to the parameters characterizing the laser pulse, namely: qmax(W/m2), the maximum laser power density, t0 the time interval required to reach qmax and td, the pulse time duration. The pulse shape q(t) is suggested in the form: q(t)=βqmax(t/td)(1-(t/td))exp-B(t-t0/td), where β and B are parameters. Fitting with published experimental pulse [Ready JF. Effects due to absorption of laser radiation. J Appl Phys 1965;36:462–68] is made. Fourier series expansion technique is considered to solve the problem. The critical time required to initiate melting tm is estimated for four metallic elements and five semiconductors, namely: Al, Cu, Ag, Au (aluminum, copper, silver, and gold), cadmium sulfide, germanium, silicon, alpha beryllium oxide, and silicon carbide. Five pulses with different characteristic parameters are considered.Computations revealed that the thermal response of the targets is highly affected by qmax and to, while the pulse time duration is less effective in determining the value of tm. Moreover, it is revealed that the relation between tm and the melting temperature for the same laser pulse is nonlinear for the considered targets under the indicated conditions. 相似文献
998.
999.
1000.
Ahmad Shaabani Heshmatollah Sepahvand Mostafa M. Amini Alireza Hashemzadeh Mahmoud Borjian Boroujeni Elham Badali 《Tetrahedron》2018,74(15):1832-1837
The tandem oxidative three-component synthesis of two types of the heterocycles such as furans and imidazopyridines, via isocyanides [1+4] cycloaddition reactions in the presence of MIL-101(Cr) under aerobic conditions are reported. When the 4-toluenesulfonylmethyl isocyanide was used, an unexpected [3+2] cycloaddition reaction of isocyanides with aldehydes accomplished and dihydrophenyloxazoles and phenyloxazoles produced. These syntheses were successfully carried out using a wide scope of the substrates. 相似文献