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The adsorption and surface reactions of CH2I2 on the K-dosed Mo2C/Mo(1 0 0) have been studied by high resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy and thermal desorption spectroscopy. Potassium is an effective promoter for the rupture of C-I bond in the adsorbed CH2I2. A partial dissociation of this compound occurred even at 100 K and was completed at 190 K at monolayer K coverage. The dissociation was further promoted by the illumination of coadsorbed layer at 100 K. As revealed by HREELS and XPS measurements the primary products of the dissociation are CH2 and I. Methylene was converted to π-bonded ethylene characterized by Tp = 160 K, and di-σ-ethylene with Tp = 350 K. Other products of the surface reaction are hydrogen and methane. The coupling reaction of CH2 species was clearly facilitated by potassium. The effect of potassium was explained by the extended electron donation to adsorbed alkyl iodide in one hand, and by the direct interaction between potassium and I on the other hand. 相似文献
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We investigate the mechanisms of fatigue behavior in nanocrystalline metals at the atomic scale using empirical force laws and molecular level simulations. A combination of molecular statics and molecular dynamics was used to deal with the time scale limitations of molecular dynamics. We show that the main atomistic mechanism of fatigue crack propagation in these materials is the formation of nanovoids ahead of the main crack. The results obtained for crack advance as a function of stress intensity amplitude are consistent with experimental studies and a Paris law exponent of about 2. 相似文献
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In [1] a two-dimensional generalized Lotka-Volterra model was established. In this paper we analyze that model which (after scaling) contains five parameters. The generalized model includes explosive, conservative, and stable systems [23]. The condition for supercritical Hopf bifurcation is established. The model also shows zip bifurcation [14]. Some integrable cases are given together with the first integrals. The model is related to nonlinear chemical and biological systems, e.g. the oscillatory BZ-reaction. 相似文献
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M Farkas 《Journal of Mathematical Analysis and Applications》1984,102(1):175-188
The Lotka-Volterra model with carrying capacity at the prey and time delay in the equation concerning the predator is considered. The time delay is taken into consideration by an integral with the weight function a exp(?at). It is shown that under certain conditions imposed upon the parameters of the system a supercritical Hopf bifurcation takes place at a certain value a0, of a and the bifurcating closed paths are orbitally asymptotically stable for values of a below a0. 相似文献
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