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The chemical products of air plasma generated by dielectric barrier discharge were investigated in this paper, which played a key role in its applications. The results showed that the high applied voltage and low flow rate contributed a transition from ozone to nitric oxide mode. In order to investigate the relationship between the physical characteristic and a chemical product, the real energy density based on the ICCD image and Lissajous figure, a plausible parameter, was proposed. It was found that when the energy density increased beyond a critical value (∼10 mJ·cm−2), the mode transition occurred, which illustrated that the high value of energy density was favorable for the generation of nitrogen oxides but not for the ozone generation. The N2O density increased and the O3 density decreased at the flow rate of 480 L/h with the increase in energy density. When the flow rate was fixed at 60 L/h, the NO density increased with the increase in energy density while other parameters changed slightly and irregularly. The time required for the development of products in a closed cavity was also studied. It showed that the NO gradually disappeared and O3 slightly decreased as the time goes on. In this paper, it was proved that the real energy density, correlating the physical and chemical characteristics, was an effective parameter to distinguish the mode transition of the chemical products.

Flexural wave in a double-walled carbon nanotube is studied. The scale effect of the carbon nanotube on the wave dispersion is investigated through the nonlocal elastic beam theories. The flexural wave dispersion predicted by the nonlocal elastic Timoshenko beam theory has a good agreement with that by molecular dynamics simulations in a wide frequency range up to the terahertz region. The results show that only the nonlocal elastic Timoshenko beam model can predict the small-scale effect on the dispersion of flexural wave in double-walled carbon nanotube when the wave number is large. Moreover, an estimation of the scale coefficient e0 for the nonlocal elastic double Timoshenko beam model is suggested by validations from the molecular dynamics simulations. The noncoaxial flexural vibration of the double-walled carbon nanotube can be observed from molecular dynamics simulations at high frequency range. The van der Waals interaction is found to have little effect on the noncoaxial flexural vibration of the carbon nanotube, and the nonlocal elastic Timoshenko beam theory is found to be inapplicable in modeling the noncoaxial wave propagation in carbon nanotubes.

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