Simulation study on kinetic temperatures of vibrated binary granular mixtures.

We study the unequal kinetic temperatures in two-dimensional binary granular mixtures heated by vertical vibrations under gravity by molecular dynamics simulations. By introducing several variable parameters describing particle and composition properties of mixtures, the coexistence of two different kinetic temperatures for the two components is exhibited. In dilute situations, our numerical results confirm the overall experimental measurements by Feitosa and Menon recently [Phys. Rev. Lett. 88, 198301 (2002)]. For example, the temperature ratio along the vertical direction is constant in the bulk of a system, and is insensitive to external driving or relative concentration of the two components, but mainly influenced by their masses. However, outside of the dilute situations, especially as the number density becomes high enough where the spatial and momentum correlations become salient, the ratio profiles show some different characteristics. Generally, the plateau shape along the vertical direction is broken, and instead, a saddlelike shape appears. Furthermore, the physical implications are discussed.