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报告内容摘要：
Thermal convection is ubiquitous in nature. It occurs in heat pipes in liquid-cooling computers where it provides high thermal conductance for heat emission; in aqueous suspensions of DNA molecules where it can en-hance the Polymerase Chain Reaction; in the Earth's mantle layer where it determines the motion of continental plates. In the _rst experimental project we presented a laboratory analogue study of the interaction between turbulent mantle convection and tectonic plates. We discovered that a freely moving boundary, which was deliberately introduced on top of a thermally convective uid, could modify the large- scale ow pattern in the uid interior and destabilized the coupled system,leading to spontaneous oscillations. As the moving boundary exceeded acritical size, the system turned into a weakly con_ned state, in which the moving boundary executed only small excursions in response to random bypassing thermal plumes. We introduced a phenomenological model and provided instability analysis of the system. Strong rotations suppress vertical heat transport in thermal convection. In 1969 H. T. Rossby observed that the heat transport _rst increased and then decreased when the rotating speed increased from zero. Ekman pump-ing is responsible for heat-transport enhancements under rotations. But recent experiments and numerical simulations showed hardly any enhanced heat ux in rotating thermal convection. In the second experimental project we reported that heat transport in rotating thermal convection was strongly dependent on the uid Prandtlnumber (Pr) and the Rayleigh number (Ra). The heat-transport enhance- ment was most prominent with relatively small Ra and large Pr (Ra_108, Pr_10). With high Ra and small Pr (Ra_ 1011, Pr_ 0:7) there was no enhanced heat transport at all. We suggested that the suppression of heat transport in these regimes was due to the breakdown of the Ekman pump-ing under larger thermal di_usion. These _ndings resolved the conicting results in previous researches. In high Rossby number regimes, with increasing rotation speed an abrupt transition from a turbulent state with nearly rotation-independent heat transport to another turbulent state with enhanced heat transport occurred at a critical Rossby number Roc that depended on the sample aspect ratio?. We attributed this turbulent bifurcation to the _nite size e_ect, and presented a Ginzburg-Landau-like model to interpret the experimental data that Roc was proportional to.