Temperature fields in two-dimensional (2D) Rayleigh-Bénard (RB) convection with no-slip and free-slip walls were simulated with parallel direct method of direct numerical simulation (PDM-DNS) at different Rayleigh numbers (Ra) and aspect ratio numbers (Γ). Different from no-slip boundary thermal convection with random plume, free-slip boundary thermal convection eventually forms a large-scale circulation without turbulent features and temperature distributes only on four walls. Temperature distribution characteristics of time-average field near floor changes gradually for no-slip boundary but overshoot occurs for free-slip boundary. Dependences of Nusselt numbers (Nu) with Ra at Γ=1 have same scale index Nu~Ra^0.3. Free-slip boundary thermal convection enhances heat transfer. Changes of Nu with Γ are obvious in free-slip boundary thermal convection. They are in two stages. At Γ=0.5, Nu_max≈250, it is five times of Nu in no-slip boundary thermal convection.

For a magnetic tunneling junction with ferromagnetic metal/magnetic potential barrier layer/ferromagnetic metal structure, tunneling conductance, spin polarization and tunneling magneto resistance rate under zero bias voltage are calculated in a quasi-free electron model. The impact of potential barrier, molecular field strength and molecular field orientation, etc. on tunneling of electrons is analyzed. It exhibits useful instructions for the design of spin electronic devices.