Centrifugal-Force-Induced Flow Bifurcations in Turbulent Thermal Convection.

An important and unresolved issue in rotating thermal turbulence is when the flow starts to feel the centrifugal effect. This onset problem is studied here by a novel experiment in which the centrifugal force can be varied over a wide range at fixed Rossby numbers by offsetting the apparatus from the rotation axis. Our experiment clearly shows that the centrifugal force starts to separate the hot and cold fluids at the onset Froude number 0.04. Additionally, this flow bifurcation leads to an unexpected heat transport enhancement and the existence of an optimal state. Based on the dynamical balance and characteristics of local flow structures, both the onset and optimal states are quantitatively explained.

A Cu(2+) ion-F center complex view on the photoluminescence quenching and correlating ferrimagnetism in (Cu2(+)/Cu1(2+))(0.044)Zn(0.956)O electrospun nanobelts.

Unlike to the most previous reports, mixed-cation Cu(+)/Cu(2+) doping-induced novel nanoscale phenomena, including photoluminescence quenching and a correlating ferrimagnetism with Néel temperature ≈ 14 K, were found in the as-calcined (Cu2(+)/Cu1(2+))0.044Zn0.956O electrospun nanobelts (NBs). There is also high strain (up to 1.98%) and shrunk lattice distortion (ΔV/V0 ∼ 0.127%) in the (Cu2(+)/Cu1(2+))0.044Zn0.956O NBs, leading to broken lattice symmetry in conjunction with nonstoichiometry (i.e., oxygen vacancies or accurate F centers), which could be possible origins of ferrimagnetism in the Cu-doped ZnO NBs. Electron paramagnetic resonance spectra reveal that there are giant and anisotropic g factors, suggesting that there is strong anisotropic spin-orbit interaction between the Cu(2+) ion and F center (i.e., forming Cu(2+)-F(+) complexes) in the (Cu2(+)/Cu1(2+))0.044Zn0.956O NBs. The above correlation enables the potential application of tuning of the optical and ferrimagnetic properties through strain and F-center engineering.