No abstract

Quantum turbulence, easily generated in superfluid helium, consists of a disordered tangle of thin, discrete vortex lines of quantised circulation which move in a fluid without viscosity. In this report we show that, in very intense quantum turbulence, the vortex tangle contains small coherent vortical structures (bundles of quantised vortices) which arise from the fundamental Biot-Savart interaction between vortices, and which are similar to the intermittent, coherent structures ("worms") observed in ordinary viscous turbulence. Our result highlights the similarity between quantum turbulence and ordinary turbulence, and sheds new light into the origin of the "worms" in ordinary turbulence.

Some physical properties (structural and electronic) of Zn-based wurtzite structures have been theoretically studied by the density functional theory (DFT). Ab-initio calculations were done using the plane-wave pseudo-potential method within the Atomistix ToolKit (ATK) software package. Detailed investigations on the structural and electronic properties of the binary bulk compounds, ZnO and ZnSe, have been conducted and compared with the obtained studies. Using the modified Becke–Johnson potential has successfully improved the calculated bandgap. From the first-principles calculations for investigated compounds, it is obtained that the valence band maximum and the conduction band minimum, mainly originate from O (Se) [Formula: see text]- and Zn [Formula: see text]-states. The calculated values of electronic bandgaps of both the compounds are closer to the experimental results, and studied compounds are direct bandgap semiconductors with the transition along with [Formula: see text]–[Formula: see text] symmetry.