Comments on the low frequency radiation impedance of a duct exhausting a hot gas.

The influence of convection and temperature on the radiation impedance of an open duct termination exhausting a hot gas is commonly described by a complex theory. A simplified analytical expression is proposed for low frequencies. Both models assume a free jet with uniform velocity bounded by infinitely thin shear layers.

Control of mixing via entropy tracking.

We study mixing of isothermal fluids by controlling the global hydrodynamic entropy . In particular, based on the statistical coupling between the evolution of and the global viscous dissipation <ϵ> , we analyze stirring protocols such that ∼t(α)⇔<ϵ>∼t(α-1), with 0<α≤1. For a model array of vortices [Fukuta and Murakami, Phys.