Beat wave interferometry for measuring relative motion.

A new approach to detecting relative motion is proposed based on measuring the beat frequency. A formula is derived for the beat frequency as a function of the speed of translation. A principal sketch of an experimental setup implementing the new idea is proposed, and the effects of possible small differences in the frequencies and phases of the sources are discussed.

Heat conduction paradox involving second-sound propagation in moving media.

In this Letter, we revisit the Maxwell-Cattaneo law of finite-speed heat conduction. We point out that the usual form of this law, which involves a partial time derivative, leads to a paradoxical result if the body is in motion. We then show that by using the material derivative of the thermal flux, in lieu of the local one, the paradox is completely resolved. Specifically, that using the material derivative yields a constitutive relation that is Galilean invariant. Finally, we show that under this invariant reformulation, the system of governing equations, while still hyperbolic, cannot be reduced to a single transport equation in the multidimensional case.