We report on parametric amplification in dynamic radiation force produced by a bichromatic acoustic beam in a fluid. To explain this effect we develop a theory taking into account the nonlinearity of the fluid. The theory is validated through an experiment to measure the dynamic radiation force on an acrylic sphere. Results exhibit an amplification of 66 dB in water and 80 dB in alcohol as the difference of the frequencies is increased from 10 Hz to 240 kHz.

No abstract

The present paper addresses the effect of aperiodicity in one-dimensional oscillatory systems. We study the nature of collective excitations in harmonic chains in the presence of aperiodic and pseudorandom mass distributions. Using the transfer matrix method and exact diagonalization on finite chains, we compute the localization length and the participation number of eigenmodes within the band of allowed frequencies. Our numerical calculations indicate that, for aperiodic arrays of masses, a new phase of extended states appears in this model. For pseudorandom masses distribution, all eigenstates remain localized except the uniform mode ͑ =0͒. Solving numerically the Hamilton equations for momentum and displacement of the chain, we compute the spreading of an initially localized energy excitation. We show that, independent of the kind of initial excitation, an aperiodic structure of masses can induce ballistic transport of energy.

No abstract

No abstract