Enhanced pulse propagation in nonlinear arrays of oscillators

The propagation of a pulse in a nonlinear array of oscillators is influence d by the nature of the array and by its coupling to a thermal environment. For example, in some arrays a pulse can be speeded up while in others a pul se can be slowed down by raising the temperature. We begin by showing that an energy pulse (one dimension) or energy front (two dimensions) travels mo re rapidly and remains more localized over greater distances in an isolated array (microcanonical) of hard springs than in a harmonic array or in a so ft-springed array. Increasing the pulse amplitude causes it to speed up in a hard chain, leaves the pulse speed unchanged in a harmonic system, and sl ows down the pulse in a soft chain. Connection of each site to a thermal en vironment (canonical) affects these results very differently in each type o f array. In a hard chain the dissipative forces slow down the pulse while r aising the temperature speeds it up. In a soft chain the opposite occurs: t he dissipative forces actually speed up the pulse, while raising the temper ature slows it down. In a harmonic chain neither dissipation nor temperatur e changes affect the pulse speed. These and other results are explained on the basis of the frequency vs energy relations in the various arrays. [S106 3-651X(99)11411-9].