A discrete nonlinear model with substrate feedback

We consider a prototypical model in which a nonlinear field (continuum or discrete) evolves on a flexible substrate which feeds back to the evolution of the main field. We identify the underlying physics and potential applications of such a model and examine its simplest one-dimensional Hamiltonian form, which turns out to be a modified Frenkel-Kontorova model coupled to an extra linear equation. We find static kink solutions and study their stability, and then examine moving kinks (the continuum limit of the model is studied too). We observe how the substrate effectively renormalizes properties of the kinks. In particular, a nontrivial finding is that branches of stable and unstable kink solutions may be extended beyond a critical point at which an effective intersite coupling vanishes; passing this critical point does not destabilize the kink. Kink-antikink collisions are also studied, demonstrating alternation between merger and transmission cases.Comment: a revtex text file and 6 ps files with figures. Physical Review E, in pres

Propagation of sound from aircraft ground operations

Atmospheric absorption effects on sound propagation losses during aircraft ground operation

The propagation of sound from airport ground operations

Noise measurements of sound propagation related to jet aircraft takeoff

Discrete Breathers in a Nonlinear Polarizability Model of Ferroelectrics

We present a family of discrete breathers, which exists in a nonlinear polarizability model of ferroelectric materials. The core-shell model is set up in its non-dimensionalized Hamiltonian form and its linear spectrum is examined. Subsequently, seeking localized solutions in the gap of the linear spectrum, we establish that numerically exact and potentially stable discrete breathers exist for a wide range of frequencies therein. In addition, we present nonlinear normal mode, extended spatial profile solutions from which the breathers bifurcate, as well as other associated phenomena such as the formation of phantom breathers within the model. The full bifurcation picture of the emergence and disappearance of the breathers is complemented by direct numerical simulations of their dynamical instability, when the latter arises.Comment: 9 pages, 7 figures, 1 tabl

Combined pyrolysis and radiochemical gas chromatography for studying the thermal degradation of polymers

Pyrolysis gas chromatography and radioactive tracer techniques have been used independently to study the thermal degradation of polymers. In these laboratories the two techniques have been combined to elucidate some of the mechanisms of the thermal degradation of epoxy resins and polyimides. This paper describes the apparatus developed for this work