A molecular-dynamics simulation is carried out for particles (tracers) interacting with a screened Coulomb potential in three dimensions. A phase transition is observed from a liquid to an fcc solid on reducing the temperature at a fixed density, consistent with previous studies. In the liquid phase, the variation of the rms displacement R "ofthe charged particles with time seems to depend on the density and the temperature. In the short-time regime, the e6'ective exponent k for the subdiffusive power-law behavior, i.e. , R"-t, decreases on increasing the density and lowering the temperature. A crossover from subdiffusive to a diC'usive behavior is observed for a wide density regime in the liquid phase. At high temperatures and large densities, a single power law does not seem to describe the variation of R" with t.
Energy from a narrow-band acoustic signal, interacting with a time-varying ocean surface, will be scattered in the spatial and frequency domains. This scattering can be modeled using range-independent normal-mode theory and a coupling scheme based on first-order perturbation theory. Simulations will be performed using a two-dimensional surface wave spectrum.
Energy from a narrow-band pulse, interacting with a time-varying ocean surface, will be spread into upper and lower sidebands. This can be modeled in a range-independent ocean environment, using normal modes and a coupling scheme based on first-order perturbation theory. The structure of the scattered signal from the two-dimensional Pierson–Moskowitz surface wave spectrum is presented. A normal-mode model with environmental inputs from a shallow sea has been used, and a comparison is made with measured data.
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