Showing papers by "Steven J. Plimpton published in 1999"
TL;DR: Using extensive molecular dynamics simulations of an equilibrium, glass-forming Lennard-Jones mixture, it is shown that spatial correlations exist among particles undergoing extremely large ("mobile") or extremely small ("immobile") displacements over a suitably chosen time interval.
Abstract: Using extensive molecular dynamics simulations of an equilibrium, glass-forming Lennard-Jones mixture, we characterize in detail the local atomic motions. We show that spatial correlations exist among particles undergoing extremely large (``mobile'') or extremely small (``immobile'') displacements over a suitably chosen time interval. The immobile particles form the cores of relatively compact clusters, while the mobile particles move cooperatively and form quasi-one-dimensional, stringlike clusters. The strength and length scale of the correlations between mobile particles are found to grow strongly with decreasing temperature, and the mean cluster size appears to diverge near the mode-coupling critical temperature. We show that these correlations in the particle displacements are related to equilibrium fluctuations in the local potential energy and local composition.
443 citations
TL;DR: NIMROD as discussed by the authors is a code development project designed to study long-wavelength, low-frequency, nonlinear phenomena in toroidal plasmas with realistic geometry and dynamics.
Abstract: NIMROD is a code development project designed to study long-wavelength, low-frequency, nonlinear phenomena in toroidal plasmas with realistic geometry and dynamics. The numerical challenges of solving the fluid equations for a fusion plasma are discussed and our discretization scheme is presented. Simulations of a resistive tearing mode show that time steps much greater than the Alfven time are possible without loss of accuracy. Validation tests of a resistive interchange mode in a shaped equilibrium, a ballooning mode and nonlinear activity in reversed-field pinches are described.
99 citations
TL;DR: In this article, the authors investigated the diffusion behavior of penetrants in simple polymer melts by molecular dynamics simulation and found that the diffusion coefficient varied more rapidly with the penetrant diameter and the velocity autocorrelation function developed a power law tail.
Abstract: The diffuse behavior of penetrants in simple polymer melts was investigated by molecular dynamics simulation. For the case where the polymer melt consisted of pearl-necklace chains, the diffusive behavior of the loose pearl penetrants was seen to be qualitatively different than would be expected in realistic models of polymer melts. In particular, there was little or no “non-Fickian” region; the variation of the diffusion coefficient with the penetrant diameter was what one would expect for diffusion through small molecular liquids; and, finally, the long time tail of the velocity autocorrelation displayed a “−3/2” power law form, also as in the small molecular liquid case. When the chains’ backbone motion was further constrained by the introduction of a bond angle potential, the qualitative nature of the penetrant diffusion became more “polymer-like.” A non-Fickian region developed; the diffusion coefficient varied more rapidly with penetrant diameter; and the velocity autocorrelation function developed a “−5/2” power law tail.
7 citations