212 research outputs found
A reduced model for shock and detonation waves. II. The reactive case
We present a mesoscopic model for reactive shock waves, which extends a
previous model proposed in [G. Stoltz, Europhys. Lett. 76 (2006), 849]. A
complex molecule (or a group of molecules) is replaced by a single
mesoparticle, evolving according to some Dissipative Particle Dynamics.
Chemical reactions can be handled in a mean way by considering an additional
variable per particle describing a rate of reaction. The evolution of this rate
is governed by the kinetics of a reversible exothermic reaction. Numerical
results give profiles in qualitative agreement with all-atom studies
Large-scale molecular dynamics simulations of shock induced plasticity in tantalum single crystals
We report on large-scale non-equilibrium molecular dynamics (NEMD) simulations of shock wave compression in Ta single crystals. The atomic interactions are modeled via a recently developed and optimized embedded-atom method (EAM) potential for Ta, which reproduces the equation of state up to 200 GPa. We examined the elastic-plastic transition and shock wave structure for wave propagation along the low index directions: (100), (110) and (111). Shock waves along (100) and (111) exhibit an elastic precursor followed by a plastic wave for particle velocities below 1.1 km/s for (100) and 1.4 km/s for (111). The nature of the plastic deformation along (110) is dominated by twinning for pressures above 41 GPa
Shock waves in one-dimensional Heisenberg ferromagnets
We use SU(2) coherent state path integral formulation with the stationary
phase approximation to investigate, both analytically and numerically, the
existence of shock waves in the one- dimensional Heisenberg ferromagnets with
anisotropic exchange interaction. As a result we show the existence of shock
waves of two types,"bright" and "dark", which can be interpreted as moving
magnetic domains.Comment: 10 pages, with 3 ps figure
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Sliding friction in compressed metals at high velocities
The properties of sliding metal interfaces under dynamic loading conditions are poorly known. For regimes of sliding speeds of order 0.1 the transverse sound speed and pressures of order shock pressures in metals, the following are essentially open questions from both a theoretical and experimental perspective: the velocity dependence of the tangential force, the nature of surface and subsurface micro structure and dislocation structure and evolution. Experimentally, there has been some recent progress in pressure-shear geometries by Prakash and Clifton for elastic materials. Theoretically, Sokoloff has treated a simplified model for which an inverse velocity dependence for g, the coefficient of sliding friction, has been predicted. In lieu of experimental work and as an incentive to perform relevant experiments it is of interest to perform numerical experiments. Of particular relevance are molecular dynamics (MD) experiments for materials with well characterized density dependent interatomic interaction potentials. For ductile metals (e.g., copper, nickel, aluminum), such potentials exist and are capable of reproducing equations of state and defect properties have shown. We shall present here the results of a series of atomistic simulations for copper-copper interfaces in a two dimensional geometry, focusing mainly on the density and velocity dependence of the coefficient of friction
On dissipationless shock waves in a discrete nonlinear Schr\"odinger equation
It is shown that the generalized discrete nonlinear Schr\"odinger equation
can be reduced in a small amplitude approximation to the KdV, mKdV, KdV(2) or
the fifth-order KdV equations, depending on values of the parameters. In
dispersionless limit these equations lead to wave breaking phenomenon for
general enough initial conditions, and, after taking into account small
dispersion effects, result in formation of dissipationless shock waves. The
Whitham theory of modulations of nonlinear waves is used for analytical
description of such waves.Comment: 15 pages, 9 figure
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Molecular dynamics simulations of dipolar dusty plasmas
The authors use molecular dynamics (MD) simulation methods to investigate dusty plasma crystal structure in an external potential, with the grains subject to both a spherically symmetric Debye-Hueckel potential and a cylindrically symmetric dipole interaction. The dipole contribution models the experimentally important effects of ion flow or intrinsic grain polarization. They find that the addition of a small dipole term changes the crystal structure from bct to one in which the grains are aligned vertically, consistent with experiments as well as recent theoretical calculations
The noise properties of stochastic processes and entropy production
Based on a Fokker-Planck description of external Ornstein-Uhlenbeck noise and
cross-correlated noise processes driving a dynamical system we examine the
interplay of the properties of noise processes and the dissipative
characteristic of the dynamical system in the steady state entropy production
and flux. Our analysis is illustrated with appropriate examples.Comment: RevTex, 1 figure, To appear in Phys. Rev.
Numerical Evidence for Divergent Burnett Coefficients
In previous papers [Phys. Rev. A {\bf 41}, 4501 (1990), Phys. Rev. E {\bf
18}, 3178 (1993)], simple equilibrium expressions were obtained for nonlinear
Burnett coefficients. A preliminary calculation of a 32 particle Lennard-Jones
fluid was presented in the previous paper. Now, sufficient resources have
become available to address the question of whether nonlinear Burnett
coefficients are finite for soft spheres. The hard sphere case is known to have
infinite nonlinear Burnett coefficients (ie a nonanalytic constitutive
relation) from mode coupling theory. This paper reports a molecular dynamics
caclulation of the third order nonlinear Burnett coefficient of a Lennard-Jones
fluid undergoing colour flow, which indicates that this term is diverges in the
thermodynamic limit.Comment: 12 pages, 9 figure
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