108 research outputs found
Stochastic Hard-Sphere Dynamics for Hydrodynamics of Non-Ideal Fluids
A novel stochastic fluid model is proposed with non-ideal structure factor
consistent with compressibility, and adjustable transport coefficients. This
Stochastic Hard Sphere Dynamics (SHSD) algorithm is a modification of the
Direct Simulation Monte Carlo (DSMC) algorithm and has several computational
advantages over event-driven hard-sphere molecular dynamics. Surprisingly, SHSD
results in an equation of state and pair correlation function identical to that
of a deterministic Hamiltonian system of penetrable spheres interacting with
linear core pair potentials. The fluctuating hydrodynamic behavior of the SHSD
fluid is verified for the Brownian motion of a nano-particle suspended in a
compressible solvent.Comment: This work performed under the auspices of the U.S. Department of
Energy by Lawrence Livermore National Laboratory under Contract
DE-AC52-07NA27344 (LLNL-JRNL-401745). To appear in Phys. Rev. Lett. 200
Dynamic scaling for the growth of non-equilibrium fluctuations during thermophoretic diffusion in microgravity
Diffusion processes are widespread in biological and chemical systems, where
they play a fundamental role in the exchange of substances at the cellular
level and in determining the rate of chemical reactions. Recently, the
classical picture that portrays diffusion as random uncorrelated motion of
molecules has been revised, when it was shown that giant non-equilibrium
fluctuations develop during diffusion processes. Under microgravity conditions
and at steady-state, non-equilibrium fluctuations exhibit scale invariance and
their size is only limited by the boundaries of the system. In this work, we
investigate the onset of non-equilibrium concentration fluctuations induced by
thermophoretic diffusion in microgravity, a regime not accessible to analytical
calculations but of great relevance for the understanding of several natural
and technological processes. A combination of state of the art simulations and
experiments allows us to attain a fully quantitative description of the
development of fluctuations during transient diffusion in microgravity. Both
experiments and simulations show that during the onset the fluctuations exhibit
scale invariance at large wave vectors. In a broader range of wave vectors
simulations predict a spinodal-like growth of fluctuations, where the amplitude
and length-scale of the dominant mode are determined by the thickness of the
diffuse layer.Comment: To appear in Scientific Report
Do Binary Hard Disks Exhibit an Ideal Glass Transition?
We demonstrate that there is no ideal glass transition in a binary hard-disk
mixture by explicitly constructing an exponential number of jammed packings
with densities spanning the spectrum from the accepted ``amorphous'' glassy
state to the phase-separated crystal. Thus the configurational entropy cannot
be zero for an ideal amorphous glass, presumed distinct from the crystal in
numerous theoretical and numerical estimates in the literature. This objection
parallels our previous critique of the idea that there is a most-dense random
(close) packing for hard spheres [Torquato et al, Phys. Rev. Lett., 84, 2064
(2000)].Comment: Submitted for publicatio
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