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  • 1990-1994  (3)
  • 1991  (3)
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  • 1990-1994  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Nonequilibrium molecular dynamics calculation of self-diffusion in a non-Newtonian fluid subject to a Couette strain field (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2149-2158 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics simulations have been performed on a simple fluid in the non-Newtonian regime in order to study the nature of diffusion in the presence of shear stress. The nonequilibrium molecular dynamics (NEMD) sllod algorithm is used to generate a homogeneous boundary driven Couette flow. The elements of the tensor of diffusion coefficients have been evaluated by three different routes: through Einstein relations with the corresponding elements of the tensor of molecule displacements, through Green–Kubo expressions involving tensor of momentum autocorrelation functions and cross-correlation functions, and by utilizing an NEMD color field method. All three routes to the tensor of diffusion coefficients are shown to yield consistent results. A simple spherically symmetric Lennard-Jones fluid at its triple point was used in the simulation study. We find that in a Couette strain field of sufficiently large strain rate, diffusion in all directions is enhanced substantially. We propose and verify a new asymptotic relationship between the diagonal elements of the tensor of diffusion coefficients and the strain rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459886
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Simulation of supercritical water and of supercritical aqueous solutions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5606-5621 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics (MD) calculations have been performed to determine equilibrium structure and properties of systems modeling supercritical (SC) water and SC aqueous solutions at two states near the critical point using the simple point charge (SPC) potential model of Berendsen et al. for water. Both thermodynamic and dielectric properties from the simulations for pure water are accurate in comparison with experimental results even though the SPC model parameters were fitted to properties of ambient water. Details of the near-critical clustering in SC water have been predicted which have not been measured to date. MD studies have also been undertaken of systems that model sodium and chloride ions and neutral argon in SC water at the same states. The first solvation shell in SC water is observed to be similar to that in ambient water, and long-range solvation structures in SC water are similar to those observed for simple SC solvents. An excess of water molecules is observed clustering around ionic solutes which behave attractively and a deficit is observed around neutral atomic solutes which behave repulsively. These results should be helpful in developing a qualitative understanding of important processes that occur in SC water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460497
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The contribution of internal degrees of freedom to the non-Newtonian rheology of model polymer fluids (1991)
    Springer
    Rheologica acta 30 (1991), S. 33-43 
    Details
    ISSN: 1435-1528
    Keywords: non-Newtonian rheoloy ; kinetic theory ; FENE dumbbells ; non-equilibrium ; molecular dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract We report non-equilibrium molecular dynamics simulations of rigid and non-rigid dumbbell fluids to determine the contribution of internal degrees of freedom to strain-rate-dependent shear viscosity. The model adopted for non-rigid molecules is a modification of the finitely extensible nonlinear elastic (FENE) dumbbell commonly used in kinetic theories of polymer solutions. We consider model polymer melts — that is, fluids composed of rigid dumbbells and of FENE dumbbells. We report the steady-state stress tensor and the transient stress response to an applied Couerte strain field for several strain rates. We find that the rheological properties of the rigid and FENE dumbbells are qualitatively and quantitatively similar. (The only exception to this is the zero strain rate shear viscosity.) Except at high strain rates, the average conformation of the FENE dumbbells in a Couette strain field is found to be very similar to that of FENE dumbbells in the absence of strain. The theological properties of the two dumbbell fluids are compared to those of a corresponding fluid of spheres which is shown to be the most non-Newtonian of the three fluids considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366792
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    Paper (German National Licenses)
    Fulltext
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