94 research outputs found
On the dependence of the Navier Stokes equations on the distribution of moleular velocities
In this work we introduce a completely general Chapman Enskog procedure in
which we divide the local distribution into an isotropic distribution with
anisotropic corrections. We obtain a recursion relation on all integrals of the
distribution function required in the derivation of the moment equations. We
obtain the hydrodynamic equations in terms only of the first few moments of the
isotropic part of an arbitrary local distribution function.
The incompressible limit of the equations is completely independent of the
form of the isotropic part of the distribution, whereas the energy equation in
the compressible case contains an additional contribution to the heat flux.
This additional term was also found by Boghosian and by Potiguar and Costa in
the derivation of the Navier Stokes equations for Tsallis thermostatistics, and
is the only additional term allowed by the Curie principle
A scaling theory of 3D spinodal turbulence
A new scaling theory for spinodal decomposition in the inertial hydrodynamic
regime is presented. The scaling involves three relevant length scales, the
domain size, the Taylor microscale and the Kolmogorov dissipation scale. This
allows for the presence of an inertial "energy cascade", familiar from theories
of turbulence, and improves on earlier scaling treatments based on a single
length: these, it is shown, cannot be reconciled with energy conservation. The
new theory reconciles the t^{2/3} scaling of the domain size, predicted by
simple scaling, with the physical expectation of a saturating Reynolds number
at late times.Comment: 5 pages, no figures, revised version submitted to Phys Rev E Rapp
Comm. Minor changes and clarification
Recommended from our members
Observation of off-Hugoniot shocked states with ultrafast time resolution
We apply ultrafast single shot interferometry to determine the pressure and density of argon shocked from up to 7.8 GPa static initial pressure in a diamond anvil cell. This method enables the observation of thermodynamic states distinct from those observed in either single shock or isothermal compression experiments, and the observation of ultrafast dynamics in shocked materials. We also present a straightforward method for interpreting ultrafast shock wave data which determines the index of refraction at the shock front, and the particle and shock velocities for shock waves in transparent materials. Based on these methods, we observe shocked thermodynamic states between the room temperature isotherm of argon and the shock adiabat of cryogenic argon at final shock pressures up to 28 GPa
Transport properties of dense fluid argon
We calculate using molecular dynamics simulations the transport properties of
realistically modeled fluid argon at pressures up to and
temperatures up to . In this context we provide a critique of some newer
theoretical predictions for the diffusion coefficients of liquids and a
discussion of the Enskog theory relevance under two different adaptations:
modified Enskog theory (MET) and effective diameter Enskog theory. We also
analyze a number of experimental data for the thermal conductivity of
monoatomic and small diatomic dense fluids.Comment: 8 pages, 6 figure
Recommended from our members
Isentropic Compression with a Rectangular Configuration for Tungstene and Tantalum, Computations and Comparison with Experiments
Isentropic compression experiments and numerical simulations on metals are performed at Z accelerator facility from Sandia National Laboratory and at Lawrence Livermore National Laboratory in order to study the isentrope, associated Hugoniot and phase changes of these metals [1]. 3D configurations have been calculated here to benchmark the new beta version of the electromagnetism package coupled with the dynamics in Ls-Dyna and compared with the ICE Z shots 1511 and 1555. The electromagnetism module is being developed in the general-purpose explicit and implicit finite element program LS-DYNA{reg_sign} in order to perform coupled mechanical/thermal/electromagnetism simulations. The Maxwell equations are solved using a Finite Element Method (FEM) for the solid conductors coupled with a Boundary Element Method (BEM) for the surrounding air (or vacuum). More details can be read in the reference [2], [3]
Electrical conductivity of lithium at megabar pressures
We report measurements of the electrical conductivity of a liquid alkali
metal - lithium - at pressures up to 1.8 Mbar and fourfold compression,
achieved through shock compression experiments. We find that the results are
consistent with a departure of the electronic properties of lithium from the
nearly free electron approximation at high pressures.Comment: RevTex, 4 pages, 4 figure
Susceptibility and Percolation in 2D Random Field Ising Magnets
The ground state structure of the two-dimensional random field Ising magnet
is studied using exact numerical calculations. First we show that the
ferromagnetism, which exists for small system sizes, vanishes with a large
excitation at a random field strength dependent length scale. This {\it
break-up length scale} scales exponentially with the squared random
field, . By adding an external field we then study the
susceptibility in the ground state. If , domains melt continuously and
the magnetization has a smooth behavior, independent of system size, and the
susceptibility decays as . We define a random field strength dependent
critical external field value , for the up and down spins to
form a percolation type of spanning cluster. The percolation transition is in
the standard short-range correlated percolation universality class. The mass of
the spanning cluster increases with decreasing and the critical
external field approaches zero for vanishing random field strength, implying
the critical field scaling (for Gaussian disorder) , where and .
Below the systems should percolate even when H=0. This implies that
even for H=0 above the domains can be fractal at low random fields, such
that the largest domain spans the system at low random field strength values
and its mass has the fractal dimension of standard percolation .
The structure of the spanning clusters is studied by defining {\it red
clusters}, in analogy to the ``red sites'' of ordinary site-percolation. The
size of red clusters defines an extra length scale, independent of .Comment: 17 pages, 28 figures, accepted for publication in Phys. Rev.
- …