5,739 research outputs found
Volume-averaged macroscopic equation for fluid flow in moving porous media
Darcy's law and the Brinkman equation are two main models used for creeping
fluid flows inside moving permeable particles. For these two models, the time
derivative and the nonlinear convective terms of fluid velocity are neglected
in the momentum equation. In this paper, a new momentum equation including
these two terms are rigorously derived from the pore-scale microscopic
equations by the volume-averaging method, which can reduces to Darcy's law and
the Brinkman equation under creeping flow conditions. Using the lattice
Boltzmann equation method, the macroscopic equations are solved for the problem
of a porous circular cylinder moving along the centerline of a channel.
Galilean invariance of the equations are investigated both with the intrinsic
phase averaged velocity and the phase averaged velocity. The results
demonstrate that the commonly used phase averaged velocity cannot serve as the
superficial velocity, while the intrinsic phase averaged velocity should be
chosen for porous particulate systems
Symmetry restoration and quantumness reestablishment
A realistic quantum many-body system, characterized by a generic microscopic
Hamiltonian, is accessible only through approximation methods. The mean field
theories, as the simplest practices of approximation methods, commonly serve as
a powerful tool, but unfortunately often violate the symmetry of the
Hamiltonian. The conventional BCS theory, as an excellent mean field approach,
violates the particle number conservation and completely erases quantumness
characterized by concurrence and quantum discord between different modes. We
restore the symmetry by using the projected BCS theory and the exact numerical
solution and find that the lost quantumness is synchronously reestablished. We
show that while entanglement remains unchanged with the particle numbers,
quantum discord behaves as an extensive quantity with respect to the system
size. Surprisingly, discord is hardly dependent on the interaction strengths.
The new feature of discord offers promising applications in modern quantum
technologies.Comment: 17 pages and 3 figure
Glueball Masses from Hamiltonian Lattice QCD
We calculate the masses of the , and glueballs from
QCD in 3+1 dimensions using an eigenvalue equation method for Hamiltonian
lattice QCD developed and described elsewhere by the authors. The mass ratios
become approximately constants in the coupling region ,
from which we estimate and
.Comment: 12 pages, Latex, figures to be sent upon reques
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