37 research outputs found
Towards direct simulations of counterflow flames with consistent differential-algebraic boundary conditions
A new approach for the formulation of boundary conditions for the counterflow configuration is presented. Upon discretization of the steady-state Navier-Stokes equations at the inflow boundaries, numerically algebraic equations are imposed as boundary conditions, while upon discretization of the unsteady Navier-Stokes equations at the outflow, differential boundaries result. It is demonstrated that the resulting numerical differential-algebraic boundary conditions are suitable to account for the multi-directional character of the flow at the boundaries of the counterflow configuration
Interplay of shear and bulk viscosity in generating flow in heavy-ion collisions
We perform viscous hydrodynamic calculations in 2+1 dimensions to investigate
the influence of bulk viscosity on the viscous suppression of elliptic flow in
non-central heavy-ion collisions at RHIC energies. Bulk and shear viscous
effects on the evolution of radial and elliptic flow are studied with different
model assumptions for the transport coefficients. We find that the temperature
dependence of the relaxation time for the bulk viscous pressure, especially its
critical slowing down near the quark-hadron phase transition at T_c, partially
offsets effects from the strong growth of the bulk viscosity itself near T_c,
and that even small values of the specific shear viscosity eta/s of the
fireball matter can be extracted without large uncertainties from poorly
controlled bulk viscous effects.Comment: 13 pages, 7 figures, 1 table. Submitted to Physical Review C. v2:
corrected typos in several entries in Table
Goldstone modes in Lyapunov spectra of hard sphere systems
In this paper, we demonstrate how the Lyapunov exponents close to zero of a
system of many hard spheres can be described as Goldstone modes, by using a
Boltzmann type of approach. At low densities, the correct form is found for the
wave number dependence of the exponents as well as for the corresponding
eigenvectors in tangent-space. The predicted values for the Lyapunov exponents
belonging to the transverse mode are within a few percent of the values found
in recent simulations, the propagation velocity for the longitudinal mode is
within 1%, but the value for the Lyapunov exponent belonging to the
longitudinal mode deviates from the simulations by 30%. For higher densities,
the predicted values deviate more from the values calculated in the
simulations. These deviations may be due to contributions from ring collisions
and similar terms, which, even at low densities, can contribute to the leading
order.Comment: 12 pages revtex, 5 figures, accepted by Physical Review
Structure and interactions of ultracold Yb ions and Rb atoms
In order to study ultracold charge-transfer processes in hybrid atom-ion
traps, we have mapped out the potential energy curves and molecular parameters
for several low lying states of the Rb, Yb system. We employ both a
multi-reference configuration interaction (MRCI) and a full configuration
interaction (FCI) approach. Turning points, crossing points, potential minima
and spectroscopic molecular constants are obtained for the lowest five
molecular states. Long-range parameters, including the dispersion coefficients
are estimated from our {\it ab initio} data. The separated-atom ionization
potentials and atomic polarizability of the ytterbium atom (
atomic units) are in good agreement with experiment and previous calculations.
We present some dynamical calculations for (adiabatic) scattering lengths for
the two lowest (Yb,Rb) channels that were carried out in our work. However,
we find that the pseudo potential approximation is rather limited in validity,
and only applies to nK temperatures. The adiabatic scattering lengths for both
the triplet and singlet channels indicate that both are large and negative in
the FCI approximation.Comment: 8 pages, 3 figures, 5 table
Detailed characteristics of drop-laden mixing layers: Large eddy simulation predictions compared to direct numerical simulation
Induced pseudoscalar coupling of the proton weak interaction
The induced pseudoscalar coupling is the least well known of the weak
coupling constants of the proton's charged--current interaction. Its size is
dictated by chiral symmetry arguments, and its measurement represents an
important test of quantum chromodynamics at low energies. During the past
decade a large body of new data relevant to the coupling has been
accumulated. This data includes measurements of radiative and non radiative
muon capture on targets ranging from hydrogen and few--nucleon systems to
complex nuclei. Herein the authors review the theoretical underpinnings of
, the experimental studies of , and the procedures and uncertainties
in extracting the coupling from data. Current puzzles are highlighted and
future opportunities are discussed.Comment: 58 pages, Latex, Revtex4, prepared for Reviews of Modern Physic