771 research outputs found
Smoothed Particle Interpolation
Smoothed particle hydrodynamics (SPH) discretization techniques are
generalized to develop a method, smoothed particle interpolation (SPI), for
solving initial value problems of systems of non-hydrodynamical nature. Under
this approach, SPH is viewed as strictly an interpolation scheme and, as such,
suitable for solving general hyperbolic and parabolic equations. The SPI method
is tested on (1) the wave equation with inhomogeneous sound speed and (2)
Burgers equation. The efficiency of SPI is studied by comparing SPI solutions
to those obtained with standard finite difference methods. It is shown that the
power of SPI arises when the smoothing particles are free to move.Comment: 13 pages (LaTeX), 9 figures (not included), [email protected]
The Imprint of Proper Motion of Nonlinear Structures on the Cosmic Microwave Background
We investigate the imprint of nonlinear matter condensations on the Cosmic
Microwave Background (CMB) in an , Cold Dark Matter (CDM) model
universe. Temperature anisotropies are obtained by numerically evolving matter
inhomogeneities and CMB photons from the beginning of decoupling until the
present epoch. The underlying density field produced by the inhomogeneities is
followed from the linear, through the weakly clustered, into the fully
nonlinear regime. We concentrate on CMB temperature distortions arising from
variations in the gravitational potentials of nonlinear structures. We find two
sources of temperature fluctuations produced by time-varying potentials: (1)
anisotropies due to intrinsic changes in the gravitational potentials of the
inhomogeneities and (2) anisotropies generated by the peculiar, bulk motion of
the structures across the microwave sky. Both effects generate CMB anisotropies
in the range of 10^{-7} \siml \Delta T/T \siml 10^{-6} on scales of . For isolated structures, anisotropies due to proper motion exhibit
a dipole-like signature in the CMB sky that in principle could yield
information on the transverse velocity of the structures.Comment: 9 pages, 7 figures (included), uuencoded postcript fil
Density of Topological Defects After a Quench
We present results of numerical studies of the Landau-Ginzburg dynamics of
the order parameter in one-dimensional models inspired by the condensed matter
analogues of cosmological phase transitions. The main goal of our work is to
show that, as proposed by one of us \cite{Zurek85b}, the density of the
frozen-out topological defects is set by the competition between the quench
rate --- the rate at which the phase transition is taking place --- and the
relaxation rate of the order parameter. In other words, the characteristic
domain size, which determines the typical separation of topological defects in
the new broken symmetry phase, is of the order of the correlation length at the
instant at which the relaxation timescale of the order parameter equals the
time remaining to the phase transition. In estimating the size of topological
domains, this scenario shares with the original Kibble mechanism the idea that
topological defects will form along the boundaries of independently selected
regions of the new broken symmetry vacuum. However, it derives the size of such
domains from non-equilibrium aspects of the transition (quench rate), as
opposed to Kibble's original proposal in which their size was estimated from
the Ginzburg temperature above which thermally activated symmetry restoration
can occur.Comment: 17 pages, 6 figures, LaTe
Cosmic Microwave Background Anisotropies from the Rees-Sciama Effect in Universes
We investigate the imprint of nonlinear matter condensations on the Cosmic
Microwave Background (CMB) in cold dark matter (CDM) model
universes. We consider simulation domains ranging from Mpc to
Mpc in size. We concentrate on the secondary temperature
anisotropies induced by time varying gravitational potentials occurring after
decoupling. Specifically, we investigate the importance of the Rees-Sciama
effect due to: (1) intrinsic changes in the gravitational potential of forming,
nonlinear structures, (2) proper motion of nonlinear structures, and (3) late
time decay of gravitational potential perturbations in open universes. CMB
temperature anisotropies are obtained by numerically evolving matter
inhomogeneities and CMB photons from an early, linear epoch () to the
present, nonlinear epoch . We test the dependence and relative
importance of these secondary temperature anisotropies as a function of the
scale of the underlying matter (voids, superclusters) and as a function of
. The results of the models are compared to a
similarly executed simulation. We find that in low density
models all three sources of anisotropy could be relevant and reach levels of
. In particular, we find that for at
large scales, secondary temperature anisotropies are dominated by the decaying
potential.Comment: 20 pages + 7 figures + 4 plates, self-expanding uuencoded compressed
tar archive of postscript file
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