2,145 research outputs found
Dust capture and long-lived density enhancements triggered by vortices in 2D protoplanetary disks
We study dust capture by vortices and its long-term consequences in global
two-fluid inviscid disk simulations using a new polar grid code RoSSBi. We
perform the longest integrations so far, several hundred disk orbits, at the
highest resolution attainable in global simulations of disks with dust, namely
2048x4096 grid points. This allows to study the dust evolution well beyond
vortex dissipation. We vary a wide range of parameters, most notably the
dust-to-gas ratio in the initial setup varies in the range to .
Irrespective of the initial dust-to-gas ratio we find rapid concentration of
the dust inside vortices, reaching dust-to-gas ratios of order unity inside the
vortex. We present an analytical model that describes very well the dust
capture process inside vortices, finding consistent results for all dust-to-gas
ratios. A vortex streaming instability develops which causes invariably vortex
destruction. After vortex dissipation large-scale dust-rings encompassing a
disk annulus form in most cases, which sustain very high dust concentration,
approaching ratios of order unity. The rings are long lived lasting as long as
the duration of the simulations. They also develop a streaming instability,
which manifests itself in eddies at various scales within which the dust forms
compact high density clumps. Such clumps would be unstable to gravitational
collapse in absence of strong dissipation by viscous forces. When vortices are
particularly long lived, rings do not form but dust clumps inside vortices
become then long lived features and would likely undergo collapse by
gravitational instability. Rings encompass almost an Earth mass of solid
material, while even larger masses of dust do accumulate inside vortices in the
earlier stage. We argue that rapid planetesimal formation would occur in the
dust clumps inside the vortices as well as in the post-vortex ring.Comment: Preprint version, submitted to the Astrophysical Journal. Due to size
constraints on ArXiv, some plots are at low resolution JPEG
A theorem on topologically massive gravity
We show that for three dimensional space-times admitting a hypersurface
orthogonal Killing vector field Deser, Jackiw and Templeton's vacuum field
equations of topologically massive gravity allow only the trivial flat
space-time solution. Thus spin is necessary to support topological mass.Comment: published in Classical and Quantum Gravity 13 (1996) L2
Multi-Black-Holes in Three Dimensions
We construct time-dependent multi-centre solutions to three-dimensional
general relativity with zero or negative cosmological constant. These solutions
correspond to dynamical systems of freely falling black holes and conical
singularities, with a multiply connected spacetime topology. Stationary
multi-black-hole solutions are possible only in the extreme black hole case.Comment: 8 pages, \LaTex, 4 figures (available on request), GCR 94/02/0
Dark Optical Lattice of Ring Traps for Cold Atoms
We propose a new geometry of optical lattice for cold atoms, namely a lattice
made of a 1D stack of dark ring traps. It is obtained through the interference
pattern of a standard Gaussian beam with a counter-propagating hollow beam
obtained using a setup with two conical lenses. The traps of the resulting
lattice are characterized by a high confinement and a filling rate much larger
than unity, even if loaded with cold atoms from a MOT. We have implemented this
system experimentally, and obtained a lattice of ring traps populated with
typically 40 atoms per site with a life time of 30 ms. Applications in
statistical physics, quantum computing and Bose-Einstein condensate dynamics
are conceivable.Comment: 4 pages, submitted to PR
Momentum-resolved study of an array of 1D strongly phase-fluctuating Bose gases
We investigate the coherence properties of an array of one-dimensional Bose
gases with short-scale phase fluctuations. The momentum distribution is
measured using Bragg spectroscopy and an effective coherence length of the
whole ensemble is defined. In addition, we propose and demonstrate that
time-of-flight absorption imaging can be used as a simple probe to directly
measure the coherence-length of 1D gases in the regime where phase-fluctuations
are strong. This method is suitable for future studies such as investigating
the effect of disorder on the phase coherence.Comment: 4 pages, 4 figure
The black holes of topologically massive gravity
We show that an analytical continuation of the Vuorio solution to
three-dimensional topologically massive gravity leads to a two-parameter family
of black hole solutions, which are geodesically complete and causally regular
within a certain parameter range. No observers can remain static in these
spacetimes. We discuss their global structure, and evaluate their mass, angular
momentum, and entropy, which satisfy a slightly modified form of the first law
of thermodynamics.Comment: 10 pages; Eq. (15) corrected, references added, version to appear in
Classical and Quantum Gravit
Exact solution of a model of time-dependent evolutionary dynamics in a rugged fitness landscape
A simplified form of the time dependent evolutionary dynamics of a
quasispecies model with a rugged fitness landscape is solved via a mapping onto
a random flux model whose asymptotic behavior can be described in terms of a
random walk. The statistics of the number of changes of the dominant genotype
from a finite set of genotypes are exactly obtained confirming existing
conjectures based on numerics.Comment: 5 pages RevTex 2 figures .ep
Anderson Localization of Bogolyubov Quasiparticles in Interacting Bose-Einstein Condensates
We study the Anderson localization of Bogolyubov quasiparticles in an
interacting Bose-Einstein condensate (with healing length \xi) subjected to a
random potential (with finite correlation length \sigma_R). We derive
analytically the Lyapunov exponent as a function of the quasiparticle momentum
k and we study the localization maximum k_{max}. For 1D speckle potentials, we
find that k_{max} is proportional to 1/\xi when \xi is much larger than
\sigma_R while k_{max} is proportional to 1/\sigma_R when \xi is much smaller
than \sigma_R, and that the localization is strongest when \xi is of the order
of \sigma_R. Numerical calculations support our analysis and our estimates
indicate that the localization of the Bogolyubov quasiparticles is accessible
in current experiments with ultracold atoms.Comment: published version (no significant changes compared to last version
Existence and uniqueness of Bowen-York Trumpets
We prove the existence of initial data sets which possess an asymptotically
flat and an asymptotically cylindrical end. Such geometries are known as
trumpets in the community of numerical relativists.Comment: This corresponds to the published version in Class. Quantum Grav. 28
(2011) 24500
Kaluza-Klein and Gauss-Bonnet cosmic strings
We make a systematic investigation of stationary cylindrically symmetric
solutions to the five-dimensional Einstein and Einstein-Gauss-Bonnet equations.
Apart from the five-dimensional neutral cosmic string metric, we find two new
exact solutions which qualify as cosmic strings, one corresponding to an
electrically charged cosmic string, the other to an extended superconducting
cosmic string surrounding a charged core. In both cases, test particles are
deflected away from the singular line source. We extend both kinds of solutions
to exact multi-cosmic string solutions.Comment: 26 pages, LaTex, no figure
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