2,204 research outputs found
Bose-Einstein Condensates with Large Number of Vortices
We show that as the number of vortices in a three dimensional Bose-Einstein
Condensate increases, the system reaches a "quantum Hall" regime where the
density profile is a Gaussian in the xy-plane and an inverted parabolic profile
along z. The angular momentum of the system increases as the vortex lattice
shrinks. However, Coriolis force prevents the unit cell of the vortex lattice
from shrinking beyond a minimum size. Although the recent MIT experiment is not
exactly in the quantum Hall regime, it is close enough for the present results
to be used as a guide. The quantum Hall regime can be easily reached by
moderate changes of the current experimental parameters.Comment: 4 pages, no figure
Energy non-equipartition in systems of inelastic, rough spheres
We calculate and verify with simulations the ratio between the average
translational and rotational energies of systems with rough, inelastic
particles, either forced or freely cooling. The ratio shows non-equipartition
of energy. In stationary flows, this ratio depends mainly on the particle
roughness, but in nonstationary flows, such as freely cooling granular media,
it also depends strongly on the normal dissipation. The approach presented here
unifies and simplifies different results obtained by more elaborate kinetic
theories. We observe that the boundary induced energy flux plays an important
role.Comment: 4 pages latex, 4 embedded eps figures, accepted by Phys Rev
Criterion for bosonic superfluidity in an optical lattice
We show that the current method of determining superfluidity in optical
lattices based on a visibly sharp bosonic momentum distribution
can be misleading, for even a normal Bose gas can have a similarly sharp
. We show that superfluidity in a homogeneous system can be
detected from the so-called visibility of that must
be 1 within , where is the number of bosons. We also show that
the T=0 visibility of trapped lattice bosons is far higher than what is
obtained in some current experiments, suggesting strong temperature effects and
that these states can be normal. These normal states allow one to explore the
physics in the quantum critical region.Comment: 4 pages, 2 figures; published versio
Dynamics of inelastically colliding rough spheres: Relaxation of translational and rotational energy
We study the exchange of kinetic energy between translational and rotational
degrees of freedom for inelastic collisions of rough spheres. Even if
equipartition holds in the initial state it is immediately destroyed by
collisions. The simplest generalisation of the homogeneous cooling state allows
for two temperatures, characterizing translational and rotational degrees of
freedom separately. For times larger than a crossover frequency, which is
determined by the Enskog frequency and the initial temperature, both energies
decay algebraically like with a fixed ratio of amplitudes, different
from one.Comment: 5 pages, RevTeX, 2 eps figures, slightly expanded discussion, new
figures with dimensionless units, added references, accepted for publication
in PRE as a Rapid Com
Two-component Bose-Einstein Condensates with Large Number of Vortices
We consider the condensate wavefunction of a rapidly rotating two-component
Bose gas with an equal number of particles in each component. If the
interactions between like and unlike species are very similar (as occurs for
two hyperfine states of Rb or Na) we find that the two components
contain identical rectangular vortex lattices, where the unit cell has an
aspect ratio of , and one lattice is displaced to the center of the
unit cell of the other. Our results are based on an exact evaluation of the
vortex lattice energy in the large angular momentum (or quantum Hall) regime.Comment: 4 pages, 2 figures, RevTe
The Class 0 Protostar BHR71: Herschel Observations and Dust Continuum Models
We use Herschel spectrophotometry of BHR71, an embedded Class 0 protostar, to
provide new constraints on its physical properties. We detect 645 (non-unique)
spectral lines amongst all spatial pixels. At least 61 different spectral lines
originate from the central region. A CO rotational diagram analysis shows four
excitation temperature components, 43 K, 197 K, 397 K, and 1057 K. Low-J CO
lines trace the outflow while the high-J CO lines are centered on the infrared
source. The low-excitation emission lines of H2O trace the large-scale outflow,
while the high-excitation emission lines trace a small-scale distribution
around the equatorial plane. We model the envelope structure using the dust
radiative transfer code, Hyperion, incorporating rotational collapse, an outer
static envelope, outflow cavity, and disk. The evolution of a rotating
collapsing envelope can be constrained by the far-infrared/millimeter SED along
with the azimuthally-averaged radial intensity profile, and the structure of
the outflow cavity plays a critical role at shorter wavelengths. Emission at
20-40 um requires a cavity with a constant-density inner region and a power-law
density outer region. The best fit model has an envelope mass of 19 solar mass
inside a radius of 0.315 pc and a central luminosity of 18.8 solar luminosity.
The time since collapse began is 24630-44000 yr, most likely around 36000 yr.
The corresponding mass infall rate in the envelope (1.2x10 solar mass
per year) is comparable to the stellar mass accretion rate, while the mass loss
rate estimated from the CO outflow is 20% of the stellar mass accretion rate.
We find no evidence for episodic accretion.Comment: Accepted for publication in ApJ. 33 pages; 34 figures; 4 table
- …