3,151 research outputs found
Photoassociation dynamics in a Bose-Einstein condensate
A dynamical many body theory of single color photoassociation in a
Bose-Einstein condensate is presented. The theory describes the time evolution
of a condensed atomic ensemble under the influence of an arbitrarily varying
near resonant laser pulse, which strongly modifies the binary scattering
properties. In particular, when considering situations with rapid variations
and high light intensities the approach described in this article leads, in a
consistent way, beyond standard mean field techniques. This allows to address
the question of limits to the photoassociation rate due to many body effects
which has caused extensive discussions in the recent past. Both, the possible
loss rate of condensate atoms and the amount of stable ground state molecules
achievable within a certain time are found to be stronger limited than
according to mean field theory. By systematically treating the dynamics of the
connected Green's function for pair correlations the resonantly driven
population of the excited molecular state as well as scattering into the
continuum of non-condensed atomic states are taken into account. A detailed
analysis of the low energy stationary scattering properties of two atoms
modified by the near resonant photoassociation laser, in particular of the
dressed state spectrum of the relative motion prepares for the analysis of the
many body dynamics. The consequences of the finite lifetime of the resonantly
coupled bound state are discussed in the two body as well as in the many body
context. Extending the two body description to scattering in a tight trap
reveals the modifications to the near resonant adiabatic dressed levels caused
by the decay of the excited molecular state.Comment: 27 pages revtex, 16 figure
Far-flung Filaments of Ejecta in the Young Supernova Remnant G292.0+1.8
New optical images of the young SNR G292.0+1.8, obtained from the 0.9-m
telescope at CTIO, show a more extensive network of filaments than had been
known previously. Filaments emitting in [O III] are distributed throughout much
of the 8 arcmin diameter shell seen in X-ray and radio images, including a few
at the very outermost shell limits. We have also detected four small complexes
of filaments that show [S II] emission along with [OIII]. In a single long-slit
spectrum we find variations of almost an order of magnitude in the relative
strengths of oxygen and sulfur lines, which must result from abundance
variations. None of the filaments, with or without [S II], shows any evidence
for hydrogen, so all appear to be fragments of pure SN ejecta. The [S II]
filaments provide the first evidence for undiluted products of oxygen burning
in the ejecta from the supernova that gave rise to G292.0+1.8. Some oxygen
burning must have occurred, but the paucity of [S II]-emitting filaments
suggests that either the oxygen burning was not extensive or that most of its
products have yet to be excited. Most of the outer filaments exhibit radial,
pencil-like morphologies that suggest an origin as Rayleigh-Taylor fingers of
ejecta, perhaps formed during the explosion. Simulations of core-collapse
supernovae predict such fingers, but these have never before been so clearly
observed in a young SNR. The total flux from the SNR in [OIII] 5007 is 5.4 *
10**-12 ergs/cm**2/s. Using a distance of 6 kpc and an extinction correction
corresponding to E(B-V) = 0.6 (lower than previous values but more consistent
both with our data and radio and X-ray estimates of NH), this leads to a
luminosity of 1.6 * 10**35 ergs/s in the 5007 Ang. line.Comment: 32 pages including 10 figures, and 3 tables, accepted for publication
in AJ. Vol 132, July 2006. Higher resolution versions of the figures and a
pdf of the manuscript can be found at
http://www-int.stsci.edu/~long/papers/g292_optical
Population Change of Counties and Incorporated Places in South Dakota: 1950-180
This publication is thirteenth in the population update series based on South Dakota\u27s 1980 population. The tables in this report have been assembled to provide a convenient source of population information for the counties and incorporated places of South Dakota. The basic data have been taken from the U.S. Bureau of the Census, 1980 Census of Population � South Dakota PC80-l-A43 and the 1960 Census of Population-South Dakota PC (1) -43A. The figures are final population counts from the various census
Vortices in atomic-molecular Bose-Einstein condensates
The structure and stability of vortices in hybrid atomic-molecular
Bose-Einstein condensates is analyzed in the framework of a two-component
Gross-Pitaevskii-type model that describes the stimulated Raman-induced
photoassociation process. New types of topological vortex states are predicted
to exist in the coherently coupled two-component condensates even without a
trap, and their nontrivial dynamics in the presence of losses is demonstrated.Comment: 7 pages, 6 figure
Detection of HI 21 cm-line absorption in the Warm Neutral Medium and in the Outer Arm of the Galaxy
Using the Westerbork Synthesis Radio Telescope, we have detected HI 21
cm-line absorption in the Warm Neutral Medium of the Galaxy toward the
extragalactic source 3C147. This absorption, at an LSR velocity of -29+/-4 km/s
with a full width at half maximum of 53+/-6 km/s, is associated with the
Perseus Arm of the Galaxy. The observed optical depth is (1.9+/-0.2)*10**(-3).
The estimated spin temperature of the gas is 3600+/-360 K. The volume density
is 0.4 per cc assuming pressure equilibrium. Toward two other sources, 3C273
and 3C295, no wide HI 21 cm-line absorption was detected. The highest of the
3sigma lower limits on the spin temperature of the Warm Neutral Medium is 2600
K. In addition, we have also detected HI 21 cm-line absorption from high
velocity clouds in the Outer Arm toward 3C147 and 3C380 at LSR velocities of
-117.3, -124.5 and -113.7 km/s respectively. We find two distinct temperature
components in the high velocity clouds with spin temperatures of greater than
1000 K and less than 200 K, respectively.Comment: 21 pages inclusive of 7 figures and 2 table
- …