797 research outputs found
Long-range potentials and molecular resonances in an ultracold rydberg gas
We have calculated long-range molecular potentials of the ,
and symmetries between highly-excited rubidium atoms. Strong
potentials characterized by these symmetries are important in
describing interaction-induced phenomena in the excitation spectra of high
Rydberg states. Long-range molecular resonances are such phenomena and they
were first reported in S.M. Farooqi {\it et al.}, Phys. Rev. Lett. {\bf 91}
183002. One class of these resonances occurs at energies corresponding to
excited atom pairs . Such resonances are attributed to -mixing
due to Rydberg-Rydberg interactions so that otherwise forbidden molecular
transitions become allowed. We calculate molecular potentials in Hund's case
(c), use them to find the resonance lineshape and compare to experimental
results.Comment: 11 pages, 7 figure
Bichromatic Slowing of Metastable Helium
We examine two approaches for significantly extending the velocity range of
the optical bichromatic force (BCF), to make it useful for laser deceleration
of atomic and molecular beams. First, we present experimental results and
calculations for BCF deceleration of metastable helium using very large BCF
detunings, and discuss the limitations of this approach. We consider in detail
the constraints, both inherent and practical, that set the usable upper limit
of the BCF. We then show that a more promising approach is to utilize a BCF
profile with a relatively small velocity range in conjunction with chirped
Doppler shifts, to keep the force resonant with the atoms as they are slowed.
In an initial experimental test of this chirped BCF method, helium atoms are
slowed by m/s using a BCF profile with a velocity width of m/s. Straightforward scaling of the present results indicates that a
decelerator for He* capable of loading a magneto-optical trap (MOT) can yield a
brightness comparable to a much larger Zeeman slower.Comment: 11 pages, 9 figures. Published in Phys. Rev.
The Mass of the Black Hole in the Quasar PG 2130+099
We present the results of a recent reverberation-mapping campaign undertaken
to improve measurements of the radius of the broad line region and the central
black hole mass of the quasar PG 2130+099. Cross correlation of the 5100
angstrom continuum and H-beta emission-line light curves yields a time lag of
22.9 (+4.4 - 4.3) days, corresponding to a central black hole mass MBH= 3.8
(+/- 1.5) x 10^7 Msun. This value supports the notion that previous
measurements yielded an incorrect lag. We re-analyzed previous datasets to
investigate the possible sources of the discrepancy and conclude that previous
measurement errors were apparently caused by a combination of undersampling of
the light curves and long-term secular changes in the H-beta emission-line
equivalent width. With our new measurements, PG 2130+099 is no longer an
outlier in either the R-L or the MBH-Sigma relationships.Comment: 21 pages, 7 figures; Accepted for publication in Ap
Abundance of adult horseshoe crabs (Limulus polylphemus) in Delaware Bay estimated from a bay-wide mark-recapture study
Estimates of the abundance of American horseshoe crabs (Limulus polyphemus) are important to determine egg production and to manage populations for the energetic needs of shorebirds that feed on horseshoe crab eggs. In 2003, over 17,500 horseshoe crabs were tagged and released throughout Delaware Bay, and recaptured crabs came from spawning surveys that were conducted during peak spawning. We used two release cohorts to test for a temporary effect of tagging on spawning behavior and we adjusted the number of releases according to relocation rates from a telemetry study. The abundance estimate was 20 million horseshoe crabs (90 % confidence interval: 13−28 million), of which 6.25 million (90% CI: 4.0−8.8 million) were females. The combined harvest rate for Delaware, New Jersey, Virginia, and Maryland in 2003 was 4% (90% CI: 3−6%) of the abundance estimate. Over-wintering of adults in Delaware Bay could explain, in part, differences in estimates from ocean-trawl surveys. Based on fecundity of 88,000 eggs per female, egg production was 5.5×1011 (90% CI: 3.5×1011, 7.7×1011), but egg availability for shorebirds also depended on overlap between horseshoe crab and shorebird migrations, density-dependent bioturbation, and wave-mediated vertical transport
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