59,288 research outputs found
Higher Order Graviton Scattering in M(atrix) Theory
In matrix theory the effective action for graviton-graviton scattering is a
double expansion in the relative velocity and inverse separation. We discuss
the systematics of this expansion and subject matrix theory to a new test. Low
energy supergravity predicts the coefficient of the term, a
two-loop effect, in agreement with explicit matrix model calculation.Comment: 15 pages, 1 epsf figure, LaTeX. Minor change
The Deep Lens Survey Transient Search I : Short Timescale and Astrometric Variability
We report on the methodology and first results from the Deep Lens Survey
transient search. We utilize image subtraction on survey data to yield all
sources of optical variability down to 24th magnitude. Images are analyzed
immediately after acquisition, at the telescope and in near-real time, to allow
for followup in the case of time-critical events. All classes of transients are
posted to the web upon detection. Our observing strategy allows sensitivity to
variability over several decades in timescale. The DLS is the first survey to
classify and report all types of photometric and astrometric variability
detected, including solar system objects, variable stars, supernovae, and short
timescale phenomena. Three unusual optical transient events were detected,
flaring on thousand-second timescales. All three events were seen in the B
passband, suggesting blue color indices for the phenomena. One event (OT
20020115) is determined to be from a flaring Galactic dwarf star of spectral
type dM4. From the remaining two events, we find an overall rate of \eta = 1.4
events deg-2 day-1 on thousand-second timescales, with a 95% confidence limit
of \eta < 4.3. One of these events (OT 20010326) originated from a compact
precursor in the field of galaxy cluster Abell 1836, and its nature is
uncertain. For the second (OT 20030305) we find strong evidence for an extended
extragalactic host. A dearth of such events in the R passband yields an upper
95% confidence limit on short timescale astronomical variability between 19.5 <
R < 23.4 of \eta_R < 5.2. We report also on our ensemble of astrometrically
variable objects, as well as an example of photometric variability with an
undetected precursor.Comment: 24 pages, 12 figures, 3 tables. Accepted for publication in ApJ.
Variability data available at http://dls.bell-labs.com/transients.htm
Coherent Control of Vibrational State Population in a Nonpolar Molecule
A coherent control scheme for the population distribution in the vibrational
states of nonpolar molecules is proposed. Our theoretical analysis and results
of numerical simulations for the interaction of the hydrogen molecular ion in
its electronic ground state with an infrared laser pulse reveal a selective
two-photon transition between the vibrational states via a coupling with the
first excited dissociative state. We demonstrate that for a given temporal
intensity profile the population transfer between vibrational states, or a
superposition of vibrational states, can be made complete for a single chirped
pulse or a train of chirped pulses, which accounts for the accumulated phase
difference due to the AC Stark effect. Effects of a spatial intensity (or,
focal) averaging are discussed
Medi-Cal Versus Employer-Based Coverage: Comparing Access to Care
This report takes a close look at access to care under Medi-Cal for nonelderly adults and children on the eve of Affordable Care Act (ACA) implementation. Using data from the 2012 and 2013 California Health Interview Surveys (CHIS), the research examines a total of 49 measures (45 on realized and potential access and 4 on health status and health behaviors) for nonelderly adults and 31 measures (28 on realized and potential access and 3 on health status and behaviors) for children.For adults, access under Medi-Cal is compared to access under employer-sponsored insurance (ESI) overall; among Medi-Cal enrollees, access is compared across subgroups defined by region, race/ethnicity, language, and other dimensions. For children, access under Medi-Cal and Healthy Families together (referred hereafter simply as "Medi-Cal") is compared against access under ESI. To account for differences in health status and socioeconomic status between those with Medi-Cal and those with ESI, for each measure, three sets of analyses are presented: unadjusted percentages, predicted percentages adjusted for health care need, and predicted percentages adjusted for both health care need and socioeconomic status. The same approach is used in the analysis of regional and subgroup differences within the Medi-Cal population
Pristine CNO abundances from Magellanic Cloud B stars II. Fast rotators in the LMC cluster NGC 2004
We present spectroscopic abundance analyses of three main-sequence B stars in
the young Large Magellanic Cloud cluster NGC 2004. All three targets have
projected rotational velocities around 130 km/s. Techniques are presented that
allow the derivation of stellar parameters and chemical abundances in spite of
these high v sin i values. Together with previous analyses of stars in this
cluster, we find no evidence among the main-sequence stars for effects due to
rotational mixing up to v sin i around 130 km/s. Unless the equatorial
rotational velocities are significantly larger than the v sin i values, this
finding is probably in line with theoretical expectations. NGC 2004/B30, a star
of uncertain evolutionary status located in the Blue Hertzsprung Gap, clearly
shows signs of mixing in its atmosphere. To verify the effects due to
rotational mixing will therefore require homogeneous analysis of statistically
significant samples of low-metallicity main-sequence B stars over a wide range
of rotational velocities.Comment: 12 pages, 5 figures, 2 tables; accepted for publication in ApJ (vol.
633, p. 899
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