3,080 research outputs found
Low-Income Subsidies for the Medicare Prescription Drug Benefit: The Impact of the Asset Test
Assesses the impact of the requirement that low-income individuals with Medicare meet an asset test in order to receive additional help paying premiums and cost sharing under the new Medicare drug benefit. Raises questions about the equity of the test
Model-robust regression and a Bayesian ``sandwich'' estimator
We present a new Bayesian approach to model-robust linear regression that
leads to uncertainty estimates with the same robustness properties as the
Huber--White sandwich estimator. The sandwich estimator is known to provide
asymptotically correct frequentist inference, even when standard modeling
assumptions such as linearity and homoscedasticity in the data-generating
mechanism are violated. Our derivation provides a compelling Bayesian
justification for using this simple and popular tool, and it also clarifies
what is being estimated when the data-generating mechanism is not linear. We
demonstrate the applicability of our approach using a simulation study and
health care cost data from an evaluation of the Washington State Basic Health
Plan.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS362 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
The Burden of Out-of-Pocket Health Spending Among Older Versus Younger Adults: Analysis from the Consumer Expenditure Survey, 1998-2003
Analyzes the extent to which health care spending as a share of income has differed among younger adults versus people ages 65 and older, both at a single point in time (2003) and over the six-year period from 1998 to 2003
Near-infrared Variability among YSOs in the Star Formation Region Cygnus OB7
We present an analysis of near-infrared time-series photometry in J, H, and K
bands for about 100 epochs of a 1 square degree region of the Lynds 1003/1004
dark cloud in the Cygnus OB7 region. Augmented by data from the Wide-field
Infrared Survey Explorer (WISE), we identify 96 candidate disk bearing young
stellar objects (YSOs) in the region. Of these, 30 are clearly Class I or
earlier. Using the Wide-Field imaging CAMera (WFCAM) on the United Kingdom
InfraRed Telescope (UKIRT), we were able to obtain photometry over three
observing seasons, with photometric uncertainty better than 0.05 mag down to J
~17. We study detailed light curves and color trajectories of ~50 of the YSOs
in the monitored field. We investigate the variability and periodicity of the
YSOs and find the data are consistent with all YSOs being variable in these
wavelengths on time scales of a few years. We divide the variability into four
observational classes: 1) stars with periodic variability stable over long
timescales, 2) variables which exhibit short-lived cyclic behavior, 3) long
duration variables, and 4) stochastic variables. Some YSO variability defies
simple classification. We can explain much of the observed variability as being
due to dynamic and rotational changes in the disk, including an asymmetric or
changing blocking fraction, changes to the inner disk hole size, as well as
changes to the accretion rate. Overall, we find that the Class I:Class II ratio
of the cluster is consistent with an age of < 1Myr, with at least one
individual, wildly varying, source ~ 100,000 yr old. We have also discovered a
Class II eclipsing binary system with a period of 17.87 days.Comment: ApJ accepted: 44 pages includes 5 tables and 16 figures. Some figures
condensed for Astro/p
Exploring the Origins of Earth's Nitrogen: Astronomical Observations of Nitrogen-bearing Organics in Protostellar Environments
It is not known whether the original carriers of Earth's nitrogen were
molecular ices or refractory dust. To investigate this question, we have used
data and results of Herschel observations towards two protostellar sources: the
high-mass hot core of Orion KL, and the low-mass protostar IRAS 16293-2422.
Towards Orion KL, our analysis of the molecular inventory of Crockett et al.
(2014) indicates that HCN is the organic molecule that contains by far the most
nitrogen, carrying of nitrogen-in-organics. Following this
evidence, we explore HCN towards IRAS 16293-2422, which we consider a solar
analog. Towards IRAS 16293-2422, we have reduced and analyzed Herschel spectra
of HCN, and fit these observations against "jump" abundance models of IRAS
16293-2422's protostellar envelope. We find an inner-envelope HCN abundance
and an outer-envelope HCN
abundance . We also find the
sublimation temperature of HCN to be ~K; this
measured enables us to predict an HCN binding energy
~K. Based on a comparison of the HCN/H2O ratio
in these protostars to N/H2O ratios in comets, we find that HCN (and, by
extension, other organics) in these protostars is incapable of providing the
total bulk N/H2O in comets. We suggest that refractory dust, not molecular
ices, was the bulk provider of nitrogen to comets. However, interstellar dust
is not known to have 15N enrichment, while high 15N enrichment is seen in both
nitrogen-bearing ices and in cometary nitrogen. This may indicate that these
15N-enriched ices were an important contributor to the nitrogen in
planetesimals and likely to the Earth.Comment: Accepted to ApJ; 21 pages, 4 figure
Parallel LISP
Projects in the past few years have looked into the problem of automatic parallelization of the Lisp programming language. Since it appears to be feasible to adapt Lisp to run on a general parallel computer, an implementation will be developed. This implementation will be as general as possible in order to locate the tradeoffs between implementing Lisp on a general parallel computer versus having an efficient interpreter. This implementation can be used to study the execution characteristics of Lisp in a parallel environment. It can also be used to derive information about architectural features which affect the performance of Lisp on parallel machines. This implementation will use a multitasking system and interprocess communication to simulate an MIMD machine. The implementation will include the formation, queuing, distribution, and execution of dataflow frames. Realistic Lisp application programs will be used with the implementation to examine the feasibility and efficiency of parallel Lisp. Measurements derivable from the simulator include number of processor cycles, processor utilization, memory requirements, and speedup. These tests will provide two main results. First, they will indicate possibilities for further gains by illustrating the bottlenecks in such a scheme. Second, they will help determine if it is indeed feasible to run Lisp on a parallel machine or if instead the overhead is too high for the application to be profitable. Most likely, some parallelism will be profitable. The simulation will provide information on the extent to which parallelism can be utilized
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