2,743 research outputs found
An Empirically Derived Three-Dimensional Laplace Resonance in the Gliese 876 Planetary System
We report constraints on the three-dimensional orbital architecture for all
four planets known to orbit the nearby M dwarf Gliese 876 based solely on
Doppler measurements and demanding long-term orbital stability. Our dataset
incorporates publicly available radial velocities taken with the ELODIE and
CORALIE spectrographs, HARPS, and Keck HIRES as well as previously unpublished
HIRES velocities. We first quantitatively assess the validity of the planets
thought to orbit GJ 876 by computing the Bayes factors for a variety of
different coplanar models using an importance sampling algorithm. We find that
a four-planet model is preferred over a three-planet model. Next, we apply a
Newtonian MCMC algorithm to perform a Bayesian analysis of the planet masses
and orbits using an n-body model in three-dimensional space. Based on the
radial velocities alone, we find that a 99% credible interval provides upper
limits on the mutual inclinations for the three resonant planets
( for the "c" and "b" pair and for
the "b" and "e" pair). Subsequent dynamical integrations of our posterior
sample find that the GJ 876 planets must be roughly coplanar
( and ), suggesting the amount of
planet-planet scattering in the system has been low. We investigate the
distribution of the respective resonant arguments of each planet pair and find
that at least one argument for each planet pair and the Laplace argument
librate. The libration amplitudes in our three-dimensional orbital model
supports the idea of the outer-three planets having undergone significant past
disk migration.Comment: 19 pages, 11 figures, 8 tables. Accepted to MNRAS. Posterior samples
available at https://github.com/benelson/GJ87
Milky Way Disk-Halo Transition in HI: Properties of the Cloud Population
Using 21cm HI observations from the Parkes Radio Telescope's Galactic All-Sky
Survey, we measure 255 HI clouds in the lower Galactic halo that are located
near the tangent points at 16.9 < l < 35.3 degrees and |b| < 20 degrees. The
clouds have a median mass of 700 Msun and a median distance from the Galactic
plane of 660 pc. This first Galactic quadrant (QI) region is symmetric to a
region of the fourth quadrant (QIV) studied previously using the same data set
and measurement criteria. The properties of the individual clouds in the two
quadrants are quite similar suggesting that they belong to the same population,
and both populations have a line of sight cloud-cloud velocity dispersion of
sigma_cc ~ 16 km/s. However, there are three times as many disk-halo clouds at
the QI tangent points and their scale height, at h=800 pc, is twice as large as
in QIV. Thus the observed line of sight random cloud motions are not connected
to the cloud scale height or its variation around the Galaxy. The surface
density of clouds is nearly constant over the QI tangent point region but is
peaked near R~4 kpc in QIV. We ascribe all of these differences to the
coincidental location of the QI region at the tip of the Milky Way's bar, where
it merges with a major spiral arm. The QIV tangent point region, in contrast,
covers only a segment of a minor spiral arm. The disk-halo HI cloud population
is thus likely tied to and driven by large-scale star formation processes,
possibly through the mechanism of supershells and feedback.Comment: 14 pages, 20 figures, to be published in ApJ (accepted August 3 2010
The COS-Halos Survey: Physical Conditions and Baryonic Mass in the Low-Redshift Circumgalactic Medium
We analyze the physical conditions of the cool, photoionized (T
K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density
measurements for 44 gaseous halos within 160 kpc of galaxies at . These data are well described by simple photoionization models, with
the gas highly ionized (n/n) by the
extragalactic ultraviolet background (EUVB). Scaling by estimates for the
virial radius, R, we show that the ionization state (tracked by the
dimensionless ionization parameter, U) increases with distance from the host
galaxy. The ionization parameters imply a decreasing volume density profile
n = (10)(R/R. Our derived
gas volume densities are several orders of magnitude lower than predictions
from standard two-phase models with a cool medium in pressure equilibrium with
a hot, coronal medium expected in virialized halos at this mass scale. Applying
the ionization corrections to the HI column densities, we estimate a lower
limit to the cool gas mass M
M for the volume within R R. Allowing for an
additional warm-hot, OVI-traced phase, the CGM accounts for at least half of
the baryons purported to be missing from dark matter halos at the 10
M scale.Comment: 19 pages, 12 Figures, and a 37-page Appendix with 36 additional
figures. Accepted to ApJ June 21 201
The COS-Dwarfs Survey: The Carbon Reservoir Around sub-L* Galaxies
We report new observations of circumgalactic gas from the COS-Dwarfs survey,
a systematic investigation of the gaseous halos around 43 low-mass z 0.1
galaxies using background QSOs observed with the Cosmic Origins Spectrograph.
From the projected 1D and 2D distribution of C IV absorption, we find that C IV
absorption is detected out to ~ 0.5 R of the host galaxies. The C IV
absorption strength falls off radially as a power law and beyond 0.5 R,
no C IV absorption is detected above our sensitivity limit of ~ 50-100 m.
We find a tentative correlation between detected C IV absorption strength and
star formation, paralleling the strong correlation seen in highly ionized
oxygen for L~L* galaxies by the COS-Halos survey. The data imply a large carbon
reservoir in the CGM of these galaxies, corresponding to a minimum carbon mass
of 1.2 out to ~ 110 kpc. This mass is
comparable to the carbon mass in the ISM and more than the carbon mass
currently in stars of these galaxies. The C IV absorption seen around these
sub-L* galaxies can account for almost two-thirds of all > 100 m C IV
absorption detected at low z. Comparing the C IV covering fraction with
hydrodynamical simulations, we find that an energy-driven wind model is
consistent with the observations whereas a wind model of constant velocity
fails to reproduce the CGM or the galaxy properties.Comment: 18 Pages, 11 Figures, ApJ 796 13
Surgical management of primary colonic lymphoma: Big data for a rare problem
Background and ObjectivesPrimary colonic lymphoma (PCL) is rare, heterogeneous, and presents a therapeutic challenge for surgeons. Optimal treatment strategies are difficult to standardize, leading to variation in therapy. Our objective was to describe the patient characteristics, short‐term outcomes, and five‐year survival of patients undergoing nonpalliative surgery for PCL.MethodsWe performed a retrospective cohort analysis in the National Cancer Database. Included patients underwent surgery for PCL between 2004 to 2014. Patients with metastases and palliative operations were excluded. Univariate predictors of overall survival were analyzed using multivariable Cox proportional hazard analysis.ResultsWe identified 2153 patients. Median patient age was 68. Diffuse large B‐cell lymphoma accounted for 57% of tumors. 30‐ and 90‐Day mortality were high (5.6% and 11.1%, respectively). Thirty‐nine percent of patients received adjuvant chemotherapy. For patients surviving 90 days, 5‐year survival was 71.8%. Chemotherapy improved survival (surgery+chemo, 75.4% vs surgery, 68.6%; P = .01). Adjuvant chemotherapy was associated with overall survival after controlling for age, comorbidity, and lymphoma subtype (HR 1.27; 95% CI, 1.07‐1.51; P = .01).ConclusionsPatients undergoing surgery for PCL have high rates of margin positivity and high short‐term mortality. Chemotherapy improves survival, but <50% receive it. These data suggest the opportunity for improvement of care in patients with PCL.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150597/1/jso25582_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150597/2/jso25582.pd
Design, Synthesis and Biological Evaluation of Aminoalkylindole Derivatives as Cannabinoid Receptor Ligands with Potential for Treatment of Alcohol Abuse
Attenuation of increased endocannabinoid signaling with a CB1R neutral antagonist might offer a new therapeutic direction for treatment of alcohol abuse. We have recently reported that a mono-hydroxylated metabolite of the synthetic aminoalkylindole cannabinoid JHW-073 (3) exhibits neutral antagonist activity at CB1Rs and thus may serve as a promising lead for the development of novel alcohol abuse therapies. In the current study, we show that systematic modification of an aminoalkylindole scaffold identified two new compounds with dual CB1R antagonist/CB2R agonist activity. Similar to the CB1R antagonist/inverse agonist rimonabant, analogues 27 and 30 decrease oral alcohol self-administration, without affecting total fluid intake and block the development of alcohol-conditioned place preference. Collectively, these initial findings suggest that design and systematic modification of aminoalkylindoles such as 3 may lead to development of novel cannabinoid ligands with dual CB1R antagonist/CB2R agonist activity with potential for use as treatments of alcohol abuse
Quantifying the Bayesian Evidence for a Planet in Radial Velocity Data
We present results from a data challenge posed to the radial velocity (RV) community: Namely, to quantify the Bayesian "evidence"for n = {0, 1, 2, 3} planets in a set of synthetically generated RV data sets containing a range of planet signals. Participating teams were provided the same likelihood function and set of priors to use in their analysis. They applied a variety of methods to estimate the marginal likelihood for each n-planet model, including cross-validation, the Laplace approximation, importance sampling, and nested sampling. We found the dispersion in across different methods grew with increasing n-planet models: ∼3 for zero planets, ∼10 for one planet, ∼102-103 for two planets, and >104 for three planets. Most internal estimates of uncertainty in for individual methods significantly underestimated the observed dispersion across all methods. Methods that adopted a Monte Carlo approach by comparing estimates from multiple runs yielded plausible uncertainties. Finally, two classes of numerical algorithms (those based on importance and nested samplers) arrived at similar conclusions regarding the ratio of for n- A nd (n + 1)-planet models. One analytic method (the Laplace approximation) demonstrated comparable performance. We express both optimism and caution: We demonstrate that it is practical to perform rigorous Bayesian model comparison for models of ≤3 planets, yet robust planet discoveries require researchers to better understand the uncertainty in and its connections to model selection.Fil: Nelson, Benjamin E.. Northwestern University; Estados UnidosFil: Ford, Eric B.. Pennsylvania State University; Estados UnidosFil: Buchner, Johannes. Pontificia Universidad Católica de Chile; Chile. Universidad Católica de Chile; ChileFil: Cloutier, Ryan. University of Toronto; CanadáFil: Díaz, Rodrigo Fernando. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Faria, Joaõ P.. Universidad de Porto; PortugalFil: Hara, Nathan C.. Universite Ifm Geneve (ifm); SuizaFil: Rajpaul, Vinesh M.. University of Cambridge; Estados UnidosFil: Rukdee, Surangkhana. Pontificia Universidad Católica de Chile; Chile. Universidad Católica de Chile; Chil
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