93 research outputs found
Concentrated Perchlorate at the Mars Phoenix Landing Site: Evidence for Thin Film Liquid Water on Mars
NASA\u27s Phoenix mission, which landed on the northern plains of Mars in 2008, returned evidence of the perchlorate anion distributed evenly throughout the soil column at the landing site. Here, we use spectral data from Phoenix\u27s Surface Stereo Imager to map the distribution of perchlorate salts at the Phoenix landing site, and find that perchlorate salt has been locally concentrated into subsurface patches, similar to salt patches that result from aqueous dissolution and redistribution on Earth. We propose that thin films of liquid water are responsible for translocating perchlorate from the surface to the subsurface, and for concentrating it in patches. The thin films are interpreted to result from melting of minor ice covers related to seasonal and long-term obliquity cycles
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Can an Off-Nominal Landing by an MMRTG-Powered Spacecraft Induce a Special Region on Mars When No Ice Is Present?
This work aims at addressing whether a catastrophic failure of an entry, descent, and landing event of a Multimission Radioisotope Thermoelectric Generator-based lander could embed the heat sources into the martian subsurface and create a local environment that (1) would temporarily satisfy the conditions for a martian Special Region and (2) could establish a transport mechanism through which introduced terrestrial organisms could be mobilized to naturally occurring Special Regions elsewhere on Mars. Two models were run, a primary model by researchers at the Lawrence Berkeley National Laboratory and a secondary model by researchers at the Jet Propulsion Laboratory, both of which were based on selected starting conditions for various surface composition cases that establish the worst-case scenario, including geological data collected by the Mars Science Laboratory at Gale Crater. The summary outputs of both modeling efforts showed similar results: that the introduction of the modeled heat source could temporarily create the conditions established for a Special Region, but that there would be no transport mechanism by which an introduced terrestrial microbe, even if it was active during the temporarily induced Special Region conditions, could be transported to a naturally occurring Special Region of Mars
Risk for Clostridium difficile Infection after Radical Cystectomy for Bladder Cancer: Analysis of a Contemporary Series
Introduction
This study seeks to evaluate the incidence and associated risk factors of Clostridium difficile infection (CDI) in patients undergoing radical cystectomy (RC) for bladder cancer.
Methods
We retrospectively reviewed a single institution׳s bladder cancer database including all patients who underwent RC between 2010 and 2013. CDI was diagnosed by detection of Clostridium difficile toxin B gene using polymerase chain reaction–based stool assay in patients with clinically significant diarrhea within 90 days of the index operation. A multivariable logistic regression model was used to identify demographics and perioperative factors associated with developing CDI.
Results
Of the 552 patients who underwent RC, postoperative CDI occurred in 49 patients (8.8%) with a median time to diagnosis after RC of 7 days (interquartile range: 5–19). Of the 122 readmissions for postoperative complications, 10% (n = 12) were related to CDI; 2 patients died of sepsis directly related to severe CDI. On multivariate logistic regression, the use of chronic antacid therapy (odds ratio = 1.9, 95% CI: 1.02–3.68, P = 0.04) and antibiotic exposure greater than 7 days (odds ratio = 2.2, 95% CI: 1.11–4.44, P = 0.02) were independently associated with developing CDI. The use of preoperative antibiotics for positive findings on urine culture within 30 days before surgery was not statistically significantly associated with development of CDI (P = 0.06).
Conclusions
The development of CDI occurs in 8.8% of patients undergoing RC. Our study demonstrates that use of chronic antacid therapy and long duration of antimicrobial exposure are associated with development of CDI. Efforts focusing on minimizing antibiotic exposure in patients undergoing RC are needed, and perioperative antimicrobial prophylaxis guidelines should be followed
Hubble Space Telescope NICMOS Polarization Observations of Three Edge-on Massive YSOs
Massive young stellar objects (YSOs), like low-mass YSOs, appear to be
surrounded by optically thick envelopes and/or disks and have regions, often
bipolar, that are seen in polarized scattered light at near-infrared
wavelengths. We are using the 0.2'' spatial resolution of NICMOS on Hubble
Space Telescope to examine the structure of the disks and outflow regions of
massive YSOs in star-forming regions within a few kpc of the Sun. Here we
report on 2 micron polarimetry of NGC 6334 V and S255 IRS1. NGC 6334 V consists
of a double-lobed bright reflection nebula seen against a dark region, probably
an optically thick molecular cloud. Our polarization measurements show that the
illuminating star lies ~ 2'' south of the line connecting the two lobes; we do
not detect this star at 2 micron, but there are a small radio source and a
mid-infrared source at this location. S255 IRS1 consists of two YSOs (NIRS1 and
NIRS3) with overlapping scattered light lobes and luminosities corresponding to
early B stars. Included in IRS1 is a cluster of stars from whose polarization
we determine the local magnetic field direction. Neither YSO has its scattered
light lobes aligned with this magnetic field. The line connecting the scattered
light lobes of NIRS1 is twisted symmetrically around the star; the best
explanation is that the star is part of a close binary and the outflow axis of
NIRS1 is precessing as a result of non-coplanar disk and orbit. The star NIRS3
is also offset from the line connecting its two scattered light lobes. We
suggest that all three YSOs show evidence of episodic ejection of material as
they accrete from dense, optically thick envelopes.Comment: 39 pages, 7 figures, 4 tables To be published in The Astrophysical
Journa
KELT-6b: A P~7.9 d Hot Saturn Transiting a Metal-Poor Star with a Long-Period Companion
We report the discovery of KELT-6b, a mildly-inflated Saturn-mass planet
transiting a metal-poor host. The initial transit signal was identified in
KELT-North survey data, and the planetary nature of the occulter was
established using a combination of follow-up photometry, high-resolution
imaging, high-resolution spectroscopy, and precise radial velocity
measurements. The fiducial model from a global analysis including constraints
from isochrones indicates that the V=10.38 host star (BD+31 2447) is a mildly
evolved, late-F star with T_eff=6102 \pm 43 K, log(g_*)=4.07_{-0.07}^{+0.04}
and [Fe/H]=-0.28 \pm 0.04, with an inferred mass M_*=1.09 \pm 0.04 M_sun and
radius R_star=1.58_{-0.09}^{+0.16} R_sun. The planetary companion has mass
M_P=0.43 \pm 0.05 M_J, radius R_P=1.19_{-0.08}^{+0.13} R_J, surface gravity
log(g_P)=2.86_{-0.08}^{+0.06}, and density rho_P=0.31_{-0.08}^{+0.07}
g~cm^{-3}. The planet is on an orbit with semimajor axis a=0.079 \pm 0.001 AU
and eccentricity e=0.22_{-0.10}^{+0.12}, which is roughly consistent with
circular, and has ephemeris of T_c(BJD_TDB)=2456347.79679 \pm 0.00036 and
P=7.845631 \pm 0.000046 d. Equally plausible fits that employ empirical
constraints on the host star parameters rather than isochrones yield a larger
planet mass and radius by ~4-7%. KELT-6b has surface gravity and incident flux
similar to HD209458b, but orbits a host that is more metal poor than HD209458
by ~0.3 dex. Thus, the KELT-6 system offers an opportunity to perform a
comparative measurement of two similar planets in similar environments around
stars of very different metallicities. The precise radial velocity data also
reveal an acceleration indicative of a longer-period third body in the system,
although the companion is not detected in Keck adaptive optics images.Comment: Published in AJ, 17 pages, 15 figures, 6 table
KELT-7b: A hot Jupiter transiting a bright V=8.54 rapidly rotating F-star
We report the discovery of KELT-7b, a transiting hot Jupiter with a mass of
MJ, radius of RJ, and an orbital
period of days. The bright host star (HD33643;
KELT-7) is an F-star with , Teff K, [Fe/H]
, and . It has a mass of
Msun, a radius of Rsun, and
is the fifth most massive, fifth hottest, and the ninth brightest star known to
host a transiting planet. It is also the brightest star around which KELT has
discovered a transiting planet. Thus, KELT-7b is an ideal target for detailed
characterization given its relatively low surface gravity, high equilibrium
temperature, and bright host star. The rapid rotation of the star (
km/s) results in a Rossiter-McLaughlin effect with an unusually large amplitude
of several hundred m/s. We find that the orbit normal of the planet is likely
to be well-aligned with the stellar spin axis, with a projected spin-orbit
alignment of degrees. This is currently the second most
rapidly rotating star to have a reflex signal (and thus mass determination) due
to a planetary companion measured.Comment: Accepted to The Astronomical Journa
Thermal inertia of near-Earth asteroids and implications for the magnitude of the Yarkovsky effect
Thermal inertia determines the temperature distribution over the surface of
an asteroid and therefore governs the magnitude the Yarkovsky effect. The
latter causes gradual drifting of the orbits of km-sized asteroids and plays an
important role in the delivery of near-Earth asteroids (NEAs) from the main
belt and in the dynamical spreading of asteroid families. At present, very
little is known about the thermal inertia of asteroids in the km size range.
Here we show that the average thermal inertia of a sample of NEAs in the
km-size range is 200 40 J m−2 s−0.5 K−1. Furthermore,
we identify a trend of increasing thermal inertia with decreasing asteroid
diameter, D. This indicates that the dependence of the drift rate of the
orbital semimajor axis on the size of asteroids due to the Yarkovsky effect is
a more complex function than the generally adopted D^(−1) dependence, and
that the size distribution of objects injected by Yarkovsky-driven orbital
mobility into the NEA source regions is less skewed to smaller sizes than
generally assumed. We discuss how this fact may help to explain the small
difference in the slope of the size distribution of km-sized NEAs and main-belt
asteroids.Comment: Icarus (30/03/2007) in pres
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