124 research outputs found
Stability of ice/rock mixtures with application to a partially differentiated Titan
Titanâs moment of inertia, calculated assuming hydrostatic equilibrium from gravity field data obtained during the CassiniâHuygens mission, implies an internal mass distribution that may be incompatible with complete differentiation. This suggests that Titan may have a mixed ice/rock core, possibly consistent with slow accretion in a gas-starved disk, which may initially spare Titan from widespread ice melting and subsequent differentiation. A partially differentiated Titan, however, must still efficiently remove radiogenic heat over geologic time. We argue that compositional heterogeneity in the major saturnian satellites indicates that Titan formed from planetesimals with disparate densities. The resulting compositional anomalies would quickly redistribute to form a vertical density gradient that would oppose thermal convection. We use elements of the theory of double-diffusive convection to create a parameterized model for the thermal evolution of ice/rock mixtures with a stabilizing compositional gradient. To account for large uncertainties in material properties and accretionary processes, we perform simulations for a wide range of initial conditions. Ultimately, for realistic density gradients, double-diffusive convection in the ice/rock interior can delay, but not prevent, ice melting and differentiation, even if a substantial fraction of potassium is leached from the rock component. Consequently, Titan is not partially differentiated
Venus: Interpreting the spatial distribution of volcanically modified craters
To understand the impact cratering record on Venus, we investigate two distinct resurfacing styles: localized, thin flows and large shield volcanoes. We statistically analyze the size-frequency distribution of volcanically modified craters and, using Monte Carlo simulations, their spatial distribution. Lava flows partially fill most craters, darkening their floors in radar images. We find that a model featuring localized, thin flows occurring throughout geologic time predicts their observed distribution. Individual flows may be morphologically indistinguishable, but, combined, they cover large provinces. Recent mantle plumes may drive a small amount of hot spot magmatism that produces the observed clusters of large shield volcanoes and obviously embayed craters. Ultimately, our analysis demonstrates that two styles of volcanism are needed to explain the observed properties of impact craters and that catastrophic resurfacing is not required
Atmospheric Characterization of the Hot Jupiter Kepler-13Ab
Kepler-13Ab (= KOI-13.01) is a unique transiting hot Jupiter. It is one of
very few known short-period planets orbiting a hot A-type star, making it one
of the hottest planets currently known. The availability of Kepler data allows
us to measure the planet's occultation (secondary eclipse) and phase curve in
the optical, which we combine with occultations observed by warm Spitzer at 4.5
mic and 3.6 mic and a ground-based occultation observation in the Ks band (2.1
mic). We derive a day-side hemisphere temperature of 2,750 +- 160 K as the
effective temperature of a black body showing the same occultation depths.
Comparing the occultation depths with one-dimensional planetary atmosphere
models suggests the presence of an atmospheric temperature inversion. Our
analysis shows evidence for a relatively high geometric albedo, Ag= 0.33 +0.04
-0.06. While measured with a simplistic method, a high Ag is supported also by
the fact that the one-dimensional atmosphere models underestimate the
occultation depth in the optical. We use stellar spectra to determine the
dilution, in the four wide bands where occultation was measured, due to the
visual stellar binary companion 1.15 +- 0.05" away. The revised stellar
parameters measured using these spectra are combined with other measurements
leading to revised planetary mass and radius estimates of Mp = 4.94 - 8.09 Mjup
and Rp = 1.406 +- 0.038 Rjup. Finally, we measure a Kepler mid-occultation time
that is 34.0 +- 6.9 s earlier than expected based on the mid-transit time and
the delay due to light travel time, and discuss possible scenarios.Comment: V2: Accepted to ApJ on 2014 April 11. Spitzer photometry and model
fitting Matlab pipeline code is publicly available at:
http://gps.caltech.edu/~shporer/spitzerphot
Reduced epithelial suppressor of cytokine signalling 1 in severe eosinophilic asthma
Severe asthma represents a major unmet clinical need. Eosinophilic inflammation persists in the airways of many patients with uncontrolled asthma, despite high-dose inhaled corticosteroid therapy. Suppressors of cytokine signalling (SOCS) are a family of molecules involved in the regulation of cytokine signalling via inhibition of the Janus kinaseâsignal transducers and activators of transcription pathway. We examined SOCS expression in the airways of asthma patients and investigated whether this is associated with persistent eosinophilia.Healthy controls, mild/moderate asthmatics and severe asthmatics were studied. Whole genome expression profiling, quantitative PCR and immunohistochemical analysis were used to examine expression of SOCS1, SOCS2 and SOCS3 in bronchial biopsies. Bronchial epithelial cells were utilised to examine the role of SOCS1 in regulating interleukin (IL)-13 signalling in vitro.SOCS1 gene expression was significantly lower in the airways of severe asthmatics compared with mild/moderate asthmatics, and was inversely associated with airway eosinophilia and other measures of T-helper type 2 (Th2) inflammation. Immunohistochemistry demonstrated SOCS1 was predominantly localised to the bronchial epithelium. SOCS1 overexpression inhibited IL-13-mediated chemokine ligand (CCL) 26 (eotaxin-3) mRNA expression in bronchial epithelial cells.Severe asthma patients with persistent airway eosinophilia and Th2 inflammation have reduced airway epithelial SOCS1 expression. SOCS1 inhibits epithelial IL-13 signalling, supporting its key role in regulating Th2-driven eosinophilia in severe asthma.</jats:p
Warm Spitzer and Palomar Near-IR Secondary Eclipse Photometry of Two Hot Jupiters: WASP-48b and HAT-P-23b
We report secondary eclipse photometry of two hot Jupiters, WASP-48b and HAT-P-23b, at 3.6 and 4.5 ÎŒm taken with the InfraRed Array Camera aboard the Spitzer Space Telescope during the warm Spitzer mission and in the H and K_S bands with the Wide Field IR Camera at the Palomar 200 inch Hale Telescope. WASP-48b and HAT-P-23b are Jupiter-mass and twice Jupiter-mass objects orbiting an old, slightly evolved F star and an early G dwarf star, respectively. In the H, K_S , 3.6 ÎŒm, and 4.5 ÎŒm bands, respectively, we measure secondary eclipse depths of 0.047% ± 0.016%, 0.109% ± 0.027%, 0.176% ± 0.013%, and 0.214% ± 0.020% for WASP-48b. In the K_S , 3.6 ÎŒm, and 4.5 ÎŒm bands, respectively, we measure secondary eclipse depths of 0.234% ± 0.046%, 0.248% ± 0.019%, and 0.309% ± 0.026% for HAT-P-23b. For WASP-48b and HAT-P-23b, respectively, we measure delays of 2.6 ± 3.9 minutes and 4.0 ± 2.4 minutes relative to the predicted times of secondary eclipse for circular orbits, placing 2Ï upper limits on |ecos Ï| of 0.0053 and 0.0080, both of which are consistent with circular orbits. The dayside emission spectra of these planets are well-described by blackbodies with effective temperatures of 2158 ± 100 K (WASP-48b) and 2154 ± 90 K (HAT-P-23b), corresponding to moderate recirculation in the zero albedo case. Our measured eclipse depths are also consistent with one-dimensional radiative transfer models featuring varying degrees of recirculation and weak thermal inversions or no inversions at all. We discuss how the absence of strong temperature inversions on these planets may be related to the activity levels and metallicities of their host stars
The long-term evolution of the atmosphere of Venus: processes and feedback mechanisms
In this chapter, we focus on the long-term evolution of the atmosphere of
Venus, and how it has been affected by interior/exterior cycles. The formation
and evolution of Venus's atmosphere, leading to the present-day surface
conditions, remain hotly debated and involve questions that tie into many
disciplines. Here, we explore the mechanisms that shaped the evolution of the
atmosphere, starting with the volatile sources and sinks. Going from the deep
interior to the top of the atmosphere, we describe fundamental processes such
as volcanic outgassing, surface-atmosphere interactions, and atmosphere escape.
Furthermore, we address more complex aspects of the history of Venus, including
the role of meteoritic impacts, how magnetic field generation is tied into
long-term evolution, and the implications of feedback cycles for atmospheric
evolution. Finally, we highlight three plausible end-member evolutionary
pathways that Venus might have followed, from the accretion to its present-day
state, based on current modeling and observations. In a first scenario, the
planet was desiccated early-on, during the magma ocean phase, by atmospheric
escape. In a second scenario, Venus could have harbored surface liquid water
for long periods of time, until its temperate climate was destabilized and it
entered a runaway greenhouse phase. In a third scenario, Venus's inefficient
outgassing could have kept water inside the planet, where hydrogen was trapped
in the core and the mantle was oxidized. We discuss existing evidence and
future observations/missions needed to refine our understanding of the planet's
history and of the complex feedback cycles between the interior, surface, and
atmosphere that operate in the past, present or future of Venus
Characterization of the Atmosphere of the Hot Jupiter HAT-P-32Ab and the M-dwarf Companion HAT-P-32B
Copyright © 2015 IOP PublishingWe report secondary eclipse photometry of the hot Jupiter HAT-P-32Ab, taken with Hale/Wide-field Infra-Red Camera (WIRC) in H and KS bands and with Spitzer/IRAC at 3.6 and 4.5 Όm. We carried out adaptive optics imaging of the planet host star HAT-P-32A and its companion HAT-P-32B in the near-IR and the visible. We clearly resolve the two stars from each other and find a separation of 2.''923 ± 0.''004 and a position angle 110fdg64 ± 0fdg12. We measure the flux ratios of the binary in g'r'i'z' and H and KS bands, and determine T eff= 3565 ± 82 K for the companion star, corresponding to an M1.5 dwarf. We use PHOENIX stellar atmosphere models to correct the dilution of the secondary eclipse depths of the hot Jupiter due to the presence of the M1.5 companion. We also improve the secondary eclipse photometry by accounting for the non-classical, flux-dependent nonlinearity of the WIRC IR detector in the H band. We measure planet-to-star flux ratios of 0.090% ± 0.033%, 0.178% ± 0.057%, 0.364% ± 0.016%, and 0.438% ± 0.020% in the H, KS , 3.6 and 4.5 Όm bands, respectively. We compare these with planetary atmospheric models, and find they prefer an atmosphere with a temperature inversion and inefficient heat redistribution. However, we also find that the data are equally well described by a blackbody model for the planet with T p = 2042 ± 50 K. Finally, we measure a secondary eclipse timing offset of 0.3 ± 1.3 minutes from the predicted mid-eclipse time, which constrains e = 0.0072 +0.0700}_-0.0064 when combined with radialNASACenter for Exoplanets and Habitable Worlds at the Pennsylvania State UniversityPennsylvania State UniversityEberly College of SciencePennsylvania Space Grant ConsortiumNational Science Foundation - Graduate Research Fellowship ProgramNatural Science and Engineering Research Council of CanadaJPL/SpitzerCalifornia Institute of Technology - NASA Sagan FellowshipAlfred P. Sloan FoundationCalifornia Institute of TechnologyInter-University Centre for Astronomy and AstrophysicsNational Science FoundationMt. Cuba Astronomical FoundationSamuel Oschi
Characterization of the atmosphere of the hot Jupiter HAT-P-32Ab and the M-dwarf companion HAT-P-32B
We report secondary eclipse photometry of the hot Jupiter HAT-P-32Ab, taken
with Hale/WIRC in H and Ks bands and with Spitzer/IRAC at 3.6 and 4.5 micron.
We carried out adaptive optics imaging of the planet host star HAT-P-32A and
its companion HAT-P-32B in the near-IR and the visible. We clearly resolve the
two stars from each other and find a separation of 2.923" +/- 0. 004" and a
position angle 110.64 deg +/- 0.12 deg. We measure the flux ratios of the
binary in g' r' i' z' and H & Ks bands, and determine Teff = 3565 +/- 82 K for
the companion star, corresponding to an M1.5 dwarf. We use PHOENIX stellar
atmosphere models to correct the dilution of the secondary eclipse depths of
the hot Jupiter due to the presence of the M1.5 companion. We also improve the
secondary eclipse photometry by accounting for the non-classical,
flux-dependent nonlinearity of the WIRC IR detector in the H band. We measure
planet-to-star flux ratios of 0.090 +/- 0.033%, 0.178 +/- 0.057%, 0.364 +/-
0.016%, and 0.438 +/- 0.020% in the H, Ks, 3.6 and 4.5 micron bands,
respectively. We compare these with planetary atmospheric models, and find they
prefer an atmosphere with a temperature inversion and inefficient heat
redistribution. However, we also find that the data are equally well-described
by a blackbody model for the planet with Tp = 2042 +/- 50 K. Finally, we
measure a secondary eclipse timing offset of 0.3 +/- 1.3 min from the predicted
mid-eclipse time, which constrains e = 0.0072 +0.0700/-0.0064 when combined
with RV data and is more consistent with a circular orbit.Comment: 16 pages, 12 figures. Accepted for publication in Ap
Volcanic and Tectonic Constraints on the Evolution of Venus
Surface geologic features form a detailed record of Venusâ evolution. Venus displays a profusion of volcanic and tectonics features, including both familiar and exotic forms. One challenge to assessing the role of these features in Venusâ evolution is that there are too few impact craters to permit age dates for specific features or regions. Similarly, without surface water, erosion is limited and cannot be used to evaluate age. These same observations indicate Venus has, on average, a very young surface (150â1000 Ma), with the most recent surface deformation and volcanism largely preserved on the surface except where covered by limited impact ejecta. In contrast, most geologic activity on Mars, the Moon, and Mercury occurred in the 1st billion years. Earthâs geologic processes are almost all a result of plate tectonics. Venusâ lacks such a network of connected, large scale plates, leaving the nature of Venusâ dominant geodynamic process up for debate. In this review article, we describe Venusâ key volcanic and tectonic features, models for their origin, and possible links to evolution. We also present current knowledge of the composition and thickness of the crust, lithospheric thickness, and heat flow given their critical role in shaping surface geology and interior evolution. Given Venusâ hot lithosphere, abundant activity and potential analogues of continents, roll-back subduction, and microplates, it may provide insights into early Earth, prior to the onset of true plate tectonics. We explore similarities and differences between Venus and the Proterozoic or Archean Earth. Finally, we describe the future measurements needed to advance our understanding of volcanism, tectonism, and the evolution of Venus
TRANSFORM (Multicenter Experience With Rapid Deployment Edwards INTUITY Valve System for Aortic Valve Replacement) US clinical trial: Performance of a rapid deployment aortic valve
Background: The TRANSFORM (Multicenter Experience With Rapid Deployment Edwards INTUITY Valve System for Aortic Valve Replacement) trial (NCT01700439) evaluated the performance of the INTUITY rapid deployment aortic valve replacement (RDAVR) system in patients with severe aortic stenosis.
Methods: TRANSFORM was a prospective, nonrandomized, multicenter (n 1Ăąïżœâ4 29), single-arm trial. INTUITY is comprised of a cloth-covered balloon- expandable frame attached to a Carpentier-Edwards PERIMOUNT Magna Ease aortic valve. Primary and effectiveness endpoints were evaluated at 1 year.
Results: Between 2012 and 2015, 839 patients underwent RDAVR. Mean age was 73.5 8.3 years. Full sternotomy (FS) was used in 59% and minimally invasive surgical incisions in 41%. Technical success rate was 95%. For isolated RDAVR, mean crossclamp and cardiopulmonary bypass times for FS were 49.3 26.9 minutes and 69.2 34.7 minutes, respectively, and for minimally invasive surgical 63.1 25.4 minutes and 84.6 33.5 minutes, respectively. These times were favorable compared with Society of Thoracic Surgeons data- base comparators for FS: 76.3 minutes and 104.2 minutes, respectively, and for minimally invasive surgical, 82.9 minutes and 111.4 minutes, respectively (P<.001). At 30 days, all-cause mortality was 0.8%; valve explant, 0.1%; throm- boembolism, 3.5%; and major bleeding, 1.3%. In patients with isolated aortic valve replacement, the rate of permanent pacemaker implantation was 11.9%. At 1 year, mean effective orifice area was 1.7 cm2; mean gradient, 10.3 mm Hg; and moderate and severe paravalvular leak, 1.2% and 0.4%, respectively
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