366 research outputs found
A Ī-Convergence Analysis of the Quasicontinuum Method
We present a Ī-convergence analysis of the quasicontinuum method focused on the behavior of the approximate energy functionals in the continuum limit of a harmonic and defect-free crystal. The analysis shows that, under general conditions of stability and boundedness of the energy, the continuum limit is attained provided that the continuum---e.g., finite-element---approximation spaces are strongly dense in an appropriate topology and provided that the lattice size converges to zero more rapidly than the mesh size. The equicoercivity of the quasicontinuum energy functionals is likewise established with broad generality, which, in conjunction with Ī-convergence, ensures the convergence of the minimizers. We also show under rather general conditions that, for interatomic energies having a clusterwise additive structure, summation or quadrature rules that suitably approximate the local element energies do not affect the continuum limit. Finally, we propose a discrete patch test that provides a practical means of assessing the convergence of quasicontinuum approximations. We demonstrate the utility of the discrete patch test by means of selected examples of application
A comparative study of WASP-67b and HAT-P-38b from WFC3 data
Atmospheric temperature and planetary gravity are thought to be the main
parameters affecting cloud formation in giant exoplanet atmospheres. Recent
attempts to understand cloud formation have explored wide regions of the
equilibrium temperature-gravity parameter space. In this study, we instead
compare the case of two giant planets with nearly identical equilibrium
temperature ( ) and gravity (. During Cycle 23, we collected WFC3/G141
observations of the two planets, WASP-67 b and HAT-P-38 b. HAT-P-38 b, with
mass 0.42 M and radius 1.4 , exhibits a relatively
clear atmosphere with a clear detection of water. We refine the orbital period
of this planet with new observations, obtaining . WASP-67 b, with mass 0.27 M and radius 0.83
, shows a more muted water absorption feature than that of
HAT-P-38 b, indicating either a higher cloud deck in the atmosphere or a more
metal-rich composition. The difference in the spectra supports the hypothesis
that giant exoplanet atmospheres carry traces of their formation history.
Future observations in the visible and mid-infrared are needed to probe the
aerosol properties and constrain the evolutionary scenario of these planets.Comment: 16 pages, 17 figures, 8 tables, accepted for publication in The
Astronomical Journa
Two Novel Susceptibility Loci for Prostate Cancer in Men of African Ancestry
Prostate cancer incidence is 1.6-fold higher in African Americans than in other populations. The risk factors that drive this disparity are unknown and potentially consist of social, environmental, and genetic influences. To investigate the genetic basis of prostate cancer in men of African ancestry, we performed a genome-wide association meta-analysis using two-sided statistical tests in 10 202 case subjects and 10 810 control subjects. We identified novel signals on chromosomes 13q34 and 22q12, with the risk-associated alleles found only in men of African ancestry (13q34: rs75823044, risk allele frequency = 2.2%, odds ratio [OR] = 1.55, 95% confidence interval [CI] = 1.37 to 1.76, P = 6.10 Ć 10ā12; 22q12.1: rs78554043, risk allele frequency = 1.5%, OR = 1.62, 95% CI = 1.39 to 1.89, P = 7.50 Ć 10ā10). At 13q34, the signal is located 5ā of the gene IRS2 and 3ā of a long noncoding RNA, while at 22q12 the candidate functional allele is a missense variant in the CHEK2 gene. These findings provide further support for the role of ancestry-specific germline variation in contributing to population differences in prostate cancer risk
TOI-216b and TOI-216 c: Two Warm, Large Exoplanets in or Slightly Wide of the 2:1 Orbital Resonance
Warm, large exoplanets with 10-100 day orbital periods pose a major challenge to our understanding of how planetary systems form and evolve. Although high eccentricity tidal migration has been invoked to explain their proximity to their host stars, a handful reside in or near orbital resonance with nearby planets, suggesting a gentler history of in situ formation or disk migration. Here we confirm and characterize a pair of warm, large exoplanets discovered by the TESS Mission orbiting K-dwarf TOI-216. Our analysis includes additional transits and transit exclusion windows observed via ground-based follow-up. We find two families of solutions, one corresponding to a sub-Saturn-mass planet accompanied by a Neptune-mass planet and the other to a Jupiter in resonance with a sub-Saturn-mass planet. We prefer the second solution based on the orbital period ratio, the planet radii, the lower free eccentricities, and libration of the 2:1 resonant argument, but cannot rule out the first. The free eccentricities and mutual inclination are compatible with stirring by other, undetected planets in the system, particularly for the second solution. We discuss prospects for better constraints on the planets' properties and orbits through follow-up, including transits observed from the ground.We gratefully acknowledge support by NASA XRP NNX16AB50G and NASA TESS GO 80NSSC18K1695. The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium. T.D. acknowledges support from MITās Kavli Institute as a Kavli postdoctoral fellow. K.H. acknowledges support from STFC grant ST/R000824/1. M.Ž. acknowledges funding from the Australian Research Council (grant DP170102233). This research was supported in part by the National Science Foundation under Grant No. NSF PHY-1748958
Vetting of 384 TESS Objects of Interest with TRICERATOPS and Statistical Validation of 12 Planet Candidates
We present TRICERATOPS, a new Bayesian tool that can be used to vet and
validate TESS Objects of Interest (TOIs). We test the tool on 68 TOIs that have
been previously confirmed as planets or rejected as astrophysical false
positives. By looking in the false positive probability (FPP) -- nearby false
positive probability (NFPP) plane, we define criteria that TOIs must meet to be
classified as validated planets (FPP < 0.015 and NFPP < 10^-3), likely planets
(FPP 10^-1).
We apply this procedure on 384 unclassified TOIs and statistically validate 12,
classify 125 as likely planets, and classify 52 as likely nearby false
positives. Of the 12 statistically validated planets, 9 are newly validated.
TRICERATOPS is currently the only TESS vetting and validation tool that models
transits from nearby contaminant stars in addition to the target star. We
therefore encourage use of this tool to prioritize follow-up observations that
confirm bona fide planets and identify false positives originating from nearby
stars.Comment: Accepted to A
Validating AU Microscopii d with Transit Timing Variations
AU Mic is a young (22 Myr) nearby exoplanetary system that exhibits excess
TTVs that cannot be accounted for by the two known transiting planets nor
stellar activity. We present the statistical "validation" of the tentative
planet AU Mic d (even though there are examples of "confirmed" planets with
ambiguous orbital periods). We add 18 new transits and nine midpoint times in
an updated TTV analysis to prior work. We perform the joint modeling of transit
light curves using EXOFASTv2 and extract the transit midpoint times. Next, we
construct an O-C diagram and use Exo-Striker to model the TTVs. We generate TTV
log-likelihood periodograms to explore possible solutions for the period of
planet d and then follow those up with detailed TTV and RV MCMC modeling and
stability tests. We find several candidate periods for AU Mic d, all of which
are near resonances with AU Mic b and c of varying order. Based on our model
comparisons, the most-favored orbital period of AU Mic d is 12.73596+/-0.00793
days (T_{C,d}=2458340.55781+/-0.11641 BJD), which puts the three planets near a
4:6:9 mean-motion orbital resonance. The mass for d is 1.053+/-0.511 M_E,
making this planet Earth-like in mass. If confirmed, AU Mic d would be the
first known Earth-mass planet orbiting a young star and would provide a
valuable opportunity in probing a young terrestrial planet's atmosphere.
Additional TTV observation of the AU Mic system are needed to further constrain
the planetary masses, search for possible transits of AU Mic d, and detect
possible additional planets beyond AU Mic c.Comment: 89 pages, 35 figures, 34 tables. Redid EXOFASTv2 transit modeling to
recover more reasonable stellar posteriors, so redid Exo-Striker TTV modeling
for consistency. Despite these changes, the overall results remain unchanged:
the 12-7-day case is still the most favored. Submitted to AAS Journals on
2023 Feb 9t
Validating AU Microscopii d with Transit Timing Variations
AU Mic is a young (22 Myr), nearby exoplanetary system that exhibits excess transit timing variations (TTVs) that cannot be accounted for by the two known transiting planets nor stellar activity. We present the statistical āvalidationā of the tentative planet AU Mic d (even though there are examples of āconfirmedā planets with ambiguous orbital periods). We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using EXOFASTv2 and extract the transit midpoint times. Next, we construct an O ā C diagram and use Exo-Striker to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for dās period, then follow those up with detailed TTV and radial velocity Markov Chain Monte Carlo modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73596 Ā± 0.00793 days ( T _C _,d = 2458340.55781 Ā± 0.11641 BJD), which puts the three planets near 4:6:9 mean-motion resonance. The mass for d is 1.053 Ā± 0.511 M _ā , making this planet Earth-like in mass. If confirmed, AU Mic d would be the first known Earth-mass planet orbiting a young star and would provide a valuable opportunity in probing a young terrestrial planetās atmosphere. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c
Investigation of Dyslexia and SLI Risk Variants in Reading- and Language-Impaired Subjects
Dyslexia (or reading disability) and specific language impairment (or SLI) are common childhood disorders that show considerable co-morbidity and diagnostic overlaps and have been suggested to share some genetic aetiology. Recently, genetic risk variants have been identified for SLI and dyslexia enabling the direct evaluation of possible shared genetic influences between these disorders. In this study we investigate the role of variants in these genes (namely MRPL19/C20RF3,ROBO1,DCDC2, KIAA0319, DYX1C1, CNTNAP2, ATP2C2 and CMIP) in the aetiology of SLI and dyslexia. We perform caseācontrol and quantitative association analyses using measures of oral and written language skills in samples of SLI and dyslexic families and cases. We replicate association between KIAA0319 and DCDC2 and dyslexia and provide evidence to support a role for KIAA0319 in oral language ability. In addition, we find association between reading-related measures and variants in CNTNAP2 and CMIP in the SLI families
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