544 research outputs found
Inner Planetary System Gap Complexity is a Predictor of Outer Giant Planets
The connection between inner small planets and outer giant planets is crucial
to our understanding of planet formation across a wide range of orbital
separations. While Kepler provided a plethora of compact multi-planet systems
at short separations ( AU), relatively little is known about the
occurrence of giant companions at larger separations and how they impact the
architectures of the inner systems. Here, we use the catalog of systems from
the Kepler Giant Planet Search (KGPS) to study how the architectures of the
inner transiting planets correlate with the presence of outer giant planets. We
find that for systems with at least three small transiting planets, the
distribution of inner-system gap complexity (), a measure of the
deviation from uniform spacings, appears to differ () between
those with an outer giant planet () and those without any outer giants. All four inner systems (with 3+
transiting planets) with outer giant(s) have a higher gap complexity
() than 79% (19/24) of the inner systems without any outer
giants (median ). This suggests that one can predict
the occurrence of outer giant companions by selecting multi-transiting systems
with highly irregular spacings. We do not find any correlation between outer
giant occurrence and the size (similarity or ordering) patterns of the inner
planets. The larger gap complexities of inner systems with an outer giant hints
that massive external planets play an important role in the formation and/or
disruption of the inner systems.Comment: Published in AJ. 16 pages, 6 figures, 1 tabl
Debiasing the Minimum-Mass Extrasolar Nebula: On the Diversity of Solid Disk Profiles
A foundational idea in the theory of in situ planet formation is the "minimum
mass extrasolar nebula" (MMEN), a surface density profile () of disk
solids that is necessary to form the planets in their present locations. While
most previous studies have fit a single power-law to all exoplanets in an
observed ensemble, it is unclear whether most exoplanetary systems form from a
universal disk template. We use an advanced statistical model for the
underlying architectures of multi-planet systems to reconstruct the MMEN. The
simulated physical and Kepler-observed catalogs allows us to directly assess
the role of detection biases, and in particular the effect of non-transiting or
otherwise undetected planets, in altering the inferred MMEN. We find that
fitting a power-law of the form to each
multi-planet system results in a broad distribution of disk profiles;
g/cm and
encompass the 16th-84th percentiles of the marginal distributions in an
underlying population, where is the normalization at
AU. Around half of inner planet-forming disks have minimum solid masses of
within 1 AU. While transit observations do not tend to
bias the median , they can lead to both significantly over- and
under-estimated and thus broaden the inferred distribution of disk
masses. Nevertheless, detection biases cannot account for the full variance in
the observed disk profiles; there is no universal MMEN if all planets formed in
situ. The great diversity of solid disk profiles suggests that a substantial
fraction () of planetary systems experienced a history of
migration.Comment: Accepted to AJ. 14 pages, 6 figures, 1 table. Accompanying code is
available via SysSimPyMMEN, a pip-installable Python package (see
https://syssimpymmen.readthedocs.io/en/latest/
Beyond 2-D Mass-Radius Relationships: A Nonparametric and Probabilistic Framework for Characterizing Planetary Samples in Higher Dimensions
Fundamental to our understanding of planetary bulk compositions is the
relationship between their masses and radii, two properties that are often not
simultaneously known for most exoplanets. However, while many previous studies
have modeled the two-dimensional relationship between planetary mass and radii,
this approach largely ignores the dependencies on other properties that may
have influenced the formation and evolution of the planets. In this work, we
extend the existing nonparametric and probabilistic framework of \texttt{MRExo}
to jointly model distributions beyond two dimensions. Our updated framework can
now simultaneously model up to four observables, while also incorporating
asymmetric measurement uncertainties and upper limits in the data. We showcase
the potential of this multi-dimensional approach to three science cases: (i) a
4-dimensional joint fit to planetary mass, radius, insolation, and stellar
mass, hinting of changes in planetary bulk density across insolation and
stellar mass; (ii) a 3-dimensional fit to the California Kepler Survey sample
showing how the planet radius valley evolves across different stellar masses;
and (iii) a 2-dimensional fit to a sample of Class-II protoplanetary disks in
Lupus while incorporating the upper-limits in dust mass measurements. In
addition, we employ bootstrap and Monte-Carlo sampling to quantify the impact
of the finite sample size as well as measurement uncertainties on the predicted
quantities. We update our existing open-source user-friendly \texttt{MRExo}
\texttt{Python} package with these changes, which allows users to apply this
highly flexible framework to a variety of datasets beyond what we have shown
here.Comment: Accepted in ApJ. Updated MRExo package and sample scripts available
here: https://github.com/shbhuk/mrexo/tree/v1.0dev. Package will be released
on PyPI (pip) along with full documentation upon publication in Ap
Developing a Drift Rate Distribution for Technosignature Searches of Exoplanets
A stable-frequency transmitter with relative radial acceleration to a
receiver will show a change in received frequency over time, known as a "drift
rate''. For a transmission from an exoplanet, we must account for multiple
components of drift rate: the exoplanet's orbit and rotation, the Earth's orbit
and rotation, and other contributions. Understanding the drift rate
distribution produced by exoplanets relative to Earth, can a) help us constrain
the range of drift rates to check in a Search for Extraterrestrial Intelligence
(SETI) project to detect radio technosignatures and b) help us decide validity
of signals-of-interest, as we can compare drifting signals with expected drift
rates from the target star. In this paper, we modeled the drift rate
distribution for 5300 confirmed exoplanets, using parameters from the
NASA Exoplanet Archive (NEA). We find that confirmed exoplanets have drift
rates such that 99\% of them fall within the 53 nHz range. This implies a
distribution-informed maximum drift rate 4 times lower than previous
work. To mitigate the observational biases inherent in the NEA, we also
simulated an exoplanet population built to reduce these biases. The results
suggest that, for a Kepler-like target star without known exoplanets, 0.44
nHz would be sufficient to account for 99\% of signals. This reduction in
recommended maximum drift rate is partially due to inclination effects and bias
towards short orbital periods in the NEA. These narrowed drift rate maxima will
increase the efficiency of searches and save significant computational effort
in future radio technosignature searches.Comment: 15 pages, 8 figure
Treatment of hyperphosphatemia in hemodialysis patients: The Calcium Acetate Renagel Evaluation (CARE Study)
Treatment of hyperphosphatemia in hemodialysis patients: The Calcium Acetate Renagel Evaluation (CARE Study).BackgroundHyperphosphatemia underlies development of hyperparathyroidism, osteodystrophy, extraosseous calcification, and is associated with increased mortality in hemodialysis patients.MethodsTo determine whether calcium acetate or sevelamer hydrochloride best achieves recently recommended treatment goals of phosphorus ≤5.5mg/dL and Ca × P product ≤55mg2/dL2, we conducted an 8-week randomized, double-blind study in 100 hemodialysis patients.ResultsComparisons of time-averaged concentrations (weeks 1 to 8) demonstrated that calcium acetate recipients had lower serum phosphorus (1.08mg/dL difference, P = 0.0006), higher serum calcium (0.63mg/dL difference, P < 0.0001), and lower Ca × P (6.1mg2/dL2 difference, P = 0.022) than sevelamer recipients. At each week, calcium acetate recipients were 20% to 24% more likely to attain goal phosphorus [odds ratio (OR) 2.37, 95% CI 1.28–4.37, P = 0.0058], and 15% to 20% more likely to attain goal Ca × P (OR 2.16, 95% CI 1.20–3.86, P = 0.0097). Transient hypercalcemia occurred in 8 of 48 (16.7%) calcium acetate recipients, all of whom received concomitant intravenous vitamin D. By regression analysis hypercalcemia was more likely with calcium acetate (OR 6.1, 95% CI 2.8–13.3, P < 0.0001). Week 8 intact PTH levels were not significantly different. Serum bicarbonate levels were significantly lower with sevelamer hydrochloride treatment (P < 0.0001).ConclusionCalcium acetate controls serum phosphorus and calcium-phosphate product more effectively than sevelamer hydrochloride. Cost-benefit analysis indicates that in the absence of hypercalcemia, calcium acetate should remain the treatment of choice for hyperphosphatemia in hemodialysis patients
Thermopower and thermal conductivity of superconducting perovskite
The thermopower and thermal conductivity of superconducting perovskite
( 8 K) have been studied. The thermopower is negative
from room temperature to 10 K. Combining with the negative Hall coefficient
reported previously, the negative thermopower definetly indicates that the
carrier in is electron-type. The nonlinear temperature dependence of
thermopower below 150 K is explained by the electron-phonon interaction
renormalization effects. The thermal conductivity is of the order for
intermetallics, larger than that of borocarbides and smaller than . In
the normal state, the electronic contribution to the total thermal conductivity
is slightly larger than the lattice contribution. The transverse
magnetoresistance of is also measured. It is found that the classical
Kohler's rule is valid above 50 K. An electronic crossover occures at , resulting in the abnormal behavior of resistivity, thermopower, and
magnetoresistance below 50 K.Comment: Revised on 12 September 2001, Phys. Rev. B in pres
Lattice symmetry breaking in cuprate superconductors: Stripes, nematics, and superconductivity
This article will give an overview on both theoretical and experimental
developments concerning states with lattice symmetry breaking in the cuprate
high-temperature superconductors. Recent experiments have provided evidence for
states with broken rotation as well as translation symmetry, and will be
discussed in terms of nematic and stripe physics. Of particular importance here
are results obtained using the techniques of neutron and x-ray scattering and
scanning tunneling spectroscopy. Ideas on the origin of lattice-symmetry-broken
states will be reviewed, and effective models accounting for various
experimentally observed phenomena will be summarized. These include both
weak-coupling and strong-coupling approaches, with a discussion on their
distinctions and connections. The collected experimental data indicate that the
tendency toward uni-directional stripe-like ordering is common to underdoped
cuprates, but becomes weaker with increasing number of adjacent CuO_2 layers.Comment: Review article prepared for Adv. Phys., 66 pg, 22 figs. Comments
welcome, (v2) extensions and clarifications, added references, final version
to be publishe
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