1,995 research outputs found
The Inuence of Misspecified Covariance on False Discovery Control when Using Posterior Probabilities
This paper focuses on the influence of a misspecified covariance structure on
false discovery rate for the large scale multiple testing problem.
Specifically, we evaluate the influence on the marginal distribution of local
fdr statistics, which are used in many multiple testing procedures and related
to Bayesian posterior probabilities. Explicit forms of the marginal
distributions under both correctly specified and incorrectly specified models
are derived. The Kullback-Leibler divergence is used to quantify the influence
caused by a misspecification. Several numerical examples are provided to
illustrate the influence. A real spatio-temporal data on soil humidity is
discussed.Comment: 22 pages, 5 figure
Social Roles, Interactions and Community Sustainability in Social Q&A Sites: A Resource-based Perspective
Online tech support communities have become valuable channels for users to seek and provide solutions to specific problems. From the resource exchange perspective, the sustainability of a social system is contingent upon the size of its members as well as their communication activities. To further extend the resource-based model, the current research identifies a variety of social roles in a large tech support Q&A forum and examines longitudinal changes in the community’s structure based on the identification. Moreover, this study also investigates the relationship between the community’s functionality and its traffic. Results suggest that the proportion of unsolved questions negatively impacts the number of future incoming questions and the outcome of a given question is not only dependent on users’ interactions within the discussion, but also on the community activities preceding the question. These observations can help community managers to improve system design and task allocation
The Apparently Decaying Orbit of WASP-12
We present new transit and occultation times for the hot Jupiter WASP-12b.
The data are compatible with a constant period derivative:
ms yr and Myr. However, it is difficult to tell whether
we have observed orbital decay, or a portion of a 14-year apsidal precession
cycle. If interpreted as decay, the star's tidal quality parameter is
about . If interpreted as precession, the planet's Love number is
. Orbital decay appears to be the more parsimonious model: it is
favored by despite having two fewer free parameters than the
precession model. The decay model implies that WASP-12 was discovered within
the final 0.2% of its existence, which is an unlikely coincidence but
harmonizes with independent evidence that the planet is nearing disruption.
Precession does not invoke any temporal coincidence, but does require some
mechanism to maintain an eccentricity of 0.002 in the face of rapid
tidal circularization. To distinguish unequivocally between decay and
precession will probably require a few more years of monitoring. Particularly
helpful will be occultation timing in 2019 and thereafter.Comment: 10 pages [AAS journals, in press, note added in proof
AESTRA: Deep Learning for Precise Radial Velocity Estimation in the Presence of Stellar Activity
Stellar activity interferes with precise radial velocity measurements and
limits our ability to detect and characterize planets, particularly Earth-like
planets. We introduce \aestra (Auto-Encoding STellar Radial-velocity and
Activity), a deep learning method for precise radial velocity measurements. It
combines a spectrum auto-encoder, which learns to create realistic models of
the star's rest-frame spectrum, and a radial-velocity estimator, which learns
to identify true Doppler shifts in the presence of spurious shifts due to
line-profile variations. Being self-supervised, \aestra does not need "ground
truth" radial velocities for training, making it applicable to exoplanet host
stars for which the truth is unknown. In tests involving 1,000 simulated
spectra, \aestra can detect planetary signals as low as 0.1 m/s even in the
presence of 3 m/s of activity-induced noise and 0.3 m/s of photon noise per
spectrum.Comment: 14 pages, 12 figures. Accepted for publication in The Astronomical
Journa
iCurate: A Research Data Management System
Scientific research activities generate a large amount of data, which varies in format, volume, structure and ownership. Although there are revision control systems and databases developed for data archiving, the traditional data management methods are not suitable for High Performance Computing (HPC) systems. The files in such systems do not have semantic annotations and cannot be archived and managed for public dissemination.
We have proposed and developed a Research Data Management (RDM)system, iCurate', which provides easy-to-use RDM facilities with semantic annotations. The system incorporates Metadata Retrieval, Departmental Archiving, Workflow Management System, Meta data Validation and Self Inferencing. The `i' emphasises the user-oriented design. iCurate will support researchers by annotating their data in a clearer and machine readable way from its production to publication for the future reus
Bottom-up Photonic Crystal Lasers
The directed growth of III–V nanopillars is used to demonstrate bottom-up photonic crystal lasers. Simultaneous formation of both the photonic band gap and active gain region is achieved via catalyst-free selective-area metal–organic chemical vapor deposition on masked GaAs substrates. The nanopillars implement a GaAs/InGaAs/GaAs axial double heterostructure for accurate, arbitrary placement of gain within the cavity and lateral InGaP shells to reduce surface recombination. The lasers operate single-mode at room temperature with low threshold peak power density of ~625 W/cm^2. Cavity resonance and lasing wavelength is lithographically defined by controlling pillar pitch and diameter to vary from 960 to 989 nm. We envision this bottom-up approach to pillar-based devices as a new platform for photonic systems integration
THE STELLAR OBLIQUITY, PLANET MASS, AND VERY LOW ALBEDO OF QATAR-2 FROM K2 PHOTOMETRY
The Qatar-2 transiting exoplanet system was recently observed by the {\it
Kepler} telescope as part of {\it K2} Campaign 6. The photometric time series
has one-minute time sampling and a precision of about 690~ppm, after filtering
out artifacts and spurious trends. We identify dozens of starspot-crossing
events, when the planet eclipsed a relatively dark region of the stellar
photosphere. The observed patterns in the sequence of these events demonstrate
that the planet always transits over the same range of stellar latitudes, and
therefore that the stellar obliquity is less than about 10. We support
this conclusion with two different modeling approaches: one based on explicit
identification and timing of the events, and the other based on fitting the
light curves with a spotted-star model. We are also able to refine the usual
transit parameters and measure the stellar rotation period (~days), corresponding to a 'gyrochronological' age of Gyr.
Coherent flux variations with the same period as the transits are seen
throughout the entire light curve. These variations are well modeled as the
combined effects of ellipsoidal light variations (~ppm) and
Doppler boosting (~ppm). The magnitudes of these effects are both
consistent with a planetary mass of , which is in
turn consistent with the mass determined by the Doppler technique. No
occultations are detected, giving a 2 upper limit of on the
planet's visual geometric albedo. The measured transit times are consistent
with a constant orbital period. In particular we find no evidence for orbital
decay, although we are only able to place a weak lower bound on the relevant
tidal quality factor: ~(95\% confidence).Comment: 13 pages, 8 figures, 6 tables. Accepted to A
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