379 research outputs found
SOME TESTS TO ESTABLISH CONFIDENCE IN PLANETS DISCOVERED BY TRANSIT PHOTOMETRY
Increased attention is being paid to transit photometry as a viable method for discovering or confirming detections of extrasolar planets. Several ground-based efforts are underway that target short-period, giant planets such as 51 Peg b, and several missions have been proposed to NASA and ESA to detect planets as small as Earth from spaceborne photometers. The success of these efforts depends in part on the ability to establish appropriate detection thresholds to control false alarm rates and the ability to assess the statistical confidence in planetary candidates drawn from any such search. This latter function attains higher importance for the space-based efforts, where direct ground-based confirmation of terrestrial-size planets is not possible. These tasks are complicated by the need to survey tens of thousands of stars to overcome the limited geometric probability of transit alignment and by the nature of the transit signals themselves. In this paper, we present empirical methods for setting appropriate detection thresholds and for establishing the confidence level in planetary candidates obtained from transit photometry of even a large number of stars. The methods are simple and allow the observer to quickly assess the statistical significance of any particular set of transits
Social Marketing–Enhanced Home Energy Education Encourages Adoption of Energy-Saving Practices
We developed a program centered on a social marketing–enhanced home energy education visit to encourage homeowner adoption of specific energy conservation measures. We randomly assigned 170 homeowners to an experimental condition that included energy education before an energy audit or a control condition that included only an energy audit. Participants in the experimental condition adopted more no-cost and low-cost one-time energy conservation changes, such as adjusting refrigerator/freezer temperatures and lowering hot water temperature. However, they did not invest more in home energy renovations or other costly changes, such as replacing inefficient appliances. We discuss implications of this experiment for enhancing effectiveness of Extension-based energy education programs
The Kepler Pixel Response Function
Kepler seeks to detect sequences of transits of Earth-size exoplanets
orbiting Solar-like stars. Such transit signals are on the order of 100 ppm.
The high photometric precision demanded by Kepler requires detailed knowledge
of how the Kepler pixels respond to starlight during a nominal observation.
This information is provided by the Kepler pixel response function (PRF),
defined as the composite of Kepler's optical point spread function, integrated
spacecraft pointing jitter during a nominal cadence and other systematic
effects. To provide sub-pixel resolution, the PRF is represented as a
piecewise-continuous polynomial on a sub-pixel mesh. This continuous
representation allows the prediction of a star's flux value on any pixel given
the star's pixel position. The advantages and difficulties of this polynomial
representation are discussed, including characterization of spatial variation
in the PRF and the smoothing of discontinuities between sub-pixel polynomial
patches. On-orbit super-resolution measurements of the PRF across the Kepler
field of view are described. Two uses of the PRF are presented: the selection
of pixels for each star that maximizes the photometric signal to noise ratio
for that star, and PRF-fitted centroids which provide robust and accurate
stellar positions on the CCD, primarily used for attitude and plate scale
tracking. Good knowledge of the PRF has been a critical component for the
successful collection of high-precision photometry by Kepler.Comment: 10 pages, 5 figures, accepted by ApJ Letters. Version accepted for
publication
Photometric Variability in Kepler Target Stars: The Sun Among Stars -- A First Look
The Kepler mission provides an exciting opportunity to study the lightcurves
of stars with unprecedented precision and continuity of coverage. This is the
first look at a large sample of stars with photometric data of a quality that
has heretofore been only available for our Sun. It provides the first
opportunity to compare the irradiance variations of our Sun to a large cohort
of stars ranging from vary similar to rather different stellar properties, at a
wide variety of ages. Although Kepler data is in an early phase of maturity,
and we only analyze the first month of coverage, it is sufficient to garner the
first meaningful measurements of our Sun's variability in the context of a
large cohort of main sequence stars in the solar neighborhood. We find that
nearly half of the full sample is more active than the active Sun, although
most of them are not more than twice as active. The active fraction is closer
to a third for the stars most similar to the Sun, and rises to well more than
half for stars cooler than mid K spectral types.Comment: 13 pages, 4 figures, accepted to ApJ Letter
TESS Data Release Notes: Sector 18 DR25
This release note discusses the science data products produced by the Science Processing Operations Center at Ames Research Center from Sector 18 observations made with the TESS spacecraft and cameras as a means to document instrument performance and data characteristics
TESS Data Release Notes: Sector 17, DR24
This release note discusses the science data products produced by the Science Processing Operations Center at Ames Research Center from Sector 17 observations made with the TESS spacecraft and cameras as a means to document instrument performance and data characteristics
Efficient and Scalable Generation of Human Ventral Midbrain Astrocytes from Human-Induced Pluripotent Stem Cells
In Parkinson's disease, progressive dysfunction and degeneration of dopamine neurons in the ventral midbrain cause life-changing symptoms. Neuronal degeneration has diverse causes in Parkinson's, including non-cell autonomous mechanisms mediated by astrocytes. Throughout the CNS, astrocytes are essential for neuronal survival and function, as they maintain metabolic homeostasis in the neural environment. Astrocytes interact with the immune cells of the CNS, microglia, to modulate neuroinflammation, which is observed from the earliest stages of Parkinson's, and has a direct impact on the progression of its pathology. In diseases with a chronic neuroinflammatory element, including Parkinson's, astrocytes acquire a neurotoxic phenotype, and thus enhance neurodegeneration. Consequently, astrocytes are a potential therapeutic target to slow or halt disease, but this will require a deeper understanding of their properties and roles in Parkinson's. Accurate models of human ventral midbrain astrocytes for in vitro study are therefore urgently required. We have developed a protocol to generate high purity cultures of ventral midbrain-specific astrocytes (vmAstros) from hiPSCs that can be used for Parkinson's research. vmAstros can be routinely produced from multiple hiPSC lines, and express specific astrocytic and ventral midbrain markers. This protocol is scalable, and thus suitable for high-throughput applications, including for drug screening. Crucially, the hiPSC derived-vmAstros demonstrate immunomodulatory characteristics typical of their in vivo counterparts, enabling mechanistic studies of neuroinflammatory signaling in Parkinson's
Single-peak and narrow-band mid-infrared thermal emitters driven by mirror-coupled plasmonic quasi-BIC metasurfaces
Wavelength-selective thermal emitters (WS-EMs) hold considerable appeal due
to the scarcity of cost-effective, narrow-band sources in the mid-to-long-wave
infrared spectrum. WS-EMs achieved via dielectric materials typically exhibit
thermal emission peaks with high quality factors (Q factors), but their optical
responses are prone to temperature fluctuations. Metallic EMs, on the other
hand, show negligible drifts with temperature changes, but their Q factors
usually hover around 10. In this study, we introduce and experimentally verify
a novel EM grounded in plasmonic quasi-bound states in the continuum (BICs)
within a mirror-coupled system. Our design numerically delivers an
ultra-narrowband single peak with a Q factor of approximately 64, and
near-unity absorptance that can be freely tuned within an expansive band of
more than 10 {\mu}m. By introducing air slots symmetrically, the Q factor can
be further augmented to around 100. Multipolar analysis and phase diagrams are
presented to elucidate the operational principle. Importantly, our infrared
spectral measurements affirm the remarkable resilience of our designs'
resonance frequency in the face of temperature fluctuations over 300 degrees
Celsius. Additionally, we develop an effective impedance model based on the
optical nanoantenna theory to understand how further tuning of the emission
properties is achieved through precise engineering of the slot. This research
thus heralds the potential of applying plasmonic quasi-BICs in designing
ultra-narrowband, temperature-stable thermal emitters in mid-infrared.
Moreover, such a concept may be adaptable to other frequency ranges, such as
near-infrared, Terahertz, and Gigahertz.Comment: 39 pages, 12 figure
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