4,185 research outputs found
A V-grooved GaAs solar cell
V-grooved GaAs solar cells promise the benefits of improved optical coupling, higher short-circuit current, and increased tolerance to particle radiation compared to planar cells. A GaAs homojunction cell was fabricated by etching a V-groove pattern into an n epilayer (2.1 x 10 to the 17th power per cu cm) grown by metalorganic chemical vapor deposition (MOCVD) on an n+ substrate (2.8 x 10 to the 18th power per cu cm) and then depositing and MOCVD p epilayer (4.2 x 10 to the 18th power per cu cm). Reflectivity measurements on cells with and without an antireflective coating confirm the expected decrease in reluctance of the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell was 13 percent higher than that of the planar control
Peeled film GaAs solar cells for space power
Gallium arsenide (GaAs) peeled film solar cells were fabricated, by Organo-Metallic Vapor Phase Epitaxy (OMVPE), incorporating an aluminum arsenide (AlAs) parting layer between the device structure and the GaAs substrate. This layer was selectively removed by etching in dilute hydrofloric (HF) acid to release the epitaxial film. Test devices exhibit high series resistance due to insufficient back contact area. A new design is presented which uses a coverglass superstrate for structural support and incorporates a coplanar back contact design. Devices based on this design should have a specific power approaching 700 W/Kg
Quantitative uniqueness for elliptic equations with singular lower order terms
We use a Carleman type inequality of Koch and Tataru to obtain quantitative
estimates of unique continuation for solutions of second order elliptic
equations with singular lower order terms. First we prove a three sphere
inequality and then describe two methods of propagation of smallness from sets
of positive measure.Comment: 23 pages, v2 small changes are done and some mistakes are correcte
Meeting Forest Restoration Challenges: Using the Target Plant Concept
Meeting forest restoration challenges relies on successful establishment of plant materials (e.g., seeds, cuttings, rooted cuttings, or seedlings, etc.; hereafter simply “seedlingsâ€). The Target Plant Concept (TPC) provides a flexible framework that nursery managers and their clients can use to improve the survival and growth of these seedlings. The key tenets of the TPC are that (1) more emphasis is placed on how seedlings perform on the outplanting site rather than on nursery performance, (2) a partnership exists between the nursery manager and the client to determine the target plant based on site characteristics, and (3) that information gleaned from post-planting monitoring is used to improve subsequent plant materials. Through the nursery manager–client partnership, answers to a matrix of interrelated questions define a target plant to meet the reforestation or forest restoration objectives. These questions focus on project objectives; site characteristics, limiting factors, and possible mitigation efforts; species and genetic criteria; stocktype; outplanting tools and techniques; and outplanting window. We provide examples from the southeastern United States, Hawai‛i, and Lebanon on how the TPC process has improved performance of seedlings deployed for reforestation and forest restoration
Large-Mass Ultra-Low Noise Germanium Detectors: Performance and Applications in Neutrino and Astroparticle Physics
A new type of radiation detector, a p-type modified electrode germanium
diode, is presented. The prototype displays, for the first time, a combination
of features (mass, energy threshold and background expectation) required for a
measurement of coherent neutrino-nucleus scattering in a nuclear reactor
experiment. The device hybridizes the mass and energy resolution of a
conventional HPGe coaxial gamma spectrometer with the low electronic noise and
threshold of a small x-ray semiconductor detector, also displaying an intrinsic
ability to distinguish multiple from single-site particle interactions. The
present performance of the prototype and possible further improvements are
discussed, as well as other applications for this new type of device in
neutrino and astroparticle physics (double-beta decay, neutrino magnetic moment
and WIMP searches).Comment: submitted to Phys. Rev.
Parent and child agreement for acute stress disorder, post-traumatic stress disorder and other psychopathology in a prospective study of children and adolescents exposed to single-event trauma
Examining parent-child agreement for Acute Stress Disorder (ASD) and Post-Traumatic Stress Disorder (PTSD) in children and adolescents is essential for informing the assessment of trauma-exposed children, yet no studies have examined this relationship using appropriate statistical techniques. Parent-child agreement for these disorders was examined by structured interview in a prospective study of assault and motor vehicle accident (MVA) child survivors, assessed at 2-4 weeks and 6 months post-trauma. Children were significantly more likely to meet criteria for ASD, as well as other ASD and PTSD symptom clusters, based on their own report than on their parent's report. Parent-child agreement for ASD was poor (Cohen's κ = -.04), but fair for PTSD (Cohen's κ = .21). Agreement ranged widely for other emotional disorders (Cohen's κ = -.07-.64), with generalised anxiety disorder found to have superior parent-child agreement (when assessed by phi coefficients) relative to ASD and PTSD. The findings support the need to directly interview children and adolescents, particularly for the early screening of posttraumatic stress, and suggest that other anxiety disorders may have a clearer presentation post-trauma
Al0.52In0.48P 55Fe x-ray-photovoltaic battery
An Al0.52In0.48P 55Fe radioisotope microbattery is demonstrated over the temperature range −20 °C to 160 °C. Al0.52In0.48P p+-i-n+ mesa structures were used to collect the photons from a 238 MBq 55Fe radioisotope x-ray source. The effects of temperature on the key microbattery parameters were studied. Increasing the temperature, the saturation current increased; whilst the open circuit voltage, the maximum power and the conversion efficiency decreased. An open circuit voltage of 0.97V and a conversion efficiency of 22% were measured in a single p+-i-n+ mesa structure at −20 °C. The highest total microbattery maximum output power using two mesa structures was 1.2 pW at −20 °C
SentiBench - a benchmark comparison of state-of-the-practice sentiment analysis methods
In the last few years thousands of scientific papers have investigated
sentiment analysis, several startups that measure opinions on real data have
emerged and a number of innovative products related to this theme have been
developed. There are multiple methods for measuring sentiments, including
lexical-based and supervised machine learning methods. Despite the vast
interest on the theme and wide popularity of some methods, it is unclear which
one is better for identifying the polarity (i.e., positive or negative) of a
message. Accordingly, there is a strong need to conduct a thorough
apple-to-apple comparison of sentiment analysis methods, \textit{as they are
used in practice}, across multiple datasets originated from different data
sources. Such a comparison is key for understanding the potential limitations,
advantages, and disadvantages of popular methods. This article aims at filling
this gap by presenting a benchmark comparison of twenty-four popular sentiment
analysis methods (which we call the state-of-the-practice methods). Our
evaluation is based on a benchmark of eighteen labeled datasets, covering
messages posted on social networks, movie and product reviews, as well as
opinions and comments in news articles. Our results highlight the extent to
which the prediction performance of these methods varies considerably across
datasets. Aiming at boosting the development of this research area, we open the
methods' codes and datasets used in this article, deploying them in a benchmark
system, which provides an open API for accessing and comparing sentence-level
sentiment analysis methods
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