391 research outputs found
Needs and challenges in model testing of wave and tidal energy device
Evaluation of the viability of wave and tidal energy converters represent the main challenge for marine energy developers and government agencies. Although the concept of wave energy conversion is very intuitive, its performance evaluation is complicated by different factors including evaluation of efficiency, components performance and maintenance costs. These factors do not scale up directly from lab experiments. Testing at 1/100 or smaller ratios cannot resolve critical details or satisfy required dynamic similarities. Full-scale testing is expensive. Additionally, varying the designs may not be an option. This implies a need for testing at larger scales. In controlled tests at 1/50 or larger scales, WEC responses can be determined to the point where they can be scaled up and modes of failure can be assessed. This presentation discusses dynamic similarity, scaling laws and how these can be applied to wave and tidal energy devices. Test methodologies, standards and specialized instrumentation, understanding and interpretation of results will also be discussed. The presentation is based on knowledge gained from tests conducted on numerous scale model hull forms and marine platforms in the towing/wave tank of the Davidson Laboratory that have resulted in military full-scale prototypes and commercial systems.
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accelerating wrf i/o performance with adios2 and network-based streaming
With the approach of Exascale computing power for large-scale High
Performance Computing (HPC) clusters, the gap between compute capabilities and
storage systems is growing larger. This is particularly problematic for the
Weather Research and Forecasting Model (WRF), a widely-used HPC application for
high-resolution forecasting and research that produces sizable datasets,
especially when analyzing transient weather phenomena. Despite this issue, the
I/O modules within WRF have not been updated in the past ten years, resulting
in subpar parallel I/O performance.
This research paper demonstrates the positive impact of integrating ADIOS2, a
next-generation parallel I/O framework, as a new I/O backend option in WRF. It
goes into detail about the challenges encountered during the integration
process and how they were addressed. The resulting I/O times show an over
tenfold improvement when using ADIOS2 compared to traditional MPI-I/O based
solutions. Furthermore, the study highlights the new features available to WRF
users worldwide, such as the Sustainable Staging Transport (SST) enabling
Unified Communication X (UCX) DataTransport, the node-local burst buffer write
capabilities and in-line lossless compression capabilities of ADIOS2.
Additionally, the research shows how ADIOS2's in-situ analysis capabilities
can be smoothly integrated with a simple WRF forecasting pipeline, resulting in
a significant improvement in overall time to solution. This study serves as a
reminder to legacy HPC applications that incorporating modern libraries and
tools can lead to considerable performance enhancements with minimal changes to
the core application.Comment: arXiv admin note: text overlap with arXiv:2201.0822
Observing Exoplanets with High-Dispersion Coronagraphy. II. Demonstration of an Active Single-Mode Fiber Injection Unit
High-dispersion coronagraphy (HDC) optimally combines high contrast imaging
techniques such as adaptive optics/wavefront control plus coronagraphy to high
spectral resolution spectroscopy. HDC is a critical pathway towards fully
characterizing exoplanet atmospheres across a broad range of masses from giant
gaseous planets down to Earth-like planets. In addition to determining the
molecular composition of exoplanet atmospheres, HDC also enables Doppler
mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as
precise measurements of exoplanet rotational velocities. Here, we demonstrate
an innovative concept for injecting the directly-imaged planet light into a
single-mode fiber, linking a high-contrast adaptively-corrected coronagraph to
a high-resolution spectrograph (diffraction-limited or not). Our laboratory
demonstration includes three key milestones: close-to-theoretical injection
efficiency, accurate pointing and tracking, on-fiber coherent modulation and
speckle nulling of spurious starlight signal coupling into the fiber. Using the
extreme modal selectivity of single-mode fibers, we also demonstrated speckle
suppression gains that outperform conventional image-based speckle nulling by
at least two orders of magnitude.Comment: 10 pages, 7 figures, accepted by Ap
Ultracool Subdwarfs: The Halo Population Down to the Substellar Limit
Ultracool subdwarfs are low luminosity, late-type M and L dwarfs that exhibit
spectroscopic indications of subsolar metallicity and halo kinematics. Their
recent discovery and ongoing investigation have led to new insights into the
role of metallicity in the opacity structure, chemistry (e.g. dust formation)
and evolution of low-temperature atmospheres; the long-term evolution of
magnetic activity and angular momentum amongst the lowest-mass stars; the form
of the halo luminosity and mass functions down to the hydrogen-burning mass
limit; and even fundamental issues such as spectral classification and absolute
brightness scales. This Splinter Session was devoted to bringing advances in
observational and theoretical ultracool subdwarf research to the attention of
the low-mass stellar and brown dwarf communities, as well as to share results
among ultracool subdwarf enthusiasts.Comment: 8 pages, 5 figures, Splinter Session contribution for Cool Stars 15
(AIP formatting
Direct Imaging in Reflected Light: Characterization of Older, Temperate Exoplanets With 30-m Telescopes
Direct detection, also known as direct imaging, is a method for discovering
and characterizing the atmospheres of planets at intermediate and wide
separations. It is the only means of obtaining spectra of non-transiting
exoplanets. Characterizing the atmospheres of planets in the <5 AU regime,
where RV surveys have revealed an abundance of other worlds, requires a
30-m-class aperture in combination with an advanced adaptive optics system,
coronagraph, and suite of spectrometers and imagers - this concept underlies
planned instruments for both TMT (the Planetary Systems Imager, or PSI) and the
GMT (GMagAO-X). These instruments could provide astrometry, photometry, and
spectroscopy of an unprecedented sample of rocky planets, ice giants, and gas
giants. For the first time habitable zone exoplanets will become accessible to
direct imaging, and these instruments have the potential to detect and
characterize the innermost regions of nearby M-dwarf planetary systems in
reflected light. High-resolution spectroscopy will not only illuminate the
physics and chemistry of exo-atmospheres, but may also probe rocky, temperate
worlds for signs of life in the form of atmospheric biomarkers (combinations of
water, oxygen and other molecular species). By completing the census of
non-transiting worlds at a range of separations from their host stars, these
instruments will provide the final pieces to the puzzle of planetary
demographics. This whitepaper explores the science goals of direct imaging on
30-m telescopes and the technology development needed to achieve them.Comment: (March 2018) Submitted to the Exoplanet Science Strategy committee of
the NA
Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey
The Canada-France High-z Quasar Survey (CFHQS) is an optical survey designed
to locate quasars during the epoch of reionization. In this paper we present
the discovery of the first four CFHQS quasars at redshift greater than 6,
including the most distant known quasar, CFHQS J2329-0301 at z=6.43. We
describe the observational method used to identify the quasars and present
optical, infrared, and millimeter photometry and optical and near-infrared
spectroscopy. We investigate the dust properties of these quasars finding an
unusual dust extinction curve for one quasar and a high far-infrared luminosity
due to dust emission for another. The mean millimeter continuum flux for CFHQS
quasars is substantially lower than that for SDSS quasars at the same redshift,
likely due to a correlation with quasar UV luminosity. For two quasars with
sufficiently high signal-to-noise optical spectra, we use the spectra to
investigate the ionization state of hydrogen at z>5. For CFHQS J1509-1749 at
z=6.12, we find significant evolution (beyond a simple extrapolation of lower
redshift data) in the Gunn-Peterson optical depth at z>5.4. The line-of-sight
to this quasar has one of the highest known optical depths at z~5.8. An
analysis of the sizes of the highly-ionized near-zones in the spectra of two
quasars at z=6.12 and z=6.43 suggest the IGM surrounding these quasars was
substantially ionized before these quasars turned on. Together, these
observations point towards an extended reionization process, but we caution
that cosmic variance is still a major limitation in z>6 quasar observations.Comment: 15 pages, 9 figures, AJ, in press, minor changes to previous versio
BEAST detection of a brown dwarf and a low-mass stellar companion around the young bright B star HIP 81208
Recent observations from B-star Exoplanet Abundance Study (BEAST) have
illustrated the existence of sub-stellar companions around very massive stars.
In this paper, we present the detection of two lower mass companions to a
relatively nearby ( pc), young ( Myr),
bright (V= mag), B9V star HIP 81208
residing in the Sco-Cen association, using the Spectro-Polarimetric
High-contrast Exoplanet REsearch (SPHERE) instrument at the Very Large
Telescope (VLT) in Chile. Analysis of the photometry obtained gives mass
estimates of for the inner companion and
for the outer companion, indicating the
former to be most likely a brown dwarf and the latter to be a low-mass star.
The system is compact but unusual, as the orbital planes of the two companions
are likely close to orthogonal. The preliminary orbital solutions we derived
for the system indicate that the star and the two companions are likely in a
Kozai resonance, rendering the system dynamically very interesting for future
studies.Comment: 18 pages, 14 figures, 5 tables Accepted for publication in the 10.
Planets and planetary systems section of A&
The Planetary Systems Imager: 2-5 Micron Channel
We summarize the red channel (2-5 micron) of the Planetary Systems Imager
(PSI), a proposed second-generation instrument for the TMT. Cold exoplanets
emit the majority of their light in the thermal infrared, which means these
exoplanets can be detected at a more modest contrast than at other wavelengths.
PSI-Red will be able to detect and characterize a wide variety of exoplanets,
including radial-velocity planets on wide orbits, accreting protoplanets in
nearby star-forming regions, and reflected-light planets around the nearest
stars. PSI-Red will feature an imager, a low-resolution lenslet integral field
spectrograph, a medium-resolution lenslet+slicer integral field spectrograph,
and a fiber-fed high-resolution spectrograph.Comment: 7 pages, 5 figure
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