168 research outputs found
Deriving offshore tidal datums using satellite altimetry around Malaysian seas
Tidal datums are important for calculating spatial coordinates especially the elevation relative to mean sea level and also crucial for defining the state sovereignty boundaries over maritime areas. Normally, sea level was measured by tide gauges along the coastal for tidal datums computation. However, knowledge of tides is still restricted in coastal areas. Furthermore, tidal range at offshore was simply assumed to be similar as coastal due to the difficulties installing offshore tide gauges. The launching of satellite altimeter technologies with precise orbit determination since 1993 had provided significant accuracy of sea surface height (SSH) measurements. The observed SSH from satellite altimetry can be offered as tide gauge measurements at each location globally. This study aims to derive offshore tidal datums using satellite altimetry around Malaysian seas. SSH time series from TOPEX, Jason-1, Jason-2 and Geosat Follow On (GFO) were analysed using harmonic analysis approach to estimate harmonic constants. A minimum of 19 years tidal predictions were then performed using UTide software to determine Lowest Astronomical Tide (LAT) and Highest Astronomical Tide (HAT). These tidal datums were interpolated into regular 0.125 grids and were assessed with ten selected coastal tide gauges. The findings showed the Root Mean Square Error (RMSE) of spline interpolation yielded better accuracy, 25.5 cm (LATMSL) and 17.4 cm (HATMSL) as compared to the RMSE of Kriging interpolation, 31.8 cm (LATMSL) and 33.8 cm (HATMSL). In conclusion, deriving offshore tidal datums can serve as input data to unify marine database with coastal areas and also can support many marine applications
The GALFA-HI Compact Cloud Catalog
We present a catalog of 1964 isolated, compact neutral hydrogen clouds from
the Galactic Arecibo L-Band Feed Array Survey Data Release One (GALFA-HI DR1).
The clouds were identified by a custom machine-vision algorithm utilizing
Difference of Gaussian kernels to search for clouds smaller than 20'. The
clouds have velocities typically between |VLSR| = 20-400 km/s, linewidths of
2.5-35 km/s, and column densities ranging from 1 - 35 x 10^18 cm^-2. The
distances to the clouds in this catalog may cover several orders of magnitude,
so the masses may range from less than a Solar mass for clouds within the
Galactic disc, to greater than 10^4 Solar Masses for HVCs at the tip of the
Magellanic Stream. To search for trends, we separate the catalog into five
populations based on position, velocity, and linewidth: high velocity clouds
(HVCs); galaxy candidates; cold low velocity clouds (LVCs); warm, low
positive-velocity clouds in the third Galactic Quadrant; and the remaining warm
LVCs. The observed HVCs are found to be associated with previously-identified
HVC complexes. We do not observe a large population of isolated clouds at high
velocities as some models predict. We see evidence for distinct histories at
low velocities in detecting populations of clouds corotating with the Galactic
disc and a set of clouds that is not corotating.Comment: 34 Pages, 9 Figures, published in ApJ (2012, ApJ, 758, 44), this
version has the corrected fluxes and corresponding flux histogram and masse
Charge-coupled devices detectors with high quantum efficiency at UV wavelengths
We report on multilayer high efficiency antireflection coating (ARC) design and development for use at UV wavelengths on CCDs and other Si-based detectors. We have previously demonstrated a set of single-layer coatings, which achieve >50% quantum efficiency (QE) in four bands from 130 to 300 nm. We now present multilayer coating designs that significantly outperform our previous work between 195 and 215 nm. Using up to 11 layers, we present several model designs to reach QE above 80%. We also demonstrate the successful performance of 5 and 11 layer ARCs on silicon and fused silica substrates. Finally, we present a five-layer coating deposited onto a thinned, delta-doped CCD and demonstrate external QE greater than 60% between 202 and 208 nm, with a peak of 67.6% at 206 nm
Probing the Halo From the Solar Vicinity to the Outer Galaxy: Connecting Stars in Local Velocity Structures to Large-Scale Clouds
(Abridged) This paper presents the first connections made between two local
features in velocity-space found in a survey of M giant stars and stellar
spatial inhomogeneities on global scales. Comparison to cosmological,
chemodynamical stellar halo models confirm that the M giant population is
particularly sensitive to rare, recent and massive accretion events. These
events can give rise to local observed velocity sequences - a signature of a
small fraction of debris from a common progenitor, passing at high velocity
through the survey volume, near the pericenters of their eccentric orbits. The
majority of the debris is found in much larger structures, whose morphologies
are more cloud-like than stream-like and which lie at the orbital apocenters.
Adopting this interpretation, the full-space motions represented by the
observed velocity features are derived under the assumption that the members
within each sequence share a common velocity. Orbit integrations are then used
to trace the past and future trajectories of these stars across the sky
revealing plausible associations with large, previously-discovered, cloud-like
structures. The connections made between nearby velocity structures and these
distant clouds represent preliminary steps towards developing coherent maps of
such giant debris systems. These maps promise to provide new insights into the
origin of debris clouds, new probes of Galactic history and structure, and new
constraints on the high-velocity tails of the local dark matter distribution
that are essential for interpreting direct detection experiments.Comment: submitted to the Astrophysical Journal, 40 pages, 13 figure
Aphasic seizures in patients with temporopolar and anterior temporobasal lesions: a video-EEG study
Studies of patients with temporal lobe epilepsy provide few descriptions of seizures that arise in the temporopolar and the anterior temporobasal brain region. Based on connectivity, it might be assumed that the semiology of these seizures is similar to that of medial temporal lobe epilepsy. However, accumulating evidence suggests that the anterior temporobasal cortex may play an important role in the language system, which could account for particular features of seizures arising here. We studied the electroclinical features of seizures in patients with circumscribed temporopolar and temporobasal lesions in order to identify specific features that might differentiate them from seizures that originate in other temporal areas. Among 172 patients with temporal lobe seizures registered in our epilepsy unit in the last 15 years, 15 (8.7%) patients had seizures caused by temporopolar or anterior temporobasal lesions (11 left-sided lesions). The main finding in our study is that patients with left-sided lesions had aphasia during their seizures as the most prominent feature. In addition, while all patients showed normal to high intellectual functioning in standard neuropsychological testing, semantic impairment was found in a subset of 9 patients with left-sided lesions. This case series demonstrates that aphasic seizures without impairment of consciousness can result from small, circumscribed left anterior temporobasal and temporopolar lesions. Thus, the presence of speech manifestation during seizures should prompt detailed assessment of the structural integrity of the basal surface of the temporal lobe in addition to the evaluation of primary language areas
Charge-coupled devices detectors with high quantum efficiency at UV wavelengths
We report on multilayer high efficiency antireflection coating (ARC) design and development for use at UV wavelengths on CCDs and other Si-based detectors. We have previously demonstrated a set of single-layer coatings, which achieve >50% quantum efficiency (QE) in four bands from 130 to 300 nm. We now present multilayer coating designs that significantly outperform our previous work between 195 and 215 nm. Using up to 11 layers, we present several model designs to reach QE above 80%. We also demonstrate the successful performance of 5 and 11 layer ARCs on silicon and fused silica substrates. Finally, we present a five-layer coating deposited onto a thinned, delta-doped CCD and demonstrate external QE greater than 60% between 202 and 208 nm, with a peak of 67.6% at 206 nm
Searches After Gravitational-waves Using ARizona Observatories (SAGUARO): System Overview and First Results from Advanced LIGO/Virgo's Third Observing Run
We present Searches After Gravitational-waves Using ARizona Observatories
(SAGUARO), a comprehensive effort dedicated to the discovery and
characterization of optical counterparts to gravitational wave (GW) events.
SAGUARO utilizes ground-based facilities ranging from 1.5m to 10m in diameter,
located primarily in the Northern Hemisphere. We provide an overview of
SAGUARO's telescopic resources, pipeline for transient detection, and database
for candidate visualization. We describe SAGUARO's discovery component, which
utilizes the ~deg field-of-view optical imager on the Mt. Lemmon 1.5m
telescope, reaching limits of ~AB mag while rapidly tiling large
areas. We also describe the follow-up component of SAGUARO, used for rapid
vetting and monitoring of optical candidates. With the onset of Advanced
LIGO/Virgo's third observing run, we present results from the first three
SAGUARO searches following the GW events S190408an, S190425z and S190426c,
which serve as a valuable proof-of-concept of SAGUARO. We triggered and
searched 15, 60 and 60 deg respectively, 17.6, 1.4 and 41.8 hrs after the
initial GW alerts. We covered 7.8, 3.0 and 5.1\% of the total probability
within the GW event localizations, reaching 3 limits of 19.8, 21.3 and
20.8 AB mag, respectively. Although no viable counterparts associated with
these events were found, we recovered 6 known transients and ruled out 5
potential candidates. We also present Large Binocular Telescope spectroscopy of
PS19eq/SN2019ebq, a promising kilonova candidate that was later determined to
be a supernova. With the ability to tile large areas and conduct detailed
follow-up, SAGUARO represents a significant addition to GW counterpart
searches.Comment: 16 pages, 7 figures, 1 table. Accepted to ApJ
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