10,788 research outputs found
Carfentrazone-ethyl Pond Dissipation and Efficacy on Floating Plants
Carfentrazone-ethyl (CE) is a reduced risk herbicide that
is currently being evaluated for the control of aquatic weeds.
Greenhouse trials were conducted to determine efficacy of
CE on water hyacinth (
Eichhornia crassipes
(Mart.) Solms-
Laub.), water lettuce (
Pistia stratiotes
L.), salvinia (
Salvinia
minima
Baker) and landoltia
(Landoltia punctata
(G. Mey.)
Les & D. J. Crawford
)
. CE controlled water lettuce, water hyacinth
and salvinia at rates less than the maximum proposed
use rate of 224 g ha
-1
. Water lettuce was the most susceptible
to CE with an EC
90
of 26.9 and 33.0 g ha
-1
in two separate trials.
Water hyacinth EC
90
values were calculated to be 86.2 to
116.3 g ha
-1
, and salvinia had a similar susceptibility to water
hyacinth with an EC
90
of 79.1 g ha
-1
. Landoltia was not adequately
controlled at the rates evaluated. In addition, CE was
applied to one-half of a 0.08 ha pond located in North Central,
Florida to determine dissipation rates in water and hydrosoil
when applied at an equivalent rate of 224 g ha
-1
. The
half-life of CE plus the primary metabolite, CE-chloropropionic
acid, was calculated to be 83.0 h from the whole pond,
and no residues were detected in water above the limit of
quantification (5 ÎŒg L
-1
) 168 h after treatment. CE dissipated
rapidly from the water column, did not occur in the sediment
above the levels of quantification, and in greenhouse
studies effectively controlled three species of aquatic weeds
at relatively low rates.(PDF contains 6 pages.
Torque control system
System stabilizes aximuth of gondolas which are carried by high-altitude balloons as platforms for tracking telescopes. When telescopes must be constantly aimed at specific targets, control system stabilizes gondola to within 5 arc-seconds
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Development and validation of a new glaucoma screening test using temporally modulated flicker
Purpose
Describing the psychometric characteristics and diagnostic accuracy of the Accelerator 4âAlternative ForcedâChoice Flicker Test prototype (A4FTp) for detecting chronic open angle glaucoma (COAG).
Methods
A4FTp measures temporallyâmodulated flicker thresholds in regions of the visual field with high susceptibility to glaucomatous loss. We initially evaluated its psychometric properties on 20 normals (aged 33.8 ± 8.5 years) who were tested multiple times over a period of 3 months. All subjects underwent four repetitions for shorter (T8) and longer (T12) staircase termination criteria, to determine the most suitable threshold criterion. Four randomly selected subjects underwent a total of 10 repetitions to study testâretest repeatability and learning effects. To determine its diagnostic accuracy, one eye of 40 participants with COAG and 38 normal controls were tested with the A4FTp in comparison with the Frequency Doubling Technology (FDT; C20â5 programme) and iVue Spectral Domain Optical Coherence Tomography (SDâOCT). Tests were conducted in a random order with results masked to the clinician conducting the reference ophthalmic examination. The accuracy of each test was determined by analysis of the area under the receiver operator characteristic curve (AUROC).
Results
A4FTp flicker thresholds were stable, with standard deviations of only 0.52 decilog (dL) for T8, increasing to 1.32 dL for T12, and no significant flicker sensitivity threshold improvement over the 10 repeat runs. T8 was superior to T12 on several other measures, so it was used for the remaining comparisons. In terms of diagnostic accuracy, the mean AUROC for the three tests were A4FTp [T8 criterion; 0.82, 95% confidence interval (0.73â0.92)]; SDâOCT [any RNFL parameter p < 1% level; 0.90 (0.83â0.97)]; and FDT [one or more locations missed at p < 5% level; 0.91 (0.82â0.96)]. There was no statistical difference in AUROC between A4FTp and SDâOCT (p = 0.18) or FDT (p = 0.12). The A4FTp test duration averaged just over 2 min per eye, taking approximately oneâthird of the time for completion of the HFA SITA 24â2 algorithm (conducted as part of the reference examination) and twice the time for the suprathreshold FDT.
Conclusion
Test accuracy for the A4FTp was comparable to those of the FDT and SDâOCT for the detection of COAG. Time taken to complete the A4FTp was relatively short and initial results are promising. With further refinement, the A4FTp could have a future role in glaucoma detection
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Computational estimation of scene structure through texture gradient cues
Analyzing the depth structure implied in two-dimensional images is one of the most active research areas in computer vision. Here, we propose a method of utilizing texture within an image to derive its depth structure. Though most approaches for deriving depth from a single still image utilize luminance edges and shading to estimate scene structure, relatively little work has been done to utilize the abundant texture information in images. Our new approach begins by analyzing the two cues of local spatial frequency and orientation distributions of the textures within an image, which are used to compute the local slant information across the image. The slant and frequency information are merged to create a unified depth map, providing an important channel for image structure information that can be combined with other available cues. The capabilities of the algorithm are illustrated for a variety of images of planar and curved surfaces under perspective projection, in most of which the depth structure is effortlessly perceived by human observers. Since these operations are readily implementable in neural hardware in early visual cortex, they therefore represent a model of the human perception of the depth structure of images from texture gradient cues
Earthshine as an Illumination Source at the Moon
Earthshine is the dominant source of natural illumination on the surface of
the Moon during lunar night, and at locations within permanently shadowed
regions that never receive direct sunlight. As such, earthshine may enable the
exploration of areas of the Moon that are hidden from solar illumination. The
heat flux from earthshine may also influence the transport and cold trapping of
volatiles present in the very coldest areas. In this study, Earth's spectral
radiance at the Moon is examined using a suite of Earth spectral models created
using the Virtual Planetary Laboratory (VPL) three dimensional modeling
capability. At the Moon, the broadband, hemispherical irradiance from Earth
near 0 phase is approximately 0.15 watts per square meter, with comparable
contributions from solar reflectance and thermal emission. Over the simulation
timeframe, spanning two lunations, Earth's thermal irradiance changes less than
a few mW per square meter as a result of cloud variability and the
south-to-north motion of sub-observer position. In solar band, Earth's
diurnally averaged light curve at phase angles < 60 degrees is well fit using a
Henyey Greenstein integral phase function. At wavelengths > 0.7 microns, near
the well known vegetation "red edge", Earth's reflected solar radiance shows
significant diurnal modulation as a result of the longitudinal asymmetry in
projected landmass, as well as from the distribution of clouds. A simple
formulation with adjustable coefficients is presented for estimating Earth's
hemispherical irradiance at the Moon as a function of wavelength, phase angle
and sub-observer coordinates. It is demonstrated that earthshine is
sufficiently bright to serve as a natural illumination source for optical
measurements from the lunar surface.Comment: 27 pages, 15 figures, 1 tabl
Numerical Linked-Cluster Algorithms. I. Spin systems on square, triangular, and kagome lattices
We discuss recently introduced numerical linked-cluster (NLC) algorithms that
allow one to obtain temperature-dependent properties of quantum lattice models,
in the thermodynamic limit, from exact diagonalization of finite clusters. We
present studies of thermodynamic observables for spin models on square,
triangular, and kagome lattices. Results for several choices of clusters and
extrapolations methods, that accelerate the convergence of NLC, are presented.
We also include a comparison of NLC results with those obtained from exact
analytical expressions (where available), high-temperature expansions (HTE),
exact diagonalization (ED) of finite periodic systems, and quantum Monte Carlo
simulations.For many models and properties NLC results are substantially more
accurate than HTE and ED.Comment: 14 pages, 16 figures, as publishe
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