2,574 research outputs found
FUSE Measurements of Far Ultraviolet Extinction. I. Galactic Sight Lines
We present extinction curves that include data down to far ultraviolet
wavelengths (FUV; 1050 - 1200 A) for nine Galactic sight lines. The FUV
extinction was measured using data from the Far Ultraviolet Spectroscopic
Explorer. The sight lines were chosen for their unusual extinction properties
in the infrared through the ultraviolet; that they probe a wide range of dust
environments is evidenced by the large spread in their measured ratios of
total-to-selective extinction, R_V = 2.43 - 3.81. We find that extrapolation of
the Fitzpatrick & Massa relationship from the ultraviolet appears to be a good
predictor of the FUV extinction behavior. We find that predictions of the FUV
extinction based upon the Cardelli, Clayton & Mathis (CCM) dependence on R_V
give mixed results. For the seven extinction curves well represented by CCM in
the infrared through ultraviolet, the FUV extinction is well predicted in three
sight lines, over-predicted in two sight lines, and under-predicted in 2 sight
lines. A Maximum Entropy Method analysis using a simple three component grain
model shows that seven of the nine sight lines in the study require a larger
fraction of grain materials to be in dust when FUV extinction is included in
the models. Most of the added grain material is in the form of small (radii <
200 A) grains.Comment: Accepted for publication in the Astrophysical Journal. 31 pages with
7 figure
The Role of Polycyclic Aromatic Hydrocarbons in Ultraviolet Extinction. I. Probing small molecular PAHs
We have obtained new STIS/HST spectra to search for structure in the
ultraviolet interstellar extinction curve, with particular emphasis on a search
for absorption features produced by polycyclic aromatic hydrocarbons (PAHs).
The presence of these molecules in the interstellar medium has been postulated
to explain the infrared emission features seen in the 3-13 m spectra of
numerous sources. UV spectra are uniquely capable of identifying specific PAH
molecules. We obtained high S/N UV spectra of stars which are significantly
more reddened than those observed in previous studies. These data put limits on
the role of small (30-50 carbon atoms) PAHs in UV extinction and call for
further observations to probe the role of larger PAHs. PAHs are of importance
because of their ubiquity and high abundance inferred from the infrared data
and also because they may link the molecular and dust phases of the
interstellar medium. A presence or absence of ultraviolet absorption bands due
to PAHs could be a definitive test of this hypothesis. We should be able to
detect a 20 \AA wide feature down to a 3 limit of 0.02 A. No
such absorption features are seen other than the well-known 2175 \AA bump.Comment: 16 pages, 3 figure, ApJ in pres
Using drones to detect and quantify wild pig damage and yield loss in corn fields throughout plant growth stages
Presently, there are an estimated 6.9 million wild pigs (Sus scrofa) in the U.S., which cause over US17.18â48.24 per ha of damage. Drone imagery, when combined with spatiallyexplicit, harvest yield data, provides an accurate assessment of crop damage and yield loss due to wild pigs in the currency required for the costâbenefit evaluation of management actions
Accounting for heterogeneous invasion rates reveals management impacts on the spatial expansion of an invasive species
Success of large-scale control programs for established invasive species is challenging to evaluate because of spatial variability in expansion rates, management techniques, and the strength of management intensity. For a well-established invasive species in the spreading phase of invasion, a useful metric of impact is the magnitude by which control slows the rate of spatial spread. The prevention of spatial spreading likely results in substantial benefits in terms of ecosystem or economic damage that is prevented by an expanding invasive species. To understand how local management actions could impact the spatial spread of an established invasive species, we analyzed distribution and management data for feral swine across contiguous United States using occupancy analysis. We quantified changes in the rate of spatial expansion of feral swine and its relationship to local management actions. We found that after 4 yr of enhanced control, invasion probability decreased by 8% on average relative to pre-program rates. This decrease was as high as 15% on average in states with low-density populations of feral swine. The amount of decrease in invasion rate was attributed to removal intensity in neighboring counties and depended on the extent of neighboring counties with feral swine (spatial heterogeneity in local invasion pressure). Although we did not find a significant overall increase in the probability of elimination, increased elimination probability tended to occur in regions with low invasion pressure. Accounting for spatial heterogeneity in invasion pressure was important for quantifying management impacts (i.e., the relationship between management intensity and spatial spreading processes) because management impacts changed depending on the strength of invasion pressure from neighboring counties. Predicting reduction in spatial spread of an invasive species is an important first step in valuation of overall damage reduction for invasive species control programs by providing estimates of where a species may be, and thus which natural and agricultural resources would be affected, if the control program had not been operating. For minimizing losses from spatial expansion of an invasive species, our framework can be used for adaptive resource prioritization to areas where spatial expansion and underlying damage potential are concurrently highest
Accounting for heterogeneous invasion rates reveals management impacts on the spatial expansion of an invasive species
Success of large-scale control programs for established invasive species is challenging to evaluate because of spatial variability in expansion rates, management techniques, and the strength of management intensity. For a well-established invasive species in the spreading phase of invasion, a useful metric of impact is the magnitude by which control slows the rate of spatial spread. The prevention of spatial spreading likely results in substantial benefits in terms of ecosystem or economic damage that is prevented by an expanding invasive species. To understand how local management actions could impact the spatial spread of an established invasive species, we analyzed distribution and management data for feral swine across contiguous United States using occupancy analysis. We quantified changes in the rate of spatial expansion of feral swine and its relationship to local management actions. We found that after 4 yr of enhanced control, invasion probability decreased by 8% on average relative to pre-program rates. This decrease was as high as 15% on average in states with low-density populations of feral swine. The amount of decrease in invasion rate was attributed to removal intensity in neighboring counties and depended on the extent of neighboring counties with feral swine (spatial heterogeneity in local invasion pressure). Although we did not find a significant overall increase in the probability of elimination, increased elimination probability tended to occur in regions with low invasion pressure. Accounting for spatial heterogeneity in invasion pressure was important for quantifying management impacts (i.e., the relationship between management intensity and spatial spreading processes) because management impacts changed depending on the strength of invasion pressure from neighboring counties. Predicting reduction in spatial spread of an invasive species is an important first step in valuation of overall damage reduction for invasive species control programs by providing estimates of where a species may be, and thus which natural and agricultural resources would be affected, if the control program had not been operating. For minimizing losses from spatial expansion of an invasive species, our framework can be used for adaptive resource prioritization to areas where spatial expansion and underlying damage potential are concurrently highest
Linking goniometer measurements to hyperspectral and multi-sensor imagery for retrieval of beach properties and coastal characterization
In June 2011, a multi-sensor airborne remote sensing campaign was flown at the Virginia Coast Reserve Long Term Ecological Research site with coordinated ground and water calibration and validation (cal/val) measurements. Remote sensing imagery acquired during the ten day exercise included hyperspectral imagery (CASI-1500), topographic LiDAR, and thermal infra-red imagery, all simultaneously from the same aircraft. Airborne synthetic aperture radar (SAR) data acquisition for a smaller subset of sites occurred in September 2011 (VCR\u2711). Focus areas for VCR\u2711 were properties of beaches and tidal flats and barrier island vegetation and, in the water column, shallow water bathymetry. On land, cal/val emphasized tidal flat and beach grain size distributions, density, moisture content, and other geotechnical properties such as shear and bearing strength (dynamic deflection modulus), which were related to hyperspectral BRDF measurements taken with the new NRL Goniometer for Outdoor Portable Hyperspectral Earth Reflectance (GOPHER). This builds on our earlier work at this site in 2007 related to beach properties and shallow water bathymetry. A priority for VCR\u2711 was to collect and model relationships between hyperspectral imagery, acquired from the aircraft at a variety of different phase angles, and geotechnical properties of beaches and tidal flats. One aspect of this effort was a demonstration that sand density differences are observable and consistent in reflectance spectra from GOPHER data, in CASI hyperspectral imagery, as well as in hyperspectral goniometer measurements conducted in our laboratory after VCR\u2711
Measurement of the total neutron scattering cross section ratios of noble gases of natural isotopic composition using a pulsed neutron beam
Precision measurements of slow neutron cross sections with atoms have several
scientific applications. In particular the n-He s-wave scattering length
is important to know both for helping to constrain the nuclear three-body
interaction and for the proper interpretation of several ongoing slow neutron
experiments searching for other types of neutron-atom interactions. We present
new measurements of the ratios of the neutron differential scattering cross
sections for natural isotopic-abundance mixtures of the noble gases He, Ar, Kr,
and Xe to natural isotopic abundance Ne. These measurements were performed
using a recently developed neutron scattering apparatus for gas samples located
on a pulsed slow neutron beamline which was designed to search for possible
exotic neutron-atom interactions and employs both neutron time of flight
information and a position-sensitive neutron detector for scattering event
reconstruction. We found agreement with the literature values of scattering
cross sections inferred from Ar/Ne, Kr/Ne and Xe/Ne differential cross section
ratios over the range of nm. However for the case of He/Ne
we find that the cross section inferred differs by 11.3% (7.6 ) from
previously-reported values inferred from neutron phase shift measurements, but
is in reasonable agreement with values from other measurements. The very large
discrepancy in the He/Ne ratio calls for a new precision measurement of the
n-He scattering length using neutron interferometry
Cold-induced mortality of invasive Burmese pythons in south Florida
Abstract A recent record cold spell in southern Florida (2-11 January 2010) provided an opportunity to evaluate responses of an established population of Burmese pythons (Python molurus bivittatus) to a prolonged period of unusually cold weather. We observed behavior, characterized thermal biology, determined fate of radio-telemetered (n = 10) and non-telemetered (n = 104) Burmese pythons, and analyzed habitat and environmental conditions experienced by pythons during and after a historic cold spell. Telemetered pythons had been implanted with radio-transmitters and temperature-recording data loggers prior to the cold snap. Only one of 10 telemetered pythons survived the cold snap, whereas 59 of 99 (60%) non-telemetered pythons for which we determined fate survived. Body temperatures of eight dead telemetered pythons fluctuated regularly prior to 9 January 2010, then declined substantially during the cold period (9-11 January) and exhibited no further evidence of active thermoregulation indicating they were likely dead. Unusually cold temperatures in January 2010 were clearly associated with mortality of Burmese pythons in the Everglades. Some radiotelemetered pythons appeared to exhibit maladaptive behavior during the cold spell, including attempting to bask instead of retreating to sheltered refugia. We discuss implications of our findings for persistence and spread of introduced Burmese pythons in the United States and for maximizing their rate of removal
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