1,556 research outputs found
The economic value of remote sensing by satellite: An ERTS overview and the value of continuity of service. Volume 2: Source document
The economic value of an ERS system with a technical capability similar to ERTS, allowing for increased coverage obtained through the use of multiple active satellites in orbit is presented. A detailed breakdown of the benefits achievable from an ERS system is given and a methodology for their estimation is established. The ECON case studies in agriculture, water use, and land cover are described along with the current ERTS system. The cost for a projected ERS system is given
Environmental and anthropogenic features mediate risk from human hunters and wolves for moose
Landscape characteristics, seasonal changes in the environment, and daylight conditions influence space use and detection of prey and predators, resulting in spatiotemporal patterns of predation risk for the prey. When predators have different hunting modes, the combined effects of multiple predators are mediated by the physical landscape and can result in overlapping or contrasting patterns of predation risk. Humans have become super-predators in many anthropogenic landscapes by harvesting game species and competing with large carnivores for prey. Here, we used the locations of wolf (Canis lupus)-killed and hunter-killed moose (Alces alces) in south-central Scandinavia to investigate whether environmental and anthropogenic features influenced where wolves and hunters killed moose. We predicted that the combined effects of wolves and hunters would result in contrasting spatial risk patterns due to differences in hunting modes. We expected these contrasting spatial risk patterns also to differ temporally. During the hunting season, the probability of a wolf kill increased with distance to bogs, whereas it decreased with increasing building density and distance to clearcuts and young forests. After the hunting season, the probability of a wolf kill increased with increasing terrain ruggedness and decreased with increasing building density, distance to main roads, and distance to clearcuts and young forests. The probability of a hunter kill was highest closer to bogs, main and secondary roads, in less rugged terrain and in areas with lower building density. Hunters killed all moose during the day, whereas wolves killed most moose at night during and after the hunting season. Our findings suggest that environmental and anthropogenic features mediate hunting and wolf predation risk. Additionally, we found that hunter- and wolf-killed moose exhibited contrasting spatial associations to landscape features, most likely due to the different hunting modes displayed by hunters and wolves. However, wolf predation and hunting risks also contrasted over time since wolves killed mostly at night and hunters were restricted to hunting during daytime and during the hunting season. This temporal segregation in risk might therefore suggest that moose could minimize risk exposure by taking advantage of spatiotemporally vacant hunting domains
Semiclassical description of multiphoton processes
We analyze strong field atomic dynamics semiclassically, based on a full
time-dependent description with the Hermann-Kluk propagator. From the
properties of the exact classical trajectories, in particular the accumulation
of action in time, the prominent features of above threshold ionization (ATI)
and higher harmonic generation (HHG) are proven to be interference phenomena.
They are reproduced quantitatively in the semiclassical approximation.
Moreover, the behavior of the action of the classical trajectories supports the
so called strong field approximation which has been devised and postulated for
strong field dynamics.Comment: 10 pages, 11 figure
Early Observations and Analysis of the Type 1a SN 2014J in M82
We present optical and near infrared (NIR) observations of the nearby Type Ia SN 2014J. Seventeen optical and 23 NIR spectra were obtained from 10 days before (-10d) to 10 days after (+10d) the time of maximum B-band brightness. The relative strengths of absorption features and their patterns of development can be compared at one day intervals throughout most of this period. Carbon is not detected in the optical spectra, but we identify C I lambda 1.0693 in the NIR spectra. Mg II lines with high oscillator strengths have higher initial velocities than other Mg II lines. We show that the velocity differences can be explained by differences in optical depths due to oscillator strengths. The spectra of SN 2014J show that it is a normal SN Ia, but many parameters are near the boundaries between normal and high-velocity subclasses. The velocities for OI, Mg II, Si II, S Ca a, and Fell suggest that SN 2014J has a layered structure with little or no mixing. That result is consistent with the delayed detonation explosion models. We also report photometric observations, obtained from -10d to +29d, in the UBVRIJH and K-s bands. The template fitting package SNooPy is used to interpret the light curves and to derive photometric parameters. Using R-v = 1.46, which is consistent with previous studies, SNooPy finds that A(v) = 1.80 for E(B - V)(host) = 1.23 +/- 0.06 mag. The maximum B-band brightness of -19.19 +/- 0.10 mag was reached on February 1.74 UT +/- 0.13 days and the supernova has a decline parameter, Delta m(15), of 1.12 +/- 0.02 mag
A Bayesian approach to strong lensing modelling of galaxy clusters
In this paper, we describe a procedure for modelling strong lensing galaxy
clusters with parametric methods, and to rank models quantitatively using the
Bayesian evidence. We use a publicly available Markov chain Monte-Carlo (MCMC)
sampler ('Bayesys'), allowing us to avoid local minima in the likelihood
functions. To illustrate the power of the MCMC technique, we simulate three
clusters of galaxies, each composed of a cluster-scale halo and a set of
perturbing galaxy-scale subhalos. We ray-trace three light beams through each
model to produce a catalogue of multiple images, and then use the MCMC sampler
to recover the model parameters in the three different lensing configurations.
We find that, for typical Hubble Space Telescope (HST)-quality imaging data,
the total mass in the Einstein radius is recovered with ~1-5% error according
to the considered lensing configuration. However, we find that the mass of the
galaxies is strongly degenerated with the cluster mass when no multiple images
appear in the cluster centre. The mass of the galaxies is generally recovered
with a 20% error, largely due to the poorly constrained cut-off radius.
Finally, we describe how to rank models quantitatively using the Bayesian
evidence. We confirm the ability of strong lensing to constrain the mass
profile in the central region of galaxy clusters in this way. Ultimately, such
a method applied to strong lensing clusters with a very large number of
multiple images may provide unique geometrical constraints on cosmology. The
implementation of the MCMC sampler used in this paper has been done within the
framework of the Lenstool software package, which is publicly available.Comment: Accepted to "Gravitational Lensing" Focus Issue of the New Journal of
Physics (invited), 35 pages, 11 figures at reduced resolutio
VIMOS-IFU survey of z~0.2 massive galaxy clusters. I. Observations of the strong lensing cluster Abell 2667
(abridged) We present extensive multi-color imaging and low resolution VIMOS
Integral Field Unit spectroscopic observations of the X-ray luminous cluster
Abell 2667 (z=0.233). An extremely bright giant gravitational arc (z=1.0334) is
easily identified as part of a triple image system and other fainter multiple
images are also revealed by the HST-WFPC2 images. The VIMOS-IFU observations
cover a field of view of 54'' x 54'' and enable us to determine the redshift of
all galaxies down to V=22.5. Furthermore, redshifts could be identified for
some sources down to V=23.2. In particular we identify 21 cluster members in
the cluster inner region, from which we derive a velocity dispersion of
\sigma=960 km/s, corresponding to a total mass of 7.1 x 10^{13} solar masses
within a 110 kpc radius. Using the multiple images constraints and priors on
the mass distribution of cluster galaxy halos we construct a detailed lensing
mass model leading to a total mass of 2.9 x 10^{13} solar masses within the
Einstein radius (16 arcsec). The lensing mass and dynamical mass are in good
agreement although the dynamical one is much less accurate. Comparing these
measurements with published X-ray analysis, is however less conclusive.
Although the X-ray temperature matches the dynamical and lensing estimates, the
published NFW mass model derived from the X-ray measurement with its small
concentration of c ~3 can not account for the large Einstein radius observed in
this cluster. A larger concentration of ~6 would however match the strong
lensing measurements. These results are likely reflecting the complex structure
of the cluster mass distribution, underlying the importance of panchromatic
studies from small to large scale in order to better understand cluster
physics.Comment: 14 pages, 12 figures. Submitted to A
Species distribution and antimicrobial susceptibility of enterococci isolated from broilers infected experimentally with Eimeria spp and fed with diets containing different supplements
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