14,948 research outputs found
On the Marginal Value of a Fish: Some Evidence from a Steelhead Fishery
Policymakers and other interested parties frequently request information on the recreational value of a fish. Although fishing valuation studies date back at least 25 years, most studies focus on the average value of a fish. If the purpose of such estimates is to measure the value of incremental changes in fish numbers, then use of average estimates may lead to an incorrect policy decisions. The objective of this analysis is to estimate the marginal value of a steelhead trout in a recreational fishery on the John Day River of Oregon. The study uses contingent valuation procedures to elicit willingness to pay estimates for improvements in fish numbers and success rates. For the anglers in this survey, the value of an additional steelhead is $6.65 under current catch conditions. This value is much lower than values currently used in public debates in the Pacific Northwest, but similar to some marginal values reported in the recent literature. Implications of these values relative to average values are discussed.Demand and Price Analysis, Environmental Economics and Policy, Research Methods/ Statistical Methods, Resource /Energy Economics and Policy,
Goldstone Gauginos
Models of supersymmetry with Dirac gauginos provide an attractive scenario
for physics beyond the standard model. The "supersoft" radiative corrections
and suppressed SUSY production at colliders provide for more natural theories
and an understanding of why no new states have been seen. Unfortunately, these
models are handicapped by a tachyon which is naturally present in existing
models of Dirac gauginos. We argue that this tachyon is absent, with the
phenomenological successes of the model preserved, if the right handed gaugino
is a (pseudo-)Goldstone field of a spontaneously broken anomalous flavor
symmetry.Comment: 5 pages, 1 figure. v2: minor changes to text, references added and
update
Models of Goldstone Gauginos
Models with Dirac gauginos provide appealing scenarios for physics beyond the
standard model. They have smaller radiative corrections to the Higgs mass, a
suppression of certain SUSY production processes, and ameliorated flavor
constraints. Unfortunately, they also generally have tachyons, the solutions to
which typically spoil these positive features. The recently proposed "Goldstone
Gaugino" mechanism provides a simple solution that eliminates these tachyonic
states. We provide details on this mechanism and explore models for its origin.
In particular, we find SUSY QCD models that realize this idea simply, and
discuss scenarios for unification.Comment: 33 pages, 4 figure
Telluric correction in the near-infrared: Standard star or synthetic transmission?
Context. The atmospheric absorption of the Earth is an important limiting
factor for ground-based spectroscopic observations and the near-infrared and
infrared regions are the most affected. Several software packages that produce
a synthetic atmospheric transmission spectrum have been developed to correct
for the telluric absorption; these are Molecfit, TelFit, and TAPAS. Aims. Our
goal is to compare the correction achieved using these three telluric
correction packages and the division by a telluric standard star. We want to
evaluate the best method to correct near-infrared high-resolution spectra as
well as the limitations of each software package and methodology. Methods. We
applied the telluric correction methods to CRIRES archival data taken in the J
and K bands. We explored how the achieved correction level varies depending on
the atmospheric T-P profile used in the modelling, the depth of the atmospheric
lines, and the molecules creating the absorption. Results. We found that the
Molecfit and TelFit corrections lead to smaller residuals for the water lines.
The standard star method corrects best the oxygen lines. The Molecfit package
and the standard star method corrections result in global offsets always below
0.5% for all lines; the offset is similar with TelFit and TAPAS for the H2O
lines and around 1% for the O2 lines. All methods and software packages result
in a scatter between 3% and 7% inside the telluric lines. The use of a tailored
atmospheric profile for the observatory leads to a scatter two times smaller,
and the correction level improves with lower values of precipitable water
vapour. Conclusions. The synthetic transmission methods lead to an improved
correction compared to the standard star method for the water lines in the J
band with no loss of telescope time, but the oxygen lines were better corrected
by the standard star method.Comment: 18 pages, 13 figures, Accepted to A&
A Neural-Endocrine Architecture for Foraging in Swarm Robotic Systems
Abstract This paper presents the novel use of the Neural-endocrine architecture for swarm robotic systems. We make use of a number of behaviours to give rise to emergent swarm behaviour to allow a swarm of robots to collaborate in the task of foraging. Results show that the architecture is amenable to such a task, with the swarm being able to successfully complete the required task.
Quasi-Periodic Oscillations from Magnetorotational Turbulence
Quasi-periodic oscillations (QPOs) in the X-ray lightcurves of accreting
neutron star and black hole binaries have been widely interpreted as being due
to standing wave modes in accretion disks. These disks are thought to be highly
turbulent due to the magnetorotational instability (MRI). We study wave
excitation by MRI turbulence in the shearing box geometry. We demonstrate that
axisymmetric sound waves and radial epicyclic motions driven by MRI turbulence
give rise to narrow, distinct peaks in the temporal power spectrum. Inertial
waves, on the other hand, do not give rise to distinct peaks which rise
significantly above the continuum noise spectrum set by MRI turbulence, even
when the fluid motions are projected onto the eigenfunctions of the modes. This
is a serious problem for QPO models based on inertial waves.Comment: 4 pages, 2 figures. submitted to ap
Voigt-Profile Analysis of the Lyman-alpha Forest in a Cold Dark Matter Universe
We use an automated Voigt-profile fitting procedure to extract statistical
properties of the Ly forest in a numerical simulation of an ,
cold dark matter (CDM) universe. Our analysis method is similar to that used in
most observational studies of the forest, and we compare the simulations to
recently published results derived from Keck HIRES spectra. With the
Voigt-profile decomposition analysis, the simulation reproduces the large
number of weak lines (N_{\rm HI}\la 10^{13}\cdunits) found in the HIRES
spectra. The column density distribution evolves significantly between
and , with the number of lines at fixed column density dropping by a
factor in the range where line blending is not severe. At , the
-parameter distribution has a median of 35 \kms and a dispersion of 20
\kms, in reasonable agreement with the observed values. The comparison between
our new analysis and recent data strengthens earlier claims that the \lya
forest arises naturally in hierarchical structure formation as photoionized gas
falls into dark matter potential wells. However, there are two statistically
signficant discrepancies between the simulated forest and the HIRES results:
the model produces too many lines at by a factor , and it
produces more narrow lines (b<20 \kms) than are seen in the data. The first
result is sensitive to our adopted normalization of the mean \lya optical
depth, and the second is sensitive to our assumption that helium reionization
has not significantly raised gas temperatures at . It is therefore too
early to say whether these discrepancies indicate a fundamental problem with
the high-redshift structure of the CDM model or reflect errors of
detail in our modeling of the gas distribution or the observational procedure.Comment: 13 pages, 3 figures, AAS LaTex, accepted to Ap
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