1,354 research outputs found
REVENUE RISK AND FISHERY CHOICE WITH LINEAR-EXPONENTIAL UTILITY: AN APPLICATION TO BERING SEA/ALEUTIAN ISLANDS TRAWL FISHERIES
A discrete choice model of 1991-96 trawl groundfish fishery participation in the Bering Sea/Aleutian Islands region is developed and estimated. The model fits well, with strong risk and seasonal effects. Notably, the model uses routinely-collected data, suggesting this type of analysis can be a regular part of the management process.Resource /Energy Economics and Policy,
TOWARD EFFICIENT BYCATCH MANAGEMENT IN MULTISPECIES FISHERIES: A NONPARAMETRIC APPROACH
Linear programming-based models of individual multispecies groundfish operations in the Bering Sea/Aleutian Islands area are developed and applied to the question of determining efficient bycatches. The policy tool is halibut quotas, which restrict the bycatch of halibut and also induce changes in the target species catch composition and bycatch of other prohibited species. Efficient quotas can be interpolated from the locus of shadow values for discrete halibut quotas relative to the opportunity cost of prohibited species bycatch induced by the policy-set quotas on halibut bycatch. Because of information limitations intrinsic to fisheries management, the efficient halibut quotas are considered in the context of ranges of marginal value and marginal opportunity cost developed using short- and long-run groundfish fishery models and standard error estimates of opportunity cost.Resource /Energy Economics and Policy,
High Thermoelectric Figure of Merit by Resonant Dopant in Half-Heusler Alloys
Half-Heusler alloys have been one of the benchmark high temperature
thermoelectric materials owing to their thermal stability and promising figure
of merit ZT. Simonson et al. early showed that small amounts of vanadium doped
in Hf0.75Zr0.25NiSn enhanced the Seebeck coefficient and correlated the change
with the increased density of states near the Fermi level. We herein report a
systematic study on the role of vanadium (V), niobium (Nb), and tantalum (Ta)
as prospective resonant dopants in enhancing the ZT of n-type half-Heusler
alloys based on Hf0.6Zr0.4NiSn0.995Sb0.005. The V doping was found to increase
the Seebeck coefficient in the temperature range 300-1000 K, consistent with a
resonant doping scheme. In contrast, Nb and Ta act as normal n-type dopants, as
evident by the systematic decrease in electrical resistivity and Seebeck
coefficient. The combination of enhanced Seebeck coefficient due to the
presence of V resonant states and the reduced thermal conductivity has led to a
state-of-the-art ZT of 1.3 near 850 K in n-type
(Hf0.6Zr0.4)0.99V0.01NiSn0.995Sb0.005 alloys.Comment: Submitted to AIP Advance
Nature Versus Nurture: Luminous Blue Variable Nebulae in and near Massive Stellar Clusters at the Galactic Center
Three Luminous Blue Variables (LBVs) are located in and near the Quintuplet
Cluster at the Galactic Center: the Pistol star, G0.120-0.048, and qF362. We
present imaging at 19, 25, 31, and 37 {\mu}m of the region containing these
three LBVs, obtained with SOFIA using FORCAST. We argue that the Pistol and
G0.120-0.048 are identical ``twins" that exhibit contrasting nebulae due to the
external influence of their different environments. Our images reveal the
asymmetric, compressed shell of hot dust surrounding the Pistol Star and
provide the first detection of the thermal emission from the symmetric, hot
dust envelope surrounding G0.120-0.048. Dust and gas composing the Pistol
nebula are primarily heated and ionized by the nearby Quintuplet Cluster stars.
The northern region of the Pistol nebula is decelerated due to the interaction
with the high-velocity (2000 km/s) winds from adjacent Wolf-Rayet Carbon (WC)
stars. With the DustEM code we determine that the Pistol nebula is composed of
a distribution of very small, transiently-heated grains (10-~35 {\AA}) and that
it exhibits a gradient of decreasing grain size from the south to the north due
to differential sputtering by the winds from the WC stars. Dust in the
G0.120-0.048 nebula is primarily heated by the central star; however, the
nebular gas is ionized externally by the Arches Cluster. Unlike the Pistol
nebula, the G0.120-0.048 nebula is freely expanding into the surrounding
medium. Given independent dust and gas mass estimates we find that the Pistol
and G0.120-0.048 nebulae exhibit similar gas-to-dust mass ratios of ~310 and
~290, respectively. Both nebulae share identical size scales (~ 0.7 pc) which
suggests that they have similar dynamical timescales of ~10^5 yrs, assuming a
shell expansion velocity of v_exp 60 km/s.Comment: 18 pages, 7 figures, accepted to Ap
Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds
Half-Heusler (HH) alloys have attracted considerable interest as promising
thermoelectric (TE) materials in the temperature range around 700 K and above,
which is close to the temperature range of most industrial waste heat sources.
The past few years have seen nanostructuing play an important role in
significantly enhancing the TE performance of several HH alloys. In this
article, we briefly review the recent progress and advances in these HH
nanocomposites. We begin by presenting the structure of HH alloys and the
different strategies that have been utilized for improving the TE properties of
HH alloys. Next, we review the details of HH nanocomposites as obtained by
different techniques. Finally, the review closes by highlighting several
promising strategies for further research directions in these very promising TE
materials.Comment: 34 pages, 22 figure
Old supernova dust factory revealed at the Galactic center
Dust formation in supernova ejecta is currently the leading candidate to
explain the large quantities of dust observed in the distant, early Universe.
However, it is unclear whether the ejecta-formed dust can survive the hot
interior of the supernova remnant (SNR). We present infrared observations of
~0.02 of warm (~100 K) dust seen near the center of the ~10,000
yr-old Sgr A East SNR at the Galactic center. Our findings signify the
detection of dust within an older SNR that is expanding into a relatively dense
surrounding medium ( ~ 100 ) and has survived the
passage of the reverse shock. The results suggest that supernovae may indeed be
the dominant dust production mechanism in the dense environment of early
Universe galaxies.Comment: 25 pages, 5 figures. Includes supplementary materials. Published
Online March 19 2015 on Science Expres
MULTISPECIES REVENUE FUNCTION ESTIMATION FOR NORTH PACIFIC GROUNDFISH FISHERIES
Multiproduct, multispecies revenue functions are estimated for the midwater and bottom-trawl pollock fisheries off Alaska. There are strong year and seasonal effects on coefficient estimates, and the technology is joint in outputs for each major operation type. The model is a step toward prediction of fishery regulatory effects.Resource /Energy Economics and Policy,
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U.S. Efforts to Prepare Regular Assessments of Overcapacity in Federally-Managed Commercial Fisheries
NOAA’s National Marine Fisheries Service (NMFS) was a key participant in the FAO technical and policy-level consultations of 1991-1999 that led to the FAO International Plan of Action for the Management of Fishing Capacity. The U.S. Plan of Action includes a commitment to prepare regular assessments of overcapacity in federally-managed fisheries. This paper describes recent NMFS efforts to determine and conduct the types of assessments that will be of use to the Regional Fishery Management Councils and NMFS as they continue their efforts to address the problems of overcapacity. Specifically, it discusses a variety of basic lessons learned concerning the assessment and management of fishing capacity and how NMFS plans to use those lessons to conduct the first round of regular assessments of overcapacity in federally-managed commercial fisheries
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