23,261 research outputs found
TROPHIC PORTFOLIOS IN MARINE FISHERIES: A STEP TOWARDS ECOSYSTEM MANAGEMENT
Marine ecologists warn that humans are "fishing down marine food webs." To explore the economic implications of this phenomenon, this paper applies portfolio theory to aggregate fisheries data. It poses two definitions of a sustainable mean-variance catch frontier. It computes a mean-variance frontier for catch using UNFAO historical fisheries data. Finally, the paper discusses the historical trend in inefficiency.Environmental Economics and Policy, Resource /Energy Economics and Policy,
Evaluation of Proposed Rocket Engines for Earth-to-Orbit Vehicles
The objective is to evaluate recently analyzed rocket engines for advanced Earth-to-orbit vehicles. The engines evaluated are full-flow staged combustion engines and split expander engines, both at mixture ratios at 6 and above with oxygen and hydrogen propellants. The vehicles considered are single-stage and two-stage fully reusable vehicles and the Space Shuttle with liquid rocket boosters. The results indicate that the split expander engine at a mixture ratio of about 7 is competitive with the full-flow staged combustion engine for all three vehicle concepts. A key factor in this result is the capability to increase the chamber pressure for the split expander as the mixture ratio is increased from 6 to 7
ANALYSIS OF A SPATIAL ROTATION PLAN FOR THE TULE LAKE NATIONAL WILDLIFE REFUGE
This paper examines the joint agro-wildfowl regulation of the Tule Lake National Wildlife Refuge in California. The area is jointly managed by the Bureau of Reclamation for both farming and wildfowl benefits. Production in both sectors has been declining recently, in farming due to nematode and soil pathogen buildup and in wildfowl production due to climax vegetation choking the lake. A novel spatial rotation plan has surfaced to solve both problems. We develop a simple model of the rotation option to identify critical variables and then we estimate some of these using data on lease bids.Resource /Energy Economics and Policy,
MARINE RESERVES WITH ENDOGENOUS PORTS: EMPIRICAL BIOECONOMICS OF THE CALIFORNIA SEA URCHIN FISHERY
Marine reserves are gaining substantial public support as tools for commercial fisheries management Harvest sector responses will influence policy performance, yet biological studies often depict harvester behavior as spread uniformly over fishing grounds and unresponsive to economic opportunities. Previous bioeconomic analyses show that these behavioral assumptions are inconsistent with empirical data and, more importantly, lead to overly optimistic predictions about harvest gains from reserves. This paper adds another layer of behavioral realism to the bioeconomics of marine reserves by endogenizing fisher home port choices with a partial adjustment share model. Estimated with Seemingly Unrelated Regression over monthly data, this approach allows simulation of both short- and long-run behavioral response to changes induced by marine reserve formation. The findings cast further doubt on the notion that marine reserves generate long-run harvest benefits.Resource /Energy Economics and Policy,
The Energy Transfer Process in Planetary Flybys
We illustrate the energy transfer during planetary flybys as a function of
time using a number of flight mission examples. The energy transfer process is
rather more complicated than a monotonic increase (or decrease) of energy with
time. It exhibits temporary maxima and minima with time which then partially
moderate before the asymptotic condition is obtained. The energy transfer to
angular momentum is exhibited by an approximate Jacobi constant for the system.
We demonstrate this with flybys that have shown unexplained behaviors: i) the
possible onset of the "Pioneer anomaly" with the gravity assist of Pioneer 11
by Saturn to hyperbolic orbit (as well as the Pioneer 10 hyperbolic gravity
assist by Jupiter) and ii) the Earth flyby anomalies of small increases in
energy {\it in the geocentric system} (Galileo-I, NEAR, and Rosetta, in
additioon discussing the Cassini and Messenger flybys). Perhaps some small, as
yet unrecognized effect in the energy-transfer process can shed light on these
anomalies.Comment: 29 pages, 43 images combined into 13 figures. Additions to answer
comments of refere
Compositional variation during monogenetic volcano growth and its implications for magma supply to continental volcanic fields
Individual volcanoes of continental monogenetic volcanic fields are generally presumed to erupt single magma batches during brief eruptions. Nevertheless, in two unrelated volcanic fields (the Waipiata volcanic field, New Zealand, and the Miocene-Pliocene volcanic field in western Hungary), we have identified pronounced and systematic compositional differences among products of individual volcanoes. We infer that this indicates a two-stage process of magma supply for these volcanoes. Each volcano records: (1) intrusion of a basanitic parent magma to lower- to mid-crustal levels and its subsequent fractionation to form a tephritic residual melt;, (2) subsequent transection of this reservoir by a second batch of basanitic melt, with tephrite rising to the surface at the head of the propagating basanite dyke. Eruption at the surface then yields initial tephrite, typically erupted as pyroclasts, followed by eruption and shallow intrusion of basanite from deeper in the dyke. By analogy with similar tephrite-basanite eruptions along rift zones of intraplate ocean-island volcanoes, we infer that fractionation to tephrite would have required decades to centuries. We conclude that the two studied continental monogenetic volcanic fields demonstrate a consistent history of early magmatic injections that fail to reach the surface, followed by capture and partial eruption of their evolved residues in the course of separate and significantly later injections of basanite that extend to the surface and erupt. This systematic behaviour probably reflects the difficulty of bringing small volumes of dense, primitive magma to the surface from mantle source regions. Ascent through continental crust is aided by the presence in the dyke head of buoyant tephrite captured during transection of the earlier-emplaced melt bodies
An Approach to Ecosystem-Based Fishery Management
Marine scientists and policymakers are encouraging ecosystem-based fishery management (EBFM), but there is limited guidance on how to operationalize the concept. We adapt financial portfolio theory as a method for EBFM that accounts for species interdependencies, uncertainty, and sustainability constraints. Illustrating our method with routinely collected data available from the Chesapeake Bay, we demonstrate the gains from taking into account species variances and covariances in setting species total allowable catches. We find over the period from 1962–2003 that managers could have increased the revenues from fishing and reduced the variance by employing ecosystem frontiers in setting catch levels.ecosystem-based fishery management, portfolio, trophic modeling, precaution
QCD corrections to stoponium production at hadron colliders
If the lighter top squark has no kinematically allowed two-body decays that
conserve flavor, then it will live long enough to form hadronic bound states.
The observation of the diphoton decays of stoponium could then provide a
uniquely precise measurement of the top squark mass. In this paper, we
calculate the cross section for the production of stoponium in a hadron
collider at next-to-leading order (NLO) in QCD. We present numerical results
for the cross section for production of stoponium at the LHC and study the
dependence on beam energy, stoponium mass, and the renormalization and
factorization scale. The cross-section is substantially increased by the NLO
corrections, counteracting a corresponding decrease found earlier in the NLO
diphoton branching ratio.Comment: 24 page
Implications of gauge-mediated supersymmetry breaking with vector-like quarks and a ~125 GeV Higgs boson
We investigate the implications of models that achieve a Standard Model-like
Higgs boson of mass near 125 GeV by introducing additional TeV-scale
supermultiplets in the vector-like 10+\bar{10} representation of SU(5), within
the context of gauge-mediated supersymmetry breaking. We study the resulting
mass spectrum of superpartners, comparing and contrasting to the usual
gauge-mediated and CMSSM scenarios, and discuss implications for LHC
supersymmetry searches. This approach implies that exotic vector-like fermions
t'_{1,2}, b',and \tau' should be within the reach of the LHC. We discuss the
masses, the couplings to electroweak bosons, and the decay branching ratios of
the exotic fermions, with and without various unification assumptions for the
mass and mixing parameters. We comment on LHC prospects for discovery of the
exotic fermion states, both for decays that are prompt and non-prompt on
detector-crossing time scales.Comment: 32 pages. v2: references added, figure caption 5.3 correcte
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