616 research outputs found
Management Strategy Evaluation for the Atlantic Surfclam (Spisula solidissima) Using a Spatially Explicit, Vessel-Based Fisheries Model
The commercially valuable Atlantic surfclam (Spisula solidissima) is harvested along the northeastern continental shelf of the United States. Its range has contracted and shifted north, driven by warmer bottom water temperatures. Declining landings per unit of effort (LPUE) in the Mid-Atlantic Bight (MAB) is one result. Declining stock abundance and LPUE suggest that overfishing may be occurring off New Jersey. A management strategy evaluation (MSE) for the Atlantic surfclam is implemented to evaluate rotating closures to enhance Atlantic surfclam productivity and increase fishery viability in the MAB. Active agents of the MSE model are individual fishing vessels with performance and quota constraints influenced by captains\u27 behavior over a spatially varying population. Management alternatives include 2 rules regarding closure locations and 3 rules regarding closure durations. Simulations showed that stock biomass increased, up to 17%, under most alternative strategies in relation to estimated stock biomass under present- day management, and LPUE increased under most alternative strategies, by up to 21%. When incidental mortality caused by the fishery increased, the benefits seen under the alternative management were enhanced. These outcomes suggest that area management involving rotating closures could be valuable in insulating the stock and the commercial fishery from further declines as a northerly shift in range proceeds
Property Taxation in Virginia
The Virginia Constitution mandates that all property within the state, except exempt property, must be taxed. In light of the constitution\u27s directive, this note examines the present Virginia property taxation structure in order to provide the practitioner with a guide to its application and operation
The Layer 0 Inner Silicon Detector of the D0 Experiment
This paper describes the design, fabrication, installation and performance of
the new inner layer called Layer 0 (L0) that was inserted in the existing Run
IIa Silicon Micro-Strip Tracker (SMT) of the D0 experiment at the Fermilab
Tevatron collider. L0 provides tracking information from two layers of sensors,
which are mounted with center lines at a radial distance of 16.1 mm and 17.6 mm
respectively from the beam axis. The sensors and readout electronics are
mounted on a specially designed and fabricated carbon fiber structure that
includes cooling for sensor and readout electronics. The structure has a thin
polyimide circuit bonded to it so that the circuit couples electrically to the
carbon fiber allowing the support structure to be used both for detector
grounding and a low impedance connection between the remotely mounted hybrids
and the sensors.Comment: 28 pages, 9 figure
Nanoscale Effects on Heterojunction Electron Gases in GaN/AlGaN Core/Shell Nanowires
The electronic properties of heterojunction electron gases formed in
GaN/AlGaN core/shell nanowires with hexagonal and triangular cross-sections are
studied theoretically. We show that at nanoscale dimensions, the non-polar
hexagonal system exhibits degenerate quasi-one-dimensional electron gases at
the hexagon corners, which transition to a core-centered electron gas at lower
doping. In contrast, polar triangular core/shell nanowires show either a
non-degenerate electron gas on the polar face or a single quasi-one-dimensional
electron gas at the corner opposite the polar face, depending on the
termination of the polar face. More generally, our results indicate that
electron gases in closed nanoscale systems are qualitatively different from
their bulk counterparts.Comment: 16 pages, 7 figures. To appear in Nano Letters. Corrected some typo
Comparison of the âCa. Liberibacter asiaticusâ Genome Adapted for an Intracellular Lifestyle with Other Members of the Rhizobiales
An intracellular plant pathogen âCandidatus Liberibacter asiaticus,â a member of the Rhizobiales, is related to Sinorhizobium meliloti, Bradyrhizobium japonicum, nitrogen fixing endosymbionts, Agrobacterium tumefaciens, a plant pathogen, and Bartonella henselae, an intracellular mammalian pathogen. Whole chromosome comparisons identified at least 50 clusters of conserved orthologous genes found on the chromosomes of all five metabolically diverse species. The intracellular pathogens âCa. Liberibacter asiaticusâ and Bartonella henselae have genomes drastically reduced in gene content and size as well as a relatively low content of guanine and cytosine. Codon and amino acid preferences that emphasize low guanosine and cytosine usage are globally employed in these genomes, including within regions of microsynteny and within signature sequences of orthologous proteins. The length of orthologous proteins is generally conserved, but not their isoelectric points, consistent with extensive amino acid substitutions to accommodate selection for low GC content. The âCa. Liberibacter asiaticusâ genome apparently has all of the genes required for DNA replication present in Sinorhizobium meliloti except it has only two, rather than three RNaseH genes. The gene set required for DNA repair has only one rather than ten DNA ligases found in Sinorhizobium meliloti, and the DNA PolI of âCa. Liberibacter asiaticusâ lacks domains needed for excision repair. Thus the ability of âCa. Liberibacter asiaticusâ to repair mutations in its genome may be impaired. Both âCa. Liberibacter asiaticus and Bartonella henselae lack enzymes needed for the metabolism of purines and pyrimidines, which must therefore be obtained from the host. The âCa. Liberibacter asiaticusâ genome also has a greatly reduced set of sigma factors used to control transcription, and lacks sigma factors 24, 28 and 38. The âCa. Liberibacter asiaticusâ genome has all of the hallmarks of a reduced genome of a pathogen adapted to an intracellular lifestyle
Prototype ATLAS IBL Modules using the FE-I4A Front-End Readout Chip
The ATLAS Collaboration will upgrade its semiconductor pixel tracking
detector with a new Insertable B-layer (IBL) between the existing pixel
detector and the vacuum pipe of the Large Hadron Collider. The extreme
operating conditions at this location have necessitated the development of new
radiation hard pixel sensor technologies and a new front-end readout chip,
called the FE-I4. Planar pixel sensors and 3D pixel sensors have been
investigated to equip this new pixel layer, and prototype modules using the
FE-I4A have been fabricated and characterized using 120 GeV pions at the CERN
SPS and 4 GeV positrons at DESY, before and after module irradiation. Beam test
results are presented, including charge collection efficiency, tracking
efficiency and charge sharing.Comment: 45 pages, 30 figures, submitted to JINS
Flexible Dye-Sensitized Solar Cell Based on Vertical ZnO Nanowire Arrays
Flexible dye-sensitized solar cells are fabricated using vertically aligned ZnO nanowire arrays that are transferred onto ITO-coated poly(ethylene terephthalate) substrates using a simple peel-off process. The solar cells demonstrate an energy conversion efficiency of 0.44% with good bending tolerance. This technique paves a new route for building large-scale cost-effective flexible photovoltaic and optoelectronic devices
Standalone vertex ďŹnding in the ATLAS muon spectrometer
A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at âs = 7 TeV collected with the ATLAS detector at the LHC during 2011
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