1,615 research outputs found
Ecosystem Approach to Small Scale Tropical Marine Fisheries
This is a 4-page brochure about a WorldFish led project. Throughout the world, poor fisheries management contributes to resource degradation, poverty, and food insecurity. This European Union project on an Ecosystem Approach to Small-scale Tropical Marine Fisheries is led by WorldFish and implemented in collaboration with national partners in Asia (Southeastern)-Indonesia; the Asia (Southeastern)-Philippines; the Solomon Islands and Tanzania. The overall objective is to use an ecosystem approach to fisheries management (EAFM) to improve governance of small-scale fisheries (SSF). The EAFM puts sustainability and equitability at the forefront of fisheries governance which enhances their contribution to poverty reduction.Specific objectives are to: 1. Assess existing institutional arrangements and identify opportunities for an EAFM to improve integrated SSF management; 2. Develop EAFM strategies and actions suitable for developing country contexts; 3. Strengthen the capacity of local fishery stakeholders and government agencies to collaborate and work within an EAFM. The project is taking a participatory and gender sensitive approach, both core philosophies of WorldFish. Representatives of all relevant stakeholder groups are involved in this action research project
Large-Scale Image Processing with the ROTSE Pipeline for Follow-Up of Gravitational Wave Events
Electromagnetic (EM) observations of gravitational-wave (GW) sources would
bring unique insights into a source which are not available from either channel
alone. However EM follow-up of GW events presents new challenges. GW events
will have large sky error regions, on the order of 10-100 square degrees, which
can be made up of many disjoint patches. When searching such large areas there
is potential contamination by EM transients unrelated to the GW event.
Furthermore, the characteristics of possible EM counterparts to GW events are
also uncertain. It is therefore desirable to be able to assess the statistical
significance of a candidate EM counterpart, which can only be done by
performing background studies of large data sets. Current image processing
pipelines such as that used by ROTSE are not usually optimised for large-scale
processing. We have automated the ROTSE image analysis, and supplemented it
with a post-processing unit for candidate validation and classification. We
also propose a simple ad hoc statistic for ranking candidates as more likely to
be associated with the GW trigger. We demonstrate the performance of the
automated pipeline and ranking statistic using archival ROTSE data. EM
candidates from a randomly selected set of images are compared to a background
estimated from the analysis of 102 additional sets of archival images. The
pipeline's detection efficiency is computed empirically by re-analysis of the
images after adding simulated optical transients that follow typical light
curves for gamma-ray burst afterglows and kilonovae. We show that the automated
pipeline rejects most background events and is sensitive to simulated
transients to limiting magnitudes consistent with the limiting magnitude of the
images
Order-N Density-Matrix Electronic-Structure Method for General Potentials
A new order-N method for calculating the electronic structure of general
(non-tight-binding) potentials is presented. The method uses a combination of
the ``purification''-based approaches used by Li, Nunes and Vanderbilt, and
Daw, and a representation of the density matrix based on ``travelling basis
orbitals''. The method is applied to several one-dimensional examples,
including the free electron gas, the ``Morse'' bound-state potential, a
discontinuous potential that mimics an interface, and an oscillatory potential
that mimics a semiconductor. The method is found to contain Friedel
oscillations, quantization of charge in bound states, and band gap formation.
Quantitatively accurate agreement with exact results is found in most cases.
Possible advantages with regard to treating electron-electron interactions and
arbitrary boundary conditions are discussed.Comment: 13 pages, REVTEX, 7 postscript figures (not quite perfect
The Decay Properties of the Finite Temperature Density Matrix in Metals
Using ordinary Fourier analysis, the asymptotic decay behavior of the density
matrix F(r,r') is derived for the case of a metal at a finite electronic
temperature. An oscillatory behavior which is damped exponentially with
increasing distance between r and r' is found. The decay rate is not only
determined by the electronic temperature, but also by the Fermi energy. The
theoretical predictions are confirmed by numerical simulations
Vacancy diffusion in the Cu(001) surface II: Random walk theory
We develop a version of the vacancy mediated tracer diffusion model, which
follows the properties of the physical system of In atoms diffusing within the
top layer of Cu(001) terraces. This model differs from the classical tracer
diffusion problem in that (i) the lattice is finite, (ii) the boundary is a
trap for the vacancy, and (iii) the diffusion rate of the vacancy is different,
in our case strongly enhanced, in the neighborhood of the tracer atom. A simple
continuum solution is formulated for this problem, which together with the
numerical solution of the discrete model compares well with our experimental
results.Comment: 13 pages, 4 figure
Understanding visual map formation through vortex dynamics of spin Hamiltonian models
The pattern formation in orientation and ocular dominance columns is one of
the most investigated problems in the brain. From a known cortical structure,
we build spin-like Hamiltonian models with long-range interactions of the
Mexican hat type. These Hamiltonian models allow a coherent interpretation of
the diverse phenomena in the visual map formation with the help of relaxation
dynamics of spin systems. In particular, we explain various phenomena of
self-organization in orientation and ocular dominance map formation including
the pinwheel annihilation and its dependency on the columnar wave vector and
boundary conditions.Comment: 4 pages, 15 figure
Calculation of Elastic Green's Functions for Lattices with Cavities
In this Brief Report, we present an algorithm for calculating the elastic
Lattice Greens Function of a regular lattice, in which defects are created by
removing lattice points. The method is computationally efficient, since the
required matrix operations are on matrices that scale with the size of the
defect subspace, and not with the size of the full lattice. This method allows
the treatment of force fields with multi-atom interactions.Comment: 3 pages. RevTeX, using epsfig.sty. One figur
Measurement of the quenching factor of Na recoils in NaI(Tl)
Measurements of the quenching factor for sodium recoils in a 5 cm diameter
NaI(Tl) crystal at room temperature have been made at a dedicated neutron
facility at the University of Sheffield. The crystal has been exposed to 2.45
MeV mono-energetic neutrons generated by a Sodern GENIE 16 neutron generator,
yielding nuclear recoils of energies between 10 and 100 keVnr. A cylindrical
BC501A detector has been used to tag neutrons that scatter off sodium nuclei in
the crystal. Cuts on pulse shape and time of flight have been performed on
pulses recorded by an Acqiris DC265 digitiser with a 2 ns sampling time.
Measured quenching factors of Na nuclei range from 19% to 26% in good agreement
with other experiments, and a value of 25.2 \pm 6.4% has been determined for 10
keV sodium recoils. From pulse shape analysis, the mean times of pulses from
electron and nuclear recoils have been compared down to 2 keVee. The
experimental results are compared to those predicted by Lindhard theory,
simulated by the SRIM Monte Carlo code, and a preliminary curve calculated by
Prof. Akira Hitachi.Comment: 21 pages, 13 figure
Long term study of the seismic environment at LIGO
The LIGO experiment aims to detect and study gravitational waves using ground
based laser interferometry. A critical factor to the performance of the
interferometers, and a major consideration in the design of possible future
upgrades, is isolation of the interferometer optics from seismic noise. We
present the results of a detailed program of measurements of the seismic
environment surrounding the LIGO interferometers. We describe the experimental
configuration used to collect the data, which was acquired over a 613 day
period. The measurements focused on the frequency range 0.1-10 Hz, in which the
secondary microseismic peak and noise due to human activity in the vicinity of
the detectors was found to be particularly critical to interferometer
performance. We compare the statistical distribution of the data sets from the
two interferometer sites, construct amplitude spectral densities of seismic
noise amplitude fluctuations with periods of up to 3 months, and analyze the
data for any long term trends in the amplitude of seismic noise in this
critical frequency range.Comment: To be published in Classical and Quantum Gravity. 24 pages, 15
figure
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