5,247 research outputs found
Legal Issues Pertaining to Community Based Fisheries Management
National and intergovernmental regulation of fisheries has not prevented many failures of fisheries management around the world. New approaches to improving the environmental sustainability of fisheries have included the certification of fisheries harvested by sustainable means, and the ecolabelling of fish and seafood products from certified fisheries. The intention is to use the power of markets as an incentive to induce more sustainable fisheries. To date, only a relatively small number of fisheries have been certified, and these have been predominantly in developed countries. Critiques from developing countries of ecolabelling, as currently formulated, focus on five general areas: a) legitimacy and credibility; b) a mismatch between certification requirements and the reality of tropical small-scale fisheries; c) potential distortions to existing practices and livelihoods; d) equity and feasibility; and e) perceived barriers to trade.This paper reviews these developing country concerns on the basis of already certified fisheries, and on experiences from forestry, aquaculture and the aquarium industry, and also examines precedents and trends in international environmental and trade issues. It suggests that ecolabelling as currently practiced is unlikely to be widely adopted in Asian countries. Certification may have sporadic success in some eco-conscious, or niche, markets but it is unlikely to stimulate global improvement of fisheries management.The paper argues that to avoid the controversy that accompanies ecolabelling, the focus should be on revision of national fisheries management and not on an ad hoc approach to individual fisheries. Improvements in fisheries management, the equitable treatment of fishing sub-sectors and stakeholders within management schemes, and the prospect of reaping increased value-added from fisheries all require government acceptance of needs and actions. Governments should be encouraged to enter into broad coalitions to improve aspects of fisheries management, and to enhance efforts to develop locally relevant indicator systems for fisheries and for the ecosystem approach. Governments of developing countries must also first address the difficult questions of access to and tenure arrangements for their fisheries, as these are essential prerequisites for successful certification and product labeling. They will also need to legislate on the form and conduct of the postharvest chain and product control, as, in export markets, these are outside the control ofthe fishing communities. International agreement and clarity on trade, environmental (and health) standards affecting fisheries will augment national efforts. Advocacy coalitions that include governments, rather than extraterritorial imposition of labelling schemes, are required
Sum rule for response function in nonequilibrium Langevin systems
We derive general properties of the linear response functions of
nonequilibrium steady states in Langevin systems. These correspond to extension
of the results which were recently found in Hamiltonian systems [A. Shimizu and
T. Yuge, J. Phys. Soc. Jpn. {\bf 79}, 013002 (2010)]. We discuss one of the
properties, the sum rule for the response function, in particular detail. We
show that the sum rule for the response function of the velocity holds in the
underdamped case, whereas it is violated in the overdamped case. This implies
that the overdamped Langevin models should be used with great care. We also
investigate the relation of the sum rule to an equality on the energy
dissipation in nonequilibrium Langevin systems, which was derived by Harada and
Sasa.Comment: 8 page
Quantum turbulence in condensate collisions: an application of the classical field method
We apply the classical field method to simulate the production of correlated
atoms during the collision of two Bose-Einstein condensates. Our
non-perturbative method includes the effect of quantum noise, and provides for
the first time a theoretical description of collisions of high density
condensates with very large out-scattered fractions. Quantum correlation
functions for the scattered atoms are calculated from a single simulation, and
show that the correlation between pairs of atoms of opposite momentum is rather
small. We also predict the existence of quantum turbulence in the field of the
scattered atoms--a property which should be straightforwardly measurable.Comment: 5 pages, 3 figures: Rewritten text, replaced figure
Tripartite entanglement and threshold properties of coupled intracavity downconversion and sum-frequency generation
The process of cascaded downconversion and sum-frequency generation inside an
optical cavity has been predicted to be a potential source of three-mode
continuous-variable entanglement. When the cavity is pumped by two fields, the
threshold properties have been analysed, showing that these are more
complicated than in well-known processes such as optical parametric
oscillation. When there is only a single pumping field, the entanglement
properties have been calculated using a linearised fluctuation analysis, but
without any consideration of the threshold properties or critical operating
points of the system. In this work we extend this analysis to demonstrate that
the singly pumped system demonstrates a rich range of threshold behaviour when
quantisation of the pump field is taken into account and that asymmetric
polychromatic entanglement is available over a wide range of operational
parameters.Comment: 24 pages, 15 figure
Quantum turbulence and correlations in Bose-Einstein condensate collisions
We investigate numerically simulated collisions between experimentally
realistic Bose-Einstein condensate wavepackets, within a regime where highly
populated scattering haloes are formed. The theoretical basis for this work is
the truncated Wigner method, for which we present a detailed derivation, paying
particular attention to its validity regime for colliding condensates. This
paper is an extension of our previous Letter [A. A. Norrie, R. J. Ballagh, and
C. W. Gardiner, Phys. Rev. Lett. 94, 040401 (2005)] and we investigate both
single-trajectory solutions, which reveal the presence of quantum turbulence in
the scattering halo, and ensembles of trajectories, which we use to calculate
quantum-mechanical correlation functions of the field
Analysis of a continuous-variable quadripartite cluster state from a single optical parametric oscillator
We examine the feasibility of generating continuous-variable multipartite
entanglement in an intra-cavity quadruply concurrent downconversion scheme that
has been proposed for the generation of cluster states by Menicucci \textit{et
al.} [Physical Review Letters \textbf{101}, 130501 (2008)]. By calculating
optimized versions of the van Loock-Furusawa correlations we demonstrate
genuine quadripartite entanglement and investigate the degree of entanglement
present. Above the oscillation threshold the basic cluster state geometry under
consideration suffers from phase diffusion. We alleviate this problem by
incorporating a small injected signal into our analysis. Finally, we
investigate squeezed joint operators. While the squeezed joint operators
approach zero in the undepleted regime, we find that this is not the case when
we consider the full interaction Hamiltonian and the presence of a cavity. In
fact, we find that the decay of these operators is minimal in a cavity, and
even depletion alone inhibits cluster state formation.Comment: 26 pages, 12 figure
Quantum Kinetic Theory VI: The Growth of a Bose-Einstein Condensate
A detailed analysis of the growth of a BEC is given, based on quantum kinetic
theory, in which we take account of the evolution of the occupations of lower
trap levels, and of the full Bose-Einstein formula for the occupations of
higher trap levels, as well as the Bose stimulated direct transfer of atoms to
the condensate level introduced by Gardiner et al. We find good agreement with
experiment at higher temperatures, but at lower temperatures the experimentally
observed growth rate is somewhat more rapid. We also confirm the picture of the
``kinetic'' region of evolution, introduced by Kagan et al., for the time up to
the initiation of the condensate. The behavior after initiation essentially
follows our original growth equation, but with a substantially increased rate
coefficient.
Our modelling of growth implicitly gives a model of the spatial shape of the
condensate vapor system as the condensate grows, and thus provides an
alternative to the present phenomenological fitting procedure, based on the sum
of a zero-chemical potential vapor and a Thomas-Fermi shaped condensate. Our
method may give substantially different results for condensate numbers and
temperatures obtained from phenomentological fits, and indicates the need for
more systematic investigation of the growth dynamics of the condensate from a
supersaturated vapor.Comment: TeX source; 29 Pages including 26 PostScript figure
Solitary-wave description of condensate micro-motion in a time-averaged orbiting potential trap
We present a detailed theoretical analysis of micro-motion in a time-averaged
orbiting potential trap. Our treatment is based on the Gross-Pitaevskii
equation, with the full time dependent behaviour of the trap systematically
approximated to reduce the trapping potential to its dominant terms. We show
that within some well specified approximations, the dynamic trap has
solitary-wave solutions, and we identify a moving frame of reference which
provides the most natural description of the system. In that frame eigenstates
of the time-averaged orbiting potential trap can be found, all of which must be
solitary-wave solutions with identical, circular centre of mass motion in the
lab frame. The validity regime for our treatment is carefully defined, and is
shown to be satisfied by existing experimental systems.Comment: 12 pages, 2 figure
Bragg scattering of Cooper pairs in an ultra-cold Fermi gas
We present a theoretical treatment of Bragg scattering of a degenerate Fermi
gas in the weakly interacting BCS regime. Our numerical calculations predict
correlated scattering of Cooper pairs into a spherical shell in momentum space.
The scattered shell of correlated atoms is centered at half the usual Bragg
momentum transfer, and can be clearly distinguished from atoms scattered by the
usual single-particle Bragg mechanism. We develop an analytic model that
explains key features of the correlated-pair Bragg scattering, and determine
the dependence of this scattering on the initial pair correlations in the gas.Comment: Manuscript substantially revised. Version 2 contains a more detailed
discussion of the collisional interaction used in our theory, and is based on
three-dimensional solution
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