17,743 research outputs found
Aquarium fisheries as a non-timber forest product: experiences from conservation through community development in North Rupununi District, Guyana
Deforestation is one of the major global conservation issues. Solutions are being sought to tackle this ongoing
forest loss, including establishment of initiatives to provide new sources of income for local communities that
promote the sustainable use of forests in the interest of biodiversity conservation. One such project âIwokramaâ,
demonstrates how tropical forests and associated habitats can be sustainably used. In the central Guyana wetlands of the Rupununi, illegal fishing of arapaima Arapaima gigas, had led to a huge
reduction in its numbers. Iwokrama responded by initiating the Arapaima Management Plan in 2002. This
highlighted the need for another source of local income from fisheries, and a business that undertakes sustainable harvest
of fish for the aquarium trade was developed. Harvesting of a few selected fish species is carried-out by
members of the local community who are paid a daily wage. Fishing methods target individual species to avoid
incidental by-catch. Four species are primarily caught as they are numerous in the Rupununi and are of high trade
value. To ensure ecological and economical sustainability, catch per unit effort is monitored; where this begins to
drop for any given species, harvesting is suspended and the population is allowed to recover before harvesting
resumes. The project has developed into a self-sustaining business, managed by the community themselves. During
2005, the project reached financial sustainability with current profits of over US$3,000 feeding back into local
community initiatives
Nonlocal vertices and analyticity: Landau equations and general Cutkosky rule
We study the analyticity properties of amplitudes in theories with nonlocal
vertices of the type occurring in string field theory and a wide class of
nonlocal field theory models. Such vertices are given in momentum space by
entire functions of rapid decay in certain (including Euclidean) directions
ensuring UV finiteness but are necessarily of rapid increase in others. A
parametric representation is obtained by integrating out the loop (Euclidean)
momenta after the introduction of generalized Schwinger parameters. Either in
the original or parametric representation, the well-defined resulting
amplitudes are then continued in the complex space of the external momenta
invariants. We obtain the alternative forms of the Landau equations determining
the singularity surfaces showing that the nonlocal vertices serve as UV
regulators but do not affect the local singularity structure. As a result the
full set of singularities known to occur in local field theory also occurs
here: normal and anomalous thresholds as well as acnodes, crunodes, and cusps
that may under certain circumstances appear even on the physical sheet.
Singularities of the second type also appear as shown from the parametric
representation. We obtain the general Cutkosky discontinuity rule for
encircling a singularity by employing contour deformations only in the finite
plane. The unitarity condition (optical theorem) is then discussed as a special
application of the rule across normal thresholds and the hermitian analyticity
property of amplitudes.Comment: 31 pages, 5 figures. Typos corrected, some additional clarifying
comments, one added referenc
Traffic, urban growth and suburban sprawl
Cities are still getting bigger in the western world. Even though urbanpopulations are barely reproducing themselves and migration from thecountryside to the town has slowed to a trickle, the demand for more livingspace shows no sign of abating as cities continue to expand their bordersthrough suburban sprawl. The automobile, of course, makes this possiblebut we show no signs of moving to other forms of transport that mightenable our cities to become a little more compact. The problems of sprawlare pervasive. Besides congestion, time wasted, and the long term costs ofusing non-renewable energy, the lack of good social infrastructure inrapidly growing suburban areas together with the erosion of agriculturalland, often of high environmental quality, has focused the debate onwhether or not such forms of development are sustainable. In this paper,we begin by noting that suburban sprawl is an age-old phenomenon whichrepresents a fine balance between the forces that are pushing peopletogether in cities and those that are forcing them out. These lead todifferent types of sprawl in different places and at different times butwhatever the variety, there are costs to be borne. We briefly review these,noting how these affect suburban sprawl in Europe, and the efforts of theEuropean Commission to understand the problem. We conclude not with aplea that cities should be compacted and all automobile traffic removedbut that we should engage in policies for ?smart growth? such as thosebeing adopted in North America
Fourth Order Algorithms for Solving the Multivariable Langevin Equation and the Kramers Equation
We develop a fourth order simulation algorithm for solving the stochastic
Langevin equation. The method consists of identifying solvable operators in the
Fokker-Planck equation, factorizing the evolution operator for small time steps
to fourth order and implementing the factorization process numerically. A key
contribution of this work is to show how certain double commutators in the
factorization process can be simulated in practice. The method is general,
applicable to the multivariable case, and systematic, with known procedures for
doing fourth order factorizations. The fourth order convergence of the
resulting algorithm allowed very large time steps to be used. In simulating the
Brownian dynamics of 121 Yukawa particles in two dimensions, the converged
result of a first order algorithm can be obtained by using time steps 50 times
as large. To further demostrate the versatility of our method, we derive two
new classes of fourth order algorithms for solving the simpler Kramers equation
without requiring the derivative of the force. The convergence of many fourth
order algorithms for solving this equation are compared.Comment: 19 pages, 2 figure
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Distance learning of engineering based subjects: A case study.
YesWith the advancement of technology, significant changes have been introduced into the learning and teaching environment. The importance of enhancing the interest of learners is an on-going challenge for educators of all levels. In this respect, teaching and learning practices are adapting to studentsÂż exposure to technological and social trends. In this presentation, a case study of using technology to enhance the learnersÂż environment for engineering-based subjects in higher education is presented. The approach consists of delivering interactive materials through a Virtual Learning Environment and integrating web
application technologies to enhance the learnersÂż experience. Due to the vast subject areas in engineering and the variety of content of each subject, a general methodology is first identified and adopted. This consists of stages that show the progress from initial development to deployment of the materials, followed by evaluation of the module and further improvements carried out on the module based on qualitative evaluation. The evaluation process consists of the application of electronic surveys for feedback on the
distance learning module. In addition, monitoring of the studentsÂż usage of the materials is also carried out. The presentation concludes with the presentation of the initial results from a current e-learning module
Any order imaginary time propagation method for solving the Schrodinger equation
The eigenvalue-function pair of the 3D Schr\"odinger equation can be
efficiently computed by use of high order, imaginary time propagators. Due to
the diffusion character of the kinetic energy operator in imaginary time,
algorithms developed so far are at most fourth-order. In this work, we show
that for a grid based algorithm, imaginary time propagation of any even order
can be devised on the basis of multi-product splitting. The effectiveness of
these algorithms, up to the 12 order, is demonstrated by computing
all 120 eigenstates of a model C molecule to very high precisions. The
algorithms are particularly useful when implemented on parallel computer
architectures.Comment: 8 pages, 3 figure
Enhancement of variation of fundamental constants in ultracold atom and molecule systems near Feshbach resonances
Scattering length, which can be measured in Bose-Einstein condensate and
Feshbach molecule experiments, is extremely sensitive to the variation of
fundamental constants, in particular, the electron-to-proton mass ratio
(m_e/m_p or m_e/Lambda_{QCD}, where Lambda_{QCD} is the QCD scale). Based on
single- and two-channel scattering model, we show how the variation of the mass
ratio propagates to the scattering length. Our results suggest that variation
of m_e/m_p on the level of 10^{-11}~10^{-14} can be detected near a narrow
magnetic or an optical Feshbach resonance by monitoring the scattering length
on the 1% level. Derived formulae may also be used to estimate the isotopic
shift of the scattering length
The Temporal Doppler Effect: When The Future Feels Closer Than The Past
People routinely remember events that have passed and imagine those that are yet to come. The past and the future are sometimes psychologically close ( just around the corner ) and other times psychologically distant ( ages away ). Four studies demonstrate a systematic asymmetry whereby future events are psychologically closer than past events of equivalent objective distance. When considering specific times (e.g., 1 year) or events (e.g., Valentine\u27s Day), people consistently reported that the future was closer than the past. We suggest that this asymmetry arises because the subjective experience of movement through time (whereby future events approach and past events recede) is analogous to the physical experience of movement through space. Consistent with this hypothesis, experimentally reversing the metaphorical arrow of time (by having participants move backward through virtual space) completely eliminated the past-future asymmetry. We discuss how reducing psychological distance to the future may function to prepare people for upcoming action
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