362 research outputs found
Etat des connaissances sur la pisciculture en Cote d'Ivoire
La pisciculture a été amorcée en Côte d’Ivoire en 1955. Cependant, la production de l’aquaculture demeure faible. Une enquête a été réalisée sur le profil socio-économique des promoteurs, l’activité piscicole et la production des fermes. Il ressort de cette enquête que la pisciculture en Côte d’Ivoire est pratiquée sur presque toute l’étendue du territoire ivoirien. La majorité des fermes (65,4 %) ont une superficie en eau exploitée inférieure à un hectare. La durée d’existence est inférieure à 10 ans pour 53,8 % des fermes. Les pisciculteurs sont majoritairement des agriculteurs (60,8 %), ivoiriens (87,4 %) de sexe masculin (94,0 %) âgés de plus de 40 ans (83,7 %). Les systèmes d’élevage les plus pratiqués sont le semi-intensif (51,8 %) et l’extensif (42,9 %). Le tilapia Oreochromis niloticus (96,68 % ) et l’hétérotis Heterotis niloticus (56,81 %) sont les espèces de poissons les plus élevées. Les étangs de dérivation (93,69 %) et les étangs de barrages (47,84 %) sont les principales structures d’élevage. Les aliments utilisés seul ou en association sont les aliments commerciaux (27,57 %), produits par les pisciculteurs eux-mêmes (17,94 %), les sous-produits agroalimentaires (71,10 %) et les aliments non conventionnels (22,26 %). Le développement de la pisciculture en Côte d’Ivoire devrait passer par la promotion de la pisciculture intensive et semi-intensive auprès des salariés et des opérateurs économiques nationaux et internationaux.Mots clés : Pisciculture, pratique, région, production, Côte d’Ivoir
Two parton shower background for associate W Higgs production
The estimates of the background for the associate W Higgs production, which
stems from the two parton shower production. It is about 1 - 2.5 times larger
than the signal. However, this background does not depend on the rapidity
difference between the W and the pair, while the signal peaks when
the rapidity difference is zero. The detailed calculations for the enhanced
diagrams' contribution to this process, are presented, and it is shown that the
overlapping singularities, being important theoretically, lead to a negligible
contribution for the LHC range of energiesComment: 35 pages and 10 figures in eps file
Experimental investigation of solar heating of bridge decks
The addition of monomers or the inclusion of wax within highway bridge decks are two methods being used to prevent salt penetration during winter deicing. Both of these methods require the addition of heat until the upper two inches of bridge deck reaches from 160-190 F. This study investigated the potential for using solar energy as a means of providing the required heat. The bridge was modeled analytically and the time varying temperature distribution was determined for both a flat plate type cover collector and focusing collector scheme did show promise for providing the required heat. Both models suffered from lack of accurate thermal properties data for the concrete. Experimental studies were conducted on a simulated bridge deck using flat plate covers and Northrup focusing Fresnel Lens collectors. Neither scheme was able to provide the desired temperatures. A major difficulty encountered was the design of an appropriate heat exchanger to transfer the collected energy from the heat transfer flud to the bridge deck. Several different designs were tested, but none of the methods used would provide the desired bridge deck temperatures for the collector area used. The collectors did not perform up to their expectations.4-77 to 6-79N
Corrections to the generalized vector dominance due to diffractive rho_3 production
The idea of the vector dominance is still in use in various analyses of
experimental data of photon-hadron reactions. It makes sense, therefore, to
recast results of microscopic calculations of such reactions in this language.
Here we present the diffractive DIS production as a specific
correction to the generalized vector dominance. We perform a coupled channel
analysis of spin-orbital excitations in diffractive photoproduction and
reiterate the point that rho_3 in diffractive DIS will be sensitive to a novel
aspect of diffraction.Comment: 12 pages, 2 figure
A Species-based Particle Swarm Optimization with Adaptive Population Size and Deactivation of Species for Dynamic Optimization Problems
Population clustering methods, which consider the position and fitness of the individuals to form sub-populations in multi-population algorithms, have shown high efficiency in tracking the moving global optimum in dynamic optimization problems. However, most of these methods use a fixed population size, making them inflexible and inefficient when the number of promising regions is unknown. The lack of a functional relationship between the population size and the number of promising regions significantly degrades performance and limits an algorithm’s agility to respond to dynamic changes. To address this issue, we propose a new species-based particle swarm optimization with adaptive population size and number of sub-populations for solving dynamic optimization problems. The proposed algorithm also benefits from a novel systematic adaptive deactivation component that, unlike the previous deactivation components, adapts the computational resource allocation to the sub-populations by considering various characteristics of both the problem and the sub-populations. We evaluate the performance of our proposed algorithm for the Generalized Moving Peaks Benchmark and compare the results with several peer approaches. The results indicate the superiority of the proposed method
f0(980) meson as a K bar K molecule in a phenomenological Lagrangian approach
We discuss a possible interpretation of the f0(980) meson as a hadronic
molecule - a bound state of K and bar K mesons. Using a phenomenological
Lagrangian approach we calculate the strong f0(980) to pi pi and
electromagnetic f0(980) to gamma gamma decays. The compositeness condition
provides a self-consistent method to determine the coupling constant between f0
and its constituents, K and bar K. Form factors governing the decays of the
f0(980) are calculated by evaluating the kaon loop integrals. The predicted
f0(980) to pi pi and f0(980) to gamma gamma decay widths are in good agreement
with available data and results of other theoretical approaches.Comment: 21 pages, 11 figures, revised version accepted for publication in
Eur. Phys. J.
Tomonaga-Luttinger parameters for quantum wires
The low-energy properties of a homogeneous one-dimensional electron system
are completely specified by two Tomonaga-Luttinger parameters and
. In this paper we discuss microscopic estimates of the values of
these parameters in semiconductor quantum wires that exploit their relationship
to thermodynamic properties. Motivated by the recognized similarity between
correlations in the ground state of a one-dimensional electron liquid and
correlations in a Wigner crystal, we evaluate these thermodynamic quantities in
a self-consistent Hartree-Fock approximation. According to our calculations,
the Hartree-Fock approximation ground state is a Wigner crystal at all electron
densities and has antiferromagnetic order that gradually evolves from
spin-density-wave to localized in character as the density is lowered. Our
results for are in good agreement with weak-coupling perturbative
estimates at high densities, but deviate strongly at low
densities, especially when the electron-electron interaction is screened at
long distances. vanishes at small carrier density
whereas we conjecture that when , implying that
should pass through a minimum at an intermediate density.
Observation of such a non-monotonic dependence on particle density would allow
to measure the range of the microscopic interaction. In the spin sector we find
that the spin velocity decreases with increasing interaction strength or
decreasing . Strong correlation effects make it difficult to obtain fully
consistent estimates of from Hartree-Fock calculations. We
conjecture that v_{\sigma}/\vf\propto n/V_0 in the limit where
is the interaction strength.Comment: RevTeX, 23 pages, 8 figures include
A complete 3D numerical study of the effects of pseudoscalar-photon mixing on quasar polarizations
We present the results of three-dimensional simulations of quasar
polarizations in the presence of pseudoscalar-photon mixing in the
intergalactic medium. The intergalactic magnetic field is assumed to be
uncorrelated in wave vector space but correlated in real space. Such a field
may be obtained if its origin is primordial. Furthermore we assume that the
quasars, located at cosmological distances, have negligible initial
polarization. In the presence of pseudoscalar-photon mixing we show, through a
direct comparison with observations, that this may explain the observed large
scale alignments in quasar polarizations within the framework of big bang
cosmology. We find that the simulation results give a reasonably good fit to
the observed data.Comment: 15 pages, 8 figures, significant changes, to appear in EPJ
Astrophysical Axion Bounds
Axion emission by hot and dense plasmas is a new energy-loss channel for
stars. Observational consequences include a modification of the solar
sound-speed profile, an increase of the solar neutrino flux, a reduction of the
helium-burning lifetime of globular-cluster stars, accelerated white-dwarf
cooling, and a reduction of the supernova SN 1987A neutrino burst duration. We
review and update these arguments and summarize the resulting axion
constraints.Comment: Contribution to Axion volume of Lecture Notes in Physics, 20 pages, 3
figure
Energy balance measurements over a banana orchard in the Semiarid region in the Northeast of Brazil
The objective of this work was to evaluate the reliability of eddy covariance measurements, analyzing the energy balance components, evapotranspiration and energy balance closure in dry and wet growing seasons, in a banana orchard. The experiment was carried out at a farm located within the irrigation district of Quixeré, in the Lower Jaguaribe basin, in Ceará state, Brazil. An eddy covariance system was used to measure the turbulent flux. An automatic weather station was installed in a grass field to obtain the reference evapotranspiration (ET0) from the combined FAO-Penman-Monteith method. Wind speed and vapor pressure deficit are the most important variables on the evaporative process in both growing seasons. In the dry season, the heat fluxes have a similar order of magnitude, and during the wet season the latent heat flux is the largest. The eddy covariance system had acceptable reliability in measuring heat flux, with actual evapotranspiration results comparing well with those obtained by using the water balance method. The energy balance closure had good results for the study area, with mean values of 0.93 and 0.86 for the dry and wet growing seasons respectively
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