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Ouagued M.,University of Hassiba Ben Bouali Chlef | Khellaf A.,Renewable Energy Development Center Algeria | Loukarfi L.,University of Hassiba Ben Bouali Chlef
Energy Conversion and Management | Year: 2013

Algeria is blessed with a very important renewable, and more particularly solar, energy potential. This potential opens for Algeria reel opportunities to cope with the increasing energy demand and the growing environmental problems link to the use of fossil fuel. In order to develop and to promote concrete actions in the areas of renewable energy and energy efficiency, Algeria has introduced a national daring program for the period 2011-2030. In this program, solar energy, and more particularly solar thermal energy plays an important role. In this paper, the potential of direct solar irradiance in Algeria and the performance of solar parabolic trough collector (PTC) are estimated under the climate conditions of the country. These two factors are treated as they play an important role in the design of solar thermal plant. In order to determine the most promising solar sites in Algeria, monthly mean daily direct solar radiation have been estimated and compared for different locations corresponding to different climatic region. Different tilted and tracking collectors are considered so as to determine the most efficient system for the PTC. In order to evaluate the performance of a tracking solar parabolic trough collector, a heat transfer model is developed. The receiver, heat collector element (HCE), is divided into several segments and heat balance is applied in each segment over a section of the solar receiver. Different oils are considered to determine the thermal performances of the heat transfer fluid (HTF). Then, the HTF temperature and heat gain evolutions are compared under the topographical and climatic conditions. © 2013 Elsevier B.V. All rights reserved.


Boudjemaa A.,University of Hassiba Ben Bouali Chlef | Al Khawaja U.,United Arab Emirates University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We investigate the stability of N-soliton molecules in dispersion-managed optical fibers with focus on the recently realized 2- and 3-soliton molecules. We calculate their binding energy using an averaged nonlinear Schrödinger equation. A combination of variational and numerical solutions to this equation shows that it describes well the intensity profiles and relative separations of the experimental molecules. Extending the calculation to larger values of N, the binding energy per soliton is found to saturate at N≥7. © 2013 American Physical Society.


Boudjemaa A.,University of Hassiba Ben Bouali Chlef
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We study the properties of a Bose-Einstein-condensate (BEC)-impurity mixture at finite temperature employing the time-dependent Hartree-Fock Bogoliubov (TDHFB) theory which is a set of coupled nonlinear equations of motion for the condensate and its normal and anomalous fluctuations on the one hand and for impurity on the other. The numerical solutions of these equations in the static quasi-one-dimensional regime show that the thermal cloud and the anomalous density are deformed as happens to the condensate and the impurity becomes less localized at nonzero temperatures. Effects of the BEC fluctuations on the self-trapping state are studied in homogeneous weakly interacting BEC-impurity at low temperature. The self-trapping threshold is also determined in such a system. The formation of solitons in the BEC-impurity mixture at finite temperature is investigated. © 2014 American Physical Society.


Boudjemaa A.,University of Hassiba Ben Bouali Chlef
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2015

We present a systematic study of dilute three-dimensional dipolar Bose gas employing a finite temperature perturbation theory (beyond the mean field). We analyze in particular the behavior of the anomalous density, we find that this quantity has a finite value in the limit of weak interactions at both zero and finite temperatures. We show that the presence of the dipole-dipole interaction enhances fluctuations, the second order correlation function and thermodynamic quantities such as the chemical potential, the ground state energy, the compressibility and the superfluid fraction. We identify the validity criterion of the small parameter of the theory for Bose-condensed dipolar gases. © 2015 IOP Publishing Ltd.


Boudjemaa A.,University of Hassiba Ben Bouali Chlef
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2015

We consider two-dimensional dipolar bosonic gas with dipoles oriented perpendicularly to the plane in a weak random potential. We investigate analytically and numerically the condensate depletion, the one-body density-matrix, the ground state energy, the sound velocity and the superfluid fraction. Concentrating on the regime where a roton-like excitation spectrum forms, our results show that the superfluidity disappears below a critical value of disorder strength yielding the transition to a non-trivial quantum regime. © 2015 Elsevier B.V.


Boudjemaa A.,University of Hassiba Ben Bouali Chlef
Journal of Physics A: Mathematical and Theoretical | Year: 2015

We study the properties of Bose-Einstein condensate-impurity mixtures at finite temperatures employing the Balian-Vénéroni variational principle. The method leads to a set of coupled nonlinear equations of motion for the condensate and its normal and anomalous fluctuations on the one hand, and for the impurity on the other. We show that the obtained equations satisfy the energy and number conserving laws. Useful analytic expressions for the chemical potential and the radius of both the condensate and anomalous components are derived in the framework of the Thomas-Fermi approximation in a d-dimensional regime. The effects of the impurity on these quantities are discussed. © 2015 IOP Publishing Ltd.


Boudjemaa A.,University of Hassiba Ben Bouali Chlef
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

The dynamics of Bose-Einstein condensate (BEC) is studied at nonzero temperatures using our variational time-dependent-Hartree-Fock-Bogoliubov formalism. We have shown that this approach is an efficient tool to study the expansion and collective excitations of the condensate, the thermal cloud, and the anomalous correlation function at nonzero temperatures. We have found that the condensate and the anomalous density have the same breathing oscillations. We have investigated, on the other hand, the behavior of a single quantized vortex in a harmonically trapped BEC at nonzero temperatures. Generalized expressions for vortex excitations, vortex core size, and Kelvin modes have been derived. An important and somehow surprising result is that the numerical solution of our equations predicts that the vortex core is partially filled by the thermal atoms at nonzero temperatures. We have shown that the effect of thermal fluctuations is important and it may lead to enhancing the size of the vortex core. The behavior of the singly anomalous vortex has also been studied at nonzero temperatures. © 2013 American Physical Society.


Boudjemga A.,University of Hassiba Ben Bouali Chlef
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We investigate the behavior of the anomalous correlation function in two-dimensional Bose gas. In the local case, we find that this quantity has a finite value in the limit of weak interactions at zero temperature. The effects of the anomalous density on some thermodynamic quantities are also considered. These effects can modify, in particular, the chemical potential, the ground-state energy, the depletion, and the superfluid fraction. Our predictions are in good agreement with recent analytical and numerical calculations. We show also that the anomalous density presents a significant importance compared to the noncondensed one at zero temperature. The single-particle anomalous correlation function is expressed in two-dimensional homogenous Bose gases by using the density-phase fluctuation. We then confirm that the anomalous average accompanies in analogous manner the true condensate at zero temperature, while it does not exist at finite temperature. © 2012 American Physical Society.


Boudjemaa A.,University of Hassiba Ben Bouali Chlef
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

We investigate the properties of a homogeneous dipolar Bose gas in a weak three-dimensional isotropic speckle disorder at finite temperatures. By using the Bogoliubov theory (beyond the mean field), we calculate the condensate and the superfluid fractions as a function of density and strengths of disorder and interaction. The disorder impact on the anomalous density, the chemical potential, and the ground-state energy is also analyzed. We show that the peculiar interplay of the dipole-dipole interaction and weak disorder makes the superfluid fraction and sound velocity anisotropic. ©2015 American Physical Society.


Boudjemaa A.,University of Hassiba Ben Bouali Chlef
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

We study the behavior of an unusual doubly quantized vortex in a harmonically trapped Bose gas at nonzero temperatures by using the time-dependent Hartree-Fock-Bogoliubov equations. This structure, which exhibits nontrivial features, generates spontaneously in the anomalous fraction when phases corresponding to the singly charged vortex are imposed in the condensed and the anomalous components of the gas. Our numerical calculations show that at low temperature, condensed atoms tend to fill the core of the anomalous vortex. We demonstrate that the decay of this vortex is attributed to dissipation induced by the anomalous fluctuations. Excitation frequency and the radius core of the anomalous vortex are also investigated. © 2015 American Physical Society.

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