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Balghouthi M.,Center Des Recherches Et Des Technologies Of Lenergie | Ali A.B.H.,Center Des Recherches Et Des Technologies Of Lenergie | Trabelsi S.E.,Center Des Recherches Et Des Technologies Of Lenergie | Guizani A.,Center Des Recherches Et Des Technologies Of Lenergie
Energy Conversion and Management | Year: 2014

Concentrated solar power technology constitute an interesting option to meet a part of future energy demand, especially when considering the high levels of solar radiation and clearness index that are available particularly in Tunisia. In this work, we study a medium temperature parabolic trough solar collector used to drive a cooling installation located at the Center of Researches and Energy Technologies (CRTEn, Bordj-Cedria, Tunisia). Optical evaluations of the collectors using photogrammetric techniques were performed. The analysis and readjustments of the optical results were conducted using a Matlab code. Therefore, slope errors ranged from -3 to +27 milliradian and the height deviations from the ideal shapes of the parabolic trough collector were 2.5 mm in average with a maximum of 7.5 mm. The intercept factor was determined using both the method of the total optical errors and the camera target method leading respectively to 0.62 and 0.7. Thus, the values of the overall optical efficiency were 0.48 and 0.514. Conversely, a thermal performance testing of the parabolic trough collector was conducted leading to the thermal efficiency and the heat losses evaluations. The instantaneous thermal efficiency reached a maximum of 0.43 but it did not exceed the value of 0.30 when the reflector becomes dirty by dust deposition. This study was also an opportunity for suggesting some recommendations for the enhancement of the PTC performances. © 2014 Elsevier Ltd. All rights reserved.


Ben Khelifa N.,CNRS Laboratory of Technology and Innovation | Ben Khelifa N.,Center Des Recherches Et Des Technologies Of Lenergie | Alloui Z.,University of Montréal | Beji H.,CNRS Laboratory of Technology and Innovation | And 2 more authors.
Journal of Non-Newtonian Fluid Mechanics | Year: 2012

This paper investigates the onset of motion and the resulting convective motion in a shallow porous cavity filled with a non-Newtonian binary fluid. The two horizontal walls of the system are subject to constant fluxes of heat and solute while the two vertical ones are impermeable and adiabatic. A power law model is used to characterize the non-Newtonian fluid behavior of the binary solution. The governing parameters for the problem are the thermal Rayleigh number R T, power-law index n, Lewis number Le, buoyancy ratio φ, aspect ratio of the cavity A, normalized porosity ξ, and parameter a defining double-diffusive convection (a=0) or Soret induced convection (a=1). An analytical solution, valid for shallow enclosures (A>> 1), is derived on the basis of the parallel flow approximation. Criteria, for supercritical and subcritical onset of motions, are predicted. In the range of the governing parameters considered in this study, a good agreement is found between the analytical predictions and the numerical results obtained by solving the full governing equations. © 2011 Elsevier B.V.


Ben Hassen A.,Center Des Recherches Et Des Technologies Of Lenergie | Trichet J.,CNRS Earth Sciences Institute of Orléans | Disnar J.-R.,CNRS Earth Sciences Institute of Orléans | Belayouni H.,Tunis el Manar University
Swiss Journal of Geosciences | Year: 2010

Paléocène-Early Eocene phosphate outcrop in the Ras-Draâ deposit (Tunisia) comprises alternances of P-rich strata (P 2O 5 ≥ 18%) and P-poor ones (P 2O 5 ≤ 2%). In phosphate rich strata, P is concentrated in rounded grains-so-called pellets-(28% ≤ P 2O 5 ≤ 38%) embedded in a matrix-so-called exogangue-much poorer in P (P 2O 5 # 7%) than pellets. The study of pellets (whose size lies mainly between 100 and 500 μm), of their surrounding matrix and of poorly phosphatic sediments, interlayered between the phosphatic strata, has been performed by optical microscopy and various chemical analyses, ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) and punctual chemical analyses by EDS (Energy Dispersive Spectroscopy). Mineralogical and chemical studies of the Tunisian phosphatic pellets show that the basic mineralogical component of these grains is carbonate-fluor-apatite, or francolite. The structural formula of a representative specimen of francolite in the basin is as follows: (Ca 4.63Mg 0.13Na 0.22)(PO 4) 2.51(CO 3) 0.48(OH 0.77F 0.23). The mineralogy of the constituents of the sediment surrounding pellets comprises carbonates, clays, silica (opal, quartz). Microscopic observations of Ras-Draâ phosphorites, added to geochemical results, establish that pellets are small bodies, allochtonous to their matrix and whose composition is independent of that of this matrix. Fecal cylindrical bodies and subspherical pellets, the latest being supposed to proceed from the fecal bodies by fragmentation, are considered to have been formed by fishes, as P-rich and organic matter-rich faeces. These faeces turn out to be resistant to mechanical dispersion and to chemical diffusion of soluble elements from and in direction of sea water. This closeness is responsible for the strong reducing conditions having prevailed inside and during the pellets diagenesis. © 2010 Swiss Geological Society.


Ben Belgacem A.,University of Paris 13 | Ben Belgacem A.,Center Des Recherches Et Des Technologies Of Lenergie | Hinkov I.,University of Chemical Technology and Metallurgy of Sofia | Yahia S.B.,Center Des Recherches Et Des Technologies Of Lenergie | And 2 more authors.
Materials Today Communications | Year: 2016

This article describes the significant roles of process parameters in the deposition of boron and nitrogen co-doped multi-walled carbon nanotubes via the arc-discharge process. The fabrication process is based on the vaporization of solid hexagonal boron nitride embedded in graphite cylinders in a nitrogen atmosphere with pressure varying from 350 mbar to 700 mbar and controlled current density between 150 and 420 A/cm2. Our results show the presence of significant amount of doped boron carbon nitride nanotubes in the cathodic deposit. These nanotubes have a narrow diameter distribution (20–30 nm) and a length up to 1 μm as analyzed by scanning electron microscopy and transmission electron microscopy. In addition to the experimental study, numerical simulations were performed to determine the temperature and chemical species distributions in the arc plasma under specific boron carbon nitride nanotubes synthesis conditions, thereby providing valuable insight into nanotubes growth and doping mechanisms in the arc. © 2016 Elsevier Ltd


Abdellaoui T.,Center Des Recherches Et Des Technologies Of Lenergie | Bennaceur J.,Center Des Recherches Et Des Technologies Of Lenergie | Chtourou R.,Center Des Recherches Et Des Technologies Of Lenergie
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2010

We present the optical properties of TiO2 deposited, by solgel method, on porous ntype GaAs substrates with different porosities and were thermally annealed at 600 °C for 15 min. The surface topography and density of grains packing at different samples were determined based on AFM images. AFM studies showed that the structure of the TiO2 thin film was nanocrystalline with grains size dependent on the etching time and ranging between 4 and 7 nm. The optical constants (n and k) of the films, as a function of etching time of GaAs substrate before and after deposition and content, were obtained using spectroscopic ellipsometer with rotating polarizer type in the ultravioletvisiblenear infrared (UVvisNIR) regions. The thickness of TiO 2 thin films (top layer) and the mixed layer of TiO2 and porous GaAs (bottom layer) were determined by scanning electroscopic spectroscopy (SEM) and confirmed by spectroscopic ellipsometry using a modified Cauchy dispersion law for optical index calculation and through an optical model with double layers dispersion, we were able to determine the change of the optical properties of porous GaAs with integration effect of the TiO2 particle. © 2010 Elsevier B.V.


Zarroug A.,Center Des Recherches Et Des Technologies Of Lenergie | Derbali L.,Center Des Recherches Et Des Technologies Of Lenergie | Ezzaouia H.,Center Des Recherches Et Des Technologies Of Lenergie
Materials Science in Semiconductor Processing | Year: 2015

This paper describes a study to understand the impact of heat treatment on the crystal Silicon (c-Si) with developed surface by Aluminum /Porous silicon (Al/PS) and evaluating their influence on the solar cell performance. In fact, the heat treatment of silicon surfaces with PS/Al is an effective means of structural and electrical adjustment and performance improvement of c-Si solar cells. The new process could be accomplished by a two-step annealing in order to benefit from both the high and low temperature processes. The advantages of such a new getter in comparison with traditional getter were demonstrated in various devices. We can estimate that the resistivity using the standard Van Der Pauw, and LBIC measurements have been performed to determine the diffusion length. The resistivity of crystalline silicon decreased when the porous layer was removed at about a depth around 70 μm. As a result, we found amelioration in the I-V characteristics and an enhancement of minority carrier lifetime. It has been shown that this simple method leads to improve the charge carrier collection and the electrical properties of c-Si based solar cells. © 2014 Elsevier Ltd. All rights reserved.


Mounir F.,Center National des Recherches en science des Materiaux | Karima H.-N.,Center National des Recherches en science des Materiaux | Khaled B.S.,Center Des Recherches Et Des Technologies Of Lenergie | Mokhtar F.,Center National des Recherches en science des Materiaux
Physica B: Condensed Matter | Year: 2012

Polycrystalline powder and single-crystal of LiLa(PO 3) 4 are synthesized by solid state reaction and flux technique, respectively. A morphological description of the obtained product was made based on scanning electron microscopy micrographs. The obtained powder was characterized by X-ray powder diffraction, FTIR and Raman spectroscopies. Ionic conductivity of the LiLa(PO 3) 4 powder was measured and evaluated over a temperature range from 553 to 913 K. Single crystals of LiLa(PO 3) 4 are characterized by single-crystal X-ray diffraction. The LiLa(PO 3) 4 structure was found to be isotypic with LiNd(PO 3) 4. It crystallizes in the monoclinic system with space group C2/c and cell parameters: a=16.635(6) Å, b=7.130(3) Å, c=9.913(3) Å, β=126.37(4)°, V=946.72(6) Å 3+ and Z=4. The LiLa(PO 3) 4 structure was described as an alternation between spiraling chains (PO 3) n and (La 3+, Li +) cations along the b direction. The small Li + ions, coordinated to four oxygen atoms, were located in the large connected cavities created between the LaO 8 polyhedra and the polyphosphate chains. The jumping of Li + through tunnels of the crystalline network was investigated using complex impedance spectroscopy. The close value of the activation energies calculated through the analysis of conductivity data and loss spectra indicate that the transport in the investigated system is through hopping mechanism. The correlation between ionic conductivity of LiLa(PO 3) 4 and its crystallographic structure was investigated and the most probably transport pathway model was determined. © 2012 Elsevier B.V. All rights reserved.


Abdellaoui T.,Center Des Recherches Et Des Technologies Of Lenergie | Daoudi M.,Center Des Recherches Et Des Technologies Of Lenergie | Bardaoui A.,Center Des Recherches Et Des Technologies Of Lenergie | Chtourou R.,Center Des Recherches Et Des Technologies Of Lenergie
Applied Surface Science | Year: 2010

Photoluminescence (PL) analysis is used to study porous layers elaborated by electrochemical etching of n+ Si-doped GaAs substrate with different etching times. Temperature and power dependence photoluminescence (PL) studies were achieved to characterize the effect of the etching time on the deep levels of the n+ Si-doped GaAs. The energy emission at about 1.46 eV is attributed to the band-to-band (B-B) (e-h) recombination of a hole gas with electrons in the conduction band. The emission band is composed of four deep levels due to the complex of (VAsSiGaVGa), a complex of a (Ga vacancy - donor - As vacancy), a (SiGa-VGa 3-) defect or Si clustering, and a (gallium antisite double acceptor-effective mass donor pair complex) and which peaked, respectively, at about (0.94, 1, 1.14, and 1.32 eV). The PL intensity behavior as function of the temperature is investigated, and the experimental results are fitted with a rate equation model with double thermal activation energies. © 2010 Elsevier B.V. All rights reserved.


Alloui Z.,University of Montréal | Ben Khelifa N.,CNRS Laboratory of Technology and Innovation | Ben Khelifa N.,Center Des Recherches Et Des Technologies Of Lenergie | Beji H.,CNRS Laboratory of Technology and Innovation | And 3 more authors.
Journal of Non-Newtonian Fluid Mechanics | Year: 2013

This paper reports an analytical and numerical study of natural convection in a shallow enclosure filled with a non-Newtonian fluid. Thermal boundary conditions of the Neumann type are applied on the horizontal walls of the enclosure while the vertical walls are assumed adiabatic. A power law model is used to characterize the non-Newtonian fluid behavior of the fluid. The governing parameters for the problem are the thermal Rayleigh number Ra, power-law index n, Prandtl number Pr and cavity aspect ratio A. An analytical solution, valid for an infinite layer, is derived on the basis of the parallel flow approximation. Rigid-rigid, free-free and rigid-free hydrodynamic boundary conditions are considered. It is demonstrated that, for shear-thinning fluids, the onset of convection is subcritical. For shear thickening fluids, convection is found to occur at a supercritical Rayleigh number equal to zero. The effects of the non-Newtonian behavior on the fluid flow, temperature field and heat transfer are discussed. A good agreement is found between the analytical predictions and the numerical results obtained by solving the full governing equations. © 2013 Elsevier B.V.


PubMed | Tunis el Manar University, Center Des Recherches Et Des Technologies Of Lenergie, CNRS Institute of Electronics, Microelectronics and Nanotechnology, Lille University of Science and Technology and 3 more.
Type: | Journal: Journal of colloid and interface science | Year: 2016

A 980nm laser-driven antimicrobial photothermal therapy using poly(vinylpyrrolidone) -coated Prussian Blue nanoparticles (PVP/PB NPs) is demonstrated. This approach allows an efficient eradication of a virulent strain of Gram-negative Escherichia coli (E. coli) associated with urinary tract infection as well as for the ablation of antibiotic resistant pathogens such as methicillin resistant Staphylococcus aureus (MRSA) and extended spectrum -lactamase (ESBL) E. coli. Interestingly the 980nm irradiation exhibits minimal effect on mammalian cells up to a PVP/PB NPs concentration of 50gmL(-1), while at this concentration bacteria are completely eradicated. This feature is certainly very promising for the selective targeting of bacteria over mammalian cells.

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