مقـــــــــالات 2010-2015

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Visualization of soot inception in turbulent pressurized flames by simultaneous measurement of laser-induced fluorescence of polycyclic aromatic hydrocarbons and laser-induced incandescence, and correlation to OH distributions
(Springer, 2015) Geigle, Klaus Peter; O’Loughlin, William; Hadef, Redjem; Meier, Wolfgang
Distributions of polycyclic aromatic hydrocarbons (PAH) and their correlation with soot formation were studied in ethylene–air swirl flames stabilized in a gas turbine model combustor at increased pressure. The combustor can be operated with secondary air injection to study the influence of soot oxidation. We employed PAH laserinduced fluorescence using UV excitation simultaneously with IR-excited laser-induced incandescence to identify soot. PAH signatures typically appear discontinuous unlike OH, yet similar to soot but exhibit more uniform intensity and larger size. The correlation of both diagnostics allowed identification of a wide range of soot formation progress, including isolated soot or PAH, as well as PAH transitioning into soot. The occurrence of soot, PAH and OH and their spatial variations are strongly dependent on the properties of the flow field. In the bottom part of the inner recirculation zone and for the reference case, a rich flame with additional oxidation air, soot levels are relatively high, while PAH intensities in this region are minimal. This correlates well with high temperatures in this region published recently, which are unfavorable for soot formation as the precursors, PAH, decompose. Consequently, soot presence here is attributed to transport. In contrast to OH and soot distributions which change significantly upon addition of secondary air downstream of the primary combustion zone, PAH distributions for both cases look relatively similar. This is attributed to a downstream consumption of PAH by different processes. Without oxidation air, PAH completely transform into soot, while additional oxidation air leads to their oxidation.
Predictive direct power control for photovoltaic grid connected system
(ELSelsevier, 2013) Barra, Kamel; Rahem, Djamel
The paper presents an improved predictive power control for a photovoltaic conversion chain connected to a grid based on finite states space model of the converter. The proposed control algorithm selects the switching state of the inverter that minimizes the error between active and reactive power predictions to their computed values for all different voltage vectors. The optimal voltage vector that minimizes a cost function is then applied to the output of the power converter. Once the proposed predictive strategy is validated, a multilevel converter is then used to improve and highlight the obtained results. The proposed predictive control strategy uses only one sample time prediction and it is very intuitive since it is very simple and provides best performances compared to other modulation techniques.
Particles of Spin Zero and 1/2 in Electromagnetic Field with Confining Scalar Potential in Modified Heisenberg Algebra
(Springer, 2015) Tilbi, A; Merad, M; Boudjedaa, T
In this paper, we propose to solve the relativistic Klein Gordon and Dirac equations subjected to the action of a uniform electomagnetic field confining scalar potential yin the presence of a minimal length in the momentum space. In both cases, the energy eigenvalues and their corresponding eigenfunctions are obtained. The limiting cases is then deduced for a small parameter of deformation.
Optimization of essential oil supercritical extraction from Algerian Myrtus communis L. leaves using response surface methodology
(ELSelsevier, 2013) Zermane, A; Larkeche, O; Meniai, A.-H; Crampon, C; Badens, E
The present work deals with the application of the supercritical fluid extraction process to extract essential oils from the leaves of an Algerian myrtle plant (Myrtus communis L.). Using the surface response methodology, an optimization of the extraction recovery was carried out, varying the pressure in the range of [10–30 MPa], the temperature within [308–323 K], a solvent flow rate fixed at 0.42 kg h−1 and a mean particle diameter equal to 0.5 mm or less than 0.315 mm. The maximum value of essential oil recovery relative to the initial mass of leaf powder was 4.89 wt%, and was obtained when the SC–CO2 extraction was carried out under 313 K, 30 MPa and with a particle diameter less than 0.315 mm. A second-order polynomial expression was used to express the oil recovery. The calculated mass of recovered oil usingthe response surface methodology was very close to the experimental value, confirming the reliability of this technique.
Vessel development and the importance of lateral flow in water transport within developing bundles of current-year shoots of grapevine (Vitis vinifera L.)
(Springer, 2012) Halis, Youcef; Djehichi, Samah; Senoussi, Mohamed Mourad
In the developing xylem bundles of young stems, the presence of immature living vessel elements can strongly restrict or even block axial hydraulic conductance, especially in newly matured vessels. Lateral connections between vessels may provide an alternative pathway for water movement to bypass these closed, living elements. Using the grapevine as a model system, the present study aimed to demonstrate the effects of living vessel elements on water movement patterns, and the importance of lateral flow for effective water conductivity in the developing bundles. Living vessel elements were detected using dye staining and the pattern of vessel development and maturation was then monitored. The importance of lateral flow was confirmed using several approaches: (1) capacity for lateral flow, (2) effect of increasing the distance of water transport, and (3) effect of ion concentrations. Living vessel elements were found along the developing bundles, they occupied a significant proportion of the distal and peripheral parts of the flow path, forming a substantial barrier to apoplastic water flow. Water in the developing xylem bundles could move easily from vessel to vessel and between secondary and primary xylem. Furthermore, data from increasing the transport length and altering the ion concentrations supported the critical contribution of the lateral flow to the total hydraulic conductance within the developing bundles. The hydraulic architecture of the developing xylem bundles is described. The results are discussed in terms of reliability and efficiency of water transport during shoot growth and development.
Two-dimensional spin-FET transistor
(Springer, 2015) Boudine, A.; Kalla, L.; Benhizia, K.; Zaabat, M.; Benaboud, A.
On the distribution of certain Pisot numbers
(Selsevier, 2012) Zaimi, Toufik
A Pisot number θ is said to be simple if the beta-expansion of its fractional part, in base θ, is finite. Let P be the set of such numbers, and S \ P be the complement of P in the set S of Pisot numbers. We show several results about the derived sets of P and of S \P. A Pisot number θ, with degree greater than 1, is said to be strong, if it has a proper real positive conjugate which is greater than the modulus of the remaining conjugates of θ. The set, say X, of such numbers has been defined by Boyd (1993) [5], and is contained in S \ P. We also prove that the infimum of the j -th derived set of X, where j runs through the set of positive rational integers, is at most j + 2. ⃝⃝c 2012 Royal Dutch Mathematical Society (KWG). Published by Elsevier B.V. All rights reserved.
Thermal effects of scanning electron microscopy on He diffusion in apatite
(Elsevier, 2013)
In order to investigate potential diffusive loss of He from apatites during SEM analysis, we performed (1) single-grain (U\Th)/He dating for 47 Durango apatite fragments (from b90 μm to 150–250 μm) which were previously examined using SEM under different analytical conditions, and (2) electron–matter interaction simulation combined with diffusion modeling. The determined (U\Th)/He ages are internally consistent within their errors, and indistinguishable from the reported 40Ar/39Ar ages of 31.44 ± 0.18 (2σ) Ma and the apatite (U\Th)/He ages of 31.02 ± 1.01 Ma (Standard Deviation; McDowell et al., 2005). The results from the electron–matter interaction simulation suggest that “temperature rise” (ΔT = temperature increase during electron bombardment) peaks within a very thin layer at the outermost of the hypothetical apatite grain, and falls below ~50 K within a depth of 0.3 μm from the surface. Based on the simulated ΔT profile combined with available He diffusion parameters, the fractional loss of He (fHe) was calculated for different apatite grain dimensions. The numerical simulation supports that the He loss from apatite grains of typical physical dimensions is negligible (b1%) under regular SEM operating conditions. The direct measurements of (U\Th)/He ages for SEM-treated apatites, as well as diffusion simulation using the electron–matter interaction model, indicate that SEM spot analysis or extensive chemical mapping prior to apatite (U\Th)/He dating does not cause any meaningful diffusive He loss for most of the apatite samples.
On solvability of the integrodifferential hyperbolic equation with purely nonlocal conditions
(Science Direct, 2015) Merad, Ahcene; Bouziani, Abdelfatah; Ozel, Cenap; Kilic¸man, Adem
In this study, we prove the existence, uniqueness, and continuous dependence upon the data of solution to integro-differential hyperbolic equation with purely nonlocal (integral) conditions. The proofs are based on a priori estimates and Laplace transform method. Finally, we obtain the solution using a numerical technique (Stehfest algorithm) by inverting the Laplace transform.
Theoretical estimation of the temperature and pressure within collapsing acoustical bubbles
(Elsevier, 2014) Merouani, Slimane; Hamdaoui, Oualid; Rezgui, Yacine; Guemini, Miloud
Formation of highly reactive species such as OH, H , HO2 and H2O2 due to transient collapse of cavitation bubbles is the primary mechanism of sonochemical reaction. The crucial parameters influencing the formation of radicals are the temperature and pressure achieved in the bubble during the strong collapse. Experimental determinations estimated a temperature of about 5000 K and pressure of several hundreds of MPa within the collapsing bubble. In this theoretical investigation, computer simulations of chemical reactions occurring in an O2-bubble oscillating in water irradiated by an ultrasonic wave have been performed for diverse combinations of various parameters such as ultrasound frequency (20–1000 kHz), acoustic amplitude (up to 0.3 MPa), static pressure (0.03–0.3 MPa) and liquid temperature (283– 333 K). The aim of this series of computations is to correlate the production of OH radicals to the temperature and pressure achieved in the bubble during the strong collapse. The employed model combines the dynamic of bubble collapse in acoustical field with the chemical kinetics of single bubble. The results of the numerical simulations revealed that the main oxidant created in an O2 bubble is OH radical. The computer simulations clearly showed the existence of an optimum bubble temperature of about 5200 ± 200 K and pressure of about 250 ± 20 MPa. The predicted value of the bubble temperature for the production of OH radicals is in excellent agreement with that furnished by the experiments. The existence of an optimum bubble temperature and pressure in collapsing bubbles results from the competitions between the reactions of production and those of consumption of OH radicals at high temperatures.
The effect of the starting powders particle size on the electrical properties of sintered Co doped ZnO varistors
(Springer, 2015) Hamdelou, S.; Guergouri, K.; Arab, L.
Pure and Co doped zinc oxide nanopowders have been synthesized by sol–gel route. The obtained powders, after calcination in air at 550, 650, 750 and 850 C, were consolidated and sintered using microwaves. The effect of sintering temperature on the density and electrical properties was investigated. The best characteristics are obtained using a sintering temperature equal to 1,075 C. The powders and sintered samples are characterized by X-ray diffraction, microstructure images, density and electrical measurements. The studied nanopowders have: a density of 5.22 (g/cm3), a breakdown voltage of 446.5 V/mm and a coefficient of non-linearity of 11.48 for ZnO doped with 7 mol% Co, and a density of 5.19 (g/cm3), a breakdown voltage of 292.5 V/mm and a non-linearity coefficient of 11.62 for ZnO doped with 5 mol% Co. The XRD results indicate that pure and Co doped ZnO powders are solid solutions crystallizing in pure wu¨ rtzite structure, and consisted of a mixture of nanoparticles with an average grain size between 36 and 210 nm. The grain size decreases with increasing Co concentration and reaches its lowest value at 7 mol% Co and increases with increasing temperature. On the other hand the increase of Co concentration leads to a decrease of the porosity and an increase of the density of samples sintered at 1,070 C and leads also to an increase of the electric field (E) in the nonlinear area. The samples of 5 mol% Co sintered at 1,075 C, show that the non-linear coefficient a decreases by increasing of calcined temperature, therefore increases with decreasing of grain and particle sizes.
The effectofgrowthconditions,pointdefectsandhydrogen on theelectronicstructureandpropertiesofp-type(Al,N) codopedZnO
(Elsevier, 2015)
The effectsofpointdefects,hydrogen,andgrowthconditionsontheelectronicstructure and propertiesofthe(Al,N)codopedp-typeZnOhavebeeninvestigatedusingthefirst principlesmethod.TheobtainedresultsshowedthattheAlZn–NO–VZn complexisa shallowacceptorthatcanplayanimportantroleinachievingthep-typeconductivityin the (Al,N)codopedZnOfilms.Ourresultsshowedalsothattheelectricalconductivitytype in the(Al,N)codopedZnOfilmsstronglydependsonthedonor/acceptorconcentrations ratio. ThecodopedZnOfilmspreparedunderbothZn-richandO-richgrowthconditions withadonors/acceptorsratioof1:2haveap-typeconductivity,whilethosepreparedwith a ratioof1:1cannotbep-typeunlessiftheyarepreparedunderO-richconditions.The achievedp-typequalitydependsalsoontheusednitrogendopingsource.Toprepare p-typeZnOfilmofhighqualityusingthe(Al,N)codopingmethod,theuseofNOorNO2 is recommended.Thepresenceofdonordefectssuchasoxygenvacanciesandhydrogenwill significantlyaffecttheelectronicpropertiesofthe(Al,N)codopedZnOfilms,andifthe concentrationofthesedefectsinthesampleishighenough,thematerialcanbeeasily convertedton-type.
Observation ofMeyer–NeldelruleinCdSthinfilms
(Elsevier, 2011) Hariech, S; Aida, M.S; Moualkia, H
A study of electrical transport in CdS thin films is reported. We have observed, for the first time, that CdS thin film conductivity obeys the Meyer–Neldel rule (MNR). This was deduced from linking the conductivity pre-exponential factor to the activation energy variation. CdS films were deposited by chemical bath deposition at different solution temperatures in order to vary the electrical activation energy of the films. A correlation between the MNR rule and the disorder in the film network is highlighted. The multi- trapping process in the band tail-localized states governs the conductivity in CdS films. This explains the MNR observation in CdS films. The variation of the electrical conductivity pre-exponential factor and activation energy are correlated to the disorder in the film network; this was explained in terms of polaron formation and phonon– electron coupling with disorder.
The EBG structure with a forest metallic carbon nanotubes analysed by iterative method WCIP
(Elsevier, 2015) Dridi, Chahrazed; Zaabat, Mourad; Boudine, Azeddine
This study is dedicated to analysis of electromagnetic bandgap circuits based on the carbon nanotubes often called EBG structure, the carbon nanotubes are very promising candidates in the future technology. The WCIP iterative method based on the concept of wave introduces a new process related to incident wave and the reflected wave by diffraction operators defined in the spectral and spatial domain. The method has the advantage of simplicity since it does not involve basic functions and neither matrix inversions, like other methods of calculation. This is a rapid method and this grace to the use of the Fourier transform for the passage of spatial domain to the spectral domain and the inverse. In this work, we used the WCIP method, to analysis a forest of carbon nanotubes to characterize the EBG structure that operates as a bandstop to remove unwanted electromagnetic waves in a certain frequency range and showed that the geometric parameters of the carbon nanotubes are very important in the responses of the filters. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights .
New interpretation of the effects of argon-saturating gas toward sonochemical reactions
(Elsevier, 2014) Merouani, Slimane; Ferkous, Hamza; Hamdaoui, Oualid; Rezgui, Yacine; Guemini, Miloud
A number of literature reports showed that argon provides a more sonochemical activity than polyatomic gases because of its higher polytropic ratio; whereas several recent studies showed that polyatomic gases, such as O2, can compensate the lower bubble temperature by the self decomposition in the bubble. In this work, we show for the first time a numerical interpretation of these controversial reported effects. Computer simulations of chemical reactions inside a collapsing acoustic bubble in water saturated by different gases (Ar, O2, air and N2) have been performed for different frequencies (213–1100 kHz). In all cases, _OH radical is the main powerful oxidant created in the bubble. Unexpectedly, the order of saturating gases toward the production rate of _OH radical was strongly frequency dependent. The rate of production decreases in the order of Ar > O2 > air > N2 for frequencies above 515 kHz, and Ar starts to lose progressively its first order to the following gases with a gradually decreasing of frequency below 515 kHz up to a final order of O2 > air _ N2 > Ar at 213 kHz. The analysis of chemical kinetic results showed a surprising aspect: in some cases, there exists an optimum bubble temperature during collapse at which the chemical yield is much higher than that of the maximum bubble temperature achieved in the bubble. On the basis of this, we have concluded that the lower sonochemical activity induced by Ar for frequencies below 515 kHz is mainly due to the forte consumption of radicals inside a bubble prior the complete collapse being reached.
The Copper Indium Selenium (CuInSe2) thin films solar cells for Hybrid Photovoltaic Thermal Collectors (PVT)
(Elsevier, 2015) Haloui, H.; Touafek, K.; Zaabat, M.; Ben cheikh el hocine, H.; Khelifa, A.
Ternary chalcopyrite compounds which may act as an absorber in thin films solar cells are mainly CuGaSe2, the CuInS2, CuInSe2 and the CuAlSe2. Because of their large optical absorption coefficient, a thickness of 1.5-2 microns is sufficient to absorb the useful portion of the solar spectrum. The most promising appears to be the CuInSe2 material, a 18.8% efficiency is obtained by the solar cells based on this material. However, its low band gap (1,04ev) limits the open circuit voltage and thus the efficiency of the solar cell. In this work we present the application of this material in hybrid photovoltaic thermal collectors (PVT). For the determination of its electrical and thermal performance through the development of a heat balance that involves heat exchange between the different components of the collector. The results obtained show that we can have a thermal efficiency equal to (85.68%) and an electrical efficiency of the order of (19.22%) for our PVT collector based on CIS are better than the values obtained by PVT collector based on monocristallin silicon.
Molecular structure, bonding analysis and redox properties of transition metal–Hapca
(Elsevier, 2015)
Density functional theory (DFT) calculations were carried out on M(Hapca)2(H2O)2 (M = Mn, Fe, Co, Ni and Hapca = bis(3-aminopyrazine-2-carboxylic acid) by means of the BP86 and B3LYP functional using the TZP basis set. The optimized structures were obtained by imposing C2 or Ci symmetries. The Ci structural arrangement consists of a slightly distorted octahedron centered by a transition-metal with bidentate Hapca ligands situated in equatorial positions and water molecules in axial ones. However, the C2 structure consists of a distorted arrangement with n con-planar Hapca ligands. The influence induced by including double polarized functions in the (TZ2P) basis set is small on the geometrical parameters. A bonding analysis of these species showed the weakness of M–O(H2O) bonds compared to M–O(Hapca) ones. The obtained MO diagrams showed substantial HOMO–LUMO gaps for the 18-MVE closed-shell configuration. Reduction of M(Hapca)2(H2O)2 led to the loss of the two water molecules, inducing four electrons downwards for [Co]_ and [Ni] species. The calculated ionization potentials (IPs) and electronic affinities (EAs) showed the oxidation and reduction ease of the manganese species contrarily to the cobalt ones. A diffuse function in the basis set (QZ3P-ndiffuse, n = 1 or 2) reduces remarkably the adiabatic electron affinities (AEAs).
The concept of 2D gated imaging for particle sizing in a laminar diffusion flame
(Springer, 2013) Hadef, Redjem; Geigle, Klaus Peter; Zerbs, Jochen; Sawchuk, Robert A.; Snelling, David R.
Abstract In this work, time-resolved laser-induced incandescence (TiRe LII) has been employed to measure primary particle diameters of soot in an atmospheric laminar ethylene diffusion flame. The generated data set complements existing data determined in one single location and takes advantage of the good spatial resolution of the ICCD detection. Time resolution is achieved by shifting the camera gate along the LII decay. One key input parameter for the analysis of time-resolved LII is the local flame temperature. This was determined on a grid throughout the flame by coherent anti-Stokes Raman scattering. The accurate temperature data, in combination with other published data from this flame, are well suited for soot model validation purposes while we showed feasibility of a shifted gate approach to deduce 2D particle sizes in the chosen standard flame.
Mechanism of the sonochemical production of hydrogen
(Elsevier, 2015) Merouani, Slimane; Hamdaoui, Oualid; Rezgui, Yacine; Guemini, Miloud
It has been long recognized that propagation of an ultrasonic wave in water results in hydrogen production. The chemical effects of ultrasound (sonochemistry) originate from acoustic cavitation, that is, the formation, growth and implosive collapse of microscopic bubbles in liquid irradiated by ultrasound wave. Enormous temperatures and pressures are generated within the bubbles at the collapse, making each bubble as a microreactor within which typical flame reactions occur. The combustion in the cavitation bubbles yield species such as _OH, H_, O, HO2 _ and others. Although H2 is the most molecular product of water sonolysis, the mechanism of its production is until now not understood and the most reported suggestions are controversial. In this paper, a comprehensive numerical work was carried out, for the first time, to explain the mechanism of ultrasound induced generation of H2 in water. Computer simulations of chemical reactions occurring inside a bubble oscillating in water irradiated by an ultrasonic wave have been performed for different conditions. A kinetics mechanism of 25 reversible chemical reactions was proposed for studying the internal bubble-chemistry. The numerical simulations have evidenced the formation of H2 as well as other products such as O2, H2O2, _OH, H_, HO2 _ and O in the bubble during implosion. In all cases, H2 was the main product formed in the bubbles at appreciable amount. Basing on the simulation results and using material balance for hydrogen in the gas and liquid phases, the production rate of H2 in each phase has been quantified. The conclusion was that the main source of H2 production during water sonolysis is the gas phase of the bubbles through the reaction H_ ‏ _OH 4 H2 ‏ O. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Sustainable urban design of historical city centers
(Elsevier, 2015) Fezzai, Soufiane; Mazouz, Said; Ahriz, Atef
In the last few decades, sustainability had been introduced as one of the major concepts of design. It is the key to preserve a safe future for our communities. This concept introduces many techniques that change the way to read the urban configuration of urban heritage to search for the main parameters in urban space that manage the relation between designers think; it changes also the configuration of urban and architectural environment. First we try to space configuration and urban behavior. This study has as aim to create a model of analyzing urban space as a support of urban behavior and a generator of social sustainability through preserving heritage and traditional values. The analysis model is drawn theorically then tested on a set of case studies of historical city centers to prove its efficiency; the main case tested in this work is the historical center of Constantine (Casbah). The analysis model is based on space syntax methods and parameters, using applied analysis based on plans of different historical phases of urban growth and on site investigation. As a conclusion, we try by this work to show parameters of sustainability in urban space and the influence of urban changes on these parameters. The analysis model can be used to show how to use these parameters in future design operations to ensure urban sustainability.

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