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Search Results: 1 - 10 of 18 matches for " Khemaies Zayani "
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Assessing Sprinkler Irrigation Performance Using Field Evaluations at the Medjerda Lower Valley of Tunisia  [PDF]
Samir Yacoubi, Khemaies Zayani, Adel Slatni, Enrique Playán
Engineering (ENG) , 2012, DOI: 10.4236/eng.2012.410087
Abstract: Irrigation uniformity and wind drift and evaporation losses (WDEL) are major concerns for the design and management of sprinkler irrigation systems under arid or semi-arid conditions. Field trials were carried out to assess irrigation uniformity and WDEL under various wind velocities, sprinkler spacings and operating pressure heads. Based on experimental data, a frequency analysis was performed to infer the occurrence probability of a given uniformity coefficient (UC). In addition, statistical regressions were used to model WDEL as a function of different climatic variables. Increasing the operating pressure head improved uniformity at low wind speeds. It was shown that UC has been severely impaired at wind speeds above 4 m/s. In the prevailing wind conditions, the frequency analysis showed that a sprinkler spacing of 12 m × 12 m provided the best uniformity. In the local conditions, it is recommended to stop irrigation when wind velocity exceeds 4 m/s. Moreover, it was shown that wind speed and relative humidity were the main significant variables influencing WDEL.
Improvement of Durum Wheat (Triticum durum) Surface Irrigation in Swelling Soils  [PDF]
Adel Slatni, Khemaies Zayani, Ali Chebil, Abdelaziz Zairi, Samir Yacoubi, Enrique Playan
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.52033
Abstract:

This study is targeted to improve surface irrigation performance of durum wheat in swelling soils. For this purpose, furrow and border irrigation trials were carried out and evaluated under different soil water depletion rates, furrow spacing and unitary inlet discharges. Irrigation was triggered whenever the soil water depletion rate reached a predetermined threshold. A comprehensive irrigation evaluation produced hydraulic, agronomic and economic indicators, such as application efficiency, distribution uniformity, crop yield, gross margin and water productivity. Experimental results showed that supplied water depths exceeded soil water deficits, inducing relevant vertical and lateral water losses. Al- though border and furrow irrigation crop yields were virtually tantamount (about 5.5 Mg/ha), furrow irrigation was the system of choice. An irrigation strategy based on a furrow spacing of 150 cm, an inlet discharge of 2 l/s/furrow and a soil water depletion rate of 30% required a gross water depth of 4300 m3/ha/yr and generated an optimum crop yield of 58 qx/ha. In the analyzed range of soil water depletion, the gross margin and water value amounted to 1064 - 1390 Tunisian Dinar per hectare (TD/ha) and 0.39 - 0.44 TD/m3, respectively, for a furrow spacing of 150 cm.

Required Lateral Inlet Pressure Head for Automated Subsurface Drip Irrigation Management
Moncef Hammami,Khemaies Zayani,Hédi Ben Ali
International Journal of Agronomy , 2013, DOI: 10.1155/2013/162354
Abstract: Subsurface drip irrigation (SDI) is one of the most promising irrigation systems. It is based on small and frequent water supplies. Because SDI emitters are buried, their discharges are dependent on the water status at the vicinity of the outlets. This paper was targeted to design the SDI laterals accounting for the soil water-retention characteristics and the roots water extraction. The proposed approach provides systematic triggering and cut-off of irrigation events based on fixed water suctions in the vadose zone. In doing so, the soil water content is maintained at an optimal threshold ascertaining the best plant growth. Knowing the soil water-retention curve, the appropriate water suction for the plant growth, and the emitter discharge-pressure head relationship, the developed method allows the computation of the required hydraulics of the lateral (e.g., inlet pressure head, inside diameter, etc.). The proposed approach is a helpful tool for best SDI systems design and appropriate water management. An illustrative example is presented for SDI laterals’ design on tomato crop. 1. Introduction In subsurface drip irrigation (SDI), water seeps from the buried emitters into the soil and spreads out in the vadose zone under the conjugate effect of capillary and gravity forces [1, 2]. Thus, SDI system allows the direct application of water to the rhizosphere maintaining dry the nonrooted topsoil. This pattern generates numerous advantages such as minimizing soil evaporation and then evapoconcentration phenomenon. The rationale is that SDI improves the water application uniformity, increases the laterals and emitters longevity, reduces the occurrence of soil-borne diseases, and allows the control of weeds infestation. Several field trials revealed relevant profits on managing SDI for crop production. Nevertheless, the appropriate depth of buried laterals remains debatable [3–6]. Comparing evaporation from surface and subsurface drip irrigation systems, Evett et al. [7] reported that 51?mm and 81?mm were saved with drip laterals buried at 15?cm and 30?cm, respectively. Neelam and Rajput [1] recorded maximum onion yield (25.7?t?ha?1) with drip laterals buried at 10?cm. According to these authors, the maximum drainage occurred when drip laterals are laid at 30?cm depth. On the other hand, numerous studies were devoted to the analysis of the effect of the soil properties on the SDI emitters discharge and water distribution uniformity [8–10]. The analytical approach proposed by Sinobas et al. [2] predicts reasonably well the soil water suction and the pressure
Structural and Optical Properties of Znx-1MgxO Ceramic Composites  [PDF]
Zayani Jaafar Othman, Adel Matoussi
Materials Sciences and Applications (MSA) , 2012, DOI: 10.4236/msa.2012.38076
Abstract: In the present work, we investigate the structural and optical properties of Znx-1MgxO composites prepared by the standard sintering method at 1200?C during 24 hours and doped with different percentages of magnesium x between 0% and 40%. For this purpose, we have used the X-ray diffraction (XRD) and the atomic force microscopy (AFM) to study the effect of the magnesium’s proportion on the crystalline and morphology proprieties of the obtained samples. XRD analysis showed that all films are polycrystalline with a hexagonal wurtzite structure, with an orientation of the grains according to directions (0002) and (10-10). The AFM characterisation show that the degree of surface roughness (RMS) increases with the increasing of MgO content. Optical properties of the ceramics were investigated by Absorbance and Reflectance measurements at room temperature in the wavelength range 200 - 2400 nm. Optical band gap energies (Eg) were determined. Further cathodoluminescence and dielectric measurements would be carried out to study the influence of MgO doping on the dielectric and luminescent properties of the ZnMgO ceramics.
Equity Market Timing and Capital Structure: Evidence from Tunisia and France
Khemaies Bougatef,Jameleddine Chichti
International Journal of Business and Management , 2010, DOI: 10.5539/ijbm.v5n10p167
Abstract: This paper investigates the relevance of market timing considerations on the debt-equity choice using a panel of tunisian and french listed firms. Consistent with the market timing theory, we find that firms tend to issue equity when their market valuations are relatively higher than their book values and after market performance improvement. As a consequence, these firms become underlevraged in the short-term and this impact of equity market timing on capital structure persists beyond eight years.
Effect of Different Kinetic Factors on the Thermochemistry of Sulfophosphoric Attack Reaction of Natural Phosphate Tunisian by DRC  [PDF]
Olfa Lachkar-Zamouri, Khemaies Brahim, Faten Bennour, Ismail Khattech
Advances in Materials Physics and Chemistry (AMPC) , 2018, DOI: 10.4236/ampc.2018.811029
Abstract:
Mixture of phosphoric and sulfuric acid solutions has been used to investigate the dissolution of natural phosphates (PN) by DRC. The effect of concentration, particle size and stirring speed reaction is examined. Thermochimique properties of each kinetic parameters reaction are determined. It was found that these parameters have a considerable effect on the thermochemical aspect of the attack reaction. It is known that the process of PN sulphophosphoric acid attack leads to the formation of dihydrate (CaSO4.2H2O: DH). The present work shows the precipitation of other residues their formula depends on factors studied. The increase in concentration leads to the formation of hemihydrate (CaSO4v1/2H2O:HH) beside DH for the low values of% H2SO4 due to the solubility of dihydrate on the etching solution and the precipitation of (Ca (H2PO4)2.2H2O) next of DH for low agitation values because of the lack of turbulence between the liquid phase and the solid phase which favors the precipitation of this latter compound.
Attack of Tunisian Phosphate Ore by a Mixture of Sulfuric and Phosphoric Acid: Thermochemical Study by Means of Differential Reaction Calorimetry  [PDF]
Olfa Lachkar-Zamouri, Khemaies Brahim, Feten Bennour-Mrad, Ismail Khattech
Advances in Materials Physics and Chemistry (AMPC) , 2018, DOI: 10.4236/ampc.2018.810028
Abstract:
A calorimetric, Differential Reaction Calorimetry (DRC), study of the thermochemical of the attack of a phosphate ore from Gafsa region (Tunisia) by a mixture of sulfuric and phosphoric acid is undertaken at different solid-liquid ratio and different temperature. The plot of the quantity of heat measured by integrating the raw signal as a function of the dissolved mass in the same volume solution at 25 presents three straight segments attributed at the formation of the hemihydrate (CaSO4·1/2H2O:HH), the dihydrate (CaSO4·2H2O:DH) or a mixture of these two products checked by X-ray diffraction, infrared spectroscopy and thermal analysis (Differential Scanning Calorimeter: DSC). The attack by the acid mixture was performed at higher temperature and showed in addition the formation of another form of calcium sulfate:anhydrous (CaSO4:AH). Moreover, the variation of mass enthalpy versus temperature presents a break at the T = 45. According to our results, it seems that the effect of the temperature on the sulfo-phosphoric attack reaction on the natural phosphate (NP) generates a change of mechanism at around 45.
Probabilistic verification and evaluation of Backoff procedure of the WSN ECo-MAC protocol
Hafedh ZAYANI,Kamel BARKAOUI,Rahma BEN AYED
International Journal of Wireless & Mobile Networks , 2010,
Abstract: Communication protocols and techniques are often evaluated using simulation techniques. However, theuse of formal modeling and analysis techniques for verification and evaluation in particular for WirelessSensor Networks (WSN) becomes a necessity. In this paper we present a formal analysis of the backoffprocedure integrated in the medium access control protocol named ECo-MAC designed for WSN. Wedescribe this backoff procedure in terms of discrete time Markov chains (DTMCs) and evaluated usingthe well known probabilistic model checker PRISM. After checking the different invariants of theproposed model, we study the effect of contention window length (in number of time contention unit) onthe acceptable number of simultaneous senders in a neighborhood of a given receiver. The obtainedquantitative results confirm those provided by the simulation using OPNET tool and justify the validity ofthe adopted value for the time contention unit TCU.
Adaptive Predistortions Based on Neural Networks Associated with Levenberg-Marquardt Algorithm for Satellite Down Links
Zayani Rafik,Bouallegue Ridha,Roviras Daniel
EURASIP Journal on Wireless Communications and Networking , 2008,
Abstract: This paper presents adaptive predistortion techniques based on a feed-forward neural network (NN) to linearize power amplifiers such as those used in satellite communications. Indeed, it presents the suitable NN structures which give the best performances for three satellite down links. The first link is a stationary memoryless travelling wave tube amplifier (TWTA), the second one is a nonstationary memoryless TWT amplifier while the third is an amplifier with memory modeled by a memoryless amplifier followed by a linear filter. Equally important, it puts forward the studies concerning the application of different NN training algorithms in order to determine the most prefermant for adaptive predistortions. This comparison examined through computer simulation for 64 carriers and 16-QAM OFDM system, with a Saleh's TWT amplifier, is based on some quality measure (mean square error), the required training time to reach a particular quality level, and computation complexity. The chosen adaptive predistortions (NN structures associated with an adaptive algorithm) have a low complexity, fast convergence, and best performance.
Adaptive Predistortions Based on Neural Networks Associated with Levenberg-Marquardt Algorithm for Satellite Down Links
Rafik Zayani,Ridha Bouallegue,Daniel Roviras
EURASIP Journal on Wireless Communications and Networking , 2008, DOI: 10.1155/2008/132729
Abstract: This paper presents adaptive predistortion techniques based on a feed-forward neural network (NN) to linearize power amplifiers such as those used in satellite communications. Indeed, it presents the suitable NN structures which give the best performances for three satellite down links. The first link is a stationary memoryless travelling wave tube amplifier (TWTA), the second one is a nonstationary memoryless TWT amplifier while the third is an amplifier with memory modeled by a memoryless amplifier followed by a linear filter. Equally important, it puts forward the studies concerning the application of different NN training algorithms in order to determine the most prefermant for adaptive predistortions. This comparison examined through computer simulation for 64 carriers and 16-QAM OFDM system, with a Saleh's TWT amplifier, is based on some quality measure (mean square error), the required training time to reach a particular quality level, and computation complexity. The chosen adaptive predistortions (NN structures associated with an adaptive algorithm) have a low complexity, fast convergence, and best performance.
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