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Search Results: 1 - 10 of 167657 matches for " E. Mrabet "
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Effects of Residue Management and Cropping Systems on Wheat Yield Stability in a Semiarid Mediterranean Clay Soil  [PDF]
Rachid Mrabet
American Journal of Plant Sciences (AJPS) , 2011, DOI: 10.4236/ajps.2011.22022
Abstract: Agriculture is the single biggest user of land and water in Morocco; however its performances are still low due to high rainfall variation and rates of soil productivity depletion. Increasing concerns about soil and environment quality degradation have raised the need to review existing tillage management systems and develop new systems for seed-bed preparation. Consequently, No-tillage is found a promising practice of soil management to improve simultaneously soil quality and wheat production in semiarid Morocco. However, residue management under No-tillage was Not yet studied in conjunction with wheat rotation. Therefore, a field study was conducted in the semiarid Chaouia Plain of Morocco during the period from 1994 to 2003, in order to evaluate the impacts of different tillage practices (conventional tillage (CT), No-tillage (NT)); No-tillage wheat residue management scenarios (total NTr, partial NTp and No-removal of residues NTm) and crop rotations (continuous wheat (CW), Wheat-Fallow (WF), Wheat-Maize-Fallow (WMF), Wheat-Lentil-Fallow (WLF) and Wheat-Barley-Fallow (WBF)) on wheat production. Over-years, conventional tillage system permitted lower yield of wheat while NT maintenance of crop residue at the surface is needed to increase it. Basically, NTp could be adopted in mixed crop-livestock systems of semiarid areas for the purpose of guarantying grain and feed. Wheat yields were the lowest under continuous wheat for all years. Wheat-fallow rotation is an important option in dry years or areas, while wheat-fallow-lentil or barley rotations are recommended in better environments. Stability analysis indicated that yields in the No-tillage system were less influenced by adverse growing conditions than conventional tillage system, particularly under low rainfall. These results indicate that improved soil quality under No-tillage enhanced wheat yield stability by reducing the impact of adverse growing conditions.
A New Criterion for the Stabilization Diagram Used with Stochastic Subspace Identification Methods: An Application to an Aircraft Skeleton
E. Mrabet,M. Abdelghani,N. Ben Kahla
Shock and Vibration , 2014, DOI: 10.1155/2014/409298
Abstract: The modal parameters of a structure that is estimated from ambient vibration measurements are always subject to bias and variance errors. Accordingly the concept of the stabilization diagram is introduced to help users identify the correct model. One of the most important problems using this diagram is the appearance of spurious modes that should be discriminated to simplify modes selections. This study presents a new stabilization criterion obtained through a novel numerical implementation of the stabilization diagram and the discussion of model validation employing the power spectral density. As an application, an aircraft skeleton is used. 1. Introduction The vibration and acoustical behaviors of a mechanical structure are determined by its dynamic characteristics. This dynamic behavior is typically described with a linear system model. The procedure for the estimation of modal parameters of structures from measured data can be split into three distinct steps [1]: data collection, system identification, and determination of modal parameters from the identified system description. Stochastic identification methods for systems with unknown input have been introduced decades ago. Among the most robust and accurate system identification methods for output-only modal analysis of mechanical structures is the stochastic subspace identification method. Two types of implementation are available: the covariance-driven (SSI-cov) [2] implementation and the data-driven (SSI-data) [3] implementation. For the first one (SSI-cov), three methods can be implemented: the balanced realization (BR), the principal component (PC), and the canonical variate analysis (CVA). For dynamic structures such as the aircraft skeleton studied in this paper, the major setback in applying system identification for large-scale structures is the selection of the model order and the corresponding system poles. To address this problem, the concept of the “stabilization diagram” is introduced, overestimating the structure model order. Therefore, spurious modes are going to surface out and we have to discriminate them. For this matter, many stabilization criteria have been implemented. The most recent one was the modal transform norm [4]. In this paper, a new stabilization criterion is implemented and a validation method is discussed. The stochastic subspace identification method used is the balanced realization. 2. Stochastic State Space Models for Vibrating Structures The finite element method [4] is one of the most common tools for modeling mechanical structures. In the case of a linear
A finite element modeling of the human lumbar unit including the spinal cord  [PDF]
Fafa Ben-Hatira, Kaouthar Saidane, Abdelfatah Mrabet
Journal of Biomedical Science and Engineering (JBiSE) , 2012, DOI: 10.4236/jbise.2012.53019
Abstract: The purpose of this present work is to provide a tool to better understand mechanically related pathologies of the lumbar unit and the spinal structure by providing spinal cord deformations in different loading cases. In fact, spinal cord injury (SCI) resulting from a traumatic movement leades to a deformation of the neural and vascular structure of the spinal cord. And since the magnitude of the spinal cord stress is correlated with the pressure of the vertebral elements, stresses will be computed on all theses components. Physical properties of the vertebrae, various ligaments, the discs, and the spinal cord are described under simple loading as compression, and combined loading, flexion and lateral bending to evaluate the pressure undergone by different components of the lumbar unit. A nonlinear three-dimensional finite element method is used as a numerical tool to perform all the computations. This study provides accurate results for the localisation and the magnitude of maximum equivalent stress and shear stress on the lumbar unit and especially for the spinal cord. These results showed that stresses are more important when a compression of 500 N is combined with a flexion and a lateral bending. In particular, shear stresses are maximum for the spinal cord and the four intervertebral discs for the case of a flexion of 3.8 N.m and a lateral bending of 6.5 N.m.
Design and Simulation of a PIFA Antenna for the Use in 4G Mobile Telecommunications Networks  [PDF]
Abdelhakim Elouadih, Ahmed Oulad-Said, Moha Mrabet Hassani
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2013, DOI: 10.4236/ijcns.2013.67035
Abstract:

This paper describes the design and simulation by HFSS simulator of a probe-fed and multi-band Planar Inverted-F Antenna (PIFA) for the 4G mobile networks. The antenna works in 8 bands. Five bands are auctioned by FCC for 4G (LTE and WiMax) such 710 MHz, 1900 MHz (PCS), 2.3 GHz (WCS band), 3.65 GHz (rural 4G) and 5.8 GHz (FCC unlicensed band). The antenna allows working around 910 MHz ISM band. The GPS signal can be received in GPS L2 band around the frequency 1575 MHz. The antenna offers also a wideband around 8.62 GHz. The simulation allowed the characterization of the designed antenna and the computing of different antenna parameters like S11 parameters, resonant frequency, bandwidth, radiation efficiency, gain and diagram pattern. The results are very interesting and respect mostly the requirements.

A Novel Methodology to Design Miniaturized Regular Planar Inverted-F Antennas Based on Parametric Simulations  [PDF]
Abdelhakim Elouadih, Ahmed Oulad-Said, Moha Mrabet Hassani
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2013, DOI: 10.4236/jemaa.2013.57047
Abstract:

This paper describes a novel methodology to design PIFA (Planar Inverted-F Antenna) antennas based on parametric simulations. The parameters considered in the parametric design are ground plan dimensions, height of radiating plate, feeding point position, shorting plate width and position. The choice of the parameters that must be varied independently or simultanously is important to design optimized antenna. The author studied two scenarios in precedent works [1,2]. He exposes here a third scenario of varing antenna parameters to design and simulate by HFSS (High Frequency Simulator Structure) simulator a probe-fed dual band PIFA for the use in GSM 850 band (824 MHz - 894 MHz) and PCS 1900 band (1850 MHz - 1990 MHz). The author compares the three scenarios and establishes a novel methodology to design optimized and miniaturized antennas mounted on mobile handsets.

Design and Simulation by HFSS of a Slim UWB PIFA Antenna  [PDF]
Abdelhakim Elouadih, Ahmed Oulad-Said, Moha Mrabet Hassani
World Journal of Engineering and Technology (WJET) , 2013, DOI: 10.4236/wjet.2013.12003
Abstract:

This paper describes the design and simulation by High Frequency Structure Simulator (HFSS) of a probe-fed Planar Inverted-F Antenna (PIFA) for the Ultra Wide Band (UWB) personal area networks. The slim antenna presents a height of 2 mm and a bandwidth of more than 766 MHz. This bandwidth was improved by etching a U-slot in the antenna patch. The bandwidth offered then by the antenna is 839 MHz around the resonant frequency of 9 GHz. The improvement of bandwidth was accompanied by decreasing in gain and radiation efficiency. The simulation allowed the characterization of the designed antenna and the computing of different antenna parameters like S11 parameter, resonant frequency, bandwidth, radiation efficiency, gain and diagram pattern. The results are very interesting and respect the Federal Communications Commission (FCC) requirements.

Design and Parametric Simulation of a Bi-Band Miniaturized PIFA Antenna for the GSM900 and DCS1800 Bands  [PDF]
Abdelhakim Elouadih, Ahmed Oulad-Said, Moha Mrabet Hassani
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2013, DOI: 10.4236/jemaa.2013.55030
Abstract:

This paper describes the design and simulation by HFSS simulator of a probe-fed Planar Inverted-F Antenna (PIFA) for the use in GSM900 band [890 MHz - 960 MHz] and DCS1800 band [1710 MHz - 1880 MHz]. A methodology based on parametric simulations (parameters are ground plan lenght, height of radiating plate, feeding point position, shorting plate width and position) was used to design optimized antenna. The simulation allowed the characterization of the designed antenna and the computing of different antenna parameters like S11 parameter, resonant frequency, VSWR, bandwidth, impedance in feeding point, gain, diagram pattern and Fields distribution. The results were very interesting and respect the GSM requirements.

Design and Parametric Simulation of a Miniaturized PIFA Antenna for the PCS Band  [PDF]
Abdelhakim Elouadih, Ahmed Oulad-Said, Moha Mrabet Hassani
Wireless Engineering and Technology (WET) , 2013, DOI: 10.4236/wet.2013.42016
Abstract:

This paper describes the design and simulation by HFSS simulator of a probe-fed Planar Inverted-F Antenna (PIFA) for the use in PCS band [1850 MHz - 1990 MHz]. A methodology based on parametric simulations (parameters are ground plan dimensions, height of radiating plate, feeding point position, shorting plate dimensions and positioning) was used to design optimized antenna. The simulation allowed the characterization of the designed antenna and the computing of different antenna parameters like S11 parameter, resonant frequency, SWR, bandwidth impedance in feeding point, gain, 2D and 3D diagram pattern, Fields distribution. The simulation results are interesting and respect the mean PCS requirements.

 

The Importance of Auditory Discrimination in the Acquisition of Mental Lexicon and Reading Automation in Arabic-Speaking Students in Kenitra (Morocco)  [PDF]
Chaouki Sadoussi, Ahmed Ahami, Abdechahid Loukili, Khaoula Mammad, Abdessamad Mrabet
Open Journal of Medical Psychology (OJMP) , 2018, DOI: 10.4236/ojmp.2018.73003
Abstract: Auditory discrimination is the ability to discriminate between words and sounds. Auditory discrimination can affect reading, spelling and writing. Several studies examined the correlation between auditory discrimination and reading performance. The aim of this study is to demonstrate the importance of auditory discrimination in the acquisition of mental lexicon and consequently the automation of reading in a sample of 101 students in their fourth year of primary education coming from four different schools in Kenitra (Morocco). The results analysis shows that reading scores correlated significantly with the auditory discrimination scores (r = 0.30, p < 0.01). This proves that the inability to discriminate words causes a disability to store them in the mental lexicon, which makes it difficult to identify these words at a later encounter. This conclusion is supported by the significant correlation between reading and auditory and visual lexical decision tasks. In this study we were able to emphasize the importance of having good acoustic discrimination capacities for language development. Students who were successful at the auditory discrimination task are more successful at reading. A remediation program based on improving auditory discrimination capacities using the language assessment battery LABBEL could see reading performance improvement in these students.
Pairings from a tensor product point of view
Nadia El Mrabet,Laurent Poinsot
Mathematics , 2013,
Abstract: Pairings are particular bilinear maps, and as any bilinear maps they factor through the tensor product as group homomorphisms. Besides, nothing seems to prevent us to construct pairings on other abelian groups than elliptic curves or more general abelian varieties. The point of view adopted in this contribution is based on these two observations. Thus we present an elliptic curve free study of pairings which is essentially based on tensor products of abelian groups (or modules). Tensor products of abelian groups are even explicitly computed under finiteness conditions. We reveal that the existence of pairings depends on the non-degeneracy of some universal bilinear map, called the canonical bilinear map. In particular it is shown that the construction of a pairing on $A\times A$ is always possible whatever a finite abelian group $A$ is. We also propose some new constructions of pairings, one of them being based on the notion of group duality which is related to the concept of non-degeneracy.
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