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Search Results: 1 - 10 of 9994 matches for " Fathi Ben Amar "
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Analytical Approach for the Systematic Research of the Periodic Ferroresonant Solutions in the Power Networks  [PDF]
Fathi Ben Amar, Rachid Dhifaoui
Energy and Power Engineering (EPE) , 2011, DOI: 10.4236/epe.2011.34056
Abstract: Ferroresonance is a complex and little known electrotechnical phenomenon. This lack of knowledge means that it is voluntarily considered responsible for a number of unexplained destructions or malfunctioning of equipment. The mathematical framework most suited to the general study of this phenomenon is the bifurcation theory, the main tool of which is the continuation method. Nevertheless, the use of a continuation process is not devoid of difficulties. In fact, to continue the solutions isolats which are closed curves, it is necessary to know a solution belonging to this isolated curve (isolat) to initialise the continuation method. The principal contribution of this article is to develop an analytical method allowing systematic calculation of this initial solution for various periodic ferroresonant modes (fundamental, harmonic and subharmonic) appearing on nonlinear electric system. The approach proposed uses a problem formulation in the frequency domain. This method enables to directly determine the solution in steady state without computing of the transient state. When we apply this method to the single-phase ferroresonant circuits (series and parallels configurations), we could easily calculate an initial solution for each ferroresonant mode that can be established. Knowing this first solution, we show how to use this analytical approach in a continuation technique to find the other solutions. The totality of the obtained solutions is represented in a plane where the abscissa is the amplitude of the supply voltage and the ordinate the amplitude of the system’s state variable (flux or voltage). The curve thus obtained is called “bifurcation diagram”. We will be able to then obtain a synthetic knowledge of the possible behaviors of the two circuits and particularly the limits of the dangerous zones of the various periodic ferroresonant modes that may appear. General results related to the series ferroresonance and parallel ferroresonance, obtained numerically starting from the theoretical and real cases, are illustrated and discussed.
Wind Energy Conversion Systems Adapted to the Tunisian Sites  [PDF]
Fathi Ben Amar, Mustapha Elamouri
Smart Grid and Renewable Energy (SGRE) , 2013, DOI: 10.4236/sgre.2013.41009

The choice of a wind turbine for a given site is a very significant operation. It is advised to make an in-depth study on the characteristics of the aerogenerator and the implantation site before any installation of a wind farm for choosing well the system best adapted to the energy needs. The objective of this study is to sensitize the users of the wind energy on the various problems involved in the aerogenerator installation on any site and to provide a decision-making aid to the judicious choice of the wind system best adapted. The idea is to estimate, for a selected implantation site, the energy production and the operating time of several wind systems. We can thus select the aerogenerator best adapted by making a compromise between a maximum recovery of energy and a high time of production. The influence height of the aerogenerator on energy profitability is also studied. We apply this step to the twenty six Tunisian synoptic sites by implantation scenarios of seven wind systems of various nominal speeds in function of the height.

Extended Generalized Riccati Equation Mapping for Thermal Traveling-Wave Distribution in Biological Tissues through a Bio-Heat Transfer Model with Linear/Quadratic Temperature-Dependent Blood Perfusion  [PDF]
Emmanuel Kengne, Fathi Ben Hamouda, Ahmed Lakhssassi
Applied Mathematics (AM) , 2013, DOI: 10.4236/am.2013.410199

Analytical thermal traveling-wave distribution in biological tissues through a bio-heat transfer (BHT) model with linear/quadratic temperature-dependent blood perfusion is discussed in this paper. Using the extended generalized Riccati equation mapping method, we find analytical traveling wave solutions of the considered BHT equation. All the travelling wave solutions obtained have been used to explicitly investigate the effect of linear and quadratic coefficients of temperature dependence on temperature distribution in tissues. We found that the parameter of the nonlinear superposition formula for Riccati can be used to control the temperature of living tissues. Our results prove that the extended generalized Riccati equation mapping method is a powerful tool for investigating thermal traveling-wave distribution in biological tissues.

On Some Fixed Point Theorems for 1-Set Weakly Contractive Multi-Valued Mappings with Weakly Sequentially Closed Graph  [PDF]
Afif Ben Amar, Aneta Sikorska-Nowak
Advances in Pure Mathematics (APM) , 2011, DOI: 10.4236/apm.2011.14030
Abstract: In this paper we prove Leray-Schauder and Furi-Pera types fixed point theorems for a class of multi-valued mappings with weakly sequentially closed graph. Our results improve and extend previous results for weakly sequentially closed maps and are very important in applications, mainly for the investigating of boundary value problems on noncompact intervals.
Design Analysis of DC-DC Converters Connected to a Photovoltaic Generator and Controlled by MPPT for Optimal Energy Transfer throughout a Clear Day  [PDF]
S. Kolsi, H. Samet, M. Ben Amar
Journal of Power and Energy Engineering (JPEE) , 2014, DOI: 10.4236/jpee.2014.21004

The DC-DC converters are widely used in photovoltaic generating systems as an interface between PV module and the load. These converters must be chosen to be able to match the maximum power point (MPP) of PV module when climatic conditions change with different resistive load values. So DC-DC converters must be used with MPPT controller in order to reduce losses in the global PV system. This article focuses on the effect of climatic conditions on design of two components (inductance, capacitance) for three topologies of DC-DC converters commonly used in PV systems. When climatic conditions change, the boundary of inductance and capacitance parameters of DC-DC converter will change. These two parameters must be properly sized to achieve optimal efficiency for each converter. The design optimization is based on two principles: 1) for a steady-state operation in a continuous conduction mode, the inductance value for all choppers must be greater than the maximum value of boundary inductance, and 2) in order to limit the output voltage ripple of DC-DC converter below a desired value, the filter capacitance must be larger than the maximum value of boundary capacitance.

The $L^2$-Alexander invariant detects the unknot
Fathi Ben Aribi
Mathematics , 2013,
Abstract: In this article, we present some of the properties of the $L^2$-Alexander invariant of a knot defined by Li and Zhang, some of which are similar to those of the classical Alexander polynomial. Notably we prove that the $L^2$-Alexander invariant detects the trivial knot.
Efficient Video Streaming Scheme for Next Generations of Mobile Networks
Majdi Ashibani,Fathi Ben Shatwan
Journal of Systemics, Cybernetics and Informatics , 2005,
Abstract: Video streaming over next generations of mobile networks has undergone enormous development recently due to the continuing growth in wireless communication, especially since the emergence of 3G wireless networks. The new generations of wireless networks pose many challenges, including supporting quality of service over wireless communication links. This is due to the time-varying characteristics of wireless channel. Therefore, a more flexible and efficient bandwidth allocation scheme is needed. This paper is a part of ongoing work to come up with a more robust scheme that is capable of rapidly adapting to changes in network conditions. The proposed scheme focuses on the wireless part of the network, providing high quality video service and better utilization of network resources.
Model-Free, Occlusion Accommodating Active Contour Tracking
Mohamed Ben Salah,Amar Mitiche
ISRN Artificial Intelligence , 2012, DOI: 10.5402/2012/672084
Morphogenesis of growing soft tissues
Julien Dervaux,Martine Ben Amar
Quantitative Biology , 2007, DOI: 10.1103/PhysRevLett.101.068101
Abstract: Recently, much attention has been given to a noteworthy property of some soft tissues: their ability to grow. Many attempts have been made to model this behaviour in biology, chemistry and physics. Using the theory of finite elasticity, Rodriguez has postulated a multiplicative decomposition of the geometric deformation gradient into a growth-induced part and an elastic one needed to ensure compatibility of the body. In order to fully explore the consequences of this hypothesis, the equations describing thin elastic objects under finite growth are derived. Under appropriate scaling assumptions for the growth rates, the proposed model is of the Foppl-von Karman type. As an illustration, the circumferential growth of a free hyperelastic disk is studied.
Selecting the Best Forecasting-Implied Volatility Model Using Genetic Programming
Wafa Abdelmalek,Sana Ben Hamida,Fathi Abid
Advances in Decision Sciences , 2009, DOI: 10.1155/2009/179230
Abstract: The volatility is a crucial variable in option pricing and hedging strategies. The aim of this paper is to provide some initial evidence of the empirical relevance of genetic programming to volatility's forecasting. By using real data from S&P500 index options, the genetic programming's ability to forecast Black and Scholes-implied volatility is compared between time series samples and moneyness-time to maturity classes. Total and out-of-sample mean squared errors are used as forecasting's performance measures. Comparisons reveal that the time series model seems to be more accurate in forecasting-implied volatility than moneyness time to maturity models. Overall, results are strongly encouraging and suggest that the genetic programming approach works well in solving financial problems.
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