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Search Results: 1 - 10 of 220007 matches for " C Fathi "
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Mean-Field Solution of the Mixed Spin-2 and Spin-5/2 Ising Ferrimagnetic System with Different Single-Ion Anisotropies  [PDF]
Fathi Abubrig
Open Journal of Applied Sciences (OJAppS) , 2013, DOI: 10.4236/ojapps.2013.33034

The mixed spin-2 and spin-5/2 Ising ferrimagnetic system with different anisotropies (DA/zJ|) for the spin-2 and (DB/zJ|) for the spin-5/2 is studied by the use of the mean-field theory based on the Bogoliubov inequality for the free energy. First, the ground state phase diagram of the system at zero temperature is obtained on the (DA/zJ,DB/zJ|) plane. Topologically, different kinds of phase diagrams are achieved by changing the temperature and the values of the single ion anisotropies DA/zJ and DB/zJ. Besides second-order transition lines, first order phase transition lines terminating at tricritical points, are found. The existence and dependence of a compensation temperature on single-ion anisotropies is also investigated.

Mean-Field Solution of a Mixed Spin-3/2 and Spin-2 Ising Ferrimagnetic System with Different Single-Ion Anisotropies  [PDF]
Fathi Abubrig
Open Journal of Applied Sciences (OJAppS) , 2013, DOI: 10.4236/ojapps.2013.32029

The mixed spin-3/2 and spin-2 Ising ferrimagnetic system with different single-ion anisotropies in the absence of an external magnetic field is studied within the mean-field theory based on Bogoliubov inequality for the Gibbs free energy. Second-order critical lines are obtained in the temperature-anisotropy plane. Tricritical line separating second-order and first-order lines is found. Finally, the existence and dependence of a compensation points on single-ion anisotropies is also investigated for the system. As a result, this mixed-spin model exhibits one, two or three compensation temperature depending on the values of the anisotropies.

Extractive Metallurgy and National Policy  [PDF]
Fathi Habashi
International Journal of Nonferrous Metallurgy (IJNM) , 2013, DOI: 10.4236/ijnm.2013.22004

Hydrometallurgical technology offers a unique possibility for developing countries to exploit their mineral resources locally instead of shipping them as concentrates. Production plants may start on a small scale with small capital investment then increase productivity later when the economy permits without financial penalty. This is in contract to smelting operations which necessitates large scale production from the start with high capital investment that may not be available locally.

Magnetic Properties of a Mixed-Spin-3/2 and Spin-2 Ising Ferrimagnetic System in an Applied Longitudinal Magnetic Field  [PDF]
Fathi Abubrig
World Journal of Condensed Matter Physics (WJCMP) , 2013, DOI: 10.4236/wjcmp.2013.32018

The magnetic properties of a mixed Ising ferrimagnetic system consisting of spin-3/2 and spin-2 with different single ion anisotropies and under the effect of an applied longitudinal magnetic field are investigated within the mean-field theory based on Bogoliubov inequality for the Gibbs free energy. The ground-state phase diagram is constructed. The thermal behaviours of magnetizations and magnetic susceptibilities are examined in detail. Finally, we find some interesting phenomena in these quantities, due to applied longitudinal magnetic field.

Electromagnetic Self-Force Mechanisms and Origin of R-1 Term  [PDF]
Saeed Fathi, Hamed Razavi
Journal of Applied Mathematics and Physics (JAMP) , 2017, DOI: 10.4236/jamp.2017.55096
Abstract: An accelerating charged particle exerts a force upon itself. If we model the particle as a spherical shell of radius R, and calculate the force of one piece of this shell on another and eventually integrate over the whole particle, there will be a net force on the particle due to the breakdown of Newton’s third law. This symmetry breaking mechanism relies on the finite size of the particle; thus, as Feynman has stated, conceptually this mechanism doesn’t make good sense for point particles. Nonetheless, in the point particle limit, two terms survive in the self-force series: R0 and R-1 terms. The R0 term can alternatively be attributed to the well-known radiation reaction but the origin of R-1 term is not clear. In this study, we will show that this new term can be accounted for by an inductive mechanism in which the changing magnetic field induces an inductive force on the particle. Using this inductive mechanism, we derive R-1 term in an extremely easy way.
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.
A Computational Approach to Financial Option Pricing Using Quasi Monte Carlo Methods via Variance Reduction Techniques  [PDF]
Farshid Mehrdoust, Kianoush Fathi Vajargah
Journal of Mathematical Finance (JMF) , 2012, DOI: 10.4236/jmf.2012.22021
Abstract: In this paper, we consider two types of pricing option in financial markets using quasi Monte Carlo algorithm with variance reduction procedures. We evaluate Asian-style and European-style options pricing based on Black-Scholes model. Finally, some numerical results presented.
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.

Ultra-Low Power, Low Phase Noise 10 GHz LC VCO in the Subthreshold Regime  [PDF]
Davood Fathi, Aboozar Gorbani Nejad
Circuits and Systems (CS) , 2013, DOI: 10.4236/cs.2013.44047

A new design for an ultra-low power, low phase noise differential 10 GHz LC voltage-controlled oscillator (VCO) which is biased in the subthreshold regime, is presented in the 0.18 μm CMOS process, for the first time. The designed circuit topology is an NMOS only cross-coupled LC-tank VCO which has an extra symmetric centre tapped inductor between the source ends of the cross-coupled transistors. Using this inductor leads to an improvement of the phase noise of VCO about 3.5 dB. At the supply voltage of 0.46 V, the output phase noise is -107.8 dBc/Hz at 1 MHz offset frequency from the carrier frequency of 10.53 GHz, so that the dc power consumption is only 0.346 mW. Tuning range is between 10.53 GHz to 11.35 GHz which is 7.5% and the figure of merit is -193.8 dB, which this result shows that this is the first VCO design in the subthreshold regime at this frequency. This VCO can be used for multi-standard wireless LAN communication protocols 802.11a/b/g easily by a frequency division of 2 or 4 respectively.

Millimeter Wave Ring Oscillator Using Carbon Nano-Tube Field Effect Transistor in 150 GHz and Beyond  [PDF]
Davood Fathi, Baback Beig Mohammadi
Circuits and Systems (CS) , 2013, DOI: 10.4236/cs.2013.42021

Carbon Nano-Tube Field Effect Transistors (CNTFETS) are the competitor of the conventional MOSFET technology due to their higher current drive capability, ballistic transport, lesser power delay product, higher thermal stability, and so on. Based on these promising properties of CNTFETs, a CNTFET-based millimeter wave ring oscillator operating around 150 GHz and beyond is introduced here in 32 nm technology node. To prevent overestimation, the CNT interconnects between transistors are also included in simulation, which are assumed to be a single layer of ballistic metallic CNTs in parallel. For the sake of simplicity in RF design, the oscillator is based on CNTFET-based inverters. The inverters with DC gain of 87.5 dB are achieved by proper design with the non-loaded delay around 0.6 ps, which is at least one order of magnitude better than the same 32 nm MOSFET-based inverters. The oscillator’s average power consumption is as low as 40 μW with the fundamental harmonic amplitude of around 6.5 dB. These values are, based on our knowledge, for the first time reported in the literature in CNTFET-based oscillator designs. Also, on the average, the performance of the designed oscillator is 5 - 6 times better than MOSFET-based designs.

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