L. EL arroum, M. Chhib, M. Mazroui and Y. Boughaleb

The classical diffusion of particles in an inhomogeneous periodic system is studied employing the Fokker-Planck equation. The full width at half-maximum (fwhm) of the quasielastic peak in the dynamic structure factorS(q,ω) is calculated numerically by the matrix continued fraction method up to large values of the momentum transfer covering several Brillouin zones. It is shown that fwhm exhibits strong oscillations with the scattering wave-vector q as it has been observed in β-Ag 2 S by the mean of neutron scattering.

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PACS numbers : 05.40.+j,82.20.Fd.05.60.w,66.30.Dn

Laboratoire de Physique de la Matière Condensée. Faculté des sciences Ben M'sik, BP 7955,Casablanca, Morocco

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F.Miskane ^1,2, A. Dezairi ^1,2, D. Saifaoui ¹, H.Imzi ¹

  Research into anomalous transport is aimed at two different sources: turbulent fluctuations in either the electric or the magnetic field. In each case a model has been developed describing the influence of fluctuating field on particles transport. The dynamic of particles guiding centers in a configuration of electric and magnetic turbulence is studied in four dimensional equations of motion. An Hamiltonian description shows that the particles trajectories are described by action angle variables system. It has been demonstrated that the island topology appears at positions near resonant surface if there are the small perturbations. Localized chaotic regions appear while increasing the perturbation and spread up to a fully stochastic situation.

The standard definition coefficient D uses the limit of the mean square excursion; an expression of D useful to describe transport in a finite region can be obtained from the exit times τ i of particles. In the present paper, we compute the numerical diffusion coefficient in the case of electric and magnetic turbulence, the comparison with quasi-linear theory is made for the two cases. This study indicates that electric fluctuations might be the dominant source of anomalous transport for the particles at low parallel velocity, whereas magnetic fluctuations effact particles transport at great parallel velocity. The D/D ql ratio converges to one for the case where numerical diffusion coefficient coincides well with the quasi-linear diffusion coefficient.

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PACS : 52.65.-y Plasma Simulation

1-Laboratoire de Physique Théorique, Faculté des sciences Ain Chok, Casablanca, Morocco
2-Laboratoire de Physique Théorique et de La matière Condensée, Faculté des Sciences Ben M'sik, Casablanca, Morocco

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H. Satori ^1,2, M. Fliyou ² and A. Sali ^2,3

We have examined the binding energy of a polaron bound to a hydrogenic donor impurity located in a spherical quantum dot by means of a variational technique for both finite and infinite potential models. The polaronic effect on the binding energy has been considered taking into account the ion-phonon coupling by using the Lee-Low-Pines variational method. The results we have obtained show that the binding energies are drastically affected by the dot radius, the potential barrier height and the polaronic effects.

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PACS : 73.20. Dx; 73.20. Mf; S7.12.

Key words :  Zero dimensional system, impurity, binding energy, polaronic effect.

1 :UFR Optique et Dynamique des Matériaux, Faculté des Sciences d’Oujda, BP. 524 Oujda- Morocco
2 : Ecole Normale Supérieure, B.P. 5206 Bensouda-FES-Morocco
3: Faculté des Sciences, Département de Physique, B.P. 4010, Beni M’hamed Meknès- Morocco.

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  A. Kaal ¹, K. Benbachir ², S. Sayouri ¹, and M. Tlemçani ³

 In this paper, magnetic properties of amorphous Gd_0.7 Y_0.3 alloys have been studied using a linear dependence on H^-1/2 of the saturation magnetization M(H); this dependence has been proved to be necessary for an adequate interpretation of magnetic behaviour of ferromagnetic amorphous compounds. Indeed, in a previous work, assuming a linear dependence on H^-1 of M(H), magnetic parameters (magnetic moment, µ_Gd , of Gd, mean exchange integral (J)) relevant to Gd_0.7 Y_0.3 have been undervalued. In the present work, these parameters, in addition to the stiffness constant, have been improved.

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Keywords : amorphous ferromagnets- Gd-based alloys- Stiffness constant- Saturation - magnetization-Spin -wave-
                    Exchange integral

1 Laboratoire de Physique du Solide, Faculté des Sciences, B.P1796, Fès Atlas Marocco .
2 Laboratoire de Magnétisme et de Physique des Hautes Energies, Faculté des Sciences, avenue Ibn Batouta,B. P. 1014, Rabat, Morocco .
3 Laboratoire de Physique du Solide, E.N.S. Fès Bensouda , Marocco.

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A. Chahboun¹ and I. Zorkani¹ , R. Coratger², F. Ajustron² and J. Beauvillain²

 Ballistic Electron Emission Microscopy (BEEM) has been used to characterise the Au/n-ZnSe contact. A mean statistical BEEM threshold of 1.63eV is in good agreement with literature. Metal - Insulator- Semiconductor (MIS) structures are invoked to explain the Schottky barrier height dispersion and the observed shift of BEEM thresholds to higher values.

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PACS :   73.30.+y, 61.16.ch, 73.23.Ad, 73.61.Ga

1 L. P. S., Faculté des Sciences Dhar Mehraz, BP 1796 – FES (Atlas), Morocco
2 CEMES/CNRS-BP 4347-31055 Toulouse cedex 04- France

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N. Benayad, A. Fathi and L. Khaya

 The diluted mixed spin Ising system consisting of spin-1/2 and spin-1 in a random field is studied by the use of finite cluster approximation the framework of a single-site cluster theory. The equations are derived using a probability distribution method based on the use of Van der Waerden identities. The complete phase diagrams are investigated in the case of the simple cubic lattice (z=6), where the random field is bimodally and trimodally distributed. In particular, the influence of the magnetic sites concentration on the tricritical behaviour is examined in detail.

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Groupe de Mécanique Statistique
Laboratoire de Physique Théorique, Faculté des Sciences Aïn Chock,
B.P. 5366, Maarif, Casablanca, Morocco.

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Houssine Bouayad^1,2 and El Kébir Omari Alaoui²

We have obtained the physical features of an isotropic and homogeneous environment on both theoretical and experimental levels, in particular when thermal features are linked through the λ = a ρC_p relation. As far as dispersed samples are particularly concerned, this largely used correlation is not confirmed in out-of balance non-homogeneous samples (transitional rate of flow /regime). So, we have developed, by electronic analogy a theoretical model that allows us to study the thermal performance and to discuss conditions of homogenization in such material.

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Key words  :  Thermal characterization, dispersed materials, thermal conductivity, thermal diffusivity and homogenization.

1 Faculty of Science and Technical Arts, Settat, PO Box 577, Morocco
2 Faculty of Science, Dhar El Mehraz, / P.O. Box 1796, Atlas, Fez Morocco

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M. F.Mahjoubi^a, M. Hamedoun^a, A. Hourmatallah^a,
F. Z. Bakkali^a, A. Chaqroune^a and A. Benyoussef^b

The effects of cationic substitutions at different concentrations within the lattice Zn_x Cd_1-xCr₂Se₄  (0.35≤x≤0.58) on the electronic transfer in chromium ions are investigated. For this propose, after taking into account the exchange integrals, we use the Anderson’s-Kanamori theory of superexchange to determine the transfer integrals b_σσ and b_πσ . With the use of the conventional molecular orbital model the covalency-mixing parameters, λ_σ and λ_π, the electron spin transfer coefficients, ƒ i (i=σ, π, s ), and the total charge, C, transferred from ligand to the chromium ions, are evaluated. The variation of bσσ and bσπ with x agree with the passage of the system from ferromagnetic to antiferromagnetic order. For the compound presenting re-entrant behaviour (0.45≤x≤0.58), f s exhibits anomalous. The increasing in C with x is consistent with the expected decrease in covalency of the non magnetic cation in tetrahedral site.

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a Laboratoire de physique du solide. Université Sidi Mohammed Ben Abdellah, Faculté des Sciences Dhar El Mahraz. B. P. 1796, Fès Atlas, Fès, Morocco
b Laboratoire de Magnétisme et de Physique des Hautes Enérgies, Département de Physique, Faculté des Sciences, Rabat. B. P. 1014 Rabat, Morocco

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S. Zaroual^1,2 , O. Sassi¹ , J. Aride¹ , J. Bernardini³ , G. Moya⁴

  Thermal defects are studied for three compositions (49, 50 and 52 at.%Fe) of the intermetallic compound FeAl with B2 structure. Magnetic measurements are used to determine the thermal defect concentrations. These concentrations are determined from fitting the experimental curves of magnetic susceptibility, obtained during an isochronal annealing after a quench. Next we have evaluated theoretically the concentrations of different point defects that exist in this compound. The used model is based in the Bragg-Williams approximation assuming the nearest-neighbour interaction. The calculated concentrations describe well the experimental values.

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1 Laboratoire de Physico-Chimie des Matériaux, Laboratoire associé à l'AUPELF•UREF, LAF n°502,
    Ecole Normale Supérieure Takaddoum B.P.5118 Rabat-Morocco
2 Laboratoire de Physique des Matériaux, Faculté des Sciences, Avenue Ibn Batouta, B.P.1014 Rabat-Morocco
3 Laboratoire de Métallurgie, U.M.R 6815, Faculté des Sciences et Techniques de St-Jérôme, 13397 Marseille Cedex 20, France
4 Laboratoire de Physique des Matériaux, E.A.2192 (D.S.O), Faculté des Sciences et Techniques de St-Jérôme, 13397 Marseille Cedex 20, France

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A. Moutie and M. Kerouad

The magnetic properties (Transition temperature and magnetizations), of a aferrimagnetic multilayer system consisting of L layers of spin-1/2 A atoms, L layers of spin-1 B atoms and a disordered interface in between that characterized by a random arrangement of A and B atoms of A_pB_{1-p} type and a negative A-B coupling, are studied within the framework of an effective-field theory. The effect of the disordered interface, interactions and different anisotropies on the magnetic properties are examined. The obtained results show a number of characteristic features, such as the possibility of two compensation points.

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Université Moulay Ismail - Faculté des Sciences Département de Physique - B.P. 4010 - Meknés - Morocco

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L. Bahmad, A. Benyoussef, and H. Ez-Zahraouy

 Using the mean field theory, a comparative study of the wetting and layering transitions of a spin-1/2 Ising model with perfect and corrugated surfaces, is established. The phase diagrams are investigated and compared in the presence of both a longitudinal and surface fields. The effect of both the temperature and the transverse field on the wetting and layering transitions are established.

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Laboratoire de Magnétisme et de la Physique des Hautes Energies, Université Mohammed V, Faculté des Sciences,
Avenue Ibn Batouta, B.P. 1014, Rabat, Morocco

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M. Chhib , A. Asaklil, L. EL Arroum, M. Mazroui and Y. Boughaleb

A general theory for diffusion mechanism of Brownian particle submitted to a bistable and metastable periodic potential is presented. It is based on the description of the kinetics in the framework of Fokker-Planck equation (F.P.E). A formal solution of the F.P.E is obtained using the Matrix Continued Fraction Method (M.C.F.M), which gives an expression for the relevant correlation function. In particular, the half width of the quasi-elastic peak of the dynamical structure factor S(q, w) and the diffusion coefficient are fully studied in a wide range of physical parameters. A comparison between the results of system in a bistable and those in a metastable potential is presented and analysed.

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PACS numbers :  numbers: 05.40.+j, 82.20.Fd, 05.60.w, 66.30.Dn

Laboratoire de physique de la matière condensée, Faculté des sciences Ben M’sik, Casablanca, BP 7955 Morocco.

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L. Khaya¹ , N. Benayad¹ and A. Dakhama^1,2

The effects of diluted surface on the phase diagram of the transverse Ising spin model is studied by the use of an effective field method within the framework of single-site cluster theory. The state equations are derived using the differential operator technique. The complete phase diagrams are investigated when the exchange interactions J_ij^S at the surface, is randomly distributed. J_ij^S is in competition with the bulk interactions. In particular, the influence of the surface transverse field and the dilution parameter on the three-dimensional transverse Ising model is examined in detail.

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PACS :  05.50.+q ; 75.10.Hk

1 Groupe de Mécanique Statistique, Laboratoire de Physique Théorique, Faculté des Sciences Aïn Chock, B.P 5366 Maarif, Casablanca, Morocco.
2 Department of Physics Northeastern University, Boston, Massachusetts 02115, USA.

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R. Aboulaich¹; S. Afilal² and J. Pousin³

When the ground is accidentally polluted with a volatile organic contaminant, it is important to know the amount of this contaminant in liquid form, in this paper it is shown that the concentration in the liquid phase of the volatile organic contaminant can be identified by analyzing the gaseous phase and using inverse problem. In order to do that we consider an inverse problem.

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Key words : mass transfer, identification of coefficients, inverse problem.

1 Ecole Mohammadia d'ingénieurs Laboratoire d'Etude et de Recherche en Mathématiques Appliquées B.P 765 Rabat-Agdal, Morocco.
2 Faculté des Sciences de Tétouan,Département de Mathématique B.P 2121 Tétouan, Morocco
3 UMR CNRS 5585 INSA-Lyon Institut National des Sciences Appliquées de Lyon, 20 Avenue A. Einstein F-69621 Villeurbanne Cedex France.

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R. Fathi and S. Ouaskit

A new model is presented to describe an irreversible absorption refrigerator, in which not only the irreversibilities of heat conduction but also the irreversibilities resulting from the friction, eddy and other irreversible effects inside the working fluid are considered. The influence of these irreversible effects on the performance of an absorption refrigerator with continuous flow is investigated. The analytical expressions of the optimal refrigeration coefficient and the cooling rate of the refrigerator are derived. The predictions of the model are compared with semi-empirical cycle model of single-stage absorption refrigeration machines. The results obtained here can describe the optimal performance of a four-temperature-level absorption refrigeration affected simultaneously by the internal and external irreversibilities and provide the theoretical base s for the optimal design and operation of real absorption refrigerators operating between four temperature level.

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Laboratoire de physique de la matière Condensée. Université Hassan II- Mohammedia, Faculté des Sciences Ben M’sik, Casablanca-Morocco.