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The magnetic properties of Ni/C multilayers were investigated using vibrating sample magnetometer and ferromagnetic resonance (FMR). Spin wave resonances were seen in FMR and the spin wave was found to be sustained through whole layers. The interlayer coupling constant was small pointing out a weak exchange coupling between Ni films through C spacers. The FMR linewidth, in parallel geometry, of the uniform mode decreases with the increase in Ni thickness from 30 to 300 A which can be understood by considering interfacial effects. The magnetization decreases with decreasing Ni thickness due to the structural imperfections associated with the presence of Ni1−xCx alloys at the interface. Density functional theory (DFT) has been performed to shed light on the decrease in magnetic moment at the interfaces.

Co/C multilayers were prepared using DC triode sputtering with different Co thicknesses (tCo), and their magnetic properties were investigated using a vibrating sample magnetometer. It is found that the magnetization of Co layers decreases with decreasing tCo, at thicknesses below 6 nm, which can be understood by the presence of a magnetically dead layer, due to intermixing between Co and C layers, i.e., the alloy formation around the former interface. A model based on the spin-wave theory was utilized to explain the change of the magnetization as function of temperature, and estimate the coupling exchange interaction. Ab initio calculations were utilized to explain the decrease of the magnetic moment within the interfacial layer (Co1-xCx). In addition, the influence of pressure on the magnetic properties of the Co1-xCx layer was studied as well.

Fe/C multilayers with different Fe thicknesses ( t Fe ) were prepared using triode sputtering with a fixed C layer thickness of 20 A, while the Fe film thickness was changed from 30 to 300 A. The magnetization strongly decreases with decreasing t Fe when t Fe was smaller than 60 A. This is attributed to the existence of a magnetically dead layer due to the presence of Fe 1 − x C x alloys at the Fe/C interface due to the diffusion of carbon in iron. First-principles calculations based on Density Functional Theory (DFT) were performed to investigate the magnetic and electronic structures of the interfacial Fe 1 − x C x alloys. It is shown that the C insertion reduces the magnetization, which becomes significant with increasing C content. In addition, the influence of pressure by changing volume on the magnetic properties was investigated as well, where the pressure reduces significantly the interfacial magnetization.

Fiber bundle model is one of the important statistical and theoretical physics approaches to investigate the fracture and breakdown of heterogeneous material extensively used both by the engineering and physics community. In this paper, using the correlation function and its properties, we study the diffusion of the failure process in composite materials that consist of a set of with randomly oriented fibers loaded by an external constant total load. The investigation is based on fiber bundle model where the fibers are randomly oriented; each fiber is subject only the cosine component of the external load, and when it fails, its load is shared by surviving neighboring fibers according to the local load sharing rule (LLS). The failure process ensures an advancing interfacial fracture and the areas of the damaged regions increases with time until a final crack of material. By using the correlation function of the fraction of broken fibers, we study the diffusion properties of micro crack created in the composite materials. The results show that the correlation decreases exponentially with time and decreases with both of applied load and temperature. We calculate then the effective diffusion coefficient cracks which increase exponentially with applied load and linearly with the temperature. The failure time tf of the materials decrease with temperature as a power law. Obtained results are compared with the one of the classical model consist of a set of parallel fibers.

Our aim is to investigate the crack diffusion created at single region of composite materials by using the fiber bundle model. So, we have applied an external single crack in one fiber of the composite material, and we then continue to increase this load at a very slow rate until the considered fiber breaks and its load is redistributed to its neighboring intact ones. This breaking and redistribution dynamics repeat itself and this process ensures an advancing interfacial fracture and the area of the damaged region increases with time until a final crack of material. Our calculations are done in the context of the local load-sharing rule. The results show that the damaged region area increases with time by following the Lifshitz-Slyozof law with an exponent growth x=2. This permits us to deduce the behavior of the crack diffusion with the applied load. The corresponding results of the life time materials exhibit an exponential decreasing with the applied load and a linear decreasing with temperature.

Magnetic and electronic properties of LiVOPO4 and VOPO4 cathodes have been studied using ab initio calculations, high temperature series expansions (HTSEs) calculations and Monte Carlo simulations (MCSs). Self-consistent ab initio calculations, based on Density Functional Theory approach (DFT) and using Full Potential Linear Augmented Plane Wave (FLAPW) method, were performed to investigate both electronic and magnetic properties of the LiVOPO4. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent V plans. Magnetic moments considered to lie along (010) axes are computed. Average equilibrium voltage over a full cycle ([Formula: see text]) of the LiVOPO4, battery have been estimated. Computed magnetic moments are used as input for HTSEs to compute other magnetic parameters using the mean field theory, MCSs and HTSEs. The obtained results by HTSEs and MCSs are comparable with experiments results.

Recent trends in electromechanical conversion using alternative materials, have demonstrated the advantages of using piezoelectric composites for energy generation. There have been several papers on ceramic/polymer composites in which the fillers have high piezoelectric constant. Basically, the energy harvested depends on the proportion of the piezoelectric properties of composite. The fillers size within the composites is also an important criterion of the composites properties. Thus, in this paper 0–3 composites, made of lead zirconate titanate (PZT) ceramic powder and polyurethane (PU) were prepared. Different sizes of ceramic grains were used: grains with average size of 10 μm, size under 80 μm and size under 100 μm. Sizes of the PZT grains was determined according to the homogenization efficiency of the composite. Piezoelectric (piezoelectric coefficient d33) and dielectric properties (dielectric constant) were investigated. They have shown an interesting improvement with the increasing grains size up to 20 pC/N and 100, respectively. In order to understand the composite behavior on the microscopic scale, a simulation was carried out by mean of a finite element method (FEM) software. Finally, an estimation of the harvested voltage was modeled according to the grains size.

In this work, we present in the weak pinning case the numerical simulation results of the one-dimensional deformable charge density wave (CDW) properties considering the potential amplitude fluctuations effect generated by different impurity types randomly distributed in the lattice. When the electric field approaches threshold value E T , the static equilibrium characteristic time τ and the polarization P CDW become large and seem to diverge at critical field E cr from below E T following a power law [ 1 − ( E / E cr ) ] − α where α is an impurity dependant critical exponent. This divergence indicates that the CDW depinning can be described in terms of a dynamical critical phenomena, where the critical field E cr plays the role of a transition temperature as in ordinary phase transitions. In agreement with several experimental results, we show that the electric current density J CDW and electric conductivity σ CDW follow respectively a power law [ ( E / E T ) − 1 ] β and ( E T / E ) [ ( E / E T ) − 1 ] ν where β and ν are critical exponents. This results are analogous to these obtained in the case of one impurity type.

We analyzed experiments designed for industrial applications in order to test the concept that in heterogeneous materials such as fiber composites concrete subjected to an external mechanical stress rupture is a genuine critical point. This prediction has been tested extensively on heterogeneous materials bases polymer from acoustic emission measurements. The investigating consists in simulating the two-dimensional model of a spring network. Also the bond percolation concept has been very helpful in the interpretation of the numerical results.

We report in this Letter a numerical study of the response of an incommensurate charge density wave (CDW) to an external electrical field in the presence of free carriers. The results show that the single particles excitations affect the local dynamical properties of the CDW, the CDW drift velocity and the time scale of the CDW relaxation phenomena.

We examine the behaviour of the current correlation function of small surfaces equivalent to the probe areas in the scanning tunnelling microscopy experiments with the interactions, the surfaces size and the coverage. The kinetics is described by the mean field master equation in the context of lattice gas model. The results show that for both the non-interacting case and in presence of repulsive interactions susceptible to produce an order–disorder transition in the system, the correlation function varies as l/Dct in the long time regime. We calculate the collective diffusion coefficient using the linear response theory as well as the correlation function method and we find a good agreement between both results except for the half full lattice.

We deal with the transition from the classical transport to the ballistic regime. This transition is considered in the generalized Maxwell–Cattaneo context. By using an evolution equation hierarchy for higher-order moments, in the frame of extended irreversible thermodynamics, we construct a continued-fraction expansion. We derive from this latter an asymptotic expression of effective transport coefficients which yield flux limiters involving a more accurate value of ballistic velocity.

Dynamic properties of Brownian particles immersed in a periodic potential with two barriers V1 and V2 (symmetric bistable potential) are studied by using the Fokker-Planck equation which we solve numerically by the matrix continued fraction method. This study will therefore serve to demonstrate the influence of this form of potential, which is of great interest for superionic conductors and for many other solid systems, on the diffusion process. Thus, we have calculated the full width at half maximum (FWHM) \(\lambda (q)\)) of the quasi-elastic line of the dynamic structure factor, for a large range of values of the wave-vectors q. Our results show clearly that, by varying the ratio of the barriers \(\Delta = {V_2}/{V_1}\)strictly between and 1, the Fokker-Planck equation describes a diffusive process which has some characteristic of jump and liquid-like regimes. While in the limit cases, i.e. when Δ tends to or 1, the diffusion process can be described only by a simple jump motion. However, the jump-lengths corresponding to each limit case are not equal. In general the change of the ratio is found to have a significant effect on the character of the diffusive motion. We have also performed Fokker-Planck dynamics calculations of the diffusion coefficient in a bistable potential. We have found a good agreement between numerical calculations and analytical approximation results obtained in the high friction limit.

The dc conductivity of a Brownian particle is presented in the linear-response regime for the wide damping range. The analytical approximation is derived in terms of the two expressions of dc conductivity available in certain limiting cases. Its comparison with different numerical treatments gives a good agreement in all ranges of friction.

We investigate the dynamic properties of two-dimensional systems composed of N interacting Brownian particles subject to a periodic potential. By employing the Langevin dynamic simulations and assuming a repulsive Yukawa potential type, we have computed the effective potential V eff . Our results show that for the incommensurate concentration c =2/3, the barrier height of V eff increases in one direction and decreases in the other compared with the that for the non-interacting particles case. This behaviour explains quantitatively the aspect of the diffusion process which becomes unidirectional. So, the two-dimensional diffusion process can be treated in one-dimensional picture. On the other hand, we have computed the frequency-dependent conductivity σ ( ω ), of the two-dimensional system with Frenkel–Kontorova pair interaction in the intermediate friction regime, by using the continued fraction expansion method (CFEM). For the determination of the remainder of the development of the continued fraction we need to know an analytical expression of the DC conductivity σ (0), by other means. We are then led to derive an expression of σ (0), in the intermediate friction regime. Moreover, this new expression allows us to recover the two known results computed in the low and high friction limits. Its behaviour is compared with that obtained by Langevin dynamics. We have found a very good agreement between the two results. By varying the density of mobile ions we discuss commensurability effects. For commensurate cases, the resonance frequency of the conductivity is determined only by the external potential.

We examine the behaviour of the concentration profiles of particles with repulsive interactions diffusing on a host lattice. At low temperature, the diffusion process is strongly influenced by the presence of ordered domains. We use mean field equations and Monte-Carlo simulations to describe the various effects which influence the kinetic behaviour. An effective diffusion coefficient is determined analytically and is compared with the simulations. Finite gradient effects on the ordered domains and on the diffusion are discussed. The kinetics studied is relevant for superionic conductors, for intercalation and also for the diffusion of particles adsorbed on a substrate.

Summary Numerical simulation based on the one dimensional (1D) Fukuyama, Lee and Rice (FLR) elastic model of randomly pinned charge density wave (CDW) systems are reported. In the weak pinning limit the threshold field E T obey a c i 2 behavior where c i is the impurity concentration. In a wide field and impurity concentration range, the current density J CDW and the excess conductivity σ CDW obey respectively J CDW ~(E/E T −1) a and σ CDW ~ (E T /E)(E/E T −) a in agreement with several previous experimental work; α is an impurites dependant exponent and E is the applied electric field.

The static structure factor and diffusion mechanism of N interacting Brownian particles immersed in a two-dimensional periodic potential are discussed, in relation with supe- rionic conductors, premelting surfaces and adsorbed monolayers. For the static structure factor we report Brownian dynamics results assuming a repulsive Yukawa pair potential. For some values of the concentration, the system can be decomposed in two equivalent or in two different subsystems along the two directions of space. To get information about the diffusion mechanism, we have computed the full width at half maximum (f.w.h.m.) A(q), of the quasi-elastic line of the dynamical structure factor S(q, WI up to large values of q covering several Brillouin zones. The entire analysis of A(q) with different physical parameters shows that the most probable dif- fusion process in good superionic conductors (concentration of mobile ions c = 2/3) consists of a competition between a back correlated hopping in one direction and forward correlated hopping in addition to liquid-like motions in the other spatial direction. The analytical treatment of this investigation is done by using different approximations such as the homogeneous approximation and the time dependent mean field approximation within the lattice gas model.

We have studied the triangular lattice gas model subject to nearest-neighbour repulsive interactions in the mean-field approach, leading to a clear understanding of the order - disorder transition and its effect on the intercalation process in transitional compounds such as . The triangular lattice division into three sublattices enables us to emphasize the appearance and the growth of the ordered phase. The computation of the incremental capacity defined as the response function of the cell to the intercalation allows us to obtain information about the global behaviour of the system with regard to the intercalation process.

We study the dynamic properties of a system of N interacting Brownian particles immersed in a two-dimensional periodic potential in relation to superionic conductors. By varying the density of the mobile ions and the strength of the pair interaction, we investigate commensurability and correlation effects on the conduction process by an analysis of the diffusion coefficient. Both the Frenkel Kontorova and Yukawa pair potentials between Brownian particles are used for this special investigation. Our numerical results, obtained form Langevin dynamics indicate a large difference between the transport properties of the one-dimensional and the two-dimensional systems, in the range of the weak pair interaction and for certain concentrations around 0.77. The maximum conductivity of two-dimensional conductors is predicted for concentration c = 2/3, while in the one-dimensional case it is always located at concentration c = 0.77. Furthermore we have evaluated analytically the dc-conductivity, in the two-dimensional case, for any value of the correlation length and for concentration c = 2/3. The analytical predictions are in good agreement with those of the numerical calculations.

We study the diffusion process of interacting Brownian particles on stepped surfaces. By employing the Langevin dynamic simulation we have calculated the diffusion coefficient D as a function of the concentration c for different values of the correlation lengths. Our results show that, on stepped surface, the diffusion process is reduced with respect to the one corresponding to the flat surface.

Materials at the nanoscale have recently attracted much attention due to their high potential for technological applications and to their size-dependent optical, nonlinear optical, electronic and chemical properties as well as their potential for incorporation into electronic circuits at the nanoscale. In particular, metal nanoparticles have been widely applied due to their ease of synthesis, stability and potential for application ranging from magnetic memory to electronics and to catalysis. In this work we report a simple one step method for assembling spherical nanoparticles into wires without need for lithographic templating. It is effective for a variety of conducting and no conducting nanoparticles and substrates and the only material requirement is that the nanoparticles be placed in a colloidal suspension that is wettable on the desired substrate. The shape of the meniscus defines the wirepsilas geometry. We report the synthesis and physical properties of gold nanoparticles wires of several millimetres long and by a few micrometers wide. As we demonstrate here, the technique is fast and easily controlled and can be used to make integrated nanoparticles wire arrays.

We study the creep rupture of fiber composites subjected to uniaxial constant load within the framework of the fiber bundle model. Our numerical studies showed that in the primary creep the deformation rate exhibits a power law relaxation followed by a power law acceleration in the tertiary creep. We also investigate the behavior of the failure time and the avalanche size distribution. A good agreement is found between experiments and the model prediction, particularly for deformation power-laws scaling in the primary-creep regime and in the tertiary-creep neighbourhood of rupture.

The challenge of this work is to prepare ceramics in the form of powders crystallized type Na2-2xA2xPbP2O7 (A = Li, K, Ag and 0 < x < 1) by the method glass. These different compositions will be characterized by different techniques such as X-ray diffraction, spectroscopy FTIR and thermal analyses ATD, ATG and DSC to determine their local structures. Indeed, the absorption bands appeared in the range of 714 - 970 cm-1 are footprint P2O7 4- groups representing different degrees of freedom from those of PO4 3- and PO3 -. In addition, structures of pyrophosphate joint alkaline and transition element type of symmetry are triclinic. The entity [Pb2P4O14]4- form layers parallel to the plane (001). The sodium atom is located between these two layers. The study of crystal glass composition Na2PbP2O7 at different speeds heating has been undertaken. We evaluated fractions crystallized glass at different temperatures and different speeds. Several models of calculation were applied to determine the activation energy of crystallization of glass diphosphate sodium. The thermal parameters obtained confirm that the crystallisation is predominant two-dimensional. The electrical properties due to the mobility of alkali ions are approached in connection with the structural buildings.

[1] The mutual interaction of cross-equatorial twin cyclones, its effect, and the effect of the planetary vorticity gradient on their motion are investigated using barotropic nondivergent and shallow water models. In comparing the behavior of a single cyclone to that of twin cyclones, it is found that each cyclone tends to accelerate the other and to turn its track westward. The causes of these changes are illuminated by investigating the motion of a single northern cyclone in a mean flow that resembles the one induced by a southern cyclone. The meridionally varying environmental vorticity gradient induced by the southern cyclone plays a key role in the explanation of the northern cyclone motion. This gradient tends to cancel the planetary vorticity gradient around the northern cyclone, resulting in a lower effective β that produces a weaker wave number 1 (WN1) asymmetry and consequently a slower motion. As the cyclone moves northward, the effective β increases, and so does the WN1 asymmetric circulation, which in turn accelerates the cyclone. Even in the linear case, the mean varying vorticity gradient causes the WN1 circulation to be no longer east–west, but to turn counterclockwise. This effect is due to the development of a strong anticyclonic circulation that is at a maximum in the northeast region as a consequence of vorticity conservation. When the nonlinear effects are included, the β gyres are turned further counterclockwise by the symmetric circulation, which is stronger than in the single cyclone case. Mutual interaction of tropical twin cyclones may increase the duration of the resulting Westerly Wind Bursts by reducing the poleward drift. The role of divergence effects on the twin cyclones' evolution is examined using a shallow water simulation with the same cyclone wind profile as in the nondivergent case. It is found that divergence tends to slow down the cyclone motion. We suggest that this effect is due to the potential vorticity conservation (compared to absolute vorticity conservation for nondivergent flows) that tends to reduce the produced WN1 asymmetry.

The Electron-Longitudinal Optical (LO) Phonon effects on the binding energy of shallow donor impurity in a superlattice GaAs-Ga1-xAlxAs are investigated. The calculations are made using the effective mass approximation within the variational approach for a superlattice potential described by the Kroning-Penney model. Our results are obtained as a function of parameters which characterize the superlattice and the position of the impurity center. The present results could be useful in understanding the spatial distribution of the donor center in the superlattice.

We propose a generalization of lattice gas models which can account for the dynamic of hopping particles in the low damping Kramers regime.

Ionic motion in framework solid electrolytes constitutes a special sort of classical many-body problem. In such electrolytes, the conductivity is due to the motion of interacting mobile ions modulated by the presence of an essentially immobile framework sublattice. Here, a one-dimensional model of interacting particles, governed by Langevin's equations of motion in a sinusoidal potential, is used to calculate particle distribution functions and effective potentials. The effective potential Veff(x), is then defined through the density distribution, ϱ(x), ϱ(x) ∞ e−βVeffx where β = 1/kT. The Langevin dynamics simulation is used to calculate ϱ(x), which in turn gives Veff(x). The dc conductivity and the other distribution functions can be used to investigate commensurability effects, pinning effects, and screening effects. Comparisons can then be made between correct numerical many-body results and various analytical approximations.

We investigate the dynamical conductivity σ(ω) of a one-dimensional system of interacting Brownian particles subject to a periodic potential in relation to superionic conductors. By varying the density of the mobile particules and the strength of the pair interaction, we discuss commensurability effects and determine how the dynamical responses are effected by the correlated motion of the ions. We start from the Fokker-Planck equation generalized to N-particles and we use continued fractions development up to fourth order of the velocity-velocity correlation function. Using the homogeneous approximation to perform the many body averages in the static correlation functions, we derive an expression of σ(ω) which does not introduce any restriction on the temperature regime or the strength of the pair interaction and which shows clearly the relationship between the dynamical behavior of the disordered sublattice and its structural properties Etude des proprietes dynamiques d'un systeme unidimensionnel de particules browniennes interagissantes et soumises a un potentiel periodique, en relation avec les conducteurs superioniques. Analyse du comportement de la conductivite dynamique σ(ω) avec l'intensite des interactions de paire et la densite des ions mobiles, en partant de l'equation de Fokker-Planck generalisee a N corps et en utilisant le developpement de σ(ω) en fractions continues au quatrieme ordre. En calculant les fonctions de correlations statiques a l'aide de l'approximation homogene, deduction une expression de σ(ω) qui n'introduit aucune restriction sur le regime de temperature ou l'intensite des interactions de paire et qui reflete clairement la relation entre le comportement dynamique du reseau desordonne et ses proprietes structurales

During a diffusion process the diffusion front fluctuates leading to a “geometrical noise”. We predict a 1/ƒ 2 noise at high frequency and a 1/ƒ noise at low frequency separated by a crossover ƒ ∗ . We give here scaling expressions sustained by numerical calculations for the fluctuations and the distribution of events as a function of time and diffusion length. The close relation of this approach with noise in invasion experiments in presence of a gravity field is also pointed out.

Whenever fractal interfaces are obtained by diffusion, they may present, besides the anomalous electrical properties due to their static geometry, an anomalous noise related to the fluctuation in time of this geometry. These fluctuations occur at very high frequencies as compared to the atomic jump rate. They may then be a source of noise in heterogeneous systems or diffused contacts which can be otherwise considered as quenched. This “geometrical” noise is calculated in the framework of gradient percolation Monte Carlo simulations in d=2. Scaling arguments based on fluctuations of cutting bonds are given to account for the results. We predict a high-frequency power noise spectrum in 1/f2 and a low-frequency power spectrum in 1/f. The cross-over between the two regimes occurs at a frequency which has a power law dependence as a function of the gradient of concentration at the interface. The scaling behaviour of these phenomena agrees with simple predictions from percolation theory.