International Journal of Modern Physics B

The autocorrelation function of the light emitted by a microcavity containing a semiconductor quantum well in the nonstationary regime is investigated. An analytical expression in the weak pumping and strong coupling regime is derived. Furthermore, it is shown that the initial entangled state can be deduced from the nonstationary autocorrelation function.

Polyvinyl alcohol (PVA) has been used as a matrix to synthesize ZnS/PVA nanocomposite film on glass substrate by chemical method. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Scanning electron microscopy (SEM) has been used for structural, morphological and compositional characterization. Optical properties have been studied by UV-Visible spectrophotometry and photoluminescence (PL) spectroscopy. Changing pH value from 4.8 to 0.8 decreases the particle size and correspondingly increases the band gap. The PL emission intensity also increases by decreasing the pH values.

This paper investigates chaotic synchronization in the generalized sense in two resistive-capacitive-inductive-shunted (RCL-shunted) Josephson junctions (RCLSJJs) by using the means of unidirectionally coupling. The numerical simulations confirm that the generalized synchronization of chaos in these two systems can be achieved with a suitable coupling intensity when the maximum condition Lyapunov exponent (MCLE) is negative. Also, the auxiliary system approach is used to detect the existence of the generalized synchronization.

The effect of aperiodicity on the charge transfer process through DNA molecules is investigated using a tight-binding model. Single-stranded aperiodic Fibonacci polyGC and polyAT sequences along with aperiodic Rudin–Shapiro poly(GCAT) sequences are used in the study. Based on the tight-binding model, molecular orbital calculations of the DNA chains are performed and ionization potentials compared, as this might be relevant to understanding the charge transfer process. Charges migrate through the sequences in a multistep hopping process. Results for current conduction through aperiodic sequences are compared with those for the corresponding periodic sequences. We find that dinucleotide aperiodic Fibonacci sequences decrease the current while tetranucleotide aperiodic Rudin–Shapiro sequences increase the current when compared with the corresponding periodic sequences. The conductance in all cases decays exponentially as the sequence length increases.

From the discrete nonlinear Schrödinger equation and the linear stability analysis, the modulational instability (MI) of dipolar Bose–Einstein Condensates (BECs) in an optical lattice is studied. The MI relation of the dipolar BECs in the optical lattice with the on-site interaction and the inter-site interaction is obtained. The results show that there is a great influence of inter-site interaction on MI of dipolar BEC in the optical lattice. This gives us some useful information for manipulating dipolar BECs in practice.

In this paper, the photon escape probability of Na 330.3 nm resonance line is calculated, both for slab and cylindrical geometries. The dependence of the photon escape probability on the optical depth in the line center is considered. The oscillator strength, the number density of the absorbing atoms in the ground state, and the optical depth in the line center are discussed in this calculation. The changes of the photon escape probabilities with different concentrations are calculated. This calculation will provide a method to calculate the photon escape probability for different lines.

The magnetic and magnetoimpedance behavior of FeCuCrVSiB and (F/SiO₂)₃/Ag/(SiO₂/F)₃(F = FeCuCrVSiB) soft magnetic amorphous films deposited in a magnetic field have been investigated systematically. The samples were deposited by the RF sputtering with or without a static magnetic field of 900 Oe applied in the film plane. It is found that the magnetic field applied during the deposition process improves the soft magnetic properties of the sample significantly. The coercive force of the sample is about 0.8 Oe, which is much smaller than that deposited without a field. Moreover, remarkable GMI effects were obtained at relatively low frequencies, which contrasts with the samples deposited without field. In the magnetic field-deposited state, the maximum GMI ratios of 21.5% and 19.5% were achieved for the single-layer films in longitudinal and transverse fields at a frequency of 13 MHz, while for the multilayered films, the maximum values of longitudinal and transverse GMI ratios are 45% and 44% at a frequency of 6.81 MHz, respectively. These superior GMI behaviors of the as-deposited films are related to the magnetic field used in the preparation process and the inserted SiO₂ layers.

Nonlinear filtering of local turbulent fluid measurements was an unexplored domain; in this paper, we present original stochastic models and efficient filters to explore it. First, we propose nonlinear filters for processes of a mean-field law and give the convergence of their particle approximations. We then define the acquisition process of a vector field along a random path, and significantly modify the Lagrangian models of fluids proposed by the physicists to make them compatible with the problem of filtering. The closure of these equations is obtained by conditioning the dynamics to the observations and to the acquisition process. Our algorithm allowed us to filter velocity measurements of a real turbulent fluid in 3D flows.

The drift of rigidly rotating spiral waves in an excitable medium induced by synchronous and asynchronous mechanical deformation is investigated numerically and analytically. The resonant drift of spiral waves induced by a mechanical deformation with ω = ω₀ and ω = 3ω₀ is observed. At ω = ω₀, synchronous and greatest degree of asynchronous mechanical deformations are specially investigated. For the case ω = 3ω₀, synchronous mechanism deformation locks the spiral while decreasing of degree of synchronization increases the drift velocity. We derive an approximate but explicit formula of the spiral drift velocity and direction which is consistent with the numerical results.

When a load is applied to a dense granular material, the stress is largely transmitted by relatively rigid, heavily stressed chains of particles forming a sparse network of larger contact forces. Force chains act as the key determinant of mechanical properties such as stability, elasticity and flowability. To understand the structure and evolution of force chains, related physical processes and three corresponding characteristic time scales are analyzed in this study. We also propose three dimensionless numbers for the measurement of the relative importance of force chains. To solely study the effect of particle surface friction on force chains, uniaxial compression tests of 11,000 equal-sized particles in 2D were numerically simulated using the discrete element method. By proposing three conditions to define a force chain, the chain length distribution is found in the form of a power law. The exponent of 1.744 is independent of the surface friction. Although these results were obtained from partially crystallized jammed packings, they provide new insight into the physical processes and the structure of force chains, and thus will be helpful in the interpretation of force chains in other dense granular systems.

We calculated the binding energies of shallow donors and acceptors in a spherical GaAs-Ga_1-xAl_xAs quantum dot under the combined effect of isotropic hydrostatic pressure and an intense laser. We used a variational approach within the effective mass approximation. The binding energy was computed as a function of hydrostatic pressure, dot sizes and laser field amplitude. The results showed that the impurity binding energy increases with pressure and decreases with the laser field amplitude when other parameters are fixed. We also found that the pressure effects are more dramatic for donor than acceptor impurities, especially for quantum dots with small radii.

We investigate within a mean-field approach the dynamics of the spin-1 Blume-Capel model with Glauber type kinetics under a random oscillating external magnetic field. It is found that the order parameter or the average magnetization is strongly affected by the introduction of the randomness into the system if the number of the realization of the system is low. For only one realization of the system, it is also observed that the increasing strength of the randomness causes more deviation on the noise free average magnetization curves. In addition, it is found that the strength of the deviation depends on the value of the initial condition m(0). Depending on the strength of the randomness, the system exhibits very confusing average magnetization behaviors. This situation occurs especially for regions of the parameter space where both noise free first and second order transitions coexist. On the other hand, for a large number of realizations of the system, the average magnetization curves are found to behave as in the noise-free cases. Consequently, we conclude that the proper order parameter in the presence of a noisy external field can be the average magnetization over the possible realization of the system.

Thermodynamic properties of a relativistic Fermi gas in any dimensional space are studied, in which the influence of particle–antiparticle pair production is taken into account. It is shown that relativistic effects cannot be ignored even at very low temperatures for the system with the Compton wavelength of a particle comparable with the average distance between particles. The pair production results in some novel characteristics, which include the asymptotic behavior of the chemical potential and the rapid increase in the heat capacity with temperature in the high temperature regions, etc.

It has been recently shown that difference between diffusion coefficients of dopant in layers of a multilayer structure leads to increasing of sharpness of diffusion-junction rectifier (see, for example, E. L. Pankratov, Phys. Rev. B72(7), 075201 (2005); E. L. Pankratov and B. Spagnolo, Eur. Phys. J. B 46(1), 15 (2005).), which was formed in the multilayer structure after appropriate choosing of materials of layers. It has been also shown that the difference between the diffusion coefficients also leads to increasing of homogeneity of dopant distribution in doped area. In this paper, both the effects (together increasing of sharpness of p–n-junction and increasing of homogeneity of dopant distribution) have been used to produce a system of p–n-junctions (such as bipolar transistors). Annealing time has been optimized to increase simultaneously the sharpness and the homogeneity.

A cobalt ferrite/nickel-zinc ferrite core/shell nanocomposite was synthesized by a polymerized complex method using iron citrate, cobalt nitrate, nickel nitrate, zinc nitrate, citric acid, ethylene glycol, benzoic acid and sodium citrate as starting materials. The XRD, TEM and VSM techniques were employed to evaluate the phase composition, morphology and magnetic properties of the samples. The XRD results indicated the coexistence of characteristic reflections of CoFe₂O₄ and Ni_0.5Zn_0.5Fe₂ O₄ spinel ferrites in the composite sample. The core/shell structure of the composite sample has been confirmed by TEM images. The size of obtained spherical core/shell nanoparticles was 20–40 nm in core diameter and about 10 nm in shell thickness. The VSM results showed that both the coercivity and the saturation magnetization of the resulting core/shell nanocomposite were decreased compared to those of the CoFe₂O₄ core, due to the interaction at the interface of CoFe₂O₄ and Ni_0.5Zn_0.5Fe₂O₄.

The exchange–coupling interaction between soft and hard phase layers and the effective anisotropy K_eff have been investigated by putting forward an expression of anisotropy at grain interface, , which is suitable for different coupling conditions in multilayered thin film. The results showed when the dimensions of soft and hard phases are the same (described by b), K_eff increases first, then decreases, and reaches a maximum at a certain value of b with increasing b. For the given hard phase dimension b_h, K_eff decreases monotonously with increasing soft phase dimension b_s. However, for the given b_s, K_eff increases monotonously with the increase of b_h. When the dimensions of soft and hard phases are the same, the variation of K_eff in multilayered thin film is very similar to that of coercivity given by Yang et al. Our results explained the experimental phenomenon better.

The isobaric thermal conductivity of solid β-SF₆, CCl₄(Ib), and C₆H₆ is investigated by using the Debye thermal conductivity model and taking into account the effect of minimum thermal conductivity. The simulation was carried out in the framework of a model where heat is transferred by phonons and "diffusive" modes with regard to the thermal expansion and phonon–rotation coupling. For this purpose the temperature dependences of the isobaric heat capacity components have been calculated numerically for β-SF₆, CCl₄(Ib), and C₆H₆. The contributions of phonon–phonon and phonon–rotational interactions to the total thermal resistance are discussed.