International Journal of Modern Physics B

With the coupling of a scalar field, a generalization of the nonlinear Klein–Gordon equation which arises in the relativistic quantum mechanics and field theory, i.e., the coupled nonlinear Klein–Gordon equations, is investigated via the Hirota method. With the truncated Painlevé expansion at the constant level term with two singular manifolds, the coupled nonlinear Klein–Gordon equations are transformed to a bilinear form. Starting from the bilinear form, with symbolic computation, we obtain the N-soliton solutions for the coupled nonlinear Klein–Gordon equations.

A microscopic theory of dielectric properties of thin molecular films, i.e., quasi 2D systems bounded by two surfaces parallel to XY planes was formulated. Harmonic exciton states were calculated using the method of two-time, retarded, temperature dependent Green's functions. It has been shown that two types of excitations can occur: bulk and surface exciton states. Analysis of the optical properties of these crystalline systems for low exciton concentration shows that the permittivity strongly depends on boundary parameters and the thickness of the film. Conditions for the appearance of localized or unoccupied exciton states have been especially analyzed.

In this paper we have evaluated inherent properties (i.e., heat of formation and cohesive energy) for chalcopyrite structured solids. We have presented two expressions relating the heat of formation and cohesive energy for and semiconductors with the product of ionic charge (Z_AZ_BZ_C) and nearest neighbor distance (d in Å). The heat of formation and cohesive energy of these solids exhibit a linear relationship when plotted on a log–log scale against the nearest neighbor distance, but fall on different straight lines according to the product of ionic charge of the compounds. We have applied the modified relations on these solids and found a better agreement with experimental data as compared to the values evaluated by previous researchers so far. The results for heat of formation differ from experimental values by the following amounts: ZnSiP₂ — 4.8%, ZnSnP₂ — 0.4%, ZnSiAs₂ — 0.7%, ZnGeAs₂ — 2.6%, ZnSnAs₂ — 1.2%, CdGeP₂ — 3.8%, CuGaSe₂ — 0.3% and AgInSe₂ — 5% and the results for cohesive energy differ from experimental values by the following amounts: ZnSiP₂ — 0.3%, ZnSnAs₂ — 1.5%, CuGaSe₂ — 3.7%, CuGaTe₂ — 2%, CuInTe₂ — 2.7%, AgGaTe₂ — 0.7%, AgInSe₂ — 3%, AgInTe₂ — 3%.

Most studies of thin film growth simulations are performed on flat substrates. However, in reality, a substrate is usually miscut leading to a vicinal surface with a small tilt. The goal of this work is to study effects of an initial configuration of a miscut substrate on the grown film. The Das Sarma–Tamborenea model with modified diffusion rules is used for the simulations. The modification is done to allow variation in the surface diffusion length and mobility of adatoms. The results show that the optimum conditions that lead to step-flow growth are long diffusion length and small step height.

In this paper, we present the empirical investigation results on the urban public transport networks (PTNs) and propose a model to understand the results obtained. We investigate some urban public traffic networks in China, which are the urban public traffic networks of Beijing, Guangzhou, Wuhan and etc. The empirical results on the big cities show that the accumulative act-degree distributions of PTNs take neither power function forms, nor exponential function forms, but they are described by a shifted power function, and the accumulative act-degree distributions of PTNs in medium-sized or small cities follow the same law. In the end, we propose a model to show a possible evolutionary mechanism for the emergence of such network. The analytic results obtained from this model are in good agreement with the empirical results.

The structure, electronic and elastic properties of CrO₂ in the high pressure orthorhombic CaCl₂ (Pnnm) phase are investigated by first-principles calculations based on density functional theory (DFT). Our calculated crystal parameters are in good agreement with the available experimental data. The electronic band structure, density of state (DOS) and projected density of state (PDOS) at 14 GPa are studied within local spin density approximation (LSDA) and generalized gradient approximation (GGA) in details. The CaCl₂ phase of CrO₂ still has the half metal character, which is in accordance with previous theoretical predictions. The elastic constants, bulk modulus, shear modulus, Young's modulus and Poisson ratio under pressures are successfully obtained for the orthorhombic CaCl₂ phase of CrO₂. This structure is mechanically stable at our applied range of pressures. The calculated elastic anisotropic factors show that the CaCl₂ phase of CrO₂ is provided with high elastic anisotropy and the elastic anisotropy decreases with increasing pressures. The propagation speed of transverse, longitudinal elastic wave together with associated Debye temperatures are also estimated.

The effect of incoherent pumping field on absorption spectrum and population inversion in a four-level quantum dot nanostructure are investigated. It is found that with incoherent pumping field the probe field absorption can be converted to probe field gain. Also, it is found that with combine effect of incoherent pumping field and electron tunneling the lasing can be obtained in the absence or presence of population inversion.

Quantum entanglement and teleportation of two qubit X-states subject to heat bath is investigated by partial teleportation protocol. We obtain the analytical expressions of the average fidelity for the X-states with one-side decoherence and two-side decoherence. The quality of quantum teleportation with various initial states is investigated by explicitly calculating the concurrence, the output concurrence and the average fidelity. The results demonstrate that the model is suitable for teleportation, which depends on the initial state. However, the mean thermal occupation number of bath and decoherence could induce the decrease of the output entanglement and the average fidelity in the quantum teleportation processing. We also find the quantum teleportation protocol of one-side decoherence is more robust than that of under two-side decoherence.

We calculate the tunneling resistance at the quantum critical point of a mesoscopic SQUIDs array in the presence of magnetic flux. We observe nonuniversal bahaviour of tunneling resistance. We find the analytical relation between the magnetic flux induced dissipation strength and the Luttinger liquid parameter of the system. We also predict the evidence of length scale independent metallic state. This study also emphasizes the importance of co-tunneling effect.

In this paper, we have investigated thermodynamic parameters of hydrogen and helium fluid mixture with assistance of statistical perturbation theory. The results have been compared with existing theoretical and Monte Carlo simulation methods based. Moreover, the effects of density, temperature and helium concentration on equation of state (EOS) of this mixture have been considered. Likewise, since exp-6 potential has given better results in comparison with MC simulations in higher temperatures than double Yukawa potential and avoiding any vague speculation, comparison between effects of these potentials has been presented. The results further suggest that EOS in this place depends sensitively on the density, the potential function and concentration of each component.