International Journal of Modern Physics B

Co uniform hierarchical microspheres were grown on a large scale at 200° by a simple hydrothermal method with the help of the surfactant polyvinylpyrrolidone (PVP). During the synthesis, the external magnetic field as a controlling factor assembled cobalt microspheres to form chain-like structures vertically on substrate. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the product. The results indicate that three-dimensional (3D) Co microspheres are constructed by the cross-sectional nanoplatelets shape with a mean thickness of ~ 250 nm. The mechanism involved for the formation of the chain-like structures is discussed. The results of the vibrating sample magnetometer (VSM) show that the magnetic Co chains possess the saturation magnetization of 125.2 emu/g. Our work may shed some light on the design of other well-defined complex nanostructures, and as-grown architectures may have potential applications.

In this paper, we study the effect of asymmetry of the potential in a bistable system with quantum fluctuations. Within the quantum Smoluchowski regime, the expressions for the mean first passage time (MFPT) and signal-to-noise ratio (SNR) of the system are obtained, respectively. Based on the MFPT and SNR, we consider both, the overdamped quantum case and its classical counterpart, the effects of the quantum fluctuations and the asymmetry of the potential on the MFPT and SNR are discussed. Our main results show that (i) the quantum fluctuations facilitate the particle to reach the destination from its original position, (ii) the resonant activation (RA) phenomena can be observed with varying asymmetry of the potential, and (iii) the quantum effects in an asymmetric bistable system about SNR are prominent for lower temperatures and smaller asymmetry of the potential. Moreover, the quantum effects enhance the stochastic resonance (SR) of the system.

Current spin polarization in ferromagnetic/organic system is theoretically studied based on the spin diffusion theory and Ohm's law, and the effects of the spin-related interfacial resistances on the spin-polarized injection are discussed. It is shown that the current spin polarization can be higher than the spin polarization of the ferromagnetic contact and may reach 100% at the interface by modulating the spin-related interfacial resistances. The proposed amplification scheme provides an efficient way to generate a highly spin-polarized current in organic materials because of the easy fabrication of ordered spin-related tunnel barriers at contact structures.

The effects of noise correlation and time delay on the transient properties of a cancer growth system are studied in terms of the mean first-passage time (MFPT), which provides a measure of the mean extinction time of the tumor cell population. The results indicate that the additive and multiplicative noises can induce the noise-enhanced stability (NES) effect. The increasing of the delay time weakens the NES effect in the presence of two noise sources and induces a shift of the maximum of the MFPT towards smaller values of the noise intensities. The increasing of cross-correlation strength between noises can only restrain the NES effect induced by the multiplicative noise and can induce a shift of the peak of the MFPT towards larger values of the noise intensities.

By considering a spin dependence for the correlation function, the thermodynamic properties of normal liquid ³He have been investigated by employing a lowest order constrained variational approach. It is seen that the spin-singlet state has a smaller contribution in the potential energy of normal liquid ³He with respect to the spin-triplet state. It is seen that at high temperatures, the free energy of normal liquid ³He in cases of spin-dependent and spin-independent correlation functions are nearly identical. The equations of state of these two cases are nearly similar too.

We have investigated the effect of an external periodic driving to the macroscopic quantum tunneling of spin-1 condensates in a double-well potential. By manipulating the frequencies of the external magnetic fields, a rich set of phenomena can be studied, and dynamical localization and self-trapping in spin states can be realized using time-dependent magnetic field. We have shown that a relatively high-frequency field may induce a fast oscillation of the macroscopic quantum localization. The larger the periodic magnetic field frequency is, the faster oscillation of the spin condensate magnetization goes. By applying a lower-frequency field to the spin-condensate, one can find that the dynamical properties of the magnetization appears similar behaviors to the results of the modulations of a constant external magnetic field. A possible realization in experiments is also presented.

Thermal diffusion or Soret effect is the directed motion of colloidal particles in temperature gradient. In this article, by assuming local thermodynamic equilibrium, the drift velocity for a molecular system composed of two connected spheres is calculated. It is shown that for this system the positive Soret coefficient is given by: S_T = (3/8)(a/l)(1/T), where l is the average linear size of the system, a is the radius of spheres and T is the local temperature. To investigate the hydrodynamic coupling in a dilute suspension of diffusers, we calculate the average drift velocity for two far diffusers. It is shown that due to the hydrodynamic interaction, an overall attraction between diffusers can be achieved.

The differential cross section (DCS) for exciton-mediated Raman scattering (EMRS) in one-dimensional semiconductor quantum dots is presented. The exciton states are considered as intermediate states in the Raman scattering process. The selection rules for the EMRS process are studied. The numerical results show that the contribution to DCS indicated by exciton is larger than that by electron. DCS of EMRS is larger when there is a bigger confinement potential frequency.

In this paper, we have proposed a novel three-dimensional Lorenz-like chaotic system. Some basic properties of the system, such as dynamical behaviors, bifurcation diagram. Lyapunov exponents and Poincare mapping are investigated either analytically or numerically. Furthermore, the control problem of the new chaotic system was studied via nonlinear backstepping method. The single backstepping control input was designed according to Lyapunov stability criterion. Numerical simulations are carried out in order to demonstrate the effectiveness of the proposed control design.

Carbon nanotubes (CNTs) were synthesized via arc discharge in aqueous solutions containing ferrous and ferric irons to reveal the effect of iron-charge mole ratio, R = [Fe²⁺]/[Fe³⁺], on the purity of CNTs and the process yield. Raman spectroscopy and transmission electron microscopy were used to analyze the cathodic deposits. It is shown that the nucleation of multi-walled CNTs is catalyzed by ferric irons while their growth is affected by ferrous ions. Well-graphitized CNTs with a high-yield are obtained at R = 1 and total iron concentration of 0.05 M. The effect of iron charge is described based on the two-stage formation mechanism.

In this paper, we propose two methods for solving general mixed variational inequalities. In the first method, the new iterate is obtained by using a descent direction while the second method can be viewed as an extension of the first one by performing an additional projection step at each iteration and another optimal step length is employed to reach substantial progress in each iteration. It is proved theoretically that the lower-bound of the progress obtained by the second method is greater than that by the first one. Under certain conditions, the global convergence of the both methods is proved. The comparison of these methods with other methods for solving the mixed genera variational inequalities is an open interesting problem.

The effects of a finite number of particles on the thermodynamic properties of ideal Bose and Fermi gases trapped in any-dimensional harmonic potential are investigated. The orders of relative corrections to the thermodynamic quantities due to the finite number of particles are estimated in different situations. The results obtained for the two trapped quantum gases are compared, and consequently, it is shown that the finite-particle-number effects for the condensed Bose gas (a Bose gas with Bose–Einstein Condensation (BEC) occurring in the system) are much more significant than those for the Fermi gas and normal Bose gas (a Bose gas without BEC).

In this paper, we suggest and analyze a new extragradient method for solving the general variational inequalities involving two operators. We also prove the global convergence of the proposed modified method under certain mild conditions. We used a self-adaptive technique to adjust parameter ρ at each iteration. It is proved theoretically that the lower-bound of the progress obtained by the proposed method is greater than that by the extragradient method. An example is given to illustrate the efficiency and its comparison with the extragradient method. Since the general variational inequalities include the classical variational inequalities and complementarity problems as special cases, our results obtained in this paper continue to hold for these problems. Results obtained in this paper may be viewed as an improvement and refinement of the previously known results in this field.

The aim of this paper is to solve one-dimensional wave equations that combine classical and integral boundary conditions using the homotopy perturbation method (HPM). The studied equations are changed into direct problems easy to be handled by the homotopy perturbation method. Several examples are given and the results are compared with exact solutions, revealing effectiveness and simplicity of the method.

Based on the interactions among car, bicycle and pedestrian, we in this paper present a bicycle-following model and a pedestrian-following model with the consideration of the honk effects. Using the relationship between the micro and macro variables, we obtain a macro model for bicycle flow and pedestrian flow. The numerical results show that the honk effects can enhance the bicycle and pedestrian speeds and flows.

Nontoxic lead-free multiferroic composites are synthesized by incorporating the dispersed 0.3CoFe₂O₄ (CFO) ferromagnetic nanoparticles into 0.7(K_0.5Na_0.5) NbO₃-LiSbO₃ (KNN-LS5.2) ferroelectric micromatrix. The multiferroicity of the composite can be verified by polarization-electric field hysteresis loop and magnetic hysteresis loop. The composite exhibits excellent magnetic properties. A dilution effect is observed in magnetic hysteresis loops. The field dependence of ME voltage coefficient is given as a function of magnetic field from -4 kOe to 4 kOe with a maximum magnetoelectric voltage coefficient of 10.7 mV⋅cm^-1⋅Oe^-1 at the frequency of 1 kHz. It is a very high value in the lead-free magnetoelectric composites system for the potential use on multifunctional devices.

In this study the electronic eigenstructure of an exciton in a parabolic quantum dot (QD) has been calculated with a high accuracy by using Finite element method (FEM). We have converted the coordinates of electron–light-hole system to relative and center of mass coordinate, then placed the Spherical Harmonics into Schrödinger equation analytically and obtained the Schrödinger equation which depends only on the radial variable. Finally we used FEM with only radial variable in order to get the accurate numerical results. We also showed first 21 energy level spectra of exciton depending on confinement and Coulomb interaction parameters.

We investigate synchronization of bursting neurons, caused by spatially correlated noise, consisting of a common Guassian noise and a local one. It is found that the degree of noise-induced synchronization between identical neurons increases with both the noise intensity and noise correlation. As for non-identical neurons, it is demonstrated that the degree of phase synchronization decreases monotonously with the noise intensity for partially correlated noise, but the degree undergoes a minimum with the common noise intensity increasing. An interpretation is provided for the noise-induced synchronization between identical neurons by investigating noise-modulated spike train pattern in a single neuron. In addition, the coherence of spike train is minimized at some noise intensities.

A coupled 2+1-dimensional discrete Chen–Lee–Liu equation is proposed, which together with two 1+1-dimensional discrete Kaup–Newell equations is decomposed into solvable ordinary differential equations with the help of the resulting Lax matrix and its finite-order expansion. Based on the theory of the algebraic curve, the Abel–Jacobi coordinates are introduced to straighten out the corresponding continuous flow and discrete flow, by which explicit solutions for the coupled 2+1-dimensional discrete Chen–Lee–Liu equation and the 1+1-dimensional discrete Kaup–Newell equations are obtained in the Abel–Jacobi coordinates.

We present the modification of optical transition probability in the superlattices (SLs) due to the presence of structural defect and the variation of layer thickness. The results show that optical transition probability between two bound states is mainly determined by the thicknesses of layer in defect region and its nearest constituent layers for a symmetric structure. When the well layer thickness varies, the variation of transition probabilities between two bound states depend on the parity of the index of minigap n, while those from the bound states to the delocalized scattering is irrelevant to n. It is believed that applying appropriate structure and layer thickness may enhance the optical transition probability in designing optical device.

The growing and rapid interest in new artificial metamaterials, whose properties differ from the normal materials has motivated further investigations. The metamaterials have simultaneously negative permittivity and permeability. In this work, we have demonstrated theoretically the existence and behavior of the TE guided waves in a ferromagnetic/metamaterial/antiferromagnetic waveguide structure. The dispersion characteristics are performed for different kinds of metamaterials. The existence and the type of the solutions to the guided waves with respect to different physical parameters are also investigated and discussed. It has been shown that the metamaterials can lead to different, new unusual properties.

The density function perturbation theory (DFPT) is employed to study the linear thermal expansion and heat capacity at constant pressure (with the quasiharmonic approximation). The calculations are performed using a pseudopotential plane wave method and local density approximation for the exchange-correlation potential. The calculated results of linear thermal expansion coefficient and heat capacity at constant pressure for zinc-blende ZnS, ZnSe are compared with the available experimental data in a wide temperature range. Generally, in low-temperature range, they have good agreement. However, in high-temperature range, due to anharmonic effect and other reasons, lead to larger errors for these properties between the theoretical results and available experimental data.

This paper studies the generalized synchronization of hyperchaos systems, and a new method, by which adaptive generalized synchronization of chaotic systems with a kind of linear and nonlinear relationship between the drive and response systems can be achieved, is proposed. This new method has more extensive application scope. Based on the Lyapunov stability theory, the correctness of the proposed scheme is strictly demonstrated. It is also illustrated by applications to hyperchaotic Chen system and hyperchaotic Lorenz system and the simulation results show the effectiveness of the proposed scheme.

The crossover of dilution in the critical exponent associated with the thermodynamic properties in the magnetic materials via Monte Carlo simulations is observed. The obtained results of critical exponent associated with the magnetic susceptibility, specific heat and correlation length for the ZnCr_2xAl_2-2xS₄, Cd_1-yCr_2-2xIn_y+2xSe₄ and Zn_1-xMn_xTe systems are comparable with those given by the experiment results.

A general method for quick and accurate evaluation of escape factor is presented, for any optical depths and any line profiles, using least square procedure. The principle of the least square procedure is discussed. As an example, the parameters are fitted when the optical depth is in the region of 0–1000, and the escape factors we obtained are in accordance with the theoretical formula.

It was generally believed that scale-free networks would be small-world. In this paper, two models, named Model A and Model B, are proposed to show that certain scale-free networks can be linear-world instead of small-world. By linear-world, it means that the average path length L of the network grows linearly with the total number of nodes N, i.e., L~N. Model A generates a deterministic scale-free network with high assortativity and numerical simulations demonstrate that the network is linear-world when it satisfies degree exponent λ>1. Model B constructs a partially deterministic scale-free network, which is connected by identical small scale-free networks following certain rules. Analytical arguments and numerical simulations both yield L~N which suggests that it is also linear-world. It is further discussed in this paper that the network generated by Model Bcould be either correlated or uncorrelated. This suggests that, inconsistent with the results in related works, uncorrelated scale-free networks can also be linear-world.

Spatial epidemiology is the study of spatial variation in disease risk or incidence, including the spatial patterns of the population. Thus, an epidemic model with spatial structure based on the cellular automata method, which is different from deterministic and probabilistic CA models, is investigated. The construction of the cellular automata is based on the work of Bussemaker et al. [Phys. Rev. Lett.78, 5018–5021 (1997)]. For the appropriately chosen parameters, Turing pattern formation can emerge from a randomly perturbed uniform state, which is shown by numerical simulations. The results obtained confirm that diffusion can form the disease being in high density and the population being more stable.

A broad set of sufficient conditions consisting of systems of linear partial differential equations are presented which guarantee that the Wronskian determinant is the solutions of the integrable variable-coefficient Korteweg-de Vries model from Bose–Einstein condensates and fluid dynamics. The generalized Wronskian solutions provide us with a comprehensive approach to construct many exact solutions including rational solutions, solitons, negatons, positons, and complexitons.

The aim of this work was to establish the feasibility of the combined photoacoustic (PA) and photopyroelectric (PPE) detection of the vapours emitted from essential oils and their corresponding uncrushed leaves or flowers. Gas traces of jasmine (Jessamine (Jasminum)), mint (Mentha arvensis L.) and Damask rose (Rosa damascena Miller) and their essential oils were tested using a combined cell fitted with both a photopyroelectric film (PVDF) and a microphone in conjunction with a pulsed wideband infrared source (PWBS) source. Infrared PA and PPE absorbances were obtained simultaneously at room temperatures with excellent reproducibility and high signal-to-noise ratios. Significant similarities found between the PA and PPE spectra of the trace gas emissions of plant parts, i.e., flowers or leaves and their related essential oils show the good correlation of their emissions and that both effects are initiated by the same absorbing molecules.

The pressure dependence of the frequency shifts 1/ω(∂ω/∂T)_P is calculated from the 1/ω(∂ω/∂P)_T for the Raman modes I and IV according to the spectroscopic modifications of the Pippard relations. The observed Raman frequencies of those modes are used for this calculation close to the I–II phase transition in s-triazine. From the frequency shifts, the isothermal compressibility κ_T and the specific heat C_P are also calculated as a function of pressure close to the I–II phase transition in s-triazine. Our calculated values of 1/ω(∂ω/∂T)_P κ_T and C_P can be compared with the experimental measurements at various pressures in the phases I and II of s-triazine.

In this paper, we use the decomposition technique of Noor and Noor [M. A. Noor and K. I. Noor, Three-step iterative methods for nonlinear equations, preprint (2006)] to suggest and analyze a new iterative methods for solving the integral equations. Our method of developing this new method is very simple as compared with other methods. Several numerical examples are given to illustrate the efficiency and performance of the new method. Results reveal that the proposed method is very effective and simple. Our method can be considered as an improvement of the existing methods.

This paper studies full state hybrid projective synchronization of the unified chaotic system with unknown parameters. Based on the Lyapunov stability theory, an adaptive controller is designed. It is proved theoretically that the controller can make the states of the dynamical system and the response system with unknown parameters asymptotically full state hybrid projective synchronized. Numerical simulations show the effectiveness of the scheme.

The present study is geared towards investigating methods to increase the tendency of fullerene structures to aggregate with biological systems. To accomplish this task, the encapsulation of metals inside a fullerene structure was performed. The calculations performed demonstrate that the Ca@C₆₀ structure leads to stronger interactions with amino acids at the DFT-BLYP/DND level of theory. Correlations of the dissociation energies, HOMO/LUMO band gaps and hardness are discussed.

Quantum mechanics allows one to encode the information in the superposition of a quantum state which embodies the nature of quantum nonlocality. Here we propose a realizable physical scheme for a multiparticle quantum dense coding (QDC) between two users in cavity quantum electrodynamics (QED). We also discuss the feasibility of our scheme within current technology.

Using a variational approach within the effective-mass approximation, we investigate the ground-state binding energy of a donor impurity in the GaAs quantum rings (QR) in the infinite confinement potential. A trial wave function with two variational parameters is used in the calculation. The binding energy as a function of the QR structure parameters and the impurity position is investigated. The results indicate that the binding energy decreases gradually as the QR structure parameters increase in the infinite confinement potential. In addition, the binding energy of the impurity exhibits a maximum as the impurity position moves along the symmetry axis of the QR from the bottom of the QR to the top. The impurity binding energy firstly increases and then decreases as the impurity moves from the internal surface of the QR to the external surface, indicating that there is a maximum.

The frequency dependency property of viscoelastic material leads to the dynamic analysis of compound structures which are complex and costly. Furthermore, using commercial finite element software, it is difficult to carry out the dynamic response analysis with this characteristic. Based on finite element iterative and modal strain energy (MSE) method, a mode superposition algorithm was proposed to solve the dynamic response of viscoelastic damping structure in this paper. Through iterative and MSE method, the modal frequency and loss factor for each mode can be obtained. Before calculating the next order modal frequency, the modal mode and corresponding load are extracted and the response of node was calculated at first in this algorithm. As a consequence, the node displacement response can be solved by summarizing the response results of each independent mode in the required frequency range. Numerical calculation of U shaped pipe with viscoelastic damping layer illustrates that the method is simple and practical. Moreover, the simulations with this method agree quite well with the experimental derived results. In the meantime, the damping layer parameters study shows that the position of the damping layer has an obvious effect of reducing the vibration response of U shaped pipe, but the width of the damping layer has little influence. The procedure proposed in this paper can be extended to analyze other more complex structures with viscoelastic material.

We investigate a new version of sandpile model which is very similar to Abelian Sandpile Model (ASM), but the height variables are continuous ones. With the toppling rule we define in our model, we show that the model can be mapped to ASM, so the general properties of the two models are identical. Yet the new model allows us to investigate some problems such as the effect of very small mass on the height probabilities, different boundary conditions, etc.

In this paper, variational iteration method (VIM) and homotopy-perturbation method (HPM) are implemented for solving analytically the nonlinear Fornberg–Whitham (FW) equation. VIM is used to construct correction functionals using general Lagrange multipliers identified optimally via the variational theory HPM converts a difficult problem into simple one, which can be easily handled. Furthermore, the solutions obtained are compared with the corresponding exact solution to show the applicability accuracy and efficiency of the present methods in solving a large class of linear and nonlinear problems arising in different fields of science and engineering.

A theoretical model for crystal melting based on the dislocation pairs is discussed in detail. The theory predicts a first-order melting transition, and the upper limit of the melting temperature is obtained. The types of dislocation mediated melting for fcc structure is different from that of the bcc one, the former mediated by the partial dislocation and the latter by the perfect one. Calculated transition temperatures, T_c, for twenty-two cubic metals are close to the experimentally determined melting temperatures. As the partial dislocation mediating the lower melting point, it may give the reason of why the bcc structure is more stable than the fcc one at high temperature.