International Journal of Modern Physics B

In the present paper, we investigate the frustration effect caused by the long-range electron hopping on ferromagnetism in atomic or molecular clusters. First, for an idealized Hubbard model with constant electron hopping amplitude, we prove rigorously that interplay between such frustration effect and the on-site Coulomb interaction produces the saturated ferromagnetism when the cluster is slightly doped with electron. Then, by exact diagonalization calculation, we study some more realistic clusters and show that the ferromagnetic ground state is still stable as long as the Coulomb repulsion interaction between electrons is sufficiently strong.

In this paper, the robust synchronization problem is investigated for a new class of continuous-time complex networks that involve parameter uncertainties, time-varying delays, constant and delayed couplings, as well as multiple stochastic disturbances. The norm-bounded uncertainties exist in all the network parameters after decoupling, and the stochastic disturbances are assumed to be Brownian motions that act on the constant coupling term, the delayed coupling term as well as the overall network dynamics. Such multiple stochastic disturbances could reflect more realistic dynamical behaviors of the coupled complex network presented within a noisy environment. By using a combination of the Lyapunov functional method, the robust analysis tool, the stochastic analysis techniques and the properties of Kronecker product, we derive several delay-dependent sufficient conditions that ensure the coupled complex network to be globally robustly synchronized in the mean square for all admissible parameter uncertainties. The criteria obtained in this paper are in the form of linear matrix inequalities whose solution can be easily calculated by using the standard numerical software. The main results are shown to be general enough to cover many existing ones reported in the literature. Simulation examples are presented to demonstrate the feasibility and applicability of the proposed results.

By developing a multiple-scale method, we study analytically the dynamics of the soliton inside the semi-infinite band gap (SIBG) of quasi-one-dimensional Bose–Einstein condensates trapped in an optical lattice. In the linear case, a stable condition of soliton formation is obtained. For a weak nonlinearity, whether there occurs a spatially propagating or localized gap soliton is determined by the lattice depth. Meanwhile, we predict the existence of the dark (bright) gap solitons for the repulsive (attractive) interactions in the SIBG, different from that of the gap solitons in other energy gaps. And the collision of two dark (or bright) solitons is nearly elastic under a safe range of atomic numbers. An experimental protocol is further designed for observing these phenomena.

The influences of the temperature and the phonons effect on the properties of the exciton, which is strongly coupled with interface optical (IO) phonons and weakly coupled with bulk longitudinal-optical (LO) phonons, in a quantum well are studied by means of Huybrechts' linear-combination operator and the Lee–Low–Pines variational method. The expressions for the induced potential of the ground state, the energy shift of the ground state, and the first internal excited state of the exciton were derived. Numerical results are illustrated for AgBr/AgCl quantum well. The results indicate that the induced potential of the ground state, the energy shift of the ground state, and the energy shift of the first internal excited state of the exciton produced by the exciton strongly coupling with IO phonons increase with increasing temperature; however, the induced potential of the ground state, the energy shift of ground state, and the energy shift of the first internal excited state of the exciton produced by the exciton weakly coupling with bulk LO phonons decrease with increasing temperature. The influence of temperature is greater to the changes of the induced potential and the energy shift of the exciton with well widths and the distances between electron and hole.

Quasi-two-dimensional structures are characterized by multiple sub-bands and depending upon the well width and electron density, several sub-bands may be occupied. With an increase in well width more sub-bands are pushed below the Fermi level leading to a possible nonmonotonic variation in transport coefficients. This paper investigates Seebeck coefficient and Lorenz factor in Si_0.9Ge_0.1 quantum wells taking into account the multiple sub-band contributions.

Heat conduction in one-dimensional lattice with double-well interaction potential is studied numerically in different temperature regions. In the low temperature case, different structures such as order, period-2, and disorder structure phases, lead to different anomalous heat conduction. In a shallow intermediate temperature region, the heat conductivity is finite in a large system size. When temperature increases high enough, the heat conduction is anomalous, as well as FPU-β model.

An effective mean-field theory based on cumulant expansion was used to deal with antiferromagnetic Heisenberg model on planar triangular lattice. The corrections of expansion were performed to the third order. By using the equation of the mean field condition, curves of internal energy E specific heat C staggered helicity K (order parameter) and the variational ratio of staggered helicity X were obtained when the proper values of effective external field were achieved. The calculated results showed that there were two phases (which were ordered antiferromagnetic phase and the disordered phase) in the spin system. The first order critical point is -kT_c/J_s = 1.65, the second is -kT_c/J_s = 1.35 and the third is -kT_c/J_s = 1.29, obviously closer to that of Monte Carlo simulation order by order. And also, the analytic expansion curves derived from this method exhibited higher proximity order by order to the Monte Carlo simulation. Such results showed that this method was a useful tool to obtain thermodynamically observables of spin system.

Multicompartment micelles have advanced applications in biological and pharmaceutical fields. The self-assembly of the block copolymers with different chain architectures provides versatile and powerful routes to obtain multicompartment micelles in water. Here we apply the dissipative particle dynamics method to study the self-assembly of H-shaped triblock copolymers in a selective solvent. It is found that the H-shaped triblock copolymers can form micelles with different morphologies, such as worm-like micelles, hamburger micelles, core-shell-corona micelles, and cylinder micelles, etc. Among them, the cylinder micelles have not been reported before in the case of the copolymers with similar chain architecture (e.g., Y-shaped copolymer). We demonstrate a convenient approach to obtain different morphologies by only adjusting the arrangement of the copolymers' blocks. These results may be helpful for the design of multicompartment micelles for various application purposes.

The results of first principles calculations of the electronic band structures, density of states, band gap, equilibrium lattice constants, cohesive energies, bulk moduli and magnetic moments are presented for the EuN with rock salt as ambient structure and cesium chloride as high-pressure structure. The tight-binding linear muffin tin orbital method within the local-density approximation is used. Both spin-polarized and non-spin polarized calculations are performed. The magnetic and structural stabilities are determined from the total energy calculations for both nonmagnetic (NM) and ferro-magnetic (FM) states. From the present study EuN illustrates half-metallic. The FM phase is more stable than NM phase. We further predict EuN undergoes a transition from NaCl-type (B₁) to CsCl-type structure (B₂) at 14.6 GPa, which could not be compared owing to the need of experimental and theoretical results. Futhermore, the bulk moduli, first-order pressure derivatives and magnetic moments are also estimated in B₁ and B₂ phases. The magnetic moment is estimated to be nearly 6 μ_B, which is in good agreement with the others reported value. A small decrease in magnetic moment is observed under pressure.

The controlled attractor with initial rectifying action, referred to as initial rectified attractor (IRA) in this paper, is introduced for the purpose of generalized and Q-S chaos synchronization. The IRA is designed to make the states of drive and response systems synchronized in the form of generalized and Q-S within a finite time interval. The reaching time is shown to be independent of the initial conditions and dynamics of the chaotic systems, and can be determined in advance. With numerical experiments it is demonstrated that perfect synchronization can be achieved between the modified Lorenz and the hyperchaotic Rössler systems in different configurations.

In this work the purpose is, in addition to the determination of microhardness, to get some information about the effect of heat treatment on the microstructure of the magnetic Nd₁₅Fe₇₇B₈ alloy. For this study we have used an optical microscope and an electronic microprobe. The results show that the structure of the Nd₂Fe₁₄B phase, which confers good mechanical and magnetic properties on the alloy, is well tetragonal, as mentioned in several works. The morphology, the concentration and the quantity of this phase depend on the temperature of annealing. The microhardness of the phase has an average value between those of the other involved phases.

This paper presents an analysis of clamping losses in microelectromechanical systems (MEMS)-based, flexural mode silicon carbide (SiC) lateral resonators. The study includes folded- and straight-beam resonators made from (111) polycrystalline 3C-SiC side by side. The device testing was conducted at 30 μTorr using a transimpedance-amplifier-based circuit to measure the total quality factor. It was found that thermoelastic damping (TED) in SiC MEMS-based lateral resonators has minimal contributions to overall energy dissipation in the aforementioned devices. Moreover, the difference in material losses of these devices is negligible due to their similar microstructure. In this case, clamping losses are responsible when one is comparing the energy dissipation mechanism of these two types of resonators. The findings showed that the total losses for a folded-beam resonator were reduced by more than 10 times that for a straight-beam resonator when the beam lengths were set at 150 μm and operated at the same level of resonant frequency. The clamping coefficient of the folded-beam resonator was between 0.7 and 1.8, suggesting that the effective dimension of a folded-beam resonator should include part of the proof mass.