Modern Physics Letters B

Nano-scale MnSi_1.7 films are prepared by thermal annealing of three-layer Si/MnSi_x/Si or bi-layer Si/MnSi_x (x < 1.7) structures at 923 K for 20–65 minutes. These layers are deposited on thermally oxidized silicon substrates at about 393 K by electron beam evaporation. It is found that the oxygen content in the MnSi_1.7 film can be reduced from about 10 at.% to 6 at.% by using the bi-layer structure MnSi_x/Si with the MnSi_x layer on top. With the reduction of oxygen content in the MnSi_1.7 film, the transition temperature from p-type to n-type decreases from 508 K to 463 K or less.

In this paper, we propose and investigate a general model of fuzzy complex networks described by the Takagi–Sugeno (T–S) fuzzy model with hybrid coupling and stochastic perturbation. The hybrid coupling includes constant coupling and discrete and distributed delay coupling. By utilizing a new Lyapunov functional form, we employ the stochastic analysis techniques and Kronecker product to develop delay-dependent synchronization criteria that ensure mean-square synchronization of the addressed T–S fuzzy delayed complex networks with stochastic disturbances. These sufficient conditions are computationally efficient, as it can be solved numerically by the LMI toolbox in Matlab. A numerical example is provided to demonstrate the effectiveness and the applicability of the proposed method.

We study the vibrational frequency and the interaction energy of the weak-coupling impurity bound magnetopolaron in an anisotropic quantum dot. The effects of the transverse and longitudinal effective confinement lengths, the electron–phonon coupling strength, the cyclotron frequency of a magnetic field and the Coulomb bound potential are taken into consideration by using an improved linear combination operator method. It is found that the vibrational frequency and the interaction energy will increase rapidly with decreasing confinement lengths and increasing the cyclotron frequency. The vibrational frequency is an increasing function of the Coulomb bound potential, whereas the interaction energy is an decreasing one of the potential and the electron–phonon coupling strength.

The spin-Hamiltonian parameters (g factors g_i and hyperfine structure constants A_i, where i = x, y, z) and optical spectrum band positions of the Yb³⁺ ion in the rhombically-distorted Tm³⁺ site of Tm₃Al₅O₁₂ garnet crystal are calculated by a complete diagonalization (of the energy matrix) method, in which the Zeeman and hyperfine interaction terms are also included in the conventional Hamiltonian. From the calculations, the observed spin-Hamiltonian parameters of Tm₃Al₅O₁₂:Yb³⁺ are explained reasonably and the optical spectrum band positions are suggested. The rationality of these suggested optical spectrum band positions is discussed by comparing them with the observed values of Yb³⁺ ions in similar aluminum garnet (Yb₃Al₅O₁₂, Y₃Al₅O₁₂ and Lu₃Al₅O₁₂) crystals.

By a transformation operator, we find that the transformation operator is not related to the unknown N-particle state. Here, we propose a multi-scheme for the teleportation of an arbitrary and unknown N-particle state by using the method of transformation operator. The proper transformation operator depends on the quantum channel and the measurement basis. The theoretical explanations of some quantum channels are given by transformation operators. Furthermore, we give the analysis for teleporting an arbitrary and unknown N-particle state.

Formulas for the transfer function and the output power gain are presented for an Er³⁺/Yb³⁺ codoped series-cascaded double microring resonator (MRR). Around the pumping wavelength of 974 nm and the central signal wavelength of 1530 nm, the effects of the pump power, signal power, Er³⁺/Yb³⁺ dopant concentrations and amplitude coupling ratios on the signal output spectrum are analyzed. The computed results show that the device can possess both the filtering and amplifying functions for the signal light. In the case of the amplitude coupling ratio between the microring and the channel being 0.17, and that between two microrings being 0.012, the device can produce more than 10.13 dB signal power gain.

The laser intensity Langevin equations for a two-mode ring laser subject to both pump noise and quantum noise have been obtained by a phase-locking method. By means of stochastic simulation, the mode competition between two modes for different combinations of the strength of the pump noise, the coupling constant and the difference of pump parameters have been investigated. The results show the following. (i) The pump noise dramatically affects the mode competition. (ii) The mode competition is quite sensitive to changing of the coupling constant near the line center. (iii) The mode competition gets stronger and stronger with increasing absolute value of the difference of pump parameters.

In this paper, based on the local information about nodes, we propose a new attack strategy, considering the average degree of the node's neighboring nodes. Adopting the cascading model proposed in Chin. Phys. Lett.25(10) (2008) 3826, we investigate the effect of the new attack strategy for the robustness against cascading failures on a typical network, i.e. BA scale-free networks. Compared with two attacks on the nodes with the highest load or the lowest load, numerically we find that our presented attack is the most efficient way to destruct the BA scale-free networks in the case of α ≤ 0.6, where α is a tunable parameter and determines to the load strength of a node. In addition, we also find that the efficiency of the new attack strategy is more obvious near the parameter α = 0.5. We expect our findings to provide insights into the protection of the key nodes for real-life networks to avoid cascading-failure-induced disasters.

Dither is a high frequency signal which is introduced into a nonlinear system with the object of augmenting stability, quenching undesirable limit cycle, and altering the apparent nonlinear element characteristics. In this paper, we investigate the performance of various high frequency dither signals with different wave forms in nonlinear feedback systems. Meanwhile, an analog experimental device is set up to simulate the nonlinear systems, which consists of dither and a nonlinear element such as a relay or a limiter. A describing function and an equivalent nonlinearity method are used to evaluate the dither performance. The performance of various dither signals having a certain wave form is examined through these studies, and the results could evaluate effectiveness of these dither-injection techniques into nonlinear feedback systems.

Glasses of x(ZnO)(50 - x)PbO:50V₂O₅ system were prepared by melt-quench process in the range x = 0 mol% to 15 mol%. Measurements are reported for DC electrical conductivity as well as thermo electrical power for these samples in both glass and crystalline forms in the temperature range of 27°C and 227°C. The ESR studies of these samples at room temperature are reported. These spectra are characterized by well-resolved eight-line powder pattern. It is observed that the ESR spectra obtained in the crystalline form, the hyperfine structure is nearly smeared out and the spectra are characterized by a relatively broad line with an isotropic g value. The experimental results are analyzed with reference to Mott's model. The analysis shows that at high temperatures the temperature dependence of DC conductivity is consistent with Mott's model for both glass and crystalline samples. The high-temperature thermoelectric power was satisfactorily explained by Heikes' relation and the data also showed evidence of small polaron formation for glass form samples and large polaron formation in crystalline samples. These results indicate that all the glass samples lead metavanadate are n-type at room temperature and the crystalline samples are p-type at room temperature.

An ensemble Monte Carlo method is used to compare the potentialities of SiC and ZnO materials for field effect transistors. First, bulk material electron transport properties are compared and then the operation of MESFETs made from them are investigated. The simulated device geometries and doping are matched to the nominal parameters described for the experimental structures as closely as possible. Simulations of SiC MESFETs of lengths 2, 2.6 and 3.2 μm have been carried out and compared these results with those on ZnO MESFETs of the same dimensions. The direct current IV characteristics of the two materials were found to be similar, though the ZnO characteristics were on the whole superior, reaching their operating point at higher drain voltages and possessing higher gains. However, oscillations in the drain current caused by changes in drain voltage in the ZnO devices were not present to the same degree in the SiC devices. This difference is caused partially by the onset of the negative differential regime in SiC at a higher electric field than in ZnO but the primary cause is the longer ballistic transport times in SiC. This suggests that ZnO MESFETs may prove to have superior frequency response characteristics than SiC MESFETs.

In this paper, the homotopy perturbation method (HPM) and the Padé approximation are employed to investigate the magneto-hydrodynamic (MHD) boundary layer flow over a nonlinear stretching sheet, which occurs in many important engineering applications, such as the power generator, the cooling of reactors and the design of heat exchangers. The validity of results is verified by comparison with exact results and is shown in tables and graphs. It is found that the HPM is a user-friendly, powerful tool for solving complicated problems in physics and mathematics, and that in particular it has good accuracy as compared with exact results.

The present paper deals with the comprehensive studies of phonon dynamics in alkali metal (M) doped C₆₀ (MC₆₀) solids in fcc phase using a rigid ion model with pairwise interionic interaction potential. The investigations include the computation of the phonon density of states, the specific heat, the Gruneisen parameters, thermal expansion and thermal expansion coefficient and the phonon-dispersion curves of RbC₆₀. The analysis incorporates the van der Waal's and Coulomb interactions for alkali metal–C₆₀ as well C₆₀–C₆₀ molecule and show fairly good agreement with reported inelastic neutron scattering results for RbC₆₀. We have found that thermal expansion coefficient at room temperature is in the range 4.3–6.2 × 10^-5K^-1, which is of the order of pure C₆₀ solid (6.1 × 10^-5K^-1). Comparing the thermal expansion coefficient of different alkali-doped solids, we conclude that doping decreases anharmonicity in general, and further it decreases with increase in size of the alkali metal. The results have been found to present an overall consistent interpretation of the available experimental data.

In the present paper, we investigate coherent bremsstrahlung of high energy electrons moving in a periodically deformed single crystal with a complex base. The formula for corresponding differential cross-section is derived for an arbitrary deformation field. The conditions are discussed under which the influence of the deformation is important. The case is considered in detail when the electron enters into the crystal at small angles with respect to a crystallographic axis. It is shown that in dependence of the parameters, the presence of the deformation can either enhance or reduce the bremsstrahlung cross-section.