Modern Physics Letters B

A brief review of recent investigations in oxide heterostructures is presented. First, experimental results are shown. Positive colossal magnetoresistance with high sensitivities are obtained at low magnetic field (<1000 Oe) nearly at room temperature. Picoseconds photoelectric effects of the rise time ~ 210 ps and the half-maximum ~ 650 ps are also found in some oxide heterostructures. Furthermore, resistance switching characteristic and electric displacement-voltage hysteresis loops have been observed in BaTiO_3-δ/Sip–n heterostructures. Second, theoretical descriptions are also shown here. A model for the mechanism causing the positive colossal magnetoresistance has been established. Moreover, the transport properties and the important role played by oxygen vacancies are theoretically investigated in oxide heterostructures. In addition, an extended percolation model is well developed, with which the transport characteristic in oxide thin films can be well simulated based on the phase separation scenario. Notably, the interface effects play a crucial role in the multifunctional properties of the oxide heterostructures.

New stochastic models of thermodiffusion are constructed and their hydrodynamical limits are studied through a first-order Chapman–Enskog expansion. These models differ from earlier ones by taking into account all first-order contributions proportional to the temperature gradient and, thus, allow for both positive and negative Soret coefficients, in accordance with observations.

In this paper, the problem of adaptive ℋ_∞ synchronization for unified chaotic systems with unknown parameter and external disturbance is studied. It is noticed that this unified chaotic system contains the noted Lorentz, Lü and Chen systems. Based on Lyapunov theory and linear matrix inequality (LMI) formulation, the novel feedback controller with adaptive law is established to not only guarantee stable synchronization of both master and slave systems but also reduce the effect of external disturbance to an ℋ_∞ norm constraint. A criterion for existence of the controller is given in terms of LMIs. Finally, a numerical example shows the effectiveness of the proposed method.

In this letter, a general model of an array of N linearly coupled chaotic neural networks with hybrid coupling is proposed, which is composed of constant coupling, time-varying delay coupling and distributed delay coupling. The complex network jumps from one mode to another according to a Markovian chain with known transition probability. Both the coupling time-varying delays and the coupling distributed delays terms are mode-dependent. By the adaptive feedback technique, several sufficient criteria have been proposed to ensure the synchronization in an array of jump chaotic neural networks with mode-dependent hybrid coupling and mixed delays in mean square. Finally, numerical simulations illustrated by mode switching between two complex networks of different structure dependent on mode switching verify the effectiveness of the proposed results.

In this letter, the resonance escape factors and spatial distribution of three resonance absorption lines that making up the Li 670.970 nm line are discussed theoretically, for both Lorentzian and Voigt profiles. The oscillator strength, the number density of the absorbing atoms in the ground state, and the optical depth in the line center are discussed also in the calculation. The results we calculated are in good agreement with the experimental results. This calculation will be significant in the research of plasma Li atom.

The drop of ferromagnetic moment in the ternary solid solutions Ni_1-x-yCu_xD_y, (D = Zn, Si, Au, Al) is analyzed in terms of the statistical model of the environment-dependent moments. This probabilistic model shows that the disappearing of one Ni atom ferromagnetic moment can be assigned to the replacement of at least four Ni–Ni bindings, out of twelve, in pure nickel. This paper aims at discussing all these features that, from the point of view of macroscopic equilibrium states, are related to the distribution of local bonds, provided by the peripheral electrons of the substitute atoms dissolved in the Ni matrix.

The thermodynamics of solid–solid and solid–liquid transitions are investigated with an account of the number of molecular orientation. The variations of the positional and orientational orders with the reduced temperature are studied. It is found out that orientational order parameter is very sensitive to the number of allowed orientation. The reduced transition temperatures, volume changes and entropy changes of the phase transitions and theoretical phase diagrams are obtained. The entropy changes of melting transitions for different numbers of allowed orientation of the present model are compared with the theoretical results and some experimental data. The quantitative predictions of the model are compared with experimental results for plastic crystals and agreement between predictions of the model and the experimental results are approximately good. Also, different numbers of allowed orientation D correspond to different experimental results HI, HBr, H₂S for D = 2; HBr, CCl₄, HI for D = 4; C₂H₁₂ for D = 6; CH₄, PH₃ for D = 20.

Single crystals of 2-Naphthalenol (2N), new organic nonlinear optical (NLO) material, have been grown by slow evaporation solution growth technique at room temperature. The crystal system has been confirmed from the single crystal X-ray diffraction analysis. The functional groups were identified using FTIR spectroscopy. UV-vis-NIR spectrum showed absence of absorption in the wavelength region 400–1400 nm. The second harmonic generation efficiency is two times higher than that of standard potassium dihydrogen phosphate (KDP).

Within the effective mass approximation, the binding energies of a Wannier exciton in a GaAs-Ga_1-xAl_xAs quantum well in an electric field are investigated using a variational method. The binding energiesare obtained upon illlumination by laser radiation. The binding energy decreases as the well size increases when the size of the well is beyond 50 Å. The above behavior is for a quantum well of finite confinement. We have investigated the metal-insulator transition in such a system and report the values of critical concentrations of excitons at which metal-insulator transition occurs for different well dimensions. The calculated diamagnetic susceptibility shows the catastrophic behavior at the critical concentration.

We have studied paramagnetic Mn²⁺ ions present in the freshwater snail, Sinotaia ingallsiana (FS), Viviparus which are abundant in Thailand. The FS shells in our study were ground into fine powder. A set of seven samples was each then separately annealed for 2 hours in air atmosphere at 300°C, 400°C, 500°C, 600°C, 700°C, 800°C and 900°C, respectively. Our detailed ESR spectral analyses of FS show that Mn²⁺ ions enter Ca²⁺ sites during a biomineralization process. The hyperfine coupling constant (A) and zero-field splitting (D) in the ESR spectrum of Mn²⁺ in calcite and aragonite were determined. The spreading of the non-central allowed transitions was analyzed and the experimental transitions were attributed. For calculating the hyperfine coupling constant, five methods for calculating the zero-field splitting, based on the analysis of the allowed and forbidden transitions, were provided. The values of the hyperfine coupling constant range from 87.50 to 89.00 G and those of the zero-field splitting range from 110.00 to 116.00 G.