International Journal of Modern Physics B

In recent years, electrical spin injection and detection has grown into a lively area of research in the field of spintronics. Spin injection into a paramagnetic material is usually achieved by means of a ferromagnetic source, whereas the induced spin accumulation or associated spin currents are detected by means of a second ferromagnet or the reciprocal spin Hall effect, respectively. This article reviews the current status of this subject, describing both recent progress and well-established results. The emphasis is on experimental techniques and accomplishments that brought about important advances in spin phenomena and possible technological applications. These advances include, amongst others, the characterization of spin diffusion and precession in a variety of materials, such as metals, semiconductors and graphene, the determination of the spin polarization of tunneling electrons as a function of the bias voltage, and the implementation of magnetization reversal in nanoscale ferromagnetic particles with pure spin currents.

The topological properties of quantum electron plasmas in three-dimensional space are presented. Starting from ϕ-mapping topological current theory, the vortex lines are just at the core of wave function obtained. It is shown that the vorticity of the vortex can be expressed by the Hopf index and the Brouwer degree. We find that the vortex lines are unstable in some conditions and the evolution of vortex lines at the bifurcation points is given.

Time-dependent joint entropy is obtained for harmonic oscillator with the time-dependent mass and frequency case. It is calculated by using time-dependent wave function obtained via Feynman path integral method. Variation of time dependence is investigated for various cases.

A set of reduced MHD equations is derived using the equation of state including plasma compressibility. By applying assumption of pressure, i.e., R²P = const., a set of reduced magnetohydrodynamic equations for toroidal plasmas are obtained for large aspect ratio, high β tokamaks. These equations include all terms of the same order as the toroidal effect and only involve three variables, namely the flux, stream function and pressure.

In this study, an accurate analytical solution for the nonlinear free vibration of a conservative oscillator with inertia and static type cubic nonlinearities is derived. This solution has been obtained using Iteration Perturbation method (IPM). This study shows that IPM leads to an accurate analytical solution, which is valid for a wide range of considered system parameters. The excellent accuracy of current results is demonstrated by comparing with available analytical and numerical results.

The influence of extinction ratio (ER) on the performance of 120 Gbps return-to-zero octal differential phase-amplitude-shift keying (RZ-ODPASK) modulation format in single-channel transmission is investigated. Based on the modulation and demodulation schemes, the structures of RZ-ODPASK transmitter and receiver are presented; and expressions for the output optical fields and electrical currents of amplitude and phase tributaries are analytically acquired. As ER is a tradeoff for good performance of the two tributaries, the optimal ER for back-to-back configuration is theoretically derived as 2.32 dB for the first time, which is verified by simulation. Then the tolerances to residual chromatic dispersion (CD) and fiber nonlinearity of RZ-ODPASK transmission are numerically studied, respectively. The results indicate that phase tributary is more robust against both dispersion and nonlinearity impairment than the amplitude tributary. To balance the performance of the two tributaries, curves of the optimal ER values with the change of residual CD and fiber nonlinearity are also obtained, respectively. The results can be useful for the design of RZ-ODPASK systems; in the meantime, the analytical methodology described in this paper is applicable to other multilevel RZ-DPASK modulation formats.

In this paper, the effect of noise in an underdamped Josephson junction equation without a periodic driving is numerically investigated. Two distinct phenomena of coherence resonance are observed by adjusting the damping coefficient and the sloping degree of the tilted periodic potential.

The present paper proposes a computing model for temperature dependence of volume thermal expansivity, volume expansion ratio and second order temperature derivative of volume based on the assumption that the product αK_T remains constant at high temperatures and zero pressure. We have taken NaCl and KCl to testify the validity of the present model. A fairly close agreement between the calculated results and experimental data strongly supports the present model.

In this paper, the nonlinear Klein–Gordon equation describing the propagation of pulse waves in plasma or waveguide is investigated. With symbolic computation, the generalized Bäcklund Transformations (BTs) for this equation are constructed under different conditions. It is shown that the BTs published in the previous literature for the Sine–Gordon equation, Sinh–Gordon equation, and Liouville equation all turn out to be special cases of the results in the present paper. Moreover, the corresponding Lax pairs are explicitly derived from the obtained BTs through some transformations.

In this paper, dielectric properties of Ni_xMn_0.4-xZn_0.6Fe₂O₄ ferrites with x varying from 0.05 to 0.35 prepared by the citrate precursor method have been investigated as a function of frequency, temperature, composition, and sintering temperature. A decrease in the dielectric constant is observed with the increase in Ni concentration except for x = 0.3. This decrease in dielectric constant with the increase in Ni concentration is justified by inverse proportionality between resistivity and dielectric constant. Dispersion in the dielectric constant with frequency in the range of 75 Hz to 30 MHz is observed. Resonance peaks were observed in tan δ_ε versus frequency curve for all the samples. A shift in the resonance frequency toward higher frequency is observed with the increase in temperature. The peak height also increases with an increase in temperature. Phase change is confirmed by differential scanning calorimetry. Structural studies have been done by X-ray diffraction technique and scanning electron microscopy. Possible theories, models, and mechanisms contributing to these processes have been discussed.

The inelastic collisions of positrons with calcium and strontium positive ions are treated for the first time as a three-channel problem within the framework of the improved coupled-static and frozen-core approximations with the assumption that the elastic, ground positronium and excited-positronium formation channels are open. The calculations of the partial and total cross sections are carried out for eight values of the total angular momentum ℓ (0 ≤ ℓ ≤7), at 20 values of the incident energy lying above the excited positronium formation threshold and extending to a wide region above the ionization threshold of the target ion. The total collisional positronium formation cross sections of e⁺–Sr⁺ scattering show a peak around the ionization threshold of Sr⁺ but display a peak at 30 eV for e⁺–Ca⁺ scattering. In both scattering problems the total excited Ps formation cross sections have considerable values in the energy range .