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As two necessary steps in phase-field simulation, parameters calculation and results storage play an important role to ensure the accuracy of simulation results. A strategy of parameters calculation and results storage was presented for phase-field simulation in α-Mg dendrite growth of Mg-5wt%Zn alloy under isothermal solidification. Based on the phase diagram and empirical formulas, key parameters of the phase-field model (equilibrium partition coefficient k, liquidus slope m, solutal diffusion coefficient in liquid Dl , solutal diffusion coefficient in solid Ds , etc.) can be obtained. Both structured grid and structured point storage methods can be used to store simulation results, but using the latter method will reduce about 60% storage space and 37.5% storage time compared to the former. Finally, convergent simulation results of α-Mg dendrite growth were obtained and in good agreement with the optical micrograph of experimental results, which verify the accuracy of parameters and stability of storage methods.

Single-crystal GaN layers have been obtained by nitriding β-Ga2O3 films in NH3 atmosphere. The effect of the temperature and time on the nitridation and conversion of Ga2O3 films have been investigated. The nitridation process results in lots of holes in the surface of films. The higher nitridation temperature and longer time can promote the nitridation and improve the crystal quality of GaN films. The converted GaN porous films show the single-crystal structures and low-stress, which can be used as templates for the epitaxial growth of high-quality GaN.

In this article, the spin-dependent electronic and transport properties of the armchair boron–phosphorous nanoribbons (ABPNRs) are mainly studied by using the non-equilibrium Green function method combined with the spin-polarized density function theory. Our calculated electronic structures indicate that the edge hydrogenated ABPNRs exhibit a ferromagnetic bipolar magnetic semiconductor property, and that the Si atom doping can make ABPNRs convert into up-spin dominated half metal. The spin-resolved transport property results show that the doped devices can realize 100% spin-filtering function, and that the interesting negative differential resistance phenomenon can be observed. Our calculations suggest that the ABPNRs can be constructed as a spin heterojunction by introducing Si doping partially, and it would be used as a spin-diode for nano-spintronics in future.

Starting from the Hamiltonian of the second quantization form, the weakly interacting Bose–Einstein condensate with spin–orbit coupling of Weyl type is investigated. It is found that the SU(2) nonsymmetric term, i.e., the spin-dependent interaction, can lift the degeneracy of the ground states with respect to the z component of the total angular momentum J z , casting the ground condensate state into a configuration of zero J z . This ground state density profile can also be affirmed by minimizing the full Gross–Pitaevskii energy functional. The spin texture of the zero J z state indicates that it is a knot structure, whose fundamental group is π 3(M) π 3(S 2) = Z.

In this paper, we design a varactor-tunable metamaterial absorber (MA). The tunable MA is based on a mushroom-type high impedance surface (HIS), in which varactors are loaded between adjacent metal patches to adjust the capacitance and tune the resonance frequency, the primary ground plane is etched as the bias network to bias all of the varactors in parallel, and another ultra-thin grounded film is attached to the bottom. Its absorption characteristics are realized for electrically dielectric loss. The simulated values of a sample indicate that a tunable frequency range from 2.85 GHz to 2.22 GHz is achieved by adjusting the varactor capacitance from 0.1 pF to 2.0 pF, and better than 0.97 absorbance is realized; in addition, the tunable frequency range is expanded from 4.12 GHz to 1.70 GHz after optimization.

An effective approach to designing a tunable electromagnetic absorber is presented and experimentally verified; it is based on an idea that an existing frequency selective surface (FSS) absorber is regarded as a loaded receiving antenna array. The existing absorber is effectively simplified by withdrawing half of the loaded resistors; a more compact one is obtained when lumped capacitors are introduced. Building on this, a varactor-tunable absorber with a proper bias network is proposed. Numerical simulations of one tunable absorber with 1.6 mm in thickness show that a wide tuning range from 3.05 GHz to 1.96 GHz is achieved by changing the capacitance of the loaded varactor from 0.5 pF to 5.0 pF. An experiment is carried out using a rectangular waveguide measurement setup and excellent agreement between the simulated and measured results is demonstrated.

The cavity-mode resonance effect could result in significant degradation of the shielding effectiveness (SE) of a shielding enclosure around its resonance frequencies. In this paper, the influence of coated wall loss on the suppression of the resonance effect is investigated. For this purpose, an equivalent circuit model is employed to analyze the SE of an apertured rectangular cavity coated with an inside layer of resistive material. The model is developed by extending Robinson's equivalent circuit model through incorporating the effect of the wall loss into both the propagation constant and the characteristic impedance of the waveguide. Calculation results show that the wall loss could lead to great improvement on the SE for frequencies near the resonance but almost no effect on the SE for frequencies far away from the resonance.

We study the thermal conduction behaviors of one-dimensional lattice models with asymmetry harmonic interparticle interactions in this paper. Normal thermal conductivity independent of the system size is observed when the lattice chains are long enough. Because only the harmonic interactions are involved, the result confirms without ambiguous interpretation that the asymmetry plays key role in resulting in the normal thermal conduction in one-dimensional momentum conserving lattices. Both equilibrium and nonequilibrium simulations are performed to support the conclusion., 4 pages,3 figures

First-principles calculations based on spin density functional theory are performed to study the spin-resolved electronic properties of ZnO codoped with Cu and N. (Cu, N)-codoped ZnO exhibits magnetism, and the total magnetic moment mainly originates from the p—d hybridization of Cu—N and Cu—O as well as p—p coupling interaction between N and O at the Fermi level. The Zn34Cu2O35N1 favors energetically a ferromagnetic ground state due to the existence of stable Cu—N—Cu complex. These results imply that the (Cu, N)-codoped ZnO is a promising dilute magnetic semiconductor free of magnetic precipitates, which could broaden the horizon of currently known magnetic systems.

We report on a theoretical and experimental study of an all-normal-dispersion (ANDi) Yb-doped mode-locked fiber laser, in which nonlinear polarization rotation (NPR) is used to realize mode-locking without any dispersion compensation. Based on the coupled nonlinear Schr?dinger (CNLS) equation, a model simulating the mode-locked process of an all-normal-dispersion ring fiber laser is developed, which shows that the achievement of stable mode-locking depends on the alignment of the polarization controller (PC) along the fast-polarization axis of the fiber, the birefringence intensity, and the net cavity dispersion. According to the theoretical analysis, stable mode-locked pulses with pulse duration 300 ps and average output power 33.9 mW at repetition rate 36 MHz are obtained.

Spectra of autoionizing states of the Sm atom in an energy region between 45948.9 cm−1 and 46943.6 cm−1 are systematically investigated by a three-color multi-step resonant excitation scheme with three different excitation paths. The three intermediate states, 4f 66s7s 7F3, 4f 66s7s 7F4, and 4f 66s7s 9F5 are employed for the three paths, respectively. Based on precise calibration of wavelength, the level energies of 112 autoionizing states are determined with the line widths and the relative line intensities of the related transitions. The possible influence of configuration interaction on the line shape of autoionizing state is also discussed. In addition, a unique value of J, the total angular momentum, is assigned to all detected states by comparing the three spectra obtained with the different excitation paths.