Modern Physics Letters B

Temperature and pressure have direct and remarkable implications for drying and dewatering effect of low rank coals such as lignite. To understand the microenergy change mechanism of lignite, the molecular dynamics simulation method was performed to study the self-diffusion of lignite/water under different temperatures and pressure. The results showed that high temperature and high pressure can promote the diffusion of lignite/water system, which facilitates the drying and dewatering of lignite. The volume and density of lignite/water system will increase and decrease with temperature increasing, respectively. Though the pressure within simulation range can make lignite density increase, the increasing pressure showed a weak impact on variation of density.

In this paper, some optical properties of pure and transition metal-doped (TM = Co and V) single-walled ZnO nanotubes (8,0) (SWZnONT(8,0)) such as, real and imaginary parts of the dielectric function, optical conductivity, refractive index and optical reflectivity, were investigated. The calculations have been performed within framework of the density functional theory (DFT) using the full potential linearized augmented plane wave (FP-LAPW) and the generalized gradient approximation (GGA). The results show that, optical properties of SWZnONT(8,0) are anisotropic, especially at low energies and this anisotropy at low energies increases with doping of V in SWZnONT(8,0) while the Co-doped SWZnONT(8,0) behaves like pure SWZnONT(8,0). Doping of ZnO nanotubes has a significant impact on the value of the dielectric constant, so that due to the presence of V atom, the dielectric constant is increased up to three times. Study of the imaginary part of the dielectric function and optical conductivity showed that the important energy range for absorption processes and optical transitions is low energy range to 15 eV. The optical transitions have been studied based on band structure and density of states. The results of the optical reflectivity showed that these nanotubes are transparent in a wide energy ranges which provide them for using in transparent coatings. In addition, due to the reported magnetic properties for V- and Co-doped ZnO nanotubes, these nanotubes are suitable for using in spintronics and magneto-optic devices.

The soliton solution for the nonlinear waves has been investigated in a composite magnetic-semiconducting medium. By using a hydrodynamic model of an infinite medium magnetized along the direction of propagation, a set of coupled nonlinear Zakharov equations has been derived. In the absence of carriers or magnetization, two extreme cases for the two independent decoupled nonlinear modes have been discussed. The propagation regions have also been numerically analyzed for the soliton solutions.

It is not easy to achieve high performance for conventional beam splitters, such as high efficiency, good uniformity, polarization-independence, and wide bandwidth. A reflective embedded double-layer grating is described for beam splitting. With optimized grating profiles, the novel beam splitter can diffract both TE and TM polarizations into two orders with high performance. For the easy production, the fabrication tolerance is investigated and given. Most importantly, efficiencies more than 45% can be split into two orders within the wide bandwidth of 1412–1647 nm for TE polarization. The beam splitter based on multilayer coatings is sensitive to the incident angle and wavelength. And the bandwidth needs to be improved for the beam splitter based on simple grating. The design is of benefit for the performance improvement of the beam splitter by new grating configuration compared with the conventional simple grating.

In this paper, the optimization and amplification of magneto-optical (MO) response of Silicon (Si)/Cobalt (Co)-nanowires (NWs) in the presence of zinc sulphide (ZnS) and SiO₂ thin layers were investigated. The existence of ZnS layer with ideal thickness on the Si/Co structure, leads to an appropriate optical cavity which amplifies the MO Kerr signal (KS). In addition, the capping layer, SiO₂, which is useful in manufacturing process, acts as a complementary layer for ZnS layer. The proposed structure Si/Co/ZnS/SiO₂ with appropriate thicknesses enhances the KS of Si/Co-nanowire up to 20 times relative to same structure without covering layers.

This study explored the optical spectrum evolution process using a pump-modulated light and a continuous-wave probe, launched simultaneously into a 1 km highly nonlinear fiber. A total of 70 optical spectra were obtained by each changing the wavelength spacing (0.4 nm) between the probe and pump lights. Simulation results indicated that wavelength spacing between the two beams caused a cyclical optical spectrum evolution process induced by cross-phase modulation. As input light wavelength spacing increased, the coupling between the two optical fields showed obvious attenuation in each neat, multi-peak cycle.

In this paper, a series of Yb (0.5mol.%):Ho (0.5mol.%):LiNbO₃ crystals doped with various concentration of Mg${}^{2+}$ (1, 3, 5 and 7mol.%) were grown by the Czochralski technique. The ability of optical damage resistance of Mg:Yb:Ho:LiNbO₃ crystals increases with increasing the Mg${}^{2+}$ doping concentration. The optical homogeneity of Mg:Yb:Ho:LiNbO₃ crystals doped with different concentration of Mg${}^{2+}$ was detected using the birefringence gradient method. The results demonstrated that the optical homogeneity is getting better with the increase of the Mg${}^{2+}$ doping concentration. The studies on the infrared transmission spectra indicated that Mg${}^{2+}$ ions first replaces anti-site Nb${}_{\mathrm{\text{Li}}}^{4+}$ in the form of Mg${}_{\mathrm{\text{Li}}}^{+}$ defect, once the concentration of Mg${}^{2+}$ reaches or exceeds the threshold concentration, it begins to substitute Li-site and Nb-site of normal lattice and form defect of Mg${}_{\mathrm{\text{Nb}}}^{3-}-$3Mg${}_{\mathrm{\text{Li}}}^{+}$. Therefore, the change of Mg${}^{2+}$ doping concentration is the fundamental reason leading to a violet shift of the OH${}^{-}$ absorption peak.

In order to research the dynamic recrystallization (DRX) and grain refinement mechanisms in the process of extrusion through the rotating container, hot compression experiment of AZ31 magnesium alloy was carried out. Through the combination of experimental data and Yada empirical model, the DRX model of AZ31 magnesium alloy was established. Based on this DRX model, the numerical simulation of AZ31 magnesium alloy extrusion through the rotating container process was performed. The research results indicated, with the same process parameters of conventional extrusion, the shear stress increased significantly at the same position during the process of extrusion through the rotating container. This stress change promoted the occurrence of DRX and the increased recrystallization volume fraction. The average grain size obviously decreased. The equiaxed grains increased and the distribution uniformity was improved. These characteristics provided a theoretical basis for a better understanding of the enhanced comprehensive mechanical properties during the extrusion through the rotating container.

For accurate simulations of wall-bounded turbulent cavitating flows, the present paper proposed a partially averaged Navier–Stokes (PANS) method derived from the $k$-$\omega$ turbulence model. Transient cavitating vortical flows around a NACA66 hydrofoil were simulated by using the $k$-$\omega$ PANS model with various filter parameters ($f_k=0.2,0.5$ and $1$, while $f_{\omega }=1/f_k$) and a mass transfer cavitation model based on the Rayleigh–Plesset equation. Compared with the available experimental data, the $k$-$\omega$ PANS model with $f_k=0.2$ can accurately reproduce the cavitation evolution with more complicated structures due to the reduction in the predicted eddy viscosity. Further analyses, using the vorticity transport equation, indicate that the transition of cavitation structure from two dimension to three dimension is associated with strong vortex–cavitation interaction, where vortex stretching and dilation may play a major role. Therefore, the $k$-$\omega$ PANS model with the filter parameter of $f_k=0.2$ is an effective method to numerically predict the transient cavitating vortical flows around hydrofoils. The results obtained in this paper are helpful to provide a physical insight into the mechanisms of cavitation shedding dynamics.

The lag-generalized synchronization of coupled time-delay chaotic systems with unknown parameters and stochastic perturbation is investigated. Based on the LaSalle-type invariance principle of stochastic differential equation, the synchronization is realized by analyzing stochastic stability of the error system. In order to achieve the synchronization, the unknown parameter update laws and the control laws are proposed. At last, two numerical examples are presented to show the effectiveness of the obtained theoretical results.

Under investigation in this paper is a variable-coefficient AB (vcAB) system, which describes marginally unstable baroclinic wave packets in geophysical fluids and ultra-short pulses in nonlinear optics. The modulation instability analysis of solutions with variable coefficients in the presence of a small perturbation is studied. The modified Darboux transformation (mDT) of the vcAB system is constructed via a gauge transformation. The first-order non-autonomous rogue wave solutions of the vcAB system are presented based on the mDT. It is found that the wave amplitude of $B$ exhibits two types of structures, i.e. the double-peak structure appears if the plane-wave solution parameter $\omega$ is equal to zero, while selecting $\omega \ne 0$ yields a single-peak one. Effects of the variable coefficients on the rogue waves are graphically discussed in detail. The periodic rogue wave and composite rogue wave are obtained with different inhomogeneous parameters. Additionally, the nonlinear tunneling of the rogue waves through a conventional hyperbolic nonlinear well and barrier are investigated.

The structural, electronic as well as the magnetic properties of the Co₂CrX (X$=$Al, Ga and In) full-Heusler alloy have been studied using first-principles calculations performed in the framework of density functional theory (DFT) within the generalized gradient approximation (GGA). It was taken into account both possible L2₁ structures (i.e. Hg₂CuTi- and Cu₂MnAl-type). Basically, for all compounds, the Cu₂MnAl-type structure is energetically more stable than Hg₂CuTi-type structure at the equilibrium volume. The electronic structure calculations for Co₂CrAl reveal that half-metallic (HM) character in Cu₂MnAl-type structure, Co₂CrGa show nearly HM behavior and Co₂CrIn has a metallic character. The predicted total magnetic moment is $3{\mu }_{\mathrm{\text{B}}}$ for Co₂CrX (X$=$Al, Ga) which is in good convergence with the Slater–Pauling (SP) rule.