International Journal of Modern Physics B

Coherent light propagating in a bulk Kerr nonlinear defocusing medium obeys nonlinear Schrödinger (NLS) equation, which is similar to the Gross–Pitaevskii equation for Bose–Einstein condensates (BECs). An equivalent hydrodynamic approach allows one to consider propagation of light as a flow of an equivalent “luminous fluid.” An analog optical event horizon can be formed when the flow velocity of this fluid equals the local sound velocity, determined by the nonlinear term in the NLS equation. The analog event horizon is characterized by a finite width, also determined by the nonlinearity length, or by the healing length in Bose–Einstein condensates. The various eigenmodes of fluctuations are found in the immediate vicinity of the event horizon and the scattering matrix due to the finite width horizon is calculated to be within the leading order corrections in the nonlinearity length. The Hawking radiation is found to be enhanced with respect to that of a Planck’s black body spectrum and is characterized by the emissivity greater than one. A procedure of paraxial quantization of the fluctuation field is discussed and its connection to the conventional quantization of the electromagnetic field is demonstrated. Quantum fluctuations of the electric field energy and those of its flow are calculated.

The effect of pressure on the structural, elastic and electronic properties of the intermetallic compound MgCu with a CsCl-type structure have been investigated using ab initio technique. The optical properties have been studied under normal pressure. We have carried out the plane-wave pseudopotential approach within the framework of the first-principles density functional theory (DFT) implemented within the CASTEP code. The calculated structural parameters show a good agreement with the experimental and other theoretical results. The most important elastic properties including the bulk modulus $B$, shear modulus $G$, Young’s modulus $E$ and Poisson’s ratio $\nu$ of the cubic-type structure MgCu are determined under pressure by using the Voigt–Reuss–Hill (VRH) averaging scheme. The results show that the MgCu intermetallic becomes unstable under pressure more than 15 GPa. The study of Cauchy pressure and Pugh’s ratio exhibit brittle nature of MgCu at ambient condition and the compound is transformed into ductile nature with the increase of pressure. For the first time we have investigated the electronic and optical properties of MgCu. The electronic band structure reveals metallic conductivity and the major contribution comes from Cu-$3d$ states. Reflectivity spectrum shows that the reflectivity is high in the ultraviolet region up to 72 eV.

Inhomogeneous re-oxidation, which causes graded NiO content along anode thickness, has been confirmed to be a key reason for Ni-based cell cracking during redox progress. In this paper, an analytical model is developed to estimate the impact of inhomogeneous re-oxidation on Ni-based solid oxide fuel cell (SOFC) oxidation resistance. And experiments, in which the SOFC was partially re-oxidized, were implemented for model trial. Model results show that electrolyte internal stress can be significantly reduced (from 367 MPa to 135 MPa, when the oxidation degree is 60%), and the electrolyte can remain intact even when the oxidation degree reaches about 70%, if the anode was re-oxidized uniformly. This impact of inhomogeneous re-oxidation on stress in the electrolyte decreases as the anode thickness increases. Scanning electron microscopic (SEM) images of partially oxidized anode cross-sections confirmed that Ni oxidation was inhomogeneous, in which the outer regions of the anode became almost fully oxidized, while the inner regions remained metallic. And the inhomogeneity increases with the redox times. Consequently, it is important to avoid gradients in NiO content during oxidation progress to prevent cell cracking.

Recently, Haj-Kacem et al. proposed an equation modeling the relationship between the two parameters of viscosity Arrhenius-type equations [Fluid Phase Equilibria 383, 11 (2014)]. The authors found that the two parameters are dependent upon each other in an exponential function form. In this paper, we reconsidered their ideas and calculated the two parameter values for 49 saturated pure fluids by using the experimental data in the NIST WebBook. Our conclusion is different with the ones of Haj-Kacem et al. We found that (the linearity shown by) the Arrhenius equation stands strongly only in low temperature range and that the two parameters of the Arrhenius equation are independent upon each other in the whole temperature range from the triple point to the critical point.

In this paper, the low-frequency and tuning characteristic of band gap in a two-dimensional phononic crystal structure, consisting of a square array of aluminum cylindrical stubs deposited on both sides of a thin rubber plate with slit structure, are investigated. Using the finite element method, the dispersion relationships and power transmission spectra of this structure are calculated. In contrast to a typical phononic crystal without slit structure, the proposed slit structure shows band gaps at lower frequencies. The vibration modes of the band gap edges are analyzed to clarify the mechanism of the lowest band gaps. Additionally, the influence of the slit parameters and stub parameters on the band gaps in slit structure are investigated. The geometrical parameters of the slits and stubs were found to influence the band gaps; this is critical to understand for practical applications. These results will help in fabricating phononic crystal structures whose band frequency can be modulated at lower frequencies.

The spin Hamiltonian parameters (SHPs) ($g$ factors, hyperfine structure constants and zero-field splittings (ZFSs)) and local structures for various $3d^3$ hexacyanometallates of paramagnetic salts K₃Cr(CN)₆ and K₄V(CN)${}_6\cdot$3H₂O with the diluents K₃Co(CN)₆, K₃Mn(CN)₆ and K₄Fe(CN)${}_6\cdot$3H₂O are theoretically investigated from the perturbation calculations of these parameters for a rhombically distorted octahedral $3d^3$ cluster. The paramagnetic systems are found to undergo the local axial distortions $\mathrm{\Delta }Z$ $(\approx -$0.19, −0.18 and 0.09 Å$)$ and the planar bond angle variations $\mathrm{\Delta }\phi$ $(\approx$ 3.5${}^{\circ }$, 5.3${}^{\circ }$ and 1.4${}^{\circ })$ for K₃Cr(CN)₆ with K₃Co(CN)₆, K₃Cr(CN)₆ with K₃Mn(CN)₆ and K₄V(CN)${}_6\cdot$3H₂O with K₄Fe(CN)${}_6\cdot$ 3H₂O, respectively. The signs for ZFSs $D$ and $E$ are analyzed in the light of those for $\mathrm{\Delta }Z$ and the rhombic distortion angle $\delta \phi$ $(={\phi }^{\prime }-\pi /4)$ related to an ideal octahedron. Microscopically, the magnitudes of $\mathrm{\Delta }Z$ and $\mathrm{\Delta }\phi$ can be conveniently illustrated by the axial (ADD) and perpendicular distortion degrees (PDD), respectively, for the paramagnetic systems with the corresponding diluents. The local structural properties are analyzed from the relative ionic radius deviation $\mathrm{\Delta }r$ of the equivalent diluent cation from the host paramagnetic cation, the axial and perpendicular ZFS variations $\mathrm{\Delta }F$ and $\mathrm{\Delta }G$ for ZFSs with the diluent related to the host, the relative deviation $\mathrm{\Delta }$Dq of the cubic crystal-field parameter for the diluent related to the host. The above studies would be helpful to the investigations on synthesis, structures and properties of $3d^3$ hexacyanometallates in paramagnetic salts.

Self-diffusion coefficients along with the mutual diffusion coefficients of nitric oxide (NO) and SPC/E water (H₂O) as solute and solvent of the mixture, have been studied within the framework of classical molecular dynamics level of calculations using GROMACS package. The radial distribution function (RDF) of the constituent compounds are calculated to study solute–solute, solute–solvent and solvent–solvent molecular interactions as a function of temperature. A dilute solution of five NO molecules (mole fraction 0.018) and 280 H₂O molecules (mole fraction 0.982) has been taken as the sample. The self-diffusion coefficient of the solvent is calculated by using mean square displacement (MSD) where as that for solute (NO) is calculated by using MSD and velocity auto-correlation function (VACF). The results are then compared with the available experimental values. The results from the present work for water come in good agreement, very precise at low temperatures, with the experimental values. The diffusion coefficients of NO, on the other hands, agree well with the available theoretical studies, and also with experiment at low temperatures (up to 310 K). The results at the higher temperatures (up to 333 K), however, deviate significantly with the experimental observations. Also, the mutual diffusion coefficients of NO in water have been calculated by using Darken’s relation. The temperature dependence of the calculated diffusion coefficients follow the Arrhenius behavior.

Using density functional theory, we have investigated the adsorption and diffusion of lithium on the two-dimensional MnO₂/graphene hybrid nanostructures. The simulation results show that the adsorption energy is increased compared with pure graphene and monolayer MnO₂. At the same time, the diffusion barrier is greatly reduced as lithium diffuses on the graphene side. The results indicate that the MnO₂/graphene hybrid nanostructure can be used as a good anode material for lithium ion batteries.

In this paper, we report on microstructural, optical and electrical properties of alternating multilayer of vanadium pentoxide (V₂O₅), 25 nm, and vanadium (V), 5 nm, thin films deposited at room temperature by radio frequency (RF) and DC magnetron sputtering, respectively. Raman and photoluminescence (PL) spectroscopy have been employed to investigate the effects of thermal annealing for 20, 30 and 40 min at 400${}^{\circ }$C in Nitrogen (N₂) atmosphere on the multiple phase formation and its impact on the film resistance and temperature coefficient of resistance (TCR). We demonstrate that the oxygen free annealing environment allows the formation of multiple phases including V₂O₅, V₆O${}_{13}$ and VO₂ through oxygen diffusion and consequent deficiency in V₂O₅ layer.

A modified barium vacancy formation mechanism in donor-doped barium titanate (BaTiO₃) ceramics is proposed. Assuming a uniform distribution of barium vacancies at sintering temperature and only oxygen partial pressure and sintering temperature related concentration of unionized barium vacancies, the electrical characteristics have been calculated by solving a differential equation about electron level. The room-temperature resistivity and positive temperature coefficient of resistivity (PTCR) behaviors of donor-doped BaTiO₃ semiconducting ceramics have been quantitatively computed. The results pointed out that the room-temperature resistivity changes as a U-type curve with an increase of donor concentration. Moreover, the PTCR effect of BaTiO₃ semiconductive ceramics was calculated quantitatively under different conditions. Theoretical and experimental results for BaTiO₃ semiconductive ceramics are compared and discussed.

Recently, Majorana fermions (MFs) have attracted intensive attention due to their exotic statistics and possible applications in topological quantum computation. They are proposed to exist in various two-dimensional (2D) topological systems, such as $p_x+i{p}_y$ topological superconductor (SC) and nanowire–superconducting hybridization system. In this paper, we point out that Majorana fermions in different topological systems obey different types of polygon sign rules. A numerical approach is described to identify the type of polygon sign rule of the Majorana fermions. Applying the approach to study two 2D topological systems, we find that vortex-induced Majorana fermions obey topological polygon sign rule and line-defect-induced Majorana fermions obey normal polygon sign rule.