Modern Physics Letters B

The mechanical stabilities and nonlinear properties of monolayer Gallium selenide (GaSe) under tension are investigated by using density functional theory (DFT). The ultimate stresses and ultimate strains and the structure evolutions of monolayer GaSe under armchair (AC), zigzag (ZZ) and equiaxial (EQ) tensions are predicted. A thermodynamically rigorous continuum description of nonlinear elastic response is given by expanding the elastic strain energy density in a Taylor series in Lagrangian strain truncated after the fifth-order term. Fourteen nonzero independent elastic constants are determined by least-square fit to the DFT calculations. Pressure-dependent elastic constants (C_ij(P)) and pressure derivatives of are also calculated. Calculated values of ultimate stresses and strains and the in-plane Young's modulus are all positive. It proves that monolayer GaSe is mechanically stable.

The band structures and optical properties of α-Fe₂O_3-xSe_x alloys are studied by means of first-principles methods, considering different Se contents x. Numerical results show that Se content has an obvious influence on band structures and optical properties of α-Fe₂O_3-xSe_x alloys. The band gap values of α-Fe₂O_3-xSe_x alloys decrease monotonically when Se concentrations increase, resulting in an obvious increase of the optical absorption edge in the visible range. In particular, our results show that α-Fe₂O_3-xSe_x alloys have the direct band gap properties with band gap values when Se content x ≈ 0.17, which is beneficial to solar cell applications.

In this paper, a (3+1)-dimensional generalized variable-coefficients Kadomtsev–Petviashvili (gvcKP) equation is proposed, which describes many nonlinear phenomena in fluid dynamics and plasma physics. By a very natural way, the integrable constraint conditions on the variable coefficients are presented to investigate the integrabilities of the gvcKP equation. Based on the generalized Bell's polynomials, we succinctly obtain its bilinear representations, bilinear Bäcklund transformation and Lax pair, respectively. Furthermore, by virtue of the binary Bell polynomial form, the infinite conservation laws of the equation are found with explicit recursion formulas as well by using its Lax equations via algebraic and differential manipulation. In addition, by using the Hirota bilinear method, its N-soliton solutions are also obtained.

Compared with the traditional finite-difference time-domain (FDTD) method, the symplectic finite-difference time-domain (SFDTD) method has the characteristics of high precision and low dispersion. However, because the higher-order difference is necessary for the calculation, a large sparse matrix is generated. It causes that the computational time is relatively long and the memory is more. To solve this problem, the incomplete Cholesky conjugate gradient (ICCG) method for solving the large sparse matrix needs to be taken into the SFDTD differential equations. The ICCG method can accelerate the iterations of the numerical calculation and reduce the memory with fast and stable convergence speed. The new ICCG–SFDTD method, which has both the advantages of the ICCG method and SFDTD method, is proposed. In this paper, the ICCG–SFDTD method is used for research on the characteristic parameters of the plasma photonic crystals (PPCs) under different conditions, such as the reflection electric field and the transmission coefficient, to verify the feasibility and accuracy of this method. The results prove that the ICCG–SFDTD method is accurate and has some advantages.

Nitrogen oxides exhaust gas assumes the important responsibility on air pollution by forming acid rain. This paper discusses the NO removal mechanism in 15 ns pulse dielectric barrier discharge (DBD) plasma through experimental and simulating method. Emission spectra collected from plasma are evaluated as sourced from N⁺ and O(³P). The corresponding zero-dimensional model is established and verified through comparing the simulated concentration evolution and the experimental time-resolved spectra of N⁺. The electron impact ionization plays major role on NO removal and the produced NO⁺ are further decomposed into N⁺ and O(³P) through electron impact dissociative excitation rather than the usual reported dissociative recombination process. Simulation also indicates that the removal process can be accelerated by NO inputted at lower initial concentration or electrons streamed at higher concentration, due to the heightened electron impact probability on NO molecules. The repetitive pulse discharge is a benefit for improving the NO removal efficiency by effectively utilizing the radicals generated from the previous pulse under the condition that the pulse period should be shorter enough to ignore the spatial diffusion of radicals. Finally, slight attenuation on NO removal has been experimentally and simulatively observed after N₂ mixed, due to the competitive consumption of electrons.

In view of difficulties and questions of quantum mechanics in description of motion of electrons in hydrogen atom, we here established their nonlinear theory of motion based on the true motions of electron and nucleon and the real interactions between them, in which the motion of electron is depicted by a nonlinear Schrödinger equation with a Coulomb potential, the nonlinear interaction b∣φ∣²φ is produced by the change of Coulomb interaction between nucleon and electron due to the motion of nucleon. Thus the natures of the electron are thoroughly changed relative to those in quantum mechanics due to the nonlinear interactions, it not only is stable and localized, but also possesses a wave–corpuscle duality. Meanwhile, if its eigenenergy is still quantized and distributed in accordance with the energy levels, then we can use the new theory to explain perfectly the spectrum features of hydrogen atom, which resembles quantum mechanics, but its sizes of eigenenergy are depressed relative to that in quantum mechanics. This means that the nonlinear interaction enhances the localized and stable nature of the electron. Therefore, the new nonlinear theory is successful and correct to the hydrogen atom.

In this paper, we apply car-following model to explore each person's travel time and the system's total travel time on an open road. The analytical and numerical results illustrate that each person's travel time and the system's total cost are directly related to each person's time headway at the origin when the road is long enough and the number of persons is large enough in the traffic system. The above results can help traffic engineers to optimize each person's arrival rate and help readers to understand the relationship between each person's travel time and his arrival rate.

We propose the design of a broadband planar metamaterial absorber (MA) at terahertz frequencies. The unit cell of the MA is composed of four dual-band sub-cells with different dimensions in a coplanar. The four dual-band sub-cell structures resonate at several neighboring frequencies. The absorber consists of two metallic layers separated by a dielectric spacer. Simulation results show that the metamaterial absorption at normal incidence is above 90% in the frequency of 6.56–8.10 THz. This design provides an effective way to construct broadband absorber. The multiple-reflection theory was used to explain the absorption mechanism of our investigated structures. The coupling of adjacent four dual-band sub-cells can introduce additional capacitance to affect the performance of absorber.