International Journal of Modern Physics B

In order to improve the castings quality of nickel-based superalloy in investment casting process, especially to reduce the shrinkage porosity, the processing parameters were optimized by numerical simulation and Taguchi method. The effects of processing parameters, such as pouring temperature, pouring time and mold shell preheating temperature, on the shrinkage porosity in the turbine nozzle investment castings prepared by K477 nickel-based superalloy were investigated. The results show that the effects of the mold shell preheating temperature, pouring temperature and pouring time are main influencing factors in turn, which are verified by the evaluation of signal-to-noise ratio and the analysis of variance. Further, based on the processing optimization, a K477 alloy turbine nozzle without shrinkage porosity was prepared with the optimized parameters: pouring temperature of ${1450}^{\circ }\text{C}$, mold shell preheating temperature of ${1050}^{\circ }\text{C}$ and pouring time of 14 s, respectively.

Stochastic noise exists widely in the nervous system, and noise plays an extremely important role in the information processing of the nervous system. Noise can enhance the ability of neurons to process information as well as decrease it. For the dynamic behavior of stochastic resonance and coherent resonance shown by neurons under the action of stochastic noise, this paper uses Fourier coefficient and coherence resonance coefficient to measure the behavior of stochastic resonance and coherence resonance, respectively, and some conclusions are drawn by analyzing the effects of additive noise and multiplicative noise. Appropriate noise can make the nonlinear system exhibit stochastic resonance behavior and enhance the detection ability of external signals. It can also make the coherent resonance behavior of the nonlinear system reach its optimal state, and the system becomes more orderly. By comparing the effects of additive and multiplicative noise on the stochastic resonance behavior and coherent resonance behavior of the system, it is found that additive and multiplicative noise can both make the system appear the phenomenon of stochastic resonance and have almost identical discharge state at the same noise intensity. However, with the increase of noise intensity, the coherent resonance of the system occurs, the multiplicative noise intensity is smaller than that of additive noise, but the coherent resonance coefficient of additive noise is smaller and the coherent resonance effect is better. The system whose system parameters are located near the bifurcation point is more prone to coherent resonance, and the closer the bifurcation point is, the more obvious the coherent resonance phenomenon is, and the more regular the system becomes. When the parameters of the system are far away from the bifurcation point, the coherent resonance will hardly appear. Besides, when additive and multiplicative noise interact together, the stochastic resonance and coherent resonance phenomena are more likely to appear at small noise, and the behavior of stochastic resonance and coherent resonance that the system shown is better in the local range.

For power-law nonlinear system in higher-dimensional setting like the three-dimensional case, we derived its bright soliton solution with specific power-law feature based on the self-similar method. The dynamical evolution pattern of the derived solution is pictorially demonstrated which illustrates the typical bright soliton feature. The theoretical results presented in this work can be used to guide experimental observation of soliton behavior in higher-dimensional system with power-law nonlinearity.

The molecular dynamics method is used to investigate the formation and properties of irradiation-induced damage (point defects). Displacement cascade simulations are performed to study the effects of primary knock-on atom (PKA) energy, temperature, vacancy concentration and tensile pre-strain on irradiation-induced damage in $\alpha$-Fe. An increase in PKA energy, vacancy concentration and tensile pre-strain can lead to an increase in defect numbers. In contrast, an increase in temperature decreases the defect numbers. After cascade collisions, tensile tests are performed to investigate the effect of point defects on mechanical properties. The yield stress and corresponding strain of irradiated Fe decrease with an increase in the number density of Frenkel pairs. Results show that irradiation accelerates damage of the internal structure, decreases the number of slip bands and increases the instability of the structure during plastic deformation.

The effects of shear deformation at 1173 K on the mechanical properties and deformation mechanism of pure tungsten are investigated by molecular dynamics (MD). The results show that the shear deformation of pure tungsten is dominated by dislocation multiplication and slip band deformation. The shear angle has a significant effect on the mechanical properties of pure tungsten. The yield strength is 4.21 Gpa at a shear angle of 11${}^{\circ }$, and it increases significantly to 11.84 Gpa while the shear angle increasing to 27${}^{\circ }$. In the plastic deformation stage, the stress–strain curve shows obvious oscillation due to the interaction of dislocations in the single-crystal tungsten and the effect of strain strengthening. In addition, the evolution of dislocation and twining in the compression system against shear angle indicates the variation of deformation behavior. When the shear angle is 11${}^{\circ }$, the lengths of dislocation 1/2$〈111〉$ and $〈100〉$ increase to a peak rapidly, which illustrates dislocation strengthening. However, when the shear angle is more than 11${}^{\circ }$, the decrease of dislocation length and the appearance of twins along $〈111〉$ direction demonstrate the twining accompanied with dislocation tangling, resulting in the additional increase of strength.

The phase transition of zinc sulfide (ZnS) from Zinc-blende (ZB) to a rocksalt (RS) structure and the elastic, thermodynamic properties of the two structures under high temperature and pressure are investigated by first-principles study based on the pseudo-potential plane-wave density functional theory (DFT) combined with the quasi-harmonic Debye model. The lattice constant $a_0$, bulk modulus $B$ and the pressure derivative of bulk modulus $B$’ of the two structures are calculated. The results are in good agreement with experimental results and the other theoretical data. From the energy–volume curve, enthalpy equal principle and mechanical stability criterion, the transition pressures from the ZB to the RS structure are 16.83, 16.96 and 16.61 GPa, respectively. The three results and the experimental values 14.7–18.1, 16 GPa are very close to each other. Then the elastic properties are also calculated under the pressure ranging from 0 to 30 GPa. Finally, through the quasi-harmonic Debye model, the thermodynamic properties dependence of temperature and pressure in the ranges between 0–1600 K and 0–30 GPa are obtained successfully.

The Su–Schrieffer–Heeger (SSH) model can occur in a one-dimensional (1D) diatomic chain photonic crystal (PC) in which a unit cell includes two same slabs (atoms). With different intervals of the two slabs, the two combined 1D PCs can support topological edge states in all photonic boundary bandgaps. These topological edge states come from the inversion of topological phase of the bands through the band folding effect. When the sum of the two atom intervals in the two different 1D PCs equals to the unit cell length, these edge state frequencies keep invariant.

Using density function theory calculation method, we investigated the charge distribution in nano- or low-dimension materials and some high pressure three-dimensional solids in many simple substances. It is found that if an atom in simple substances has different atomic environment from the other(s) nearby, they always have spontaneous charge inhomogeneity within local area. Charge inhomogeneity introduced by inequivalent atomic positions is a general phenomenon in simple substances, especially in their nano-materials. Such self-ionization significantly changes elemental matter’s physical and chemical properties. These results can advance the understanding on condensed matters, especially the internal structures and physical or chemical properties of elemental nano-materials, and could be a starting point for experimental investigation of self-ionization in them. The charge inhomogeneity of simple substances means their nonzero oxidation state or nonzero valence.

The ferromagnetism of Au nanograins is analyzed based on a two-dimensional itinerant lattice model with on-site Coulomb repulsion, many-body spin–orbit interactions, and holding two hybridized bands, one correlated and one uncorrelated. Using periodic boundary conditions in both directions, an exact ferromagnetic ground state is deduced for this non-integrable system by applying special techniques based on positive semidefinite operators.

Multi-particle cluster states play a significant role in quantum information processing. However, due to the inevitable interaction with the environment in the transmission process, the fidelity of entanglement decreases. To distill the perfect cluster states, we present two schemes for arbitrary six-particle cluster states. POVM local unitary operators that are obtained by solving the equation according to the properties of cluster states are used in the first protocol. The second protocol is based on cross-Kerr nonlinearity which is exploited to check parity between original qubit with ancillary single qubit and it can achieve a higher probability of success through iteration. Furthermore, we can generalize the first method to concentrate entanglement on even number of particles. Our protocol will be useful in practical applications.