Modern Physics Letters B

This study was conducted to investigate effects of surface roughness on self-excited cavitating water jet intensity in an organ-pipe nozzle. Roughness average (Ra) values are 0.8, 1.6, 3.2, 6.3, 12.5, and 25 $\mu$m, respectively. Numerical simulation results indicate that at inlet pressure of 10 MPa, the maximum, minimum, and real-time pressures in the self-excited oscillation chamber reach their respective peak values. The turbulent kinetic energy intensity in the external flow region is also most intense at this point, the vapor volume fraction in orifice is the highest, the vortex distribution scope in the orifice is the largest under $Ra=12.5\mu \mathrm{\text{m}}$, and the self-excited cavitating water jet intensity is the strongest. The opposite variations emerge at $Ra=25\mu \mathrm{\text{m}}$ compared to those of $Ra=12.5\mu \mathrm{\text{m}}$, where the intensity is weakest. Pressure varies only slightly as Ra varies from 0.8 $\mu$m to 6.3 $\mu$m. Turbulent kinetic energy intensity behaves similarly as Ra increases from 0.8 $\mu$m to 3.2 $\mu$m. At $Ra=6.3\mu \mathrm{\text{m}}$, it was weaker than at Ra = 0.8–3.2 $\mu$m. Similarly, there are only slight differences in vapor volume fraction and vortex distribution scope with Ra from 0.8 $\mu$m to 6.3 $\mu$m. The intensities at Ra = 0.8–3.2 $\mu$m are similar, and weaker at Ra = 6.3 $\mu$m. Pressure values are maximal at inlet pressure of 20 MPa, turbulent kinetic energy intensity is most intense, vapor volume fraction is highest, vortex distribution scope is largest under $Ra=6.3$ $\mu$m, and intensity is strongest. Distinctions among pressure, turbulent kinetic energy intensity, vapor volume fraction, and vortex distribution scope values with Ra from 0.8 $\mu$m to 3.2 $\mu$m are slight. Differences in the corresponding intensities are also slight; all decrease with Ra from 12.5 $\mu$m to 25 $\mu$m as the intensity gradually weakens. Numerical simulation results were validated by comparison against corresponding experimental phenomena.

Electronic and luminescence characteristics of Bi/Al co-doped silica optical fiber model were investigated by using first-principle methods. Our results show that the preference Al substitution site is the adjacent Si site rather than O site. The doping of Al can contribute to the dispersion of Bi${}^{3+}$ luminescence center and generate new luminescence center at $\sim$1100 nm by affecting $p$ orbital of the O atom near Bi atom. Our results give a possible explanation of the near-infrared (NIR) luminescence in Bi/Al co-doped silica optical fibers.

This paper proposes an image encryption scheme based on cat mapping and matrix magic transformation (MMT) replacement method. First, the secure hash algorithm SHA-512 is used to generate 12 sets of keys, which are used for the initial values of the system and the required values of the algorithm for cat mapping and 2D-Logistic-adjusted-Sine map (LASM). Secondly, the plaintext image is scrambled by the cat mapping. Then, the matrix after the cat map replacement is again scrambled by the MMT replacement method to generate the permutation matrix. Finally, the permutation matrix is used for the bitxor operation with the chaotic sequence matrix generated by the 2D LASM system to realize the diffusion process of the scrambled image. Experimental results and security analysis show that the encryption algorithm has good performance and can resist various typical attacks.

In this work, we studied the electronic and optical properties of ${\mathrm{\text{Er}}}_x{\mathrm{\text{Ga}}}_{1-x}\mathrm{\text{N}}$ with a concentration $x=0.0625$. Based on a first-principle calculation and using the FP-LAPW full-linearized augmented plane wave method, to see the doping phenomenon with Erbium (Er) ${\mathrm{\text{4f}}}^{12}{\mathrm{\text{6s}}}^2$, we used the three approximations: local spin density approximation (LSDA), the LSDA$+U$ with $U$ is the Hubbard potential and the Becke–Johnson modification (mBJ). Our results show that the values of the structural parameters increase with the substitution of Ga by the Erbium atom. The analysis of the electronic structures in this study shows that the Er-doped GaN has a semi-metallic ferromagnetic character with the LSDA and mBJ approximations and a semiconductor behavior when we apply the Hubbard potential $U$. The real and imaginary part of the dielectric function, refractive index, and extinction coefficient are also calculated and presented in the photon energy range up to 14 eV. In the optical spectrum, the intensity of the absorption coefficient is observed in the imaginary part of both doped and undoped GaN in the ultraviolet regions.

In this paper, by introducing a stream function and new coordinates, we transform classical Euler–Boussinesq equations into a vorticity form. We further construct traveling wave solutions and similarity reduction for the vorticity form of Euler–Boussinesq equations. In fact, our similarity reduction provides a kind of linearization transformation of Euler–Boussinesq equations.

In this paper, abundant interaction solutions for the (1+1)-dimensional generalized Drinfel’d–Sokolov–Wilson (gDSW) equation are presented. First, two groups of lump-soliton-type interaction solutions are constructed by using a combination of quadratic function and two exponential functions. Especially, lump-twin soliton-type solution therein can generate rogue wave, which rarely appears in (1+1)-dimensional nonlinear systems in comparison with (2+1)-dimensional nonlinear systems. When certain parameters are taken to zero, these exact solutions are reduced to corresponding lump, soliton and lumpoff solutions. Second, the lump-periodic wave-type and soliton-periodic wave-type interaction solutions are also found on the basis of the bilinear form of gDSW equation. In the concrete analysis, we use mathematical software Maple to deal with some complicated symbolic computations. Figures are presented to show the dynamical features of these solutions.

The combustion characteristics of high-speed ejector mode in a 2-dimensional strut-based RBCC (rocket-based combined cycle) combustor had been investigated numerically in a Mach 2.5 supersonic flow. The numerical approach had been validated by comparing numerical results with available experimental data. Besides, three different hydrogen-air chemical reaction mechanisms had also been compared. The effect of the combustor geometry on the combustion process was then discussed by analyzing the heat release distribution and flow field. It was found that the wall configuration, closeout angle of the converging location and converging ratio all have significant influences on the heat release distribution and flow field structures. It is demonstrated that a converging–diverging wall configuration is beneficial for the combustion process with significant heat release increase compared to the other wall configurations. In addition, the closeout angle of the converging location is also closely related to the combustion performance, and there exists an optimized closeout angle in a specific combustor geometry. It is also revealed that the major heat release region moves upstream obviously with increase in the converging ratio, leading to an enhanced combustion process. However, the converging ratio is still to be optimized to keep a balance between heat release increase and total pressure loss of the supersonic flow.

Evolutionary processes of many complex networks in reality are dominated by duplication and divergence. This mechanism leads to redundant structures, i.e. some nodes share most of their neighbors and some local patterns are similar, called redundancy of network. An interesting reverse problem is to discover evolutionary information from the present topological structure. We propose a quantitative measure of redundancy of network from the perspective of principal component analysis. The redundancy of a community in the empirical human metabolic network is negatively and closely related with its evolutionary age, which is consistent with that for the communities in the modeling protein–protein network. This behavior can be used to find the evolutionary difference stored in cellular networks.

In a previous work [N. H. Tong, Phys. Rev. B 92 (2015) 165126], an equation-of-motion-based series expansion formalism was used to do the second-order strong-coupling expansion for the single-particle Green function of the Anderson impurity model (AIM). In this paper, we improve this theory in two aspects. We first use a more accurate scheme to self-consistently calculate the averages that appear in $G_1$. In the resummation process, we use updated coefficients for the continued fraction (CF), guided by the formally exact CF from the Mori–Zwanzig theory. These changes lead to more accurate impurity spin responses to the magnetic bias of the bath. Combined with the dynamical mean-field theory, our theory gives improved description for the antiferromagnetism of Hubbard model at half-filling.

We consider a generalized fourth-order nonlinear Schrödinger (NLS) equation. Based on the ansatz method, its bright, dark single-soliton is constructed under some constraint conditions. Furthermore, combining the Riccati equation extension approach, we also derive some exact singular solutions. With several parameters to play with, we display the dynamic behaviors of bright, dark single-soliton. Finally, the condition for the modulational instability (MI) of continuous wave solutions for the equation is generated. It is hoped that our results can help enrich the nonlinear dynamics of the NLS equations.

Exact envelop patterns of nonlinear Schrödinger equation (NLSE) with perturbation terms are constructed to describe optical solitons in quadratic-cubic nonlinear medium by proposing a complex version of Liu’s trial equation method. These four families of envelop solutions show various properties of patterns of amplitudes including singularity, periodicity and double periodicity.

In this paper, gadolinium orthophosphate (GdPO₄) hollow spheres with good luminescent properties, better drug loading and sustainable release have been synthesized by a template-oriented route. The precursor with core–shell structure was facilely prepared by a homogeneous precipitation and followed solvothermal method with 3-aminophenol-formaldehyde (APF) resin spheres as template. Subsequently, the APF template was eliminated and the crystalline GdPO₄ hollow spheres were obtained after an annealing process. The structure, morphology, and formation process of the as-obtained GdPO₄ hollow spheres have been investigated in detail. It is worth noting that lanthanide activator ions doped GdPO₄ can perform optical and MRI dual-mode imaging functions. Moreover, the as-obtained GdPO₄ hollow spheres exhibit good drug loading and sustained drug release behaviors. The unique hollow structure, dual-mode optical and MRI imaging capabilities, and good drug loading/release patterns enable the as-synthesized products to have enormous potential in bioimaging, drug delivery, and disease diagnosis.

In this study, ZnO nanoparticles and MnO-doped SnO₂-based thick film varistors (TFVs) were fabricated using screen printing technique. The sintering temperature had significant impact on the SZM-based TFVs, especially in terms of grain growth, even at a low sintering temperature of 1100${}^{\circ }$C. The strong solid-state reaction during sintering may be attributed to the large surface area of the 20 nm ZnO nanoparticles that promoted strong surface reaction even at low sintering temperatures. Moreover, the X-ray diffraction lattice constant and full wave at half maximum data indicated that the sintering process also improved the grain crystallinity with the decrease in intrinsic compressive stress. The sintering temperatures also significantly influenced the electrical properties of the SZM-based TFVs with a significant decrease in the breakdown field from 360 V/mm (sample at 1100${}^{\circ }$C) to 158 V/mm (sample at 1250${}^{\circ }$C). The grain boundary resistance ($R_{\mathrm{\text{GB}}})$ also experienced a dramatic drop from 266.4 k$\mathrm{\Omega }$ (sample at 1100${}^{\circ }$C) to 89.46 k$\mathrm{\Omega }$ (sample at 1250${}^{\circ }$C). The sample sintered at 1200${}^{\circ }$C exhibited superior electrical behaviors with a nonlinear exponent of 61 and leakage current of 115 $\mu$A. Furthermore, it achieved high permittivity and low dissipation factor at the low frequency range. The conduction behaviors of ${\mathrm{\text{O}}}^{\prime }$ ions with activation energy of approximately 0.6 eV was dominated by decreasing ${\mathrm{\text{Zn}}}_{\mathrm{\text{Sn}}}^{\prime \prime }$ and ${\mathrm{\text{Mn}}}_{\mathrm{\text{Sn}}}^{\prime \prime }$ defects (around 0.4 eV) with increasing sintering temperature. Therefore, the sintering process can be applied to control the conduction behaviors of SZM-based TFVs doped with ZnO nanoparticle powder and achieve improved structural and electrical properties with good nonlinear behaviors.

The expressions for the renormalized phonon group velocity (RPGV) has been developed from renormalized phonon dispersion relations obtained with the help of impurity-induced anharmonic quantum dynamics of phonons via Green’s functions. It is observed that RPGV shows dependence on doping, phonon frequency, temperature, and anharmonicity. The ${\mathrm{\text{La}}}_{2-x}{\mathrm{\text{Sr}}}_x{\mathrm{\text{CuO}}}_4$ superconductor has been taken for model calculations to successfully apply the new results of RPGV.