Modern Physics Letters B

This paper reports the flow and heat transfer augmentation on Reiner–Philippoff nanofluid over stretching sheet. The effect of transverse magnetic field and thermal radiation are explored for temperature distributions. Transformations are used to reduce system of partial differential equations into ordinary ones and are solved numerically by using RKF-45 Method. Expressions for velocity and temperature profile are derived and plotted under the assumption of flow parameter. Influence of various parameters on surface drag force and heat transfer rates have been discussed with the help of tables and plots. It is noticed that the impact of pseudo plastic fluid, Newtonian fluid and dilatant fluid are highly contrasted in higher Ha. Furthermore, production of heat transfer is more in nonlinear radiation when compared to linear radiation.

In this research, a novel phononic crystal (PC) is investigated theoretically to enhance acoustic pressure confinement. It consists of multiple nested resonators based on a tapered configuration. Nested phononic crystal resonator (NPCR) can enhance the acoustic pressure amplification at resonant cavity to a great degree better than the traditional one with same dimensions. The resonant frequency of NPCR is mainly located within outermost phononic crystal resonator’s (PCR) band gap. Meanwhile, it does not move significantly to high frequency with the addition of inner tapered resonators. The enhanced acoustic pressure resonant amplification is attributed to the improvement of the confinement mode owing to the nested structure working as a taper. Then effects of geometrical dimensions of inner PCRs on acoustic confinement are studied. It shows that resonant frequency and resonant acoustic pressure can be affected by the geometric parameters. NPCR has stronger acoustic confinement effects, which are conducive to improve acoustic sensing sensitivity, acoustic signal frequency resolution and acoustic energy harvesting efficiency.

We use a first-principles calculation to explore the effects of vacancies on structural, electronic and optical properties of $\beta$-${\mathrm{\text{Si}}}_3{\mathrm{\text{N}}}_4$ based on density functional theory (DFT). The results show that after optimization, the Si vacancy system of $\beta$-${\mathrm{\text{Si}}}_3{\mathrm{\text{N}}}_4$ is more difficult to produce than N vacancy system under the same thermodynamic conditions. The band gaps including N vacancy and Si vacancy systems are smaller than that of the perfect crystal. The charge density difference and population analysis show that the bonding near Si vacancy has stronger covalent property, whereas those near nitrogen vacancy have stronger ionic property. For Si vacancy system, the materials have much higher values of the imaginary part of the dielectric constant than those of N vacancies and perfect $\beta$-${\mathrm{\text{Si}}}_3{\mathrm{\text{N}}}_4$. The maximum value of the Si vacancy system in absorption and reflection spectra is lower than those in different nitrogen vacancy systems.

The dynamics of a two-soliton molecule bouncing on the reflecting atomic mirror under the effect of gravity have been studied by analytical and numerical methods. The analytical description is based on the variational approximation. In numerical simulations, we observe the resonance oscillations of the two-soliton’s center-of-mass position and width, induced by modulated atomic mirror. Theoretical predictions are verified by numerical simulations of the nonlocal Gross–Pitaevskii equation (GPE) and qualitative agreement between them is found. Hamiltonian dynamic system for a dipolar Bose–Einstein condensates (BECs) has been studied.

In this paper, the two-dimensional (2D) turbulence perturbed by arrays of cylinders placed both horizontally and vertically is investigated by Immersed Boundary Lattice Boltzmann Method (IB-LBM). The energy spectrum reveals the coexistence of the inverse and direct cascades in 2D grid turbulence. By observing at the distribution of fluxes in space, the energy and enstrophy fluxes have explained the physical mechanism of the double cascades where the two Kolmogorov laws for structure functions are simultaneously observed. The results of vortex statistics by the conditional analysis, which are based on a new and accurate vortex identification criteria called Liutex, show that the algebraic number density $n(A)\sim A^{-2}$, where $A$ is vortex area. The time-evolving vortex number density distribution constructs a theoretical framework involving a three-part: $n(A,t)=A^{-0.5}(A_{min}\le A<A_{-})$; $t^{-1}{A}^{-1}(A_{-}<A<A_{+})$; $t^7{A}^{-8}(A_{+}<A\le A_{max})$, which is satisfied with the prediction well. The relationship between the vortex circulation $\left|\mathrm{\Gamma }\right|(A)$ and vortex area $A$ is $\left|\mathrm{\Gamma }\right|(A)\sim A$ and the one between the kinetic energy of vortex $Ee(A)$ and $A$ is $Ee(A)\sim A$ in the range where $n(A)\sim A^{-2}$. Moreover, it has been found that vortices contain about 30% of the total energy of the flow by studying the energy ratio of all vortices to the entire flow field. What is more, it is an interesting phenomenon is that there is only a range where $E(k)\sim k^{-5/3}$ in the energy spectrum for the coherent structure field which is obtained by using Liutex as the extraction of vortices. The probability density function (PDF) of the fluctuations of longitudinal velocity shows that an indication of small intermittency in the direct cascade and the absence of intermittency in the inverse cascade range. On the other hand, the scaling exponents $\zeta (p)$ of the structure function for the inverse cascade are consistent with Kr67 model, which shows the absence of intermittency. While the measured intermittency parameters are $J=0.006$ and $H=0.921$, which explains that there is a very weak intermittent correction in the direct cascade, and ESS has verified the existence of intermittency in our 2D turbulence.

This paper investigates novel adaptive observation control for synchronization of uncertain chaotic coronary artery system (CCAS). Novel adaptive observers are developed to obtain the estimated system states of uncertain CCAS which has unknown parameters. By utilizing the adaptive observers and controller we proposed, the adaptation of unknown parameters has been achieved and the asymptotic stability of the synchronization error as well as the estimation errors are guaranteed. For the purpose of further reducing the conservatism, new Lyapunov Krasovskii functions (LKFs) which maintain more system states have been constructed in terms of Wirtinger-based inequality, a new double integral inequality and improved reciprocally convex inequality. Using $H_{\infty }$ control to ensure robust performance of CCAS which has unknown parameters and external disturbance. The adaptive observer gain matrices and controller gain matrix could be obtained by employing a decoupling approach. The effectiveness of this control methodology has been illustrated by a numerical simulation result.

We examined heat and mass transfer characteristics of mixed convective slip flow over a wedge taking into account the effect of variable transport properties. Unlike other studies, we have utilized non-similar transformation to get the non-similar features of the mixed convective slip flow. For comparison, stream function formulation is used to reduce the governing equation into a convenient form for short- and long-time regimes. We have determined the series solutions by adopting the perturbation techniques. The agreement between the numerical and series solutions is found to be excellent. Numerical solutions reveal that the slip parameters augment the momentum, thermal and concentration boundary layers. The local skin friction coefficient, the local Nusselt number and the local Sherwood number are found to decrease for higher value of slip parameters. For the increasing value of the variable viscosity parameter, the velocity is stronger, but the temperature and concentration lessen. Contrary to this, this parameter diminishes the local skin friction coefficient, local Nusselt number and local Sherwood number. Due to the increase of mass diffusivity parameter, the velocity and concentration significantly increase whereas the temperature remains almost unaffected. Moreover, the mass diffusivity variation parameter leads to an increase in the local skin friction coefficient and local Nusselt number, but it reduces the local Sherwood number.

The nonlinear optical properties of a nanoparticle polyaniline/polyacrylonitrile (PAn/PANr) copolymer newly prepared via experimental and theoretical findings are reported. Diffraction ring patterns result in the far field when a CW, visible, 473 nm, low power laser beam traverses the solution of PAn/PANr in the solvent ethanol. The diffraction ring patterns are usually used to estimate the nonlinear refractive index while the Z-scan is used to measure both nonlinear refractive index and its sign and nonlinear absorption coefficient. The experimentally observed ring patterns are numerically reproduced via the use of the Fresnel–Kirchhoff procedure. Good agreement between experimental findings and the numerical ones are obtained. The obtained diffraction ring patterns suffer modification in the vertical direction due to convection current as a result of local heating of the sample and the presence of gravity.

The aim of this paper is to show that there exist lump solutions and interaction solutions to linear partial differential equations in 2+1 dimensions. Through symbolic computations with Maple, we exhibit a great variety of exact solutions to a class of (2+1)-dimensional linear partial differential equations, and present a specific example which possesses lump, lump-kink and lump-soliton solutions. This supplements the study on lump, rogue wave and breather solutions and their interaction solutions to nonlinear integrable equations.

The acoustic black hole has good sound insulation performance in low frequency range. The transmission and insulation characteristics of acoustic black hole is investigated by experiments. First, we study the transmission and insulation characteristics of the acoustic black hole by numerical simulation. Second, we studied the sound transmission characteristic of multi-level acoustic black hole. Finally, the sound transmission and insulation characteristics of the acoustic black hole are studied by experiments. The influence of the acoustic black hole tip’s diameter on sound insulation coefficient is studied. The sound transmission characteristics of the first, two and three level acoustic black holes are also studied by experiments. Our numerical results show that low frequency acoustic energy can be effectively focused at the tip of the acoustic black hole, and can be effectively insulated by the acoustic black hole. Our numerical results are verified by the experimental results. Our study can provide a feasible method for controlling the low frequency noise.

The structures, electronic and magnetic properties of the transition metals (TMs) (subgroup = 8, 9, 10 and 11) substituted ${\mathrm{\text{Mg}}}_9{\mathrm{\text{O}}}_9$ nanotube clusters have been investigated using first-principles at the PBE functional. The results show that as for the ${\mathrm{\text{TMMg}}}_8{\mathrm{\text{O}}}_9$ clusters, $3d$ atoms and Re atoms prefer to substitute the Mg atoms which occupy the edge position of the ${\mathrm{\text{Mg}}}_9{\mathrm{\text{O}}}_9$ nanotube clusters, while $4d$ and $5d$ atoms prefer to substitute the Mg atoms which occupy the middle hexagonal ring ${\mathrm{\text{Mg}}}_9{\mathrm{\text{O}}}_9$ nanotube clusters expect for Re atoms. The ${\mathrm{\text{Tc}}}_2{\mathrm{\text{Mg}}}_7{\mathrm{\text{O}}}_9$, ${\mathrm{\text{Fe}}}_2{\mathrm{\text{Mg}}}_7{\mathrm{\text{O}}}_9$, ${\mathrm{\text{Co}}}_2{\mathrm{\text{Mg}}}_7{\mathrm{\text{O}}}_9$ and ${\mathrm{\text{Ni}}}_2{\mathrm{\text{Mg}}}_7$O₉ clusters are more stable than other TMs-substituted ${\mathrm{\text{Mg}}}_9{\mathrm{\text{O}}}_9$ nanotube clusters. TM substituting significantly improves the kinetic activity of the ${\mathrm{\text{Mg}}}_9{\mathrm{\text{O}}}_9$ nanotube clusters. The HOMO and LUMO states display evident hybridization between the TMs $d$ and O $2p$ band states. A few $s$ orbital electrons of the TM atoms transfers to O atoms. As for the spins of the $3d$ TM atoms for the ground state ${\mathrm{\text{TMMg}}}_8{\mathrm{\text{O}}}_9$ and ${\mathrm{\text{TM}}}_2{\mathrm{\text{Mg}}}_7{\mathrm{\text{O}}}_9$ (subgroup = 8, 9, 10 and 11) clusters, ${\mathrm{\text{Spin}}}_{\mathrm{\text{Mn}}}>{\mathrm{\text{Spin}}}_{\mathrm{\text{Fe}}}>{\mathrm{\text{Spin}}}_{\mathrm{\text{Co}}}>{\mathrm{\text{Spin}}}_{\mathrm{\text{Ni}}}$.

In this work, we present the analysis and design of a perfect metamaterial absorber (MA) based on quarter mode rectangular cavity in the terahertz region. This structure is consisted of a metal plate where three different size quarter mode rectangular cavities are vertically placed on. Based on rectangular-cavity-theory, a formula is proposed to calculate the resonant frequency, which provides a guidance for designing MAs of such type. In terms of normal incidence, the simulated results show that the MA has three resonance points on 4.1301 THz, 4.6051 THz and 5.1088 THz, respectively, which is in good agreement with the calculated results. Furthermore, we present the distribution of E-field in the cavity and use the standing wave theory to explain the physical mechanism of the perfect absorption. These results verify the application of resonant cavities in the field of MA.

In this study, a leaf-like ${\mathrm{\text{Cu}}}_2\mathrm{\text{O}}/\mathrm{\text{CuO}}$ mixed phase nanosheets array was successfully prepared by anodization. XRD, EDS, and XPS analysis confirmed the formation of ${\mathrm{\text{Cu}}}_2\mathrm{\text{O}}/\mathrm{\text{CuO}}$ mixed phase nanostructures. SEM images indicate that the fabricated ${\mathrm{\text{Cu}}}_2\mathrm{\text{O}}/\mathrm{\text{CuO}}$ mixed phase nanosheets almost grow vertically on the substrate. The average height of nanosheets is approximately 500 nm. The optical absorption of the mixed phase covers the entire wavelength region of visible light and a little part of the near-infrared region of short wavelength.

The spin-1 quantum Ising systems with three-spin interactions on two-dimensional triangular lattices are studied by mean-field method. The thermal variations of order parameters and phase diagrams are investigated in detail. The stable, metastable and unstable branches of the order parameters are obtained. According to the stable conditions at critical point, we find that the systems exhibit tricritical points. With crystal field and biquadratic interactions, the system has rich phase diagrams with single reentrant or double reentrant phase transitions for appropriate ranges of the both parameters.