Volume 77, Issue 2

In this paper, a delayed eco-epidemiological model including susceptible migratory birds, infected migratory birds and predator population is proposed by us. The interaction between predator and prey is represented by functional response of Leslie–Gower Holling-type II. Fear effect is considered in the model. We assume that the growth rate and activity of prey population can be reduced because of fear effect of predator, and this series of behaviors will indirectly slow down the spread of diseases. Positivity, boundedness, persistence criterion, and stability of equilibrium points of the system are analyzed. Transcritical bifurcation and Hopf-bifurcation respect to important parameters of the system have been discussed both analytically and numerically (e.g. fear of predator, disease transmission rate of prey, and delay). Numerical simulation results show that fear can not only eliminate the oscillation behavior caused by high disease transmission rate and long delay in the model system, but also eliminate the disease.

The nonlinear propagation of ion-acoustic (IA) electrostatic solitary waves (SWs) is studied in a magnetized electron–ion (e–i) plasma in the presence of pressure anisotropy with electrons following Tsallis distribution. The Korteweg–de Vries (KdV) type equation is derived by employing the reductive perturbation method (RPM) and its solitary wave (SW) solution is determined and analyzed. The effect of nonextensive parameter q , parallel component of anisotropic ion pressure p 1 , perpendicular component of anisotropic ion pressure p 2 , obliqueness angle θ , and magnetic field strength Ω on the characteristics of SW structures is investigated. The present investigation could be useful in space and astrophysical plasma systems.

In this paper, we examine a steady laminar flow for an incompressible fluid located in a semi porous annular pipe and subjected to a favorable constant pressure gradient applied between the two borders of the pipe. The inner wall is impermeable and the fluid is sucked or injected at the outer wall at constant and uniform velocity, orthogonally to the wall. The problem under study depends on three parameters: the pipe gap ratio, the dimensionless external pressure gradient, and the Reynolds number defined from the sum of the suction or injection velocity and the maximum Hagen–Poiseuille velocity. The conservation of mass induces the zero-divergence velocity field which allows replacing the steady-flow Navier–Stokes equations with a single equation satisfied by the stream function and called the vorticity equation. Assuming the similarity-solution hypothesis, the problem under consideration is reduced to a fourth-order nonlinear ordinary differential equation with two boundary conditions at each wall. The numerical shooting technique including the Runge–Kutta algorithm and the Newton–Raphson optimization method is applied to obtain the solution for the steady flow. For various values of the dimensionless external pressure gradient, the profiles of the velocity components are found and investigations on the wall shear stress for both walls are performed. The results obtained are discussed and physical understandings for the problem studied are derived.

Vortex motion of a cylindrical quantum plasma containing degenerate inertialess electrons and strongly correlated, non-degenerate inertial ions is studied. The electron exchange–correlation and ion–neutral collisional effects are taken into consideration, along with vertical external magnetic field and radial electric field. Considering generalized viscoelastic momentum equation for strongly coupled ions in quasi-crystalline state, variation of different rotational characteristics along radial distance are discussed numerically. Existence of shear rotation is observed near both the core and the periphery of the vortex, which is found to be modified by ion–ion correlation, quantum effects of the degenerate electrons, the ion–neutral collision, as well as by the magnetic field. It is noticed that electron exchange–correlation potential and quantum diffraction play major roles in modifying the rotational characteristics. Vorticity and the rate of increment of enstrophy with respect to radial distance, diminish to zero towards the periphery of the vortex. Also, it is noted that the ion–neutral collision may be responsible for reducing the increment of enstrophy.

Detoxification of water bodies from industrial pollutant dyes by semiconductor heterojunction composites briefed. Synthesis of ZnO/SnS core/shell nanocomposites by ecofriendly hydrothermal method presented. Characterization by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–Vis absorption spectroscopy photoluminescence (PL) etc., were presented. Abundance of orthorhombic ZnO and hexagonal SnS was confirmed by X-ray diffraction. Compression of hexagonal ZnO planes (as core nanorods) and SnS core nanoparticles infers growth of core shell structure. Average crystallite size is found to be 5.8 nm. Structure and TEM morphology correlated. XPS reveals abundance of elemental oxidation state. Photocatalytic activity was studied by using visible light irradiation. Photoluminescence for ZnO/SnS core/shell nanocomposites inferred significant emission peaks. Enhanced PCA observed against visible light. Methylene blue dye characteristic PCAby its degradation evinced. PCA is found optimal for Z-S3. Configuration of bandgap promoted growth of novel hetero junction. Physical mechanism is proposed for the enhanced photocatalytic activity as accompanied by degradation of MB dye.

The dynamic and thermodynamic properties of wurtzite (wz) and zinc-blend (zb) CdS are investigated within the density functional theory using different approximation methods such as LDA, PBE, and DFT+U. Hellmann–Feynman approach is implemented for the relaxation of atomic position for both phases. To guarantee the accuracy of calculation, the convergence test of total energy with respect to energy cutoff and k -point sampling is performed. The dynamic properties such as phonon dispersion, phonon density of state, frequency along with high symmetry points, static and dynamic polarizability, and dielectric constants are calculated. The obtained values are compared with previous theoretical results. DFT + U approximation gives a good result that is consistent with the available theory. Moreover, the vibrational energy, vibrational free energy, entropy, electron chemical potential, and constant-volume specific heat are obtained within LDA, PBE, and DFT + U approximations.

We theoretically studied and optimized the thermal rectification of spherical and cylindrical conductive thermal diodes operating with two phase-change materials (PCMs), whose thermal conductivities significantly changes in a narrow interval of temperatures. This is done by deriving simple analytical expressions for the heat flows, temperature profiles and rectification factors of both diodes. It is shown that diode geometry has a significant impact on the heat flows and temperature profiles, but not so much on the thermal diode rectification factor. Optimal rectification factors of 63.5 and 63.2% are obtained for the spherical and cylindrical thermal diodes operating between the terminals of VO 2 and polyethylene with a temperature difference of 150 K spanning the metal–insulator transition of both PCMs. These similar rectification factors could be enhanced even more with a phase-change material exhibiting higher contrast thermal conductivity than the ones in the present study. The obtained results can thus be useful to guide the development of PCMs capable of optimizing the rectification of conductive heat flows with different geometries.

This paper presents the development of mathematical model to obtain the approximate analytical solutions for isothermal flows behind the strong shock (blast) wave in a van der Waals gas and small solid particles mixture. The small solid particles are continuously distributed in the mixture and the equilibrium conditions for flow are maintained. To derive the analytical solutions, the physical variables such as density, pressure, and velocity are expanded using perturbation method in power series. The solutions are derived in analytical form for first approximation, and for second order approximation the set of differential equations are also obtained. The effects of an increase in the problem parameters value on the physical variables are investigated for first order approximation. A comparison is also, made between the solution of cylindrical shock and spherical shock. It is found that the fluid density and fluid pressure become zero near the point or axis of symmetry in spherical or cylindrical symmetry, respectively, and therefore a vacuum is created near the point or axis of symmetry which is in tremendous conformity with the physical condition in laboratory to generate the shock wave.