Band 76, Heft 3

We propose a simple generalization of axion-electrodynamics (A-ED) for the general case in which both scalar and pseudoscalar axion-like fields are present in the (scalar) Lagrangian of the system. We make some remarks on the problem of finding solutions to the differential equations of motion characterizing the propagation of coupled axion fields and electromagnetic (EM) waves. Our primary goal (which is not explored here) is to understand and predict novel phenomena that have no counterpart in pseudoscalar A-ED. With this end in view, we discuss on very general grounds possible processes related to scalar (and pseudoscalar) axions, e.g., the Primakoff effect; the Compton scattering; and, notably, the EM two-photon axion decay.

The present study uses the theory of weakly nonlinear geometrical acoustics to derive the high-frequency small amplitude asymptotic solution of the one-dimensional quasilinear hyperbolic system of partial differential equations characterizing compressible, unsteady flow with generalized geometry in ideal gas flow with dust particles. The method of multiple time scales is applied to derive the transport equations for the amplitude of resonantly interacting high-frequency waves in a dusty gas. These transport equations are used for the qualitative analysis of nonlinear wave interaction process and self-interaction of nonlinear waves which exist in the system under study. Further, the evolutionary behavior of weak shock waves propagating in ideal gas flow with dust particles is examined here. The progressive wave nature of nonresonant waves terminating into the shock wave and its location is also studied. Further, we analyze the effect of the small solid particles on the propagation of shock wave.

Based on the ferrohydrodynamic theory by R. E. Rosensweig and continuity equation, ferrofluid (FF) lubricated different exponential squeeze film-bearing designs are studied. Since uniform magnetic field does not effect on the performance of the bearing design system, variable form of magnetic field is considered to control FF flow behaviour. Expressions for pressure and load-carrying capacity are obtained by the methods of averaged inertia and regular perturbation. Results for dimensionless load-carrying capacity are calculated and compared. Some comparisons are also made with the previous study. Results show the significant contribution of FF on the designed problem.

Most of the viscoelastic fluids have deformation while flowing over a heated plate. A typical feature of a thin viscous or viscoelastic fluid is the formation of the capillary ridges over locally heated plates. The creation of such ridges in the thin-film surface can affect the smoothness of the coating. This work particularly concerned the flow of non-Newtonian third-grade fluid over an inclined heated plate and the formation of ridges. The conservation laws associated with free surface and wall boundary conditions model the two-dimensional fluid flow. The long wave approximation of the model results in an equation of evolution to explain the structure of free surfaces. The resulting equation is discretized implicitly using the finite volume method. The obtained results are discussed for different flow parameters that affect capillary ridge emergence on the free surface. Variation in the height of capillary ridges of third-grade fluid is compared with the second-grade fluid and Newtonian fluid flow. We observe, the ridge size gets smaller for the third-grade fluid compared to the Newtonian and the second-grade fluid. Our analysis investigates how the third-grade viscoelastic parameters affect the dynamics of the free surface and the size of the capillary ridge concerning temperature changes and other phenomena of interest.

Increasing knowledge of hybrid nanofluid can be traced to its unique improvement of thermal performance and enhancement of heat transfer rate as applicable in the dynamics of fuel and coolant in automobiles. However, the case of water-based nanofluid conveying three kinds of nanoparticles (i.e., ternary-hybrid nanofluid) with various shapes and densities is far-fetched. The transport phenomena of water conveying smaller densities nanoparticles (i.e., copper nanotubes, graphene, and aluminum oxide) and substantial large densities of nanoparticles (i.e., copper oxide, copper, and silver) of various types through a rectangular closed domain with major emphasis on the significance of suction and dual stretching was investigated. The dimensional equation that model the aforementioned transport phenomenon, for the two cases, were non-dimenzionalized using appropriate similarity variables, parameterized, and solved numerically using shooting techniques together with fourth-order Runge-Kutta integration scheme and in-built bvp4c package of MATLAB. Enhancement in suction and stretching ratio causes the vertical velocity of the motion along x -direction and Nusselt number to be an increasing function. Due to an increase in suction and stretching ratio, fluid flow along ( x ,  y )-directions, temperature distribution, and the local skin friction coefficients are decreasing functions. At all the levels of suction and stretching ratio, higher Nusselt numbers were found in the case of water conveying Copper oxide, Copper, and Silver nanoparticles due to their heavy densities.

We have systematically studied the effect of Fe co-doped on electronic and magnetic properties of wurtzite gallium nitride (GaN) based on the framework of density functional theory (DFT). It is found that GaN doped with Fe at Ga site is more stable than that at N-site. We calculate the electronic structure of pure and single Fe doped GaN within GGA and GGA +  U method and find that Fe doped GaN is a magnetic semiconductor with the total magnetization of 5 μ B . The magnetic coupling between Fe spins in Fe-doped GaN is an antiferromagnetic (AFM) under the super-exchange mechanism.

Additive Manufacturing (AM) methods, in the field of production, are increasing rapidly. In particular, the use of Ti alloys has an important role in AM methods. The major disadvantage of AM methods is low surface quality of the manufactured parts. Therefore, parts produced using AM methods need subsequent surface treatment. Electro Discharge Machining (EDM) is one of the nontraditional machining methods, which can be used to improve the surface quality with appropriate parameters. In this study, EDM was investigated to improve the surface quality of sintered Ti–6Al–4V alloy by using 160 different finish parameters. It was observed that Current (I) has a notable effect on surface roughness showing that best surface quality is achieved with low current values, which is under R a  = 2 µm. To estimate the final result of EDM, roughness values obtained from the experiments were modeled by using the Genetic Expression Programming (GEP), and a mathematical relationship between the obtained roughness values and EDM parameters was proposed. As a result of 830,900 iterations, GEP model created can estimate the final surface roughness of the parts with 84% accuracy.

The approximate analytical solution for the propagation of gas ionizing cylindrical blast (shock) wave in a rotational axisymmetric non-ideal gas with azimuthal or axial magnetic field is investigated. The axial and azimuthal components of fluid velocity are taken into consideration and these flow variables, magnetic field in the ambient medium are assumed to be varying according to the power laws with distance from the axis of symmetry. The shock is supposed to be strong one for the ratio C0Vs2${\left(\frac{{C}_{0}}{{V}_{s}}\right)}^{2}$ to be a negligible small quantity, where C 0 is the sound velocity in undisturbed fluid and V S is the shock velocity. In the undisturbed medium the density is assumed to be constant to obtain the similarity solution. The flow variables in power series of C0Vs2${\left(\frac{{C}_{0}}{{V}_{s}}\right)}^{2}$ are expanded to obtain the approximate analytical solutions. The first order and second order approximations to the solutions are discussed with the help of power series expansion. For the first order approximation the analytical solutions are derived. In the flow-field region behind the blast wave the distribution of the flow variables in the case of first order approximation is shown in graphs. It is observed that in the flow field region the quantity J 0 increases with an increase in the value of gas non-idealness parameter or Alfven-Mach number or rotational parameter. Hence, the non-idealness of the gas and the presence of rotation or magnetic field have decaying effect on shock wave.

Thermography is a fully noninvasive technique that discerns the thermal profiles of highly viable rheological parameters in heat and mass transference. In this paper, the free convection flow of viscous fluid among two vertical and parallel plates in the existence of a transverse magnetic field is investigated. The Caputo time-fractional derivative is manipulated for introducing a thermal transport equation along with a weak memory. The analytical and closed-form fractional solution for the temperature and velocity profiles are obtained through Laplace paired in conjunction with the finite Sine-Fourier transforms technique. The solution to the classical model is concluded as a special case for the solutions to the fractional modeled problem when the memory factor (the order of fractional derivative) approaches 1. Also, the solutions are stated in connection with the Mittag–Leffler function. The influences of variations of fractional and material parameters are depicted through MathCad15.