• Volume 91, Issue 5

November 2018

• Transient entropy analysis of the magnetohydrodynamics flow of a Jeffrey fluid past an isothermal vertical flat plate

This study presents the analysis of entropy generation concept for unsteady magnetohydrodynamics Jeffrey fluid flow over a semi-infinite vertical flat plate. This physical problem is constituted by transient coupled highly nonlinear equations and is evaluated numerically by using an implicit scheme. The average values of wall shear stress and Nusselt number, entropy generation number and Jeffrey fluid-flow variables are analysed for distinct values of physical parameters at both transient and steady states. The results show that the time needed for achieving a steady state pertaining to the temperature and velocity gets augmented with the increased values of Jeffrey fluid parameter. The results also specify that the entropy generation number increases with the increasing values of Jeffrey fluid parameter, group parameter and Grashof number while the opposite trend is seen for the magnetic parameter.

• Numerical approach for stagnation point flow of Sutterby fluid impinging to Cattaneo–Christov heat flux model

The present study examines the stagnation point flow of a non-Newtonian fluid along with the Cattaneo–Christov heat flux model. The coupled system is simplified using suitable similar solutions and solved numerically by incorporating the shooting method with the Runge–Kutta of order five. The motivation is to analyse the heat transfer using an amended form of Fourier law of heat conduction known as the Cattaneo–Christov heat flux model. The influences of significant parameters are taken into the account. The computed results of velocity and temperature profiles are displayed by means of graphs. The notable findings are as follows. The viscous and thermal boundary layer exhibits opposite trends for Reynolds number, Deborah number and power-law index. The shear stress at the wall displays reverse patterns for shear thinning and shear thickening fluids. The Prandtl number contributes to increasing the Nusselt number while the Deborah number of heat flux plays the role of reducing it.

• Investigating pedestrian evacuation using ant algorithms

Ants communicate with each other by depositing a chemical called pheromone on the substrate while they crawl forward. By this way, they follow their predecessor and large trail systems are built. Inspired by the communication via chemical signals of ants, we have proposed a model to investigate the collective motion in humans during an emergency. It is considered that pedestrians use some kind of virtual chemotaxis to find the shortest way to the exit. This basic idea is implemented with the floor field model which is the most popular cellular automata model. The dependence of the evacuation from a room on the virtual chemotaxis evaporating rate $f$ and the presence of the obstacle are investigated in this paper. The simulation results show that the increase in evaporation rate has been seen to slow down the evacuation. Moreover, it is found that positioning the obstacles in the room could lead to the phase transitions and decrease the evacuation time.

• Impact of autocatalysis chemical reaction on nonlinear radiative heat transfer of unsteady three-dimensional Eyring–Powell magneto-nanofluid flow

The pursuit of superior working liquids for heat/mass transfer mechanisms in engineering is on the rise, not only to maximise revenue but also to accommodate heat dissipation or chemical separation under extreme conditions. The addition of a small amount of nanoparticle, i.e. a product called nanofluid, has been initiated over the last decade. In this paper, we present a comprehensive study of unsteady three-dimensional (3D) flow of the Eyring–Powell nanofluid under convective and nanoparticles mass flux conditions. The effects of constructive/destructivechemical reactions and nonlinear thermal radiation are also considered in the Eyring–Powell nanofluid model. Additionally, suitable transformations are utilised to obtain coupled ordinary differential equations (ODEs) from the system of partial differential equations (PDEs) and the numerical solution of the system of the coupled ODEs is obtained by means of the bvp4c scheme. The obtained numerical data are plotted for the temperature and concentration profiles of nanofluids for various and converging values of physical parameters. Our findings demonstrate that the temperature of the Eyring–Powell nanofluid fall-off by changing the heat sink parameter. Furthermore, it is perceived from the sketches that the concentration of Eyring–Powell magneto-nanofluid decays at higher values of chemical reaction parameter.

• Permeability of hydrogen in two-dimensional graphene and hexagonal boron nitride sheets

We study the permeability of atomic hydrogen in monolayer hexagonal boron nitride (h-BN) and graphene using first-principles density functional theory-based simulations. For the specific cases of physisorptionand chemisorption, barrier heights are calculated using the nudged elastic band approach. We find that the barrier potential for physisorption through the ring is lower for graphene than for h-BN. In the case of chemisorption, we have studied three specific cases where the H atom passes through by making bonds with the atoms at different sites in the ring. The chemisorption barrier height for graphene is found to be, in general, higher than that of h-BN. We conclude that the dominant mechanism of tunnelling through the graphene sheet and h-BN sheets would be physisorption and chemisorption, respectively.

• Performance improvement of organic light emitting diode using 4,4'-N,N'-dicarbazole-biphenyl (CBP) layer over fluorine-doped tin oxide (FTO) surface with doped light emitting region

In this study, high performance of organic light emitting diodes (OLEDs) with a buffer layer of dicarbazole-biphenyl (CBP) film is demonstrated. With an optimal thickness of CBP (12 nm), the luminance efficiency of OLED is found to increase compared to the single-layer anode OLED. To study the performance of OLED using the buffer layer, we deposited CBP films of different thicknesses on the fluorine-doped tin oxide (FTO) surface and observed their $J–V$ and $L–V$ characteristics. Further analysis was carried out by making the host–guest combination within the light emitting region using iridium (III) complexes $\rm{(Ir(ppy)_{3})}$ as the dopant material to enhance the efficiency of the device. We also measure the sheet resistance, optical transmittance and surface morphology of both the single and bilayer electrode surfaces using the FE-SEM images. Here the maximum value of current efficiency is found to be 12.45 cd/A under optimised doped and quantum tunnelling conditions.

• Design and study on square lattice-based photonic crystal fibre under different air holes for supercontinuum generation

In this work, a comparative study is made on photonic crystal fibre (PCF) with circular and elliptical air holes in square lattice for supercontinuum generation. Using finite-element method analysis in COMSOL MULTIPHYSICS 4.3b software, numerical investigation on optical parameters such as dispersion, confinement loss, birefringence and nonlinearity has been carried out. Change in each optical parameter is observed by varying the radius of the circular air hole and the radius of the major axis of the elliptical air hole. The supercontinuum generation for the proposed PCF is also numerically simulated and studied under different power and pulse width.

• Solitary wave solutions for some nonlinear time-fractional partial differential equations

In this work, we have considered the Riccati–Bernoulli sub-ODE method for obtaining the exact solutions of nonlinear fractional-order differential equations. The fractional derivatives are described in Jumarie’smodified Riemann–Liouville sense. The space–time fractional modified equal width (mEW) equation and timefractional generalised Hirota–Satsuma coupled Korteweg–de Vries (KdV) equations are considered for illustrating the effectiveness of the algorithm. It has been observed that all exact solutions obtained in this paper verify the nonlinear ordinary differential equations (ODEs), which were obtained from the nonlinear fractional-order differential equations under the terms of wave transformation relationship. The obtained results are shown graphically.

• Computational soliton solutions to (3 + 1)-dimensional generalised Kadomtsev–Petviashvili and (2 + 1)-dimensional Gardner–Kadomtsev–Petviashvili models and their applications

In this paper, the auxiliary equation method is successfully applied to compute analytical solutions for (3+1)-dimensional generalised Kadomtsev–Petviashvili and (2+1)-dimensional Gardner–Kadomtsev–Petviashvili equations, by introducing simple transformations. These results hold numerous travelling wave solutions that areof key importance which provide a powerful mathematical tool for solving nonlinear wave equations in recent era of applied science and engineering. The method can also be extended to other nonlinear evolution models arisingin contemporary physics.

• Passivity analysis of coupled inertial neural networks with time-varying delays and impulsive effects

This paper is devoted to the passivity analysis of an array model for coupled inertial delayed neural networks (NNs) with impulses under different network structures, namely directed and undirected topologies. Firstly, utilising the information of eigenvectors for the directed coupling matrix, a new Lyapunov functional is constructed, by which, together with the aid of some inequality techniques and network characteristics, the two sets of sufficient criteria are established to, respectively, guarantee the strictly input passivity and strictly output passivity of the impulsive network with directed coupling. Secondly, benefited from the properties of the undirectedcoupling matrix, some more concise conditions that are easier to be verified for the passivities of the undirected coupled network accompanied by impulsive effects are proposed. Finally, two numerical examples are designed to execute the verification of the derived theoretical results.

• Systematic study of rigid triaxiality in Ba–Pt nuclei and role of Z = 64 subshell effect

A systematic variation of shape variables $\beta$ and $\gamma$ with $N$ and $N_{p}N_{n}$ is studied in the framework of an asymmetric rotor model of Davydov and Filippov for the Z =50–82, N =82–126 major shell space. The role of the Z = 64 subshell in producing smooth systematics has been discussed. The quadrupole moments are extracted after considering both axially symmetric and axially asymmetric nuclei. The correlation of $\beta$ with $\gamma$ together with the measured quadrupole moments indicates that $\gamma$ -rigidity is better observed in nuclei with modest deformation.

• Thermal transport of rate-type fluid impinging obliquely over a heated sheet

The main objective of this study is to examine the two-dimensional (2D) oblique Oldroyd-B flow on a stretching heated sheet. The flow governing problem is converted into nonlinear ordinary differential equations through proper scaling transformations. The prevailing set of equations is solved computationally with a tolerance level of $10^{−5}$. The velocity and temperature of a fluid model under consideration are portrayed to discuss the influence of all associated parameters on momentum and thermal characteristics. Heat flux at the wall has been computed numerically and analysed in a physical manner. The results obtained depict a reversed flow region for non-positive values of shear flow components once a free parameter is varied. It is noticed that heat transfer at the wall drops due to a rise in Deborah number $\beta_{1}$ as well as Biot number Bi.

• Non-smooth bursting analysis of a Filippov-type system with multiple-frequency excitations

The main purpose of this paper is to explore the patterns of the bursting oscillations and the non-smooth dynamical behaviours in a Filippov-type system which possesses parametric and external periodic excitations.We take a coupled system consisting of Duffing and Van der Pol oscillators as an example. Owing to the existence of an order gap between the exciting frequency and the natural one, we can regard a single periodic excitation as a slow-varying parameter, and the other periodic excitations can be transformed as functions of the slow-varying parameter when the exciting frequency is far less than the natural one. By analysing the subsystems, we derive equilibrium branches and related bifurcations with the variation of the slow-varying parameter. Even though the equilibrium branches with two different frequencies of the parametric excitation have a similar structure, the tortuousness of the equilibrium branches is diverse, and the number of extremepoints is changed from 6 to 10. Overlying the equilibrium branches with the transformed phase portrait and employing the evolutionary process of the limit cycle induced by the Hopf bifurcation, the critical conditionsof the homoclinic bifurcation and multisliding bifurcation are derived. Numerical simulation verifies the results well.

• # Pramana – Journal of Physics

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November 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019