Pramana

Entropy generation optimisation in the nanofluid flow of a second grade fluid with nonlinear thermal radiation Abstract The flow of a second grade fluid by a rotating stretched disk is considered. Brownian motion and thermophoresis characterise the nanofluid. Entropy generation in the presence of heat generation / absorption, Joule heating and nonlinear thermal radiation is discussed. Homotopic convergent solutions are developed. The behaviour of velocities (radial, axial, tangential), temperature, entropy generation, Bejan number, Nusselt number, skin friction and concentration is evaluated. The radial, axial and tangential velocities increase for larger viscoelastic parameters while the opposite trend is noted for temperature. Concentration decreases when Schmidt number and Brownian diffusion increase. Entropy generation increases when the Bejan number increase while the opposite is true for the Brinkman number and the magnetic parameter.

Determination of classical behaviour of the Earth for large quantum numbers using quantum guiding equation Abstract For quantum systems, we expect to see the classical behaviour at the limit of large quantum numbers. Hence, we apply Bohmian approach for describing the evolution of Earth around the Sun. We obtain possible trajectories of the Earth system with different initial conditions which converge to a certain stable orbit, known as the Kepler orbit, after a given time. The trajectories are resulted from the guiding equation \(p=\nabla S\) in the Bohmian mechanics, which relates the momentum of the system to the phase part of the wave function. Except at some special situations, Bohmian trajectories are not Newtonian in character. We show that the classic behaviour of the Earth can be interpreted as the consequence of the guiding equation at the limit of large quantum numbers.

Enhancement in heat and mass transfer over a permeable sheet with Newtonian heating effects on nanofluid: Multiple solutions using spectral method and stability analysis Abstract This paper investigates the Newtonian heating effect on nanofluid flow over a nonlinear permeable stretching / shrinking sheet near the region of stagnation point. Only two important mechanisms on the transportation of nanoparticles in base fluid are discussed: the Brownian motion and thermophoresis. This physical problem is modelled using the Buongiorno (ASME J. Heat Transfer 128, 240 (2006) model in terms of nonlinear governing partial differential equations and transformed into dimensionless ordinary differential equations by using similarity transformation and the solution is calculated using the numerical scheme known as the Chebyshev spectral collocation method. The main interest of this study is the region of the boundary layer where viscous effects are dominant. Dual solutions are reported against the shrinking parameter in which the first solution is stable due to positive eigenvalues and the second is unstable due to negative eigenvalues and ranges of these solutions are effected by the suction parameter which is discussed using graphs and tables. The effects of dimensionless parameters, namely, velocity ratio, suction, Schmidt number, Prandtl number, thermophoresis and Brownian motion on temperature and concentration profiles, skin friction coefficient and Nusselt number are also shown using graphs. For the validity of the applied scheme, a comparison is established with published studies in the limiting case. Through the results, it is concluded that temperature and concentration increase by increasing the values of the thermophoresis parameter and the opposite behaviour is observed in the case of Brownian motion and Schmidt number. Skin friction coefficient, Nusselt and Sherwood numbers increase on increasing the suction parameter. Also, an enhancement in temperature and concentration profiles is observed in the presence of Newtonian heating parameter.

Effective optical properties of the one-dimensional periodic structure of $$\hbox {TiO}_{{2}}$$ TiO 2 and $$\hbox {SiO}_{2 }$$ SiO 2 layers with a defect layer of nanocomposite consisting of silver nanoparticle and E7 liquid crystal Abstract In this work, the dielectric property of a nanocomposite (NC) consisting of silver nanoparticle and E7 liquid crystal (LC) has been investigated theoretically at different temperatures. The study shows that the surface plasmon resonance (SPR) and filling fraction of the silver nanoparticle significantly change the dielectric property of the NC. To study the optical property of the defective periodic structure, the NC was considered as a defect layer in a semifinite one-dimensional periodic structure (1DPS) of \(\hbox {TiO}_{{2}}\) and \(\hbox {SiO}_{{2}}\) layers, i.e. ( \(\hbox {TiO}_{{2}}{\vert }\hbox {SiO}_{2})^{5}{\vert }\hbox {NC}{\vert }(\hbox {TiO}_{{2}}{\vert }\hbox {SiO}_{2})^{5}\) . The optical properties of the 1DPS with the NC as the defect layer have been studied by the simple transfer matrix method (TMM). Moreover, the transmission and absorption characteristics of the 1DPS in the presence of silver nanoparticle in the NC have been studied with different orientations of the LC molecule.

The synchronisation of two floating memristor-based oscillators and the circuit design Abstract The synchronisation between two floating memristor-based Colpitts oscillators is studied in this paper. Firstly, the mathematical and circuit models of Colpitts oscillator based on a floating memristor with a diode bridge structure are built. On this basis, numerical simulations on the features of both the independent memristor and the floating memristor are conducted and compared using MATLAB software. Secondly, circuit simulation is made on the synchronisation of two floating memristor-based systems by using MULTISIM software. Finally, the physical circuit on the synchronisation of the two coupling Colpitts systems based on the diode bridge memristors is implemented by using the linear error feedback scheme and improved by the capacitor coupling scheme and the adaptive nonlinear feedback control scheme, respectively. The experimental results by the oscilloscope and simulation results show that approximate synchronisation is achieved.

Excitation performance of  $$\hbox {Ba}_{0.8}\hbox {Mg}_{0.2}(\hbox {Zr}_{0.1}\hbox {Ti}_{0.8}\hbox {Ce}_{0.1})\hbox {O}_{3}$$ Ba 0.8 Mg 0.2 ( Zr 0.1 Ti 0.8 Ce 0.1 ) O 3  materials in an electrical field Abstract Dense and stoichiometric \(\hbox {Ba}_{0.8}\hbox {Mg}_{0.2}(\hbox {Zr}_{0.1}\hbox {Ti}_{0.8}\hbox {Ce}_{0.1})\hbox {O}_{3}\) (BMZTCO) ceramics have been synthesised and their excitation was experimentally evaluated by applying an electric field. The processed sample exhibits superior frequency-independent and temperature-dependent dielectric parameters. The prepared sample has combined the tetragonal and cubic phases of \(\hbox {BaTiO}_{3}\) and \(\hbox {Ce}_{2}\hbox {O}_{3}\) . The Bode plots suggest non-Debye type of relaxation mechanism and positive temperature coefficient-type behaviour. The excitation intensity reaches a peak when the driving frequency matches with the natural frequency of the prepared sample.

Influence of material parameters on the performance of niobium-based superconducting radiofrequency cavities Abstract A detailed thermal analysis of a niobium (Nb)-based superconducting radiofrequency (SRF) cavity in a liquid helium bath is presented, by taking into account the temperature and magnetic field dependence of surface resistance and thermal conductivity in the superconducting state of the starting Nb material (for SRF cavity fabrication) with different impurity levels. The drop in SRF cavity quality factor ( \(Q_{0}\) ) in the high acceleration gradient regime (before the ultimate breakdown of the SRF cavity) is studied in detail. It is argued that the high-field \(Q_0\) -drop in SRF cavity is considerably influenced by the intrinsic material parameters such as electrical conductivity and thermal diffusivity. The detailed analysis reveals that the current specification on the purity of Nb material for SRF cavity fabrication is somewhat overspecified, as also inferred by the experimental work reported by some of the laboratories in the recent past. In line with these encouraging experimental results, in this paper, based on a rigorous calculation, we show that the Nb material with relatively low purity can very well serve the purpose for the accelerators dedicated for spallation neutron source (SNS) or accelerator-driven subcritical system (ADSS) applications, where the required accelerating gradient is typically up to \(20~\hbox {MV m}^{-1}\) . This information will have important implication towards the cost reduction of superconducting technology-based particle accelerators for various applications. We think this theoretical work will be complementary to the experimental efforts performed in various laboratories at different corners of the globe.

Soliton, Wronskian and Grammian solutions to the generalised $$(3+1)$$ ( 3 + 1 ) -dimensional Kadomtsev–Petviashvili equation Abstract In this paper, a generalised \((3+1)\) -dimensional Kadomtsev–Petviashvili (KP) equation is considered. By transforming it into the bilinear form, one-, two- and multisoliton solutions are obtained. What is more, the Wronskian and Grammian solutions are also presented according to the Plücker relation and the Jacobi identity for determinants. In order to have an in-depth understanding of the dynamical properties of the equation, examples of each solution are given and some of them are plotted.

The impact of magnetohydrodynamics and heat transfer on the unsteady flow of Casson fluid in an oscillating cylinder via integral transform: A Caputo–Fabrizio fractional model Abstract Casson fluid flow has numerous functional applications in food processing, metallurgy, drilling and bio-engineering operations. The significance of Casson fluid in cylindrical coordinates has recently attracted researchers because of the numerical and experimental analyses of the fluid. Due to the lack of fractional analytical approaches, this paper is trying to examine the magnetic effect and thermal effect on Casson fluid with oscillatory boundary conditions in cylindrical coordinates. The constitutive model of Casson fluid is solved by using the Caputo–Fabrizio time fractional derivative approach. The fluid moves in the vertical oscillating cylinder under the influence of a transverse applied magnetic field. Closed-form solutions are obtained via integral transforms (Laplace and Hankel transformations) for velocity and temperature distributions. Graphical results are shown for various physical parameters such as the Casson fluid parameter \(\beta \) , magnetic parameter M, Grashoff number Gr, Prandtl number Pr and fractional parameter \(\alpha \) . The corresponding expressions for Nusselt number are also evaluated for various embedded parameters in a tabular form.

Effect of strain on the structural and electronic properties of transition metal-doped arsenene nanoribbons: An ab-initio approach Abstract Recently, arsenene, having a monolayer honeycomb structure of grey arsenic, has been manufactured successfully. Motivated by this, here we have calculated the electronic properties and stability of arsenene by employing the first-principles method for calculations. We have considered two different structures, namely planar and puckered. Based on the analysis, the puckered structure was found to be semiconducting in nature. Additionally, we have estimated the electronic properties of different 3d transition metal (TM) atoms doped in arsenene. Here, straining the nanoribbons also modulates the band gap. It closes the band gap for puckered arsenene under the 8% strain application. Specifically, a 4% strain is considerably sufficient to transform metallic arsenene to a direct band-gap semiconductor. Also, the bond angle between the nearest atoms becomes almost equal. We have observed that Ni-doped arsenene is the most stable. We have also studied the electronic band structures of the pristine and TM-doped antimonene. Planar antimonene is metallic while rhombohedral antimonene is semiconducting. Our results will play vital roles in sensors and various nanoelectronics applications.