Combined effects of blockage and yield stress on drag and heat transfer from an in-line array of three spheres

This work reports results on the drag and heat transfer from an in-line array of three isothermal spheres falling in a cylindrical confinement filled with Bingham plastic fluids. The effects of dimensionless parameters, such as the Reynolds number (1 ≤ Re?≤?100), Prandtl number (1 ≤ Pr?≤?100), Bingham number (0 ≤ Bn?≤?100), blockage ratio (2 ≤ β?≤?4) and sphere-to-sphere distance (1.5 ≤ t?≤?6) have been elucidated. The flow and heat transfer characteristics were analysed in terms of yielded/unyielded regions, streamline and isotherm contours, drag coefficient, pressure coefficient, and local and average Nusselt number. Broadly, the drag coefficient shows a positive dependence on Bn and sphere-to-sphere distance (t) while it exhibits an inverse dependence on Re and β. On the other hand, the Nusselt number shows a positive dependence on Re, Pr, Bn and β; and a complex dependence on t for each sphere. Simple predictive expressions for the average Nusselt number for each sphere are formulated, thereby enabling its prediction in a new application.     

Jeans Instability of Self Gravitating Dust Cloud in Presence of Effective Electrostatic Pressure

The role of viscosity coefficient (η'), coulomb coupling parameter (Γ) and dust mass on the growth of jeans mode is investigated in strongly coupled dusty plasma using equations of Generalized Hydrodynamics (GH) Model. The novel aspect of this work is that the force arising due to electrostatic pressure caused by grain grain interaction has been included in the dynamics of dust particles. This force is found to play a significant role in counter balancing the self gravity effect, thereby reducing the growth rate of jeans instability. The present work may provide more physical insight in understanding the mechanisms behind formation of planetesimals, stars etc.     

The privileged spectrum of cnoidal ion holes and its extension by imperfect ion trapping

The fundamental properties of nonlinear ion hole modes propagating in current-driven collisionless plasmas are derived. Making use of Schamel's alternative method their spatial structure $?(x)$ and phase velocities $u_0$ are analyzed and found to depend crucially on the used trapped ion distribution $f_{it}$. A regular $f_{it}$ represents a continuous spectrum, which is called privileged or perfect since it yields a definite $u_0$ and appears most realistic. A singular $f_{it}$, on the other hand, involving jumps and moderate slope singularities at the separatrix, does reveal further classes of hole equilibria at the cost, however, of a well-defined $u_0$. This explains why Bernstein, Greene, Kruskal (BGK)-solutions of the Vlasov–Poisson system, exhibiting a strong slope singularity of their derived trapped particle distribution, can principally not provide definite $u_{0}s$. The nonlinear dispersion relation (or $u_0$) of privileged ion holes, on the other hand, is equivalent with that of cnoidal electron holes, i.e. in addition to the ordinary ion acoustic branch there exists a correspondence to the “Langmuir” branch and to the multiple “slow electron acoustic” branches, reflecting different trapping scenarios.     

A conductivity study of polyelectrolytes based on 4-vinyl pyridine and butylmethacrylate

Abstract  In this paper, the chain flexibility of P4-VP was tried to increase by lowering its glass transition temperature (T _g) and by increasing its amorphous region by copolymerizing with butyl methacrylate. The copolymers were prepared in five different feed molar ratios to optimize the required properties such as higher room temperature conductivity and film-forming capacity. The conductivity and conduction behavior of the copolymers, as well as their hydrochloride and hydrobromide salts, have been reported. The copolymers were prepared by solution polymerization technique, using tetrahydrofuran as solvent at 60 °C, and the salts were prepared by simple acidification. The copolymers and their salts were characterized by scanning electron micrographs, infrared, proton nuclear magnetic resonance, thermogravimetric, differential scanning calorimetry and AC impedance measurements. There was about 10³- to 10⁴-fold increase in room temperature conductivity of these plasticized polyelectrolytes. The conduction behavior was found to be predominantly ionic. The scientific importance of this paper is that, unlike polymer electrolytes, no external salt is used; instead the virgin polymer and polyelectrolytes are used for conductivity measurements.     

Optimization of plasma parameters for high rate deposition of titanium nitride films as protective coating on bell-metal by reactive sputtering in cylindrical magnetron device

Nano-structured titanium nitride (TiN) thin film coating is deposited by reactive sputtering in cylindrical magnetron device in argon and nitrogen gas mixtures at low temperature. This method of deposition using DC cylindrical magnetron configuration provides high uniform yield of film coating over large substrate area of different shapes desirous for various technological applications. The influence of nitrogen gas on the properties of TiN thin film as suitable surface protective coating on bell-metal has been studied. Structural morphological study of the deposited thin film carried out by employing X-ray diffraction exhibits a strong (2 0 0) lattice texture corresponding to TiN in single phase. The surface morphology of the film coating is studied using scanning electron microscope and atomic force microscope techniques. The optimized condition for the deposition of good quality TiN film coating is found to be at Ar:N₂ gas partial pressure ratio of 1:1. This coating of TiN serves a dual purpose of providing an anti-corrosive and hard protective layer over the bell-metal surface which is used for various commercial applications. The TiN film's radiant golden colour at proper deposition condition makes it a very suitable candidate for decorative applications.     

Dynamical behaviour of non-linear quantum ion acoustic wave in weakly magnetized electron–positron–ion plasma

In order to investigate the propagation characteristics of linear and non-linear ion acoustic waves (IAWs) in electron–positron–ion quantum plasma in the presence of external weak magnetic field, we have used a quantum hydrodynamic model, and degenerate statistics for the electrons and positrons are taken into account. It is found that the linear dispersion relation of the IAW was modified by the externally applied magnetic field. By using the reductive perturbation technique, a gyration-modified Korteweg-de Vries equation is derived for finite amplitude non-linear IAWs. Time-dependent numerical simulation shows the formation of an oscillating tail in front of the ion acoustic solitons in the presence of a weak magnetic field. It is also seen that the amplitude and width of solitons and oscillating tails are affected by the relevant plasma parameters such as quantum diffraction, positron concentration, and magnetic field. We have performed our analysis by extending it to account for approximate soliton solution by asymptotic perturbation technique and non-linear analysis via a dynamical system approach. The analytical results show the distortion of the shape of the localized soliton with time, and the non-linear analysis confirms the generation of oscillating tails.     

Jeans Instability of Self Gravitating Dust Cloud in Presence of Effective Electrostatic Pressure

The role of viscosity coefficient(η′), coulomb coupling parameter(Γ) and dust mass on the growth of jeans mode is investigated in strongly coupled dusty plasma using equations of Generalized Hydrodynamics(GH) Model. The novel aspect of this work is that the force arising due to electrostatic pressure caused by grain grain interaction has been included in the dynamics of dust particles. This force is found to play a significant role in counter balancing the self gravity effect, thereby reducing the growth rate of jeans instability. The present work may provide more physical insight in understanding the mechanisms behind formation of planetesimals, stars etc.