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[en] Ion-acoustic nonlinear periodic waves, namely, ion-acoustic cnoidal waves have been studied in electron-positron-ion plasma. Using reductive perturbation method and appropriate boundary condition for nonlinear periodic waves, the Korteweg-de Vries (KdV) equation is derived for the system. The cnoidal wave solution of the KdV equation is discussed in detail. It is found that the frequency of the cnoidal wave is a function of its amplitude. It is also found that the positron concentration modifies the properties of the ion-acoustic cnoidal waves. The existence regions for ion-acoustic cnoidal wave in the parameters space (p,σ), where p and σ are the positron concentration and temperature ratio of electron to positron, are discussed in detail. In the limiting case these ion-acoustic cnoidal waves reduce to the ion-acoustic soliton solutions. The effect of other parameters on the characteristics of the nonlinear periodic waves is also discussed.
[en] Ion–acoustic solitons in a warm positive and negative ion species with different masses, concentrations, and charge states with two electron temperature distributions are studied. Using reductive perturbation method, Korteweg de-Vries (KdV) and modified-KdV (m-KdV) equations are derived for the system. The soliton solution of the KdV and m-KdV equations is discussed in detail. It is found that if the ions have finite temperatures, then there exist two types of modes, namely slow and fast ion-acoustic modes. It is also investigated that the parameter determining the nature of soliton (i.e., whether the system will support compressive or rarefactive solitons) is different for slow and fast modes. For the slow mode, the parameter is the relative temperature of the two ion species; whereas for the fast mode, it is the relative concentration of the two ion species. At a critical concentration of negative ions, both compressive and rarefactive solitons coexist. The amplitude and width of the solitons are discussed in detail at critical concentration for m-KdV solitons. The effect of the relative temperature of the two-electron and cold-electron concentration on the characteristics of the solitons are also discussed.
[en] Ion-acoustic double layers has been studied in multicomponent plasma with positrons. Using the reductive perturbation method, the modified Korteweg-de Vries (mKdV) equation is derived for the system. The double-layer solution of the mKdV equation is discussed in detail. It is found that there exist two critical concentrations of positrons, αR and αQ, which decide the existence and nature of the ion-acoustic double layers. It is also found that the system supports ion-acoustic double layers only when the positron concentration (α) is less than the critical concentration αR (i.e., α<αR). It is also investigated that for the given set of parameter values, if αR<αQ, the system supports only rarefactive double layers for the values of α lying in the range 0<α<αR. However, for the given set of parameter values αR>αQ, the system supports rarefactive double layers for α<αQ, and for α>αQ, compressive double layers exist. The present theory also predicts that for a given set of parameter values on increasing the positron concentration, the amplitude of the rarefactive (compressive) double layer decreases (increases), whereas as positron concentration is increased, the width of the rarefactive (compressive) double layer increases (decreases). The effects of positron concentration and temperature ratio on the characteristics of the double layers (namely amplitude and width) are discussed in detail
[en] It is experimentally demonstrated that a relatively strong ion-rich sheath formed at a fixed negative bias of the grid can be changed to a rather weak ion sheath (sheath potential weakly retards electrons) only by increasing the discharge voltage in the system. At sufficiently high negative grid bias, an increase of discharge voltage enhances the ion collection current at the grid. An explanation is put forward in support of this experimental observation. A slight density enhancement with a fall in plasma electron temperature is also observed with the increasing negative grid bias
[en] In this paper, the effects of viscous and Ohmic heating and heat genera-tion/absorption on magnetohydrodynamic flow of an electrically conducting Casson thin film fluid over an unsteady horizontal stretching sheet in a non-Darcy porous medium are investigated. The fluid is assumed to slip along the boundary of the sheet. Similar-ity transformation is used to translate the governing partial differential equations into ordinary differential equations. A shooting technique in conjunction with the 4th order Runge-Kutta method is used to solve the transformed equations. Computations are car-ried out for velocity and temperature of the fluid thin film along with local skin friction coefficient and local Nusselt number for a range of values of pertinent flow parameters. It is observed that the Casson parameter has the ability to enhance free surface velocity and film thickness, whereas the Forchheimer parameter, which is responsible for the inertial drag has an adverse effect on the fluid velocity inside the film. The velocity slip along the boundary tends to decrease the fluid velocity. This investigation has various applications in engineering and in practical problems such as very large scale integration (VLSI) of electronic chips and film coating.
[en] It is shown that plasma parameters, such as the electron density, electron temperature, and plasma potential, in multidipole discharge plasma can be controlled by a negatively biased movable metal plate. Here, plasma is produced in the target region by a flux of energetic electrons coming from the source region of a double plasma device. Further, the thickness of the ion sheath formed in front of the biased metal plate varies depending on its axial position inside the cage.
[en] This paper examines the small-scale solar wind turbulence driven in view of the Alfvén waves subjected to ponderomotive nonlinearity. Filamentation instability is known to take place for the case of dispersive Alfvén wave (DAW) propagating parallel to the ambient magnetic field. The ponderomotive force associated with DAW is responsible for wave localization and these webs of filaments become more intense and irregular as one proceeds along the spatial domain. The ponderomotive force associated with pump changes with pump parameters giving rise to different evolution patterns. This paper studies in detail the nonlinear evolution of filamentation instability introduced by dispersive Alfven waves (DAWs) which becomes dispersive on account of the finite frequency of DAW i.e., pump frequency is comparable to the ion cyclotron frequency. We have explicitly obtained the perturbation dynamics and then examined the impact of pump magnitude on the driven magnetic turbulence using numerical simulation. The results show steepening at small scales with increasing pump amplitude. The compressibility associated with acoustic fluctuations may explain the variation in spectral scaling of solar wind turbulence as observed by Alexandrova et al. (Astrophys. J. 674:1157, 2008).
[en] Characteristics of ion-acoustic soliton in dusty plasma, including the dynamics of heavily charged massive dust grains, are investigated following the Sagdeev Potential formalism. Retaining fourth order nonlinearities of electric potential in the expansion of the Sagdeev Potential in the energy equation for a pseudo particle and integrating the resulting energy equation, large amplitude soliton solution is determined. Variation of amplitude (A), half width (W) at half maxima and the product P = AW2 of the Korteweg-deVries (KdV), dressed and large amplitude soliton as a function of wide range of dust concentration are numerically studied for recently observed parameters of dusty plasmas. We have also presented the region of existence of large amplitude ion-acoustic soliton in the dusty plasma by analyzing the structure of the pseudo potential. It is found that in the presence of positively charged dust grains, system supports only compressive solitons, on the other hand, in the presence of negatively charged dust grains, the system supports compressive solitons up to certain critical concentration of dust grains and above this critical concentration, the system can support rarefactive solitons also. The effects of dust concentration, charge, and mass of the dust grains, on the characteristics of KdV, dressed and large amplitude the soliton, i.e., amplitude (A), half width at half maxima (W), and product of amplitude (A) and half width at half maxima (P = AW2), are discussed in detail
[en] Using reductive perturbation method with appropriate boundary conditions, coupled evolution equations for first and second order potentials are derived for ion-acoustic waves in a collisionless, un-magnetized plasma consisting of hot isothermal electrons, cold ions, and massive mobile charged dust grains. The boundary conditions give rise to renormalization term, which enable us to eliminate secular contribution in higher order terms. Determining the non secular solution of these coupled equations, expressions for wave phase velocity and averaged non-linear ion flux associated with ion-acoustic cnoidal wave are obtained. Variation of the wave phase velocity and averaged non-linear ion flux as a function of modulus (k2) dependent wave amplitude are numerically examined for different values of dust concentration, charge on dust grains, and mass ratio of dust grains with plasma ions. It is found that for a given amplitude, the presence of positively (negatively) charged dust grains in plasma decreases (increases) the wave phase velocity. This behavior is more pronounced with increase in dust concentrations or increase in charge on dust grains or decrease in mass ratio of dust grains. The averaged non-linear ion flux associated with wave is positive (negative) for negatively (positively) charged dust grains in the plasma and increases (decreases) with modulus (k2) dependent wave amplitude. For given amplitude, it increases (decreases) as dust concentration or charge of negatively (positively) charged dust grains increases in the plasma.
[en] A theoretical study of mixed convection stagnation point flow towards a stretching surface is presented. The governing boundary layer equations are transformed into a set of highly nonlinear ordinary differential equations using suitable similarity transforms. The semi-analytical solution is obtained using optimal homotopy analysis method (OHAM) and the numerical solution is obtained via finite element method (FEM). Solutions obtained via two different approaches are in excellent agreement, which validates the accuracy of present analysis. In a special case, the present OHAM solution is also validated with the earlier available results. Effect of pertinent flow parameters on the skin friction coefficient and Nusselt number is presented in tabular form, whereas the velocity, temperature and nanoparticle distribution are presented in graphical forms. Further, a quadratic multiple regression analysis on numeric data of skin friction coefficient and Nusselt number is performed. The findings suggest that velocity slip assists the fluid motion in presence of buoyancy forces, whereas it exhibits a retarding nature on fluid motion when no buoyancy forces exist.