الفهرس | Only 14 pages are availabe for public view |
Abstract In this thesis, we have studied the propagation of ion acoustic solitary waves in relativistic degenerate electron-ion plasmas. Also nonlinear electromagnetic waves in a degenerate electron-positron plasma are investigated. Moreover, study of higher-order corrections to nonlinear dust-ion-acoustic shock waves in a degenerate dense space plasma is done. In chapter 2, a reductive perturbation technique (RPT) is employed, a rigorous study of ion acoustic solitary waves (IASWs) in dense electron-ion (EI) plasmas is carried out leading to two evolution equations. These equations are Korteweg-de Vries (KdV) and KdV type equations. Both of nonrelativistic and ultrarelativistic degenerate electrons cases are considered. The higher-order contributions of nonlinear and dispersion terms are calculated. Stationary solutions of the derived evolution equations are estimated. Two different applications; one is for hydrogen (H⁺) and the other is for singly charged helium (He⁺) ions, which are the main components of dense astrophysical objects (white dwarf stars), are analyzed. It is found that the relativistic parameter, R₀, affects on the IASW phase velocity. The higher-order corrections are included in ultrarelativistic electrons; where it affects on both the amplitude and the shape of the produced solitary waves. The plasma model with He⁺ ions has larger amplitude and wider width compared to H⁺ case. These findings are devoted for explaining the observed solitary waves propagating in the outer periphery of compact dense stars which mostly consist of hydrogen and helium ions with degenerate electrons. In chapter 3, the nonlinear propagation of magnetosonic solitary waves in an ultracold, degenerate (extremely dense) electron-positron (EP) plasma (containing ultracold, degenerate electron and positron fluids) is investigated also using a RPT. The set of basic equations is reduced to KdV equation for the lowest-order perturbed magnetic field and to a KdV type equation for the higher-order perturbed magnetic field. The solutions of these evolution equations are obtained. For a better accuracy and searching on new features, the new solutions are analyzed numerically based on compact objects (white dwarf) parameters. It is found that including the higher-order corrections results as a reduction (increment) of the fast (slow) electromagnetic wave amplitude but its width is increased in both cases.The ranges where the RPT can describe adequately the total magnetic field including different conditions are discussed. In chapter 4, a RPT is also used to study the contribution of higher-order nonlinearity and dissipation to nonlinear dust ion acoustic (DIA) shock waves in three-component degenerate dense space plasma. The model consists of degenerate electron (being either ultrarelativistic or nonrelativistic), nonrelativistic ion fluid and stationary heavy dust grains. A nonlinear Burger equation and a linear inhomogeneous Burger-type equation are derived. The present model admits only compressive DIA shocks. Including these higher-order corrections results in creating new solitary wave structures that we call ”humped DIA shock” waves. For the case of ultrarelativistic (nonrelativistic) electrons, one (two) humped DIA shock is (are) created. The DIA shock wave amplitude and velocity are larger in case of ultrarelativistic electrons than that of nonrelativistic electrons. It is shown that the effects of kinematic viscosity, heavy dust grains number density, and equilibrium ion number density have important roles on the basic features of the produced DIA shocks and the associated electric fields. The implications of our results to dense plasmas in astrophysical objects (e.g., non-rotating white dwarf stars) are discussed. Due to introducing the higher-order nonlinear and dispersion corrections, the produced IASW solitons and DIA shocks are changed. It was found that the present findings due to incorporating these higher-order corrections show. |