الفهرس 
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Abstract
In this thesis, the formation and properties of some nonlinear waves have been carried out for two different systems of plasma. In the first one, the formation and properties of one dimensional nonlinear electron acoustic rogue waves in an unmagnetized collisionless four-component plasma system consisting of a cold electron fluid, hot electrons obeying two different distributions namely, Maxwellian and non-thermal distributions, beam electrons and stationary ions have been obtained and investigated. Employing the modified reductive perturbation theory, the basic set of fluid equations is reduced to a nonlinear Schrödinger equation. As a result, the nonlinear electron acoustic rogue waves are obtained. Also, the dependence of rogue wave profiles on the carrier wave number, ratio of hot electron density to cold electron density, ratio of beam electron density to cold electron density, ratio of hot electron temperature to cold electron temperature and the ratio of hot electron temperature to beam electron temperature are discussed. The conditions for existence rogue waves and envelope structures are obtained. The advantage of using these conditions is that one can determine the instability regimes of the plasma that depend crucially on the plasma parameters. In the second plasma system, the formation and properties of two dimensional electron acoustic solitary and shock waves in a homogeneous system of unmagnetized collisionless plasma consisted of a cold electron fluid, hot electrons and stationary ions have been investigated. Using the standard reductive perturbation technique, the basic set of equations is reduced to the Kadomtsev-Petviashvili-Burgers (KP-Burgers) equation. Without solving the KP-Burgers equation explicitly, the bifurcation analysis is considered to recognize different classes of solutions. In the absence of kinematic viscosity, the predicted solutions are related to soliton, periodic, explosive and breaking waves whereas in the presence of kinematic viscosity, two different mathematical approaches namely, tangent hyperbolic (tanh) method and EXP-function method are considered. First, the tangent hyperbolic (tanh) method is applied in the case of superthermal hot electron distribution and the obtained solution represents a combination between shock and soliton waves solutions. Second, the EXP-function method has been used in case of q-nonextensive hot electrons distribution and yields wide classes of solutions than those obtained by tangent hyperbolic method. The obtained solutions are related to explosive, periodic and soliton solutions and in addition, the shock and breaking wave solutions and their behavior have been discussed.