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1.
Korteweg-de-Vries-Burger (K-dVB) equation is derived for ion acoustic shock waves in electron-positron-ion plasmas. Electrons and positrons are considered superthermal and are effectively modeled by a kappa distribution in which ions are as cold fluid. The analytical traveling wave solutions of the K-dVB equation investigated, through the (G′/G)-expansion method. These traveling wave solutions are expressed by hyperbolic function, trigonometric functions are rational functions. When the parameters are taken special values, the shock waves are derived from the traveling waves. It is observed that the amplitude ion acoustic shock waves increase as spectral index κ and kinematic viscosity η i,0 increases in which with increasing positron density β and electron temperature σ the shock amplitude decreases. Also, numerically the effect different parameters on the nonlinearity A and dispersive B terms and wave velocity V investigated.  相似文献   

2.
Ion acoustic shock waves (IASWs) are studied in a plasma consisting of electrons, positrons and ions. Boltzmann distributed positrons and superthermal electrons are considered in the plasma. The dissipation is taken into account the kinematic viscosity among the plasma constituents. The Korteweg–de Vries–Burgers (KdV–Burgers) equation is derived by reductive perturbation method. Shock waves are solutions of KdV–Burgers equation. It is observed that an increasing positron concentration decreases the amplitude of the waves. Furthermore, in the existence of the kinematic viscosity among the plasma, the shock wave structure appears. The effects of ion kinematic viscosity (η 0) and the superthermal parameter (k) on the ion acoustic waves are found.  相似文献   

3.
The nonlinear wave structures of ion acoustic waves (IAWs) in an unmagnetized plasma consisting of nonextensive electrons and thermal positrons are studied in bounded nonplanar geometry. Using reductive perturbation technique we have derived cylindrical and spherical Korteweg-de Vries-Burgers’ (KdVB) equations for IAWs. The presence of nonextensive q-distributed electrons is shown to influence the solitary and shock waves. Furthermore, in the existence of ion kinematic viscosity, the shock wave structure appears. Also, the effects of nonextensivity of electrons, ion kinematic viscosities, positron concentration on the properties of ion acoustic shock waves (IASWs) are discussed in nonplanar geometry. It is found that both compressive and rarefactive type solitons or shock waves are obtained depending on the plasma parameter.  相似文献   

4.
Bianchi Type I magnetized string cosmological model following the techniques used by Letelier and Stachel, is investigated. To get a determinate model, we assume a condition ∊ = λ (geometric string) where ∊ is the rest energy density, λ the string tension density and expansion (θ) is proportional to eigen value σ1 1 of shear tensor (σ j i ), which leads to A = ℓ (BC) n where A, B, C are metric potentials and ℓ and n are constants. The behaviour of the model in presence and absence of magnetic field is discussed. The physical and geometrical aspects of the model are also discussed.  相似文献   

5.
The nonlinear ion-acoustic double layers (IADLs) in a warm magnetoplasma with positive-negative ions and nonthermal electrons are investigated. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density distribution, and the Poisson equation are used to derive a modified Zakharov–Kuznetsov (MZK) equation, in the small amplitude regime. It is found that compressive and rarefactive IADLs strongly depend on the mass and density ratios of the negative-to-positive ions as well as the nonthermal electron parameter. Also, it is shown that there are one critical value for the density ratio of the negative-to-positive ions (ν), the ratio between unperturbed electron-to-positive ion density (μ), and the nonthermal electron parameter (β), which decide the existence of positive and negative IADLs. The present study is applied to examine the small amplitude nonlinear IADL excitations for the (H+, O2-)(\mathrm{H}^{+}, \mathrm{O}_{2}^{-}) and (H+,H−) plasmas, where they are found in the D- and F-regions of the Earth’s ionosphere. This investigation should be helpful in understanding the salient features of the nonlinear IADLs in either space or laboratory plasmas where two distinct groups of ions and non-Boltzmann distributed electrons are present.  相似文献   

6.
Nonlinear cylindrical fast magnetoacoustic waves are investigated in a dissipative magnetoplasma comprising of electrons, positrons, and ions. In this regard, cylindrical Kadomtsev-Petviashvili-Burgers (CKPB) equation is derived using the small amplitude perturbation expansion method. Furthermore, cylindrical Burgers-Kadomtsev-Petviashvili (Cyl Burgers-KP) for a fast magnetoacoustic wave is derived, for the first time, for spatial scales larger than the electron/positron skin depths, c/ω p(e,p). Using the tangent hyperbolic method, the solutions of both planar KPB and Burgers-KP equations are obtained and then subsequently used as an initial profile to solve their respective counterparts in the cylindrical geometry. The effect of positron concentration, kinematic viscosity, and plasma β are explored both for the KPB and the Burgers-KP shock waves and the differences between the two are highlighted. The temporal evolution of the cylindrical fast magnetoacoustic wave is also numerically investigated. The present study may be beneficial to study the propagation characteristics of nonlinear electromagnetic shock waves in planetary magnetospheres.  相似文献   

7.
Korteweg-de Vries (KdV) equation for electrostatic ion acoustic wave in a three component plasma containing positive and negative ions along with the nonextensive electrons is derived. Fast and slow ion acoustic modes which propagate with different velocities are excited. The effects of variation of quantities like q (nonextensive parameter), Q (mass ratio of positive to negative ion), μ (electron to positive ion number density ratio), θ i (positive ion to electron temperature ratio) and θ n (negative ion to electron temperature ratio) have been presented for fast and slow ion acoustic modes. Both compressive and rarefactive solitons are observed. It is found that the solitary excitations strongly depend on the mass and density ratios of the positive and negative ions as well as on nonextensive electron parameter.  相似文献   

8.
A rigorous theoretical investigation of nonlinear electron-acoustic (EA) waves in a plasma system (containing cold electrons, hot electrons obeying a Boltzmann distribution, and hot ions obeying a nonthermal distribution) is studied by the reductive perturbation method. The modified Gardner (MG) equation is derived and numerically solved. It has been found that the basic characteristics of the EA Gardner solitons (GSs), which are shown to exist for α around its critical value α c [where α is the nonthermal parameter, α c is the value of α corresponding to the vanishing of the nonlinear coefficient of the Korteweg-de Vries (K-dV) equation, e.g. α c ≃0.31 for μ=n h0/n i0=0.5, σ=T h /T i =10, n h0, n i0 are, respectively, hot electron and nonthermal ion number densities at equilibrium, T h (T i ) is the hot electron (ion) temperature], are different from those of the K-dV solitons, which do not exist for α around α c , and mixed K-dV solitons, which are valid around α∼α c , but do not have any corresponding double layers (DLs) solution. The parametric regimes for the existence of the DLs, which are found to be associated with positive potential, are obtained. The present investigations can be observed in various space plasma environments (viz. the geomagnetic tail, the auroral regions, the cusp of the terrestrial magnetosphere, etc.).  相似文献   

9.
Bianchi Type I string dust cosmological models in presence and absence of magnetic field following the techniques used by Letelier and Stachel, are investigated. To get the deterministic solution, we have assumed that σ 11 is proportional to the expansion (θ) where σ 11 is the eigen value of shear tensor (σ i j ) and which leads to A=N(BC)−n , n>0 where A,B,C are metric potentials and , N and ℓ are constants. The behaviour of the models in presence and absence of magnetic field are discussed. The other physical and geometrical aspects of the model are also discussed.  相似文献   

10.
A rigorous theoretical investigation on the characteristics of dust-ion-acoustic (DIA) shock waves in an unmagnetized multi component electron-positron-ion dusty plasma (consisting of inertial ions, electrons of two distinct temperatures referred to as low and high temperature superthermal electrons where superthermality is introduced via the κ-type of nonthermal distribution, Boltzmann distributed positrons, and negatively charged immobile dust grains) has been made both theoretically and analytically. The hydrodynamic equation for inertial ions has been used to derive the Burgers equation. The influence of superthermal electrons, Maxwellian positrons and ion kinematic viscosity, which are found in this investigation, significantly modify the basic features of DIA shock waves, are briefly discussed. The present investigation can be very effective for studying and understanding the basic characteristics of shock wave propagation through different astrophysical situations where distinct temperature superthermal electrons dominate the wave dynamics.  相似文献   

11.
We estimate the values of the cosmological parameters using the data about peculiar velocities of 1493 flat edge-on spirals from the RFGC catalogue. The obtained values Ω m = 0.21− 0.09 + 0.22, σ8 = 1.07− 0.24 + 0.28 differ from the WMAP values by approximately 2–3σ, but well agree with modern constraints on these parameters. Due to a strong correlation between these quantities the shape of the 1σ, 2σ and 3σ-boundaries are rather narrow. This gives us the opportunity to use this estimation to verify the corresponding values, obtained by different methods.  相似文献   

12.
The nonlinear propagation of ion acoustic shock waves (IASWs) are studied in an unmagnetized plasma consisting of nonthermal electrons, nonthermal positrons, and singly charged adiabatically hot positive ions, whose dynamics is governed by the two dimensional nonplanar Kadomstev-Petviashvili-Burgers (KPB) equation. The shock solution of the KPB equations is obtained numerically. The effects of several parameters and ion kinematic viscosities on the properties of ion acoustic shock waves are discussed in planar and nonplanar geometry. It is shown that the ion acoustic shock wave propagating in cylindrical/spherical geometry with transverse perturbation will be deformed as time goes on. Also, it is seen that the strength and the steepness of the IASWs increases with increasing β, the nonthermal parameter.  相似文献   

13.
A series of solar cm-radio bursts are analyzed by a new inverse method estimating spatial changes of the superthermal electron distribution in solar cm-radio burst sources. It is found that the measure of the spatial change of superthermal electrons in the radio source ν n is always greater than that for the magnetic field ν B and it is linearly dependent on the spectral index of the electrons δ as ν n ≈0.5δ. This relation is explained in the simplified flare-loop model integrating the analytical solutions of the Fokker – Planck equation. The mean value of ν B is found to be 0.36±0.04, which is very close to the value of ν B =0.38±0.02 derived from the dependence of the magnetic field strength on the height in the active region measured by RATAN-600.  相似文献   

14.
A theoretical model is presented to investigate the existence, formation, and possible realization of nonlinear envelope ion acoustic solitary waves which accompany collisionless electron-positron-ion plasmas with high-energy electrons and positrons (represented by kappa distribution). By employing the reductive perturbation method, the hydrodynamic model and the Poisson equation are reduced to nonlinear Schr?dinger equation. The effects of the superthermal parameters, as well as ion-to-electron temperature ratio on the propagation and stability of the envelope solitary waves are examined. The superthermal parameters (ion-to-electron temperature ratio) give rise to instability (stability) of the solitary excitations, since the instability window is strongly modified. Finally, the present results should elucidate the excitation of the nonlinear ion-acoustic solitary wave packets in superthermal electron-positron-ion plasmas, particularly in interstellar medium.  相似文献   

15.
We present the condition of vanishing shear in a spatially homogeneous spacetime in terms of the Ricci rotation co-efficients corresponding to an orthonormal tetrad (ν α. A η α) (whereν α is the unit vector along the time axis and A η α are the three independent reciprocal group vectors). Assuming that the velocity vector can be expanded in the direction ofν α and any one of the A η α’s it is shown that shear-free motion is possible only in case of some special Bianchi types, and these cases are studied assuming the velocity vector to be geodetic and that there may be a nonvanishing heat flux term.  相似文献   

16.
We have studied the structure of hot accretion flow bathed in a general large-scale magnetic field. We have considered magnetic parameters , where are the Alfvén sound speeds in three direction of cylindrical coordinate (r,φ,z). The dominant mechanism of energy dissipation is assumed to be the magnetic diffusivity due to turbulence and viscosity in the accretion flow. Also, we adopt a more realistic model for kinematic viscosity (ν=αc s H), with both c s and H as a function of magnetic field. As a result in our model, the kinematic viscosity and magnetic diffusivity (η=η 0 c s H) are not constant. In order to solve the integrated equations that govern the behavior of the accretion flow, a self-similar method is used. It is found that the existence of magnetic resistivity will increase the radial infall velocity as well as sound speed and vertical thickness of the disk. However the rotational velocity of the disk decreases by the increase of magnetic resistivity. Moreover, we study the effect of three components of global magnetic field on the structure of the disk. We found out that the radial velocity and sound speed are Sub-Keplerian for all values of magnetic field parameters, but the rotational velocity can be Super-Keplerian by the increase of toroidal magnetic field. Also, Our numerical results show that all components of magnetic field can be important and have a considerable effect on velocities and vertical thickness of the disk.  相似文献   

17.
It is shown that the three-dimensional cylindrical Kadomtsev-Petviashvili (CKP) and the extended cylindrical Kadomtsev-Petviashvili (ECKP) equations can describe the propagation of nonplanar dust ion-acoustic excitations in a dusty plasma composed of positive ions, negative ions, stationary dust particles, as well as trapped electrons or a small percentage of trapped electrons. It is found that the solution of the CKP equation supports only solitary pulses, while the ECKP equation describes the propagation of both solitary and shock excitations. The effects of physical parameters, namely negative ions density, dust grains density, positive-to-negative mass ratio, direction cosine of the wave propagation on the pulses profile are examined. Furthermore, the existence regions of either localized or shock pulses are investigated. The relevance of nonlinear structures in the Earth’s ionosphere and plasma experiment is discussed.  相似文献   

18.
This article presents the first study of the head-on collision of two ion-acoustic solitary waves (IASWs) in magnetized plasmas with nonextensive electrons and positrons using the extended Poincaré-Lighthill-Kuo (PLK) method. The effects of the ion gyro-frequency to ion plasma frequency ratio, the positron to ion number density ratio, the electrons temperature to positrons temperature ratio, and the nonextensive parameter q on the phase shifts are investigated. It is shown that these factors significantly modify the phase shifts.  相似文献   

19.
Propagation of ion acoustic solitary waves are studied in e-p-i plasmas containing high relativistic ions, Maxwell–Boltzmann distributed positrons and nonthermal electrons. Reductive perturbation method is used and the Korteweg-de Vries (KdV) equation is derived. The effects of high relativistic ions and nonthermal electrons on soliton characters are studied.  相似文献   

20.
Some Bianchi type-I viscous fluid string cosmological models with magnetic field are investigated. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density ξ(t)=ξ 0 ρ m , where ξ 0 and m are constants. To get a determinate model, we assume conditions ρ=(1+ω)λ, where ρ is rest energy density, ω a positive constant and λ the string tension density and expansion θ is proportional to eigen value σ 11 of the shear tensor σ j i . The behaviour of the models from physical and geometrical aspects in presence and absence of magnetic field is discussed.   相似文献   

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