共查询到20条相似文献，搜索用时 15 毫秒
1.
M. S. Alam M. G. Hafez M. R. Talukder M. Hossain Ali 《Astrophysics and Space Science》2018,363(5):102
The head-on collision between positron acoustic solitary waves (PASWs) as well as the production of rogue waves (RWs) in homogeneous and PASWs in inhomogeneous unmagnetized plasma systems are investigated deriving the nonlinear evolution equations. The plasmas are composed of immobile positive ions, mobile cold and hot positrons, and hot electrons, where the hot positrons and hot electrons are assumed to follow the Kappa distributions. The evolution equations are derived using the appropriate coordinate transformation and the reductive perturbation technique. The effects of concentrations, kappa parameters of hot electrons and positrons, and temperature ratios on the characteristics of PASWs and RWs are examined. It is found that the kappa parameters and temperature ratios significantly modify phase shifts after head-on collisions and RWs in homogeneous as well as PASWs in inhomogeneous plasmas. The amplitudes of the PASWs in inhomogeneous plasmas are diminished with increasing kappa parameters, concentration and temperature ratios. Further, the amplitudes of RWs are reduced with increasing charged particles concentration, while it enhances with increasing kappa- and temperature parameters. Besides, the compressive and rarefactive solitons are produced at critical densities from KdV equation for hot and cold positrons, while the compressive solitons are only produced from mKdV equation for both in homogeneous and inhomogeneous plasmas. 相似文献
2.
Hamid Reza Pakzad 《Astrophysics and Space Science》2012,337(1):217-222
The propagation of nonlinear waves in plasmas consisting of cold electron fluid and superthermal hot electrons and stationary
ions is studied. The Korteweg-de Vries (KdV) equation is derived using the reductive perturbation theory. It is found that
only the rarefractive solitons can be created. Moreover, the linear dispersion relation and energy of solitary waves in the
presence of hot superthermal electrons are derived. Our investigation is of wide relevance to astronomers and space scientists
working on interstellar space plasmas. 相似文献
3.
Propagation of cylindrical and spherical electron-acoustic solitary waves in unmagnetized plasmas consisting of cold electron
fluid, hot electrons obeying a superthermal distribution and stationary ions are investigated. The standard reductive perturbation
method is employed to derive the cylindrical/spherical Korteweg-de-Vries equation which governs the dynamics of electron-acoustic
solitons. The effects of nonplanar geometry and superthermal hot electrons on the behavior of cylindrical and spherical electron
acoustic soliton and its structure are also studied using numerical simulations. 相似文献
4.
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6.
Nonlinear electron-acoustic solitary waves (EASWs) are studied using Sagdeev’s pseudo-potential technique in a collisionless
unmagnetized plasma consisting of a cold electron fluid, nonthermal hot electrons and stationary ions. It is shown that the
presence of fast nonthermal electrons may modify the parametric region where electron-acoustic solitons may exist. Our investigation
is of wide relevance to astronomers and space scientists working on interstellar space plasmas. 相似文献
7.
B. Lehnert 《Astrophysics and Space Science》1978,55(1):25-37
The influence of plasma-neutral gas interaction on cosmical phenomena is discussed. with applications to steady and non-steady phenomena in cool interstellar and interplanetary clouds, in the photospheres, chromospheres, prominences and filaments of the Sun and other stars, in the planetary ionospheres, as well as in certain cosmogonical theories Special attention is given to filamentary structures of hot plasmas embedded in cooler regions, and to the internal properties of cool partially ionized clouds.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May, 1978. 相似文献
8.
A theoretical investigation has been performed on the nonlinear propagation of nonplanar (cylindrical and spherical) Gardner solitons (GSs) associated with the positron-acoustic (PA) waves in a four component plasma system consisting of nonthermal distributed electrons and hot positrons, mobile cold positrons, and immobile positive ions. The well-known reductive perturbation method has been employed to derive the modified Gardner (MG) equation. The basic features (viz. amplitude, polarity, speed, etc.) of nonplanar PA Gardner solitons (GSs) have been examined by the numerical analysis of the MG equation. It has been observed that the properties of the PA GSs in a nonplanar geometry differ from those in a planar geometry. It has been also investigated that the presence of nonthermal (Cairns distributed) electrons and hot positrons significantly modify the amplitude, polarity, speed, and thickness of such PA GSs. The results of our investigation should play an important role in understanding various interstellar space plasma environments as well as laboratory plasmas. 相似文献
9.
The electrostatic shocks and solitons are studied in weakly relativistic and collisional electron-positron-ion plasmas occurring
in polar regions of pulsar. The plasma system is composed of relativistically streaming electrons, positrons while ions are
taken to be stationary. Dissipative effects in the system are due to collision phenomena among the constituents of relativistic
plasma. Nonlinear dynamics of the dissipation and dispersion dominated relativistic plasma systems are governed by Korteweg-de
Vries Burger (KdVB) and Korteweg-de Vries (KdV) equations respectively. Numerical results, exploring the effects of plasma
parameters on the profile of nonlinear waves are expedited graphically for illustration. Positron to electron temperature
ratio plays the role of a decisive parameter. It is noticed that compressive shocks and solitons evolve in the system if the
positron to electron temperature ratio is less than a critical value. However, there exists a threshold value of positron
to electron temperature ratio beyond which the system supports the rarefactive shocks and solitons. The results may have importance
in the relativistic plasmas of pulsar magnetosphere. 相似文献
10.
It is shown that nonlinear propagation of sound waves in partially ionized collisional plasmas is governed by a modified Korteweg-de Vries (mKdV) equation when the electron distribution function deviates from the Boltzmann distribution. The mKdV equation admits a sharply localized solitary sound pulse, the profile and width of which are different from that which involves the Boltzmann electron number density response. Since the electron-vortex distribution induced solitary sound pulses are more pronounced, it can easily be identified in partially ionized plasmas. 相似文献
11.
Existence and characteristics of ion-acoustic (IA) wave modulation are studied in a plasma with two-temperature electron satisfying kappa distribution. Based on the multiple time scales perturbation, a nonlinear Schrödinger equation (NLS) is derived. Similar to the case of double Maxwellian electrons, both polarities of envelope soliton can exist over restricted ranges of the fractional hot electron density ratio and two-temperature superthermal electrons. The transition from stable dark solitons to unstable bright ones shifts to the smaller wavelength regions in the presence of cool and hot superthermal electrons. It is shown that the small values of the hot electron populations leads to shrinking the modulation instability region. It is also found the instability growth rate reduces due to the presence of hot electrons. The result of present investigation contributes to the physics of wave modulation in Saturn’s magnetosphere where two-temperature electrons with kappa distribution exist. 相似文献
12.
B. Schmieder P. Heinzel J. E. Wiik J. Lemen B. Anwar P. Kotrč E. Hiei 《Solar physics》1995,156(2):337-361
We have analyzed the physical conditions of the plasma in post-flare loops with special emphasis on dynamics and energy transport using SXT-data (hot plasma) and optical ground-based data from Pic du Midi, Wrocaw, and Ondejov (cool plasma). By combining the H observations with the SXT images we can understand the relationship between cool and hot plasmas, the process of cooling post-flare loops and the mechanism which maintains the long duration of these loops. Using recent results of NLTE modeling of prominence-like plasmas, we derive the emission measure of cool H loops and this gives us a realistic estimate of the electron density (2.2 × 1010 cm–3). Then, by comparing this emission measure with that of hot loops derived from SXT data, we are able to estimate the ratio between electron densities in hot and cool loops taking into account the effect of geometrical filling factors. This leads to the electron density in hot loops 7 × 109 cm–3. We also derive the temperature of hot X-ray loops ( 5.5 × 106 K), which, together with the electron density, provides the initial values for solving the time-dependent energy balance equation. We obtain the cooling times which are compared to a typical growth-time of the whole loop system ( 2000 s). In the legs of cool H loops, we observe an excess of the emission measure which we attribute to the effect of Doppler brightening (due to large downflow velocities). 相似文献
13.
The large amplitude Ion-acoustic solitons in collisionless plasma consisting of warm adiabatic ions, isothermal positrons and two-temperature distribution of electrons are investigated. Using pseudo-potential approach, an energy integral equation for the system has been derived which encompasses complete nonlinearity for the plasma system. The existence region of the solitons is analyzed numerically. It is found that for selected set of plasma parameters, both rarefactive and compressive solitons exist in the electron-positron-ion (EPI) plasma. It is also found that due to finite positron concentration both subsonic and supersonic rarefactive soliton exist in EPI plasma. An increase in finite ion temperature ratio decreases the amplitude of the rarefactive solitons. In the case of small amplitude, it is found that there exist supersonic compressive as well as rarefactive solitons simultaneously. The amplitude of the solitons decreases with increase in ion temperature ratio (σ), however an increase in positron concentration (α) and temperature ratio of positron to electrons (γ) increases the amplitude of the solitons. Effect of various plasma parameters on the characteristics of the solitons are discussed in detail. The results of the investigation may be helpful to understand the nonlinear structures in auroral plasma, pulsars and magnetospheric astrophysical environment as well as laboratory plasmas. 相似文献
14.
Hamid Reza Pakzad 《Astrophysics and Space Science》2009,323(4):345-350
In this paper, the characteristics of ion acoustic solitary waves are studied in plasmas containing warm ion fluid, non-thermally
distributed electron and positron. We study the effects of non-thermal electrons and ion temperature on solitons by Pseudo-potential
method and show that the parametric region where ion acoustic solitons can exist is modified. We also obtain linear dispersion
relation by using the standard normal-modes analysis. 相似文献
15.
Large amplitude solitons are investigated in an electron-positron plasma consisting of a hot and cold component for each charged species. The existence (and amplitudes) of the solitons are studied as a function of plasma parameters such as particle number densities and temperatures. Both compressive and rarefactive solitons are found to occur. Possible applications to pulsar magnetospheres are discussed.Also attached to Plasma Physics Research Institute, University of Natal, Durban, South Africa. 相似文献
16.
The self-modulation of weakly relativistic plasma waves in equal mass (electron-positron) plasmas has been investigated by employing the Krylov-Bogoliubov-Mitropolsky perturbation technique. It is found that one-dimensional electron plasma waves are modulationally stable and that they can propagate in the form of dark envelope solitons. 相似文献
17.
Propagation of small but finite amplitude ion acoustic solitons and double layers are investigated in electron–positron–ion
plasmas in presence of highly negatively charged impurities or dust. The presence of negatively charged dust particulates
can result in existence of two critical concentrations of ion–electron density ratio α. One of them α
D
decides the existence of double layers, whereas the other one α
R
decides the nature of the solitons and double layers. The system supports both compressive and rarefactive solitons as well
as double layers. The parameter regimes of transitions from compressive to rarefactive solitons and double layers are also
specified. 相似文献
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19.
The nonlinear interaction between the high frequency Langmuir wave and the low frequency density fluctuation in ultrarelativistic
isothermal electron positron plasmas is investigated from kinetic Vlasov equation. One dimensional Langmuir solitons are obtained,
the width of which is so large that it is not relevant to the coherent pulsar radio emission. 相似文献
20.
Van Driel-Gesztelyi L. Wiik J.E. Schmieder B. Tarbell T. Kitai R. Funakoshi Y. Anwar B. 《Solar physics》1997,174(1-2):151-162
Observations of the post-flare loops after the X3.9 flare which occurred on 25 June, 1992 at 20:11 UT by the Yohkoh/SXT in X-rays, as well as in H obtained at 5 different observatories, have provided a unique, longest ever, set of data for a study of the relationship between the hot and cool post-flare loops as they evolve. At any given time, the altitude difference between the hot X-ray loops of 6–7× 106 K and the cool H loops of 1.5× 104 K is related to the expansion rate of the loop systems and their cooling time. Therefore, measurements of the expansion rate and relative height of hot and cool loops can provide direct observational values for their cooling times. We measured the altitude of hot and cool loops for 15 and 19 hours, respectively, and found that the cooling time increased as the density of the loops decreased. We found a reasonably good agreement between the observed cooling times and those obtained from model calculations, although the observed values were always somewhat longer than the theoretical ones. Taking into account evolutionary effects, we also found similar shapes and configurations of hot and cool loops during the entire observing period and confirmed that, at any time, hot loops are at higher altitude than cool loops, suggesting that cool loops indeed evolve from hot loops. These results were used to check the validity of the reconnection model. 相似文献