共查询到20条相似文献，搜索用时 734 毫秒
1.
Linear and nonlinear analysis of low frequency magnetoacoustic waves propagating at an angle θ with the ambient magnetic field are investigated in dense electron-positron-ion (e-p-i) plasmas using the quantum magnetohydrodynamic
(QMHD) model. In this regard, a quantum Kadomtsev-Petviashvili-Burgers (KPB) equation is derived in the small amplitude limit.
The stability of KPB equation is also presented. The variation of the nonlinear fast and slow magnetoacoustic shock waves
with the positron concentration, kinematic viscosity, obliqueness parameter θ, and the magnetic field, are also investigated. It is observed that the aforementioned plasma parameters significantly modify
the propagation characteristics of two dimensional nonlinear magnetoacoustic shock waves in dissipative quantum magnetoplasmas.
The relevance of the present investigation with regard to dense astrophysical environments is also pointed out. 相似文献
2.
M. Mehdipoor 《Astrophysics and Space Science》2012,338(1):73-79
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
3.
Prasanta Chatterjee Deb Kumar Ghosh Biswajit Sahu 《Astrophysics and Space Science》2012,339(2):261-267
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
4.
Biswajit Sahu 《Astrophysics and Space Science》2012,338(2):251-257
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
5.
Hamid Reza Pakzad 《Astrophysics and Space Science》2011,333(1):247-255
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
6.
Cylindrical Korteweg-de Vries-Burgers (cKdVB) equation for magnetoacoustic wave is derived for dissipative magneto plasmas. Two fluid collisionless electromagnetic model is considered and reductive perturbation method is employed to study the propagation of magnetoacoustic shock waves in cylindrical geometry. Two level finite difference method is employed by using Runge-Kutta method to solve cKdVB equation numerically. The effects of nonplanar geometry, plasma density, magnetic field strength, temperature dependence and kinematic viscosity on magnetoacoustic shocks are investigated. The numerical results are also presented for illustration. 相似文献
7.
A dm-radio emission with fiber bursts observed on 11 July 2005 was analyzed using wavelet filtration and spectral methods.
In filtered radio spectra we found structures with different characteristic period P and frequency drift FD: i) fiber substructures (composed of dot emissions) with P
1≈ 0.5 s, FD1=− 87 MHz s−1 on average, ii) fiber structures with P
2≈1.9 s, and iii) drifting structures with P
3≈81.4 s, FD2=− 8.7, + 98.5, and − 21.8 MHz s−1. In the wavelet spectra we recognized patterns having the form of tadpoles. They were detected with the same characteristic
periods P as found for the filtered structures. The frequency drift of the tadpole heads is found to be equal to the frequency drift
of some groups of fibers for the long-period wavelet tadpoles (P
3) and to the frequency drift of individual fibers for the short-period tadpoles (P
2). Considering these wavelet tadpoles as signatures of propagating magnetoacoustic wave trains, the results indicate the presence
of several wave trains in the fibers’ source. While the long-period wave trains trigger or modulate a whole group of fibers,
the short-period ones look like being connected with individual fiber bursts. This result supports the model of fibers based
on magnetoacoustic waves. Using a density model of the solar atmosphere we derived the velocities of the magnetoacoustic waves,
107 and 562 km s−1, and setting them equal to the Alfvén ones we estimated the magnetic field in the source of fiber bursts as 10.7 and 47.8 G. 相似文献
8.
The occurrence of magnetoacoustic surface waves at a single magnetic interface one side of which is field-free is explored for the case of non-parallel propagation. Phase-speeds and penetration depths of the waves are investigated for various Alfvén speeds, sound speeds and angles of propagation to the applied field. Both slow and fast magnetoacoustic surface waves can exist depending on the values of sound speeds and propagation angle. The fast waves penetrate more than the slow waves.The parallel propagation of fast and slow magnetoacoustic surface waves on a magnetic-magnetic interface is investigated. The slow surface wave is unable to propagate below a critical sound speed. In a low -plasma, only the fast mode exists (0 0). 相似文献
9.
Properties of three-dimensional ion-acoustic solitary and shock waves accompining electron-positron-ion magnetoplasma with
high-energy (superthermal) electrons and positrons are investigated. For this purpose, a Zakharov-Kuznetsov-Burgers (ZKB)
equation is derived from the ion continuity equation, ion momentum equation with kinematic viscosity among ions fluid, electrons,
and positrons having kappa distribution together with the Poisson equation. The dependence of the solitary and shock excitations
characteristics on the parameter measuring the superthermality κ, the ion gyrofrequency Ω, the unperturbed positrons-to-ions density ratio ν, the viscosity parameter η, the direction cosine ℓ, the ion-to-electron temperature ratio σ
i
, and the electron-to-positron temperature ratio σ
p
have been investigated. Moreover, it is found that the parameters κ, Ω, ν, η, and ℓ lead to accelerate the particles, whereas the parameters σ
i
and σ
p
would lead to decelerate them. Numerical calculations reveal that the nonlinear pulses polarity are always positive. This
study could be useful to understand the nonlinear electrostatic excitations in interstellar medium. 相似文献
10.
We study the fundamental modes of radiation hydrodynamic waves arising from one-dimensional small-amplitude initial fluctuations
with wave number k in a radiating and scattering grey medium using the Eddington approximation. The dispersion relation analyzed is the same
as that of Paper I (Kaneko et al., 2000), but is solved as a quintic in angular frequency ω while a quadratic in k
2 in Paper I. Numerical results reveal that wave patterns of five solutions are distinguished into three types of the radiation-dominated
and type 1 and type 2 matter-dominated cases. The following wave modes appear in our problem: radiation wave, conservative
radiation wave, entropy wave, Newtonian-cooling wave, opacity-damped and cooling-damped waves, constant-volume and constant-pressure
diffusion modes, adiabatic sound wave, cooling-damped and drag–force-damped isothermal sound waves, isentropic radiation-acoustic
wave, and gap mode. The radiation-dominated case is characterized by the gap between the isothermal sound and isentropic radiation-acoustic
speeds within which there is not any acoustic wave propagating with real phase speed. One of the differences between type
1 and type 2 matter-dominated cases is the connectivity of the constant-volume diffusion mode, which originates from the radiative
mode in the former case, while from the Newtonian-cooling wave in the latter case. Analytic solutions are derived for all
wave modes to discuss their physical significance. The criterion, which distinguishes between radiation-dominated and type
1 matter-dominated cases, is given by Γ0 = 9, where Γ0 = C
p
(tot)/C
V
(tot) is the ratio of total specific heats at constant pressure and constant volume. Waves in a scattering grey medium are also
analyzed, which provides us some hints for the effects of energy and momentum exchange between matter and radiation. 相似文献
11.
The nonlinear propagation of ion acoustic waves in an ideal plasmas containing degenerate electrons is investigated. The Korteweg-de-Vries
(K-dV) equation is derived for ion acoustic waves by using reductive perturbation method. The analytical traveling wave solutions
of the K-dV 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 solitary waves are derived from the traveling waves. Also, numerically
the effect different parameters on these solitary waves investigated and it is seen that exist only the compressive solitary
waves in Thomas-Fermi plasmas. 相似文献
12.
We study a nonlinear mechanism for the excitation of kinetic Alfvén waves (KAWs) by fast magneto-acoustic waves (FWs) in the
solar atmosphere. Our focus is on the excitation of KAWs that have very small wavelengths in the direction perpendicular to
the background magnetic field. Because of their small perpendicular length scales, these waves are very efficient in the energy
exchange with plasmas and other waves. We show that the nonlinear coupling of the energy of the finite-amplitude FWs to the
small-scale KAWs can be much faster than other dissipation mechanisms for fast wave, such as electron viscous damping, Landau
damping, and modulational instability. The nonlinear damping of the FWs due to decay FW = KAW + KAW places a limit on the
amplitude of the magnetic field in the fast waves in the solar corona and solar-wind at the level B/B
0∼10−2. In turn, the nonlinearly excited small-scale KAWs undergo strong dissipation due to resistive or Landau damping and can
provide coronal and solar-wind heating. The transient coronal heating observed by Yohkoh and SOHO may be produced by the kinetic Alfvén waves that are excited by parametric decay of fast waves propagating from
the reconnection sites. 相似文献
13.
V. P. Dokuchaev 《Astronomy Letters》2003,29(3):170-174
Radially pulsating stars are shown to radiate fast and slow magnetoacoustic waves into the interstellar gas. No Alfvén waves are excited, because the oscillations are radially symmetric. Calculations were performed for the following two limiting cases: hot, weakly magnetized interstellar plasma and cold plasma with a strong magnetic field. In these limiting cases, pulsating stars excite mostly fast magnetoacoustic waves, while the excitation of slow magnetoacoustic waves is weak. Magnetogasdynamic fields of density, velocity, and magnetic-field perturbations in the interstellar medium were found. Relations were derived to calculate the radiated power and its estimates are given for various conditions in the medium. It is shown that radially stratified wave structures with wavelengths from 1 AU to several tenths of a parsec must exist in the vicinity of pulsating stars. 相似文献
14.
The nature of magnetoacoustic surface waves at a single magnetic interface, one side of which is field-free, is explored for the case of parallel propagation. The interface may support a slow surface wave or both slow and fast surface waves, depending upon the ordering of the sound speeds in the two media. Phase-speeds and penetration depths of the waves and the associated pressure perturbations and motions are investigated for a variety of field strengths and sound speeds. The fast wave disturbs the interface more than the slow wave. In the magnetic field region the slow wave is mainly longitudinal in nature whilst the fast surface wave is transverse for strong fields, longitudinal for weaker fields. In the field-free region both waves are longitudinal in character. The running penumbral wave phenomenon may provide an example of a magnetoacoustic surface mode, though any direct comparison requires the inclusion of gravitational effects. 相似文献
15.
Jordanova V.K. Thorne R.M. Farrugia C.J. Dotan Y. Fennell J.F. Thomsen M.F. Reeves G.D. McComas D.J. 《Solar physics》2001,204(1-2):361-375
We study the development of the terrestrial ring current during the time interval of 13–18 July, 2000, which consisted of
two small to moderate geomagnetic storms followed by a great storm with indices Dst=−300 nT and Kp=9. This period of intense geomagnetic activity was caused by three interplanetary coronal mass ejecta (ICME) each driving
interplanetary shocks, the last shock being very strong and reaching Earth at ∼ 14 UT on 15 July. We note that (a) the sheath
region behind the third shock was characterized by B
z fluctuations of ∼35 nT peak-to-peak amplitude, and (b) the ICME contained a negative to positive B
z variation extending for about 1 day, with a ∼ 6-hour long negative phase and a minimum B
z of about −55 nT. Both of these interplanetary sources caused considerable geomagnetic activity (Kp=8 to 9) despite their disparity as interplanetary triggers. We used our global ring current-atmosphere interaction model
with initial and boundary conditions inferred from measurements from the hot plasma instruments on the Polar spacecraft and the geosynchronous Los Alamos satellites, and simulated the time evolution of H+, O+, and He+ ring current ion distributions. We found that the O+ content of the ring current increased after each shock and reached maximum values of ∼ 60% near minimum Dst of the great storm. We calculated the growth rate of electromagnetic ion cyclotron waves considering for the first time wave
excitation at frequencies below O+ gyrofrequency. We found that the wave gain of O+ band waves is greater and is located at larger L shells than that of the He+ band waves during this storm interval. Isotropic pitch angle distributions indicating strong plasma wave scattering were
observed by the imaging proton sensor (IPS) on Polar at the locations of maximum predicted wave gain, in good agreement with model simulations. 相似文献
16.
The propagation of magnetoacoustic waves in the neighbourhood of a 2D null point is investigated for both β=0 and β ≠ 0 plasmas. Previous work has shown that the Alfvén speed, here v A ∝r, plays a vital role in such systems and so a natural choice is to switch to polar coordinates. For β=0 plasma, we derive an analytical solution for the behaviour of the fast magnetoacoustic wave in terms of the Klein–Gordon equation. We also solve the system with a semi-analytical WKB approximation which shows that the β=0 wave focuses on the null and contracts around it but, due to exponential decay, never reaches the null in a finite time. For the β ≠ 0 plasma, we solve the system numerically and find the behaviour to be similar to that of the β=0 system at large radii, but completely different close to the null. We show that for an initially cylindrically-symmetric fast magnetoacoustic wave perturbation, there is a decrease in wave speed along the separatrices and so the perturbation starts to take on a quasi-diamond shape; with the corners located along the separatrices. This is due to the growth in pressure gradients that reach a maximum along the separatrices, which in turn reduces the acceleration of the fast wave along the separatrices leading to a deformation of the wave morphology. 相似文献
17.
Propagation of two dimensional cylindrical fast magnetoacoustic solitary waves in a warm dust plasma
A set of multi-fluid equations and Maxwell’s equations are carried out to investigate the properties of nonlinear fast magnetoacoustic solitary waves with the combined effects of dusty plasma pressure and transverse perturbation in the bounded cylindrical geometry. The reductive perturbation method has been applied to the dynamical system causeway and the derived two dimensional cylindrical Kadomtsev–Petviashvili equation (CKP) predicts different natures of solitons in complex plasma. Under a suitable coordinate transformation the CKP equation can be solved analytically. The change in the soliton structure due to mass of dust, ion temperature, ion density, and dust temperature is studied by numerical calculation of the CKP equation. It is noted that the dust cylindrical fast magnetoacoustic solitary waves in warm plasmas may disappear slowly because of an increase in dust mass. The present analysis could be helpful for understanding the nonlinear ion-acoustic solitary waves propagating in interstellar medium and pulsar wind,which contain an excess of superthermal particles. 相似文献
18.
Comet outburst activity and the structure of solar wind streams were compared on the basis of Pioneer 10, 11, Vela 3 and IMP
7, 8 measurements at the heliocentric distance r ≈ 1–6 AU. It is shown that the solar wind velocity waves which are evolving into corotating shock waves beyond the Earth
orbit may be responsible for comet outburst activity. The correlation between variations of comet outburst activity with heliocentric
distance and the behavior of the solar wind velocity waves is established. The closeness of the characteristic times for the
velocity waves and comet outburst activity (7–8 days at r = 1 AU) as well as the simultaneous growth of both the characteristic times with r are noted. The observed distribution of the comet outburst activity parameters during the 11-year cycle is also in good agreement
with the phase distributions during the 11-year cycle of variations of the coronal hole areas and the rate of change of the
sunspot area δS
p. 相似文献
19.
Resonant absorption of fast magnetoacoustic (FMA) waves in an inhomogeneous, weakly dissipative, one-dimensional planar, strongly
anisotropic and dispersive plasma is investigated. The magnetic configuration consists of an inhomogeneous magnetic slab sandwiched
between two regions of semi-infinite homogeneous magnetic plasmas. Laterally driven FMA waves penetrate the inhomogeneous
slab interacting with the localised slow or Alfvén waves present in the inhomogeneous layer and are partly reflected, dissipated
and transmitted by this region. The presented research aims to find the coefficient of wave energy absorption under solar
chromospheric and coronal conditions. Numerical results are analysed to find the coefficient of wave energy absorption at
both the slow and Alfvén resonance positions. The mathematical derivations are based on the two simplifying assumptions that
i) nonlinearity is weak, and ii) the thickness of the inhomogeneous layer is small in comparison to the wavelength of the wave, i.e. we employ the so-called long wavelength approximation. Slow resonance is found to be described by the nonlinear theory, while
the dynamics at the Alvén resonance can be described within the linear framework. We introduce a new concept of coupled resonances,
which occurs when two different resonances are in close proximity to each other, causing the incoming wave to act as though it has been influenced by the two resonances simultaneously. Our results show that the wave energy absorption is heavily
dependent on the angle of the incident wave in combination with the inclination angle of the equilibrium magnetic field. In
addition, it is found that FMA waves are very efficiently absorbed at the Alvén resonance under coronal conditions. Under
chromospheric conditions the FMA waves are far less efficiently absorbed, despite an increase in efficiency due to the coupled
resonances. 相似文献
20.
The positron acoustic shock and solitary wave are explored in nonextensive electron-positron-ion plasma. The plasma system under-consideration, consists of a classical positron beam, q distributed electrons and positively charged bulky ions constitute a neutralizing background. The nonlinear Korteweg-de Vries and Burger equations are derived by employing the standard reductive perturbation method. The positron acoustic wave in linear limit is also discussed for dissipative as well as nondissipative cases of nonextensive plasmas. The plasma parameters such as, the concentration of neutralizing ions background, beam velocity, temperature and q parameter of the nonextensive electrons are noticed to significantly affect the positron acoustic shock and solitary waves. Our findings may be helpful in the understanding of laboratory beam plasma interaction experiments as well as the astrophysical nonextensive plasmas interacting with positron beam. 相似文献