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1.
In the framework of non-linear fluid theory we use a lower hybrid (LH) wave of the form
as a pump which interacts with the small fluctuations with the low-frequency vibrations
i
or =0, where
i
, is the hydrogen ion-cyclotron (HIC) gyrofrequency. The ponderomotive force generated by the beating of the high-frequency pump wave 0 and the sideband LH waves (±0) produces a non-linear coupling between the high- and low-frequency motions of electrons and ions. Under certain conditions the HIC waves and the zero-frequency waves both become parametrically unstable and start to grow. These excited waves then heat the ions by stochastic acceleration in the transverse direction, thus explaining the formation of ion comics along the auroral field lines. Electrons would be heated in the parallel direction directly by the pump field as well as by low-frequency waves. Thus a single mechanism can explain the existence of ion-cyclotron waves, zero-frequency waves, ion conics, and energetic electrons along the auroral field lines. 相似文献
2.
V. I. Karpman Ju. K. Alekhin N. D. Borisov N. A. Rjabova 《Astrophysics and Space Science》1973,22(2):267-278
Electrostatic waves with >
c
in a plasma with temperature anisotropy and loss-cone are considered. An analytical asymptotic analysis is made for waves propagating nearly perpendicular to the magnetic field and having wave-length small compared with the Larmor radius. Numerical computations are done for carried out waves with arbitrary direction of propagation. The frequency range of instability, growth damping rates, and dispersion curves have been found. The results can be used for the interpretation of magnetospheric experiments. 相似文献
3.
Nonlinear propagation of strong low-frequency waves, as emitted by pulsars or compact galactic nuclei at their rotation frequencies, in a magnetized plasma is investigated. It is shown that even rather small amplitude waves can drive electrons to ultrarelativistic energies. In the limit when the electrons are ultrarelativistic but the ions are immobile, two types of circularly polarized waves (i.e., ± modes) are excited. In the wave zone of the Crab pulsar, both the electric field ( 3 V m–1) and the wavelength (108 m) of the - mode are larger, by an order of magnitude, than those of the + wave mode. Both ± modes can become modulationally unstable due to their nonlinear interaction with density fluctuations induced by the electrostatic waves. 相似文献
4.
D. B. Melrose 《Astrophysics and Space Science》1972,18(2):267-272
It is shown that bremsstrahlung from electrons with Lorentz factor 1 is suppressed for >p in a plasma with plasma frequency p compared with emission in vacuo. For p the ratio of the power emitted per unit frequency in the plasma to that in vacuo varies as 2.This suppression effect is analogous to the suppression of synchrotron radiation in a plasma (Razin-Tsytovich effect). It is argued that such suppression is a characteristic property of emission by relativistic particles in a plasma. 相似文献
5.
Polarization properties of solar and stellar radio emission require, in some cases, emission below the third or fourth coronal electron gyro level, < 3,_c; 4, _c. In the context of plasma radiation, the source parameters should be such that the intermediate magnetic field condition 1 <
p
2
/
c
2
< 3 is satisfied. Supposing this condition, we investigate the generation of electrostatic waves in a warm background plasma with a high-energy component of magnetically trapped electrons. We invoke the conversion of upper-hybrid waves and Bernstein waves into electromagnetic radiation as being responsible for intense radio emission from a coronal magnetic loop. Moreover, odd-half harmonic emissions in the solar radio spectrum as well as the o-mode polarization at the second harmonic of the plasma frequency are natural consequence of this proposed model. 相似文献
6.
A two-component scheme for the generation of type III fundamental radiation is proposed. The first component of the fundamental arises at a plasma level
L
t
because of the Rayleigh scattering of the plasma waves into electromagnetic radiation. The other component arises at
L
t
/2 because of the decay of the first component into plasma waves and the subsequent rescattering of the plasma waves into electromagnetic radiation
t
2(
t
/2). By its properties (location, directivity, polarization) the second component is essentially the same as the second harmonic radiation produced by a stream of fast electrons at
L
(
t
/2). This scheme is used to solve the main problems (localization and directivity of the source, polarization of type III fundamental) of the harmonic theory of type III solar bursts. 相似文献
7.
P. S. Goraya 《Astrophysics and Space Science》1981,78(2):419-425
The photoelectric spectrophotometric scans of the Be stars Gem, Ori, Mon and CMa have been analyzed to find out few stellar parameters. The absolute energy distributions of these stars in the wavelength range 350–750 nm have been given. Their effective temperatures and gravities have been estimated from comparisons with non-LTE model atmospheres. The stars Gem and Mon have been found to have Balmer discontinuities in emission. The excess emission in the region 620–750 nm has been observed for Mon and CMa. The evolutionary aspects of these stars are discussed and their masses have been estimated. 相似文献
8.
The stability of triangular libration points, when the bigger primary is a source of radiation and the smaller primary is an oblate spheroid. has been investigated in the resonance cases 1 = 22 and 1 = 32. The motion is unstable for all the values of parameters q and A when 1 = 22 and the motion is unstable and stable depending upon the values of the parameters q and A when 1 = 32. Here q is the radiation parameter and A is the oblateness parameter. 相似文献
9.
G. Contopoulos 《Celestial Mechanics and Dynamical Astronomy》1981,24(4):355-366
We study the resonance 12 = 41 and some near-resonance cases. The main peculiarity of this resonance is that for 12 < 4 the characteristic of the central periodic orbits is broken into two and each part is joined with a resonant characteristic. This behaviour is described theoretically by means of the third integral. It seems that there are infinite families of simple periodic orbits near the escape region. Finally, a comparison is made with the cases near the 12 = 21 resonance. 相似文献
10.
Using a 2-D MHD model, the magnetic field reconnection in the current sheet and corresponding plasma resonance lines (surfaces in 3-D), where the upper-hybrid frequency equals one of harmonics of the electron gyrofrequency, UH=(pe
2+Be
2)1/2=sBe (UH, pe, and Be are the upper hybrid, electron plasma, and cyclotron frequencies, respectively, and s is the integer harmonic number) are computed. Then at selected times and positions in the magnetic reconnection the spatial and time spectra of upper hybrid frequencies along the resonance lines are calculated. These spectra are discussed from the point of view of radio fine structures as narrowband dm-spikes, zebras, and lace bursts. It is shown that not only turbulent plasma outflows, suggested in the paper by Bárta and Karlický (2001), but also perturbed zones near the reconnection slow-mode shocks can be locations of the narrowband dm-spikes (and/or continua). Sources of the lace bursts (i.e. bursts with irregular lines) can be located in the reconnection space, too. On the other hand, the zebras (bursts with regular separations of zebra lines) need to be generated out of strongly perturbed reconnection areas. 相似文献
11.
I. Lerche 《Astrophysics and Space Science》1978,53(1):21-37
We investigate the one-dimensional self-similar flow behind a blast wave from a plane explosion in a medium whose density varies with distance asx
– with the assumption that the flow is isothermal. If <0 a continuous solution passing through the origin and the shock does not exist. If 1/3>>0 one critical point exists. To be physically acceptable the flow must by-pass this critical point. It is shown that a continuous solution passing through both the origin and through the shock and by-passing the critical point does exist. If 1>>1/3 the first critical point does not exist but a second one appears. To be physically acceptable the flow must again by-pass this new critical point. We show that a continuous solution passing through both the origin and the shock and by-passing the new critical point exists in this case. If >1 no physically acceptable solution exists since the mass behind the shock is infinite.The dependence of the solutions on the parameter is analytic for >0 so that interpolation between neighboring values of is permitted.We investigate the stability of these isothermal blast waves to one-dimensional but non-self-similar perturbations. If 0<<5/7, the solutions are shown to be linearly unstable against short wavelength perturbations near the origin. If the solution crosses the shock with a normalized velocityu>2 the solution is linearly unstable against short wavelength perturbations near the shock for 1>>0. If the solution crosses the shock with normalized velocity 2>u>1 (and it must cross the shock withu>1), the solution is certainly unstable against short wavelength perturbations near the shock for >11/19 and, depending on the crossing velocity, can be unstable there for all .Thus for 1>>0, the solution is always unstable somewhere. Since there is no characteristic time scale in the system all instabilities grow as a power law of time rather than exponentially. The existence of these instabilities implies that initial deviations do not decay and the system does not tend to a self-similar form. 相似文献
12.
I. Stellmacher 《Celestial Mechanics and Dynamical Astronomy》1984,32(3):247-256
Resume On étudie la stabilité des solutions périodiques d'un couplage de systèmes linéaires au voisinage de résonances. Les valeurs propres distinctes k de la matrice du système linéaire non perturbé sont telles que k–j=iq pour tout couple [k, j]; i=–1, q est un nombre entier, la fréquence de la solution. Une application est faite pour un système à trois degrés de liberté au voisinage de la résonance 221.
Hamiltonian systems in the neighbourhood of an equilibrium solution. II:The stability of periodic solutions
The stability of the periodic solutions for an Hamiltonian system is investigated. Here the distinct eigen values k of the matrix of the unperturbated linear system are such that k–j=iq for any [k, j]; i=–1, q is an integer, is the frequency of the periodic solution. An application is made for a system with three degrees of freedom, near the resonance 221.相似文献
13.
N. A. Silant'ev 《Astrophysics and Space Science》1982,82(2):363-395
On the ground of the proper wave representation the general theory is developed of radiative transfer in a homogeneous plasma with the strong magnetic field (
B
/1). The linear and nonlinear equations are derived which generalize the corresponding equations of scalar radiative transfer theory in isotropic media. The solutions of some problems are given for the cases when the magnetic field is perpendicular to the surface: diffuse reflection of radiation from a semiinfinite medium, provided the sources are placed far from the surface (Milne's problem) and have constant intensity, increase linearly or quadratically with the optical depths, or decrease exponentially from the surface. 相似文献
14.
I. Stellmacher 《Celestial Mechanics and Dynamical Astronomy》1984,32(3):231-246
Resume On étudie les solutions périodiques d'un système Hamiltonien au voisinage des résonances i/j Ni et Nj sont des nombres entiers premiers entre eux.Dans le cas ou l'hamiltonien à la forme H=H0+H1, une procédure générale est donnée pour trouver les familles de solutions périodiques. Le développement asymptotique de la solution peut être calculé explicitement. L'étude de la stabilité est traitée (Stellmacher, 1984).Une application aux problèmes de dynamique galactique pour un système à trois degrés de liberté est faite pour le voisinage de la résonance 221.
Hamiltonian systems in the neighbourhood of an equilibrium solution. I:Periodic orbits in cases of resonance
We study the periodic solutions of an Hamiltonian system with n degrees of freedom, near an equilibrium point, in the vicinity of the resonances i/jNi/Nj. Ni/Nj are fractions in their lowest terms for any pair (i, j).In this case, a general procedure to find the families of periodic solutions is given. The asymptotic solutions can explicitly be calculated including the periods. (The stability will be presented in Stellmacher (1984).) An application to a galactic dynamics problem in a system with three degrees of freedom near the resonances 221, is analytically treated in detail.相似文献
15.
Efi Meletlidou Simos Ichtiaroglou Fabian Josef Winterberg 《Celestial Mechanics and Dynamical Astronomy》2001,80(2):145-156
We prove that Hill's lunar problem does not possess a second analytic integral of motion, independent of the Hamiltonian. In order to obtain this result, we avoid the usual normalization in which the angular velocity of the rotating reference frame is put equal to unit. We construct an artificial Hamiltonian that includes an arbitrary parameter b and show that this Hamiltonian does not possess an analytic integral of motion for in an open interval around zero. Then, by selecting suitable values of , b and using the invariance of the Hamiltonian under scaling in the units of length and time, we show that the Hamiltonian of Hill's problem does not possess an integral of motion, analytically continued from the integrable two–body problem in a rotating frame. 相似文献
16.
Carlos A. De Azevedo Altair S. De Assis Hisataki Shigueoka Paulo H. Sakanaka 《Solar physics》1991,131(1):119-127
It is shown that a discrete Alfvén wave can explain the natural oscillations of solar loop prominences by considering the existence of a current flow. Discrete Alfvén waves are a new class of Alfvén waves which is described by the inclusion of the finite ion cyclotron frequency (/
cl
0) and/or the equilibrium plasma current. In this paper we consider only the effect of the current since in solar prominences (/
cl
0). We have modeled the solar prominences as a cylindrical plasma, surrounded by vacuum (corona), with L a where L and a are the plasma column, length, and radius, respectively. We have calculated the spectrum of the discrete Alfvén waves as function of the magnitude and shape of the plasma current. 相似文献
17.
On the basis of diffusion approach for normal modes, solutions of the radiative transfer problem are obtained and analysed for an optically thick tenuous plasma with a strong magnetic field. The case is considered when the scattering processes without change of photon frequency are dominant. The radiative transfer coefficients as well as spectra, angular dependences and polarization of the outgoing radiation are investigated in detail for a cold plasma,kT
emc
2, |–s
B|kT
e/mc
2 )1/2|cos|, whereT
e is the electron plasma temperature,
B=eB/mc the electron cyclotron frequency,s=1,2,... the number of cyclotron harmonic and the angle between the magnetic field and wave vector. The effects of electronpositron vacuum polarization are taken into account and shown to be very significant. Simple analytic solutions are obtained for various limiting cases (small and large vacuum polarization; high, low and close to the cyclotron resonance radiation frequencies; different orientations of the magnetic field, etc). The results obtained are necessary for analysing X-ray and gamma-ray radiation from strongly magnetized neutron stars. 相似文献
18.
L. Mollwo 《Solar physics》1973,30(2):497-511
The generation of space charge waves by micro instabilities of the Harris type and their conversion into electromagnetic waves is discussed in the framework of the dispersion curves of the extraordinary wave mode in the warm plasma. Acceleration of electrons as also nonlinear interactions of waves are taken into account. A survey of the parameter regions of the Harris instabilities is given. Distinct values
p
/
c
and
p
/
c
result, enabling the instability as well as the conversion. The moving type IVmA bursts, and on the other side the impulsive cm-bursts and the first phase of type IV bursts are correlated to different values
p
/
c
and corresponding heights in the corona. The space charge waves can produce hydromagnetic waves by parametric excitation, too (type II bursts). The proposed mechanism is discussed with respect to the energy balance and to the magnetic configurations derived from observations with the Culgoora radioheliograph. 相似文献
19.
We obtain an approximate analytic solution of a set of nonlinear model -dynamo equations. The reaction of the Lorentz force on the velocity shear which stretches and, hence, amplifies the magnetic field, is incorporated into the model. To single out the effect of the Lorentz force on the -effect, the effect of the Lorentz force on the -effect is neglected in this study. The solution represents a nonlinear oscillation with the amplitude and period determined by the dynamo numberN. The amplitude is proportional toN–1, while the period is almost exactly the same as the dissipation time of the unstable mode [proportional toN; note the linear oscillation period is proportional toN/(N–1) which is quite different for the solar situation whereN1]. 相似文献
20.
R. V. Isakov A. A. Ruzmaikin D. D. Sokoloff M. V. Faminskaya 《Astrophysics and Space Science》1981,80(1):145-155
The asymptotic properties of a turbulent disk dynamo at large dimensionless numbersR
andR
characterizing the helicity and the differential rotation are analysed. Three types of generations in the dependence of the relations betweenR
andR
are found: 2-dynamo and two types of -dynamo. For each of these types the rates of growth are obtained and the forms of solution are pointed out. Boundaries of the disk dynamo approximation are given. 相似文献