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1.
The equation of radiative acoustics is derived by taking into account the effect of a non-transverse magnetic field, and the solutions are schematically represented. The main results shown in Paper I and Paper II are valid even in the presence of a non-transverse magnetic field, and the only difference is that theadiabatic, isothermal, andisentropic speeds of sound and theradiation-acoustic speed in Paper I which respectively correspond to theadiabatic, isothermal, andisentropic magnetoacoustic speeds and theradiation-magnetoacoustic speed in Paper II are replaced by the sets of speeds ofadiabatic, isothermal, isentropic, andradiation-acoustic fast andslow waves, respectively.  相似文献   

2.
The aim of this series of papers is to develop straightforward methods of computing the response of flat galaxies to small perturbations. This Paper I considers steady state problems; Paper II considers time varying perturbations and the effects of resonances; and Paper III applies the methods developed in Papers I and II to a numerical study of the stability of flat galaxies.The general approach is to study the dynamics of each individual orbit. The orbits are described by their apocentric and pericentric radii,r a andr p , and the distribution function of an equilibrium model is a function ofr a andr p . The mass density and potential corresponding to a distribution function is found by means of an expansion in Hankel-Laguerre functions; the coefficients of the expansion being found by taking moments of the mass density of the individual orbits. This leads to a simple method of constructing equilibrium models.The response to a small perturbation is found by seeking the response of each orbit. When the perturbations are axisymmetric and slowly varying, the response can be easily found using adiabatic invariants. The potential is expanded in a series of Hankel-Laguerre functions, and the response operator becomes a discrete matrix. The condition that the model is stable against adiabatic radial perturbations is that the largest eigenvalue of the response matrix should be less than one.An analytic approximation to the response matrix is derived, and applied to estimate the eccentricity needed for stability against local perturbations.  相似文献   

3.
Although the sunspots migrate towards the equator, the large-scale weak diffuse magnetic fields of the Sun migrate poleward with the solar cycle, the polar field reversing at the time of the sunspot maxima. We apply the vector model of Dikpati and Choudhuri (1994, Paper I) to fit these observations. The dynamo layer at the base of the convection zone is taken to be the source of the diffuse field, which is then evolved in the convection zone subject to meridional circulation and turbulent diffusion. We find that the longitudinally averaged observational data can be fitted reasonably well both for positive and negative values of the-effect by adjusting the subsurface meridional flow suitably. The model will be extended in a future paper to include the decay of active regions as an extra source of the diffuse field, which may be necessary to explain the probable phase lag betweenB r andB at lower latitudes.  相似文献   

4.
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   

5.
An analysis of the transverse magnetic field effects on the free convective flow of an incompressible, electrically conducting viscous fluid past an infinite non-conducting and non-magnetic, vertical limiting surface (e.g., of a star), has been carried out. The limiting surface is assumed to move after receiving an initial impulse. Exact solutions to equations governing the flow are derived with the help of the Laplace transform technique. The velocity, the induced magnetic field, the skin-friction and the electric current density are shown graphically. The effects of the Grashof numberG, the Prandtl numberP, and the magnetic parameterM are described during the course of discussion.  相似文献   

6.
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   

7.
The self-gravitational instability of an ionized, thermally-conducting, magnetized, rotating plasma flow through a porous medium has been studied in the presence of suspended particles. The ionized gas-particle medium has been considered rotating along and perpendicular to the vertical magnetic field. Propagation of the plasma waves has been studied for the longitudinal and the transverse modes for both the cases of rotation. A general dispersion relation has been derived with the help of relevant perturbation equations, using the method of normal mode analysis. The Jeans criterion determines the condition of gravitational instability in all the cases with some modifications introduced by the various parameters considered. Thermal conductivity replaces the adiabatic sonic speed by the isothermal one. Considering the longitudinal mode of propagation with perpendicular rotational axis, for an inviscid plasma with adiabatic behaviour the effect of both, the rotation and the suspended particles has been removed by the magnetic field. For the transverse mode of propagation with the axis of rotation parallel to the magnetic field, the viscosity removes the effect of both, the rotation and the suspended particles. Porosity reduces the effect of both, the rotation and the magnetic field, whereas the concentration of the suspended particles reduces the rotational effect.  相似文献   

8.
Solar wind speeds (SWSs) estimated by interplanetary scintillation (IPS) observations during Carrington rotation 1753 are projected onto the so-called source-surface of 2.5 solar radii along magnetic field lines in interplanetary space. The following two working hypotheses are examined from different points of view: (1) The SWS is a weighted mean along the line of sight to a radio source; the weight for the SWS depends on the distance from theP-point, the closest approach to the Sun on the line of sight. (2) The weighting function has a very sharp peak at theP-point, so that the SWS shows a real solar wind speed at theP-point. In both the two cases, the SWSs projected onto the source surface are further projected onto the photosphere along magnetic field lines in the corona. Footpoints of these field lines are inferred as photospheric source regions of the solar wind. The intensity of the Hei (1083 nm) absorption line (HEI) in the chromosphere corresponding to these photospheric sources is interpolated from observational data. The weighted mean of the HEI is calculated in case 1. The HEI corresponding to theP-point is used in case 2. The SWS is compared with the HEI in both the two cases. It is found that the correlation between the SWS and the HEI is better in case 2 than in case 1. It is further inferred by correlation analysis between the SWS and the HEI that the solar wind is accelerated within 27 solar radii on average. Although the data examined in this paper were limited to just one solar rotation, these results suggest that the SWS estimated by the IPS technique corresponds to the solar wind speed near theP-point and the weighting function along the line of sight may have a very sharp peak near theP-point.  相似文献   

9.
In this paper we develop a new exact method combined with finite Laplace transform and theory of linear singular operators to obtain a solution of transport equation in finite plane-parallel steady-state scattering atmosphere both for angular distribution of radiation from the bounding faces of the atmosphere and for intensity of radiation at any depth of the atmosphere. The emergent intensity of radiation from the bounding faces are determined from simultaneous linear integral equations of the emergent intensity of radiation in terms ofX andY equations of Chandrasekhar. The intensity of radiation at any optical depth for a positive and negative direction parameter is derived by inversion of the Laplace transform in terms of intergrals of the emergent intensity of radiation. A new expression of theX andY equation is also derived for easy numerical computation. This is a new and exact method applicable to all problems in finite plane parallel steady scattering atmosphere.  相似文献   

10.
Magnetohydrodynamics waves and instabilities in rotating, self-gravitating, anisotropic and collision-less plasma were investigated. The general dispersion relation was obtained using standard mode analysis by constructing the linearized set of equations. The wave mode solutions and stability properties of the dispersion relations are discussed in the propagations transverse and parallel to the magnetic field. These special cases are discussed considering the axis of rotation to be in transverse and along the magnetic field. In the case of propagation transverse to the magnetic field with axis of rotation parallel to the magnetic field, we derived the dispersion relation modified by rotation and self-gravitation. In the case of propagation parallel to the magnetic field with axis of rotation perpendicular to the magnetic field, we obtained two separate modes affected by rotation and self-gravitation. This indicates that the Slow mode and fire hose instability are not affected by rotation. Numerical analysis was performed for oblique propagation to show the effect of rotation and self-gravitation. It is found that rotation has an effect of reducing the value of the phase speeds on the fast and Alfven wave modes, but self-gravitation affect only on the Slow modes, thereby reducing the phase speed compare to the ideal magneto hydrodynamic (MHD) case.  相似文献   

11.
In Paper I (Hu, 1982), we discussed the the influence of fluctuation fields on the force-free field for the case of conventional turbulence and demonstrated the general relationships. In the present paper, by using the approach of local expansion, the equation of average force-free field is obtained as (1+b)?×B 0=(α#x002B;a)B 0#x002B;a (1)×B 0#x002B;K. The average coefficientsa,a (1),b, andK show the influence of the fluctuation fields in small scale on the configurations of magnetic field in large scale. As the average magnetic field is no longer parallel to the average electric current, the average configurations of force-free fields are more general and complex than the usual ones. From the view point of physics, the energy and momentum of the turbulent structures should have influence on the equilibrium of the average fields. Several examples are discussed, and they show the basic features of the fluctuation fields and the influence of fluctuation fields on the average configurations of magnetic fields. The astrophysical environments are often in the turbulent state, the results of the present paper may be applied to the turbulent plasma where the magnetic field is strong.  相似文献   

12.
The StokesV asymmetries observed in solar faculae can be interpreted by invoking the presence of magnetic and velocity fields variations along the line-of-sight. By means of a perturbative approach, we develop the theoretical dependence on magnetic and velocity fields of the StokesV profile around its zero-crossing point. We find that the empirical curves of growth for theV zero-crossing point and the slope, as well as the curve of growth for the integral (previously derived by Sánchez Almeidaet al., 1989, through the same approach), are reproduced quite well with a single atmosphere which assumes such simultaneous variations.The depth dependence of the fields that give the best fit in our model presents several striking properties which cannot be released without totally compromising the goodness of the fit. Namely, the magnetic field strength increases towards the observer while the downflowing velocity field decreases. Both variations must occur co-spatially, in the same atmospheric layers. This fact seems to contradict theoretical models for the fanning out parts of magnetic concentrations which foresee a sharp separation between a static magnetic layer and a deep zone with velocity fields. We discuss a possible solution of such contradiction in terms of a finite optical thickness of the boundary layer between zones with and without magnetic field in faculae.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

13.
Trapezium type multiple systems are one of the youngest systems in the galaxy. Ambartsumian (1954) regards many of the Trapezium-type multiple systems as having positive total energy.The examination of Table I, compiled from theAbastumani Catalogue of Trapezia (Salukvadze, 1978; Povedaet al., 1977) and theIndex Catalogue of Visual Binary Stars, shows that real trapezia are met among multiple stars with their primaries of O and B spectral types.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.  相似文献   

14.
SW Lacertae is a short-period variable star of the W UMa-type. A total of 261 photoelectric observations for eachU, B, andV filter were obtained in 1986 while 522 photoelectric observations for eachB andV filter were obtained in 1987. All these observations were transformed to theU, B, andV colours of theUBV standard system. Nine light curves for primary and secondary eclipses were obtained, their times of minima were determined and a new linear ephemeris was obtained. The period changes of the system were also discussed.  相似文献   

15.
A survey for emission line stars was carried out in 1980 with the Schmidt telescope of Konkoly Observatory in the region of IC 1396 (Kun, 1986a, hereafter referred to as Paper I). This work was aimed at a preliminary mapping of the probable medium mass members of the association Cepheus OB 2. The stars of the region have been followed since then with the same telescope in order to obtain a more complete view on the stellar content of this giant star-forming region. The common variability of the H emission strength makes the sense of repeating such surveys. The new survey resulted in the discovery of 65 further emission stars. Equatorial coordinates and finding charts are given for them.PhotographicBVRI photometry was carried out for all known emission stars of the field. The colourmagnitude and two-colour diagrams derived from theB, V, R, andI magnitudes show that these stars are probably F-G-type (1.5M <M<3M ), partly pre-Main-Sequence members of Cep OB 2, whereas a few of them may be distant red giants.The youngest objects of the region can be found among the IRAS point sources. Their properties are discussed on the basis of IRAS data alone.  相似文献   

16.
In this paper we provide two new alternative derivations of the equation of transport for cosmic-ray particles in the interplanetary region. Both derivations are carried out by using particle positionr and timet in a frame of reference fixed in the solar system, and the particle momentump is specified relative to a local frame of reference moving with the solar wind. The first derivation is carried out by writing down a continuity equation for the cosmic rays, taking into account particle streaming and energy changes, and subsequently deriving the streaming and energy change terms in this equation. The momentum change term in the continuity equation, previously considered to be due to the adiabatic deceleration of particles in the expanding magnetic fields carried by the solar wind, appears in the present analysis as a dynamic effect in which the Lorentz force on the particle does not appear explicitly. An alternative derivation based on the ensemble averaged Liouville equation for charged particles in the stochastic interplanetary magnetic field using (r, p,t) as independent coordinates is also given. The latter derivation confirms the momentum change interpretation of the first derivation. We also provide a new derivation of the adiabatic rate as a combination of inverse-Fermi and betatron deceleration processes.  相似文献   

17.
The propagation of hydromagnetic and low frequency radio waves in all directions in a fully ionized gas containing a magnetic field is examined. For longitudinal and transverse propagation the addition of one extra term in the magneto-ionic formulae (without collisions) accounts for the presence of heavy ions.

The partition of energy of disturbance between kinetic (K) and magnetic (M) for longitudinal propagation of all frequencies is given by

where V is the Alfvén speed. Thus approximate equipartition may exist for some audio- and radio-frequencies in the Earth's exosphere.

Some errors in Paper I of this series are corrected.  相似文献   


18.
An Abelian Higgs model of sunspot generalized in a Chern-Simons-like fashion is discussed. It is shown, in particular, that both themagnetic andelectric fields are present inside the sunspot, and that the latterrotates. One demonstrates that the total angular momentum of a static, cylindrically symmetric sunspot is proportional top 2, wherep — an integer — stands for the number of magnetic fluxquanta carried by the spot. Finally, the behaviour of the Higgs field amplitude, magnetic and electric field strengths are illustrated for the spots carrying one to five flux quanta, all having the penumbra-to-umbra radius ratio of the value .  相似文献   

19.
The Ideal Resonance Problem, as formulated in 1966 (Paper I), is defined by the Hamiltonian Following the procedure adopted in the construction of a first-orderglobal solution (Papers II, III, and V), we derive a second-order solution from the von Zeipel-Bohlin recursive algorithm of Paper II. The singularities inherent in the Bohlin expansion in powers of μ have been suppressed by means of theregularizing function of Paper III, and the singularities in the coefficients atAB″=0 have been removed by thenormalization technique of Paper V. As a check, it is shown that the global solution includes asymptotically theclassical solution, expanded in powers ofμ 2, and carrying thecritical divisor B′.  相似文献   

20.
During the past decade, significant advances in thein situ measurements of planetary magnetic fields have been made. The U.S.A. and U.S.S.R. have conducted spacecraft investigations of all the planets, from innermost Mercury out to Jupiter. Unexpectedly, Mercury was found to possess a global magnetic field but neither the Moon nor Venus do. The results at Mars are incomplete butif a global field exists, it is clearly quite weak. The main magnetic field of Jupiter has been measured directly for the first time and confirms, as well as augments appreciably, the past 2 decades of groundbased radio astronomical studies which provided indirect evidence of the field. Progress in developing analytically complete models of the dynamo process suggests a possible common origin for Mercury, Earth and Jupiter.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May, 1978.  相似文献   

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