共查询到20条相似文献，搜索用时 15 毫秒
1.
In the present paper self-similar solutions have been investigated for the propagation of piston driven, radiative gas-dynamic shocks into an inhomogeneous ideal gas permeated by a current free azimuthal magnetic field for spherical symmetry. The effects of radiation flux and magnetic field together have been seen in the region of interest on the other flow variables. The total energy of the flow between the piston and the shock is taken to be dependent on the shock radius obeying a power law. The radiative pressure and energy have been neglected. This problem is more general than the others done so far. The word piston implies some means to drive plasma radially onwards. 相似文献
2.
Self-similar flows of a perfect gas behind a cylindrical blast wave with radiation heat flux in the presence of an azimuthal magnetic field have been investigated. The effects of radiation flux and magnetic field together on the other flow variables have been studied in the region of interest. The magnetic field and density distribution vary as an inverse power of radial distance from the axis of symmetry. The electrical conductivity of the gas is taken to be infinite. The total energy of the flow between the inner expanding surface and the shock is assumed to be constant. We also have supposed the gas to be grey and opaque and the shock to be transparent and isothermal. 相似文献
3.
Y. E. Lyubarsky 《Monthly notices of the Royal Astronomical Society》2003,345(1):153-160
The origin of radio emission from plerions is considered. Recent observations suggest that radio-emitting electrons are presently accelerated rather than having been injected at early stages of the plerion evolution. The observed flat spectra without a low-frequency cut-off imply an acceleration mechanism that raises the average particle energy by orders of magnitude but leaves most of the particles at an energy of less than approximately a few hundred MeV. It is suggested that annihilation of the alternating magnetic field at the pulsar wind termination shock provides the necessary mechanism. Toroidal stripes of opposite magnetic polarity are formed in the wind emanating from an obliquely rotating pulsar magnetosphere (the striped wind). At the termination shock, the flow compresses and the magnetic field annihilates by driven reconnection. Jump conditions are obtained for the shock in a striped wind. It is shown that the post-shock magnetohydrodynamic parameters of the flow are the same as if the energy of the alternating field had already been converted into plasma energy upstream of the shock. Therefore, the available estimates of the ratio of the Poynting flux to the matter energy flux, σ, should be attributed not to the total upstream Poynting flux but only to that associated with the average magnetic field. A simple model for the particle acceleration in the shocked striped wind is presented. 相似文献
4.
Similarity solutions describing the flow of a perfect gas behind a cylindrical shock wave with transverse magnetic field are investigated in an inhomogeneous medium. The total energy of the shock wave is assumed to be constant. A comparative study has been made between the results with and without magnetic field. 相似文献
5.
D. Lorenz 《Astrophysics and Space Science》1982,83(1-2):69-74
Self-similar solution for isothermal flows driven by an expanding piston are investigated in the presence of magnetic field. The total energy of the flow between the shock and the piston is taken to be dependent on time obeying a power law. The shock is assumed to be strong and propagating into a perfect gas at rest with non uniform density and magnetic field. 相似文献
6.
A similarity solution for the flow variables behind a radiation-driven magnetohydrodynamic shock wave has been obtained. Owing to absorption of radiation incident on the shock layer, it is assumed that the total energy contained behind the shock surface is increasing. The ambient medium in which shock wave moves is non-uniform and it is optically thin so that there is no interaction with the incident radiation. A comparison has been made between the results with and without the magnetic field when the density and azimuthal magnetic field distributions are variable.While this paper was in press, Professor Verma passed away on 4 April 1985, without being able to read its proofs. 相似文献
7.
The propagation of magnetogasdynamic cylindrical shock waves in an exponentially increasing medium including the effects of the azimuthal magnetic field, is investigated. The shock wave moves with variable velocity and the total energy of the wave is variable. It is shown that the magnetic field has its significant effect on the pressure flow velocity and the inner expanding vacuum region. 相似文献
8.
A comparative study has been made between the effects of transverse and axial components of the magnetic field on the self-similar flow variables of the field behind the cylindrical shock waves propagating into a non-uniform atmosphere at rest. The total energy of the wave is constant. 相似文献
9.
In this paper, we present an expanding disc model to derive the polarization properties of the Crab nebula. The distribution function of the plasma and the energy density of the magnetic field are prescribed as functions of the distance from the pulsar using the model derived by Kennel and Coroniti with σ= 0.003 , where σ is the ratio of the Poynting flux to the kinetic energy flux in the bulk motion just before the termination shock. Unlike the case for previous models, we introduce a disordered magnetic field, which is parametrized by the fractional energy density of the disordered component. The flow dynamics are not solved, and the mean field is toroidal.
The averaged degree of polarization over the disc is obtained as a function of the inclination angle and fractional energy density of the disordered magnetic field. It is found for the Crab Nebula that the disordered component contains about 60 per cent of the magnetic field energy. This value is supported by the facts that the disc appears not as 'lip-shaped' but as 'rings' in the observed intensity map, and that the highest degree of polarization of ∼40 per cent is reproduced for rings, which is consistent with the observations.
We suggest that, because the disordered field contributes to the pressure rather than to the tension, the pinch force may have been overestimated in previous relativistic magnetohydrodynamic simulations. The disruption of the oppositely directed magnetic fields, which is proposed by Lyuvarsky, may actually take place. The relativistic flow speed, which is indicated by the front–back contrast, can be detected in the asymmetry of distributions of the position angle and depolarization. 相似文献
The averaged degree of polarization over the disc is obtained as a function of the inclination angle and fractional energy density of the disordered magnetic field. It is found for the Crab Nebula that the disordered component contains about 60 per cent of the magnetic field energy. This value is supported by the facts that the disc appears not as 'lip-shaped' but as 'rings' in the observed intensity map, and that the highest degree of polarization of ∼40 per cent is reproduced for rings, which is consistent with the observations.
We suggest that, because the disordered field contributes to the pressure rather than to the tension, the pinch force may have been overestimated in previous relativistic magnetohydrodynamic simulations. The disruption of the oppositely directed magnetic fields, which is proposed by Lyuvarsky, may actually take place. The relativistic flow speed, which is indicated by the front–back contrast, can be detected in the asymmetry of distributions of the position angle and depolarization. 相似文献
10.
Similarity solutions, for a point explosion in a spheroid with axially symmetric density distribution obeying power laws in the presence of magnetic field, are obtained. A new technique suggested by Bhowmick (1978) has been utilised to study the character of flow variables behind the shock front in an axisymmetric model. The total energy of the wave is constant. 相似文献
11.
An approximate analytical solution for self-similar flow behind a spherically-symmetric magnetogasdynamic strong shock wave is investigated using the method of Laumbach and Probstein (1969). The total energy of flow is taken to be dependent on the shock radius obeying a power law. The shock is propagating into a perfect gas at rest with non-uniform density and magnetic field. 相似文献
12.
Similarity solutions describing the flow of a perfect gas behind a spherical and cylindrical shock wave in a magnetic field with radiation heat flux have been investigated. The total energy of the expanding wave has been assumed to remain constant. The solutions, however, are only applicable to a gaseous medium where the undisturbed pressure falls as the inverse square of the distance from the line of explosion. 相似文献
13.
A. K. Dwivedi 《Astrophysics and Space Science》1993,202(1):185-200
Similarity solutions of an isothermal flow of a perfect gas behind spherical shock waves are studied in the presence of magnetic field. The flow is caused by a propelling contact surface (or expanding piston) and its total energy increases with time. The shock is propagating in a medium at rest with uniform and non-uniform density. The two important models have been also considered here in which the magnetic field is proportional to
–1 and
–3/2. 相似文献
14.
An exact similarity solution for a spherical magnetogasdynamic shock is obtained in the case when radiation energy, radiation pressure and radiative heat flux are important. The total energy of the shock wave increase with time. We have shown that due to the magnetic field the flow variables are considerably changed. Also, due to increases in radiation pressure number the radiation flux is increased. 相似文献
15.
Self-similar solutions for adiabatic and isothermal flows driven out by a propelling contact surface, moving into a quiet solar wind region, are investigated in the presence of magnetic field. The total energy of the flow between the shock and the contact surface is taken to be time-dependent obeying a power-law. The shock is assumed to be strong and propagating into a perfect gas at rest with non uniform density and magnetic field. 相似文献
16.
J. B. Singh 《Astrophysics and Space Science》1988,150(1):43-52
Using a well-known similarity method, different aspects of cylindrical shock waves in magnetogasdynamics are investigated. Weak and strong shocks have been discussed in strong magnetic field. Combined effects of both the components of magnetic field on flow variables are studied. 相似文献
17.
The effect of radiation up on the state of gas behind strong M.H.D. shock front has been studied. The jump conditions for flow variables across the shock boundary have been obtained and temperature decay behind the shock front is determined for a optically-thin brehmsstrahlung radiation plasma. It has been found that, for a shock within strong magnetic field, the temperature decay is much quicker. 相似文献
18.
In this paper propagation of magnetogasdynamic spherical shock waves is considered in an exponentially increasing medium. The shock wave moves with variable velocity and the total energy of the wave is variable. It is shown that the magnetic field changes the flow velocity, density and pressure. 相似文献
19.
I. N. Toptygin 《Astronomy Letters》2004,30(6):393-403
We offer a possible explanation for the observational data on the magnetic-field structure in young supernova remnants (SN 1006, Tycho, Kepler, Cas A) that have been obtained by analyzing the polarizations of electromagnetic radiation in the radio, infrared, and other wavelength ranges. The authors of observational works interpret these data as evidence that the ordered magnetic-field component is predominantly radial, but it can be much smaller in amplitude than the stochastic field component that accounts for the bulk of the total magnetic energy. We calculate the magnetic field in supernova remnants by taking into account the shock compression of the primary field and the generation of a large-scale magnetic field by the particles accelerated at the shock front. The assumption that the field in the supernova remnant is the explosion-compressed primary field near the star is inconsistent with observational data, because the tangential (relative to the shock front) field component perpendicular to the radius must prevail in this case. However, allowing for the generation of an additional magnetic field by the electric current of the particles accelerated by a strong shock front leads us to conclude that the field components parallel to the front are suppressed by accelerated particles by several orders of magnitude. Only the component perpendicular to the front remains. Such a field configuration for uniform injection does not lead to the generation of an additional magnetic field, and, in this sense, it is stable. This explains the data on the radial direction of the ordered field component. As regards the stochastic field component, we show that it is effectively generated by accelerated particles if their injection into acceleration at the shock front is nonuniform along the front. Injection nonuniformity can be caused by upstream density nonuniformities. A relative density nonuniformity of the order of several percent is enough for an observable magnetic field with scales on the order of the density nonuniformity scales to be generated. 相似文献
20.
A theoretical model of shock-wave propagation has been studied in a heat-conducting and a self-gravitating medium. The effects of magnetic field has been taken into consideration. The shock is strong enough to neglect the ambient gas pressure. The variation of flow variables behind the shock have been investigated numerically. 相似文献