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1.
It is known that for a thin domain wall the pressure in the perpendicular direction to the wall is negligible. In this paper,
we have evaluated solutions for thin domain walls with spherical symmetry following two different approaches. The exact solutions
are obtained using functional separability of the metric coefficients.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
In this paper we have discussed two models of domain walls within the framework of Lyra geometry. An exact solution is obtained
for a thick non static domain wall. The space time is non singular both in its spatial and temporal behavior and the gravitational
field experienced by a test particle is attractive. It is found that these exists no particle horizon in our case. Also we
have presented a spherical domain wall with nonvanishing stress components in the direction perpendicular to the plane of
the wall. The gravitational field of the domain wall is shown to be attractive in nature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
In this paper, we study the gravitational field of domain wall in fivedimensional space-time. Exact solutions of Einstein's equations for a scalarfield with a potential V(Ø) are presented, describing thegravitational field of plane symmetric domain walls. The solution showsthat the energy density as well as pressure in the perpendicular directionon both sides of the walls to be reflection symmetric with respect to thewalls.PACS numbers: 98.80 cq, 0450 相似文献
4.
Mingyu Wu Quanming Lu Can Huang Peiran Wang Rongsheng Wang Shui Wang 《Astrophysics and Space Science》2014,352(2):565-570
An electron phase-space hole (electron hole) is considered to be unstable to the transverse instability. In this paper, two-dimensional (2D) electrostatic particle-in-cell (PIC) simulations are used to explore the dissipation process of a one-dimensional (1D) electron hole in a weakly magnetized plasma and its consequence on electron heating, which consists of two stages. In the first stage, the electron hole is still kept as a quasi-1D structure, however, with the excitation of the transverse instability and the generation of the perpendicular electric field, the electrons are scattered and then heated along the perpendicular direction in the electron hole. In the second stage, the quasi-1D electron hole is broken into several 2D electron holes. The temperature of the electrons outside of these 2D electron holes also increase, and at last the velocity distribution of the electrons become almost isotropic in the whole simulation domain. Our results provide a new dissipation mechanism of an electron hole. 相似文献
5.
The gravitational instability of an infinite homogeneous finitely conducting viscid fluid through porous medium is studied in the presence of a uniform vertical magnetic field and finite ion Larmor radius (FLR) effects. The medium is considered uniformly rotating along and perpendicular to the direction of the prevalent magnetic field. A general dispersion relation is obtained from the relevant linearized perturbation equations of the problem. Furthermore, the wave propagation along and perpendicular to the direction of existing magnetic field has been discussed for each direction of the rotation. It is found that the simultaneous presence of viscosity finite conductivity, rotation, medium porosity, and FLR corrections does not essentially change the Jeans's instability condition. The stabilizing influence of FLR in the case of transverse propagation is reasserted for a non-rotating and inviscid porous medium. It is shown that the finite conductivity has destabilizing influence on the transverse wave propagation whereas for longitudinal propagation finite conductivity does not affect the Jean's criterion. 相似文献
6.
The magneto-gravitational instability of an infinite, homogenous, and infinitely conducting plasma flowing through a porous medium is studied. The finite ion Larmor radius (FLR) effects and viscosity are also incorporated in the analysis. The prevalent magnetic field is assumed to be uniform and acting in the vertical direction. A general dispersion relation has been obtained from the relevant linearized perturbation equations of the problem. The wave propagation parallel and perpendicular to the direction of the magnetic field have been discussed. It is found that the condition of the instability is determined by the Jeans criterion for a self-gravitating, infinitely conducting, magnetized fluid through a porous medium. Furthermore, for transverse perturbation FLR is found to have stabilizing influence when the medium is considered inviscid. 相似文献
7.
We consider the ejection of one stellar system from the centre of another stellar system, representing both by Plummer models. Using the impulsive appoximation, we derive analytically the overall and differential energy changes and also the mass escape from the systems. We compare the results with those obtained for colliding systems.We find that the disruptive effects are considerably less in the case of ejection. If the ejected system is compact, it escapes with negligible disruptive effects.In the case of ejections, stars are also accelerated in the direction of motion of the system. Using a dimensionless parameter λ defined as the ratio of the squares of the stellar velocity perturbations in the direction of motion of the system and perpendicular to it, we find a significant difference between ejecting systems and colliding systems. In fast head-on collisions of spherical stellar systems, the systems become elongated in the direction perpendicular to the direction of motion whereas in the case of ejecting systems, they also become elongated in the direction of motion. These effects are more pronounced in the outer regions of the smaller system and the innner regions of the bigger system. These effects are enhanced if the ejected system is compact. 相似文献
8.
We present three-dimensional (3D) hydrodynamical simulations of ram pressure stripping of massive disc galaxies in clusters. Studies of galaxies that move face-on have predicted that in such a geometry the galaxy can lose a substantial amount of its interstellar medium. But only a small fraction of galaxies is moving face-on. In this work we focus on a systematic study of the effect of the inclination angle between the direction of motion and the galaxy's rotation axis.
In agreement with some previous works, we find that the inclination angle does not play a major role for the mass loss as long as the galaxy is not moving close to edge-on (inclination angle ≲60°). We explain this behaviour by extending Gunn & Gott's estimate of the stripping radius, which is valid for face-on geometries, to moderate inclinations.
The inclination plays a role as long as the ram pressure is comparable to pressures in the galactic plane, which can span two orders of magnitude. For very strong ram pressures, the disc will be stripped completely, and for very weak ram pressures, mass loss is negligible independent of inclination. We show that in non-edge-on geometries the stripping proceeds remarkably similar. A major difference between different inclinations is the degree of asymmetry introduced in the remaining gas disc.
We demonstrate that the tail of gas stripped from the galaxy does not necessarily point in a direction opposite to the galaxy's direction of motion. Therefore, the observation of a galaxy's gas tail may be misleading about the galaxy's direction of motion. 相似文献
In agreement with some previous works, we find that the inclination angle does not play a major role for the mass loss as long as the galaxy is not moving close to edge-on (inclination angle ≲60°). We explain this behaviour by extending Gunn & Gott's estimate of the stripping radius, which is valid for face-on geometries, to moderate inclinations.
The inclination plays a role as long as the ram pressure is comparable to pressures in the galactic plane, which can span two orders of magnitude. For very strong ram pressures, the disc will be stripped completely, and for very weak ram pressures, mass loss is negligible independent of inclination. We show that in non-edge-on geometries the stripping proceeds remarkably similar. A major difference between different inclinations is the degree of asymmetry introduced in the remaining gas disc.
We demonstrate that the tail of gas stripped from the galaxy does not necessarily point in a direction opposite to the galaxy's direction of motion. Therefore, the observation of a galaxy's gas tail may be misleading about the galaxy's direction of motion. 相似文献
9.
In this paper, we study the domain wall with time dependent displacement vectors based on Lyra geometry in normal gauge i.e. displacement vector φ i * =[β(t),0,0,0]. The field theoretic energy momentum tensor is considered with zero pressure perpendicular to the wall. We find an exact solutions of Einstein’s equation for a scalar field φ with a potential V(φ) describing the gravitational field of a plane symmetric domain wall. We have seen that the hyper surfaces parallel to the wall (z=constant) are three dimensional de-sitter spaces. It is also shown that the gravitational field experienced by test particle is attractive. 相似文献
10.
N. G. Kafousias A. A. Raptis G. A. Georgantopoulos C. L. Goudas 《Astrophysics and Space Science》1981,76(1):133-148
Unsteady two-dimensional free convection flow of an electrically conducting, viscous, incompressible fluid, past an infinite vertical porous limiting surface in the presence of a transverse magnetic field is studied, when the limiting surface is moved impulsively with a constant velocity, either in the direction of the flow or in the opposite direction. The magnetic Reynolds number of the flow is not taken to be small enough so that the induced magnetic field is not negligible. The obtained results, for the mean steady flow phenomena, are discussed with the aid of graphs and tables for different values of the dimensionless parameters entering into the problem. 相似文献
11.
Ahmed E. Radwan 《Astrophysics and Space Science》1992,187(2):241-260
The stability of a self-gravitating streaming fluid cylinder acting upon the electromagnetic force ambient with a tenuous medium of negligible inertia but pervaded by a transverse varying fields, has been developed. The stability criterion is derived, discussed analytically and the results are verified numerically. The cylinder is purely self-gravitating unstable in small axisymmetric domain and stable in all the rest states. modes while the transverse field exterior the cylinder is stabilizing or destabilizing according to restrictions in the asymmetric modes and purely destabilizing in the symmetric one. The streaming has a strong destabilizing influence and that influence is independent of the kind of the perturbation and wavelengths. Both the streaming and the electromagnetic influences increase the gravitational axisymmetric unstable domain and shrink those of stability in the axisymmetric and non-axisymmetric perturbations. Moreover, the stabilizing character of the Lorentz force of some states, is physicaly interpreted, will not be able to suppress the gravitational instability because the gravitational instability of sufficiently long waves will persist. 相似文献
12.
The gravitational instability of an infinite homogenous rotating plasma through a porous medium in the presence of a uniform magnetic field with finite electrical and thermal conductivities has been studied. With the help of relevant linearized perturbation equations of the problem, a general dispersion relation is obtained, which is further reduced for the special cases of rotation, parallel and perpendicular to the megnetic field acting in the vertical direction. Longitudinal and transverse modes of propagation are discussed separately. It is found that the joint effect of various parameters is simply to modify the Jeans's condition of instability. The effect of finite electrical conductivity is to remove the effect of magnetic field where as the effect of thermal conductivity is to replace the adiabatic velocity of sound by the isothermal one. Rotation has its effect only along the magnetic field in the transverse mode of propagation for an inviscid plasma, thereby stabilizing the system. Porosity reduces the effect of both, the magnetic field and the rotation, in the transverse mode of propagation in both the cases of rotation. The effect of viscosity is to remove the rotational effects parallel to the magnetic field in the transverse mode of propagation. 相似文献
13.
Unsteady hydromagnetic thermal boundary layer flow past a non-conducting infinite porous wall in presence of a transverse magnetic field is considered. The magnetic Reynolds number of the flow is taken to be small enough so that the induced magnetic field is negligible. It is assumed that the normal velocity of suction/injection at the wall varies att ?/12. Solution of the problem, in the form of power series, is obtained for two cases:
- When the wall temperature is the same as that of the free-stream, and
- When the difference in the temperatures of the wall and that of the free-stream varies as some power of time. The variations of the skin-friction, the temperature and the rate of heat transfer are shown graphically followed by a quantitative discussion.
14.
VLBI total intensity and linear polarization images of the BL Lacertae object OJ 287 have been obtained at using a global ground array and the HALCA orbiting antenna, and at two weeks earlier using the VLBA. In the ground-based 6-cm images, the source is dominated by a core–jet double structure the components of which are essentially unresolved. The baselines to the orbiting antenna resolve both of these compact components. In the VSOP images, the ground-based 'core' breaks up into several distinct components, demonstrating that this region is dominated by the contribution of bright, optically thin knots of jet emission. A very similar structure is observed in the 1.3-cm image. The magnetic field in the core is transverse, becomes longitudinal in the inner jet, then makes a sharp transition to a region of transverse field further from the core. This suggests that the field in the outer jet has become highly ordered in the transverse direction owing to the action of a shock; the physical nature of the extended region of longitudinal field closer to the core is not clear. The availability of nearly simultaneous observations with comparable resolution at widely spaced frequencies enabled detection of a ≃90° rotation in polarization position angle for the core, owing to the transition from the optically thick (6 cm) to the optically thin (1.3 cm) regime. 相似文献
15.
Prominences and filaments are thought to arise as a consequence of a magnetized plasma undergoing thermal instability. Therefore, the thermal stability of a magnetized plasma is investigated under coronal conditions. The equilibrium structure of the plasma is approximated by a 1-D slab configuration. This is investigated in thermal instability taking into account optically thin plasma radiation and anisotropic thermal conduction. The thermal conduction perpendicular to the magnetic field is taken to be small but non-zero.The classic rigid wall boundary conditions which are often applied in the literature, either directly on the plasma or indirectly through some other medium, are replaced by a more physical situation in which the plasma column is placed in a low-density background stretching towards infinity. Results for a uniform equilibrium structure indicate the major effect of this change is on the eigenfunctions rather than on the growth rate. Essentially, perpendicular thermal conduction introduces field-aligned fine structure. It is also shown that in the presence of perpendicular thermal conduction, thermal instability in a slab model is only possible if the inner plasma has the shortest thermal instability time scale.Research Assistant of the National Fund for Scientific Research (Belgium). 相似文献
16.
D. C. Gabuzda T. V. Cawthorne 《Monthly notices of the Royal Astronomical Society》2000,319(4):1056-1066
Global VLBI images in intensity and linear polarization at of the BL Lacertae objects 0235+164, 0300+470, 0735+178, 0954+658, 1803+784, 1823+568, and BL Lac and OVV quasar 3C 279 are presented and analysed. These are the highest resolution polarization images currently available for several of these sources. On the whole, the tendencies observed at longer centimetre wavelengths are also exhibited in these 1.3-cm images. When core polarization is detected, the corresponding polarization angles χ tend to lie either parallel or perpendicular to the direction of the inner jet. The core degrees of polarization are usually comparable to those typical at 6 cm, but somewhat lower in several cases, suggesting that the higher resolution data are better separating the contributions of intrinsically weakly polarized cores and highly polarized emerging knots. The observed χ vectors in the jets of 0735+178, 0954+658, 1823+568, BL Lac and 3C 279 are aligned with the jet, implying the presence of transverse magnetic fields. In 0300+470 and BL Lac, there are regions where the direction of χ seems to be neither parallel nor perpendicular to the jet; it is not clear whether this is due to genuine obliquity of the magnetic field structure or to inadequate knowledge of the local flow direction. 相似文献
17.
Farook Rahaman 《Astrophysics and Space Science》2002,282(4):625-633
Thick domain walls with time dependent displacement vector based on Lyra's geometry are considered. Their exact solutions are obtained in the background of a five-dimensional space time. The field theoretic energy-momentum tensor is considered assuming with $$T_t^t = T_x^x = T_y^y = T_\psi ^\psi .$$ Acceleration due to the domain wall has been evaluated by studyinggeodesic equation. 相似文献
18.
Many coronal transient exhibit a circular aspect, which has been interpreted up to now as a loop structure. From polarization measurements of the 10 August, 1973 transient observed by the ATM coronagraph, which allows the location of material away from the plane of the sky, we show that this particular transient is more likely to be a 3-dimensional, bubble-shaped structure, than a loop. The radial component of the speed is evaluated. A thin streamer close to the transient is displaced by its passage, both in the plane of the sky and in the direction perpendicular to it. 相似文献
19.
M. S. Ruderman 《Solar physics》2014,289(7):2473-2485
We consider kink oscillations of thin magnetic tubes with the equilibrium density discontinuous in the axial direction. The aim is to find out what boundary conditions have to be used at a contact discontinuity where the equilibrium density jumps. At a contact discontinuity perturbations of all quantities but the density have to be continuous. However, in the thin-tube approximation, all these conditions cannot be satisfied simultaneously. It is shown that in the thin-tube approximation, there is a boundary layer with the thickness of the order of the tube radius that embraces the contact discontinuity. In this boundary layer the variation of the loop displacement and its axial derivative is negligible. In contrast, the total pressure variation in the boundary layer is very strong. Hence, the correct boundary conditions at a contact discontinuity in the thin-tube approximation are the continuity of the tube displacement and its axial derivative. 相似文献
20.
The problem of incipient fragmentation of interstellar matter to form condensation is investigated taking into account the porosity, viscosity, thermal conductivity, and effect of finite ion-Larmor radius (FLR) on the self-gravitating plasma having a uniform magnetic field acting in vertical direction. Relevant linearized equations are stated and dispersion relation is obtained. Wave propagation in longitudinal and transverse direction to the magnetic field is considered. Stability and instability of the medium is discussed. It is found that if the Jeans's instability condition is not fulfilled the medium must remain stable. Magnetic field, FLR and porosity do not affect the Jeans's criterion of instability in longitudinal direction but in transverse direction, the magnetic field and FLR have stabilizing effect which is reduced due to porosity of the medium. Thermal conductivity destabilizes the medium in both the directions. In transverse direction contribution of FLR on the Jeans's expression for instability is not observed in thermally conducting medium. 相似文献