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1.
In the present article we have obtained a class of analytical solutions for an anisotropic charged fluid distribution. The neutral anisotropic fluid sphere has already been obtained by Maurya and Gupta (Phys. Scr. 86:025009, 2012). The solutions depend upon both the anisotropic and the charge parameter. The anisotropy parameter and the electric intensity is zero at the centre and monotonically increasing towards the pressure free interface. All the physical entities such as energy density, radial pressure, tangential pressure, and velocity of sound are monotonically decreasing towards the surface. 相似文献
2.
D. Hubert 《Planetary and Space Science》1982,30(11):1137-1146
The velocity distribution of ion populations is calculated for auroral conditions where strong convection electric fields exist. The Boltzmann equation has been solved for the E and F regions of the ionosphere where plasma is weakly dense, weakly ionized and where the ion-neutral collision frequency is small in regard to the ion cyclotron frequency. The ion distribution function has been expanded in a generalized orthogonal polynomial series about a bi-Maxwellian “temperature” varying weight function. This generalized Grad solution expansion enables us to obtain good approximations for electric field strengths as large as 75 mV m?1 and 115 mV m?1 respectively, for both the resonant charge exchange and the polarization collision models. The instability threshold of these distribution functions appears to be higher than the two respective electric field strengths considered above. 相似文献
3.
王行翔 《中国天文和天体物理学报》1988,(3)
本文在假设荷电球体内部物质密度为ρ_m=μγ~α,电荷密度为ρ_e=ρ_0γ~(b_e-λ/2)的情况下,严格求解Einstein-Maxwell场方程,求得了静态荷电球体的一个较为普遍的内部解。这个解可以看作是Wyman得到的内部解推广到荷电情况下的结果,并且将Wilson,李鉴增,Santos,Pant和Sah等人给出的许多结果作为自己的特例包括在内。 相似文献
4.
D. Hubert 《Planetary and Space Science》1983,31(1):119-127
The ion distribution function is calculated for the E and the F regions of the auroral latitudes. In these regions the plasma is weakly ionized and there exist convective electric fields which may attain very significant intensities. Boltzmann's equation is solved in the limit where the ion-neutral collision frequency is much lower than the ion gyrofrequency. This solution is obtained in the form of a generalized polynomial series expansion starting from a good zeroth-order approximation. With this weight function, and considering a development to the order of the 32 moments, good approximations are obtained for high electric fields. The resonant charge exchange model and the polarization model are successively considered. The Post-Rosenbluth instability threshold is discussed for the above two models. 相似文献
5.
An analytical solution in terms of elliptic integrals is found for the problem connected to the isolthermal collapse of a gaseous sphere. In this way the time-dependence of spatial density distribution is promptly obtained in each point inside the sphere itself. An application for interstellar clouds is given. 相似文献
6.
《New Astronomy》2020
We have studied a new solution of charged gravastars with isotropic matter configuration in the framework of f(R, T) theory of gravity. For this purpose, we have assumed the electric charge as a constant. This stellar structure divided into three different regions: The preliminary part shows the interior charged region in which pressure equals to the negative density, second is the intermediate charged shell which is assumed to be very thin and filled with ultrarelativistic stiff fluid and the last corresponds to the electrovacuum region which is defined by an exterior Reissner-Nordström solution. Under these assumptions, we have found some physical aspects like length, energy, entropy and equation of state for charged spherical gravastar distribution. Moreover, we present an exact solution that free from event horizon and non-singular for this our new model. 相似文献
7.
A. A. Solov’ev 《Solar physics》2013,286(2):441-451
We consider the dissipative evolution of a spherical magnetic vortex with a force-free internal structure, located in a resistive medium and held in equilibrium by the potential external field. The magnetic field inside the sphere is force-free (the model of Chandrasekhar in Proc. Natl. Acad. Sci. 42, 1, 1956). Topologically, it is a set of magnetic toroids enclosed in spherical layers. A new exact MHD solution has been derived, describing a slow, uniform, radial compression of a magnetic spheroid under the pressure of an ambient field, when the plasma density and pressure are growing inside it. There is no dissipation in the potential field outside the sphere, but inside the sphere, where the current density can be high enough, the magnetic energy is continuously converted into heat. Joule dissipation lowers the magnetic pressure inside the sphere, which balances the pressure of the ambient field. This results in radial contraction of the magnetic sphere with a speed defined by the conductivity of the plasma and the characteristic spatial scale of the magnetic field inside the sphere. Formally, the sphere shrinks to zero within a finite time interval (magnetic collapse). The time of compression can be relatively small, within a day, even for a sphere with a radius of about 1 Mm, if the magnetic helicity trapped initially in the sphere (which is proportional to the number of magnetic toroids in the sphere) is quite large. The magnetic system is open along its axis of symmetry. On this axis, the magnetic and electric fields are strictly radial and sign-variable along the radius, so the plasma will be ejected along the axis of magnetic sphere outwards in both directions (as jets) at a rate much higher than the diffusive one, and the charged particles will be accelerated unevenly, in spurts, creating quasi-regular X-ray spikes. The applications of the solution to solar flares are discussed. 相似文献
8.
Details of the solution are derived for a steady, self-similar, comoving, isothermal cooling flow. The distribution of gas phases can be expressed in terms of the mass flow function, ̇( r, T ), which gives the mass per unit time of gas hotter than temperature T flowing into a sphere of radius r . Self-similarity allows this to be separated as ̇( r, T ) =̇ (r) g (T) , where ̇ (r) is the usual mass flow rate and g(T) is a dimensionless function expressing the distribution of the phases. It is shown that, for ̇ (r)∝r η ,
where Tm is the maximum temperature of the hot gas. In the units used here, the corresponding solution for the differential emission measure from within a sphere of radius r is
where ̇=̇ (r) is the total mass flow rate into the sphere. 相似文献
where T
where ̇=̇ (r) is the total mass flow rate into the sphere. 相似文献
9.
I. C. Simpson 《Astrophysics and Space Science》1978,57(2):381-400
The electrostatic interaction of charged dust grains is analysed by considering the interaction of two charged conducting spheres, rather than the hitherto considered model of a sphere and a point charge. Considerable mofification of the induced charge effects results when the nonzero radius of the second sphere is taken into account.In particular, it is shown that image charge or polarization effects can only be of significance as far as collision rates are concerned when modulus of the charge ratio of two colliding grains is very different from the ratio of their radii. Such a charge ratio deviates from the original Spitzer calculation, where grains have identical charge, irrespective of the grain material, for a given radius. This deviation may occur in cool gas clouds such as Hi regions and dense molecular clouds where the discreteness of electron charge is important, or in interstellar clouds where considerable photo-ionization of a mixture of grain materials of widely varying photoelectric efficiencies takes place.It is further argued that, with regard to the induced charge effects, the accretion rate will not be significantly different for dielectric as compared to conducting grains, regardless of the type of gas cloud under consideration. 相似文献
10.
A. N. Timokhin 《Astrophysics and Space Science》2007,308(1-4):345-351
Pulsar “standard model”, that considers a pulsar as a rotating magnetized conducting sphere surrounded by plasma, is generalized
to the case of oscillating star. We developed an algorithm for calculation of the Goldreich-Julian charge density for this
case. We consider distortion of the accelerating zone in the polar cap of pulsar by neutron star oscillations. It is shown
that for oscillation modes with high harmonic numbers (l,m) changes in the Goldreich-Julian charge density caused by pulsations of neutron star could lead to significant altering of
an accelerating electric field in the polar cap of pulsar. In the moderately optimistic scenario, that assumes excitation
of the neutron star oscillations by glitches, it could be possible to detect altering of the pulsar radioemission due to modulation
of the accelerating field.
This work was partially supported by RFBR grant 04-02-16720, and by the grants N.Sh.-5218.2006.2 and RNP-2.1.1.5940. 相似文献
11.
In this work, the charged black hole solution to the Brans-Dicke gravity theory in the presence of the nonlinear electrodynamics has been investigated. To simplify the field equations, a suitable conformal transformation has been used which transforms the Brans-Dicke-Born-Infeld Lagrangian to that of Einstein-dilaton theory with new nonlinear electrodynamics field. A new class of 4-dimensional black hole solution has been constructed out as the exact solution to the Brans-Dicke theory in the presence of the Born-Infeld nonlinear electrodynamics. The physical properties of the solutions have been studied. The black hole charge and temperature have been calculated making use of the Gauss’s law and the concept of surface gravity, respectively. Also, the black hole mass and entropy have been obtained from geometrical methods. Through a Smarr-type mass formula as a function of the black hole charge and entropy the black hole temperature and electric potential, as the intensive parameters conjugate to the black hole entropy and charge, have been calculated. 相似文献
12.
A time-dependent analysis is made of the temperature distribution within the boundary layer when a sphere is set impulsively into motion in a fluid of different temperature. The method of successive approximations is used for the solution of the equations of motion. The method provides satisfactory results for small time intervals after the commencement of the motion. 相似文献
13.
For application to the auroral ionosphere we have calculated ion velocity distributions for a weakly-ionized plasma subjected to crossed electric and magnetic fields. By replacing the Boltzmann collision integral with a simple relaxation model, we have been able to obtain an exact solution to Boltzmann's equation. This solution has the advantage over a series expansion in that all the higher order velocity moments are inherent in it. The exact solution is particularly advantageous when studying large departures of the distribution from its Maxwellian form because these departures are caused by the higher velocity moments. In general, however, a simple relaxation model can only be used to obtain qualitative information on the distribution function. Consequently, we can determine when the higher order velocity moments affect the ion velocity distribution and the nature of their effect, but we cannot obtain accurate quantitative results. The higher velocity moments have their greatest effect on the distribution function above about 120 km, where the ion-neutral collision frequency is less than the ion cyclotron frequency. As the magnitude of the electric field increases, these higher moments act to decrease the number of ions at the peak of the distribution function. Peak densities are reduced by a few per cent for perpendicular electric fields of about 20 mV m?1. 相似文献
14.
A numerical model is used to simulate the buildup of an electric field from below the Venusian cloud layer to the surface. The steady-state profiles of the ion concentration, net space charge, diffusion and conduction current, and electric field are calculated. Two electric field sources are considered. The first is that produced by the higher diffusivity of positive ions relative to negative ions, which results in charging the surface with a net positive charge. The results show that the magnitude of the electric field and the net space charge developed near the surface are mainly dependent on the mixing conditions in the boundary layer. However, even in the case of relatively strong mixing, the maximum electric field is found to be 1.5 V m?1 and it decays rapidly above 100 m. The second source of an electric field is assumed to be charge separation inside Venusian clouds. A steady-state conduction current in the region below the layer of clouds which represents the intensity of charge separation inside the clouds is used as a parameter. When this parameter is assumed to be 10?12 A m?2, which is about the fair-weather conduction current in the atmosphere of Earth, an electric field of 5 kV m?1 is developed near the surface. This electric field exists up to a few kilometers, decreases by an order of magnitude at about 20 km, and then decays rapidly. 相似文献
15.
Hyun KyuLee Chul H.Lee Maurice H. P. M.van Putten 《Monthly notices of the Royal Astronomical Society》2001,324(3):781-784
The electric charge on rotating black holes is calculated to be ∼ BJ in the force-free configuration of Ghosh, with a horizon flux of ∼ BM 2 . This charge is gravitationally weak for B ∼1015 G , so that the Kerr metric applies. Being similar to the electric charge of a magnetar, both electric charge and magnetic flux should be, in sign and order of magnitude, continuous during stellar collapse into a black hole. Extraction of the rotational energy from newly formed black holes may proceed by interaction with the magnetic field. 相似文献
16.
For application to studies of the high latitude ionosphere, we have calculated ion velocity distributions for a weekly-ionized plasma subjected to crossed electric and magnetic fields. An exact solution to Boltzmann's equation has been obtained by replacing the Boltzmann collision integral with a simple relaxation model. At altitudes above about 150 km, where the ion collision frequency is much less than the ion cyclotron frequency, the ion distribution takes the shape of a torus in velocity space for electric fields greater than 40 mV m?1. This shape persists for 1–2 hr after application of the electric field. At altitudes where the ion collision and cyclotron frequencies are approximately equal (about 120 km), the ion velocity distribution is shaped like a bean for large electric field strengths. This bean-shaped distribution persists throughout the lifetime of ionospheric electric fileds. These highly non-Maxwellian ion velocity distributions may have an appreciable affect on the interpretation of ion temperature measurements. 相似文献
17.
We study Maxwell equations in the external background spacetime of a slowly rotating magnetized NUT star and find analytical
solutions for the exterior electric fields after separating the equations for electric field into angular and radial parts
in the lowest order in angular momentum and NUT charge approximation. The star is considered isolated and in vacuum, with
dipolar magnetic field aligned with the axis of rotation. The contribution to the external electric field of star from the
NUT charge is considered in detail. 相似文献
18.
The topological structure of the electric topological current of the locally gauge invariant Maxwell-Chern-Simons Model and
its bifurcation is studied. The electric topological charge is quantized in term of winding number. The Hopf indices and Brouwer
degree labeled the local topological structure of the electric topological current. Using Φ-mapping method and implicit function
theory, the electric topological current is found generating or annihilating at the limit points and splitting or merging
at the bifurcate points. The total electric charge holds invariant during the evolution.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
The Deutsch solution to the electromagnetic field in a vacuum surrounding a perfectly conducting obliquely rotating sphere with a dipolar distribution of magnetic flux is extended to the oblique rotator with a general axisymmetric surface flux. It is shown that the torque component perpendicular to the rotation axis is always of opposite sign to the decelerating component parallel to the rotation axis. It is emphasized that this unambiguous result may not apply to more realistic pulsar models with magnetospheres containing charges. 相似文献
20.
W. Barreto 《Astrophysics and Space Science》1993,201(2):191-201
The influence of viscosity on the gravitational collapse in radiating fluid spheres is investigated. The interior solution is matched with the Vaidya metric at the boundary of the fluid distribution. Prescribing an equation of state to take into account the degree of induced anisotropy by the viscosity and using the Herrera, Jiménez and Ruggeri method, we obtain an explicit Tolman VI-like exploding model. The sphere explodes more violently when the anisotropy due to the viscosity is smaller. The shear viscosity diminishes with the expansion of the distribution of matter. 相似文献