共查询到20条相似文献，搜索用时 31 毫秒
1.
Dieter Lorenz-Petzold 《Astrophysics and Space Science》1986,128(2):441-442
We make some critical remarks on the recent papers by Beesham (1986a-c) concerning exact solutions of the scale-covariant theory. 相似文献
2.
Static Friedmann-Robertson-Walker vacuum models are derived in the scale-covariant theory. Specific functional forms are obtained for the gauge function which occurs in the theory. This is in contrast to the nonstatic vacuum solutions where the gauge function is arbitrary. 相似文献
3.
The Raychaudhuri equation is written in terms of atomic units in the scale-covariant theory of Canutoet al. (1977) and it is pointed out that even dust-filled nonrotating cosmological models may not have an observable singularity of infinite density in the beginning. Simple explicit solutions of Einstein's equations are also constructed in terms of atomic units and its is shown that the Einstein-de Sitter solution in gravitational units may appear to be a static or an oscillating universe in atomic units. 相似文献
4.
The scale-covariant theory of gravitation, which was proposed by Canutoet al. (1977), assumes that gravitational and atomic units are related by a scalar function of space-time. The cosmology based on this theory can explain very well the 3K radiation, as well as Hubble's redshift law. However, Falik (1979) derived a result from the scale-covariant cosmology which was in conflict with the observed helium abundance. Contrary to Falik, we show in this paper that if we choose a gauge functionβ～t α and α satisfies the condition ?1/3<α<1, the scale-covariant cosmology will be consistent with the observed cosmic-helium abundance. The value α=1/2 has recently been suggested by Canuto and Goldman (1982) on general grounds. 相似文献
5.
A. Beesham 《Astrophysics and Space Science》1986,125(1):99-102
We derive tilted Bianchi type-V cosmological models in the scale-covariant theory. The solution for radiation is discussed separately from that for the non-radiative case. 相似文献
6.
It is shown that an analog of Birkhoff's theorem of general relativity exists in the scale-covariant theory of gravitation when the gauge function which occurs in the theory is independent of time. 相似文献
7.
A. Beesham 《Astrophysics and Space Science》1986,123(2):389-391
A solution of the field equations in the scale-covariant theory for a Bianchi type-V spacetime is obtained. It is shown that this solution represents a generalization of the general relativistic one. 相似文献
8.
A. Beesham 《Astrophysics and Space Science》1988,150(2):393-394
Recently in an interesting article Reddy and Venkateswarlu (1987) have shown that a Birkhoff-type theorem holds in the scale-covariant theory of gravitation when the gauge-function which occurs in the theory is independent of time. We show that their result can be deduced simply and easily without actually having to solve the field equations. 相似文献
9.
Field equations in the presence of a perfect fluid distributionc for Einstein-Rosen cylindrically symmetric metric are obtained in the scale-covariant theory of gravitation proposed by Canuto et al. (1977a). A static vacuum model and a non-static cosmological model corresponding to perfect fluid are presented. Physical and Kinematical properties of the models are also discussed. 相似文献
10.
An axially symmetric Bianchi type-I space-time is considered in the presence of perfect fluid source in the scale-covariant
theory of gravitation formulated by Canuto et al. [1977a, Phys. Rev. Lett. 39, 429]. With the help of special law of variation for Hubble’s parameter proposed by Bermann [1983, Nuovo Cimento 74B, 182] a cosmological model with a negative constant declaration parameter is obtained in this theory. Some physical properties
of the model are also discussed. 相似文献
11.
Abdul Ahmad 《Celestial Mechanics and Dynamical Astronomy》1995,61(2):181-196
The periodic solutions of the restricted three-body problem representing analytic continuations of Keplerian rectilinear periodic motions are well known (Kurcheeva, 1973). Here the stability of these solutions are examined by applying Poncaré's characteristic equation for periodic solutions. It is found that the isoperiodic solutions are stable and all other solutions are unstable. 相似文献
12.
We study the self-similar magnetohydrodynamics (MHD) of a quasi-spherical expanding void (viz. cavity or bubble) surrounding the centre of a self-gravitating gas sphere with a general polytropic equation of state. We show various analytic asymptotic solutions near the void boundary in different parameter regimes and obtain the corresponding void solutions by extensive numerical explorations. We find novel void solutions of zero density on the void boundary. These new void solutions exist only in a general polytropic gas and feature shell-type density profiles. These void solutions, if not encountering the magnetosonic critical curve (MCC), generally approach the asymptotic expansion solution far from the central void with a velocity proportional to radial distance. We identify and examine free-expansion solutions, Einstein–de Sitter expansion solutions, and thermal-expansion solutions in three different parameter regimes. Under certain conditions, void solutions may cross the MCC either smoothly or by MHD shocks, and then merge into asymptotic solutions with finite velocity and density far from the centre. Our general polytropic MHD void solutions provide physical insight for void evolution, and may have astrophysical applications such as massive star collapses and explosions, shell-type supernova remnants and hot bubbles in the interstellar and intergalactic media, and planetary nebulae. 相似文献
13.
In this paper we obtain the general axially symmetric space-times in scalar-tensor theory of gravitation proposed by Sáez and Ballester. The only possible solutions of these space-times in this theory are dust solutions. One of the obtained solutions here has a similar considerations to Van Stockum dust solution. A detailed study of geometric and kinematical properties of the obtained solutions are carried out. Furthermore, closed timelike curves are present in these solutions. 相似文献
14.
Arthur L. Whipple 《Celestial Mechanics and Dynamical Astronomy》1984,33(3):271-294
Fourteen equilibrium solutions of the restricted problem of 2+2 bodies are shown to exist. Six of these solutions are located about the collinear Lagrangian points of the classical restricted problem of three bodies. Eight solutions are found in the neighborhood of the triangular Lagrangian points. Linear stability analysis reveals that all of the equilibrium solutions are unstable with the exception of four solutions; two in the vicinity of each of the triangular Lagrangian points. These four solutions are found to be stable provided the mass parameter of the primary masses is less than a critical value which depends also on the mass of the minor bodies. 相似文献
15.
16.
Solution to steady-state, bigroup neutrino transport with isoenergetic and neutrino-electron scattering have been obtained for idealized conditions representative of the outer core or envelope of a star whose inner core is undergoing gravitational collapse. The solutions are presented in a form suitable for comparison with other numerical schemes. The incident neutrino distribution was chosen to be nonequilibrium, and the solutions clearly show the tendency of the neutrinos to equilibrate via neutrino-electron scattering as they propagate through the material. Care is taken to compare solutions obtained by two completely different techniques to ensure that the solutions presented here are accurate and error free. The solutions are compared with those obtained by a simple diffusion scheme, and by a flux limited diffusion scheme. The solutions given by the latter agree well with the solutions derived here, except when the neutrino angular distribution becomes oblate. 相似文献
17.
D. Lorenz-Petzold 《Astrophysics and Space Science》1984,100(1-2):475-479
Exact cosmological solutions of the vacuum Brans-Dicke field equations are derived. The solutions are the anisotropic generalizations of the isotropic de Sitter solutions of the general theory of relativity. 相似文献
18.
L. G. Luk’yanov 《Astronomy Letters》2012,38(3):201-211
Families of conditionally periodic solutions have been found by a slightly modified Lyapunov method of determining periodic
solutions near the libration points of the restricted three-body problem. When the frequencies of free oscillations are commensurable,
the solutions found are transformed into planar or spatial periodic solutions. The results are confirmed by numerically integrating
the starting nonlinear differential equations of motion. 相似文献
19.
We explore semicomplete self-similar solutions for the polytropic gas dynamics involving self-gravity under spherical symmetry, examine behaviours of the sonic critical curve and present new asymptotic collapse solutions that describe 'quasi-static' asymptotic behaviours at small radii and large times. These new 'quasi-static' solutions with divergent mass density approaching the core can have self-similar oscillations. Earlier known solutions are summarized. Various semicomplete self-similar solutions involving such novel asymptotic solutions are constructed, either with or without a shock. In contexts of stellar core collapse and supernova explosion, a hydrodynamic model of a rebound shock initiated around the stellar degenerate core of a massive progenitor star is presented. With this dynamic model framework, we attempt to relate progenitor stars and the corresponding remnant compact stars: neutron stars, black holes and white dwarfs. 相似文献
20.
Robert A. Van Gorder 《New Astronomy》2011,16(2):65-67
Perturbation solutions are obtained for the Lane–Emden equation of the second kind which describe Bonnor–Ebert gas spheres. In particular, we employ the field-theoretic perturbative procedure due to Bender et al. to obtain analytical solutions to the nonlinear initial value problem. We find that the method allows one to construct perturbation solutions which converge rapidly to the true solutions in many cases, as it allows one to more accurately represent the influence of nonlinear terms in the linearized equations. The rapid convergence of the method results in qualitatively accurate solutions in relatively few iterations. 相似文献