Is the Stephani-Krasiński solution a viable model of the Universe?

We present a detailed study of the inhomogeneous Stephani-Krasinski solution with time-dependent curvature index. In general, the cosmological behaviour of the models depends on six arbitrary functions of time. Such models are termed ‘private universes’ and cannot be in accord with observation in the most general case. Two simple models with changing topology are considered as illustrating examples. In one of these models the pressure turns out to be negative and hence a violation of the weak energy condition in the singularity theorems is possible. A brief review of other inhomogeneous cosmologies is included for the sake of clarity. It is shown that the geodesic equation can be reduced to a complicated differential equation, which depends on the three arbitrary functions involved. Therefore, it is difficult to obtain explicit formulas for the various observational relations.     

The maximum mass of neutron stars

Summary. The maximum mass of neutron stars plays an important role in determining the end point of the evolution of massive stars. As the number of stellar mass black holes in binary x-ray sources grows, and as the mass spectrum of the black holes emerges, the value of the maximum mass of neutron stars has acquired great significance. Although it is now more than sixty years since the first attempt by Oppenheimer and Volkoff, no definitive answer can be given. This review will attempt to outline the main difficulties, both conceptual as well as technical, that stand in the way of a reliable estimate of the maximum mass. We shall also highlight how laboratory experiments, as well as astronomical observations, may help to clarify the true nature of the interior of neutron stars. Received 26 November 2001 / Published online 22 April 2002     

Bianchi type-III cosmological model in four- and five-dimensional bimetric theory of relativity

Four- and five-dimensional Bianchi type-III cosmological model in Rosen (1980) bimetric theory of gravitation is considered. Restricting to a particular type of background metric, it is observed that the Bianchi type-III cosmological model does not exist in case of both meson field and mesonic perfect fluid. Hence only vacuum model can be obtained.     

Simulations of the axisymmetric magnetospheres of neutron stars

In this paper we present the results of time-dependent simulations of the dipolar axisymmetric magnetospheres of neutron stars carried out within the frameworks of both relativistic magnetohydrodynamics (MHD) and resistive force-free electrodynamics. The results of force-free simulations reveal the inability of our numerical method to accommodate the equatorial current sheets of pulsar magnetospheres, and raise a question mark about the robustness of this approach. On the other hand, the MHD approach allows us to make significant progress. We start with a non-rotating magnetically dominated dipolar magnetosphere and follow its evolution as the stellar rotation is switched on. We find that the time-dependent solution gradually approaches a steady state that is very close to the stationary solution of the pulsar equation found in 1999 by Contopoulos, Kazanas & Fendt. This result suggests that other stationary solutions that have the Y-point located well inside the light cylinder are unstable. The role of particle inertia and pressure on the structure and dynamics of MHD magnetospheres is studied in detail, as well as the potential implications of dissipative processes in the equatorial current sheet. We argue that pulsars may have differentially rotating magnetospheres which develop noticeable structural oscillations, and that this may help to explain the nature of the subpulse phenomena.     

Gravitational Lensing in A Model With Non-Interacting Matter and Vacuum Energies

The gravitational lensing rate in a flat cosmological model of noninteracting matter and vacuum energies is investigated. It turns out to be very close to that in a recently studied modified general relativity model and that it is consistent with observations.     

运动电荷激发的电场是有源有旋场的一种证明

根据狭义相对论 ,讨论相对于静止参照系运动的源电荷在空间产生的电场。并证明该电场是有源有旋场。