Some anisotropic spatially-homogeneous cosmological models with electromagnetic field

Considering Bianchi type-I metric, cosmological models of a perfect fluid with an electromagnetic field have been obtained, using a supplementary condition between the metric potentials. The four-current is either zero or space-like. The model has expanding and shearing but non-rotating fluid flow which is also geodetic. The requirement of positive conductivity imposes an additional restriction on the model. Various physical and mathematical properties of the model have been discussed.     

Thermal convection instability of liquid metals in magneto-hydrodynamics

The problem of thermal convection instability of a horizontal layer of magnetized fluid has been studied to occur crystal growing under the effect of horizontal temperature gradient. In the study, the problem has been reduced to an eigen-value problem for a stream function. The dispersion relations for low viscosity fluid and high viscosity fluid respectively have been discussed analytically and some numerical results have been obtained. It is shown that the critical Rayleigh number and other its related constants for low viscosity fluid (i.e., mercury) are much differ than the high viscosity fluid (i.e., glycerol).     

Nonlinear electrostatic drift Kelvin-Helmholtz instability

Nonlinear analysis of electrostatic drift Kelvin-Helmholtz instability is performed. It is shown that the analysis leads to the propagation of the weakly nonlinear dispersive waves and the nonlinear behaviour is governed by the nonlinear Burger's equation.     

Diffusion coefficient of neutrinos in a pre-supernova star

The diffusion coefficient of neutrinos in the trapping regime in a presupernova star,where the scattering of neutrinos by nuclei is the dominant effect, is calculated within the framework of relativistic kinetic theory in the lowest order Chapman-Enskog approximation. The screening of the nuclei by ion-ion and electron-electron correlations is also taken into account.     

Eclipsing binary system AV Hydrae

The eclipsing binary AV Hya has been observed photoelectrically inU, B andV filters on 15 nights. The primary eclipse appeared to be total with a totality of 23 min duration. A modified period of 0^d.6 834 062 has been obtained. Geometrical elements could only be determined for partial transit case.     

Anisotropic propagation of magnetogasdynamic sonic waves in conducting and radiating atmosphere

The propagation of sonic discontinuity in conducting and radiating atmosphere has been discussed under the influence of magnetic field. The velocity of sonic wave and its termination into shock wave has been obtained. We have also obtained the critical time at which sonic wave terminates into shock wave. There is significant effect of magnetic field on sonic velocity and its termination into shock wave.     

An analysis of the light changes of the eclipsing binary XY ceti in the frequency-domain

The photoelectric observations of the eclipsing binary XY Ceti presented by us (see Srivastava and Padalia, 1975) have been analysed by Okazaki (1978) and Ramellaet al. (1980). They presented different sets of elements from the same set of our observations. This necessitated us to obtain the elements of XY Ceti again employing recent method of determination of elements.The revised geometrical elements of the eclipsing binary XY Ceti have been obtained by the method of Fourier analysis of the light changes in the frequency-domain, which was developed by Kopal (1979). These have been compared with our earlier (Srivastava and Padalia, 1975) results obtained by employing Russell and Merrill's (1952) method. The revised absolute dimensions of XY Ceti have been obtained using the spectroscopic elements given by Popper (1971), and the newly derived geometrical elements. The Roche radii have been derived to discuss the evolution of the system. The secondary component lies reasonably near to the Main Sequence, while the primary component falls above it. The evolutionary discussion indicates that the system is a detached one.     

An exact similarity solution in radiation magneto-gas-dynamics for the flows behind a spherical shock wave

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.     

Eclipsing binary UW Bootis

Photometric observations of primary minimum inU, B, andV filters have been discussed. The amplitude of variation in all the three filters is 0 ^m .66. We do not find variations in the period and its revised value is 1^d.0047115.     

Propagation of exponential shock waves in magnetogasdynamics

Self-similar flows of a perfect gas behind the cylindrical shock wave propagating exponentially in an atmosphere whose density varies inversely as the fourth power of shock radius are investigated. The effects of radiation flux has also been taken into consideration. The total energy of the wave is constant.