The onset of shock wave in an electrically conducting and radiating gas

The present work applies the method of characteristics to study the behaviour of planar and cylindrical wave-heads propagating through a perfectly electrically conducting and thermally radiating inviscid gas under the optically thin limit in the presence of a transverse magnetic field. The true nonlinear progress of the flow variable gradients at the wavefront is predicted and the critical distance at which the characteristics pile up at the wavefront to form a shock wave is obtained. It is investigated as to how the effects of radiative flux, the magnetic field strength and the specific heat ratio influence the process of steepening or flattening of the characteristic wavefront.     

Anisotropic Bianchi Type-II Cosmological Models in Self-Creation Cosmology

Totally anisotropic Bianchi type-II cosmological solutions are presented in Barber's second self-creation theory of gravitation both in vacuum and in the presence of stiff-matter. The corresponding cosmological models have no finite singularity. The stiff-matter model gives essentially an empty universe for large time. Some physical and kinematical properties of the models are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Probabilities and distribution of monsoon rainfall in normal, flood and drought years over India

Summary The paper deals with the variability of summer-monsoon rainfall during normal, flood and drought years over India. During flood years the monsoon rainfall increases mostly all over parts of the country and large area less than 100 cm isohytel covers Orissa and adjoining Madhya Pradesh. During drought years the rainfall amount decreases over the entire country and isohytel of 100 cm shrinks to almost a point. The variability of monsoon rainfall from flood to normal to drought years depends upon the number of depression/low-pressure area which form over the North Bay and move inland. To understand the intraseasonal and interannual variability of the monsoon rainfall, daily and seasonal anomalies has been performed by using the Empirical Orthogonal Function analysis. Further Empirical Orthogonal Function (EOF) analysis is carried out on these data to find out the nature of rainfall distribution in different monsoon categories namely normal, flood and drought years. This technique thus serves to identify spatial and temporal patterns characteristics of possible physical significance. Received July 25, 2000/Revised September 26, 2000     

Spatial assessment and redesign of a groundwater quality monitoring network using entropy theory, Gaza Strip, Palestine

Using entropy theory, a methodology was developed for the evaluation and redesign of groundwater quality monitoring wells in the Gaza Strip in Palestine. Essential to the methodology is the development of a Transinformation Model (TM) which yields the amount of information transfer and the dependency between the wells as a function of distance. The TM parameters, such as the minimum transinformation and the range, were employed for evaluating the network which revealed that most of the distances between wells were less than the range. It also indicated that a high percentage of redundant information existed in the network. Therefore, the network was reduced by superimposing a square pattern over the monitored area and selecting one well per square block in a stratified pattern. The methodology was tested using the chloride data collected from 1972–2000 from 417 groundwater quality monitoring wells in the Gaza Strip. The number of the groundwater quality monitoring wells in the Gaza Strip was reduced by 53%, while there was 26% redundant information based on the minimum existing distance between wells. This methodology is meant to help monitor the groundwater quality (salinity) in the Gaza Strip.     

Effect of solar pressure on the motion and stability of the system of two inter-connected satellites in an elliptical orbit

The effect of solar pressure on the two-dimensional motion of two cable-connected satellites in the Earth's central gravitational field of force for the elliptical orbit of the centre-of-mass of the system has been analysed. The equations of motion obtianed are nonlinear and non-autonomous.It is concluded with the aid of non-resonant solution that the system experiences resonance main as well as parametric. If the eccentricity is small, the system will always oscillate about the position of equilibrium with tight string like dumb-bell satellite with changing phase and constant amplitude.     

The effect of solar pressure on the motion and stability of interconnected satellites in orbit

The paper deals with the effect of solar pressure on the motion and stability of two satellites connected by an inextensible string in a central gravitational field of force. A system of nonlinear, nonhomogeneous, and non-autonomous equations under the rotating frame of reference in Nechvíle's coordinate system have been obtained. The general solution of the above system of equations is beyond our reach. The particular solutions have been obtained.The particular solution in which the system lies, wholly along the radius vector joining the attracting centre and the centre of mass of the system under the central attracting force along was found to be stable (Singh, 1973). Naturally we got interested in examining the effect of solar radiation pressure on the stability of this particular solution.     

Thermal-convective instability of a composite rotating stellar atmosphere in the presence of a variable magnetic field

The thermal-convective instability of a composite stellar atmosphere is considered in the presence of rotation, variable horizontal magnetic field, and collisional effects. The criteria for monotonic instability are obtained which generalize the criterion derived for thermal-convective instability in the absence of above effects.     

Effect of rotational and tidal distortions on the periods of small adiabatic oscillations of stellar models

Kopal's method of representing the inner structure of a rotationally and tidally-distorted star by a rotationally-and tidally-distorted Roche model has been used in conjunction with an averaging concept introduced by Kippenhahn and Thomas of representing the equipotential surfaces of a rotationally and tidally distorted stellar model by the equipotential surfaces of an equivalent spherical model to determine the combined effects of rotation and tidal distortion on the periods of small adiabatic oscillations of a stellar model.     

A self-similar flow in Generalized Roche model with increasing energy

The self-similar flow of a gas, moving under the gravitational attraction of a central body of fixed mass behind a spherical shock wave driven out by a propelling contact surface into quiet solar wind region, is investigated. The total energy content between the inner expanding surface and the shock front increases with time. In the last section we briefly pose the self-similar isothermal flow of a gas behind a spherical shock wave.     

Rhodophycean algae from the Lower Cretaceous of the Cauvery Basin,South India

The present paper records eight Rhodophycean taxa from the Kallakudi limestone of the Uttatur Group (Lower Cretaceous) exposed in the quarries at Kallakudi and Olaipadi near Govindarajapatnam of the Cauvery Basin, south India. Of these, four species (Melobesioideae gen. et sp. indet 1, Melobesioideae gen. et sp. indet 2, Lithophyllum alternicellum and Pseudoamphiroa propria) belong to corallinaceae family, one species (Polystrata alba) is assigned to Peyssonneliaceae family, two species (Solenopora urgoniana and Parachaetetes asvapatii) are placed under Solenoporaceae; and one species (Sporolithon sp.) is referable to Sporolithaceae family. Among these, three taxa (Solenopora urgoniana, Lithophyllum alternicellum and Pseudoamphiroa propria) are recorded for the first time from India. The study also includes observations on ultrastructural morphological features of Parachaetetes asvapatii. The observations reveal absence of cell fusions, which confirms its affinities with Solenoporaceae. Palaeoecological data indicate that the assemblage from the sequence at the Kallakudi quarry is characteristic of lagoonal to reefal environment, whereas the Olaipadi quarry sequence near Govindarajapatnam points to 20 m to 30 m deep environment characterized by high- to moderate energy conditions.