Studies on the behaviour of nutrients in the Mandovi Estuary during premonsoon

Behaviour of silicate, nitrate and phosphate in the Mandovi Estuary was studied during the premonsoon season. The study shows that silicate is removed from the water column while nitrate showed an internal source. This nitrate source has been identified as the wash water from an iron ore screening plant which discharges the muddy waste directly into the river. Applying mixing relations, the distribution of this nitrate both up- and downstream of the outfall has been studied. Phosphate showed very low concentrations in the low salinity region; however, its concentration increased slightly towards the higher salinity region.     

Criterion for propagation of magnetohydrodynamic waves: An equivalence

It is shown that the requirement that a magnetohydrodynamic wave propagate over a distance equal to a large number of wavelengths without substantial attenuation is equivalent to the requirement that the lateral velocity of displacement of the field lines far exceed a characteristic velocity. This latter velocity is the velocity of slippage of the field lines with respect to the medium.     

Hydromagnetic interaction in a fluid dielectric

It is shown that a dielectric fluid is capable of hydromagnetic interaction, much like a conducting fluid. The physical principle of this interaction is outlined and the criteria for dominance of the interaction are derived.     

Prominence Motions Observed at High Cadences in Temperatures from 10 000 to 250 000 K

Solar Physics - We report here for the first time observations of prominence velocities over a wide range of temperatures and with a high time cadence. Our study of ultraviolet movies of...     

Generation of gravity waves within the ionosphere by transient heating during high-power wave propagation

Generation of short-range gravity waves within the ionosphere due to inhomogenous heating in the presence of space-localized inhomogeneities during high-power radio wave-propagation has been investigated. The magnitude and from of the anticipated atmospheric wave-trains are obtained. The derived experession of electric field within the ionosphere under the stated perturbed condition may be considered to be manifested through Lorentz-force and Joule-dissipation that influence the neutral gas of the atmosphere via collision-mechanism and thereby gravity waves are launched. The expressions for the low-frequency part of the fractional pressure variations have been derived which are applied to theE-region of the ionosphere. The results are presented graphically.     

Radiation from a dipole in an anisotropic plasma medium containing time-varying irregularities

The expression for power radiated from a dipole within an anisotropic plasma has been obtained in presence of a current source and time-varying irregularities. This may be useful for numerical computation in lossy media.     

Influence of the resonance in a gravity-gradient stabilized satellite

Using Hamiltonian formalism the translational-rotational motion of a satellite is studied near a resonance considering the orbital and rotational motions. A first order perturbation theory is derived by Hori's transformation in order to eliminate short and long periodic terms, preserving in the new Hamiltonian secular and resonant terms. This theory is again applied to study the resonant system whose analysis lead us to a system of equations equivalent to the equations of a simple pendulum which is integrable in terms of elliptical integrals.     

1-2GHz太阳射电动态频谱仪

本文描述了北京天文台研制的１－２ＧＨｚ太阳射电动态频谱仪的性能、结构、初步观测结果及进一步改进计划．