The late time radio emission from SN 1993J at meter wavelengths

We present the investigations of SN 1993J using low frequency observations with the Giant Meterwave Radio Telescope. We analyze the light curves of SN 1993J at 1420, 610, 325 and 243 MHz during $7.5-10$ years since explosion.The supernova has become optically thin early on in the 1420 MHz and 610 MHz bands while it has only recently entered the optically thin phase in the 325 MHz band. The radio light curve in the 235 MHz band is more or less flat. This indicates that the supernova is undergoing a transition from an optically thick to optically thin limit in this frequency band. In addition, we analyze the SN radio spectra at five epochs on day 3000, 3200, 3266, 3460 and 3730 since explosion. Day 3200 spectrum shows a synchrotron cooling break. SN 1993J is the only young supernova for which the magnetic field and the size of the radio emitting region are determined through unrelated methods. Thus the mechanism that controls the evolution of the radio spectra can be identified. We suggest that at all epochs, the synchrotron self absorption mechanism is primarily responsible for the turn-over in the spectra. Light curve models based on free free absorption in homogeneous or inhomogeneous media at high frequencies overpredict the flux densities at low frequencies. The discrepancy is increasingly larger at lower and lower frequencies. We suggest that an extra opacity, sensitively dependent on frequency, is likely to account for the difference at lower frequencies. The evolution of the magnetic field (determined from synchrotron self absorption turn-over) is roughly consistent with $B \propto t^{-1}$. Radio spectral index in the optically thin part evolves from $\alpha \sim 0.8-1.0$ at few tens of days to $\sim 0.6$ in about 10 years.Comment: 37 pages, 9 figures in LaTex; scheduled for ApJ 10 September 2004, v612 issue; send comments to: [email protected]

Recovery on non-ferrous metallic values from metallurgical wastes

WITH the increased tempo of industrial expansion and ever-increasing consumption of common nonferrous metals like Al, Cu, Pb, Zn, Sri in India, conservation, substitution and reclamation from waste products and substandard raw materials are of paramount importance for the country, not only to tide over the present crisis but also in the larger interests of economic growth and self-sufficiency. Self-sufficiency can be attained by developing processes for the utilization of low grade and complex ores,recovery of metals from waste products, like slags, ashes, drosses, apart from conservation of the non-ferrous metals not available in the country, by their judicious use and also by substitution wherever possible

Recovery of Non-ferrous Metallic Values from Metallurgical Wastes

With the increased industrial expansion and ever incre-asing consumption of non-ferrous metals in India, utili-sation of low grade and complex ores, recovery of metals from waste products like slag, ashes and dross, apart from conservation of the non-ferrous metals not available in the country, by their judicious uses and by substitution, wherever possible, is a matter of great importance

Synchrotron aging and the radio spectrum of SN 1993J

We combine the GMRT low frequency radio observations of SN 1993J with the VLA high frequency radio data to get a near simultaneous spectrum around day 3200 since explosion. The low frequency measurements of the supernova determine the turnover frequency and flux scale of the composite spectrum and help reveal a steepening in the spectral index, $\Delta \alpha \sim 0.6$, in the optically thin part of the spectrum. This is the first observational evidence of a break in the radio spectrum of a young supernova. We associate this break with the phenomenon of synchrotron aging of radiating electrons. From the break in the spectrum we calculate the magnetic field in the shocked region independent of the equipartition assumption between energy density of relativistic particles and magnetic energy density. We determine the ratio of these two energy densities and find that this ratio is in the range: $8\times 10^{-6}-5\times 10^{-4}$. We also predict the nature of the evolution of the synchrotron break frequency with time, with competing effects due to diffusive Fermi acceleration and adiabatic expansion of the radiative electron plasma.Comment: 12 pages, 2 figures. Accepted for publication in ApJ

The Scope for Development of Magnesium Industry in India

IN THIS era of "sputniks" and "space flights", weight saving poses to be a problem of prince importance with its direct influence over increasing speed and fuel economy. Magnesium and magnesium base alloys are known to be the lightest structural materials today, and have been employed not only for space research and rocketry but for various types of aero, marine and road trans-portation vehicles

Metallurgy of Complex Pb, Cu and Zinc Sulfides

For the winning of Pb, Cu and from sulfides ores by conventional methods, it is essential that these be beneficiated to high grade concentrates. The ore mine- rals in polymetallic and complex deposits are often found to be in close mutual penetration with each other and to the non-metallic gangue.In many cases where the attempts have been made to concentrate these ores; it is either difficult to obtain - a suitable grade of the concentrate by conventional flotation methods or the recovery of metals into the respective concentrate is poor. Zinc that finds its way to a copper concentrate is always discarded in the slag as a waste, while copper in a Pb concentrate leads to serious smelting problems. In such cases the cost of production by a smelting process becomes unfavourable and new approaches to process these ores become more attractive. Hydrometallurgical processes, based on leach-ing and precipitation alone, or in combination with conv-entional extractive metallurgical methods will play an important role in meeting the requirements of such complex ores. Such processes can more easily be adopted to small scale operation than conventional smelting and refining

Treatment of Complex lead, Copper and Zinc sulfides

FOR the adoption of conventional methods for the recovery of lead , copper and zinc from the complex sulfide ores, it is essential that these be beneticiated to a high grade concentrate. The minerals present in such complex ores are often found in such close inter -growth that it is either difficult to obtain a suitable grade of the concentrate by physical methods or the recovery of metals in the respe-ctive concentrates is poor. For example, the zinc that finds its way to a copper concentrate is always discarded in the slag as a waste, while copper in a lead concentrate leads to serious smelting problems. In such cases the cost of production by conventional smelting process becomes unfavourable and new approaches to process the ores become more attractive