Vikram Sarabhai Space Centre

About: Vikram Sarabhai Space Centre is a facility organization based out in Thiruvananthapuram, India. It is known for research contribution in the topics: Aerosol & Ultimate tensile strength. The organization has 2092 authors who have published 3058 publications receiving 47975 citations. The organization is also known as: VSSC.

Effects of solar eclipse on the electrodynamical processes of the equatorial ionosphere: a case study during 11 August 1999 dusk time total solar eclipse over India

Abstract: . The effects on the electrodynamics of the equatorial E- and F-regions of the ionosphere, due to the occurrence of the solar eclipse during sunset hours on 11 August 1999, were investigated in a unique observational campaign involving ground based ionosondes, VHF and HF radars from the equatorial location of Trivandrum (8.5° N; 77° E; dip lat. 0.5° N), India. The study revealed the nature of changes brought about by the eclipse in the evening time E- and F-regions in terms of (i) the sudden intensification of a weak blanketing ES-layer and the associated large enhancement of the VHF backscattered returns, (ii) significant increase in h' F immediately following the eclipse and (iii) distinctly different spatial and temporal structures in the spread-F irregularity drift velocities as observed by the HF radar. The significantly large enhancement of the backscattered returns from the E-region coincident with the onset of the eclipse is attributed to the generation of steep electron density gradients associated with the blanketing ES , possibly triggered by the eclipse phenomena. The increase in F-region base height immediately after the eclipse is explained as due to the reduction in the conductivity of the conjugate E-region in the path of totality connected to the F-region over the equator along the magnetic field lines, and this, with the peculiar local and regional conditions, seems to have reduced the E-region loading of the F-region dynamo, resulting in a larger post sunset F-region height (h' F) rise. These aspects of E-and F-region behaviour on the eclipse day are discussed in relation to those observed on the control day. Key words. Ionosphere (electric fields and currents; equatorial ionosphere; ionospheric irregularities)

Development of rapidly solidified (RS) magnesium-aluminium-zinc alloy

Abstract: Applications of magnesium alloys in the aerospace industry are limited because of their poor mechanical properties, corrosion resistance and workability. Refinement of microstructure through rapid solidification processing is one of the highly potential approaches to overcome these limitations. In the present study, the technology of processing of rapidly solidified (RS) ribbons in Mg-9%Al-1%Zn-0.2%Mn alloy has been established using melt spinning technique. The effect of wheel speed on thickness and microhardness of the ribbons is presented. Microhardness is found to increase with the wheel speed. It is further observed that microhardness of the ribbons increases with the heat treatment temperature upto 200°C and thereafter it starts decreasing. Precipitation of the intermetallic phase Mg17Al12, at temperatures upto 200°C is found to prevent the grain growth and improve the properties of the ribbons. This in-turn reveals that the temperature for secondary processing of RS ribbons in Mg-9%Al-1%Zn-0.2%Mn alloy should not exceed 200°C in order to retain the benefits of rapid solidification processing.