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.

Wintertime aerosol characteristics at a north Indian site Kharagpur in the Indo‐Gangetic plains located at the outflow region into Bay of Bengal

Abstract: [1] Keeping the importance of aerosol characterization in the out flow regions from the Indian subcontinent in view, a campaign mode observation on aerosol physical properties was made at Indian Institute of Technology campus, Kharagpur located under the vent region in the Indo-Gangetic plains during the winter month of December 2004. The aerosol spectral optical depths and near-surface mass concentrations were high with a mean aerosol optical depth of 0.7 at 500 nm and a percent share of fine mode particle concentration as high as 90. However, the share of the BC aerosol to fine mode aerosol was consistently 10%, which is typical of an urban location. The vertical profiles of aerosol backscatter intensity derived using a micropulse lidar show that the boundary layer height variation accounts for the day-to-day variability in the surface mass concentrations. The negative correlation between aerosol backscatter intensity at two representative altitudes above and below the boundary layer implicates only vertical redistribution of aerosols. The lidar data also suggest that no aerosol transport has taken place over the location to account for the day-to-day variability. The forward trajectories at three representative altitudes with source point at the observing site indicate a possible aerosol transport from the outflow regions into Bay of Bengal, southern peninsular India and Arabian Sea. The results were discussed in light of the earlier mobile campaign observations on the spatial variability of aerosol physical properties over the peninsular India. Citation: Niranjan, K., V. Sreekanth, B. L. Madhavan, and K. Krishna Moorthy (2006), Wintertime aerosol characteristics at a north Indian site Kharagpur in the Indo-Gangetic plains located at the outflow region into Bay of Bengal, J. Geophys. Res., 111, D24209,

Seasonal variations of equatorial spread-F

Abstract: . The occurrence of spread-F at Trivandrum (8.5°N, 77°E, dip 0.5°N) has been investigated on a seasonal basis in sunspot maximum and minimum years in terms of the growth rate of irregularities by the generalized collisional Rayleigh-Taylor (GRT) instability mechanism which includes the gravitational and cross-field instability terms. The occurrence statistics of spread-F at Trivandrum have been obtained using quarter hourly ionograms. The nocturnal variations of the growth rate of irregularities by the GRT mechanism have been estimated for different seasons in sunspot maximum and minimum years at Trivandrum using h'F values and vertical drift velocities obtained from ionograms. It is found that the seasonal variation of spread-F occurrence at Trivandrum can, in general, be accounted for on the basis of the GRT mechanism.

Catalysis of the cure reaction of bisphenol A dicyanate. A DSC study

Abstract: The kinetics of the thermal cure reaction of Bisphenol A dicyanate (BACY) in presence of various transition metal acetyl acetonates and dibutyl tin dilaurate (DBTDL) was investigated using dynamic differential scanning calorimetry (DSC). The cure reaction involved a pregel stage corresponding to around 60% conversion and a postgel stage beyond that. Influence of nature and concentration of catalysts on the cure characteristics was examined and compared with the uncatalyzed thermal cure reaction. The activation energy (E), preexponential factor (A), and order of reaction (n) were computed by the Coats–Redfern method. A kinetic compensation correction was applied to the data in both stages to normalize the E values. The normalized activation energy showed a systematic decrease with increase in catalyst concentration. The exponential relationship between E and catalyst concentration substantiated the high propensity of the system for catalysis. At fixed concentration of the catalyst, the catalytic efficiency as measured by the decrease in E value showed dependency on the nature of the coordinated metal and stability of the acetyl acetonate complex. Among the acetyl acetonates, for a given oxidation state of the metal ions, E decreased with decrease in the stability of the complex. A linear relationship was found to exist between activation energy and the gel temperature for all the systems. Manganese and iron acetyl acetonates were identified as the most efficient catalysts. In comparison to DBTDL, ferric acetyl acetonate proved to be a more efficient catalyst. The activation parameters computed using the Coats–Redfern method agreed well with the results from two other well known integral equations. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1103–1114, 1999