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.

Thermochemical characterization of phenolic resins

Abstract: Phenol-formaldehyde resins (I andII), synthesised at a monomer feed ratio of F/P = 1.0 and 1.5, were cured at 130‡C for 48 h without any catalyst (Ia, IIa), with 0.1% ferric acetyl acetonate (Ib, IIb) and with 0.1 %p-toluenesulphonic acid (Ic, IIc). Thermogravimetric studies indicate that the decomposition of the cured products takes place in two distinct stages: The first stage (T=340–480‡C; α=0.045–0.16; δE 1 = 140±10-239±24 and 60±3–65±2 kJ mol−1 for seriesI andII respectively) was attributed to the predominant cleavage of formal linkages. The main stage decomposition (T=460–640‡C; α=0.114–0.393; δE 2=115±8–169±8 and 91±6–103±7 kJ mol−1 for seriesI andII respectively) was attributed to reactions leading to graphitisation. δE 2 values were correlated to the extent of cure as measured by IR spectroscopy and pyrolysis-GC. The effect of catalysts on the extent of cure and on the activation energy was evaluated.

Equatorial waves in temperature in the altitude range 4 to 70 km

Abstract: Using altitude profiles of temperature in the range 4 to 70 km derived from Mesosphere–Stratosphere–Troposphere radar and lidar observations at Gadanki (13.5°N,79.2°E) from 18 January 1999 to 5 March 1999, characteristics of equatorial waves are studied. Two-dimensional Fourier-transform analysis of the temperature profiles is carried out to identify the periodicities and their vertical wave numbers. From the characteristics obtained, equatorial slow Kelvin waves with periodicities 15.7 d, 9.4 d, 7.8 d and 6.7 d are identified in the troposphere and stratosphere regions and among these 7.8 d and 6.7 d periodicities are found to penetrate into the mesosphere. Equatorial waves with smaller periodicities in the range 5.2 d to 3.6 d are also observed. The vertical flux of horizontal momentum (zonal) of the identified slow Kelvin-wave periodicities in the altitude region 4–25 km is estimated. It is found that equatorial waves modulate tropical tropopause temperature and altitude. Copyright © 2002 Royal Meteorological Society.

An analysis of near-circular lunar mapping orbits

Abstract: Numerical investigations have been carried out to analyse the evolution of lunar circular orbits and the influence of the higher order harmonics of the lunar gravity field. The aim is to select the appropriate near-circular orbit characteristics, which extend orbit life through passive orbit maintenance. The spherical harmonic terms that make major contributions to the orbital behaviour are identified through many case studies. It is found that for low circular orbits, the 7th and the 9th zonal harmonics have predominant effect in the case of orbits for which the evolution is stable and the life is longer, and also in the case of orbits for which the evolution is unstable and a crash takes place in a short duration. By analysing the contribution of the harmonic terms to the orbit behaviour, the appropriate near-circular orbit characteristics are identified.

Thermodynamic structure of the Atmospheric Boundary Layer over the Arabian Sea and the Indian Ocean during pre-INDOEX and INDOEX-FFP campaigns

Abstract: . Spatial and temporal variability of the Marine Atmospheric Boundary Layer (MABL) height for the Indian Ocean Experiment (INDOEX) study period are examined using the data collected through Cross-chained LORAN (Long-Range Aid to Navigation) Atmospheric Sounding System (CLASS) launchings during the Northern Hemispheric winter monsoon period. This paper reports the results of the analyses of the data collected during the pre-INDOEX (1997) and the INDOEX-First Field Phase (FFP; 1998) in the latitude range 14°N to 20°S over the Arabian Sea and the Indian Ocean. Mixed layer heights are derived from thermodynamic profiles and they indicated the variability of heights ranging from 400m to 1100m during daytime depending upon the location. Mixed layer heights over the Indian Ocean are slightly higher during the INDOEX-FFP than the pre-INDOEX due to anomalous conditions prevailing during the INDOEX-FFP. The trade wind inversion height varied from 2.3km to 4.5km during the pre-INDOEX and from 0.4km to 2.5km during the INDOEX-FFP. Elevated plumes of polluted air (lofted aerosol plumes) above the marine boundary layer are observed from thermodynamic profiles of the lower troposphere during the INDOEX-FFP. These elevated plumes are examined using 5-day back trajectory analysis and show that one group of air mass travelled a long way from Saudi Arabia and Iran/Iraq through India before reaching the location of measurement, while the other air mass originates from India and the Bay of Bengal.

Chitosan-graft-poly(vinyl acetate) for hemodialysis applications

Abstract: Chitosan was graft copolymerized with vinyl acetate using ceric ammonium nitrate as the initiator. The chitosan-g-poly(vinyl acetate) (chitosan-g-PVAc) membranes were found to be blood compatible, noncytotoxic, and biodegradable. The physicochemical characterization of the membranes revealed that the membranes possess the synergistic effect of the natural-synthetic hybrids of chitosan and PVAc with excellent mechanical stability and tunable hydrophilic/hydrophobic characteristics. The permeation characteristics of chitosan-g-PVAc membranes for four different solutes creatinine, urea, glucose, and albumin was studied in vitro at 37°C for assessment of the suitability of them as hemodialysis membranes. The studies showed that the membranes exhibit higher permeability to creatinine, urea, and glucose compared with the commercial cellulose membrane and are impermeable to the essential nutrient albumin. Hence, the need for the development of biocompatible, mechanically strong dialysis membranes could be addressed with the modification of chitosan through grafting with PVAc. Potential applications like artificial kidney, artificial pancreas, and so forth, are envisaged from these membranes. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012