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.

Phthalonitrile resin bearing cyanate ester groups: synthesis and characterization

Abstract: Novolac resins bearing both cyanate and phthalonitrile groups in different proportions in the same backbone were synthesized and characterized. The resin was thermally cured to a network. Differential scanning calorimetric studies showed that cyanate and phthalonitrile groups underwent independent curing reactions. No evidence was obtained for co-curing of the two groups. Polymerization of cyanate groups preceded that of phthalonitrile groups and the former reaction was susceptible for catalysis. Incorporation of cyanate groups facilitated an early gelation of the resin and thus, the processability of the resin. However, this impaired marginally the moisture resistance and thermal stability of the otherwise inherently water resistant and thermally stable phthalonitrile resins.

Condensation–addition‐type resole resins with phenyl ethynyl functions: Synthesis, characterization, and thermal properties

Abstract: Novel phenolic resins bearing methylol and phenyl ethynyl functions and curing by both condensation and addition mechanisms were synthesized by the reaction of 3-(phenyl ethynyl) phenol (PEP) with formaldehyde under alkaline conditions. Resins with varying relative concentration of the two functional groups were synthesized and characterized. The resins underwent a two-stage cure, confirmed by both DSC and DMA analyses. The low-temperature cure due to methylol condensation led to early gelation of the system. The ultimate curing through addition reaction of phenylethynyl group required heating at 275°C. The cured resins exhibited better thermal stability and anaerobic char yield in comparison to a conventional resole. The thermal stability and char-yielding property showed a diminishing trend with enhanced methylol substitution. Resin with F/P ratio less than unity offered excellent thermal stability and anaerobic char yield. The thermal degradation of the cured resins occurred in two kinetic steps. Methylene groups favored the initial degradation, whereas the higher temperature carbonization process was independent of the network structure. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3371–3377, 2001

Boundaries of tropical tropopause layer (TTL): A new perspective based on thermal and stability profiles

Abstract: The structure of tropical tropopause layer (TTL) is delineated based on static stability criteria. It is defined as the region extending from the level of minimum static stability to the level of maximum static stability. The static stability and dynamic instability steadily increase from the base to the top of the TTL. Radiosonde data from three tropical stations and Constellation Observing System for Meteorology, Ionosphere, and Climate GPS radio occultation (COSMIC) data over the tropics are used for this investigation. This study suggests that in terms of stability, the TTL can further be considered as a composite of three sublayers: a bottom layer (BL), a middle layer (ML), and an upper layer (UL) embedded between the potential temperatures ~350–360 K, ~360–380 K, and 380–420 K, respectively. While the BL is significantly influenced by frequent convective outflows, the influence of convection declines across the ML. Ozone and water vapor mixing ratios show a discernible change in their gradients across these sublayers. Occurrences of small-scale turbulence and cirrus are maximum in the BL and decrease in the ML and UL. Longitudinally, the BL is broad and the ML and UL are narrow over the deep convective cores. Strength of static stability in the UL (BL) is relatively strong (weak) centered about the equator, with pronounced features over the deep convective regions. These features of static stability centered about the equator in the BL could be attributed to the convective outflows in the troposphere and that in the UL to the dynamic and radiative processes in the upper troposphere and lower stratosphere.

Addition-fragmentation behavior of a capto-dative group-substituted acrylic ester in free-radical polymerization and reactivity of the derived macromonomers

Abstract: Ethyl-2-(2-cyano-2-ethylthio)-ethyl-propenoate (ECEP) was synthesized and examined as free-radical addition–fragmentation chain transfer agent (AFCTA) in the bulk polymerization of methyl methacrylate (MMA) and styrene at various temperatures A better chain transfer constant (Ctr) was observed for styrene than for MMA, projecting the potentiality of the compound as a better end-functionalizing agent for the former In both cases, copolymerization of ECEP with the monomer predominated over fragmentation, the relative proportions of which were dependent on the monomer The ECEP-terminated radical fragmented to an extent of 26% in the presence of MMA, whereas it was only 95% in the case of styrene The relative extent of fragmentation and copolymerization was in conformation to the calculated reactivity ratios and chain transfer constants Addition–fragmentation chain transfer resulted in the formation of methacrylic-functional macromonomers The copolymerizability of the resultant macromonomer was found to depend on the nature of the backbone and on the comonomer On copolymerizing with MMA, the terminal monomer moiety on polystyrene (PS)-based macromonomers preferred to undergo fragmentation, whereas that of the polymethyl methacrylate (PMMA)-based one copolymerized readily with styrene because of thermodynamic and kinetic factors © 1999 John Wiley & Sons, Inc J Polym Sci A: Polym Chem 37: 2511–2524, 1999

Plasma Waves Around Venus and Mars

Abstract: Plasma waves are observed around almost all the solar system objects – Sun, planets and their satellites, comets, interplanetary medium, etc. The plasma environment around a planet has sufficient p...