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.

Evaluation by various experimental approaches of the crosslink density of urethane networks based on hydroxyl-terminated polybutadiene

Abstract: Crosslink density (CLD) is an important characteristic for elastomeric polymer networks. The mechanical and viscoelastic properties of the elastomers are critically dependant on the CLD. Several methods have been adopted for its determination, but swelling and stress–strain methods continue to be more popular because of the convenience associated with these techniques. In this article, the determination of CLD of allophanate–urethane networks based on hydroxyl-terminated polybutadiene and toluene diisocyanate with swelling and stress–strain methods is reported. The Flory–Rhener relationship was applied to calculate CLD from the swelling data. CLDs were also calculated from the initial slope of the stress–strain curve (Young's modulus), Mooney–Rivlin plots, equilibrium relaxation moduli, and dynamic mechanical properties. A comparison was drawn among the values obtained with the various methods. Although the CLD values obtained from Mooney–Rivlin plots were slightly lower than those obtained from swelling data, the values obtained with Young's modulus and storage modulus were considerably higher. The values obtained with swelling and equilibrium relaxation moduli data were very close to each other. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3129–3133, 2007

Deterministic prediction of post‐sunset ESF based on the strength and asymmetry of EIA from ground based TEC measurements: Preliminary results

Abstract: [1] This paper provides the first observations of EIA asymmetry by receiving beacon transmissions onboard low earth orbiting satellites from a single station ground-based receiver The EIA strength and asymmetry are derived from the latitudinal profiles of TEC obtained from a radio beacon receiver at Trivandrum (85°N, 77°E, diplat ∼05°N) These two parameters, obtained well ahead of the onset time ol ESF, are shown to have a definite role on the subsequent ESF activity In the present paper, both these factors are combined to define a new 'threshold parameter' for the generation ol ESF It has been shown that this parameter can define the state of the 'background ionosphere' conducive for the generation of ESF irregularities much prior to its onset

Aerosol characterization during the summer monsoon period over a tropical coastal Indian station, Visakhapatnam

Abstract: [1] Columnar optical depth and near-surface mass concentration of aerosols over Visakhapatnam, an urban location along the east coast of India during the summer monsoon period (May–August 2005), were measured simultaneously along with chemical sampling for water-soluble ionic species (NH4+, Na+, K+, Mg2+, Ca2+, Cl−, NO3−, SO42−, and HCO3−). The mean aerosol optical depth (AOD) (0.5 μm) and Angstrom parameters (α, β) during this period were obtained as 0.72 ± 0.39 and 0.88 ± 0.39, 0.48 ± 0.36, respectively. The total surface aerosol mass concentration varied from 95 to 128 (μg/m3), out of which coarse mode dominated by 45%. While Cl−, Na+, K+, and Mg2+ (sea salts) contributed nearly 56%, SO42− and NO3− (anthropogenic constituents) contributed 33% in surface aerosol constituents. During this period, high spectral variability in AOD, negative curvature of second-order Angstrom coefficient (α1), abundance of columnar submicron aerosols, role of air mass trajectories as tracers of long-range transport, cation deficiency, and sea-salt dependence on wind speed are some of the observations over Visakhapatnam. The synergy of the results from these complementary measurements can be reflected while computing the aerosol radiative forcing.

Thermomechanical and Morphological Characteristics of Cross‐Linked GAP and GAP–HTPB Networks with Different Diisocyanates

Abstract: This paper describes the mechanical and thermal characterisation of cross-linked glycidyl azide polymer (GAP) and GAP–hydroxyl terminated polybutadiene (HTPB) networks. Cross-linked GAP and GAP–HTPB networks were prepared by reacting GAP diol and GAP–HTPB diol mixture with different diisocyanates. The physical and mechanical characteristics were found to be influenced by the type of isocyanate curing agents, [NCO]/[OH] equivalent ratios and concentration of GAP. For all the three types of curing agents, GAP–HTPB blends of 50 : 50 to 30 : 70 ratios show higher mechanical strength over the virgin networks of GAP or HTPB. Thermal decomposition of cross-linked GAP–HTPB networks was evaluated by thermogravimetric analysis (TGA). The kinetic parameters for the decomposition of GAP–HTPB blends were found to be dependant on the concentration of GAP and HTPB in the blend. The cross-linked GAP–HTPB blends were subjected to dynamic mechanical analysis (DMA). The glass transition characteristics of the blends were evaluated by DMA and it was found that blends prepared with GAP content up to 30% showed single transition in the loss tangent trace indicating no phase separation in the cured network.