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.

Radiative properties of Bay of Bengal aerosols: Spatial distinctiveness and source impacts

Abstract: [1] Simultaneous and collocated measurements of spectrally resolved scattering and absorption coefficients and mass concentration of near-surface composite aerosols in the marine atmosphere over the Bay of Bengal (BOB), along with incoming shortwave (0.3–3 μm) global solar radiation and columnar spectral aerosol optical depths (AOD), were made on a research cruise during the winter phase of the Integrated Campaign for Aerosols, Gases and Radiation Budget (W-ICARB). The aerosol radiative properties revealed distinct spatial features associated with the contrasting outflows from Indo-Gangetic Plain (IGP) and East Asia. Both scattering and absorption coefficients depicted very high values (>200 and >15 Mm−1) over the northwestern and southeastern BOB and extremely low values (<50 and <10 Mm−1) over the central BOB. The mean value of the total scattering coefficient at 550 nm (∼123.7 ± 85.3 Mm−1) over the entire BOB during winter was higher than the mean values (∼94 ± 47 Mm−1) reported for the premonsoon season. While SSA at 550 nm showed very low values (<0.8) over a very large region in the central BOB and moderately low values over the southern BOB (∼0.85–0.9), the columnar AOD varied from the least values of ∼0.1 over the northeastern BOB to the highest values of ∼0.8 over the northwestern BOB. While significant cooling was observed at the top of the atmosphere and surface over the northwestern BOB, the atmospheric forcing was found to be significantly high (∼15 W m−2) over the southern BOB, where the aerosol radiative forcing efficiency (ARFE) at the surface was also found to be high. Examination of the Moderate Resolution Imaging Spectroradiometer (MODIS)-derived fire count along with the advection pathways revealed a strong contribution from the emissions of biomass smoke from East Asia, which might be contributing to the enhanced aerosol induced warming over the southern BOB. However, the ARFE at the surface was low over the northwestern BOB, where the advection from IGP was predominant.

Imidazolium based energetic ionic liquids for monopropellant applications: a theoretical study

Abstract: A large variety of 1-ethyl-3-methylimidazolium ([EMIm]+) based energetic ionic liquids (ILs) have been studied via their ion pair ([EMIm]+[X]−) formation using high accuracy G3MP2 method and density functional theory (DFT) methods M06L, M05-2X, M06-2X and B3LYP. The selected X− includes nitrogen rich derivatives of tetrazolate and triazolate, dinitramine, dicyanamide as well as conventional anions BF4− and PF6−. The nitrogen enrichment in the system produces energetic ionic liquids (EILs) which showed comparable and in some cases superior thermochemical, fluid and specific impulse (Isp) properties than conventional ionic liquids. The binding energy values for [EMIm]+[X]− are in the range 336–400 kJ mol−1 at DFT levels while the atomization procedure used to compute their heat of formation (ΔfH°) at the G3MP2 level produced results in very close agreement with available experimental data (maximum deviation < 5%). The ΔfH° of conventional ILs is negative whereas that of EILs (167–559 kJ mol−1) confirmed their high energy state. The predicted Isp of all EILs are slightly lower compared to hydrazine in monopropellant systems whereas a significant increase in Isp is observed with the addition of hydroxyl ammonium nitrate (HAN). A good linear correlation between Isp and the wt% of (N + O) content of the EIL is also observed. Our results suggest that imidazolium based energetic ionic liquids have attractive thermochemical properties for use as green substitutes to hazardous hydrazine for monopropellant application in spacecraft technology.

Preparation, characterization, thermo‐mechanical, and barrier properties of exfoliated thermoplastic toughened epoxy clay ternary nanocomposites

Abstract: Ternary nanocomposites are prepared by blending hydroxyl-terminated poly ether ether ketone having pendant methyl groups (PEEKMOH) with epoxy resin along with Nanolin DK1, followed by curing with 4,4′-diamino diphenyl sulphone. Differential scanning calorimetry shows a two-stage cure behavior indicating the catalytic effect of the primary amine and proton, which are generated by the dissociation of organic modifier. Tensile and flexural moduli are increased while tensile strength and glass transition temperature are decreased with increase in clay concentration. Fracture toughness and strain at break are increased by 59 and 62%, respectively, with 1 phr clay loading. Transition electron microscopy and X-ray diffraction (XRD) analysis reveal exfoliated morphology for the nanocomposites. Scanning electron micrographs show a decrease in both, domain size as well as inter domain distance of the thermoplastic phase with the addition of clay, indicating the occurrence of gelation before phase separation. Analysis of the fracture surface reveals crack path deflection and ductile fracture behavior, confirming that toughness has been improved with the addition of clay and PEEKMOH. Coefficient of thermal expansion (CTE) of the nanocomposites is decreased up to 3 phr clay loading. Oxygen gas permeability is compared with Bharadwaj's and Neilson's models. A marginal improvement in thermal stability is observed with the addition of clay. Copyright © 2009 John Wiley & Sons, Ltd.

Microstructure and optical properties of Ba0.6Sr0.4TiO3 thin films prepared by pulsed laser deposition

Abstract: Growth aspects of barium strontium titanate, Ba0.6Sr0.4TiO3 (BST) thin films grown on Si (100) and quartz substrates by pulsed laser deposition technique were investigated. The main objective of the work was to study the effect of substrate temperature and oxygen partial pressure on the microstructure and optical properties of the BST films. X-ray diffraction results revealed that the thin films were amorphous when the substrate temperature was up to 673 K and the crystallinity was found to be improved at the substrate temperature of 873 K. There was an increase in the lattice parameter value from 3.97 to 4.01 A with an increase in the oxygen partial pressure. Scanning electron microscopy revealed smooth and uniform surfaces, while atomic force microscopy revealed that the particle size increased with decreasing oxygen partial pressure. UV-visible spectroscopy showed that the band gap of the BST films deposited on quartz substrate decreased from 4.41 to 3.73 eV as deposition temperature increased from 303 K to 873 K.