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.

On the development of instability criteria during hotworking with reference to IN 718

Abstract: A simple instability condition based on the Ziegler’s continuum principles as applied to large plastic flow, is developed for delineating the regions of unstable metal flow during hot deformation. It can be used for any type of the flow stress versus strain rate curve. This criterion has been validated using the flow stress data of IN 718 with microstructural observations. The optimum hot working conditions for the superalloy IN 718 are suggested based on the instability map.

Aerosol characteristics at a high‐altitude location in central Himalayas: Optical properties and radiative forcing

Abstract: [1] Collocated measurements of the mass concentrations of aerosol black carbon (BC) and composite aerosols near the surface were carried out along with spectral aerosol optical depths (AODs) from a high-altitude station, Manora Peak in central Himalayas, during a comprehensive aerosol field campaign in December 2004. Despite being a pristine location in the Shivalik Ranges of central Himalayas and having a monthly mean AOD (at 500 nm) of 0.059 ± 0.033 (typical to this site), total suspended particulate (TSP) concentration was in the range 15–40 μg m−3 (mean value 27.1 ± 8.3 μg m−3). Interestingly, aerosol BC had a mean concentration of 1.36 ± 0.99 μg m−3 and contributed ∼5.0 ± 1.3% to the composite aerosol mass. This large abundance of BC is found to have linkages to the human activities in the adjoining valley and to the boundary layer dynamics. Consequently, the inferred single scattering albedo lies in the range of 0.87 to 0.94 (mean value 0.90 ± 0.03), indicating significant aerosol absorption. The estimated aerosol radiative forcing was as low as −4.2 W m−2 at the surface, +0.7 W m−2 at the top of the atmosphere, implying an atmospheric forcing of +4.9 W m−2. Though absolute value of the atmospheric forcing is quite small, which arises primarily from the very low AOD (or the column abundance of aerosols), the forcing efficiency (forcing per unit optical depth) was ∼88 W m−2, which is attributed to the high BC mass fraction.

Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB): An overview

Abstract: During March–May 2006, an extensive, multi-institution, multi-instrument, and multi-platform integrated field experiment ‘Integrated Campaign for Aerosols, gases and Radiation Budget’ (ICARB) was carried out under the Geosphere Biosphere Programme of the Indian Space Research Organization (ISRO-GBP). The objective of this largest and most exhaustive field campaign, ever conducted in the Indian region, was to characterize the physico-chemical properties and radiative effects of atmospheric aerosols and trace gases over the Indian landmass and the adjoining oceanic regions of the Arabian Sea, northern Indian Ocean, and Bay of Bengal through intensive, simultaneous observations. A network of ground-based observatories (over the mainland and islands), a dedicated ship cruise over the oceanic regions using a fully equipped research vessel, the Sagar Kanya, and altitude profiling over selected regions using an instrumented aircraft and balloonsondes formed the three segments of this integrated experiment, which were carried out in tandem. This paper presents an overview of the ICARB field experiment, the database generated, and some of its interesting outcomes though these are preliminary in nature. The ICARB has revealed significant spatio-temporal heterogeneity in most of the aerosol characteristics both over land and ocean. Observed aerosol loading and optical depths were comparable to or in certain regions, a little lower than those reported in some of the earlier campaigns for these regions. The preliminary results indicate: • low (< 0.2) aerosol optical depths (AOD) over most part of the Arabian Sea, except two pockets; one off Mangalore and the other, less intense, in the central Arabian Sea at ∼ 18 ◦ N latitude;

Efficient π electrons delocalization in prospective push–pull non-linear optical chromophore 4-[N,N-dimethylamino]-4′-nitro stilbene (DANS): A vibrational spectroscopic study

Abstract: A comprehensive investigation on the intramolecular charge transfer (ICT) of an efficient π-conjugated potential push–pull NLO chromophore, 4-[ N , N -dimethylamino]-4′-nitro stilbene (DANS), from a strong electron-donor group (dimethylamino- N (CH 3 ) 2 ) to a strong electron-acceptor group (nitro-NO 2 ) through the π-conjugated bridge ( trans -stilbene) has been carried out from their vibrational spectra. The NIR FT-Raman and FT-IR spectra supported by the density functional theory (DFT) quantum chemical computations have been employed to analyze the effects of intramolecular charge transfer on the geometries and the vibrational modes contributing to the linear electro-optic effect of the organic NLO material. It has been observed that the changes in the endocyclic and exocyclic angles result from the charge-transfer interaction of the phenyl ring and the amino group in the electron-donor side of the NLO chromophore. The strongest vibrational modes contributing to the electro-optic effect have been identified and examined from the concurrent IR and Raman activation of ν (C C/C–C) mode, ring C C stretching modes, in-plane deformation modes, nitro modes and the umbrella mode of methyl groups. Furthermore, the splitting of the vinyl stretching modes and the electronic effects such as hyperconjugation and backdonation on the methyl hydrogen atoms causing the decrease of stretching frequencies and infrared intensities have also been analyzed in detail. The effect of frontier orbitals transition of electron density transfer and the influence of planarity between the phenyl rings of the stilbene moiety on the first hyperpolarizability have also been discussed.