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.

Seasonal trends in chemical composition of aerosols at a tropical coastal site of India

Abstract: [1] Chemical composition of near-surface aerosols at the tropical coastal location Trivandrum (8.55°N, 77°E) has been studied by analyzing the aerosol samples collected during a period of 16 months from October 2003 to January 2005. The annual mean aerosol mass loading at this site averages to around 54 ± 19 μg m−3. The chemical analysis of samples revealed Cl−, SO42−, and NO3− to be the major anionic species and Na, NH4+, Fe, and Ca to be the major cationic species. The total mass loading and the mass concentration of various chemical species showed pronounced seasonal dependence. The active aerosol sources at this location have been investigated in detail to delineate their relative dominance in different seasons. Ions like Na, Cl, Mg, and K, which are mainly of oceanic origin, showed peak during monsoon, indicating sea spray to be the most important source mechanism during the period. On the other hand, mass loading of SO42−, NH4+, PO43−, Fe, and Al and that of trace elements exhibited their maximum in winter/summer, indicating the dominance of continental/crustal sources during the period. The sea salt and non-sea salt components of individual ions like SO42−, K, Ca, and Mg also revealed distinctly different seasonal patterns. In spite of being a coastal site, the non-sea salt components dominated at this location. Dominance of non-sea salt SO42− throughout the year indicates significant anthropogenic influence at this location. On the basis of this study, a first-cut model for the chemical composition of aerosols at this tropical coastal site has been evolved.

Phenol‐containing phthalonitrile polymers – synthesis, cure characteristics and laminate properties

Abstract: Novolac–phthalonitrile polymers bearing a controlled concentration of phthalonitrile groups were synthesized by condensation of novolac with 4-nitrophthalonitrile. The cure characteristics monitored by DSC and rheometry indicated acceleration of the cure reaction by the phenolic groups. Fourier transform infrared analysis of the cured products indicated that the cure mechanism was dependent on the extent of phthalonitrile substitution. In phenol-rich systems, evidence was obtained for the phenol-mediated reaction of nitrile groups resulting in the formation of isoindoline groups. The phthalonitrile-rich system underwent crosslinking through formation of triazine and phthalocyanine groups. The phenol groups in the phthalonitrile backbone were conducive to building a stronger interphase in their carbon composites, resulting in better mechanical properties. This was corroborated by morphological studies by SEM. However, these groups were detrimental to the thermal stability of the cured resins. The polymers exhibited very high flame retardancy which improved further on increasing the degree of phthalonitrilation. Copyright © 2012 Society of Chemical Industry

Processing and characterization of Al–Cu–Li alloy AA2195 undergoing scale up production through the vacuum induction melting technique

Abstract: The inherent properties of lithium, such as high reactivity and toxicity, relatively low density, low melting point, along with its high cost requires a special technological approach to cast Al–Cu–Li alloy AA2195 as compared to the conventional Direct Chill (DC) casting of aluminum alloys. This paper describes the processing requirements for melting and casting of 200 kg of Al–Cu–Li alloy in a Vacuum Induction Melting (VIM) furnace under dynamic inert atmosphere. The as-cast billets have been homogenized to remove microsegregation as well as to avoid incipient melting, and subsequently subjected for secondary metal processing operations viz., forging and rolling. The product in the form of 4 mm thick sheets was subjected to various heat treatments in T8 (Solution Treatment+WQ+CW+Aging) condition. Mechanical properties were evaluated at room temperature and were correlated with microstructures of the sheets processed under different conditions using transmission electron microscopy (TEM).

TIMED/SABER observations of global gravity wave climatology and their interannual variability from stratosphere to mesosphere lower thermosphere

Abstract: The present study for the first time reports the global gravity wave activity in terms of their potential energy derived from TIMED/SABER observations right from the stratosphere to the mesosphere lower thermosphere (MLT) region. The potential energy profiles obtained from SABER temperature are validated by comparing them with ground based LIDAR observations over a low latitude site, Gadanki (13.5° N, 79.2° E). The stratospheric and mesospheric global maps of gravity wave energy showed pronounced maxima over high and polar latitudes of the winter hemisphere. The interannual variability of the stratospheric gravity wave activity exhibited prominent annual oscillation over mid-latitudes. The equatorial gravity wave activity exhibited quasi-biennial oscillation in the lower stratosphere and semi-annual oscillation in the upper stratosphere. The MLT region maps revealed summer hemispheric maxima over polar latitudes and secondary maxima over the equatorial region. The results are discussed in the light of present understanding of global gravity wave observations. The significance of the present study lies in emphasizing the importance of satellite measurements in elucidating gravity waves, which is envisaged to have profound impact on parameterizing these waves.