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.

Ionogram signatures of large‐scale wave structure and their relation to equatorial spread F

Abstract: [1] Observations of signatures of the large-scale wave structure (LSWS) and subsequent development of equatorial spread F (ESF) by using data from a newly installed digital ionosonde at Trivandrum (8.5°N; 77°E; 0.5°N magnetic dip latitude) are presented. The LSWS signatures are observed using the ionograms with echo directions. The ‘satellite’ traces are shown as echoes from oblique directions, when an upwelling (associated with LSWS) is not directly over the ionosonde location. When an upwelling is centered overhead, and the radius of curvature of the isodensity contours matches the height of reflection, signals from various directions can add in phase to enhance the ionospheric reflection coefficient, and produce another ionogram signature, referred to as multireflected echoes (MREs). It is also shown that the generation of ESF is related to the presence of LSWS. The skymaps also show the presence of small-scale wave structures in the bottomsideFregion. The investigation also indicates that the range spread F (RSF) occurs because of the reflections from the embedded smaller-scale structures within the large-scale upwelling.

Thermo-structural analysis of composite structures

Abstract: Thermo-structural analyses of passive and active hot composite structures considering temperature dependent material properties under thermal and mechanical loads are carried out. The behaviour of the composite material under thermal, thermo-chemical and mechanical loads is studied. A general approach to carry out thermo-structural analysis and how the behaviour is incorporated in the modelling are briefly discussed. Thermo-structural analysis shows that thermal stresses are very much predominant when compared to stresses due to mechanical loads. A parametric study on variation of coefficient of thermal expansion (α) due to change in fibre orientation of carbon–carbon cap type structure is studied and it is concluded that one of the critical design variables identified is the α value across the thickness of the laminate.

Cryogenic Mechanical Properties of Warm Multi-Pass Caliber-Rolled Fine-Grained Titanium Alloys: Ti-6Al-4V (Normal and ELI Grades) and VT14

Abstract: The effect of microstructural refinement and the β phase fraction, V β, on the mechanical properties at cryogenic temperatures (up to 20 K) of two commercially important aerospace titanium alloys: Ti-6Al-4V (normal as well as extra low interstitial grades) and VT14 was examined. Multi-pass caliber rolling in the temperature range of 973 K to 1223 K (700 °C to 950 °C) was employed to refine the microstructure, as V β was found to increase nonlinearly with the rolling temperature. Detailed microstructural characterization of the alloys after caliber rolling was carried out using optical microscopy (OM), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscopy (TEM). Complete spheroidization of the primary α laths along with formation of bimodal microstructure occurred when the alloys are rolled at temperatures above 1123 K (850 °C). For rolling temperatures less than 1123 K (850 °C), complete fragmentation of the β phase with limited spheroidization of α laths was observed. The microstructural refinement due to caliber rolling was found to significantly enhance the strength with no penalty on ductility both at room and cryogenic temperatures. This was attributed to a complex interplay between microstructural refinement and reduced transformed β phase fraction. TEM suggests that the serrated stress–strain responses observed in the post-yield deformation regime of specimens tested at 20 K were due to the activation of $$ \left\{ {10\bar{1}2} \right\} $$ tensile twins.

Influence of continental outflow and ocean biogeochemistry on the distribution of fine and ultrafine particles in the marine atmospheric boundary layer over Arabian Sea and Bay of Bengal

Abstract: [1] Extensive measurements of aerosol number size distributions (in the size range of 10 to 875 nm) carried out over the oceanic regions of the Bay of Bengal and Arabian Sea during two large cruise experiments (one during pre-monsoon and the other during winter) are used to investigate the spatial distribution of aerosol size distributions, in general, and that of fine particles, in particular, within the marine atmospheric boundary layer. The size distributions over the northwestern Bay of Bengal, lying downwind of the continental outflow from the Indo-Gangetic Plain, and over the eastern Bay of Bengal, under the influence of the East Asian outflow, showed a bimodal structure with prominent mode (100–125 nm) in the accumulation regime and weak mode (30–40 nm) in the Aitken regime during both pre-monsoon and winter seasons. While the Aitken mode was found to be relatively quite weak in the Indo-Gangetic Plain outflow during both seasons, it was prominent in the East Asian outflow regions, especially during the winter season. The distributions over the northern Arabian Sea, a region quite prone to advection of dust during pre-monsoon and summer seasons, showed a prominent Aitken mode (~45 nm) followed by a weaker accumulation mode during pre-monsoon season. Analysis of SeaWiFS data revealed a systematic collocation of Aitken mode aerosols and the high chlorophyll concentration in the northern Arabian Sea, implying the role of ocean biogeochemistry in influencing the aerosol size distributions. Such a feature implying biogeochemical influence was not seen over the eastern and northern Bay of Bengal during pre-monsoon and winter seasons.