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.

Local electrodynamics of a solar eclipse at the magnetic equator in the early afternoon hours

Abstract: The path of maximum obscuration for the annular solar eclipse of January 15, 2010, crossed the magnetic equator at Trivandrum, India, in the early afternoon hours. A strong counter-electrojet was observed shortly after maximum obscuration. Moreover, as the eclipse passed overhead, the F region density peak underwent a large amplitude vertical oscillation. At the same moment, there was an oscillation in the zonal electric field inferred from the magnetometer data. The electric field turned westward after the time of maximum obscurity, reaching its largest westward value one hour before the end of the local eclipse. We show that these data are consistent with a fast eastward moving local neutral wind dynamo generated by a low pressure system postulated to have been triggered by the cold temperatures in the region of maximum obscuration.

Morphology, viscoelastic properties, and mechanical behavior of epoxy resin modified with hydroxyl-terminated poly(ether ether ketone) oligomer with pendent tert-butyl groups

Abstract: Hydroxyl-terminated poly (ether ether ketone) with pendent tert-butyl groups (PEEKTOH) synthesized from 4,4′-difluorobenzophenone and tert-butyl hydroquinone was blended with diglycidyl ether of bisphenol-A (DGEBA) epoxy resin. A diamine, 4,4′-diaminodiphenyl sulfone (DDS) was used as the curing agent. The thermal and mechanical properties, fracture toughness, and morphology of the blends were investigated. Morphological analysis of the blends revealed a particulate structure with PEEKTOH phase dispersed in the epoxy matrix. Unlike classical polymer blend systems, increase in concentration of PEEKTOH does not increase the domain size. Instead, a decrease is obtained. The fracture toughness increased with the addition of oligomer without much decrease in tensile and flexural strengths. Addition of 15 phr oligomer gave maximum toughness. The dispersed PEEKTOH initiated several mechanisms that improved the fracture toughness of the blends. The cross-link density calculated from the storage modulus in the rubbery plateau region decreased with the increase in PEEKTOH. The thermal stability of epoxy resin remained unaffected even after blending with PEEKTOH. POLYM. ENG. SCI., 45:1645–1654, 2005. © 2005 Society of Plastics Engineers

X-rays from Saturn: a study with XMM-Newton and Chandra over the years 2002–05

Abstract: Aims. We approach the study of Saturn and its environment in a novel way using X-ray data, by making a systematic and uniform spectral analysis of all the X-ray observations of the planet to date. Methods. We present the results of the two most recent (2005) XMM-Newton observations of Saturn together with the re-analysis of an earlier (2002) observation from the XMM-Newton archive and of three Chandra observations in 2003 and 2004. While the XMM-Newton telescope resolution does not enable us to resolve spatially the contributions of the planet's disk and rings to the X-ray flux, we can estimate their strengths and their evolution over the years from spectral analysis, and compare them with those observed with Chandra.Results. The spectrum of the X-ray emission is well fitted by an optically thin coronal model with an average temperature of 0.5 keV. The addition of a fluorescent oxygen emission line at ~0.53 keV improves the fits significantly. In accordance with earlier reports, we interpret the coronal component as emission from the planetary disk, produced by the scattering of solar X-rays in Saturn's upper atmosphere, and the line as originating from the Saturnian rings. The strength of the disk X-ray emission is seen to decrease over the period 2002–2005, following the decay of solar activity towards the current minimum in the solar cycle. By comparing the relative fluxes of the disk X-ray emission and the oxygen line, we suggest that the line strength does not vary over the years in the same fashion as the disk flux. We consider possible alternatives for the origin of the line. The connection between solar activity and the strength of Saturn's disk X-ray emission is investigated and compared with that of Jupiter. We also discuss the apparent lack of X-ray aurorae on Saturn; by comparing the planet's parameters relevant to aurora production with those of Jupiter we conclude that Saturnian X-ray aurorae are likely to have gone undetected because they are below the sensitivity threshold of current Earth-bound observatories. A similar comparison for Uranus and Neptune leads to the same disappointing conclusion, which is likely to hold true also with the planned next generation International X-ray Observatory. The next step in advancing this research can only be realised with in-situ X-ray observations at the planets.

Effect of tropical cyclones on the stratosphere–troposphere exchangeobserved using satellite observations over the north Indian Ocean

Abstract: . Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere–troposphere exchange (STE) processes in the upper troposphere and lower stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the north Indian Ocean during 2007–2013 on the STE processes is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) radio occultation (RO) measurements, and ozone and water vapour concentrations in the UTLS region are obtained from Aura Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km of the centre of the tropical cyclone. In our earlier study, we observed a decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K), and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within 500 km of the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from the cyclone centre, whereas the enhancement in the water vapour in the lower stratosphere is more significant on the south-east side, extending from 500 to 1000 km away from the cyclone centre. The cross-tropopause mass flux for different intensities of cyclones is estimated and it is found that the mean flux from the stratosphere to the troposphere for cyclonic storms is 0.05 ± 0.29 × 10−3 kg m−2, and for very severe cyclonic storms it is 0.5 ± 1.07 × 10−3 kg m−2. More downward flux is noticed on the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget, and consequentially the STE in the UTLS region.

Microstructure and micro-texture evolution during large strain deformation of aluminium alloy AA 2219

Abstract: Aluminium alloy AA2219 is widely used in the fabrication of propellant tanks of cryogenic stages of satellite launch vehicles. These propellant tanks are welded structures and a fine grained microstructure is usually preferred for sheets/plates and ring rolled rings used in their fabrication. In order to study the effect of large strain deformation on the microstructural evolution, hot isothermal plane strain compression (PSC) tests were conducted on AA 2219 in the temperature range of 250 °C–400 °C and at strain rates of 0.01 s −1 and 1 s −1 . Flow curves obtained at different temperatures and strain rates exhibited two types of behavior; one with a clear stress peak followed by softening, occurring below Z=2.5E+15 and steady state flow behavior above it. Electron Back-Scatter Diffraction (EBSD) analysis of the PSC tested samples at the location of maximum strain revealed the presence of lamellar microstructures with very low fraction of transverse high angle boundaries (HABs). The loss of HABs during large strain deformation is attributed to the occurrence of dynamic recovery (DRV) as the ratio of calculated to measured lamellar boundary width is less than unity. Based on detailed microstructure and micro texture analysis, it was concluded that it is very difficult to obtain large fraction of HABs through uniaxial large strain deformation. Therefore, to obtain fine grain microstructure in thermo-mechanically processed AA2219 products, multi-axial deformation is essential.