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.

Three different types of electric field disturbances affecting equatorial ionosphere during a long-duration prompt penetration event

Abstract: Coordinated digisonde and OI 630.0 nm airglow observations from Thumba (TVM), an Indian dip equatorial station, in conjunction with magnetic and geosynchronous particle flux measurements, reveal three different types of electric field disturbances in the equatorial ionosphere-thermosphere system (ITS) occurring in succession over a period of 6 h on a single night (22–23 January,2012; Ap = 24). These include (1) westward electric field perturbations owing to a pseudo-breakup and a substorm event, each lasting for about 30 min; (2) eastward electric field perturbations continuing for about an hour, owing to the southward excursion of Z component of interplanetary magnetic field (Bz); and (3) DP2-type fluctuating (period ∼40 min) electric field perturbation sustaining for about 4 h. The pseudo-breakup and the fully grown substorm events are found to be longitudinally localized and different in terms of response in the westward auroral electrojet index (AL) as well as geosynchronous electron/proton injections. The polarity of the prompt penetration of interplanetary electric field that affects the equatorial ionosphere is observed to be eastward during 2100–2200 IST (Indian Standard Time) which is observationally sparse but consistent with modeling studies. Interestingly, on the same night, DP2-type electric field fluctuations with ∼40 min periodicity and occasional eastward polarity (akin to daytime) are also found to affect the equatorial ITS for about 4 h (2200–0200 IST). The case study, thus, brings out different processes that constitute a long duration prompt penetration event which, otherwise, would have been categorized as a single event.

Thermoanalytical Investigations on the Effect of Atmospheric Oxygen on HTPB resin

Abstract: Des etudes TG-DSC realisees dans une atmosphere d'air ou d'azote sur des polybutadienes a terminaison hydroxy (HTPB) ont montre trois transitions qui ont entraine (1) un pic DSC exotherme et une augmentation de la masse lors de la TG a 170°C-240°C, seulement dans l'air, (2) un pic exotherme et une faible perte de masse dans l'air ainsi que dans l'azote, causes par la depolarisation, la cyclisation et la reticulation, et (3) une perte de masse due a la pyrolyse dans l'azote ou la combustion dans l'air, ce qui se traduit respectivement par un pic endotherme et un pic exotherme aigu dans les deux atmospheres. L'analyse FTIR des produits isoles lors de la TG a l'issue de l'augmentation de masse revele que de l'oxygene a ete ajoute a la structure butadiene. Les parametres d'activation d'Arrhenius (E et A) ont ete calcules pour l'addition exotherme d'oxygene. La methode selon Ozawa amelioree par l'equation d'approximation a deux termes pour la fonction p(x) (d'apres VSSC) a donne des resultats tout a fait comparables a ceux obtenus par la methode Kissinger.

Electrodynamical response of the Indian low-mid latitude ionosphere to the very large solar flare of 28 October 2003 - a case study

Abstract: The electrodynamic effects on the low-mid lat- itude ionospheric region have been investigated using GPS (global positioning system) data, ionosonde data and 1H values, during the very large solar flare (X17.2/4B) of 28 Oc- tober 2003. The results bring out the flare induced unusual behaviour of the equatorial ionosphere on this day just prior to sunset. The important observations are i) Large and pro- longed Ne enhancements observed from ionosonde data just after the flare-related peak enhancement in EUV flux. The observed enhancement in Ne is due to the increase in ioniza- tion production due to the enhanced EUV flux and the persis- tence of the enhancement is probably due to the prompt pene- tration related upliftment of the F layer (just prior to the flare peak phase) to higher altitudes, where recombination rates are lower. ii) A significant enhancement in total electron content (TEC) ( 10 TEC units) at regions around the Equa- torial Ionization Anomaly (EIA) crest region (Ahmedabad) during the flare in association with the flare related EUV flux enhancement. iii) Similar enhancements seen at stations of Jodhpur and Delhi in the mid latitude sector. iv)The flare re- lated flux enhancements in different longitude sectors in the equatorial electrojet region have been shown to produce pos- itive and negative variations in electrojet strength indicating the presence of current systems having positive and nega- tive polarities in different longitude sectors. Thus the flare effect reveals the longitudinal variation of the counter elec- trojet events in the Equatorial Electrojet (EEJ) region.