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 uniqueness of large deflections of a uniform cantilever beam under a tip-concentrated rotational load

Abstract: The problem of a uniform cantilever beam under a tip-concentrated load, which rotates in relation with the tip-rotation of the beam, is studied in this paper. The formulation of the problem results in non-linear ordinary differential equations amenable to numerical integration. A relation is obtained for the applied tip-concentrated load in terms of the tip-angle of the beam. When the tip-concentrated load acts always normal to the undeformed axis of the beam (the rotation parameter, β = 0 ) there is a possibility of obtaining non-unique solution for the applied load. This phenomenon is also observed for other rotation parameters less than unity. When the tip-concentrated load is acting normal to the deformed axis of the beam ( β = 1 ) , many load parameters are obtained for a tip-angle with different deformed configurations of the beam. However, each load parameter corresponds to a tip-angle, which confirms the uniqueness on the solution of non-linear differential equations.

Effect of reactivity of different types of hydroxyl groups of HTPB on mechanical properties of the cured product

Abstract: The amount of three types of hydroxyl functional groups (GOH, HOH, and VOH) in hydroxyl terminated polybutadiene (HTPB), remaining in samples acetylated to the same extent under two different conditions, viz., fast acetylation using acetyl chloride in presence of N-methyl imidazole catalyst and slow acetylation by acetic anhydride, differed significantly. For the fast acetylation there is a uniform reduction in all the three types of hydroxyls, probably because the reaction becomes random at rapid rates and the reactivity of the different types of hydroxyls does not play a major role. However, in the slow reaction, the reduction of G-type hydroxyls was 30% more than the expected value and there was a corresponding increase in the amount of V-type hydroxyls remaining in the acetylated product, showing reactivity of OH in the order of G > H > V. When the reaction is slow, it becomes selective and the change in reactivity of the three types of OH groups is reflected in the extent of conversion. The mechanical properties and the crosslink density data show a reduction in the samples containing lesser amounts of GOH, confirming the branching nature of GOH, which is involved in the crosslinking reaction. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1313–1320, 1997

On the sunrise oscillation of the F region in the equatorial ionosphere

Abstract: [1] This paper shows that, contrary to previous explanations, the apparent undulating motion of the equatorial F region peak at sunrise is produced by photochemistry rather than dynamics. Our study is based on an investigation of the behavior of the early morning ionosphere observed by a Digital Ionosonde at Trivandrum, India. The phenomenon is rooted in the production of new plasma at the upper F region altitudes soon after sunrise. As the peak photoproduction rate moves down in altitude and increases in magnitude the newly formed plasma follows a similar trend. Once the density becomes large enough to be detected by an ionosonde, a jump is observed in the F region peak altitude. The jump is followed by a quick downward motion of the increasingly strong F peak. Chemistry causes the downward motion of the F peak to end near 250 km. Electrodynamics is not responsible for the sunrise undulation, but plays an indirect role in the detection of the sunrise effect by simultaneously lowering during the night the peak height and decreasing the density. When detectable, the remnant plasma introduces a lower peak height that facilitates the observation of the initial increase in peak height, while the lower background density allows the relatively small initial density increase from photoionization to be observed.