Showing papers by "Vikram Sarabhai Space Centre published in 1985"
TL;DR: In this paper, the authors used the VHF backscatter radar observations at Thumba during the geomagnetic storm of February 16, 1980, and showed that the decreases and increases of the storm-time electric fields in the equatorial electrojet are completely in phase with the decreases in the mean latitude of the polar cusp region.
Abstract: The Doppler frequency of the VHF radar signals backscattered from the drifting ionization irregularities in the equatorial electrojet is proportional to the east-west electric field Ey in the equatorial electrojet. Using the VHF backscatter radar observations at Thumba during the geomagnetic storm of February 16, 1980, it is shown that the decreases and increases of the storm-time electric fields in the equatorial electrojet are completely in phase with the decreases and increases in the mean latitude of the polar cusp region. This observation has important implications for understanding the magnetosphere-ionosphere interactions, particularly the effect of the magnetospheric electric fields on the low latitude ionosphere.
19 citations
19 citations
TL;DR: In this paper, a comparative study of some formulation variables was made for their effect in improving the flow characteristics and mechanical properties of an aluminized polyurethane (PU) propellant system based on hydroxyl terminated natural rubber (HTNR).
Abstract: Hydroxyl terminated natural rubber (HTNR) was prepared by the depolymerization of masticated natural rubber in the presence of H2O2 in toluene. Probable mechanisms leading to the formation of side reaction products are proposed based on the analytical data. A comparative study of some formulation variables was made for their effect in improving the flow characteristics and mechanical properties of an aluminized polyurethane (PU) propellant system based on HTNR. This PU system has also been compared for its theoretical performance characteristics with some other state-of-the-art systems.
17 citations
TL;DR: In this paper, the postbuckling behavior of tapered circular plates with cylindrically orthotropic material properties is studied through a finite element formulation and the results in the form of an empirical formula for the radial load ratios are presented for various values of the taper parameter and orthotropy parameter.
14 citations
TL;DR: In this paper, the thermal decomposition of Thioped, a liquid polysulfide polymer based on dichloroethyl formal, was studied using pyrolysis-GC-MS.
Abstract: The thermal decomposition of Thioped, a liquid polysulfide polymer based on dichloroethyl formal, was studied using pyrolysis–GC–MS. The nature and composition of the products of pyrolysis at 358 and 485°C are given. A striking feature of the product analysis is the presence of several disulfide compounds only at the higher decomposition temperature. The pyrolysis-GC of other liquid polysulfide polymers (LP-2, LP-32, LP-3, and LP-33) showed that molecular weight had only marginal effect on the product composition. Ionic and radical mechanisms were considered to account for the product formation. Isothermal and dynamic thermogravimetric studies were carried out to differentiate between the two mechanisms. The results were found to be in agreement with a free radical mechanism, with cleavage of the formal CO linkage as the preferred mode of initiation. The overall activation energy for the decomposition was found to be 190 kJ mol−1.
11 citations
TL;DR: The mechanism of the single-step dehydration of ZnC 2 O 4 · 2H 2 O has been established from TG, DTA and DSC studies as discussed by the authors, where the rate-controlling process for the reaction is random nucleation with the formation of one nucleus on each particle.
9 citations
TL;DR: Titanium oxide on silica-alumina support is described to be an efficient regenerable catalyst for alkylation of aromatic compounds with alkyl halides, alcohols and olefins, and the reaction is initiated by the protonated metal active species present in the catalyst.
9 citations
TL;DR: In this article, the effect of curing agents on the properties of polysulfide sealant composition was investigated and it was established that curing agents affect joint strengths, stress-strain properties, dynamic mechanical properties, and thermal stability of the sealant.
Abstract: The effect of curing agents on the properties of a polysulfide sealant composition was investigated. Commercially used curing agents, namely, lead dioxide, manganese dioxide, and ammonium dichromate, were selected for this study. It was established that curing agents affect joint strengths, stress–strain properties, dynamic mechanical properties, and thermal stability of the sealant. Sealant cured with ammonium dichromate had highest shear bond strength, ultimate tensile strength, modulus, and thermal stability, whereas these properties were lowest for lead-dioxide-cured sealant. Peel bond strength and elongation at break were highest for lead-dioxide-cured sealant. The observed changes in properties were attributed to the difference in crosslink density of the cured sealant, produced by the curing agents. The curing agents have no appreciable effect on the fuel resistance of the polysulfide sealant.
7 citations
TL;DR: Titanium oxide on silica-alumina support is found to be effective for oligomerisation of phenyl acetylene as mentioned in this paper. But it is not suitable for the use of catalytic catalysts.
7 citations
TL;DR: A 0.3 m diameter, 2 m long and 0.0015 m thick, 18 nickel 1800 MNm−2 grade maraging steel motor case was designed, fabricated and burst tested to gain experience for using the steel as booster case material in satellite launch vehicles as discussed by the authors.
Abstract: A 0.3 m diameter, 2 m long and 0.0015 m thick, 18 nickel 1800 MNm−2 grade maraging steel motor case was designed, fabricated and burst tested to gain experience for using the steel as booster case material in satellite launch vehicles. The bursting occurred at 15.2 MPa for which the effective hoop stress worked out to be 1754 MNm−2 almost equal to the ultimate tensile strength (1764 MNm−2) of the material in the solution treated and aged condition. The failure analysis revealed that the material failed due to normal tensile overload fracture. The burst test data was used to arrive at fracture mechanics parameters like crack size, gross section area stress and the stress for leak before bursting.
6 citations
TL;DR: In this paper, activation energy, E, and preexponential factor, A, have been evaluated for the dehydration of zinc oxalate dihydrate from isothermal mass-loss measurements.
TL;DR: In this paper, tris(hydroxy phenoxy) cyclotriphosphazenes based on the reaction of hexachlorocyclotrisphophosphazene, (NPCl 2 ) 3 with bisphenol-A, thiodiphenol and hydroquinone were prepared and characterized for degree of substitution of chlorine, product distribution and purity.
TL;DR: The kinetic parameters and the heat of polymerisation for the cure reaction of reactive polyamide (made from dimer acid) with epoxide have been established using DSC as mentioned in this paper.
TL;DR: In this article, the proton noise-decoupled 13C NMR spectra were used to characterize the terpolymer of butadiene (BD), acrylonitrile (AN), and methacrylic acid (MMA) prepared by emulsion polymerisation.
Abstract: The proton noise-decoupled 13C NMR spectra were used to characterize the terpolymer of butadiene (BD), acrylonitrile (AN), and methacrylic acid (MMA) prepared by emulsion polymerisation. Assignments for the various triads of butadiene units adjacent to acrylonitrile in the terpolymer were made by comparing the olefinic and aliphatic carbon resonances of a butadiene (B)-acrylonitrile (A) copolymer. Measurement of intensities of olefinic resonances in the nitrile environment for the terpolymer gives information about the BBB, BBA, ABB and ABA triads distribution, BBA and ABA being predominant. The intensities of methylene carbon resonances of the various triads for BD units connected to AN show a similar trend. The relative populations of various triads calculated from the peak intensities show that the terpolymer has a random structure. The assignments pertaining to BD units were made by comparison with 13C resonances of polybutadiene. The distribution of trans-1,4-, cis-1,4- and 1,2-units in the terpolymer indicates that the terpolymer has a random structure.
TL;DR: In this article, six semi-aromatic polyamides were synthesized by low temperature solution polycondensation of aromatic diamines (1a, f), containing flexible groups such as CH2, CH2CH2, O, S, and SO2, with 2,′2-[sulfonylbis(1,4-phenyleneoxy)]-diacetyl chloride (2) in a solvent mixture of NMP and HMPT (vol. ratio 2 : 1).
Abstract: Six semi-aromatic polyamides (3a–f) were synthesized by low temperature solution polycondensation of aromatic diamines (1a–;f), containing flexible groups such as CH2, CH2CH2, O, S, and SO2, with 2,′2-[sulfonylbis(1,4-phenyleneoxy)]-diacetyl chloride (2) in a solvent mixture of NMP and HMPT (vol. ratio 2 : 1). All the polyamides posses inherent viscosities in the range of 0,31 to 0,73 dl/g. They are soluble in polar amides and DMSO. The molecular weights, molecular weight distributions, thermal stabilities, thermal degradation kinetics and percentages of crystallinity were determined.
TL;DR: In this article, a methode numerique simple de resolution de l'equation integro-differentielle non lineaire decrivant le champ de temperatures dans la paroi d'un tube parcouru par un courant de gaz chaud transparent, avec conduction thermique axiale dans the paroi and variation du coefficient de transfert convectif de chaleur dans les zones d'entree.
TL;DR: In this paper, an attempt is made to utilize Bayesian statistics for reliability measurement of a complex system by combining prior information actual test data for each subsystem, as applied herein, codes the information available from past experience into a prior probability distribution which is updated with test results as they became available.
TL;DR: An 8085-based ATC with IEEE-STD-488 interface has been designed and developed for the batch-testing of on-board avionics units like pre-amplifiers.
Abstract: An 8085-based ATC with IEEE-STD-488 interface has been designed and developed for the batch-testing of on-board avionics units like pre-amplifiers.
TL;DR: In this article, the stress strength interference theory is used to evaluate the structural reliability of a rocket motor, and the reliability at a specified confidence level is obtained using a Monte Carlo simulation technique.
TL;DR: In this article, an explicit form of velocity to be gained guidance algorithm is proposed for ASLV mission of Indian Space Research Organisation (ISRO), which is to inject a 150 kg payload into a 400 Km near circular orbit using a four stage solid propellant system.
TL;DR: In this paper, the effects of the electromagnetic loading parameter, the magnetic interaction parameter and the ratio of the wall temperature to the free stream temperature on the boundary layer physical parameters have been discussed.
Abstract: Studies are made on laminar compressible magnetohydrodynamic (MHD) boundary layer flow over an insulated wall with variable tensor electrical conductivity. The effects of the electromagnetic loading parameter, the magnetic interaction parameter and the ratio of the wall temperature to the free stream temperature on the boundary layer physical parameters have been discussed.
TL;DR: In this paper, the boundary layer growth with tensor electrical conductivity and the transpiration number has been examined using local nonsimilarity solutions method and it is found that suction will cause the increase in wall shearing stress and decrease in thickness of the boundary layers.
Abstract: The boundary layer growth with tensor electrical conductivity and the transpiration number has been examined using local nonsimilarity solutions method. It is found that suction will cause the increase in wall shearing stress and decrease in thicknesses of the boundary layer.