Showing papers by "Vikram Sarabhai Space Centre published in 1989"
TL;DR: In this article, the typical quiet day variations of the equatorial electrojet (EEJ) current intensity with time of the day, season, sunspot number, and geomagnetic latitude are presented in terms of the corresponding variations of ΔH which is the deviation of the horizontal component (H) from its steady nighttime level.
Abstract: The typical quiet day variations of the equatorial electrojet (EEJ) current intensity with time of the day, season, sunspot number, and geomagnetic latitude are presented in terms of the corresponding variations of ΔH which is the deviation of the horizontal component (H) of the geomagnetic field from its steady nighttime level. The observed height structure of the current density in the EEJ as measured in rocket flights is presented, along with the theoretically computed structure. Theoretical model results on the polarization electric fields and east-west currents as generated by the local interactions of height-varying winds in the EEJ show large height gradients and reversals for both currents and electric fields; experimental evidence for the reality of such height structures is also shown. The characteristics of the counter-electrojet events are presented and the possible causative mechanisms are discussed critically.
97 citations
56 citations
TL;DR: In this paper, the thermal decomposition studies of bis(ethylenediamine)copper(II) chloride monohydrate and bis(methylenediaminescopper (II) bromide monohydrate were carried out using thermogravimetry (TG), derivative thermogram (DTG) and differential thermal analysis (DTA) to evaluate the kinetics and mechanism of the dehydration and the deamination stages of both the complexes.
26 citations
TL;DR: In this article, the kinetics and mechanism of the thermal decomposition of tetrammine copper(II) sulphate monohydrate have been studied using non-isothermal thermogravimetry.
26 citations
TL;DR: In this article, a second order nonlinear integro-differential equation for large deflection problems of a uniform cantilever beam under a rotational distributed loading is formulated by means of a second-order nonlinear integral differential equation.
Abstract: Large deflection problems of a uniform cantilever beam under a rotational distributed loading are formulated by means of a second order nonlinear integro-differential equation. The problem is numerically solved by considering a uniform rotational distributed load and a linearly varying rotational distributed load along the span of the beam. The details of load deflection curves are presented. Assuming Dirac delta function as a load distribution function along the span of the beam, the present general formulation yields the solution for the problem of a uniform cantilever beam with end rotational concentrated load. The numerical results for this case are found to be in good agreement with existing closed form solutions. As the formulation is general, the problem with nonuniform rotational distributed load of any complexity can be solved following the present numerical procedure which is quite simple, accurate and involves less computational time.
22 citations
TL;DR: In this paper, the thermal post-buckling behavior of orthotropic square plates with simply supported edges has been studied using the Rayleigh-Ritz method and the formulation and the solution for the linear buckling temperature and postbuckling temperature are presented in closed form together with a set of numerical results.
21 citations
TL;DR: In this paper, a comparative analysis of ester type plasticizers such as dioctyl adipate (DOA), DOP, DBS, isodecyl pelargonate (IDP), trioctylphosphate (TOF), diethyl phthalate (DEP), tricresyl phosphate (TCP) and dibutyl phthylate (DBP) is presented.
Abstract: In this paper a comparative analysis on the energetics of ester type plasticizers such as dioctyl adipate (DOA), dioctyl phthalate (DOP),dibutyl sebacate (DBS), isodecyl pelargonate (IDP), trioctylphosphate (TOF), diethyl phthalate (DEP), tricresyl phosphate (TCP)and dibutyl phthalate (DBP) and hydrocarbon type plasticizers such as polybutene (PB), spindle oil, naphthenic oil, polymer extender oil(PEO) and poly isobutylene (PIB) and the impact of some of the plasticizers on the work ability, pot life and mechanical properties of propellants based on two selected polymeric binders namely polybutadiene-acrylic acid-acrylonitrile (PBAN) ter polymer andhydroxyl terminated polybutadiene (HTPB) have been reported. The compatibility of all the plasticizers on HTPB binder was also studied at different concentration levels and temperatures using Brookfield viscometer and reported. The mechanism of plasticization is also reviewed.
15 citations
TL;DR: The kinetics and mechanism of thermal decomposition of diaquobis(ethylenediamine)copper(II) oxalate were studied using non-isothermal thermogravimetry (TG) and differential scanning calorimetry(DSC) as mentioned in this paper.
13 citations
TL;DR: In this paper, the effect of two commercially available metal oxide curing agents, PbO2 and MnO2, on the cure time, kinetic parameters and ultimate tensile strength of polysulphide polymer was investigated.
Abstract: The effect of two commercially available metal oxide curing agents, PbO2 and MnO2, on the cure time, kinetic parameters and ultimate tensile strength of the polysulphide polymer was investigated. The kinetic parameters for the thermal decomposition of the two systems were evaluated from their TG data. Both the energy of activation and pre-exponential factor showed a systematic increase with increase in cure and levelled off after the reaction. The cure time was also followed by determining the mechanical properties of the samples at regular intervals. The ultimate tensile strength values and the kinetic parameters follow similar trend with respect to the cure time. The kinetic parameters and the ultimate tensile strength for the PbO2 cured polysulphide system were on the higher side.
13 citations
TL;DR: In this article, a first-order shear deformation laminate theory that accounts for the Green Lagrange strain vector is described and its finite element model is developed, which is used to study the effects of anisotropy, transverse shear moduli, aspect ratio and boundary conditions on the buckling behaviour under in-plane triangular loading.
13 citations
TL;DR: In this article, the existence of periodic orbits of the second kind was established through analytic continuation using Giacaglia's canonical variables in the planar restricted three-body problem when the more massive primary is an oblate spheroid with its equatorial plane coincident with the plane of motion.
Abstract: Utilizing secular perturbing potential due to oblateness, the existence of periodic orbits of the second kind is established through analytic continuation using Giacaglia's canonical variables in the planar restricted three-body problem when the more massive primary is an oblate spheroid with its equatorial plane coincident with the plane of motion.
TL;DR: In this article, the effects of the excess temperature reported earlier and the rest of the measured parameters on the electron density profiles are evaluated using models and compared with the measurements, and the significance of the changes in the neutral composition due to the enhanced neutral temperature and the low turbopause level, in increasing the base-level plasma densities by a factor of 3-5 are demonstrated and the possible role of plasma dynamics discussed.
TL;DR: In this paper, the Earth's zonal harmonic J2 perturbation is considered, and analytical solutions using KS elements are derived for short-term orbit computations, where only two of the nine KS element equations are integrated analytically due to the reasons of symmetry.
Abstract: Analytical solutions using KS elements are derived. The perturbation considered is the Earth's zonal harmonic J
2. The series expansions include terms of fourth power in the eccentricity. Only two of the nine KS element equations are integrated analytically due to the reasons of symmetry. The analytical solution is suitable for short-term orbit computations. Numerical studies show that reasonably good estimates of the orbital elements can be obtained in one step of 10 to 30 degrees of eccentric anomaly for near-Earth orbits of moderate eccentricity. For application purposes, the analytical solution can be effectively used for onboard computation in the navigation and guidance packages, where the modelling of J
2 effect becomes necessary.
TL;DR: In this article, the reflection and radiative damping of the Kelvin and Rossby-gravity (RG) waves propagating upward in the 20-90 km altitude region were investigated.
Abstract: Quantitative theoretical estimates are made of the reflection and radiative damping of the Kelvin and Rossby-gravity (RG) waves propagating upward in the 20–90 km altitude region. An atmosphere with realistic temperature, wind and cooling rate coefficient values is approximated by a model of vertically stacked, thin, homogeneous layers. The amplitude reflection coefficients are shown for different wave periods (T) and zonal wavenumbers (kx). Combining the attenuation due to radiative cooling with the growth due to density decrease, the net changes of wave amplitudes with height in the 20–90 km region are shown for various wave modes.
For Kelvin waves the reflected wave energy is generally less than 15% of the incident wave energy, but the reflected wave amplitude can be 20%-30% of the incident wave amplitude for many modes, at 20 km height. In contrast, many RG wave modes suffer strong or total reflection at various heights if they are not severely damped at lower heights. Calculations for January and July wind conditions reveal a good deal of sensitivity of RG wave reflection to wind conditions.
Radiative damping is found to be severe in the mesosphere for Kelvin waves with T ⩾ 6–8 days, depending on wind conditions; it is severe even in the lower stratosphere for RG waves with T > 4 days. Considerable changes in the damping rates and wave amplitudes at various heights take place from January to July owing to wind changes. Kelvin waves in the 2–8-day period range and RG waves in the 1.5-3-day range can propagate into the upper mesosphere/lower thermosphere without large attenuation, depending upon wind conditions.
It is shown that our theoretical results can explain several observed characteristics of equatorial waves in the stratosphere and mesosphere, including the recent results on wave disturbances in satellite-measured temperatures. Further modelling studies based on our methodology can lead to a good physical insight and quantitative interpretations of the SAO- and the QBO-generation processes.
TL;DR: In this article, a relation between the elastic stress intensity factor and the elastic nominal stress (net section) at failure is established using the crack growth resistance curve (R- curve ), generated from a compact tension specimen.
TL;DR: In this article, a modification in the existing empirical relation correlating the Charpy V-notch impact testing results with plane strain fracture toughness is suggested, and the estimates of fracture toughness from the present modified emperical correlation are found to be in good agreement with the valid fracture toughness test values obtained from compact tension specimens as per ASTM E 399 standards.
TL;DR: In this article, the effect of SiO2 as a coprecipitant on the photochemical behavior of polycrystalline n-TiO2 electrode is investigated, and it is observed that incorporation of silica into titania based photoanodes improved their photochemical efficiency.
TL;DR: Determination des rapports de reactivite par les methodes de Fineman-Ross, Kelen-Tudos et Mayo-Lewis. as mentioned in this paper compare avec les resultats obtenus pour d'autres hydroxy-4 styrenes proteges montrant l'influence faible du groupe protecteur sur la copolymerisation
Abstract: Determination des rapports de reactivite par les methodes de Fineman-Ross, Kelen-Tudos et Mayo-Lewis. Comparaison avec les resultats obtenus pour d'autres hydroxy-4 styrenes proteges montrant l'influence faible du groupe protecteur sur la copolymerisation
TL;DR: In this article, the stability parameter values for moderately thick annular plates under uniform radial compression at the outer edge were evaluated through the finite element method, and the effect of constraining the in-plane displacement at the inner edge on the buckling loads was also studied.
TL;DR: In this article, a polymeric (octacyano phthalocyaninato polysiloxane) was prepared by reacting 1, 2, 4, 5 tetracyano benzene (TCNB) with silicon tetrachloride in refluxing quinolene and hydrolysing the resulting product with dilute alkali.
TL;DR: In this article, the authors discuss the development of composite propellantextrusion technique and the study of burning rate pressure indices n with respect to compositional variations with specific reference to plateau and mesaburning additives.
Abstract: This paper discusses the development of composite propellantextrusion technique and the study of burning rate pressure indices nwith respect to compositional variations. The n is found to vary from0.35 to plateau and plateau to mesa by suitable compositionalmodifications. Compositional influence on burning rate with specificreference to plateau and mesaburning additives is described. Detailsof the process parameters like fluidity of the slurry, extrusion pressure,extrusion rate and die-swell are presented. This propellant is based onISRO-CTPB binder using ISRO-AP as oxidizer. Ammonium perchlorate (AP) particle size variation and inclusion of additives likePVC, lead stearate, ammonium sulphate, lithium fluoride etc. are foundto influence the burning rate pressure index n.
TL;DR: In this article, an eight-noded, shear flexible quadratic rectangular element with five degrees of freedom per node was developed to study the effects of transverse shear on the stability of layered composite plates, under uni-axial and biaxial compression for various boundary conditions.
TL;DR: In this article, the stability of square plates resting on four symmetrically placed point supports on their diagonals is studied using a high precision, triangular plate bending element, and it is shown that the stability parameters of these plates under constant uniform biaxial compressive, loads are independent of point support location.
TL;DR: Etude de l'evolution de la reaction par ATD, TG et RX; effet de Mo et KClO 4 sur la vitesse de the reaction, profils de temperature, sequence reactionnelle as mentioned in this paper.
Abstract: Etude de l'evolution de la reaction par ATD, TG et RX; effet de Mo et KClO 4 sur la vitesse de la reaction, profils de temperature, sequence reactionnelle
TL;DR: In this paper, the microstructure of a composite matrices en alliage Al-Zn-Mg renforcee par des particules de TiO 2 was analyzed.
Abstract: Analyse de la microstructure d'un composite a matrice en alliage Al-Zn-Mg renforcee par des particules de TiO 2 . Etude de l'influence d'un recuit d'homogeneisation sur la structure dendritique du materiau. Etude des caracteristiques de forgeage entre 460 et 420˚C.
TL;DR: In this article, hydroxy-terminated ether-and ester-based prepolymers more suitable for propellant binder applications were prepared from tetrahydrofuran, propyleneoxide, and various discarboxylic acids.
Abstract: Hydroxy-terminated ether- and ester-based prepolymers more suitable for propellant binder applications were prepared from tetrahydrofuran, propyleneoxide, and various discarboxylic acids. Polyurethanes were prepared from these prepolymers with various diisocyanates such as hexamethylenediisocyanate, toluene diisocyanate, and diphenylmethanediisocyanate, and the mechanical properties such as hardness, tensile strength, and elongation of these polyurethane elastomers were compared. The thermal degradation study of these polyurethanes was studied in the atmosphere of oxygen. Composite propellants were formed using these prepolymers as binder resins, toluene diisocyanate as the curing agent, ammonium perchlorate as the oxidizer, and aluminum as the fuel. Propellants having two different solid loadings (85 and 82%) were made and compared with respect to their unloading slurry viscosity and mechanical properties. The tensile strength, elongation, and ballistic performance parameters (theoretical) of these new propellant systems were promising.
TL;DR: In this article, N,N′-bis(3,3′-itaconimidophenyl) sulfone has been synthesized by reacting itaconic anhydride with 3, 3′-diamino diphenyl sulfone.
Abstract: N,N′-bis(3,3′-itaconimidophenyl) sulfone has been synthesized by reacting itaconic anhydride with 3,3′-diamino diphenyl sulfone. The bisitaconimides and the intermediates were characterized by chemical analysis, IR, NMR, TG, and GPC. The degree of polymerization (DP) of the prepolymers of the bisitaconimide was followed by GPC and from the NMR data on vinylidene and aromatic proton ratios. The correlation between DP and intrinsic viscosity of the prepolymers was made use of to determine the Mark–Houwink constants (K and α). The thermal stability and the decomposition kinetics of the prepolymers were evaluated from TG data. The kinetic parameters, viz. energy of activation, E, and preexponential factor A, were computed using four nonisothermal integral equations, and their values are not appreciably affected by the degree of polymerization, within the range studied.
TL;DR: In this article, the impact energy and compact tension (CT) and Charpy notch (CVN) specimens of 18 Ni 1800 MPa maraging steel (parent metal and weldment) were used to determine plane strain fracture toughness.
Abstract: Compact tension (CT) and Charpy “V” notch (CVN) (impact and three-point bend) specimens of 18 Ni 1800 MPa maraging steel (parent metal and weldment) were used to determine plane strain fracture toughness (K
IC) and CVN impact energy (CVNIE), respectively. Using an empirical equation,K
IC-CVNIE correlation is attempted which could be advantageously utilized for routine quality control of inward material to effect savings in cost and time. Investigations reveal betterK
IC-CVNIE correlation for tests using the precracked CVN specimens. Scanning electron microscopic (SEM) observations reveal good correlation between fractographic features and fracture toughness.
TL;DR: The relative binding powers of three solid propellant binders [Indian Space Research Organization (ISRO) polyol, polypropylene glycol (PPG) and hydroxy-terminated polybutadiene (HTPB)] have been studied by evaluating solvation numbers using the Passynsky equation based on ultrasonic velocity and density data in a common solvent, viz. tetrahydrofuran as discussed by the authors.
TL;DR: In this article, an implementation of the force method is proposed in which the forces and the displacements are simultaneously obtained by the solution of a sparse symmetric indefinite system, where the matrix of coefficients is formed by just the concatenation of the element flexibility and equilibrium matrices.
Abstract: An implementation of the force method is proposed in which the forces and the displacements are simultaneously obtained by the solution of a sparse symmetric indefinite system. The matrix of coefficients is formed by just the concatenation of the element flexibility and equilibrium matrices. No computational procedure is required to generate the compatibility conditions (or the self-stress matrix) and no partitioning of the force vector is made into a basic set and a redundant set, unlike the conventional force method. A slightly modified sparse unsymmetric system can be written in which the stresses and the displacements are the unknowns. This is used as constraints in the formulation of the minimum weight design problem for large structures under static loading conditions. A sparse generalized reduced gradient package is used as the optimizer. A class of test problems involving large truss structures is solved. The results indicate that the present implementation of the force method is better than the displacement method for the optimum design of large structures.