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Showing papers by "Vikram Sarabhai Space Centre published in 1976"


Journal ArticleDOI
TL;DR: In this article, the locations of the five equilibrium points were investigated by taking into account the effect of oblateness of the more massive primary for some systems of astronomical interest, and the periodic solutions of the linearized equations of motion around the five equilibria were analyzed.
Abstract: This paper deals with the numerical investigations of the locations of the five equilibrium points by taking into consideration the effect of oblateness of the more massive primary for some systems of astronomical interest. This note is further concerned with the periodic solutions of the linearized equations of motion around the five equilibrium points. Interesting differences in the trends of the angular frequencies of these motions have been noticed.

137 citations


Journal ArticleDOI
TL;DR: In this paper, a finite element formulation for large amplitude free oscillations of beams and orthotropic circular plates is presented, which does not need the knowledge of longitudinal/inplane forces developed due to large displacements and thus avoids the use of corresponding geometric stiffness matrices.

129 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of longitudinal or inplane deformation and inertia on the flexural frequency-amplitude relationship was investigated for the case of thin and circular plates.

95 citations


Journal ArticleDOI
TL;DR: In this paper, large amplitude asymmetric vibrations of shells of revolution are analyzed by using a finite element method and Sanders' non-linear strain displacement relations are used to derive the element stiffness matrix.

74 citations



Journal ArticleDOI
TL;DR: In this article, the large amplitude flexural vibrations of rectangular plates are studied using a direct finite element formulation, which is based on an appropriate linearisation of strain displacement relations and uses an iterative method of solution.

52 citations


Journal ArticleDOI
TL;DR: It is shown that any given problem can be formulated within the framework of linear programming and that there exists a lower limit CLB to the number of bits.
Abstract: This paper suggests a new method for minimizing the width or bit dimension of control store words in microprogrammed digital computers. It is shown that any given problem can be formulated within the framework of linear programming and that there exists a lower limit CLB to the number of bits. The optimal grouping of subcommands which gives this minimal width is also readily obtainable.

38 citations


Journal ArticleDOI
TL;DR: In this paper, high precision finite elements for both thin plate and stiffener are developed to analyse the stability of thin plates subjected to arbitrary membrane loading with arbitrarily oriented stiffeners, and application of these elements to some complex stability problems show high accuracy even with a relatively coarse finite element mesh.

29 citations


Journal ArticleDOI
TL;DR: In this article, a Galerkin finite element method is used to solve the governing differential equation with variable coefficients, and the effect of the stiffness of the spring hinge on the critical load is also studied.

28 citations


Journal ArticleDOI
TL;DR: In this paper, a finite difference solution for the transient non-linear heat conduction with phase change in a finite slab is proposed, where a two-time level implicit method is used while Taylor's forward projection method is employed for taking into account the nonlinearities.
Abstract: A finite difference solution for the transient non-linear heat conduction with phase change in a finite slab is proposed. A two-time level implicit method is used while Taylor's forward projection method is employed for taking into account the non-linearities. The stability due to the boundary conditions at the moving front is verified. The numerical solution is compared with the analytical solutions and found to be in close agreement.

24 citations


Journal ArticleDOI
03 Jun 1976-Nature
TL;DR: In this paper, the signal strength and Doppler frequency spectra of v.h.f. backscatter radar echoes from the equatorial electrojet are recorded at Thumba near Trivandrum (dip ∼ 1 °S).
Abstract: THE signal strength and Doppler frequency spectra of v.h.f. backscatter radar echoes from the equatorial electrojet are being recorded at Thumba near Trivandrum (dip ∼ 1 °S). The v.h.f. radar operates on 54.95 MHz, with identical arrays of Yagi antennae for transmission and reception; the beam axis is orientated either vertically or obliquely at 30° to the vertical. Analysis of the radar backscatter signals and the magnetograms at Thumba has revealed that quasi-periodic fluctuations of the electrojet on time scales of a few tens of minutes are very frequent. We report here some typical experimental results on this phenomenon.


Journal ArticleDOI
TL;DR: Sodium tetraphenylborate [NaB(C 6 H 5 ) 4 ] undergoes a two-stage decomposition on heating in air as discussed by the authors, the DTG peak temperatures are at about 320 and 500°C, the corresponding DTA peaks are at 330 and 520°C.

Journal ArticleDOI
01 Jul 1976-Nature
TL;DR: In this paper, the frequency variation of the scintillation index has been investigated at the Trivandrum station close to the magnetic equator, and the amplitude and phase scintillations of the radio beacon transmissions on 40, 140 and 360 MHz as well as the amplitude scintILLations of 860 MHz television downlink from the geostationary satellite ATS-6 have been recorded since August 1975.
Abstract: THE fluctuations in the signal strength of v.h.f. and u.h.f. transmissions from satellites received at ground level contain valuable information about ionospheric irregularities. These fluctuations, usually called scintillations, depend on the frequency of transmission, characteristics of the irregularities and the angle of incidence. At equatorial latitudes, there have as yet been few such observations, and there are reasons to expect the scintillation characteristics at equatorial latitudes to be quite different from those at higher latitudes because the ionospheric irregularities (mainly spread F irregularities) responsible for scintillations differ widely in their characteristics with latitude. It is also well recognised that the equatorial region is a strong scintillation zone. At Trivandrum (dip 0°57′S, geographic longitude 76°57′E), a station close to the magnetic equator, amplitude and phase scintillations of the radio beacon transmissions on 40, 140 and 360 MHz as well as the amplitude scintillations of the 860–MHz television downlink from the geostationary satellite ATS–6 have been recorded since August 1975. Here we present preliminary results on the frequency variation of the scintillation index.

Journal ArticleDOI
TL;DR: In this article, a cubic spline approximation was used to produce finite difference representations of the homogeneous heat equation in one spatial variable, and the usual explicit and implicit formulae are particular cases of the formulations given here.

Journal ArticleDOI
02 Sep 1976-Nature
TL;DR: In this paper, the effect of magnetic activity on equatorial spread F is reported, and the authors conclude that the initial storm phase does not have any inhibiting effect on spread F occurrence and that spread F occurs in general during the main phase of the magnetic storms.
Abstract: STATISTICAL studies based on a published data of f0F2 have revealed that equatorial spread F depends inversely on magnetic activity during the sunspot maximum period but tends to disappear or even become positive in some seasons during the sunspot minimum period1–3. Somayajulu et al.4, using a different technique, considered the occurrence of spread F during different phases of magnetic storms, and they concluded that the initial storm phase does not have any inhibiting effect on spread F occurrence and that spread F occurs in general during the main phase of the magnetic storms. They observed that, during the recovery phase when the field value is quite different from the normal value, there is no spread F but it is present when the magnetic field value is close to its normal value. To investigate this discrepancy with the earlier results further, the spread F behaviour has been studied4 in relation to Kp indices, and for the Trivandrum data of 1970, and though the overall correlation between spread F and magnetic activity is negative, occurrence of spread F was found to decrease initially with increasing ΣKP and then to start increasing at higher ΣKP values. The effect of magnetic activity on equatorial spread F is reported here.

Journal ArticleDOI
TL;DR: In this paper, stiffened cylindrical panels and waffle plates are designed with constraints on static instabilities, natural frequencies and initially stressed vibration frequencies, and the erosion of structural safety when instability and free vibrations are assumed to be independent of each other.

Book ChapterDOI
TL;DR: In this paper, it was deduced that a small change in the Coriolis force from unity results in a perturbation of the critical mass by a factor of -8∛/81√69.
Abstract: Based upon the authors’ result (Astron. Astrophys. 43, 331–333, 1975) that oblateness of the more massive primary decreases the value of the critical mass, this note is concerned primarily with a few observations on Szebehely’s result (Astron. J. 72, 7–9, 1967) that the Coriolis force is a stabilizing force. It has been deduced that a small change ɛ in the Coriolis force from unity results in a perturbation of the critical mass by a factor of -8ɛ/81√69.

Journal ArticleDOI
TL;DR: In this article, the expressions for stresses are derived for single stepped lap joints and for smoothly tapered joints, the approximate solution technique is suggested, and the adherends are assumed to be orthotropic.

Journal ArticleDOI
TL;DR: In this paper, a detailed analysis of the least square finite element solution of nonlinear boundary value problems is presented with reference to a particular example of non-linear coupled differential equations governing the flow of an incompressible viscous fluid in the vicinity of a forward stagnation point at a blunt body.

Journal ArticleDOI
TL;DR: In this paper, the effect of acoustic field on the thermal conductivity of composite propellants based on poly-butadiene and polyurethane binders was investigated and it was shown that the thermal properties of composite materials increase when they are subjected to an acoustic field.
Abstract: A study is conducted to determine the effect of acoustic field on the thermal conductivity of composite propellants based on poly- butadiene and polyurethane binders. The thermal conductivity of the propellant is determined by a specially designed equipment. The thermal conductivity measurements are made in steady state conditions and in an acoustic field of constant amplitude at various frequencies ranging from 1 kHz to 6 kHz and at different temperatures ranging from 30°C to 50°C. The results indicate that the thermal conductivities of the composite propellants increase when they are subjected to an acoustic field. The data obtained are presented in the paper. Since the burning behaviour of solid propellants is influenced also by its thermal conductivity, the present work may be of direct relevance in improving upon some of the existing burning rate and combustion models.


Journal ArticleDOI
TL;DR: Generalized quadrature is used for the numerical solution of two Fredholm integral equations which occur in electrostatics and aerodynamics as discussed by the authors, and it is shown that generalized quadratures can be used to solve these integral equations.
Abstract: Generalized quadrature is used for the numerical solution of two Fredholm integral equations which occur in electrostatics and aerodynamics.

Journal ArticleDOI
TL;DR: In this paper, two graphical methods for determining the action of a system of polarizers and retarders are presented, which are simple and direct and do not involve the conventional Poincare sphere representation or quarternions.
Abstract: Two new graphical methods for determining the action of a system of polarizers and retarders are presented. The derivation and construction of these graphical methods are simple and direct and do not involve the conventional Poincare sphere representation or quarternions.


Journal ArticleDOI
TL;DR: In this paper, the salient features of a stabilized crystal oscillator, which makes use of the phase lock techniques, are discussed, and a phase lock-based phase lock technique is used.
Abstract: This paper discusses the salient features of a stabilized crystal oscillator, which makes use of the phase lock techniques Experimental results are given


Journal ArticleDOI
TL;DR: In this article, the health hazards caused by radar irradiation on operating personnel are discussed and the instrumentation to monitor the field strength and different methods of protection are also discussed in this paper.
Abstract: This paper discusses the health hazards caused by radar irradiation on operating personnel. The instrumentation to monitor the field strength and different methods of protection are also discussed in this paper.