Showing papers by "Indian Institute of Technology Bombay published in 1983"
TL;DR: In this article, a 25 mm I.D. copper tube, tightly fitted with helical-wire-coil inserts of varying pitch (p), helix angle (x), and wire diameter (e), was used for heat transfer.
133 citations
TL;DR: In this article, the Hartree-Fock relation between the kinetic and the exchange energy density was used for the direct calculation of electron density ρ (r) in many-electron systems.
Abstract: A new density-functional equation is suggested for the direct calculation of electron density ρ (r) in many-electron systems. This employs a kinetic energy functional T 2 + f(r)T 0 , where T 2 is the original Weizsacker correction, T 0 is the Thomas-Fermi term, and f(r) is a correction factor that depends on both r and the number of electrons N. Using the Hartree-Fock relation between the kinetic and the exchange energy density, and a nonlocal approximation to the latter, the kinetic energy-density functional is written (in a.u.) t[ρ]=1/4∇ 2 ρ+1/8(∇ρ. ∇ρ)/ρ+C k f(r)ρ 5/3 , where C k =2/10(3π 2 ) 2/3 . Incorporating the above expression in the total energy density functional and minimizing the latter subject to N representability conditions for ρ(r) result in an Euler-Lagrange nonlinear second-order differential equation [-1/2∇ 2 + ν nuc (r) + ν cou (r) + ν XC (r) +5/3C k g(r)ρ 2/3 ] Φ(r)= μΦ(r) where μ is the chemical potential, we have ρ(r) = |(r)| 2 , and g(r) is related to f(r). Numerical solutions of the above equation for Ne, Ar, Kr, and Xe, by modeling f(r) and g(r) as simple sums over Gaussians, show excellent agreement with the corresponding Hartree-Fock ground-state densities and energies, indicating that this is likely to be a promising method for calculating fairly accurate electron densities in atoms and molecules.
94 citations
TL;DR: In this article, the effect of soaking in salt water and distilled water at various temperatures on the mechanical properties of glass and carbon fiber reinforced plastics has been studied, and the results indicate that the degradation in compressive, interlaminar and flexural strengths is much more severe in salt than in distilled water.
32 citations
TL;DR: In this paper, it was observed that there is an initial decrease in resistivity up to a temperature of 700 degrees C which is followed by an increase in resistivities beyond 700 degreesC.
Abstract: Transparent conducting tin oxide films were prepared by a chemical vapour deposition technique. The films were deposited at substrate temperatures of 400, 450 and 500 degrees C. The films were annealed (above the deposition temperatures) up to 1000 degrees C in various gas atmospheres (argon, oxygen, nitrogen and air). It is observed that there is an initial decrease in resistivity up to a temperature of 700 degrees C which is followed by an increase in resistivity beyond 700 degrees C. X-ray and electron diffraction studies have been carried out on the annealed films and the behaviour of this decrease and increase in resistivity has been explained.
24 citations
23 May 1983
22 citations
TL;DR: In this paper, the authors investigated the origin of Verwey transition in magnetite and showed that the transport properties in the high temperature phase of magnetite can be accounted by a phonon-induced correlated electron transfer mechanism.
Abstract: The origin of Verwey transition in magnetite is investigated. It is shown that the transport properties in the high temperature phase of magnetite can be accounted by a phonon-induced correlated electron transfer mechanism. Assuming that the condensation of this phonon mode leads to Verwey transition, the isotope and pressure effects have been explained. The electron energy band diagram consistent with the electrical transport behaviour in the low temperature phase has been constructed.
19 citations
TL;DR: Using a very simple trial function and unperturbed electron densities calculated by a new procedure, the frequency-dependent dipole polarizability α (ω) of Ne, Ar, Kr and Xe has been calculated in the range 0 ≤ ω ≤ 045 au, by a Karplus-Kolker-type variation-perturbation method.
Abstract: Using a very simple trial function and unperturbed electron densities calculated by a new procedure, the frequency-dependent dipole polarizability α (ω) of Ne, Ar, Kr and Xe has been calculated in the range 0 ≤ ω ≤ 045 au, by a Karplus-Kolker-type variation-perturbation method Results progressively worsen for larger systems so that, for Xe, α(0) is only 75% of the experimental value Probable reasons for this are discussed
18 citations
TL;DR: In this paper, the authors proposed a process for the production of iron and steel powders from scrap. But the process is not suitable for high dimensional materials such as steel and aluminium.
17 citations
TL;DR: The results of fracture toughness of the glass/carbon fiber reinforced epoxy hybrid composites, as expressed by critical stress intensity factor and critical strain energy release rate respectively, in the crack open ing mode are presented in this article.
Abstract: The results of fracture toughness of the glass/carbon fibre reinforced epoxy hybrid composites, as expressed by KIC and GIC—the critical stress intensity factor and the critical strain energy release rate respectively, in the crack open ing mode—are presented in the following paper. The tests have been conducted in the 3-point bending configuration for the specimens having a total reinforce ment content of about 55%. The K IC has been evaluated from the GIC and also from the standard expressions normally used for isotropic materials. Similarly, the GIC and KIC have been evaluated by using both Pmax, the maximum load, and PQ, the point of intersection on the load displacement curve with a line having 5% less slope than the slope of the curve at the origin. The trend of the results obtained by these two methods is considerably different particularly with increasing glass content in the hybrids. The values of GIC and KIC obtain ed from PQ exhibit a distinct positive hybrid effect. The hybrids having both the...
16 citations
TL;DR: In this article, frequency-dependent 2L-pole polarizabilities of He, Ne, Ar, Kr and Xe in their ground states have been calculated by numerically solving for each frequency only two, instead of 2N (N = number of electrons), perturbative equations.
Abstract: Using a new density-functional equation proposed by us recently, frequency-dependent 2L-pole (L = 1, 2, 3, 4) polarizabilities of He, Ne, Ar, Kr and Xe in their ground states have been calculated by numerically solving for each frequency only two, instead of 2N (N = number of electrons), perturbative equations. Results obtained with our calculated densities are satisfactory for Kr and Xe, but are considerably overestimated for He, Ne and Ar due to the adoption of local density approximation for the exchange-correlation potential and to the errors in the unperturbed densities for r<1 a.u. However, 2L-pole polarizabilities and dipole shielding factors for all the five atoms, calculated by using Hartree-Fock densities as unperturbed functions, show uniformly good agreement with available experimental and other calculated values. Therefore, for these quantities the present rather simple approach has considerable promise, further justifying the search for a density-based alternative quantum mechanics of many-electron systems.
15 citations
TL;DR: In this article, an attempt is made to develop an equation for pumping speed as a function of free air displacement conditions, vapour pressure of the sealant liquid, pressure and index of expansion process in the system to be evacuated and index z representing the set of operating conditions.
TL;DR: In this article, the combined effects of the Hall and the ionslip currents in a magnetohydrodynamic boundary layer flow were studied, and it was found that the skin-friction coefficient decreases and the displacement thickness increases due to these currents.
Abstract: The combined effects of the Hall and the ionslip currents in a magnetohydrodynamic (MHD) boundary layer flow are studied. It is found that the skin-friction coefficient decreases and the displacement thickness increases due to these currents.
TL;DR: In this paper, the empirical phase shifts are calculated from the theoretical X-ray absorption fine structure phase functions in a large number of systems with different atom-pairs in varying surroundings.
Abstract: The empirical phase shifts are calculated from the theoretical X-ray absorption fine structure phase functions in a large number of systems with different atom-pairs in varying surroundings. Measured extended X-ray absorption fine structure (EXAFS) data are used to estimate the linearly dependent term on k in the phase shift and to compare it with theoretical values. Attempts are made to explain the behaviour of the phase shift of a given atom-pair in different chemical surroundings and for different atom-pairs in a given isoelectronic series of elements.
Es werden die empirischen Phasenverschiebungen einer grosen Anzahl von Systemen mit unterschiedlichen Atompaaren mit veranderlichen Umgebungen aus den theoretischen Rontgen-absorptionsfeinstruktur-Phasenfunktionen berechnet. Die gemessenen Daten der ausgedehnten Rontgenabsorptionsfeinstruktur (EXAFS) werden benutzt, um den linear von k abhangigen Term der Phasenverschiebung abzuschatzen und ihn mit theoretischen Werten zu vergleichen. Es wird versucht, das Verhalten der Phasenverschiebung eines gegebenen Atompaares bei verschiedenen chemischen Umgebungen und fur unterschiedliche Atompaare in einer gegebenen isoelektronischen Serie von Elementen zu erklaren.
TL;DR: In this article, self consistent calculations for the dynamic image potential are carried out, taking the finite acceleration of the incoming charge into account, and it is shown that the effect of the inclusion of acceleration is rather small, and the simpler self consistent approach neglecting the acceleration and using a local speed approximation seems to be adequate.
TL;DR: In this article, the k-absorption edge shifts of copper in aqueous solutions as well as in polycrystalline form were measured using the x-ray absorption spectroscopic technique.
Abstract: K-absorption edge-shifts of copper in CuCl22H2O CuSo45H2O, Cu(NO3)23H2O, Cu(en)3Cl2, Cu(en)3SO4 and Cu(en)3(NO3)2 in aqueous solutions as well as in polycrystalline form were measured using the x-ray absorption spectroscopic technique. Effective charge on copper ions are estimated using the method of Gianturco and Coulson. The results of the present study reveal interesting results regarding the nature of chemical bonding. An attempt is made to interpret the results in the light of the available data on these samples.
TL;DR: In this article, an analysis was made to evaluate the values of the activation volume for the forward flow of dislocations in aluminium, copper and nickel from stress relaxation experiments using the equation proposed by Feltham.
TL;DR: In this paper, an attempt has been made to reduce the series electrode resistance by using aluminum as an underlayer, and the results of these investigations are reported together with other electrical properties of these capacitors.
TL;DR: A digital adaptive filter based on a modified Widrow-Hoff algorithm that uses LSI components as main elements converges faster than other realizations reported hitherto because its weight vector is updated at every sampling instant.
Abstract: The design and operation of a digital adaptive filter based on a modified Widrow-Hoff algorithm is described. It uses LSI components as main elements. This filter realization converges faster than other realizations reported hitherto because its weight vector is updated at every sampling instant.
01 Jan 1983
TL;DR: This paper concludes by giving some hints for the realization of integrated, computer supported design systems with uniform and user adapted application interfaces.
Abstract: The design of automatic control systems requires the correct and complete execution of several design steps or phases, in order to achieve a reliable and economic system performance corresponding to the system requirements. These design phases are introduced irrespective of possible computer support. The evaluation of some existing computerized design tools for automatic control systems shows their incompletenes regarding all the design phases or the formulation of real-time conditions. Therefore this paper concludes by giving some hints for the realization of integrated, computer supported design systems with uniform and user adapted application interfaces.
TL;DR: In this paper, self-similar unsteady flows with zero temperature gradient behind strong spherical shocks propagating in non-uniform perfect gas at rest are investigated, where the total energy of the flow is assumed to be varying with the shock radius obeying a power law.
Abstract: Self-similar unsteady flows with zero temperature gradient behind strong spherical shocks propagating in non-uniform perfect gas at rest are investigated. The total energy of the flow is assumed to be varying with the shock radius obeying a power law. Approximate solutions in a closed analytical form are obtained using the integral method. Also these solutions are shown to be useful to calculate easily and quickly the shock temperature, X-ray surface brightness and luminosity which are important in astrophysical problems. It is found that these approximate solutions are in close agreement with numerical solutions.
TL;DR: In this paper, two operational quasistatistical models have been developed for doing atmospheric corrections to brightness temperature data, one applicable under cloud-free conditions and the other under all weather conditions.
TL;DR: Error bounds for the iterative computation of the eigenvectors in the Rayleigh-Schrodinger series were given in this paper, which removed the discrepancy in the theoretical behaviour and numerical results, noted by Redont, under the assumption of collectively compact convergence.
Abstract: Error bounds are given for the iterative computation of the eigenvectors in the Rayleigh-Schrodinger series. These bounds remove the discrepancy in the theoretical behaviour and numerical results, noted by Redont, under the assumption of collectively compact convergence. As a particular case, it follows that the eigenvector in the iterative Galerkin method proposed by Sloan improves upon the eigenvector in the Galerkin method. This is illustrated by numerical experiments.
TL;DR: Magnetic and Mossbauer studies are carried out on compounds Mx, Ln1−x, CoO3 where M is Ba or Sr and Ln is La, Nd or Dy as mentioned in this paper.
Abstract: Magnetic and Mossbauer studies are carried out on compounds Mx, Ln1−x, CoO3 where M is Ba or Sr and Ln is La, Nd or Dy. All compositions with x > 0.2 with the exception of the dysprosium compounds are ferromagnetic at low temperatures. From hysteresis and initial susceptibility studies, it is concluded that they contain a number of single domain clusters in a paramagnetic matrix. Mossbauer spectra of Ba0.3Nd0.7CoO3 and Ba0.5Dy0.5CoO3 show two resonance lines and that of Sr0.5La0.5CoO3 shows a single line spectrum at all temperatures, and no hyperfine spectra are shown even far below TC. The results are interpreted in terms of short-range magnetic ordering in these systems.
An MxLn1−x, CoO3,-Verbindungen, wobei M = Ba oder Sr und Ln = La, Nd oder Dy bedeuten, werden magnetische und Mosbaueruntersuchungen durchgefuhrt. Alle Zusammensetzungen mit × > 0,2 mit Ausnahme der Dysprosiumverbindungen sind ferromagnetisch bei tiefen Tempera-turen. Aus den Untersuchungen der Hysteresis und der Anfangssuszeptibilitat wird geschlossen, dar sie eine Anzahl von Ein-Domanenklustern in einer paramagnetischen Matrix enthalten. Die Mosbauerspektren von Ba0,3Nd0,7CoO3 und Ba0,5Dy0,5O3, zeigen zwei Resonanzlinien und die von Sr0,5La0,5CoO3 bei allen Temperaturen ein Ein-Linienspektrum und bis weit unterhalb Tc werden keine Hyperfeinspektren beobachtet. Die Ergebnisse werden rnit magnetischer Nahordnung in diesen Systemen interpretiert.
TL;DR: In this paper, the authors extracted zirconium from the organic phase with 2 M hydrochloric acid and was determined spectrophotometrically at 665 nm as its complex with arsenazo III.
Abstract: Zirconium was quantitatively extracted with 8 × 10−2 M of Amberlite LA-1 or LA-2 xylene from 0.001 M citric acid at pH 3.5 and it was stripped from the organic phase with 2 M hydrochloric acid and was determined spectrophotometrically at 665 nm as its complex with arsenazo III. Zirconium was separated from binary as well as tertiary mixtures by exploiting the difference in the distribution coefficient or by selective extraction or selective stripping. The method was applied for the analysis of zircon. Zirconium was extracted as its anionic complex with various mineral acids by liquid anion exchanger. The chlorocomplex of zirconium was extracted from 6–10 M hydrochloric acid with trioctylamine1–5, triisooctylamine6 or Aliquat 33657. The sulphotocomplex of zirconium was extracted with Aliquat 33658, Primine JMT9, Alamine 33610. The nitratocomplex was less extensively utilised for the extractive separation of zirconium11, 12. Zirconium was extracted quantitatively from oxalate13, 14 and malonate med...
TL;DR: In this article, the single $f$-state impurity problem involved in a local-intermediate-valence model has been solved by using time-dependent multiple-scattering theory.
Abstract: The single $f$-state impurity problem involved in a local-intermediate-valence model has been solved by using time-dependent multiple-scattering theory. The density operator of the impurity state has been obtained in terms of $S$-matrix elements. It has been found that the present theory leads to a new type of hybridization which remains finite even when the crystal has inversion symmetry. General features of the method and its importance from an experimental viewpoint have been discussed.
TL;DR: In this article, the authors dealt with stresses around quasi-rectangular holes with minimum stress concentration in large orthotropic plates and presented numerical results in terms of quasirectangular hole shapes with minimal stress concentration and stress distribution around these holes.
Abstract: This paper deals with stresses around quasi-rectangular holes with minimum stress concentration in large orthotropic plates. The method given by Lekhnitskii is used. Numerical results are presented in terms of quasi-rectangular hole shapes with minimum stress concentration and stress distribution around these holes. Unidirec tional carbon/epoxy orthotropic composite materials are considered for a range of hole shapes under uniaxial and biaxial loading conditions.