Showing papers by "Indian Institute of Technology Bombay published in 1973"

The Force Concept in Chemistry

Abstract: The applications, most of which have been developed in the last decade, of the Hellmann-Feynman (H-F) theorem in molecular quantum mechanics are reviewed. In general, the forces (on the nuclei of molecules) calculated with the use of this theorem provide great qualitative insight into the nature of the phenomena investigated; outstanding examples of these are in the concepts of chemical binding and molecular shapes. However, there are serious limitations in quantitative applications of the H-F theorem with approximate wave functions, since the calculated forces are extremely sensitive to small inaccuracies in the wave functions, especially near the nuclei of interest. Nevertheless, in view of the fact that it is difficult to discern general qualitative features in very accurate or ab initio molecular calculations, the H-F theorem is likely to be a highly useful tool for developing much needed qualitative chemical models which will be based on firm quantum mechanical foundations and will also remain open to quantitative extension, at least in principle.

Optimization of System Reliability Using a Parametric Approach

Abstract: This paper presents a new method for the optimization of system reliability with linear constraints, using the parametric approach [1]. The classical nonlinear programming technique is used for the solution. This method, which is analytically complete, sufficiently accurate and computationally simple, gives optimum or near optimum design. The procedure is illustrated with examples, and flow charts for the problems are given.

MHD free convective flow in a vertical channel

Abstract: An analysis of the fully-developed MHD free convective flow between two vertical, electrically conducting plates has been carried out. The effects of the external circuit, heat sources and modified boundary conditions on the temperature at the non-perfect thermally conducting plates have been studied. The nonlinear integro-differential equations, governing the flow, have been solved by perturbation method. Velocity and temperature profiles have been shown on graphs and the numerical values of other quantities are entered in tables. It is observed that the flow is stable at small values ofM, the Hartmann number, whereas at large values ofM, an increase inΦ 1 (the thermal conductance ratio) or λ (line heat source) leads to an instability of the flow. However, instability of the flow may be avoided by selecting the plates of high electrical conductivity.

Analysis of Curved Box Girder Bridges

Abstract: A discrete strip energy method is presented for the analysis of curved box girder bridges of arbitrary cross section and various forms of curved folded plate structures simply supported at the two ends and composed of elements that may, in general, be segments of conical frustra. The method is based on harmonic analysis in the circumferential direction. The total potential energy of the structure is discretized into energy due to extension and bending and energy due to shear and twisting. The two types of circumferential strip elements are obtained by using a modified finite difference discretization in the transverse direction. The use of minimum energy principles yields two types of element matrices which are assembled to form the overall stiffness matrix of the structure following stiffness matrix procedures. Results of two examples obtained by the method are compared with available solutions.

Digital computation of cycloconverter operation

Abstract: The flow chart for the SCR trigger module for use in a three-pulse cycloconverter circuit is discussed. Generalized equations for simulating the cycloconverter operation are derived. A mathematical expression for the digital computation of output voltage harmoniic components is derived in terms of the Fourier transform. The computed results of cycloconverter operation for an R-L load are presented.

Anion exchange studies of indium(III) in malonate and ascorbate solutions separation from mixtures

Abstract: Systematic studies are presented on the anion-exchange behaviour of indium on Dowex 21K in malonic acid and ascorbic acid solutions. Hydrochloric, sulphuric, nitric and perchloric acids, also sodium and ammonium nitrate at different concentrations were tested as eluants in the two systems. Their efficiency was evaluated in terms of elution constants. Methods have been developed for the separation of indium from several elements in malonate as well as ascorbate media with the technique of selective sorption, selective elution or by gradient elution.

Oil Flow Through Journal Bearing

Abstract: Oil feed rate is an important parameter governing the operating characteristics of a journal bearing. In the present paper investigation is carried out to explore the effect of oil groove location and supply pressure on the oil feed rate to the bearing. These results are further used to get variation in Sommerfeld number and attitude angle for different oil groove locations and supply pressures. The results indicate that oil groove location has a great influence on oil feed rate to the bearing. It is also observed that oil supply arrangement does not have a significant influence on Sommerfeld number and attitude angle.

Liquid-Liquid Extraction of Antimony (III) with Mesityl Oxide

Abstract: Mesityl oxide [(CH3)2C[dbnd]CHCOCH3] was used for the liquid-liquid extraction of antimony. It can be quantitatively extracted from 3 M hydrochloric acid within 10 sec of equilibration with 15 ml of mesityl oxide. The metal from the organic phase was stripped with 10 ml of water and was determined photometrically as its iodide complex at 425 mm. The probable composition of the extractable species at 3 M hydrochloric acid was either SbCl3 · 3MeO or [HSbCl4 (MeO)3] where MeO is mesityl oxide. The method is simple, rapid, and selective, as it was possible to separate antimony from a large number of elements which are associated with it in alloys and minerals. The method is applicable for the analysis of antimony in solder. The standard deviation is ± 1%.

Simultaneous extraction and spectrophotometric determination of cobalt(ii) with thiothenoyltrifluoroacetone

Abstract: Thiothenoyltrifluoroacetone (1,1,1-trifluoro 4-(2-thienyl) 4-mer-captoput-en-3-2-one) is used for the simultaneous extraction and spectrophotometric determination ofμg amounts of cobalt(II). 10 ml of 0.001M STTA in carbon tetrachloride quantitatively extracts, at pH 6.5, 20μg of cobalt(II) as red orange colored complex which can be measured photometrically at 490 nm. The system conforms to Beer's law in the concentration range of 0.5–6.0μg/ml of Cobalt(II). Studies on the effect of varying volume and concentration of the reagent, stability of the complex, and the period of equilibration were also reported. It is possible to extract and determine cobalt(II) quantitatively in the presence of large number of cations and anions. The method can be made selective by making use of appropriate masking agents.

Extractive Separation and Direct Colorimetric Determination of Cadmium with Thiothenoyltrifluoroacetone

Abstract: Thiothenoyltrifluoroacetone (STTA) was used for the quantitative extraction of cadmium at tracer level. Cadmium was extracted completely at pH 6.5-7.5 with 0.001 M STTA in carbon tetrachloride as the yellow colored complex which could be measured colorimetrically at 450 nm. The system adhered to Beer's law in the concentration range of 0.9 to 19 μg/ml. The complex was stable for at least 96 hr. Ten milliliters 0.001 M STTA in carbon tetrachloride was adequate for quantitative extraction of cadmium. The optimum period of equilibration was 10 min. It was possible to effect extractive separation and colorimetric determination of cadmium in the presence of 1 : 200 of alkali, alkaline earths, thallium, germanium, and organic complexing acids. Other ions were tolerated in the ratio ≥ 1 : 20. The method was rendered selective by using sequestering agents, such as citric acid, tartaric acid, or alkali cyanide, or by resorting to selective extraction process with either tributylphosphate or acetylacetone.

Incremental Describing Function Analysis of Subharmonic Oscillations in Control Systems with Thyristor Converters

Abstract: Often subharmonic oscillations of firing angle of thyristor converters with large magnitude in negative feedback control systems are a kind of jump phenomena. For their investigation rectifiers may be modeled by an asymmetrical saturation type nonlinearity in series with a linear block whose factors depend upon the number of pulses of the rectifier and the order of subharmonic in question. Application of the incremental describing function technique results in a set of curves, which is useful for the determination of the critical gain of the system and its design. Results of digital computer simulated systems are in good agreement with the predicted values

Effective charges and lattice dynamics of zincblende structure crystals

Abstract: In an earlier paper (referred to as I) effective charges for a number of II-VT and III-V compounds have been obtained from a model of the chemical bond in these crystals. In the present paper, the dynamics of GaAs is studied using a variety of rigid-ion models and some empirical rules are deduced regarding their accuracy. These rules are used to evaluate the zone-boundary phonon frequencies for CdTe, InSb, and AlSb, which have nearly the same effective charges (in the scheme of the present work) as GaAs. Phonon frequencies have also been calculated for ZnS, which is more ionic than the crystals mentioned above. The two and three phonon spectra of AlSb are calculated in order to show a possible way of refining lattice dynamical calculations. In einer fruheren Arbeit (Teil I) wurden effektive Ladungen fur eine Anzahl von II-VI-und III-V-Verbindungen aus einem Modell der chemischen Bindungen dieser Kristalle erhalten. In dieser Arbeit wird die Gitterdynamik von GaAs mit mehreren starren lonen-modellen untersucht und einige empirische Regeln fur ihre Genauigkeit abgeleitet. Diese Regeln werden benutzt, um die Phononenfrequenzen an den Zonengrenzen fur CdTe, InSb und AlSb zu berechnen, die nahezu die gleichen effektiven Ladungen (in dieser Arbeit) wie GaAs haben. Fur ZnS, das starker ionisch ist als die oben erwahnten Kristalle, werden die Phononenfrequenzen ebenfalls berechnet. Das Zwei- und Drei-Phononenspektrum von AlSb wird berechnet, um Moglichkeiten fur verbesserte gitterdynamische Berechnungen zu zeigen.