Showing papers by "Indian Institute of Technology Bombay published in 1977"

Applications of a non-perturbative many-body formalism to general open-shell atomic and molecular problems: calculation of the ground and the lowest π-π* singlet and triplet energies and the first ionization potential of trans-butadiene

Abstract: In this paper we explore the feasibility of widening the scope of the non-perturbative open-shell many-body formalism recently developed by us [1], which utilizes an Ursell type of cluster expansion about certain starting wavefunctions spanning a model space. We show that, by generalizing the definition of the cluster expansion operator, we can incorporate into the model space (a) determinants differing widely in energy and (b) determinants differing in their number of electrons. This flexibility is useful for the calculation of difference energies of interest, like transition energies and ionization potentials of atomic and molecular systems. The generalized scheme has been tested on the 4π-electron problem trans-butadiene for which, by choosing a very general model space, we have calculated the energies of the ground, the lowest π-π* singlet and triplet and the first ionization potential by choosing a single composite cluster expansion operator for all states. Results for some more restricted choice of ...

MHD Oscillatory Flow past a Semi-Infinite Plate

Abstract: Theme L IGHTHILL studied effects of small amplitude oscillations and Lin studied effects of finite amplitude oscillations on the boundary-layer flow. Lighthill's results were experimentally confirmed by Hill and Stenning. They assumed the freestream to consist of a constant mean velocity over which is superimposed a purely time-dependent oscillatory flow. Kestin et al. and Patel studied the effects of oscillatory progressive wave type of freestream on the boundary-layer flow. In the energy equation, the viscous dissipation effects were neglected by Kestin et al. So taking into account viscous dissipative heat, Kestin's problem was solved again by Takhar and Soundalgekar. We now consider the effects of a transverse magnetic field on the flow past a semi-infinite plate, taking into account the progressive wave type of disturbance in the freestream. By assuming the disturbance in the form (/oo(0 =U0(1 + te), a similar problem was solved by Evans. Evans solved it by assuming a series in powers of two parameters s(wx/w0), the Strouhal number, and \(oByx/pU0 = Ha//Re), the magnetic field parameter. We have solved the problem by assuming a series in powers of Vs only and x > 1 • The induced magnetic field is assumed to be negligible (Cowling) which is true when magnetic Reynolds numer is small.

Symmetrically Pulse Width Modulated AC Chopper

Abstract: Output voltage, output current and line current waveforms in a symmetrically pulse width modulated (SPWM) ac chopper are analyzed for harmonic content, displacement factor, distortion factor, power factor and efficiency. The results are compared with those of phase controlled ac chopper circuit to assess the superiority of SPWM ac chopper. A novel SPWM ac chopper with minimum number of active components is presented. The circuit operation and the design considerations are discussed.

Chemical-shifts and effective charges in ternary and complex systems

Abstract: Effective charges, q, in ternary and complex systems are estimated. The semiempirical method of Suchet (1965) is extended to ternary compounds such as manganites and ferrites while the semi-experimental method of Gianturco and Coulson (1968) is applied to complex Co-Zn ferrites and cobalt complexes. An attempt is made to obtain correlation between the estimated values of q and the measured chemical shifts, Delta E. It is found that although the effective charge governs the chemical shift, its magnitude is profoundly affected by the cation distribution in spinels. A comparison of the values of q obtained from the Suchet's method with those estimated from Gianturco and Coulson's method for the same family of compounds shows good agreement.

Generalization of some duality theorems in nonlinear-programming

Abstract: Pseudoconvexity of a function on one set with respect to some other set is defined and duality theorems are proved for nonlinear programming problems by assuming a certain kind of convexity property for a particular linear combination of functions involved in the problem rather than assuming the convexity property for the individual functions as is usually done. This approach generalizes some of the well-known duality theorems and gives some additional strict converse duality theorems which are not comparable with the earlier duality results of this type. Further it is shown that the duality theory for nonlinear fractional programming problems follows as a particular case of the results established here.

A neutron diffraction study of the spinel oxide CuMn2O4

Abstract: The crystallographic properties of the oxidic spinel CuMn2O4 are investigated by neutron diffraction method. The present study indicates that CuMn2O4 is about 25% inverted. The value of the oxygen parameter ‘u’ is found to be 0.2629. Further it is possible to assign the structural formula (CuCuMn) [CuMnMn] O which satisfactorily explains the observed properties of the compound.

Extended X-Ray Absorption Fine Structures and Chemical Shifts for the Heavy Rare-Earth Oxides

Abstract: L3-absorption edges and the associated extended X-ray absorption fine structures (EXAFS) for dysprosium, holmmm, thulium, ytterbium, and lutetium in pure oxide form are investigated using a 600 mm curved crystal spectrograph. A forbidden transition corresponding to an electron transition, 2p3/2 - 4f (unoccupied), is detected for Dy2.,O3, Ho203, and Tm2O3 with open 4f-shell. Chemical shifts are measured and an attempt made to correlate these with the estimated effective charges on the ions indicates a new trend not reported by others. A prominent absorption peak, A (white line), is also recorded for the oxides. The reduced width of these white lines for oxides indicates the narrowing of the 5d band. The metal-oxygen distances determined using EXAFS methods agree with the crystallographie data. Shapes of the EXAFS for oxides resemble with each other while they differ from those recorded for the corresponding metals. Die L3-Absorptionskanten und die verknupften ausgedehnten Rontgenabsorptionsfeinstruk-turen (EXAFS) fur Dysprosium, Holmium, Thulium, Ytterbium and Lutetium in reiner Oxidform werden mit einem gebogenen 600 mm-Kristallspektrographen untersucht. Es wird em ver-botener ubergang entsprechend einem elektronischen Ubergang, 2p3/2 - 4f (unbesetzt), fur Dy2O3, Ho2O3 und Tm203 mit offener 4f-Schale cntdeckt. Chemische Verschiebungen werden gemessen und der Versuch, diese mit berechneten effektiven Ladungen an den lonen zu korrelieren, ergibt einen neuen Trend der bisher noch nicht veroffentlicht wurde. Ein herausragendes Absorp-tionsmaximum A (weise Linie) wird ebenfalls fur die Oxide gefunden. Die reduzierte Breite dieser weisen Linien fur Oxide zeigt die Verschmalerung der 5d-Bande. Die mit den EXAFS-Methoden bcstimmten Metall-Sauerstoff-Abstande stimmen mit kristallographischen Werten uberein. Die Form der EXAFS fur Oxide stimmen untereinander uberein, wahrend sie sich von denen unter-scheiden, die fur die entsprechenden Metalle bestimmt werden.

Flow in 180° Open Channel Rigid Boundary Bends

Abstract: The present experimental investigations were made in a 180° open channel bend to study the maximum development of spiral motion (conveyance-capacity) and bottom, as well as wall shear (erosive capacity), in the subcritical range of Froude numbers likely to be encountered in narrow and wide channels.

Extended X‐ray absorption fine structure (EXAFS) studies of the lanthanides

Abstract: Extended X-ray absorption fine structures (EXAFS) of the L3-edges of dysprosium, holmium, thulium, ytterbium, and lutetium metals are investigated using a focussing X-ray crystal spectrograph of transmission type. The present results are interpreted in the light of the EXAFS theories proposed by Hayasi and by Lytle and the interatomic distances in these metals are determined using Lytle's method. It is found that Moseley's law applies to the white lines in the lanthanides. A comparison of the widths of the white lines with the positron annihilation rates in lanthanides reveals interesting correlations. #Untersuchungen der Rontgenstrahlenabsorptions-Feinstrukturen (EXAFS) der L3-Kanten von Dysprosium-, Holmium-, Thulium-, Ytterbium- und Lutetiummetallen werden mittels eines fokussierenden Rontgen-Transmissions-Kristallspektrographen untersucht. Die Ergebnisse werden mit den von Hayasi und von Lytle vorgeschlagenen Theorien der EXAFS interpretiert und die Atomabstande dieser Metalle mit der Lytleschen Methode bestimmt. Es wird gefunden, das das Moseleysche Gesetz fur die weisen Linien in den Lanthaniden anwendbar ist. Ein Vergleich der Breite der weisen Linien mit der Annihilationsrate der Positronen in den Lanthaniden ergibt interessante Korrelationen.

An ab-initio derivation of the pi-electron hamiltonian by a nonperturbative open-shell formalism

Abstract: A method for generating a pi-electron hamiltonian in an ab-initio manner using the non-perturbative open-shell many-body formalism recently developed by us is presented. The π-hamiltonian thus derived is energy-independent, and is also proved to be spin-independent. A recipe is given with the help of which Goldstone—like matrix-elements ofH π can be extracted up to three body terms. It has been demonstrated that the use of diagrammatics considerably simplifies the algebra and allows one to keep track of the various quantities involved. Up to a given order of approximation, an explicit form ofH π containing up to the three body terms has been given, and some of the important physical effects embedded in the hamiltonian are discussed. A comparative analysis of the various formalisms currently in use forms the concluding section of the paper.

Anion-exchange separation of scandium from yttrium, lanthanum, cerium and other elements in malonic and ascorbic acid media

Abstract: The anion-exchange behaviour of scandium was studied in malonate and ascorbate media on Dowex 2×8 colums (1.4×18 cm). It forms anionic complexes with 8% malonic acid at pH 5.0 and 5% ascorbic acid at pH 6.5. Various eluants such as mineral acids and their corresponding salts were tested eluants and their efficiencies evaluated. Scandium was separated from alkali metals, alkaline earth metals Tl(I), Hg(II) and Fe(II). It was separated from Co, Ni, Pd, Mn, Cd and Zn by selective washing of the column and from other elements by selective elution in both systems. The separation of scandium from Y, La, Ce, Pr, Nd, Sm, Gd and Dy were a remarkable feature of the method.

A misfitting elastic inclusion in an infinite plane containing a crack

Abstract: The problem discussed in this paper is that of a misfitting circular inclusion in an infinite elastic medium which contains a straight crack. The crack is stress free. The stresses develop in the elastic medium because of the misfit. The point force method is used to solve the problem. The problem reduces to finding two sets of complex potential functions: {ϕ(z), ψ(z)}: One for the infinite medium and the other for the misfitting inclusion. The solution has been obtained in closed form. Graphs are drawn for stress intensity at the crack tip and also for normal, shear and hoop stresses at the common interface of medium and misfitting inclusion.

Anion-exchange separation of uranium (VI) from thorium, zirconium, titanium, lanthanides and other elements in malonic and ascorbic acid media

Abstract: The anion-exchange behaviour of uranium (VI) has been studied extensively in various mineral acid media [1], but similar studies with organic acid solutions are lacking. Although the negatively charged complex of uranium in acetic acid was studied [2, 3], very small amounts of uranium could be separated and phosphate interfered. Such studies were further extended to non-aqueous media [4]. The anionic ascorbate complex of uranium and thorium were separated by selective elution with 1 mol dm−3 hydrochloric acid and 3 mol dm−3 sulphuric acid [5–7] respectively. Some attempts were also made to study complexes of uranium in formic and propionic acid [1] and it was separated from copper and thorium in oxalate media [4]. However systematic studies in malonate and to some extent in ascorbate media are lacking. This paper presents such studies.

Jet Impingement on a Curved Surface

Abstract: Theme F LOW near the impingement region of a two-dimensional incompressible jet over a curved surface is analyzed to predict curvature effects. The flow regime in the neighborhood of the stagnation point is divided into inviscid and viscous flow regions in a curvilinear coordinate system. The inviscid flow solution is obtained by solving full Euler's equations. The viscous flow is analyzed by using zerothand first-order boundary -layer equations, the latter accounting for the curvature effects. The numerical solutions are valid in the impingement region extending approximately to half the free jet width on either side of the stagnation point.

Effect of Circuit and Induction Motor Parameters on Current Source Inverter Operation

Abstract: Circuit equations are derived for the current source inverter operation. The effect of commutating capacitor, feed inductance and the induction motor parameters on the inverter operation are discussed. Guide lines for suitable choice of components are given. Nomograms are given to evaluate the component ratings.

Electrical and magnetic properties of 3d-transition metal vanadates

Abstract: The electrical and magnetic properties of vanadates of the general formula (MO)n.V2O5, where M=Mn, Co, Ni, Cu and Zn, andn=1, 2 and 3, are discussed. Conduction in these materials occurs due to small deviations from the stoichiometric composition in the form of anion-(n-type) or cation—(p-type) vacancies. The mechanism of electrical transport is of a thermally activated hopping of charge carriers on equivalent cation lattice sites. It has been found that the meta vanadates (n=1) are alln-type while the pyro—(n=2) and ortho—(n=3) compounds of Mn, Co and Ni arep-type; but Cu and Zn analogues remainn-type only.

CNDO/2 calculations on the structure and properties of chlorine difluoride

Abstract: According to the open-shell CNDO/2 calculations on ClF2, performed by using the computer programme developed by Pople, Beveridge and Dobosh, the molecule is linear and stable, with equilibrium bond length 1.507A and binding energy −173.7 kcal/mole. The molecule has a tendency to dimerise and to disproportionate into ClF3 and ClF. The netd-orbital population in the monomer is 0.88. Bonding characteristics and other molecular properties are also discussed.

A simple frequency multiplier

Abstract: The paper describes a scheme of a frequency multiplier that can be used for multiplying the frequency by n times. By connecting such m circuits in sequence it is possible to achieve frequency multiplication of mn.