Generalized mean-square amplitudes of vibration in some XY4 type ions (II)

The generalized mean-square amplitudes of vibration and mean amplitudes of vibration have been computed for CrO^3-₄, Mn¹⁸O^-₄, MoSe^2-₄ and WSe^2-₄ ions at three temperatures, T = 0°K, T = 298°K, T = 500°K, employing Cyvin's method. The results have been discussed in the light of atomic weight and electronegativity of the atom in the ionic system.     

Static,anharmonic and phonon properties of ND4I

A detailed investigation of the phonon dispersion and static and anharmonic properties has been carried out for ND₄I using an extended three-body force shell model (ETSM) developed by Singh and Chandra. The ETSM results for phonon dispersion show better agreement with the experimental data than those obtained from the deformation dipole and rigid shell models. Calculated values have also been obtained for some other properties.     

Anharmonic oxygen vibration and mode softening in Tl2Ba2Ca2Cu3O10 superconductor

The softening of the IR active 300 cm⁻¹ phonon mode in Tl-2223 superconductor, aroundT _c has been explained by considering a sixth order polarization potential at the off-center oxygen ion site in the Tl-O plane, and by using a nonlinear lattice dynamical theory. The present theory explains, more or less satisfactorily, the unusual temperature dependence of oxygen ion vibration and frequency shifts at higher temperature. The existence of strong nonlinear electron-phonon interaction atT _c has been emphasized.     

Nonlinear travelling waves in φ6 polarizable model

We present a complete theoretical analysis of the periodic and non-periodic travelling waves in a diatomic chain model, in the continuum limit by incorporating nonlinear sixth order polarization potential (φ⁶) at the anion site. We have formulated a nonlinear lattice dynamical theory in which various energy curves are obtained for different types and magnitudes of the core-shell force constants. For periodic solutions, we have obtained two types of commensurate wave amplitudes which propagate in the opposite direction with respect to each other. For nonperiodic solutions, we have obtained various travelling excitations such as kink, antikink, excitons etc. for different values of the mass ratio and velocity parameter. The dipole moment per unit charge for SrTiO₃ has been calculated and it is found that the nonlinear excitations in this model carry large amount of energy as compared to those obtained from harmonic and anharmonic optical phonons in the φ⁴-polarizable model.     

New characterizations of digraphs represented by intervals

We present new characterizations of interval digraphs, interval graphs, and indifference digraphs, using linear orderings of edges and vertices. © 1996 John Wiley & Sons, Inc.     

Interaction of dimethyl sulphoxide with chloranil by ESR and optical methods

The molecular charge-transfer absorption bands have been observed in solution of dimethyl sulphoxide (DMSO) and tetrachloro-p-benzoquinone (chloranil) in chloroform and cyclohexanone. The stability constant, the thermodynamic parameter of the complex and the extinction co-efficient of CT bands at 350 nm in chloroform and 360 nm in cylohexanone have been estimated on the assumption of the 1:1 complex formation. Detection of ESR signal of the solution of chloranil in pure DMSO (g ≈ 2) indicates the formation of chloranil radical anion, the precursor being the charge-transfer complex, which dissociates partly in high dielectric constant DMSO.     

Phonon structure and dynamics of boron nitride single wall nanotube

We report a detailed study of the phonon properties of hexagonal boron nitride (BN) monolayers as well as nanotubes by using De Launay type of angular force model. The force constants used for calculation of phonon dispersion relations of the nanotube are derived from those for the monolayers of hexagonal by employing force constant method. These force constants have been modified to include the effect of curvature of the tubule. The results are then used to derive the phonon dispersion relations for (10,10) BN nanotubes using ‘zone-folding’ method. Calculated phonon modes are in good agreement with the experimental values obtained so far, for (10,10) armchair BN nanotubes.     

A Novel Implementation Technique of Conical Scan Radar Using A Programmable Phased Array

In radar, planar phased array antenna plays vital role in electronic scanning in the azimuth and elevation direction to the horizon. In most operations using planar phased array both the coordinates of azimuth and elevation, are steered electronically. In this paper a conceptual schematic of a phased array antenna with programmable time delay units has been presented. It is shown that by suitably exploiting the time delay matrix one can have electronic beam rotation around the target axis as required in conical scan. Thus both the elevation and azimuth motors in conical scan system are replaced by electronic scanning. Heuristically, we have selected eight consecutive points for beam rotation in a polygon shape and can also be extended almost circular shape by increasing number of array elements and phase shifter (delays) in the delay matrix. The array requires dual control of phase gradient and individual phase values. The whole array is controlled by micro-controller. This presents exciting possibilities in radar operation.