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.     

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.     

On hydromagnetic turbulent shear flow between moving parallel planes

Hydromagnetic turbulent shear flow of viscous, incompressible, electrically conducting fluid between two infinite uniformly porous moving parallel planes in the presence of axial and transverse magnetic field has been studied by the semi-empirical method. The expressions for the mean distributions for velocity and magnetic field for turbulent shear flow have been obtained for both the cases. As particular cases, the results have been obtained if the planes are fixed. The solutions obtained when the magnetic field is axial have been shown graphically for turbulent and laminar flows.     

Oscillator strengths and polarizabilities of the hot-dense plasma-embedded helium atom

The effect of weakly coupled hot plasma environment on the oscillator strengths of the ultraviolet and visible series and the polarizabilities of helium has been investigated using variational highly correlated wave functions within the non-relativistic framework. The Debye shielding approach that admits a variety of plasma conditions is used to simulate the plasma effects. For each shielding parameter, dipole oscillator strengths are calculated for the 1 ¹S-n¹P (n=2, 3), 2 ¹S-2 ¹P, 2 ³S-n³P (n=2, 3) and 2 ^1,3P-n^1,3D (n=3, 4) transitions. The dipole and quadrupole polarizabilities for the ground He (1s²¹S) state are also reported for each screening parameter. Results obtained are useful in plasma diagnostic purposes besides several other applications.     

Thermoelectric power of (Me4N)2Ag13I15 and (Et4N)2Ag13I15

Thermoelectric power using reversible silver electrodes and electrical conductivity on the compressed pellets of (Me₄N)₂Ag₁₃I₁₅, and (Et₄N)₂Ag₁₃I₁₅ have been measured between room temperature and below 160°C. The results of θ can be expressed by the equations:?θ = 0.115 (10³/T)+0.2905VK^?1 and ?θ = 0.150 (10³/T) + 0.305mV K^?1; and those of conductivity by the equations; σ = 28.7 exp (?0.17eV/kT) ohm^?1cm^?1 and $\text{σ = 216.6 exp (?0.24e}\text{V}\text{kT}\text{)}$ ohm^?1cm^?1; respectively for Me- and Et-electrolytes. The results are discussed and compared with those of previous authors.     

Doubly Excited <Superscript>1,3</Superscript><Emphasis Type="Italic">P</Emphasis><Superscript>e</Superscript> Resonance States of the Positronium Negative Ion with Coulomb and Screened Coulomb Potentials

We have investigated the doubly excited ^1,3 P ^e resonance states of positronium negative ion with Coulomb and screened Coulomb potentials using highly accurate correlated exponential wavefunctions. For Coulomb interaction, the stabilization and the complex-rotation methods are employed to extract resonance parameters (resonance positions and widths). We have obtained two ¹ P ^e resonances and three ³ P ^e resonances below the n = 3 Ps threshold. In addition to Feshbach resonances lying below n = 3 Ps threshold, we have calculated one ³ P ^e shape resonances lying above the Ps (n = 2) threshold. For screened Coulomb (Yukawa) interaction, we employ the stabilization method to extract resonance parameters as functions screening parameter. The resonance energies and widths for ^1,3 P ^e resonance states of Ps⁻ below the n = 3 Ps threshold for different screening parameters ranging from infinity (Coulomb case) to small values are reported, along with the Ps(3S) and Ps(3P) threshold energies. The screened Coulomb results for the ^1,3 P ^e resonance states are reported for the first time in the literature.     

Baryon inhomogeneities due to cosmic string wakes at the quark-hadron transition

Baryon inhomogeneities generated during the quark-hadron transition may alter the abundances of light elements if they persist up to the time of nucleosynthesis. These inhomogeneities survive up to the nucleosynthesis epoch if they are separated by a distance of at least a few metres. In this work we present a model where large sheets of these inhomogeneities separated by a distance of a few km are formed by cosmic string wakes during the quark-hadron transition. The effect of these sheets on nucleosynthesis will also put constraints on the various cosmic string parameters.     

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.     

Non-projectability of polytope skeleta

We investigate necessary conditions for the existence of projections of polytopes that preserve full k-skeleta. More precisely, given the combinatorics of a polytope and the dimension e of the target space, what are obstructions to the existence of a geometric realization of a polytope with the given combinatorial type such that a linear projection to e-space strictly preserves the k-skeleton. Building on the work of Sanyal (2009), we develop a general framework to calculate obstructions to the existence of such realizations using topological combinatorics. Our obstructions take the form of graph colorings and linear integer programs. We focus on polytopes of product type and calculate the obstructions for products of polygons, products of simplices, and wedge products of polytopes. Our results show the limitations of constructions for the deformed products of polygons of Sanyal and Ziegler (2010) and the wedge product surfaces of Rörig and Ziegler (2011) and complement their results.