Showing papers by "Government College published in 1992"

Energy transfer excitation in an N2-laser-pumped coumarin 485-rhodamine B dye mixture through optical gain characteristics

Abstract: The tunability of organic dye lasers has been reviewed by investigating the optical gain characteristics of a coumarin 485-rhodamine B (C 485-Rh B) dye mixture in ethanol subject to N 2 laser excitation. The energy transfer parameters (rate constants of radiative and non-radiative energy transfer processes and the critical transfer radius) have been evaluated with the help of Stern-Volmer plots and the pump power dependence of the gain. The calculated values of radiative and non-radiative energy transfer processes are 0.86 × 10 −11 and 0.45 × 10 −11 L mol −1 s −1 respectively, which shows that the two processes are contributing equally in the present mixture.

Quantitative structure-activity relationship study of some benzodiazepine-receptor ligands having inverse agonist/antagonist and agonist actions.

Abstract: Quantitative structure-activity relationship (QSAR) analyses of three different series of benzodiazepine ligands, pyridodiindoles, and beta-carbolines, having inverse agonist/antagonist and agonist actions have been performed with a view to understanding their likely mode of action at the benzodiazepine-receptor (BzR). From this study, the in vitro radioligand displacement activities of substituted 7,12-dihydropyrido[3,2-b: 5,4-b']diindoles (Figure 1) were found to be significantly correlated with resonance effect of R-substituents, van der Waals volumes at positions-1 and -3, hydrophobic constant at position-2 and field effect at position-4 of X-substituents. For 3-substituted beta-carbolines, a similar analysis has established that R-substituents at position-3 of beta-carbolines (Figure 2) are involved in strong hydrophobic interaction with some hydrophobic pocket on the receptor. For the analogues of 6-(benzyloxy)-4-(methoxymethyl)-beta-carbolines-3-carboxylic acid ethyl ester (Figure 3), however, the combined hydrophobicities of 6- and 4-substituents were shown to be important in determining ligand binding behaviour. The significant correlations so obtained are in agreement with the proposed models (Figures 4 and 5) of pharmacophores of inverse agonist/antagonist and of agonist sites at the BzR.

Thermal instability in Maxwellian and Oldroydian viscoelastic fluids with suspended particles in porous medium

Abstract: The effect of suspended particles on thermal instability is considered separately in Maxwellian and Oldroydian viscoelastic fluids in a porous medium. The principle of exchange of stabilities is found to hold well under a condition which is the same for Maxwellian as well as Oldroydian fluid. For stationary convection, both the Maxwellian and Oldroydian fluids behave like Newtonian fluid and the medium permeability and the suspended particles have destabilizing effects on the system. The sufficient conditions for the non-existence of overstability for both Maxwellian and Oldroydian viscoelastic fluids are also obtained.

Stringy Restrictions on the Backgrounds in the Heterotic Sigma Model

Abstract: We show that for the heterotic string theory in the presence of arbitrary background gauge, gravitational and antisymmetric tensor fields, truncated by a general coordinate dependent compactification a la Scherk-Schwarz, the requirement of 2D conformal invariance is as restrictive as to inhibit supersymmetry breaking with vanishing cosmological constant.

Measurement of intensities of some newly observed diagram lines in the L-emission spectra of 57La to 63Eu

Abstract: A method is described for the estimation of relative intensities of weak diagram lines from the microphotometer records of x-ray emission spectra registered on photographic films. The method is based on first correlating the experimentally determined relative intensities of two intense diagram lines with the theoretically calculated relative intensities. The experimental relative intensities of weak diagram lines are then interpolated to yield the corrected experimental relative intensities. These interpolated experimental relative intensities are found to be in good agreement with the theoretical relative intensities. The method has been applied to some recently reported weak lines in the L-emission spectra of the rare earth 57La to 63Eu.

Goldstone excitation and symmetry-breaking mechanism in superfluid-He4

Abstract: The form of Goldstone excitation in superfluid He4 is envisaged by the formalism of scaling transformation. This is achieved within the framework of symmetry-breaking mechanism which is akin to that of the relativistic quantum field theory.

Identification of the lines in the L emission spectrum of cerium and samarium

Abstract: The occurrence of a line at 2.1556 A in the L emission spectrum of cerium and two lines at 1.6679 and 1.8379 A in the L emission spectrum of samarium, reported many years ago, has remained a puzzle. These have now been identified as EXAFS minima occurring at the L absorption edges of the respective elements.