B. G. Mulimani

Simple setup to measure electrical properties of polymeric films

A simple method to measure electrical conductivity of conducting organic films has been described. A setup, based on four-probe technique, is specifically designed and fabricated for nondestructive electrical conductivity measurements of freestanding thin films. The current-voltage and temperature dependent characteristics of thin films of polyethylenedioxythiophene and polypyrrole and thick wafers of germanium have been used to test the setup. The results obtained are highly reproducible and are in good agreement with the reported values in the literature, employing different techniques.

Electrical characterization of a phenylacetylene-modified silicon surface via mercury probe

The influence of phenylacetylene molecules on a silicon (100) surface has been investigated by formation of metal–molecule–semiconductor junctions with soft mercury contacts. Molecules are bonded covalently to the semiconductor surface via Si–C bonds by thermochemical reaction. The chemical bonding of these molecules is confirmed by XPS measurements. Current–voltage and capacitance–voltage curves were recorded under dark and light on these junctions to understand the role of the organic molecules. Junctions with phenylacetylene molecules are more ideal, with an extra density of surface states which are responsible for quenching photoconductivity. The presence of surface states is reflected as well-defined peaks in low frequency photocapacitance curves.

Fluorescence Quenching of UVITEX‐OB by Aniline in Alcohols and Alkanes

Abstract Fluorescence quenching of UVITEX‐OB [2,5‐thiophenediylbis(5‐tert‐butyl‐1,3‐benzoxazole)] by aniline in different polar and nonpolar solvents was examined at room temperature by steady‐state fluorescence measurements. Positive deviations from the nonlinear Stern–Volmer plots were observed in most of the solvents indicating the extent of quenching to be large. The quencher concentration dependence data were analyzed using ground‐state complex and sphere of action static quenching models in order to interpret the results. The magnitudes of the quenching rate parameters suggest that a sphere of action static quenching model is expected to describe the data most accurately. Also, the results are suggestive of both static and dynamic quenching processes being responsible for the observed positive deviation in the Stern–Volmer plot. Experimental results are described by an equation derived using the finite sink approximation model, which allows the evaluation of diffusion‐limited interaction and the estimation of encounter distance and mutual diffusion coefficient independently.

ENERGY TRANSFER MECHANISMS IN LASER DYE MIXTURES

ABSTRACT Measurements of fluorescence intensities in optically thick (lasing) and thin (non-lasing) solutions and fluorescence lifetimes of donor in binary mixtures of laser dyes have been made. Various energy transfer parameters such as energy transfer rate parameters, critical transfer radii and mean diffusion lengths for four pairs of dyes have been determined. Fluorescence intensities measured for optically thick solutions were corrected to account for radiative transfer and direct absorption of excitation by the acceptor. Energy transfer rate parameters obtained from intensity as well as lifetime measurements strongly support the dominance of energy transfer via resonance mechanism.

UV laser radiation alters the embryonic protein profile of adrenal-kidney-gonadal complex and gonadal differentiation in the lizard, Calotes Versicolor

Abstract Purpose: To examine the impact of ultraviolet (UV) laser radiation on the embryos of Calotes versicolor in terms of its effects on the protein profile of the adrenal-kidney-gonadal complex (AKG), sex determination and differentiation, embryonic development and hatching synchrony. Materials and methods: The eggs of C. versicolor, during thermo-sensitive period (TSP), were exposed to third harmonic laser pulses at 355 nm from a Q-switched Nd:YAG laser for 180 sec. Subsequent to the exposure they were incubated at the male-producing temperature (MPT) of 25.5 ± 0.5°C. The AKG of hatchlings was subjected to protein analysis by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and to histology. Results: The UV laser radiation altered the expression of the protein banding pattern in the AKG complex of hatchlings and it also affected the gonadal sex differentiation. SDS-PAGE of AKG of one-day-old hatchlings revealed a total of nine protein bands in the control group whereas UV laser irradiated hatchlings expressed a total of seven protein bands only one of which had the same Rf as a control band. The UV laser treated hatchlings have an ovotestes kind of gonad exhibiting a tendency towards femaleness instead of the typical testes. Conclusions: It is inferred that 355 nm UV laser radiation during TSP induces changes in the expression of proteins as well as their secretions. UV laser radiation had an impact on the gonadal differentiation pathway but no morphological anomalies were noticed.