Essay on gravitation: Present-time variation of Newton's gravitational constant in superstring theories

Superstring theories provide an appropriate framework for studying the time variation of fundamental coupling constants. The present time variation of coupling constants in Superstring theories with currently favorable internal backgrounds critically depends on the shape of the potential for the size of internal space. If the potential is almost flat, as in perturbation theory to all orders, the present value of ¦/G¦ for Newton's gravitational constant is calculable and estimated to be 1×10^–11±1yr^–1, which is just at the edge of the present observational bound for/G. If the potential has a minimum with finite curvature due to unknown nonperturbative effects,/G will become unobservably small. The improvement of the measurement of/G of 1 or 2 orders of magnitude would discriminate between the two situations. Problems with the time variation of other coupling constants are also discussed.This essay received the fourth award from the Gravity Research Foundation for the year 1987-Ed.     

Bioaccumulation and voltammetry of gold at flower-biomass modified electrodes

The bioaccumulation of gold at antheral cells from flower Datura innoxia is investigated by incorporating these plant cells into a carbon paste matrix. The resulting plant-modified electrode offers a preferential uptake of gold from dilute solutions. The voltammetric behavior of the surface-bound gold is examined under different preconcentration conditions. Scanning electron microscopy offers useful insights into the gold collection process. Convenient measurements of micromolar gold concentrations are possible, with effective self cleaning allowing the use of a single electrode in multiple determinations (R.S.D. of 4.8% for 50 repetitions). The sensitivity and selectivity enhancements associated with the preferential bioaccumulation process, and the convenient surface regeneration, offer the prospect of using the flower-biomass containing electrodes as sensors for gold.     

Amperometric flow-injection analysis of hydrazine by electrocatalytic oxidation at cobalt tetraphenylporphyrin modified electrode with heat treatment

Chemically modified electrodes prepared by treating the cobalt tetraphenylporphyrin modified glassy-carbon electrode at 750 degrees (HCME) are shown to catalyze the electrooxidation of hydrazine. The oxidation occurred at +0.63 V vs. Ag/AgCl (saturated potassium chloride) in pH 2.5 media. The catalytic response is evaluated with respect to solution pH, potential scan-rate, concentration dependence and flow-rate. The catalytic stability of the HCME is compared with that of the cobalt tetraphenylporphyrin adsorbed glassy-carbon electrode. The stability of the HCME was excellent in acidic solution and even in solutions containing organic solvent (50% CH(3)OH). When used as the sensing electrode in amperometric detection in flow-injection analysis, the HCME permitted sensitive detection of hydrazine at 0.5 V. The limit of detection was 0.1 ng. The linear range was from 50 ng to 2.4 mug. The method is very sensitive and selective.