Regulation of veterinary chemicals in Australia.

For many years the regulation of veterinary chemicals has been a State responsibility. The clearance process involves the evaluation of a wide range of aspects for each candidate product including quality, efficacy and safety. In recent years the clearance process has been governed by the Commonwealth Agricultural and Veterinary Chemicals Act 1988. The Act established the Australian Agricultural and Veterinary Chemicals Council responsible for the evaluation and the granting or refusal of clearance. Clearance of veterinary chemicals by the Commonwealth is required as a precursor to registration. It is an offence for anyone to sell an unregistered product unless authorised by relevant legislation. Control is therefore exercised principally at the point of sale. These functions are now the responsibility of the National Registration Authority, which was established on 15 June 1993. Changes are now underway for the Commonwealth to take over the registration responsibilities from the States. A legislative package that will enable the Commonwealth to assume registration responsibilities will be enacted later this year or early 1995.

Picosecond spectroscopy: applications in biochemistry. Part I: Techniques.

A number of sources of picosecond optical pulses and the means by which they may be used to investigate fast molecular processes have been described. In addition, it should be pointed out that most of these techniques can be extended to take advantage of other properties of the laser pulses; in particular, the polarization is of use in measuring time-dependent antisotropy. The state of the art is now the generation of 30fs pulses; it seems likely that this is all the time resolution that one is likely to need for investigating biological and other molecular processes as at such short times the uncertainty principle leads to a considerable loss of spectral resolution.

Structural features in ethanol-water mixtures revealed by picosecond fluorescence anisotropy.

When an ensemble of molecules is excited with polarized light an anisotropic orientational distribution with respect to the transition dipole moment is produced. This anisotropy can decay in time due to the rotational motion of the molecules and consequently leads to depolarization of the fluorescence1-6. The rate of this rotational motion has been successfully predicted from hydrodynamic theory. How much the rotational relaxation depends on molecular geometry and how much on specific solvent-solute interactions has been studied by picosecond spectroscopy1-6 and other techniques7-9. In all cases so far reported, the rotational behaviour seems to be accounted for by the Debye-Stokes-Einstein (DSE) equation τR = f/kT. This relates the rotational relaxation time τR (inversely related to the rotational diffusion coefficient) to the frictional coefficient, f, which is proportional to the product of the shear viscosity, the molecular volume and a constant dependent on the 'stick' or 'slip' boundary conditions3,10,11. We report here, however, that large deviations from DSE behaviour have been observed in the rotational diffusion of the dye cresyl violet in ethanol-water mixtures. Different rotational relaxation times are observed in solutions of the same viscosity but differing composition. This behaviour can be rationalized using previously proposed models for water-ethanol mixtures.