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  • Author: S.-K. Yeh, x
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Abstract

Magnetorheological (MR) fluids have the unique ability to change properties from those of a fluid to those of a solid in the presence of a magnetic field. In this paper, we present a phenomenological theory for MR fluids within the framework of extended irreversible thermodynamics (EIT), which relates the dynamics of the fluxes to the form of the nonequilibrium equation of state and introduces the elasticity of MR fluids in a natural way. The Gibbs equation and the entropy inequality are derived to present the energy transfer and dissipative mechanisms. In particular, the viscoelastic behavior of the pre-yield regime and the fluid behavior of the post-yield regime are discussed in depth. Finally, according to the entropy inequality, we propose a mechanical model of MR fluids that can characterize the duplicate phenomena of the fluid-solid transition. The results of a numerical analysis of this model correspond with those of the functional tests of an MR damper.

Synopsis:Since the 1960’s there has been a growing body of data regarding the presence of pesticides in the atmosphere. The monitoring results obtained show that traces of pesticides may undergo long range transport and be deposited considerable distances away from the treatment areas, including remote areas such as the Arctic and Antarctic regions. Pesticides have been found in air, rain, cloud water, fog and snow. The appearance and subsequent behaviour of pesticides in the atmosphere are complex processes and the concentrations found depend on several variables such as their volatility, photostability, method of application and extent of use. Whilst volatility of pesticides can be linked to their Henry’s Law constant this is very much a simplification since it is also influenced by the surfaces treated, e.g. soil or leaves, and by the extent to which aerosols are formed during the application. The disappearance of pesticides from the atmosphere is due to hydrolysis, indirect photolysis via OH. radicals and to deposition in rain. Pesticides which are resistant to hydrolysis and photolysis can be transported over great distances, for example, organochlorine insecticides have been detected in the Arctic regions. In general, concentrations in rainwater are, when detected, in the low or sub mg/l range and highest concentrations are found during the time of application. The use of fugacity models has been shown to be a useful approach to predict concentrations in air. Under most conditions the presence of pesticides in air, or rainwater, has no significant effects on non-target systems, including direct and indirect effects. Exceptions to this are damage by auxin-type herbicides to sensitive plants which has resulted on restrictions in their use in certain areas and transient chlorotic spotting thought to be caused by drift of aerosols from application of low rate sulfonyl urea herbicides. For animal species one possible exception has been postulated. This is for persistent organochlorine pesticides in Arctic regions where, due to the very oligotrophic nature of the Arctic ocean, they are more liable to bioaccumulate and be transported in the food web giving enhanced levels in mothers’ milk.