A new hydrodynamic microelectrochemical reactor design is presented for the voltammetric sensing of chemical species contained within two immiscible liquid streams flowing within rectangular ducts, in direct contact. This article describes the design, fabrication and experimental characterisation of the device. A microfabricated rectangular duct (of typical dimensions: height 75μm, width 500μm and length 3 cm) was constructed using FOTURAN glass and standard photolithographic procedures. Microelectrode sensors were positioned on one internal duct wall with a geometry to permit separate voltammetric monitoring of the two solvent phases. Reagent solutions containing N,N,N′,N′-tetramethyl-1,4-phenylene diamine in 1,2-dichloroethane and hexaamineruthenium(III)chloride in water were pumped through the device under laminar flow conditions. Linear sweep voltammetric measurements were performed separately on the two electrolyte streams and the variation of the transport limited current as a function of volume flow rate through the cell monitored. Under conditions where stable flow was obtained the current flow rate relationship was observed to follow analogous voltammetric behaviour to that observed in macroscopic flow cell devices.

A novel approach to the visualisation and quantification of mass transfer in liquid flow is presented. The technique utilises an array of microstrip electrodes sited within a duct through which the electrolyte solution is pumped. The electrolyte solution contains a reagent that may be oxidised and in the process undergo a colour change. The electrolysis products are then swept through the cell and the pathway imaged via a digital video. Results are presented for an experimental geometry where a rectangular obstruction is deliberately introduced into the duct. Transport rates within the cell are restricted such that Stokes flow conditions are maintained throughout and the streamlines generated from the electrolysis used to map the flow profiles through the devices. The merits of the approach are discussed and the potential of numerical modelling to provide quantitative analysis are highlighted.

A previous model addressed the within-herd transmission of bovine Tb (Mycobacterium bovis) in New Zealand cattle herds. This complementary model considers transmission between herds, in an area of New Zealand's North Island (the Waikato) largely free from wildlife reservoirs. The model is used to account for the observed pattern of Tb breakdowns and to assess the likely impact of changes in management on the percentage of herds on movement control between 1988 and 1993 (an average of 0.76% in the Waikato region). It partitions the region into two sub-areas: one small, with significant infection from wildlife; the other much larger and lacking external sources of infection. The observed pattern of herd breakdowns (in different parts of the Waikato and in the region as a whole) could be accounted for in the model by infection from wildlife reservoirs in the southern sub-area (Waitomo) and infection due to movement of cattle from infected but undiagnosed herds to uninfected herds throughout the whole region. During the above period, the model suggests that about 0.8% of herds became infected each year, that most new infections (81% of the total) occurred between herds in the larger sub-area, and that about 13% of the total occurred through infection from wildlife in the smaller sub-area. The whole situation appears to be in a state of near-neutral balance (even without input of new infection), with removal through testing of new infections almost exactly balancing the rate of infection by between-herd movement. Therefore, if the external input is removed, the number of infected herds and of herds on movement control in the whole region declines so slowly that the decline is almost undetectable. Other management changes had a more dramatic effect – particularly, reducing the testing interval to a maximum of 1 year in the whole district. This also appeared to be a necessary condition for achieving ≤0.2% herds on movement control within 10 years (whatever other strategies were employed). The greatest reduction in the percentage of herds on movement control came from yearly testing plus a 50% reduction in infection from wildlife. A further but smaller additional improvement was gained by reducing cattle movements throughout the region by 50%.