Free-Surface Aeration and Momentum Exchange at a Bottom Outlet

This study aims to provide some new understanding of the air-water flow properties in high-velocity water jets discharging past an abrupt drop. Such a setup has been little studied to date despite the relevance to bottom outlets. Downstream of the step brink, the free-jet entrains air at both upper and lower air-water interfaces, as well as along the sides. An air-water shear layer develops at the lower nappe interface. At the lower nappe, the velocity redistribution was successfully modelled and the velocity field was found to be similar to that in two-dimensional wake flow. The results highlighted further two distinct flow regions. Close to the brink (Wex < 5000), the flow was dominated by momentum transfer. Further downstream (Wex > 5000), a strong competition between air bubble diffusion and momentum exchanges took place.

Oxygen transport capacity in the air-breathing fish, Megalops cyprinoides: compensations for strenuous exercise

Tarpon have high resting or routine hematocrits (Hct) (37.6+/-3.4%) and hemoglobin concentrations (120.6+/-7.3 g 1(-1)) that increased significantly following bouts of angling-induced exercise (51.9+/-3.7% and 142.8+/-13.5 g 1(-1), respectively). Strenuous exercise was accompanied by an approximately tenfold increase in blood lactate and a muscle metabolite profile indicative of a high energy demand teleost. Routine blood values were quickly restored only when this facultative air-breathing fish was given access to atmospheric air. In vitro studies of oxygen transport capacity, a function of carrying capacity and viscosity, revealed that the optimal Hct range corresponded to that observed in fish under routine behaviour. During strenuous exercise however, further increase in viscosity was largely offset by a pronounced reduction in the shear-dependence of blood which conformed closely to an ideal Newtonian fluid. The mechanism for this behaviour of the erythrocytes appears to involve the activation of surface adrenergic receptors because pre-treatment with propranolol abolished the response. High levels of activity in tarpon living in hypoxic habitats are therefore supported by an elevated Hct with adrenergically mediated viscosity reduction, and air-breathing behaviour that enables rapid metabolic recovery. (C) 2002 Elsevier Science Inc. All rights reserved.

Characterisation of Leucaena condensed tannins by size and protein precipitation capacity

The ability of differently sized condensed tannins from the genus Leucaena, a fodder tree-legume, to bind protein at different pH values was evaluated to characterise their potential biological effects. Two factors affecting the ability of condensed tannin to bind protein, its major biological activity, have been purported to be the condensed tannin size and the pH of the reaction environment. To test these hypotheses, the protein-precipitating capacities of condensed tannin extracted from four Leucaena genotypes, L leucocephala (UHK636), L pallida (CQ3439), L trichandra (CP146568) and L collinsii (OFI52/88), were assessed. Condensed tannin from L leucocephala had approximately 50% of the ability to precipitate protein on a gg(-1) basis than L pallida or L trichandra, while L collinsii gave no measurable ability to precipitate protein (reaction environment pH 5.0). Increasing or decreasing the pH of the reaction solution away from pH 5.0 (approximately the isoelectric point of the protein) reduced the ability of condensed tannin from all the species to precipitate protein, the decrease being higher at pH 2.5 than at pH 7.5. Condensed tannins from each Leucaena species were also separated by size exclusion chromatography, and the fractions examined for protein-precipitating capacity. In general, it was found that the larger-sized condensed tannin of the accessions L pallida and L trichandra could precipitate more protein than the smaller-sized condensed tannin. This pattern was not found for L leucocephala. (C) 2001 Society of Chemical Industry.