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A physical model of a Burgers vortex was created in the laboratory with characteristics corresponding to dissipative‐scale eddies that copepods are likely to encounter in turbulent flows. The swimming behavior of three marine copepod species is assessed as a function of vortex strength in and around the flow structure with the vortex axis aligned vertically or horizontally in the water. The studied species are Acartia tonsa, an estuarine copepod with a hop‐sink swimming style; Temora longicornis, a coastal copepod with a cruise swimming style; and Calanus finmarchicus, an open‐ocean copepod with a cruise‐sink swimming style. The results show that copepods change their swimming behavior with the intensity of the Burgers vortex and reveal species‐specific responses in nearly all kinematic parameters. A. tonsaand C. finmarchicusexhibited the strongest behavioral response to increasing vortex strength and T. longicornisexhibited the weakest response. A. tonsaand T. longicornisshowed no response to changes in vortex orientation, whereas the behavior of C. finmarchicusrevealed some vortex orientation dependence. One common behavior among the species is that the swimming trajectory shape becomes increasingly curved and spiral around the vortex core with increasing vortex strength, which provides a means of local aggregation and increased encounter rate with food and mates. The results are interpreted in relation to differences in swimming style and setal morphology among the species.

In a recent study, Sotiropoulos et al. (2001) studied numerically the chaotic particle paths in the interior of stationary vortex-breakdown bubbles that form in a closed cylindrical container with a rotating lid. Here we report the first experimental verification of these numerical findings along with new insights into the dynamics of vortex-breakdown bubbles. We visualize the Lagrangian transport within the bubbles using planar laser-induced fluorescence (LIF) and show that even though the flow fields are steady – from the Eulerian standpoint – the spatial distribution of the dye tracer varies continuously, and in a seemingly random manner, over very long observation intervals. This finding is consistent with the arbitrarily long Šil'nikov transients of upstream-originating orbits documented numerically by Sotiropoulos et al. (2001). Sequences of instantaneous LIF images also show that the steady bubbles exchange fluid with the outer flow via random bursting events during which blobs of dye exit the bubble through the spiral-in saddle. We construct experimental Poincaré maps by time-averaging a sufficiently long sequence of instantaneous LIF images. Ergodic theory concepts (Mezić & Sotiropoulos 2002) can be used to formally show that the level sets of the resulting time-averaged light intensity field reveal the invariant sets (unmixed islands) of the flow. The experimental Poincaré maps are in good agreement with the numerical computations. We apply this method to visualize the dynamics in the interior of the vortex-breakdown bubble that forms in the wake of the first bubble for governing parameters in the steady, two-bubble regime. In striking contrast with the asymmetric image obtained for the first bubble, the time-averaged light intensity field for the second bubble is remarkably axisymmetric. Numerical computations confirm this finding and further reveal that the apparent axisymmetry of this bubble is due to the fact that orbits in its interior exhibit quasi-periodic dynamics. We argue that this stark contrast in dynamics should be attributed to differences in the swirl-to-axial velocity ratio in the vicinity of each bubble. By studying the bifurcations of a simple dynamical system, with manifold topology resembling that of a vortex-breakdown bubble, we show that sufficiently high swirl intensities can stabilize the chaotic orbits, leading to quasi-periodic dynamics.

A bench‐top model of a chemical plume in a turbulent flow, a Virtual Plume, was built to simulate the behavior of a turbulent chemical plume. It is based on an eight‐channel FIA/SIA system and an array of eight amperometric sensors. A plug of sample solution was delivered to the sensors after passing through delay and dispersion elements. Adjusting these two elements enabled us to simulate the time‐concentration profile at any arbitrary point in the plume. It has been shown that an eight‐channel system can simulate an arbitrary sensor array positioned in a turbulent plume. Preliminary correlation of the shape of the peaks obtained in the VP with those recorded using planar laser‐induced fluorescence in a turbulent flow shows the value of this approach.

1. Daily intramuscular injections of 1 mg of nitroglycerine embedded in a mixture of beeswax and mineral oil does not provoke gastric or duodenal ulceration in rabbits within a period of 15 days.2. Bilateral subdiaphragmatic vagotomy does not produce gastric or duodenal ulcera- tion within periods as long as 47 days in rabbits maintained on a diet of Purina rabbit pellets, carrots and' water.3. Daily intramuscular injections of histamine (30 mg) and nitroglycerine (1 mg) embedded in a mixture of beeswax and mineral oil produce acute, necrotic, perforating lesions of the stomach or duodenum of approximately 30% of rabbits. These lesions are fundamentally different from typical human peptic ulcers.4. Bilateral subdiaphragmatic vagotomy apparently exerts a measure of protection against the development of acute ulcerative lesions of the stomach and duodenum of rabbits produced by the chronic action of histamine and nitroglycerine.5. Gastric and buodenal ulcers produced in rabbits by chronic combined histamine and nitroglycerine stimulation are not considered to be suitable lesions for the experimental assessment of ulcer prevention measures.

This study quantifies the behavioral response of a marine copepod (Acartia tonsa) to individual, small-scale, dissipative vortices that are ubiquitous in turbulence. Vortex structures were created in the laboratory using a physical model of a Burgers vortex with characteristics corresponding to typical dissipative vortices that copepods are likely to encounter in the turbulent cascade. To examine the directional response of copepods, vortices were generated with the vortex axis aligned in either the horizontal or vertical direction. Tomographic particle image velocimetry was used to measure the volumetric velocity field of the vortex. Three-dimensional copepod trajectories were digitally reconstructed and overlaid on the vortex flow field to quantify A. tonsa’s swimming kinematics relative to the velocity field and to provide insight into the copepod behavioral response to hydrodynamic cues. The data show significant changes in swimming kinematics and an increase in relative swimming velocity and hop frequency with increasing vortex strength. Furthermore, in moderate-to-strong vortices, A. tonsamoved at elevated speed in the same direction as the swirling flow and followed spiral trajectories around the vortex, which would retain the copepod within the feature and increase encounter rates with other similarly behaving Acartia. While changes in swimming kinematics depended on vortex intensity, orientation of the vortex axis showed minimal significant effect. Hop and escape jump densities were largest in the vortex core, which is spatially coincident with the peak in vorticity, suggesting that vorticity is the hydrodynamic cue that evokes these behaviors.

Abstract not available.